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High Tensile Strength Steel Stamping Solutions

Providing Solutions to Make You More Profitable

high tensile strength steel stamping image

Dayton Progress Understands that Stamping High Tensile Strength Steel Is Hard—Literally

  1. Low punch performance & cycle life
  2. Impact resistance
  3. Punch edge chipping, edge wear or breakage
  4. Stopping production to service or re-sharpen tooling

Ultimately you have more downtime and increased maintenance costs; robbing your company of profit.

You can rely on solutions from Dayton Progress to increase profits.

The Dayton Progress Solution

We have developed punches specially designed for stamping today's high tensile strength steels. The combination of the right punch material, design, coating, and finish will improve your day-to-day operations.

Punch Design: Features that perforate cleanly and eject slugs efficiently.

Punch Material: Durable tool steel, heat treated in-house in our modern vacuum ovens.

Coatings: Dayton Progress uses long lasting coatings that reduce friction and increase wear life.

Finishes: Precision micro finishes that enhance the performance of our coatings.

Options That Fit Your Situation and Budget

Production Good Better Best Callout

Punch Material M2 PS4 PS4 M2, PS4
Chamfer Yes Yes XS20 (round) or XS25 (shape)
Jektole Yes Yes BJ_, AJ_F, TJ_F
Back Taper Yes XAR (round)
Coating Yes XAN

Order Examples

Good VPX 37 1020 P.250 M2 XAN XS20 A7° DPO 08 1371 P4.20 W3.5 M2 XAN XS25 A15° Y0.5

Better VJX 37 1020 P.250 PS4 XAN XS20 A5° DJX 08 1371 P4.20 M2 XAN XS20 A5°

Best VJX 37 1020 P.250 PS XAN XS20 A5° XAR DJX 08 1371 P4.20 PS XAN XS20 A7° XAR

Optimizing Punch Performance

Chamfer Shear Angles

chamfer punchXS20, XS25—Shear Angles are used primarily to reduce slug pulling. This feature has been proven effective to generate longer cycle life.

Studies show that the XS20 (round) and XS25 (shape) shear angle can improve life cycles by 200-300%.

chamfer diagram

Jektole® Punch

jektole punchMany high tensile strength material applications require extreme lubrication throughout the die. The increased lubrication magnifies surface tension and increases the possibility of slug bonding. 

The benefits of using a Jektole punch are twofold. The spring loaded Jektole pin (extending from the face of the punch) is a method to retain the slug in the die button after perforating. The Jektole punch also has a side vent hole which allows air to get in, breaking the vacuum and lubrication seal between the punch and slug.

Back Taper

back taper punchXAR—Round punches can be ground with a back taper to reduce stripping pressure, heat, and material build up on point. This precise change in the size facilitates stripping material and is much less likely to adhere to the punch. Grind life is not affected. The reduction in diameter is so small that the punch remains within normal tolerances for both hole size and die clearance throughout its life.

back taper diagram

High-Aluminum Coating

coated punchXAN—This ultra-hard (harder than carbide), high-aluminum coating provides high temperature resistance. It is well-suited for applications where surface heat is generated. High tensile strength, dual phase, TRIP, and newer GIGA steels benefit from this coating.(Approximate hardness: Vickers 3400)

Select the Coating that Matches Your Specific Needs

Dayton's leading-edge coatings and other unique surface treatments have been developed to improve inplant performance by increasing tool hardness and wear resistance.

 

Aluminum Stamping Solutions

Reducing Downtime, Increasing Profit

Aluminum stamping image

Dayton Progress Understands the Issues Associated with Stamping Aluminum

  • Aluminum Oxide buildup
  • Perforating problems
  • Accelerated die component wear
  • Galling (adhesive wear)

Ultimately you have more downtime and increased maintenance costs; robbing your company of profit.

You can rely on solutions from Dayton Progress to increase profits.

The Dayton Progress Solution

We have developed punches specially designed for stamping aluminum. The combination of the right punch material, design, coating, and finish will improve your day-to-day operations.

Punch Design: Features that perforate cleanly and eject slugs efficiently.

Punch Material: Durable tool steel, heat treated in-house in our modern vacuum ovens.

Coatings: Dayton Progress uses long lasting coatings that reduce friction and increase wear life.

Finishes: Precision micro finishes that enhance the performance of our coatings.

Options That Fit Your Situation and Budget

Production Good Better Best Callout

Punch Material M2 PS4 PS M2, PS4, PS
Chamfer Yes Yes XS20 (round) or XS25 (shape)
Jektole Yes Yes BJ_, DJ_, VJ_
Back Taper Yes XAR (round)
Diamond Coating Yes XCD
Polished Diamond Coating Yes Yes XCDP

Order Examples

Good VPX 37 1020 P.250 M2 XCD XS20 A7° DPO 08 1371 P4.20 W3.5 M2 XCD XS25 A15° Y0.5

Better VJX 37 1020 P.250 PS4 XCDP XS20 A5° DJX 08 1371 P4.20 M2 XCDP XS20 A5°

Best VJX 37 1020 P.250 PS XCDP XS20 A5° XAR DJX 08 1371 P4.20 PS XCDP XS20 A7° XAR

Optimizing Punch Performance

Chamfer Shear Angles

chamfer punchXS20, XS25—Shear Angles are used primarily to reduce slug pulling. This feature has been proven effective to generate longer cycle life.

Studies show that the XS20 (round) and XS25 (shape) shear angle can improve life cycles by 200-300%.

chamfer diagram

Jektole® Punch

jektole punchMany aluminum material applications use lubrication throughout the die and some materials contain a wax coating. This combination acts a bonding agent between the punch and slug. This magnifies surface tension and increases the possibility of slug bonding.

The benefits of using a Jektole punch are twofold. The spring loaded Jektole pin (extending from the face of the punch) is a method to retain the slug in the die button after perforating. The Jektole punch also has a side vent hole which allows air to get in, breaking the vacuum and lubrication seal between the punch and slug.

Back Taper

back taper punchXAR—Round punches can be ground with a back taper to reduce stripping pressure, heat, and material build up on point. This precise change in the size facilitates stripping material and is much less likely to adhere to the punch. Grind life is not affected. The reduction in diameter is so small that the punch remains within normal tolerances for both hole size and die clearance throughout its life.

back taper diagram

Diamond-like Carbon Coating

polished punchXCD—This diamond-like carbon coating combines high hardness with an extremely low coefficient of friction. Offering good protection against abrasive and adhesive wear, it is ideal for aluminum.
(Approximate hardness: Vickers 5000)

XCDP—This super-smooth, polished finish is combined with a DLC coating for a very low coefficient of friction with high wear resistance. It is excellent for stamping aluminum. (Approximate hardness: Vickers 2800)

Galling Solutions for Aluminum

One of the most frequent problems encountered with perforating aluminum is punch galling. Aluminum, in general, possesses a gummy characteristic which causes it to adhere to a surface of the punch when it’s drawn, pulled, trimmed, perforated, or pierced. This accumulation of material on the punch is known as galling (adhesive wear). The galling occurs both on the initial penetration into the material and extraction from the material. The elastic nature of the aluminum collapses back into the hole as the punch is extracted, creating drag and pull on the punch. The tensile nature of the material must be considered in determining the correct die button. Dayton’s Engineered Clearance will aid in developing the proper clearance.

The galling of aluminum on the punch tip over time will cause the hole size to expand. This creates an out of tolerance hole quality issue on the part. Several remedies are available for this situation. These solutions may be incorporated separately or used in conjunction with one another to alleviate the galling and prolong punch life.

The initial solution considers how to offset the adhesive influence of the aluminum. To counteract the galling, we must reduce the co-efficient of friction between the punch and aluminum. This can be accomplished through several venues. One is to use a low co-efficient of friction coating on the punch. But coatings containing aluminum in their chemistry must be avoided. The trace aluminum will create an intense adhesive issue. OEM manufacturers have had great success with Dayton’s XCDP coating.

Perforating Considerations

The various grades of aluminum behave differently when perforating holes. A selection of M2 or PS4 or PS tool steel for the punch material generally achieves very good results. When punching the 5000 and 6000 aluminum series, the perforated hole size movement is minimal. By using the proper die clearance, the hole will be slightly larger than the punch.

