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Buck Gibson
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But the hole in the material and the punch are the exact same diameter so removing the material would be difficult without some kind of stripping device.

On kick operated machines, the die is secured by a set screw in the die holder and the punch is secured directly into the ram.

1 theartofpressbrake.com Punch press tooling Tooling Strippers When a hole is punched the body of the tool passes through the material, pushing the slug free. But the hole in the material and the punch are the exact same diameter so removing the material would be difficult without some kind of stripping device. And just as punches and dies vary, so do the methods of stripping the workpiece from the tool. On kick operated machines, the die is secured by a set screw in the die holder and the punch is secured directly into the ram. Figure 1 This style of tooling design does not generally incorporate a stripper body for removing the workpiece from the punch; it should have a bolton stripping framework. Without the stripper the workpiece will tend to remain firmly impaled on the punch body. Pictured in figure 1 is a piece of material impaled Figure 2 on a punch body. Without a stripper or stripper frame work, a piece of low durometer urethane works well. Figure 2 shows how pieces are cut from a sheet of urethane to produce a working stripper. The urethane can be a homemade remedy; however, there are some urethane manufacturers producing pre-cut and pre-holed urethane strippers. The urethane is purchased in sheets or blocks that are cut to size and drilled to fit by the operator who needs to use it. Urethane has only one minor problem being used this way; that problem is hysteresis. Hysteresis is the build-up of internal heat within the pad itself. Urethane works very well in a hand-operated equipment and single station machines. However, it doesn t work well in an automated setting; it will tend to wear out too quickly. Still the urethane is a good bet for hand or fly wheel driven equipment, single station, stylus activated machines like the Strippit 18-30, circa the 1960 s. As the world of punching matured into mechanical punch press, one of the first tooling related changes was the edition of the stripper body, figure 3. These stripping bodies are designed so that a spring loaded punch would protrude through the stripper body, through the material and into the die cavity. Figure 3 Then when the punch is withdrawn the stripper allows the punch back up while acting as a solid barrier to the material. Figure 4 is an exploded view of a standard punch body, stripper, and spring assembly. There can be a lot of reasons for the material not stripping from the die: weak springs, the punch or die being too

short, material compression in die build up on the punch or stripper body, or just a dull tool. One of the following suggestions should help resolve tough stripping problem: 1.

Check die clearance and tool sharpness. 6. Cut a back taper into the punch. 7. Possibly use a JK shear cut on your punch. See below for an explanation of this type of shear.

While some manufacturers run their punches dry, they run the risk of galling when working on softer materials like H-series aluminum.

2 short, material compression in die build up on the punch or stripper body, or just a dull tool. One of the following suggestions should help resolve tough stripping problem: 1. Oil the sheet with a light lubricant. 2. Double check the punch and the die height. 3. Clean the punch, die and stripper body. 4. Shim the punch spring to pre-load the spring tension. 5. Check die clearance and tool sharpness. 6. Cut a back taper into the punch. 7. Possibly use a JK shear cut on your punch. See below for an explanation of this type of shear. Figure 4 Lubrication Without proper lubrication the life expectancy of most tools will be reduced by 50 to 60%. While some manufacturers run their punches dry, they run the risk of galling when working on softer materials like H-series aluminum. There are a lot of choices for lubricants, for example, WD40 (in bulk) mixed with Kerosene are great for aluminum and cold rolled steel. For stainless steel, or hot rolled steel a heavier one may be called for, something like hydraulic fluid, automatic transmission fluid, most any lighter oil. Lubrication should always be the foremost consideration when considering the ease of operation and the life of the tool. Galling Galling is best removed through the use of a fine polishing stone, the stone should be used in a motion that is parallel to the direction of the galling or the direction of the punching motion, figure 6. The purpose for the fine stone to clean up the galling and to replace the damaged surfaces with polished surfaces, figure 7. By polishing the surface of the punch that comes into contact with the material, the chances of the galling re-occurring will be decreased. Figure 5 Under no circumstances should you ever bead blast or use harsh abrasives like those of a belt sander to remove galling. Just as polishing helps to reduce the amount of galling through the polishing of the surface, roughing the surface up by using harsh abrasives only gives the punched material something to grab onto, worsening the galling. Correct die clearance can and does make a big difference, as does the application of lubricants or light oils to stop galling. Heat build-up Heat build-up in the tools is not uncommon and is one of the main reasons for galling. Should lubricants not help or cannot be used, some other method will need to be employed. Figure 6 The most obvious are: slow the machine or program down to ensure that heat is not built-up in the first place; program a break in the use of that tool within the program; allowing the tool to cool while punching continues with a different punch and die set. After the punch has some time to dissipate the heat, it can be re-entered into the programming and

