9. Excessive Clearance Tool lasts longer ! Large Burr, not compressed and can be removed easily More Rollover & Less Burnish zone
10. Proper Die Clearance Note: 1) In general: shear strength determines clearance (10% is already good for low shear strength aluminium) 2) Minimum die clearance recommended : 0.08 mm
16. Tonnage calculation Required Punch Tonnage (tons) = hole perimeter (mm) * material thickness (mm) * shear factor (kpmm²) 1000 Some important shear factors ( ): Aluminium 22 -25kp/mm 2 Mild Steel 40 kp/mm 2 Stainless Steel 60 kp/mm 2 Cluster tools : multiply by number of punches Tonnage reduction by ‘step’-punching: step = ½ material thickness F (tons) = P x t x S / 1000 Note : try not to exceed 80% of punch press capacity
18. Formula: Tonnage = hole perimeter (mm) * material thickness (mm) * shear factor (kpmm²) 1000 Ø 30mm hole 3mm stainless steel Material shear factors ( ) : Aluminum = 22-25 kp/mm 2 Mild steel = 40 kp / mm 2 Stainless steel = 60 kp /mm 2 Example: Ø 30mm hole in 3mm stainless steel Tonnage = ( 30 x 3.14) x 3 x 60 = 16,96 t 1000 Tonnage calculation
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20. Perimeter Calculations Calculate diagonals to determine station size Calculate perimeters for tonnage calculations A = Diagonal Dimension (Station Size) L = Hole Perimeter
21. Calculator program for Clearance / Tonnage / Station Size
25. Treated Punches Please note! Nitrated punches not recommended for diameter or width less than 6 mm !!
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28. Treatment vs. Coating Nitride Treatment Nitriding is a heat treatment feature for HSS punches. Punches are more wear resistant , but also more brittle (esp. during stripping). Recommended for materials that cause galling, such as stainless steel, galvanized steel, or aluminum, but not if the material is too thick, as stripping might cause chipping. Can also be used for mild steel, will increase tool life (up to 4x). Also recommended for punching abrasive materials such as fiberglass. It is not recommended for punches smaller than 6mm in diameter or width, as punch is too brittle and may chip off. Maxima ® Coating Maxima is a hard, wear-resistant, multilayer Zirconium Titanium Nitride (ZrTiN) coating , It puts a hard surface on the punch, adds wear resistance and ‘ lubricates ’ the process. The coating acts as a barrier between the punch and the sheet metal being punched. Its exceptional lubricity, reduces the friction that occurs during the stripping portion of the punching cycle, thus especially recommended in thicker material. Less friction means less heat build up, less galling and longer tool life. Also recommended upon high use of the punch, or as a problem solver. Maxima Coating is more expensive than Nitride Treatment.
31. Slug Free ® Die Detail Material held securely by stripper before punch makes contact Penetration begins and metal deforms into the entry taper Material begins to fracture at stress points Slug fractures away from sheet Pressure point constricts slug Punch stroke bottoms out as slug squeezes past pressure point Punch retracts and slug is free to fall down and away through exit taper Punch Stripper Material Slug Free ® Die
36. Heavy Duty Back-taper 1 degree per side (2 degrees TOTAL) Punch Size Recommended when punching force over 18 tons and/or thickness above 4 mm
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39. Slitting Tip Bridge Hitting As consecutive nibbling may cause unbalanced forces, apply bridge hitting to avoid side loading during slitting operations:
40. Large Holes Without Exceeding Press Tonnage The customer wants to pierce a 50.0mm dia. hole in thick mild steel. He does not want to buy a special shape radius tool, but wants to use standard tooling. Tool 1 Use one Square 10mm and pre-pierce along the 50mm periphery 8 holes with equal pitch. Tool 2 Finalize the hole with a 50mm flat punch 8 hits 10mm sq.. Final Hit 50mm round
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44. ‘ Shaving’ – Make Straight Walled Holes Without Drilling Finished hole size is the starting point. Punch #1 = finished hole size – clearance (20%) Die #1 = finished hole size + 0.1 mm Punch #2 = finished hole size (full mat’l contact : Maxima !) Die #2 = die #1 .
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51. Minimum Spacing Between Holes and Forms Minimum = 2 x Material Thickness between holes Minimum = 2 1/2 x Material Thickness to sheet edge Top view of sheet To avoid hole distortion :
52. Minimum Spacing Between Holes and Forms Minimum = 2 1/2 x Material Thickness to sheet edge Spacing between forms
55. Excessive Nibbling Nibbling patterns can be done with much less hits with a banana tool or multi-radius tool (with tool rotation)
56. Punching Tip Combating Warpage To avoid sheet warpage when punching multiple holes, punch every other hole first, then come back
57. Cluster Tools In order to reduce noise , vibrations and tonnage on cluster tools it is recommended to shorten 50 % of the cluster punches with about 50 – 60% of the sheet – thickness. Example: Cluster of 16 x square 10mm Perforating in 1mm mild steel Insert Punch length 37mm Shorten 8 Punches to length 36,5mm ( Balanced Shortening)
58. Blanking -- When the slug becomes the “good” or the “saved part” Blanking Operations
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