However, when perforating the softer 3000 and 4000 aluminum grades, dramatic hole shrinkage may be experienced. Again utilizing the proper die clearance, the amount of hole shrinkage can be managed. Edge radius punch points for the softer aluminum grades should be avoided. A flat, sharp edged punch point without any shear angle performs best. The shear has a tendency to only deform the aluminum and cause more rollover in the hole in the softer aluminum grades.

Punch to die clearance is a key factor when perforating aluminum. The recommended die clearance is directly related to the type of aluminum, its tensile strength, and the aluminum sheet thickness. The die clearances can run within a range of 3% to as high as 20% per side.

How to Select the Proper Clearance

Identify the tensile strength from the last rows in the chart.

Determine the recommended clearance from the shaded area for alloys.

Multiply the recommended clearance with the thickness scaling factor table.

Engineered (Jektole®) Die Clearance and Tensile Strength

clearance table

A New Look at Die Clearance

Improve productivity and tool life in stamping applications, starting with selection of optimum clearance in piercing and trimming applications.

Optimum Clearance – one number fits all?

Die designers, tool builders and Dayton Progress have advocated the use of optimum cutting clearance to improve tool life. With higher strength steels and other new sheet materials emerging in the market, the old clearance percentages seldom appear to provide reliable tool life. Why?

While working with the older sheet material grades, the tensile strength was lower. So even when the sheet gage or thickness increased, the loads experienced by the tools did not increase significantly. In turn, stampers generally applied a single clearance percentage across all thickness ranges. But with the newer grades, the tensile strength is much higher, and the load on the tools increases considerably with not just the tensile strength of the sheet, but also with the sheet thickness. For example, thicker sheets apply higher load on tools than thinner gage materials. Under these conditions, it is easy to see that one clearance percentage is no longer optimum.

New Clearance – one solution for each application!

With this finding in mind, stampers need to consider selecting clearances by material grade and thickness. Extensive tests on different sheet materials and thickness have generated an optimum clearance table similar to the one shown here. A typical clearance table shows the sheet tensile strength (X-axis) and gage thickness (Y-axis), and with increasing tensile strength and gage thickness should increase to improve tool life and productivity.

Clearance table
Typical clearance matrix by sheet tensile strength and gage thickness

Care should be taken when picking a clearance percentage from this table, and should favor recommended clearances for the particular sheet material, i.e. recommended clearance tables for Aluminum would differ from recommended clearance tables for DP Steel. Additionally, clearance selected will influence other process conditions such as tool load, resulting hole quality (roll-over), and tool life (failure mode), and will need to be considered.

We should now understand the need for selecting clearance based not only on the material being formed, but also upon the thickness of the material, and the material’s shear strength. But as always there are trade-offs while selecting a die clearance too near the minimum or maximum range. Let's look at the influence clearance selection can have on piercing loads in further detail.

Optimum Clearance & Punching Loads

Traditional tooling practice has shown that increasing clearance will decrease piercing or shearing loads on the tools, thereby effectively increasing tool life. However, the effects of using the largest possible clearance on every application have never been studied fully until now. The graph below illustrates how the piercing load on a punch changes as we increase the clearance from 6% per side to 14% per side while piercing MART1400 steel (203KSI,1400MPa) of 0.040” [1mm] thickness. It is evident that when clearance is increased, the load does decrease – in this case by approximately 10%. One can imagine that the reduction in piercing load would decrease as the shear strength of the sheet material increases, i.e more reduction in load could be observed for low strength grades than high strength grades. Hence explaining the wide spread use of larger clearances to alleviate loads on tools by stampers.

Force chart
Piercing load recorded during piercing of 0.040” [1mm] thick MART 1400 grade sheet material (Courtesy: Börje, UT)

Perhaps the most important observation from this study is that vibration has been introduced and is larger than at smaller clearances. One can imagine that with increasing shear strengths of the sheet material, this effect will be more pronounced, i.e. higher strength steels will induce more vibration during piercing than low strength steels.

But why is this finding important? Well for one, when the tool assembly is not rigid, the hole geometry and location could differ between consecutive parts, resulting in quality issues. But more importantly, with larger clearance and greater vibration, tools are going to have a tendency to move during the piercing operation and become more prone to chipping rather than a gradual wear. Armed with this knowledge, stampers can work around this issue if larger clearances need to be used for an application, by using a headed retention system rather than a ball-lock retention system. While the use of the headed system will not completely eliminate or compensate for the vibration, it will greatly reduce the play in the assembly compared to a ball-lock system.

Clearance & Hole Quality

Another aspect to be considered while increasing clearance is the resulting hole quality. When the pierced hole is functioning as a clearance hole, the resultant burnish and break characteristics from the larger clearance is unimportant. However, when secondary operations are performed, such as tapping then stampers need to pay close attention to the effect of larger clearances on the resulting hole quality.

The micrographs below show the different hole quality for the same material pierced using two different clearances. It is clearly observable that the hole pierced with the larger clearance has larger roll-over and in turn may be unsuitable for secondary operations, even though the quality of the shear and break surfaces are clean. In turn, stampers need to select a clearance window that provides them with the best hole quality desirable and balanced with acceptable tool life.

6% clearance


14% clearance
Hole quality conditions recorded during piercing of 0.040” [1mm] thick MART 1400 grade sheet material with different clearances (Courtesy: Börje, UT)

Perhaps the greatest influence clearance selection will have is on how tools perform and ultimately fail in production.

Tool Failure and Optimal Die Clearances

The HSLA steels require new considerations for tooling performance which are dramatically different than the old school one size fits all approach of lower carbon steels. Let's revisit the general concept of die clearance and the measurement of hole quality.

The process of punching a hole involves impact and loading forces being exerted and focused upon the material confined between the punch point and die button. The material must fail during the perforating process in the anticipated manner or else the resultant hole is unacceptable. The success of creating the desired effect, the proper hole characteristics is heavily reliant upon the correct punch steel and the correct die clearance.

The "rule of thumb" clearance used for many years has been five percent per side. Clearance is defined as the percentage of material thickness per side, ie the distance between the punch point and the die button opening. The five percent was a good baseline but did not always consider the material characteristics and its thickness. These material traits can adversely affect the tool life and the hole size.

If the die clearance is too tight, the hole can be as much as .0005 in smaller than the punch. This condition creates excessive wear, extreme stripping pressure, and excessive burrs. When the die clearance is increased, the hole can be .0002-.0005 in larger than the punch. This leaves a slip fit condition and can decrease the abrasive punch wear by as much as two-thirds.

Hole Size Comparison

Burr Generation

Hole quality is usually gauged by the burr generated during the piercing process. Measurement of the burr is the leading indicator of tool wear. As the burr increases, distinct wear can be clearly seen on the punch, which requires either punch sharpening or replacement. More die clearance does not mean more burr height. Actually as depicted in the chart, as the die clearance is increased and the size of the hole becomes larger than the punch, the burr height drops dramatically.

If the hole continues to decrease, without changing die clearance abrasive wear is occurring on the punch, from the pierced material eroding the surface of the punch. If the hole begins to increase, an adhesive wear condition is underway with the material seizing onto the punch.

Choosing the Proper Die Springs

Dayton ProgressDanly-IEMLaminaLempco

Springs

Extend operating life with well-chosen Dayton Lamina die springs

Die springs, an essential stamping die component, create the optimal pressure for restraining the sheet material in a fixed position while it is being pierced, formed, flanged, or trimmed. The springs also provide controlled return pressure for the die stripper to permit the punches and other die-mounted tools to evacuate the material during the press' return stroke.

Die springs are most commonly used to actuate strippers, but they can also be found behind form pressure pads and binder rings in draw dies. The goal is to provide adequate die spring pressure within the limited remaining space of the die.

Spring Selection Process

Figure 1

To select a die spring, you first should gather information about three different aspects of the die design: how much pressure is needed; what spring size and how many are needed to produce that pressure; and how far these springs must collapse or travel.

