1. Basic Punching Theory

2. The ‘BIG 3’ Problems Die clearance too small
Poor or no maintenance on the tool
Turret alignment requires adjustment

3. Basic Hole Punching Theory
 Punching a hole
Die Clearance
Punch Tonnage
Choosing the right tool
Correct tool maintenance …

4. Punching Cycle Impact Penetration Fracture (@ 30% t) Stripping
Roll-over
Material
Punch
Die
Fracture 30% t)
Stripping
Burnish zone
Fracture
 Slug to go approx. 3 mm into die for slug free dies
Punch force diagram

5. Cross Section of a Quality Hole
Slug
Burr height graphs

6. The ‘BIG 3’ Problems Die clearance too small
Poor or no maintenance on the tool
Turret alignment requires adjustment

7. Proper vs. Tight Clearance

8. Proper vs. Tight Clearance
Fracture lines meet
- Punching forces are balanced, - Maximum piece part quality and tool life
Fracture lines do not meet
Secondary shear cracks, - Extra energy required,
Higher tool wear (dies wear quicker)
Extra energy does not disappear,
but is converted into heat !!

9. Excessive Clearance More Rollover & Less Burnish zone
Large Burr, not compressed and can be removed easily
More Rollover & Less Burnish zone
Tool lasts longer !

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

11. Improper Die Clearance

12. Piercing vs. Blanking Piercing
The slug is scrap. The interior of the sheet is the product.
Depending on the tool design, more than one hole can be punched at one time. Cluster tools for example.
In piercing operations, the die clearance is calculated from the punch size.

13. Piercing vs. Blanking Blanking
The punched item is of value. The slug is important.
Special shapes are used mostly in blanking operations.
Blanking operations calculate the die clearance from the desired blank dimensions.

14. Punching Techniques Blanking
When the slug becomes the “good” or the “saved part”

15. Punching Techniques
Blanking rather than punching can save time, tool life and sheet usage

16. Ordering Punches and Dies
Piercing a Hole
Punch Size =
Desired Hole Size
Die Size =
Punch Size +
Total Clearance
Blanking a Part
Die Size =
Desired Blank Size
(no Slug Free dies !)
Punch Size =
Die Size – Total Clearance

17. Tonnage calculation F (tons) = P x t x S / 1000
Required Punch Tonnage (tons) =
hole perimeter (mm) * material thickness (mm) * shear factor (kpmm²)
1000
Some important shear factors (): Aluminium kp/mm2
Mild Steel kp/mm2
Stainless Steel 60 kp/mm2
Cluster tools : multiply by number of punches
Tonnage reduction by ‘step’-punching: step = ½ material thickness
Note : try not to exceed 80% of punch press capacity

18. Tonnage calculation Material shear factors (  ) :
Aluminum = kp/mm2
Mild steel = 40 kp / mm2
Stainless steel = 60 kp /mm2 18 18

19. hole perimeter (mm) * material thickness (mm) * shear factor (kpmm²)
Tonnage calculation
Ø 30mm hole
Material shear factors (  ) :
Aluminum = kp/mm2
Mild steel = 40 kp / mm2
Stainless steel = 60 kp /mm2
3mm stainless steel
Formula: Tonnage =
hole perimeter (mm) * material thickness (mm) * shear factor (kpmm²)
1000
Example: Ø 30mm hole in 3mm stainless steel
Tonnage = (30 x 3.14) x 3 x 60 = 16,96 t

20. Keep in mind : Stripping springs !
Required Tonnage + Stripping Force must be Tonnage to be within Machine Capacity !

21. Perimeter Calculations
A = Diagonal Dimension
(Station Size)
L = Hole Perimeter
Perimeter Calculations
Calculate diagonals to determine station size
Calculate perimeters for tonnage calculations

22.  Calculator program for Clearance / Tonnage / Station Size

23. Use of Shear on Punches Shear typically 1.5 – 2 mm
Max up to 80% of machine capacity
Shear punches need sharp edges (sharpen frequently)
Best shear is rooftop; use min % of length; can be used at high tonnage
Concave shear: inverts stresses, good alternative for nibbling; max 15 Ton
One-way: good blanking shear
Four-way: very good on squares; hard to regrind
Trumpf ‘Whisper’ very good, but hard to regrind
Cup shear on rounds (Tr)

24. Punch Shear Examples
Concave
Rooftop
Four-Way
One-way & Whisper
Cup

25. Advantages of Shear Tonnage reduction Noise reduction Slug control
Reduced shock loads on the machine
Flatter sheets
Improved stripping
Increased tool life

