3 Punching Cycle Impact Penetration Stripping Fracture Material Punch DieImpactPenetrationStrippingFractureSlugNow that we understand what the punch, die, and stripper are, and what a punching machine does, let’s see how the tools actually work by looking at the punching cycle.Impact – the punch is pushed downwards by machine until the tip of the punch pinches the material between the punch and the die.Penetration – the punch continues to push down, or penetrate, into the material.Fracture – Eventually the punch pushes so far into the metal that the metal fractures. This produces a hole in the metal. The waste portion is called the slug. The slug is pushed into the die far enough so that it falls away into the scrap bin under the press.Finally, Stripping - the punch starts to move upwards, and is pulled out of the metal. The stripper holds the metal onto the die, so that it does not lift up with the punch.
4 Anatomy of a Quality Hole Rollover DepthRollover WidthBurnished LengthMaterial ThicknessBurr HeightSlug
5 Die ClearanceDefinition: The size of the gap between the punch and the die.Total Die Clearance (TC)Dependent on material type and thicknessThinner material requires less clearanceThicker material requires more clearanceAs I just mentioned the die opening must be larger than the punch to allow the punch to pass through it. The die clearance is the size of the gap between the punch and die. In the illustration on this slide we can see the die clearance on both sides of the punch: die clearance 1 and die clearance 2. Mate always refers to total die clearance. Total die clearance is the sum of die clearance 1 and die clearance 2. The die clearance varies depending upon the material type and thickness to be punched. For example, thinner materiel requires less clearance. Thicker material requires more clearance.Total clearance = Die Clearance 1 + Die Clearance 2
6 Correct Die ClearanceUsing the correct die clearance is important to achieve the best piece part quality. Here we illustrate how optimum die clearance works.As the material is pinched between the punch and the die, the cutting edge of the punch causes the top surface of the metal to start to crack or shear. At the same time, the cutting edge of the die causes the bottom surface of the sheet metal to start to crack. When the correct die clearance is assigned, these two shear cracks line up and the hole is punched cleanly.With the correct die clearance, the punching forces are balanced, a quality piece part is produced, and the tool life is extended.Optimum Die Clearance – Shear cracks join, balancing punch force, piece part quality and tool life.
7 Tight Die ClearanceOne of the most common problems among punch press tool users is the use of a die clearance that is too small, or too tight.When the die clearance is too tight, two separate cracks form in the metal between the punch and the die. These two cracks do not meet in a straight line.Instead these two separate cracks must be ripped apart in order to punch the hole. This additional ripping is called secondary shear. Secondary shear results in higher punching forces and it reduces tool life.Tight die clearance is not recommended.Clearance Too Small – secondary cracks are created, raising punching force and shortening tool life.
8 Excessive Die Clearance Large BurrBurr is not compressed and is easily removedMore Rollover & Less Burnish
9 Calculating Die Clearance Now, you may be wondering how to calculate the correct die clearance. As you learned earlier, there are two important factors to consider when calculating the die clearance: the type of material and the material thickness.Die clearance is always specified in inches or millimeters. It is calculated by multiplying the material thickness by the die clearance percentage.Mate has created this chart to help you assign the correct die clearance percentage.In the left column are the three most common types of sheet metal: aluminum, mild steel, and stainless steel.The second column shows the material thicknesses ranges.The third column lists the recommended die clearance percentage for piercing a hole.The fourth column lists the recommended die clearance percentage for blanking, which is a topic that we’ll discuss in a later presentation.Die Clearance is based on type and thickness of material being punched.Total Clearance = Material thickness x Total Die Clearance % (shown on chart)
10 Calculating Die Clearance Let’s look at an example:The customer is punching mild steel. The mild steel is .079” thick. The customer is piercing, not blanking. The correct die clearance percentage would be 20% of the material thickness. 20% of .079” is .016”. The die clearance is .016”.0.079” x 20% = 0.016” Total Die Clearance
11 Calculating Die Clearance Let’s look at another example:The customer is punching stainless steel. The stainless steel is 2.0mm thick. The customer is piercing, not blanking. The correct die clearance percentage would be 25% of the material thickness. 25% of 2.5mm is .50mm. The die clearance is .50mm.Assigning the proper die clearance will you get better piece part quality and longer tool life.2.0mm x 25% = 0.50mm Total Die Clearance
12 Benefits of Proper Die Clearance Longer tool lifeBetter strippingSmaller burr height, minimum rolloverMore uniform holesFewer shavingsReduced gallingFlatter work piecesMore accurate hole locationLess wear on the machineThe benefits of proper die clearance include: longer tool life, better stripping performance, smaller burr height and minimum rollover for better piece part quality, more uniform holes, fewer shavings, reduced galling(material adhered to the punch tip), flatter work pieces, more accurate hole location, and less wear on the machine.