Pressure Requirements

To determine spring pressure for a spring used in a stripper, first calculate the perforating pressure for the entire die. To do this, you need to know the thickness and shear strength of the part material as well as the length of shear or cutting distance. These elements multiplied together will give you the perforating pressure. The formula reads:

Perforating pressure = S × T × L

Where:

  • S = Shear strength of the part material
  • T = Part material thickness
  • L = Total length of shear or cutting distance

 

A pressure equal to 10 to 15% of the total perforating pressure typically is used to actuate the stripper (the range accommodates the potential differences among spring manufacturers). This allows for the downward ram speed to align safely and engage the die shoe components into their guided, mated components before material contact.

Spring Stripper

Figure 2

As the ram moves down, the stripper makes contact with the part material and stops. The spring continues to compress, or travel, until the ram reaches the bottom of its stroke.

Stripping pressure = Perforating pressure × 0.10 to 0.15

Although the formula for determining pad pressure in a form die is different from that of a stripper, it must still contain the same three elements of (1) pressure, (2) quantity and size of springs, and (3) the travel. The pad pressure in a forming operation should be at least 1.5 times greater than the force required for bending the part.

Bending pressure = ((S × 0.166 × T2) / (T + R1/2 + R2/2)) × L

Where:

  • S = Tensile strength
  • T = Material thickness
  • R1 = Radius on form punch
  • R2 = Radius on form die
  • L = Length of form

 

Pad pressure = Bending pressure × 1.5

A forming operation requires more pad pressure than a bending operation because of the need to control sheet material movement over the forms and maintain its new shape. The pad pressure also helps to prevent material from scoring or tearing as it is being formed.

Pressure requirements for binder rings in draw dies tend to be less scientific, determined by trial and error. It is not uncommon to find a note on a draw die design stating the spring requirement as "springs to suit."

As the binder ring holds the material in its locating position, the spring pressure required tends to be adjusted to eliminate the tearing and shearing that may occur while the material is being drawn or stretched. A too-high spring pressure will inhibit the drawing of the material, while too little pressure will draw material up the form and fail to provide a uniform wall thickness.

Spring Size and Quantity

The amount of available space in the die will help determine how many springs to use and what sizes to choose. Whenever possible, try using numerous low-pressure springs rather than a few high-pressure springs. This will reduce stress on the springs.

As long as the tool layout permits the necessary space, more springs of lower pressure allow for more evenly distributed pressure and a more balanced stripper pad. This enhances sheet material control throughout the complete press stroke. Also, if just one die spring becomes fatigued, the die pad will continue to operate with the other springs.

Die spring placement, when applicable, should be nearest the area being pierced, formed, flanged, or trimmed. This enhances the ability to locate the most pressure on the area being worked upon while maintaining sheet material control. The use of spring cams, retainer bolts, or spring pockets serve to guard the springs from debris and protect the tool die details in the event of a fatigued or broken die spring.

Travel Requirements

When springs are installed in a die, they are compressed approximately 0.125 inch. Called preload, this compression is necessary to keep the springs from working their way out of the die. As a side benefit, the preload reduces the shock associated with rapid loading and unloading of the die and increases the spring life.

Figure 3

The bottom of the stripper draws up just short of being flush with the end of the punch. This ensures that the part material strips completely off the end of the punch. When the press cycle starts, the ram begins to move downward. The stripper makes contact with the part material and stops. As the ram continues descending, the springs compress, allowing the punches to extend through the part material and into the die button until the ram reaches the bottom of its stroke. This compression is called stripper travel.

The travel of a spring is determined by the spring preload, thickness of the material, entry of the punch into the die button, and the distance the stripper hangs below the bottom of the punch. Put simply, preload plus the stripper travel equals the total spring travel.

The same is true in form and draw dies. Pressure pads or binder rings will also travel and compress the springs. Preload plus travel of the stripper or comparable component will give you the total travel of the spring.

To reduce stress and allow for maximum spring life, you should keep preload and travel to a minimum. The more rapidly a spring works in compressing and decompressing, the greater the fatigue factor. Slower-spring applications permit longer spring travels, longer spring life, and the ability to operate near maximum spring deflection levels. The faster a die spring cycles, the shorter the spring life expectancy. In such fast cycling applications, you should lower the spring deflection.

Spring Selection

Now that you know the pressure, approximate size, and travel, you can begin the actual spring selection process. This starts by combining the three aspects of the die design. First, divide the total stripping force required by the number of springs to be used.

The selected spring must deliver the desired pressure at preload. To determine the pressure of the spring at a given preload, multiply the amount of preload by the amount of pressure the spring develops over one inch. Most spring catalogs give pressure ratings over one inch as well as various other amounts of compression or travel.

Keep in mind that the spring must offer sufficient travel within its normal operating range. For example, the maximum operating range of a medium-pressure spring is approximately 50% of the free, or static, length. The efficient operating range of this spring is between 10 and 35% of the free length. Higher-pressure springs will have a shorter range of travel.

Although springs will compress beyond the maximum operating range, you should avoid this at all cost. Compressing beyond maximum range will severely hinder spring life and could damage the die. It is also a good idea to choose a spring with extra travel to prevent over-traveling the spring after a tool has been re-sharpened.

Tough Under Pressure

Whatever your application might be, you can be sure that die springs from Dayton Lamina provide rugged, dependable performance. The brands of Dayton, Lamina, Danly-IEM, and Lempco offer a wide selection of NAAMS, ISO, and JIS standard springs.

Component Lubrication

Lamina

Ball Bearing Components

Recommended Lubrication

  • BALL-LUBE™
  • Pint BALL-LUBE™ spray # ARL0161
  • Gallon BALL-LUBE™ # ARL1281

Notes

  • Lubricates assemblies providing protection against wear, oxidation and rust
  • MSDS available upon request
  • Alternative / refined mineral oil of viscosity 290/340 SSU @ 100 degrees F containing "EP" additives and rust inhibitors

Self-Lubricating Style Bushings or Wear Plates with Oil Impregnated Graphite Plugs

Recommended Lubrication

  • Light 20 wt. oil should be applied to pre-lube the wear surface of the bushing.

Notes

  • When bushing reaches 80-90 degrees F° because of friction between the components, oil is drawn from the plug thus lubricating the wear surface.

NEVER USE GREASE with the Self-Lubricating oil impregnated graphite plug products. Grease on the oil impregnated graphite plugs will prevent the self-lubricating process.


Plain Bearing Friction

Recommended Lubrication

  • Quart # 9-01-52
  • Gallon # 9-02-52
  • (15) Gallons # 9-02-522
  • (55) Gallons # 9-02-521

Notes

  • Above die lubricant is specially prepared to provide efficient lubrication for guide post in plain bearing applications.
  • Alternative, lithium complex white grease or multi-purpose grease.

MSDS

MSDS is available here.

Recommendations are based on applications in typical ambient temperatures. For high / low temperature applications, a reputable Lubricant Company or lubrication specialist should be consulted.

Tool Steels

Properties, Comparisons, & Benefits

Choosing Tool Steels—Balancing Toughness, Wear Resistance, & Compressive Strength

Tool steels refer to a variety of carbon and alloy steels that are well-suited and widely used to make tools primarily used for perforating and fabrication. Tool steels are made to a number of grades for different forming and fabrication applications. The most common scale used to identify various grades of steel is the AISI-SAE scale.

In addition, each grade of tool steel has heat treatment guidelines that must be followed to achieve optimum results. (The heat treating processes for stamping applications are different from those used for cutting tools.)

Let's examine tool steel types (characteristics and features) and the heat treatment processes and options.

Tool Steel Characteristics

Tool steels are very different from steels used in consumer goods. They are made on a smaller scale with stringent quality requirements, and are designed to perform in specific applications, such as machining or perforating.

Different applications are made possible by adding a particular alloy along with the appropriate amount of carbon. The alloy combines with the carbon to enhance the steel's wear, strength, or toughness characteristics. These alloys also contribute to the steel's ability to resist thermal and mechanical stresses.

The chart shows some of the commonly used tool steels and their alloy content.

Side Effects

Each alloy element shown in the chart below contributes to a specific characteristic in the finished steel. It can also create an undesirable side effect, particularly when used in excessive amounts. In addition, alloys can react with each other–either enhancing or detracting from the desired results.