The concave and double concave design is best used in nibbling applications in light gauge materials as it inverts the stress of punching; this same stress can also cause the punch to break under

Nibbling can be done but with only 50 to 70% of the punch s maximum bite. Figure 8 also shows an inverted rooftop; again this is a great punch cut for nibbling because of the stress inversion.

Figure 7 The double valley shear is the best, bar none, of the nibbling processes for long narrow shapes like slitting tools, figure 9.

3 finish the pattern that it started. Tool Grinds There are five basic types of grinds used on punch tooling: roof top[/glossary, [glossary]concave and double concave, inverted roof top, double valley shear and the JK shear. The concave and double concave design is best used in nibbling applications in light gauge materials as it inverts the stress of punching; this same stress can also cause the punch to break under higher work loads, figure 8. The roof top design is at its best when punching heavy tonnages. However, it has a tendency to side load in nibbling applications. Nibbling can be done but with only 50 to 70% of the punch s maximum bite. Figure 8 also shows an inverted rooftop; again this is a great punch cut for nibbling because of the stress inversion. This cut leaves the tool open to an increase in breakage due in part to the sharp focal point taking the brunt of the stress. Figure 7 The double valley shear is the best, bar none, of the nibbling processes for long narrow shapes like slitting tools, figure 9. The JK shear is a special cut that allows the punch to withstand the stress and strains of heavy gauge punching. Tool Sharpening When to sharpen a tool is open for debate; the general rule of thumb here is, if it takes more than.010 (.25mm) to bring a tool back to a decent state of sharpness you have waited too long to do it! If the tooling is allowed to be run while dull it will produce a sub-standard workpiece and greatly reduce the expected life of that tool. As tooling starts to wear, the rate of wear will increase. It is much better to spend the time to remove a little material now than to wait and remove a lot. Tool steels are heat sensitive and should NEVER be allowed to get hot. When sharpening a tool you should always use a wet grind. Figure 9 Figure 8 By wet grinding you can avoid burning the tool. Make sure the wheel of the surface grinder is dressed regularly to keep it clean and unplugged. Use quick light passes over the tool to avoid heat build up,.001 per pass (.02mm). NEVER TAKE A BIG BITE of the tool at the surface grinder; it can ruin the tool and is a very big safety problem. Figure 10 shows you the right and the wrong way to use a surface grinder to sharpen your tool. Cleaning the grinding wheel requires a diamond dressing stone mounted to the table and then run under the wheel, removing very small amounts of the wheel. Figure 10 By sharpening the tool before it gets too dull the small amount of cut needed to resharpen can easily be doubled over the life of the tool. The amount of grindable tool is roughly.250 (6.38mm), but does vary from manufacturer to manufacturer

Figure 11 Wheel dressing Wrong Way Right way The Angles, Depths, and Dimensions of Sharpening Figure 12 shows the three faces of correct punch sharpening: shear angle, shear depth and the distance to

If you know any two pieces of data, dimension b and the shear depth, you can find the correct shear angle. Close adherence to the formula will ensure the proper functioning of the tool.

the percentage of shear by material gauge and by punch type. Reading this chart is simple, for example take the 1/8 concave shear. In 14- gauge.078 (1.99mm) the shear factor should be 50%.