13 When to Re-sharpen Punches and Dies Sharpen when a .010” (0.25mm) radius forms on the punch or the dieR = .010” (0.25mm)
14 Sharpening Rules Sharpen frequently. Provide proper face geometry. Use coolant.Coarse wheel(46).Soft wheel. (G) (Norton SGB46KVX)Radius on wheel.Minimal surface contact.Observe proper set-up practices.Establish written maintenance procedures.
15 Inspect Tools Before Sharpening Fractures on dies or punchesDamaged guides or slotsGrind life
16 Calculating Grind Life StripperMaterial ThicknessDie PenetrationUsable Grind LifeGrind Life = SBR - (Stripper Thickness + Material Thickness + Die Penetration)
17 Galling Punches with galling cause: Fractured or broken punches Stripping problemsPoor quality holesFast tool wear
18 Galling Solutions: Remove galling from punches Consider Nitride or MaximaRun machine at slower speedLubricate the sheetCheck die clearanceCauses: Heat, tight die clearance, lack of lubrication
23 Importance of Frequent Maintenance More than DOUBLE the tool life when sharpened frequently!Note: Theoretical example only. Tool life will vary.
24 Sharpening Problems Waves on surface are due to overheating. Heat changes the metallurgical base fo the material and speeds up tool wear.
25 Sharpening Problems Undressed wheel Lack of coolant Excessive material removalWrong grinding wheel choice
26 Spring MaintenanceNote: springs have a finite life and require maintenance.Be aware of the different type springs used in various tooling lines and their maintenance requirements.
27 Broken Disc Springs Disc springs require lubrication. Stripping problems and guide damage can occur if springs are not maintained.If one disc spring is broken replace the entire stack.Maintain proper spring count and pattern.
28 A & B station Original Style coil springs Fatigued Coil SpringsNew LengthThrow away lengthA & B station Original Style coil springsThrow away length =75% of new length.
29 Misalignment-Punches Uneven punch surface wear on any one side of the tool (marking and or galling).More evident on long, narrow shapes but can happen on any shape or size tool.
32 Mate Pilot Calibration System for Thick Turret LED color indicatorRed – not alignedYellow – Aligned within mmGreen – aligned within mmUpper ToolElectronic SensorSurface Contact SensorLower Tool
33 Benefits of Proper Tool Maintenance Flatter sheetsCleaner holesLess stress on tool and machineLonger tool lifeMore accurate hole locations
34 Troubleshooting and Tool Ordering Recommendations
35 Prevent Slug Pulling Use Slug Free® dies. Eliminate magnetism in tools.Lightly dull recently sharpened tools.Increase die clearance.Maximize die penetration.Use shear.Use urethane ejectors.
36 Mate Slug Free® Die Cycle Material held securely by stripper before punch makes contact.Punch penetrates the material. 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 of the Slug Free die.Mate Slug Free® dies eliminate slug pulling. Slug pulling is a condition where the slug returns to the top of the sheet during the stripping portion of the punching cycle. The slug comes between the punch and the top of the sheet on the next cycle. This causes damage to the piece part and the tooling. Slug Free dies eliminate this problem.The Slug Free die has been designed with an opening that has a constriction point below the surface so the slug cannot return once it passes this point. Once the slug is separated from the punch, it is free to fall away from the punching area. Slug pulling is eliminated.
37 Advantages of Punch Shear Tonnage reduction (up to 60%).Noise reduction.Slug control.Reduced shock loads -- tooling and machine.Flatter sheets.Improved stripping.
39 Punching Non-Metallic Materials Use sharp punches and dies.Reduce die clearance by 5%-8%.Run the machine on slow cycle.Lubricate hard plastic if possible.Use Maxima™ or Nitride treated punches.If marking occurs use urethane pads.Support thin material when possible.