Tool Steels/Alloys

Typical Composition

Steel AISI JIS DIN C Mn Si Cr W Mo V
H13 H13 SKD 61 1.2344 0.40 0.40 1.00 5.25   1.35 1.00
S7 S7 * 1.2357 0.50 0.75 0.25 3.25   1.40  
A2 A2 SKD 12 1.2363 1.00 0.75 0.30 5.00   1.00 0.25
PM 1V * * * 0.55 0.40 0.50 4.50 2.15 2.75 1.00
D2 D2 SKD 11 1.2379 1.50 0.30 0.30 12.00   0.75 0.90
PM 3V * * * 0.80 0.30 1.00 7.50   1.30 2.75
M2 M2 SKH 51 1.3343 0.85 0.28 0.30 4.15 6.15 5.00 1.85
PM M4 (PS4) M4 SKH 54 * 1.42 0.30 0.25 4.00 5.50 5.25 4.00
PM 9V * * * 1.90 0.50 0.90 5.25   1.30 9.10
PM 10V (PS) A11 * * 2.45 0.50 0.90 5.25   1.30 9.75
PM 15V * * * 3.40 0.50 0.90 5.25   1.30 14.50

Note: The steels shown above are a representative sampling of commonly used steels and their alloy content.
*No designation

 

Tool Steel Comparison

Tool Steel Comparison

 

Toughness

Toughness of tool steel is defined as the relative resistance to breakage, chipping, or cracking under impact or stress. Using toughness as the only criterion for selecting a tool steel, H13 or S7 (shown in the chart above) would be the obvious choice. However, all desired characteristics–and the needs of the job–must be considered when making your selection.

Tool steel toughness tends to decrease as the alloy content increases. Toughness is also affected by the manufacturing process of the steel. The PM (particle metallurgy) production process can enhance the toughness of the steel grade due to the uniformity of its microstructure.

Hardness also affects toughness. Any given grade of tool steel will have greater toughness at a lower hardness. The lower hardness, however, could have a negative effect on other characteristics necessary to achieve acceptable tool life.

Wear Resistance

Wear resistance is the ability of the tool steel to resist being abraded or eroded by contact with the work material, other tools, or outside influences such as scale, grit, etc. There are two types of wear damage in tool steels–abrasive and adhesive. Abrasive wear involves erosion or breaking down the cutting edge. Adhesive wear is experienced when the work piece material adheres to the punch point, reducing the coefficient of friction, which increases the perforating pressure.

Increased alloy content typically means increased wear resistance because more carbides are present in the steel, as illustrated in the chart.

Carbides are hard particles that provide wear resistance. The size and dispersion of the majority of carbides are formed when alloys, such as vanadium, tungsten, molybdenum, and chromium combine with carbon as the molten steel begins to solidify.

Greater amounts of carbide improve wear resistance, but reduce toughness.

Compressive Strength

Compressive strength is a little known and often overlooked characteristic of tool steels. It is a measurement of the maximum load an item can withstand before deforming or before a catastrophic failure occurs.

Two factors affect compressive strength. They are alloy content and tool steel hardness.

Alloy elements such as Molybdenum and Tungsten contribute to compressive strength. Higher hardness also improves compressive strength.

Tool Steel Benefits

  • H13–54 HRC
    • Popular hot work mold steel
    • Good balance of toughness, heat check resistance, & high temp. strength
    • Moderate wear resistance
  • S7–57 HRC
    • High impact resistance at relatively high hardness
    • Very high toughness to withstand chipping and breaking
  • A2–62 HRC
    • Good toughness
    • Moderate wear resistance
    • Combination of properties and low cost make it well suited for a variety of tooling applications
  • PM 1V–60 HRC
    • Very high impact toughness
    • High heat resistance
    • Good wear resistance
  • PM 3V–60 HRC
    • High toughness
    • Wear-resistant
    • Maximum resistance to breakage and chipping in a wear-resistant steel
  • D2–61 HRC
    • High carbon, high chromium
    • Good wear resistance
    • Moderate toughness
  • M2–62 HRC
    • Tungsten-molybdenum high speed steel
    • Very good wear resistance
    • Good toughness
  • PM M4 (PS4)–62 HRC
    • Excellent wear resistance
    • High impact toughness
    • High transverse bend strength
  • PM 9V–56 HRC
    • Good toughness and wear resistance
    • Resists cracking
    • Not for applications requiring high compressive strength
  • PM 10V (PS)–63 HRC
    • Extremely high wear resistance
    • Relatively high impact toughness
    • Excellent candidate to replace carbide in cold work tooling applications
  • PM 15V–62 HRC
    • Exceptional wear resistance, second only to carbide.
    • An alternative to solid carbide where carbide fails by fracture or where intricate tool design makes carbide difficult or risky to fabricate.

In-house Metallurgical Lab—Solutions-based Testing & Analyses

Dayton's in-house metallurgy lab is designed to develop new products and to test and analyze the quality and viability of materials used in the manufacture of Dayton products. Laboratory services include: hardness testing; metallography (e.g., coating thickness); and failure analysis.

Metallurgical Lab

Equipment includes a high-resolution scanning electron microscope used to evaluate metal structures and a full complement of high-tech equipment used for specimen preparation, routine testing, microscopy, heat treatment evaluation, and failure analysis.

Metallurgical Services

  • Micro Structure Analysis
  • Stereoscopic Analysis
  • Material Qualification
  • Metallurgical Qualification
  • Surface Treatment Analysis
  • Conventional Hardness Testing
  • Micro Hardness Testing
  • Wear Analysis
  • Failure Mode Analysis
  • Scanning Electron Microscopy

Dayton's metallurgy lab utilizes leading-edge equipment, employs professional, experienced metallurgists; and is the first full-service laboratory of its kind in the industry.

Heat Treating–Optimizing Tool Steel Properties

Heat treatment involves a number of processes that are used to alter the physical and mechanical properties of the tool steel. Heat treatment–which includes both the heating and cooling of the material–is an efficient method for manipulating the properties of the steel to achieve the desired results.

A vacuum furnace is used to heat the metals to very high temperatures and allow high consistency and low contamination in the process. Each grade of tool steel has specific heat treating guidelines that must be followed to acquire optimum results for a given application. Unlike cutting tools, the nature of the stamping operation places a high demand on toughness. Thus, a specific steel grade used as a tool steel for stamping must be heat treated differently than one used in a cutting tool.

Tool steel heat treatment processes include: material segregation; fixturing; pre-heating; soaking; quenching; and tempering. The following procedures are general guidelines for tool steel heat treatment. Certain steels require different timing, preheating and soaking temperatures, and number of tempers, e.g., M2, PM-M4, & CPM-10V.

Material Segregation & Fixturing

Segregation by size is extremely important because different individual sizes require different rates in preheat, soak, and quench. Fixturing ensures even support and uniform exposure during heating and cooling.

Pre-heating & Soaking

During pre-heating, both cold-work & high speed tool steels are evenly heated to prevent distortion and cracking. Soaking (austenitizing) is done for a specific time to force some of the alloy elements into the matrix of the steel.

Quenching

Quenching is the sudden cooling of the parts from the austenitizing temperature through the martensite transfer range. The steel is transformed from austenite to martensite, resulting in hardened parts.

Tempering

Untempered martensitic steel is very hard, but too brittle for most applications. Tempering is heating the steel to a lower-than-critical temperature to improve toughness. Tool steels are typically tempered at temperatures between 400° - 1000°F.

Cryogenics

Cryogenics is a process that aids in transformation of austenite to martensite, ensuring greater hardness results and reduced internal stresses. This process takes place at temperatures between -150° and -310°F and will vary in duration, depending on the size of the parts.

The Vacuum Furnace

Furnace Illustration

  1. The process starts by removing the atmosphere creating a vacuum and electrically heating the parts in the hot zone.
  2. After the parts are properly heated (austenitized) the system is backfilled with nitrogen. Nitrogen is used as a means of conducting heat away from the parts. A large turbine blower forces room temperature nitrogen across the parts, cooling (quenching) them through the martensite transfer range.
  3. Hot nitrogen exits the hot zone through gates at the front and rear of the chamber.
  4. The nitrogen circulates through a heat exchanger where it is cooled.
  5. The cooled nitrogen is recirculated over the parts until they reach room temperature.

Dayton maintains a state-of-the-art heat treatment facility, including support equipment and systems monitored by our in-house metallurgist.