4 Figure 11 Wheel dressing Wrong Way Right way The Angles, Depths, and Dimensions of Sharpening Figure 12 shows the three faces of correct punch sharpening: shear angle, shear depth and the distance to the peak of the shear angle. Any of these can be solved as long as any other two pieces of the puzzle are available. For example, look at the shear formula. If you know any two pieces of data, dimension b and the shear depth, you can find the correct shear angle. Close adherence to the formula will ensure the proper functioning of the tool. Shear angle = shear depth / dim b = Tangent of angle Figure 12 Shear depth = dim b x Tangent of shear angle Dimension b = shear depth / Tangent of shear angle The following shear factor chart shows the percentage of shear by material gauge and by punch type. Reading this chart is simple, for example take the 1/8 concave shear. In 14- gauge.078 (1.99mm) the shear factor should be 50%. In other words, if you looked at the material edge on you should see the shear ending at roughly 50% of the material thickness. Obviously, this chart is not material specific but it does act well as a general guidepost for optimum shear and tool capability. Tooling Selection (tonnage) Figure 13 The greatest single limiting factor for punch press tooling is tonnage.tonnage is developed from the type of material to be punched, the thickness of that material and, the area of the punch tips surface. The surface area of the punch is called the land distance and is mathematically referred to as L. The letter A represents the diameter or the diagonal dimension, B represents the width and C is the length. Figure 14 shows five basic shapes of punches: round, square, rectangle, obround, and multifaceted [hexagon, octagon, etc.)

From those drawings and mathematical formulas the total land area (distance) is developed. Once the land area L is known the rest of the formula for tonnage can be completed.

5 From those drawings and mathematical formulas the total land area (distance) is developed. Once the land area L is known the rest of the formula for tonnage can be completed. Find the value for S (the shear factorshear factor)and find material factor value of F from the chart below. Material Multiplication Factors F Aluminum 5052H32 (soft sheets).30 Aluminum 2024T4 (half hard sheets).38 Aluminum 6061T6 (full hard sheets).50 Brass (half hard).70 Copper (soft sheets).57 Steel (cold rolled sheets) 1.00 Steel ASTM A36 sheet 1.20 Figure 14 Steel carbon 1.40 Steel stainless 1.40 Spring steel 4.00 Table 1 Note: the factors above are based on mild cold rolled steel with a shear strength of 60,000 PSI (345 MPa) In the following two formulas tonnage inches, and Kn (metric) will give you the tonnage kn requirements for punching. From there, it is up to you to decide if the feature that you wish to punch is within the abilities of the tool and the machine. Those formulas are: Tonnage (inch) = L x Mt x 25 x F x S kn (metric) = L x Mt x.345 x F x S where 1 ton = 8.9 kn and 1kN =.112 tons Tooling Installation (cleanliness) When it comes to punching there are few things more important in maintaining the integrity of the tooling than cleanliness. These machines and tooling MUST BE KEPT CLEAN AT ALL TIMES! As with any machine, grease and oil are necessary for the smooth functioning of the moving parts. Because of the amount of grease required, it is not uncommon to find a coating of grease on top of the upper turret. If grease is allowed to accumulate on the turret, it will become a catch all for slivers, slugs and assorted dirt. With continued use these slivers and slugs can and will be drawn into the workings of the punch, stripper, and turret

6 Custom tooling, Forming, Embossing, etc. There are many different types of punch press tooling; some are meant for embossing and some for forming. There is tooling that will form small tabs and flanges in the punch. There are others for slitting and gang punches for multiple hole punching. Figure 15 The Countersink The countersink tool itself is capable of producing a wide variety of counter sink sizes and angles. For sheet metal operations, the countersink tool uses a replaceable tip called a chip a figure 15. The process itself requires that a pre-hole be punched at a specific size. This pre-hole needs to be.015 (.39mm) to.035 (.89mm) larger than the required diameter of the hole after punching and countersinking. Fine tuning the diameter of the counter sink is done through adjustments in the punch body length itself. Figure 16 There is one other type of countersink punch body, the solid style. These have fixed diameters and angles, and are designed for heavier materials and work loads, figure 16. Determining the different dimensions of the counter sink, we use the following chart which works well for counter sinks that are punched or drilled: Countersink factors Degree K K Table 2 1. The diameter of the countersink:(k x the called depth) + hole diameter 2. The base diameter of a countersink: The diameter of the counter sink (K x material) 3. The theoretical extension of hardware beyond the bottom of the material:((countersink hole diameter diameter of the hardware shaft) x K2) /