26. Treated Punches Please note!
Nitrated punches not recommended for diameter or width less than 6 mm !!

27. Treatment vs. Coating Nitride Treatment Maxima® Coating
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.

28. Treatment vs. Coating

29. Mate Slug Free® Die Slug Free® Die Components Hole/Slug Geometry
1. Punch
2. Stripper
3. Material
4. Slug Free® Die
5. Slug
6. Grind Life
7. Entry -- Constricting Taper 0.5°
8. Pressure Point (at specific depth (*))
9. Exit -- Relief Taper 5.0°
Hole/Slug Geometry
A. Rollover
B. Burnish
C. Fracture
D. Burr
(*) depth = 1.5 mm * thickness (max = 3.0 mm)

30. Slug Free® Die Detail Punch Stripper Material Slug Free® Die
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

31. Uniform Clearance Dies
No corner burrs with Constant Clearance in shaped die corners
Stress relief in die corners

32. Uniform Clearance Dies
Corner burrs when non-uniform clearance dies are used

33. Recommended Material Maximum
Slug Free Light ®
Optional Die Land to prevent slug-pulling in problem materials or extremely thin material.
Blips 0,05mm deep are cut into the die wall to allow the slug to expand into the slots. Blips act as mechanical locks to trap the slug.
Material Type
Recommended Material Maximum
Stainless Steel
0.80mm
Mild Steel
1.00mm
Aluminum
1.20mm
Especially for bigger diameters and thin material (max. 1,5 mm).

34. Standard Back-taper
1/8 degree per side
(1/4 degree TOTAL)
Punch Size

35. Heavy Duty Back-taper Punch Size 1 degree per side
Recommended when punching force over 18 tons and/or thickness above 4 mm
1 degree per side
(2 degrees TOTAL)
Punch Size

36. Punching Thick Material (>4mm)
When ordering tools:
HD tool configuration (Rooftop punch with extra Backtaper)
Clearance of 25-30% of Material Thickness
0.5mm radius on all punch corners
Punch to material thickness ratio of 1 minimum
When punching:
Lubricate the sheet / punch / guide
Run Machine on slow cycle
Inspect tools frequently for wear / Use sharp Punches & Dies

37. Punching Thick Material (>4mm)
Common Poblems / Solutions
Stripping problems
HD configuration – Lubrication – Coating on punch – Use bigger station – Gas canister
Excessive tonnage / High tool wear / High vibrations
Make sure tonnage calculation is correct – Use Lubrication – Sharp tools – HD configuration – Maxima coating – Shear on punch – Correct die clearance – Pre-pierce holes – Bridge hitting
Work piece distortion/stretching
Change punch pattern (bridge hitting) – Slow down machine – Use Fully Guided – Sharpen tools

38. Slitting Tip Bridge Hitting
As consecutive nibbling may cause unbalanced forces,
apply bridge hitting to avoid side loading during slitting operations:

39. 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 2 Finalize the hole with a 50mm flat punch
Tool 1 Use one Square 10mm and pre-pierce along the 50mm periphery 8 holes with equal pitch.
8 hits 10mm sq..
Final Hit 50mm round

40. Punching Thin Material (<1mm)
When ordering tools:
You may require
Ultra Light canisters
Light shear on punches
Fully Guided guide/stripper solution
Urethane stripper pads
Slug Free Light dies
When punching:
Run Machine on slower cycle
Inspect tools frequently for wear
Use sharp punches & dies

41. Punching Thin Material (<1mm)
Common Poblems / Solutions
Sheet marking
Urethane stripper pads – Ultra Light
Slug pulling
Maximize die penetration – Demagnetise tools – Slug Free Light – Correct die clearance – Slug ejectors – Shear on punch
High tool wear due to small clearance
Maintain turret alignment
Work piece distortion/stretching
Change punch pattern – Slow down machine – Sharpen tools – Use Fully Guided

42. Punching non-metallic material
Use concave shear punches
Use Maxima or Nitride punches
Reduce die clearance with 5 %
Use sharp punches and dies
Run the machine on a slower cycle
Lubricate hard plastics if possible
Use urethane pads if marking occurs
Support thin material if needed

43. ‘Shaving’ – Make Straight Walled Holes Without Drilling
Finished hole size is the starting point.
Punch #1 = finished hole size – clearance (20%) Die # = finished hole size mm
Punch #2 = finished hole size (full mat’l contact : Maxima !) Die # = die #1 .

44. Preventing Slug Pulling
Use Slug Free® Dies
Eliminate Magnetism In Tools
Lightly Dull Recently Sharpened Tools (with oil stone)
Decrease Die Clearance
Maximize Die Penetration
Use Shear on Punches
Use Urethane Slug Ejectors (need replacement !)

45. Overcoming Stripping Problems
Use Sharp Punches & Dies
Lubricate Sheets
Remove Galling
Check Stripping Springs For Fatigue
Use Additional Back-Taper on Punches
Increase Die Clearance
Use HD Tool Configurations
With Spring Tooling Use Larger Station

46. Galling
Galling is an adhesion to the punch tip by the metal being punched, caused by pressure and heat.
The best technique for removing galling is to rub it off with a fine stone. The rubbing should be done parallel to the direction of the punching motion. This will polish the surface that contacts the material, decreasing any chance of future galling. Do not sandblast, belt sand or use other harsh abrasive methods. These create a coarse surface finish to which material adheres more easily.