Dayton's Engineered Clearance

Punch-to-die Clearance: What Works & What Doesn't?

Punch-to-die clearance (Δ) is the space between the cutting edge of the punch and the cutting edge of the die button, which is determined by the thickness and the type of material being punched.

Optimizing the die clearance is one of the most important steps to punching success. Too large or too tight, an improper clearance can lead to poor edge quality, reduced tool life, and more.

Part Material

The material being punched has a polycrystalline structure with a pre-determined fracture plane. When the punch penetrates the material originating at the cutting edges of the punch and die button on both the upper and lower surfaces of the material, it produces fracture–and pushes it into the die button. When the die button has the correct clearance, these upper and lower fractures connect. This frees the slug and releases the punching force.

Considerations

A common mistake is to specify a too-tight clearance, assuming it will improve the edge quality. This is not the case. When the die clearance is too tight, the upper and lower fractures essentially miss each other. Secondary cracks and/or double breaks are created.

In addition, with tight clearances the material has a higher tendency to grab the punch, thereby increasing the stripping force on the punch. Excessive stripping forces will result in abrasive wear and diminished punch and die button life. In general, increasing the clearance percentage will result in better hole quality and smaller burrs. However, it can increase the tendency for rollover and slug pulling.

For instance, the figure below shows the effect of clearance on roll-over and shear zones. Roll-over is minimized with tighter clearance, but results in uneven burnish and breakage. The opposite is observed with Dayton's Engineered Clearance.

This change in hole quality is critical for holes where a secondary operation is performed.

Slug Inspection

Slugs are a mirror image of the hole, and can tell you if the clearance is appropriate for the application.

If the slug has a rough fracture plane, a small burnished land area, and excessive burr, the clearance is excessive.

Slugs with an irregular fracture plane, an uneven burnished land, and secondary shear indicate insufficient clearance.

Optimal die clearance produces a slug with a consistent burnished land that is approximately one third of the material thickness and an even fracture plane in line with the land.

Increasing Punch-to-die Clearance

Perforating a Hole

Punching (or perforating) a hole seems a relatively simple process. It is, however, a multiple step operation (shown below), and best product quality results can be obtained by optimizing the punch-to-die clearance.

If the clearance between the punch and die button is too tight, the pressure can cause the slug to expand and jam in the die button. It will cause excessive wear, and can cause breakage and chipping of the punch–and result in slug pulling or jamming (stacking).

Industry Standard Clearance

A long-time industry "rule of thumb" used by die makers for the clearance between the punch and the die button is 5% of the stock thickness per side. This provided an acceptable burr height and slug control.

Extensive research and testing have shown that a significant increase in punch-to-die clearance can reduce burr height, increase the life of the punch, and improve hole quality–all good reasons to consider Dayton Engineered Clearance as the new industry standard.

The Dayton Engineered Clearance

The Dayton Engineered Clearance, considered by many as the "new" standard, offers a wider range of clearances, reaching as high as 28% Δ. ( Δ = clearance per side.)

The clearance itself depends on the stock thickness, the tensile strength, and the type of material–all driven by the requirements of the specific job.

A regular clearance of 5% per side can produce a hole 0.0001" or smaller than the point of the punch. This creates a press-fit condition on the point during withdrawal, causing excessive wear on the punch and the die button. The Dayton Engineered Clearance produces a hole that is larger than the point of the punch, thus eliminating as much as two-thirds of the wear on the punch.

Optimization

Optimum benefits from The Dayton Engineered Clearance can be achieved by utilizing a Dayton product called a Jektole® Punch. The Dayton Jektole® Punch employs a built-in, spring-loaded ejector with a side vent hole, which helps reduce slug pulling by not allowing the slug to stick to the face of the punch. Thus, optimum punch performance and product quality are achieved.

Dayton Jektole® Punches are used with all types of materials and applications (including high-speed, high-volume punching), and are a key part of the Dayton Engineered Clearance.

Dayton Jektole® Punches, utilizing the tested and proven Dayton Engineered Clearance standard, prevent slug pulling, breakage, and chipping, and help improve punch performance and product quality.

Improve Your Productivity: Select the Proper Clearance

The two charts below show the Dayton Engineered Clearance for various steels and other materials. In the Ferrous Materials chart, both the tensile strength and the hardness ratings are shown. Tensile strength is presented as MPa, along with the appropriate KSI (Kilogram per Square Inch or PSI x 1000) conversion. Hardness values are shown in HB (Brinnel Rating Scale) or HRC (Rockwell Rating Scale), whichever applies.

The punch-to-die clearance depends on the thickness, type, and strength of the material. The Dayton Engineered Clearance offers a wider range of clearances, thus allowing you to optimize the performance of your materials.

How To Select The Proper Clearance

  1. Identify your grade of material on left side of chart.
  2. Identify the tensile strength of the material from the last row of the chart.
  3. If the material is HSS, AHSS, UHSS, or Aluminum, look up the thickness scaling factor based on the material thickness (see chart below)
  4. Multipy the recommended clearance from the chart with the scaling factor table.
    Examples:
  • SAE Grade 280B (Bake Hardenable), Tensile strength 421 MPa. =10-11% Δ per side of Material Thickness
  • SAE Grade 800 DL (Dual Phase), Tensile strength 860 MPa, Material Thickness=2.0mm (14% x 1.20 scaling factor). =16-17% Δ per side of Material Thickness.

Ferrous Materials–Engineered (Jektole®) Die Clearance, Tensile Strength, and Approximate Hardness Values

Other Materials–Engineered (Jektole®) Die Clearance and Tensile Strength

The ranges shown above are the result of more than 10,000 clearance tests performed by Dayton Lamina on actual customer provided materials. The optimum clearance will vary, depending on your requirements for burnish length, burr height, and tool life. See the next page to find out how to have your material tested by Dayton Lamina.

Jektole® Clearance Testing–Exclusively from Dayton

Clearance Testing

Dayton Lamina has performed extensive research, completing and validating more than 10,000 clearance tests. The Dayton Engineered Clearance does, in fact, offer many positive benefits:

  • Reduces punch wear by reducing the force required to strip the punch
  • Produces less burr/reduces the need for grinding
  • Reduces downtime from re-grinding
  • Reduces total punch and PM costs
  • Requires less press tonnage
  • Increases bottom line profit

 

Customer Clearance Testing

Customer clearance testing–an exclusive Dayton Lamina testing service–is available to any company interested in using the Dayton Engineered Clearance. In the test, a series of .188" diameter holes are punched, using varying clearances to determine the optimum clearance for a given material. The chart shows typical test results.

The Process

  1. Provide Dayton Lamina with four samples of your material. Samples must be 25 mm (1") x 100 mm (4") up to 4.8 mm thickness; burrs removed; flat; and free of holes and material spurs. Note: Depending on the material tensile strength, the maximum thickness could be lower than 4.8 mm (.188").
  2. Test results are analyzed and recorded on data sheets, showing clearance ranges and corresponding hole characteristics.
  3. After the samples and data sheets are returned, select the clearance based on hole size and burr height. If you desire a specific hole characteristics (e.g., more burnish length), select the clearance to meet your requirements by examining the test strip.

Clearance Test Sample

Jektole® vs. Regular Clearance

The bar graph above illustrates the dramatic differences in individual test results for both the standard 5% Δ clearance and the Dayton Engineered Clearance. Under similar test conditions, the standard 5% Δ clearance requires 41 hours of maintenance per million parts, while the Dayton Engineered Clearance requires 12.5 hours of maintenance per million parts!

Contact your nearest Dayton representative for Jektole® Clearance Testing.

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Surface Treatments and Coatings for Improved Productivity

Dayton Progress

Dayton's leading-edge coatings and other unique surface treatments have been developed to improve inplant performance by increasing tool hardness and wear resistance.

Surface Treatments

DayKool™ (XCR)

A cryogenic steel conditioning process used in addition to heat treating. An effective way to achieve optimum toughness, improved strength, and dimensional stability. Used primarily with hard, thick materials.

DayTride® (XN)

A low temperature, cost-effective surface application that treats all exposed surfaces. Provides increased dimensional stability. Ideal for punches and die buttons. Approx. hardness: RC73.