Material thickness (Mt) Major diameter of the countersink (MD) Minor diameter (hole size) = (HD) Depth (D) = (K x Depth) + HD Base Diameter (B) = D (K x Mt) Extension = (D-MD)/2 x K2 Tapping and

7 Material thickness (Mt) Major diameter of the countersink (MD) Minor diameter (hole size) = (HD) Depth (D) = (K x Depth) + HD Base Diameter (B) = D (K x Mt) Extension = (D-MD)/2 x K2 Tapping and Extruding An extrusion used for tapping begins with the punching of a pre-determined hole size in the worksheet. The hole is then drawn out to the desired inside dimension. It is mainly used in applications where the sheet is too thin to support threading. The pre-pierce punch must be selected carefully. The diameter will control the height and the appearance. The height of the extrusion should never exceed twice the material thickness. As for the tapping process, many newer punch presses can be fitted with a tapping head that can tap the newly extruded holes or the sheet. Slug pulling Slug pulling can be caused by one or more of the following reasons: air flow around the tool and turret, one tool sharper than the other, compression between the current slug and previous slugs, and many more. To help reduce or eliminate slug pulling, try a change in die clearance; by tightening up the clearance the slug will tend to stay put in the die. Figure 17 positive tapper Another way to reduce slug pulling is through the use of a negative tapper[/glossary die, figure 17. This taper is somewhere between three and seven degrees, with five degrees being the most common. This adds just enough pinching to hold the slug in the die without really increasing the punching tonnage, but there are some limitations due to compression. The positive taper die is the most common style of die taper. Slug pulling in a [glossary]positive tapper die may be reduced by adjusting the punch length to increase the penetration into the die space, thereby forcing the slug farther into the die. Watch for slug compression! Figure 17 Negative tapper Both the punch and the die should have an maximum of an.020 edge radius when sharp. If the punch is sharper then the slug is more likely to pull. Figure 18 shows the addition of extra material beneath the die face in a manner similar to welding, but, only a.0001 inch of extra material at a time. This in essence shrinks the die opening, helping to hold the slug. The process is called Rocklinizing. Slug pulling from punches that have been cut to shear rather than punch could be the shearing action that s causing the problem

This warp allows the material to pop back and forth and will not lay flat. A cluster punch is used to perform this operation. This is a punch and die set with multiple hole capabilities, figure 19.

8 Figure 18 A note of caution: be sure to check your tonnage, removing the shear will increase the force that is required to punch a given shape. Rocklinizer Short Video Rocklinizing Courtesy of Rocklin Mfg. Oil Canning Oil canning refers to the warp of the material after punching a pattern of small holes. This warp allows the material to pop back and forth and will not lay flat. A cluster punch is used to perform this operation. This is a punch and die set with multiple hole capabilities, figure 19. Each punch within the main tool is called a quill. The best way to reduce oil canning is to use tools that are sharp. Besides sharpening, oil canning can be reduced by using the largest number of quills possible and punch the pattern from the outside in. Sometimes staggering the pattern will reduce oil canning. Make sure the die is shimmed to the correct height and that both sides of the material are lubricated. Oil canning can also be partially cured at the press brakes through the use of a very light cross break, two bends running from corner to corner of the hole pattern. Figure 19 Slitting Tools Slitting is done using a long thin punch i.e.: a rectangle usually.250 (6.35mm) by (76.20mm). This process is not without some of its own problems, most notably a saw tooth effect along the cut edge of the workpiece. This may be caused by any or all of the following reasons: 1) Poor turret alignment. 2) Worn out bushings or keys. 3) Dull tools causing side loading. 4) Machine accuracy. Dimpling in the corners of the rectangle is caused by the expansion of the material after being struck by the punch and the subsequent contraction during the stripping operation. The dimpling that occurs in a rectangle cut can be alleviated by using an obround on the long straight edges and then finishing with a square punch in the corners

The positive taper keeps these non-metallic materials from compressing in the die, and run the punch in its slow cycle or setting.