47. Reduce Galling Use sharp Punches & Dies Lubricate Work Piece
Adjust Machine Hit Rate (Slower)
Use ABS If Available (Tool Lubrication)
Increase Die Clearance
Use Maxima or Nitride Treated Punch

48. Small Diameter or Narrow Holes
When punching small diameter or narrow holes, maintain the following ratio of punch size (minimum) to material thickness:
Material
Aluminum
Mild Steel
Stainless Steel
Punch to Material Ratio
0.75 to 1
1 to 1
2 to 1

49. Small Diameter or Narrow Holes
With Fully Guided
Material
Aluminum
Mild Steel
Stainless Steel
Punch to Material Ratio
0.75 to 1 (Fully Guided to 1)
1 to (Fully Guided to 1)
2 to (Fully Guided 1 to 1)

50. 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:

51. Minimum Spacing Between Holes and Forms
Spacing between forms
Minimum = 2 1/2 x Material Thickness to sheet edge

52. Nibbling
Nibbling
Minimum feed rate is equal to material thickness.

53. Nibbling
Nibbling is not always recommended …

54. Excessive Nibbling
Nibbling patterns can be done with much less hits with a banana tool or multi-radius tool (with tool rotation) 54

55. Punching Tip Combating Warpage
To avoid sheet warpage when punching multiple holes,
punch every other hole first, then come back

56. 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)

57. Blanking Operations Blanking --
When the slug becomes the “good” or the “saved part”

58. Blanking Operations
Blanking rather than punching can save time, tool life and sheet usage …
Special shapes can be done with a combination of standard tooling

59. Blanking Operations Extremely sharp punches and dies
Reduce die clearance by 5%
Determine which blank dimensions & tolerances are critical
Notify tooling provider that tooling required will be used for blanking
Use non-slug free or straight taper dies
Punches should be flat faced or with slight one-way shear
Frequently inspect tools for wear
Note: Be aware of the changing of burr side when piercing and blanking is combined.

60. Blanking Punch Configuration
mm flat
degree one-way shear
can be used
Note: Shear punches give flatter workpieces
©1999 Mate Precision Tooling

61. The ‘BIG 3’ Problems Poor or no maintenance on the tool
Die clearance too small
Poor or no maintenance on the tool
Turret alignment requires adjustment

62. Close-up of a burr

63. Sharpen when a 0.25 mm radius forms on the punch or the die
When to Grind ?
Recognize dull tools
Sharpen when a 0.25 mm radius forms on the punch or the die
R = 0.25mm
When the cutting edge shines
When hole quality changes
When the sound of punching changes

64. Calculating grind life
How much to Grind ?
Calculating grind life
Stripper Land - Ultra A-B = 4 mm - Ultra C-D-E = 8 mm
Material Thickness
Die Penetration
Usable Grind Life
Grind Life = SBR - (Stripper Thickness + Material Thickness + Die Penetration)
Max. Thickness
SBR
Ultra A
3,8
18,9 B
6,4
C-D-E
25,5
Punches have a bigger grind life in smaller thickness

65. How frequent to Grind ? Importance of frequent grinding
More than DOUBLE the tool life when sharpened frequently!

66. How to Grind ? Sharpening Rules
Sharpen frequently  Shear punches to be reground more often than flat punches
Use coolant
Correct wheel parameters
Demagnetize all tooling after regrinding
Break edges with oil stone

67. Sharpening
Excellent sharpening results

68. IMPORTANCE OF CORRECT MAINTENANCE : bad sharpening practices

69. Benefits of Proper Tool Maintenance
Flatter sheets (Note: Shear punches give flatter sheets)
Cleaner holes
Less stress on tool and machine
Longer tool life
 Maxima coating not affected

70. Maximizing Tool Life Sharpen frequently Use proper die clearance
Use proper shear configuration
Lubricate punch, guide and sheet
Inspect tool holders for wear
Use treated tools for special applications
Use radii on all sharp corners
Demagnetize all tooling after regrinding
Check turret alignment regularly

71. The ‘BIG 3’ Problems Turret alignment requires adjustment
Die clearance too small
Poor or no maintenance on the tool
Turret alignment requires adjustment

72. Thick Turret Alignment Tools
Mate PILOT Alignment System
NEW!
Standard Alignment tool

73. PILOT Alignment Tool

74. PILOT Alignment Tool

75. Mate PILOT Indicator light color : Red – not aligned
Yellow – aligned within (0.030)
Green - aligned within (0.008)

76. Mate PILOT
Loosen upper and lower tool holder retaining screws

77. Mate PILOT Station Alignment to machine
alignment bar and dial-indicator

78. Questions?

79. Thank you !