XVP

A thin film coating provides superior hardness (harder than carbide). Super-smooth finish on the point helps reduce galling and maintenance. Ideal for higher-than-normal punching frequency.

XPS

Super-smooth polish on the point to reduce galling and improve punch life. Use with the appropriate coating for your application to maximize punch life and reduce maintenance costs. Excellent for extruding applications.

Abrasive Wear

DayTiN® (XNT)

Excellent wear resistance and lubricity. Not recommended for stainless steel, copper, or nickel. A good general-purpose coating. Approx. hardness: *Vickers 2300.

TiCN (XCN)

Ultra-hard (harder than carbide), thin coating. Provides superior abrasive wear resistance and lubricity. A very good general-purpose coating for all materials. Upgrade over XNT. Approx. hardness: *Vickers 3000.

DayTAN™ (XAN)

Ultra-hard (harder than carbide), high-aluminum coating. Provides high temperature resistance. Well-suited for applications where surface heat is generated. Ideal for HSLA, dual phase, and TRIP steels. Upgrade over XCN. Approx. hardness: *Vickers 3400.

ZertonPlus™ (XNA)

Superior hardness (harder than carbide); provides superior abrasive wear resistance and excellent lubricity. Provides highest temperature resistance, thermal shock stability, & hot hardness. Approx. hardness: *Vickers 3200.

Adhesive Wear

XNM

A solid lubricant coating. Provides both lubricity and wear resistance not available from other PVD or CVD processes. Ideal for aluminum, copper, pre-painted, and galvanized steels. Approx. hardness: *Vickers 2000.

XANL

High hardness and temperature resistance of XAN coating topped with an anti-frictional coating with excellent lubrication properties. Approx. Hardness: Vickers 3000.

XCD

Diamond-like carbon coating. Combines high hardness with an extremely low coefficient of friction. Good protection against abrasive and adhesive wear. Ideal for aluminum. Approx. hardness: *Vickers 5000.

XCDH

Super-smooth finnish combined with advanced DLC coating for a very low coeficient of friction with extremely high wear resistance. Approx. hardness:  *Vickers 5000.

XCDP

Super-smooth finish combined with a DLC coating for a very low coefficient of friction with high wear resistance. Excellent for stamping aluminum. Approx. Hardness: Vickers 2800.

Extrusion Coatings

XNP

The ultimate coating for improved resistance to galling; excellent wear resistance, superior surface finish, and high lubricity. Ideal for extruding and forming applications. Tolerance is ±.0002". Approx. hardness: *Vickers 3100.

XNAProgress (XNAP)

Ultra-hard coating that absorbs shear stress; provides excellent high-temperature resistance. Ideal for stamping where tools are exposed to extreme stress profiles. A good alternative to TD coating without the dimensional changes associated with that process. Approx hardness: *Vickers 3200.

Miscellaneous Coating

CRN

Excellent adhesion, high toughness, and good corrosion resistance. Primary applications are metal forming (copper, brass, & bronze), metal die casting, and plastic injection molding. Approx. hardness: *Vickers 1800-2100.

 

 

* Vickers used when RC exceeds 80.
® DayTride and DayTiN are registered trademarks of Dayton Lamina.
™ DayTAN, DayKool, and ZertonPlus are trademarks of Dayton Lamina.

Birth of a Hole

The dynamics of the perforating process is often considered to be a simple two step process of driving a punch through a piece of sheet steel and then withdrawal of the punch from the hole.

There are in fact six steps to perforating a hole. Each step contains elements critical to the overall process. An understanding of these steps will assist in the selection of die construction, tool steels, and punch to die clearance.

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Stamping Basics

This report defines basic stamping terminology and illustrates basic stamping functions. We explore the common types of die construction, compare stripper design options, and analyze common die operations.

 

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High Speed Stamping

This report addresses the special concerns of high-speed stamping. We define high-speed stamping and discuss operating factors - such as the effects of die clearance and methods of slug control - that will help improve your stamping operation. We explore tool steel and selecting the proper surface treatment for your application. We further describe how stripper design affects your high-speed stamping operation. Finally, we discuss application problems and possible solutions.

 

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Tools Steels For Punch & Matrix Components

Selecting the proper Tool Steels, Heat Treatment, & Surface Treatments for a stamping application can be a complex and confusing process. To simplify this process, a few basic facts should be understood. This publication will present and examine facts using terms familiar to the nonmetallurgist.

 

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The Ball Lock System

This illustrated booklet describes the features, benefits, and value of working with True-Position Ball Lock Punch & Matrix retainers. A comparison of End & Square Retainers with Backing Plates is covered, along with the inherent problems associated with these products.

Through the years ball lock components have been continually refined to improve precision and reliability. The most significant improvement was the introduction of the backing plug with in-line primary dowel. This change eliminated the need for a packing plate. Backing Plugs along with many other features introduced by Dayton Lamina are discussed in the program.

 

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Protecting Your Punching Tool Investment

Economic shortcuts in the build process almost always add to production costs in the form of increased maintenance and production scrap. To avoid these costs, initial concerns should be directed toward the type of die construction.

Elements such as the stripper design, type of punch retention, and whether to use a hardened backing plate in a particular application tend to have the greatest effect on tool life.

 

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Balancing Wear, Strength, & Toughness

Selecting the proper tool steels, heat treatment, and surface treatments for stamping of coated materials can be a complex and confusing process. To simplify this process, you first must understand a few basic facts about the available choices.

 

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Die Clinic: The Tooling

Like an iceberg, most of your die costs lurk below the surface. How many times has someone compromised quality or service for price? Die Clinic assists in reducing the true cost of producing metal stampings.

This Dayton Lamina technical presentation will show you how to:

  • Increase Production Runs
  • Reduce Downtime
  • Reduce Breakage
  • Reduce Burrs
  • Increase Tool Life

Problem Solving Guide

Problem Solver brochureSolutions for punch wear, breakage, and other problems come from both time-tested techniques (e.g., adding a larger-than-normal radius under the head) as well as consideration for a wide range of leading-edge engineering solutions (e.g., head alterations) and specialty coatings designed to maximize the life of the punch.

This troubleshooting guide can help you determine the cause for your broken, chipped, or worn punches. It can also help you select the best solution—including Dayton products and services.

 





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Perforating Round Tubing

Dayton Progress

Perforating holes through one side of a round tube can present several unique problems for metal stampers. The most common are tube deformation, punch point chipping, and slug control.

Tube Deformation and Punch Point Chipping

The first two problems, tube deformation and punch point chipping, are typically caused by tube movement. A nesting die can be used to reduce this movement. The ideal nest should be a radius pocket that is machined a few thousandths of an inch larger than the outside diameter (OD) of the tubing. This will help locate the tube and offer some lateral support.


FIGURE 1: The ideal nest should be a radius pocket that is machined a few thousandths of an inch larger than the OD of the tubing.

The depth of this nest should be slightly more than one-half the OD of the tubing to minimize tool marks and reduce tube deformation.

In addition to proper nesting, it is equally important to lock the tube into position using a "V" groove in a spring stripper. A "V" groove with a 60- to 80-degree included angle will prevent tube rolling and offer additional lateral support. Without this die and stripper support, the tube will be deformed while the hole size will be inconsistent and out-of-round.

Slug Control

The third major concern when perforating tubing is slug control. Slugs that do not break free in manufacturing may interfere with mating parts at assembly or break free and rattle around in the part while in use—neither of which is desirable.

One approach of solving this slug problem is to put shear on the point of the punch. Shear angles and contours play a major part in slug control when perforating a hole without a matrix. They minimize the deformation of the tube by preventing the slug from pulling to one side of the hole as the punch penetrates the tube wall.

Several different shear configurations can be applied, some of which are limited to specific types of tubing materials.

A concave shear that nearly matches the OD of the tube works well for ridged plastics and thick-wall aluminum tubing. It locks the slug into place and cuts it free.


FIGURE 2: This illustrates a concave shear.

Be aware that the two feathered edges are prone to breakage, and wear prematurely. In more severe applications, the feathered edges of a convex shear will chip and the punch may split up the middle.

A flat-bottom punch will work on mild steels. Although not typically considered a shear angle, a flat bottom punch will have a shear effect reducing deformation when perforating contoured material.