40 Punching Thick Material +4mm Sharp punches and dies.Clearance of 25-30% of material thickness.Extra back-taper on punches.Punch to material thickness ratio of 1 minimum.0.5mm radius on all punch corners.Inspect tools frequently for wear.Lubricate the sheet, punch and guide.Run machine on slow cycle.Use Heavy Duty tool configuration.
41 Overcoming Stripping Problems Use additional back-taper on punches.Increase die clearance.Check stripping springs for fatigue.Use sharp tools.Use Heavy Duty tool configurations.Remove galling.Lubricate sheets.Use sharp punches and die.With spring tooling use larger station.
42 Standard Back-taper1/8 degree per side(1/4 degree TOTAL)Punch Size
43 Reduce Galling Sharp punches and dies. Lubricate work piece. Use Maxima™ or Nitride treated punch.Increase die clearance.Adjust machine hit rate (slower).Use tool lubrication if available.
44 Small Diameter or Narrow Holes When punching small diameter or narrow holes, maintain the following ratio ofpunch size (minimum) to material thickness:MaterialAluminumMild SteelStainless SteelPunch to Material Ratio.75 to 1 (.5 to 1 Fully Guided)1 to 1 (.75 to 1 Fully Guided)2 to 1 (1 to 1 Fully Guided)
45 Perimeter Calculations A = Diagonal Dimension(Station Size)L = Hole PerimeterPerimeter CalculationsCalculate diagonals to determine station sizeCalculate perimeters for tonnage calculations
46 Tonnage = (30 x 3.14) x 3 x .0352 x 1.5 = 13.93 metric tons Tonnage CalculationsTonnage Formula:Punch Perimeter x Material thickness x Material Tonnage Value x Material MultiplierL dimension from charton previous slideMaterial tonnage values:Metric tons =Imperial tons = 2530mm round hole3mm stainless steelMetric Tons Example:30mm round hole in 3mm stainless steel:Tonnage = (30 x 3.14) x 3 x x 1.5 = metric tonsMaterial Type Material MultiplierAluminum (soft sheet) 0.3Aluminum (1/2 hard) 0.38Aluminum (full hard) 0.5Brass (soft sheet) 0.6Brass (1/2 hard) 0.7Copper (rolled) 0.57Mild Steel 1Stainless Steel 1.5
47 BlankingBlanking --When the slug becomes the “good” or the “saved part”
48 Blanking Punch Configuration mm flatdegreeone-way shear can be used
49 Blanking Operations Extremely sharp punches and dies. Reduce die clearance by 5%.Determine which blank dimensions and 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.Inspect tools for wear frequently.
50 Ordering Punches and Dies Punching a HolePunch Size = Hole SizeDie Size =Punch Size + ClearanceBlanking a PartDie Size =Blank Size desiredPunch Size =Die Size - Clearance (determined by material thickness)
51 Minimum Spacing Between Holes and Forms Minimum = 2 x Material Thickness between holesMinimum = 2 1/2 x Material Thickness to sheet edgeTop view of sheetSpacing between forms
52 Making Straight Walled Holes Without Drilling Finished hole size is the starting point. Order Punch for Hit #2 to the finished hole size. The punch for Hit #1 equals finished hole size less 20% of material thickness. The die size equals finished hole size plus 0.1mm.
53 Large Holes Without Exceeding Press Tonnage The customer has a Thick Turret machine with a C station auto-index.He should pierce a hole 47.0mmdiameter in mild steel T=6.0mmSuggested Solution: 1st hit-pre-pierce in the center of the 47mm hole a punch with a 25.0mm diameter. Hits 2, 3 &4-Special shape punch finish 47mm diameter with three hits.Tooling characteristics: Punch-roof top shear, Die-HD with 30% die clearanceR=23.52nd Hit140 Degrees1st Hit3rd Hit4th HitR =2.0Special Punch Shape For Hits 2,3 & 4Overlap
54 Large Holes Without Exceeding Press Tonnage Customer wants to pierce a 50.0mm diameter hole in mild steel T=8mmThe customer 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 punchTool 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
56 Forming Tools Order Recommendations Material Type & ThicknessAccurate DimensionsSpacing between formsTool StylePunch press modelOther useful informationIf tool is replacement, provide Mate etch number.Has tool been manufcatured by another supplier?Is the design flexible?Is the tool required for a specific station?