9 Punching Plastic Punching plastic or other non-metallic materials are occasionally done on the punch press. Along with making sure that both your punch and die are extremely sharp, try to use die clearances of 10% or less of the material thickness with no taper or a positive taper. The positive taper keeps these non-metallic materials from compressing in the die, and run the punch in its slow cycle or setting. Special care must be taken to make sure the work material is stripping correctly; some of these materials will stick on the punch and may require some kind of lubricant. For extra hard plastics a lubricant is necessary. It is unwise to use a lubricant on the softer non-metallic materials because it will add to the compression of material in the die body. Reinforced materials (i.e.: laminated epoxies, fiberglass, Lexan s, etc.) should be done using a high carbon punch and die set to reduce the tooling wear from these types of materials. Shaker parts Some blanks run in the punch press carry nested or multiple parts. So some method must be employed to hold the workpieces in the blank until the entire sheet is removed from the punch. In order to do this a web is employed to do the holding, this is done with the use of an inverted diamond tool, figure 20. The thickness of the web can be as little as.006 (.16mm) in the thicker material and will increase as the material gets thinner, perhaps as much as.020. To find the right working web may require some experimentation. There are too many variables from material considerations, part configuration, or where the web is actually located, to pre-determine what will work in a given situation. Staggering the diamonds around the workpiece is always a good practice. Figure 20 The frame that holds the individual pieces is referred to as the skeleton; this is the throwaway. Tool Alignment There are two types of alignment done to the turret: station alignment; and making sure that the tools are loaded, centered on their axes and aligned with the other tool. Here, tool alignment refers to whether or not one tool is keyed the same as the other. This doesn t matter with rounds or squares, but for other shapes, being off can make for some very bad crashes. The modern multi-station NC turret press is keyed in some fashion to reduce the incidence of tool crossing. A single station machine is also keyed, but on some single station punches, the tool holder swings out 90-degrees to the working axis. With this type of configuration extra attention is necessary to ensure the tool is not crossed up when the holder is returned to its working position, figure 21. Should a tool get crossed it can be extremely difficult to remove from the punch. Figure

10 Tooling Alignment (the Machine) With the frequent use of the punch, deterioration of the turret and machine alignment is to be expected. Product quality will begin to suffer and your tools will dull and break more often if the alignment is not corrected. Check the alignment pins at both the top and bottom halves of the turret, these are the pins that lock the top and bottom of the turret in place. Examine the die holder seats for wear or damage. Check the bores in the turret body for burrs or other damage to the hole or guides. Check to make sure there is no damage to the punch holder / stripper keys. Tool Life If the cutting edges of the punch are allowed to dull the same kind of stretching forces are exerted to the material again, causing burring. While there are hundreds of ways to control burring, here are a few of the best ways to control the problem: 1) Use a lot of lubricant to make moving pieces work freely. 2) Make sure the strippers are holding the work piece to the table during punching. 3) Never use too small of a die clearance, the resistance to shearing is exerting a greater workload on the cutting edge and creating excessive tool wear. 4) Before loading material into the machine be sure the punch and die height are in proper adjustment. 5) During nibbling operations use the maximum tooling pitch (the distance between hit centers). Remember: When looking for ways to control burring, a sharp tool is your best defense and the first place to look

12912 Farnham Avenue White Bear Lake, Minnesota WILSON WHEEL OPERATOR S MANUAL. for Amada Thick Turret Punch Presses

12912 Farnham Avenue White Bear Lake, Minnesota 55110 WILSON WHEEL OPERATOR S MANUAL for Amada Thick Turret Punch Presses Rolling Shear Rolling Rib Rolling Offset Rolling Pincher Revised: September 20,