FIGURE 3: This illustrates a flat-bottom punch.

One drawback to a flat-bottom punch is that it does not prevent the slug from pulling to one side. This setup may leave an occasional slug partially attached to the tube.

The most effective shear configuration is a two-dimensional convex radius that is slightly larger than the OD of the tube. It reduces tube deformation while offering good slug control. A positive side effect from this configuration is that it reduces punch-point chipping, making it ideal for stainless steel and thin-wall tubing applications.


FIGURE 4: Shown here is a convex radius.

Piercing

Another method of slug control is to not remove the slug at all. By piercing instead of perforating, the excess material from the hole is rolled over or formed down into the hole, leaving no free slug to contend with.


FIGURE 5: Another method of slug control is not to remove the slug at all.

This method of slug control is accomplished by using steep shear angles on the point of the punch. The punch will have three or four flats ground on the point similar to that of a nail. The angle should be between 20 and 60 degrees included.

These shear angles are the result of development (trial and error). Changes in the shear angle will have a direct effect on how much the tube will be flattened or deformed. These angles are limited by how far the tip of the punch can enter through one side of the tube and not contact the opposite wall.

Steeper angles will produce the least amount of deformation, but will be more likely to contact the opposite wall. This type of pierce is most effective when working with aluminum or mild steel.

These are the most common shear configurations. However, many others have been developed and will also work well.

Conclusion

When perforating tubing on a stamping press, please consider the above recommendations. They are sound methods for reducing current problems and will serve as a good foundation for further development.

Perforating tubing through both sides, at an angle, or with a mandrel are considerably different circumstances, all of which are topics in themselves.

High Strength Steels

A Key Material in Critical Safety Components

Auto manufacturers are challenged by increasing oil prices, stricter emission standards, and greater demands on safety. Lighter and stronger steels in structural components are now required from OEMs and suppliers. How does a die designer handle forming and piercing with these new High Strength Steels (HSS)?

Typical High Strength Steel components in Automotive bodies

Typical High Strength Steel Components in Automotive Bodies
(Courtesy: VW-EU)

Types of high strength steels

HSS grades are varied. Some grades have elongation similar to that of conventional cold or hot rolled steels with higher yield and tensile strengths such as High Strength Low Alloy (HSLA) 420. Other grades have very little elongation and exhibit very high yield tensile strengths. Some grades achieve high tensile strengths through a hardening process. These materials behave differently enough to warrant special treatment in the die design and presswork.

Dent resistant grades

One of the earlier forms of high strength steel used for automotive components came in the form of Dent Resistance (DR) grades. These DR grades were desirable in auto components that required increased load carrying capability and improved crash energy management. But their most important factor for mass reduction was a reduction in sheet metal thickness. However, it is well known that an increase in strength typically comes with a loss in ductility or formability. Steel manufacturers made these grades available in two flavors — a Bake Hardenable (BH) grade and a Non-Bake Hardenable (NBH) grade.

The difference between BH and NBH

BH grades achieve an increase in strength through the process of post draw baking cycle. This is typically done in a paint dry oven after forming. NBH grades gain their increase during the forming operation through work hardening. Die design should account for larger forming forces on tools used in NBH forming, and should favor a relatively more generous drawing geometry (corner radii). You could expect higher contact pressures during forming with NBH grades. Severe galling is a possibility and coatings may be recommended on certain applications.

 

Productivity Selector

The Productivity Selector correlates different types of stock, grouped by tensile strength, type of clearance and the resultant burnish length and productivity rating. The Productivity Rating, simply stated, shows that Jektole Clearance will produce over three times as many parts between sharpenings as Regular Clearance. Selecting the proper Jektole Clearance can do more for your stamping productivity than any other single factor.

How to Select the Proper Clearance

  1. Determine the Stock Group by tensile strength of the part material. (See Material Chart at bottom if you don’t know tensile).
     
  2. Select the Jektole Clearance expressed as % i (% of stock thickness [T]) for maximum productivity. i = clearance per side.
     
  3. If your material is in the high range of tensile, use the higher clearance; if in the low range, use the lower clearance. Ex.: 40,000 P.S.I. 10%; 60,000 P.S.I. 11%
     
  4. If burnish length is the main criterion, select the clearance that produces burnish needed. If the burnish length with Jektole Clearance does not meet your needs, choose Regular Clearance. Reducing the clearance increases the burnish length and wear on the punch.

Productivity Selector

Hardness values are based on commercial data available from various sources and are considered approximate.

The Rockwell scale readings used include:

C hard steels and materials harder than B100

B soft steels and non-ferrous alloys

F annealed non-ferrous alloys and thin soft metal strips and sheets. Low “F” values have been interpolated from Brinell readings.

NOTE:

  1. The values shown are from the averaged results of over 2000 clearance tests. If you want a test of your material, contact your local Dayton Distributor.
     
  2. The Regular clearances shown are the “old rule of thumb’ which applied the same clearance to different stocks.
     
  3. "Burr Free" stamped parts do not exist without some tumbling or with tool sharpness, cutting clearance and material character. Values shown were produced with a .002” – .004” radius on punch point.
     
  4. The percent of burnish shown is for a hole whose diameter is greater than 1.5 times the stock thickness. Hole diameters less than 1.5 times stock thickness extend the burnish length. For the latter condition, clearance should be increased beyond the values shown.
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Jektole Clearance

Jektole IllustrationThe key to increased productivity

Perforating punch to matrix (die) clearances in metal stamping dies have been universally expressed as a percentage of stock thickness, and for clarity should be expressed as percent per side.

The old "rule of thumb" called for clearance per side of 5% and is commonly known as regular clearance. It has been applied to nearly all applications in perforating ferrous materials.

Jektole, the engineered clearance, is approximately twice regular clearance per side of 10-12%. However, even greater clearances are not uncommon on some hard materials. Over 5,000 clearance tests have been performed by Dayton to prove that increasing the clearance does not lessen hole quality as has been thought by many people. Dayton clearance tests do, in fact, prove that Jektole clearance...

In production:

  • requires less press tonnage
  • reduces pressure required to strip the punch ...which in turn reduces punch wear
  • produces minimal burr
  • doubles (and often triples) piece output per grind
  • reduces total punch costs

In maintenance:

  • keeper key-holds pin in retracted position
  • eliminates the need for disassembly before grinding
  • maintains proper pin extension
  • reduces downtime from re-grinding

Jektole Clearance Testing

To assist you in determining the correct Jektole clearance for your job, Dayton offers a clearance testing service. Dayton will perforate your material with a range of clearances and return a sample with an analysis report.

download a clearance test form Download a clearance test form.

Here's all it takes:

  1. Just provide your local Dayton distributor with two samples of your material. Samples must be 1" x 4" long with a maximum .188 thickness, burrs removed, flat, and free of holes.
  2. We test-perforate your material under simulated production conditions.
  3. Test results are analyzed and recorded on data sheets showing clearance ranges and corresponding hole characteristics.
  4. Test specimen and data sheet is returned for your examination. Allow ten working days for the completion of test and delivery time through the mail.
  5. Select the clearance based on hole size and burr height. If you desire specific hole characteristics, such as more burnish length, select the clearance to meet your requirements by examining the test strip.

Clearance Test SampleHere's Proof That Jektole Works

A typical report

The sample is 16 GA. (.0598") Cold Rolled Steel #1 Temper

All holes were perforated by Jektole punches with .1875" point diameter-radiused to .004" to simulate a wear condition. Matrix diameters were varied to produce the clearances shown.

Proven Results with Jektole Clearance

Case History #155

Die Set-Up

Perforating 29 holes, .125" dia. on .1875" centers. Material was #4 Temper, CRS, .036" thick and 4.835" wide, lightly oiled.

Press Set-Up

Press was continuously operated at 120 spm to produce approximately 57,000 hits per 8 hour shift.

Maintenance

Regular Clearance - 41 hours per million parts

Jektole Clearance -12.5 hours per million parts

Regular vs Jektole Clearance

Case History - Figure 1

  Punch Life
Average Hits Between Grinds   Total Punch Life (# of Hits)

 

 

The 6 Steps of Perforating

The perforation process involves driving a punch through material and the rapid failure of the material as the slug breaks free. For this reason, perforating often is mistakenly considered to be a simple two-step process.

In fact, there are six definable steps in the perforating process: impact, penetration, break, snap-through, bottom, and withdrawal. Each of these steps contains elements that are critical to the overall process. An understanding of these steps assists in selecting die construction, tool steels, and punch-to-matrix clearance.

  1. Impact
    The punch first makes contact with the material upon impact. The punch comes to a stop momentarily as the backlash and flex of the ram and press are taken up. A compressive load builds rapidly, sending a shock wave up through the punch. The material begins to bulge out from under the point of the punch.

    Impact
     

  2. Penetration
    As the power of the press exceeds the yield strength of the material, the punch point begins to penetrate the part's surface. Both the punch and matrix begin to cut from their respective sides. The leverage set up by the die clearance allows the punch to bend the slug. The center of the slug bows away from the punch, creating a vacuum pocket that will become a factor in later steps.

    Penetration
     

  3. Break
    Once the material is deformed and stretched to its tensile limits, it begins to crack between the cutting edges of the punch and matrix. This subsequently generates the break found in the finished hole and on the outside diameter of the slug.
     
  4. Snap-through
    When the tensile limits of the material are exceeded, the slug separates from the part.
     
  5. Bottom
    The ram of the press reaches the bottom of its stroke.


     

  6. Withdrawal
    The punch is withdrawn from the part material.

 

 

Improving Perforating Die Performance

The effects of stress, clearance and material

Perforating is defined as a process of making a hole by removing a slug. During perforating in a stamping operation, a punch shears and breaks a slug out of the part material and then pushes the slug into a matrix (die bushing). The matrix hole is larger than the punch point. A clearance must be maintained constantly around the entire punch point.

To perforate the part material, the material must fail. The harder the part material, the greater the forces on the punch and matrix become, resulting in sudden shock, excessive wear, high compressive loading, and fatigue-related failures.

During impact and penetration, the cutting edges on both the punch and matrix are subject to extreme pressure, which can result in chipping, heavy wear, and eventual breakage.

During snap-through, the sudden unloading of pressure on the punch generates a reverse shock that often leads to punch head breakage.

When the press ram reaches the bottom of its stroke, the punch should enter the matrix only about 0.020 to 0.030 inch. Overentry of the punch creates excessive wear and can cause slug pulling. The farther a punch enters, the more vacuum it creates at withdrawal. This vacuum can pull slugs.

Withdrawal of the punch from the part material can account for as much as two-thirds of punch wear and may be responsible for slug pulling.

Alleviating Pressure With Correct Clearance

Punch-to-matrix clearance can be described in two ways-total clearance and clearance per side (i). Both are correct; however, to minimize confusion, this article uses clearance per side as the standard.

Clearance per side is the distance between the cutting edges of the punch and the matrix. This distance is maintained around the entire perimeter of the cutting edges regardless of their shape.

Engineered Clearance 0f 10% Per Side

For many years toolmakers used 5 percent of stock thickness per side as a standard, or regular, punch-to-die clearance. This provided an acceptable burr height and slug control. Research and testing have revealed that a radical increase in punch-to-matrix clearance can reduce burr height to the lowest point and increase tool life exponentially. This increased clearance is referred to as engineered clearance.

The side effect of this approach is slug pulling. When punch-to-matrix clearance is increased, the size of the slug is reduced. This leaves it loose and free to pull up at withdrawal. A spring-loaded ejector pin extending from the center of the punch face will remedy the slug pulling in most cases by pushing the slug free of the punch face. Or instead of the ejector pin, pressurized air blown through an air hole in the center of the punch pushes the slug free. Engineered clearance can be applied as long as there is a means of slug control.

Because regular clearance can produce a hole that is as much as 0.002 inch smaller than the point of the punch, it creates a press-fit condition on the point of the punch with every hit during withdrawal, causing excessive abrasive wear on both punch and matrix. An engineered clearance produces a hole that is larger than the point of the punch, leaving a slip-fit condition and eliminating as much as two-thirds of the wear incurred with regular clearance.

Characteristics of a Hole

Regular vs. Engineered ClearanceHole characteristics vary with different clearances. Regular clearance typically results in a high percentage of shear or burnish with minimal rollover and break. The hole tends to be smaller than the punch point. Engineered clearance achieves a low percentage of shear or burnish, with greater rollover and break. The hole size with engineered clearance will be larger than the point of the punch.

A comparison of holes perforated with regular clearance versus holes perforated using engineered clearance reveals the advantage of increasing clearance between the punch and matrix. As punch-to-matrix clearance increases, the hole size in relation to punch point size becomes larger, reducing stripping friction and wear. The result is longer punch life.

Burr HeightBurr height also is affected by punch-to-matrix clearance. Regular clearance produces acceptable burrs in many cases. As the clearance increases, the burr height Increases. A substantial increase in punch-to-matrix clearance reduces the burr height below that produced with regular clearance in most applications.

Because the burr height initially gets worse before dropping to its lowest point with an engineered clearance, a compromise between regular and engineered clearance is not recommended.

Material Considerations

Type

Soft materials such as aluminum, brass, and draw-quality cold-rolled steels generally run best between 9 and 11 percent clearance per side. Low-carbon cold-rolled and hot-rolled, pickled and oiled steels, CDA 110 copper, and hardened brass tend to run best at about 12 or 13 percent clearance per side. Higher carbon spring steel and annealed stainless steel run best at 14 percent per side. Hardened materials require additional punch-to-matrix clearance.

Strength

Optimal clearance for a part depends on that material's tensile and yield strengths. The higher the tensile and yield strength, the greater the recommended punch-to-matrix clearance. The greater the difference between the tensile and yield strengths, the greater the burr will be regardless of the clearance being used.

Snap-through shock has a direct relationship to material hardness. Harder and stronger materials generate the greatest shock. Once the slug has broken free, the direction of part material springback should be examined. With regular clearance, the hole in the part contracts and grabs the end of the punch. The slug expands and becomes jammed in the matrix.

The opposite reaction occurs when engineered clearance is applied, which minimizes potential slug jamming problems. A hole in the side of the punch vents the vacuum pocket, allowing the ejector pin to push the slug away without resistance.

Thickness

Part material thickness should also be taken into consideration when determining optimal punch-to-matrix clearance. Heavy-gauge material (more than ¼ in. thick) tends to benefit from an additional 1 or 2 percent of clearance per side to reduce the chance of double break and slivers in the die.

Thin materials (less than 0.020 in. thick) create the greatest challenge for determining optimal punch-to-matrix clearance. These clearances can be radically higher than what is traditionally used. It is not uncommon for aluminum to run best at 15 to 20 percent clearance per side and for spring steel and stainless to exceed 25 percent clearance per side.

A general practice in designing and building a stamping tool is to apply a common punch-to-matrix clearance to all of the perforated holes regardless of size. Unfortunately, there comes a point when a hole size becomes too small in relation to the part material thickness for that clearance to be effective. This results in higher punch loading, longer burnish in the hole, and excessive burr.

This phenomenon begins to occur when the hole size drops below 1½ times the part material thickness. At that point it becomes more difficult to bend and cleanly break the slug free.

Increased leverage to bend and break the slug can be achieved by increasing the punch-to-matrix clearance. One percent clearance per side should be added to the existing clearance when the hole size is 1½ times the part material thickness and increased more as the hole size becomes smaller in relation to the material thickness. A hole size that is equal to the part material thickness needs approximately 4 percent additional clearance per side.

The resulting hole from a nearly 1:1 ratio of punch point diameter to material thickness will have different characteristics than a larger-diameter hole in the same part. Small holes that are less than 1½ times the material thickness have a longer burnish length, larger burr, and tend to be smaller than the point of the punch point size. Slug burnish and break are affected in much the same manner as the hole is.

The slug becomes difficult to bend and break out of the part when the diameter is less than 1½ times the material thickness. This increases load and forces the punch and matrix to cut a greater portion of the slug before it breaks free, resulting in excessive galling, wear, slug jamming, and punch breakage.

The bottom line is, when the objective is to achieve a high percentage of shear or burnish in one hit, or to have a very short production run, regular clearance may be suitable. However, in all other circumstances, engineered punch-to-matrix clearance should be a strong consideration.

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