TROUBLE SHOOTING IN METAL STAMPING

A wide verity of problems can be encountered in the use of different dies Many caused by improper press selection Or poor alignment, poor manufacturing, and poor design, etcSome common die problems, their causes, and suggested remedies INTRODUCTION

CLASSIFICATION Cutting diesForming diesDrawing dies

1. Burring Of Stamping Cause Dull cutting steelImproper clearanceThickness is too large Material not lying flat during blanking operationRemedySharpen cutting steelReset correct clearance CUTTING DIES

2. Premature Dulling Of Punch Or Die Cause Faulty hardeningWrong type of steelLack of cutting coolantNon uniform clearanceMisalignment RemedyMore carefully hardeningSelection of higher carbon tool steelUse coolant or die lubricantRelocate punch or die

3. Faulty Stripper ActionCause Unbalanced stripping force (broken springs or poor selection of springs)Binding of stripper Sloppy fit of stripper to punchRemedyRefit stripper to punch allowing more clearance Balancing of the spring

4. Loading Of Punches And Dies Or Cutting Steels Cause Insufficient clearance Rough surface on cutting steelsLack of cutting coolant RemedyProvide more clearancePolish cutting steelsUse coolant or die lubricant

5. Concave Surface Around Edge Of BlankCause Too much clearance between stripper and punchRemedyMake stripper fit closer to punch

6. Tapered walls on pierced holes Cause Found on thick stock which required large clearance RemedyFollow punching operation with shaving operation Decrease clearance

7. Poor shedding of scrap on trim diesCause Scrap extend too far around diesRemedyAdd more scrap cutters

8. Slugs jamming on dieCause Insufficient clearance angle on dieMore land area RemedyAllow (1.6mm) minimum land on cutting edge Back taper 2 minimum angle

9. Breakage of punches and cutting steelsCause Misalignment of ram of press.Loose fit on guide pins. Dull cutting steels. Cocked punch or die.RemedyAlign ram of press.Refit guide pins.Sharpen cutting steelsBe sure that punch and die shoes are clean and free from burrs and slugs.

10. Blanks not flat Cause Wrong type of die operation. Poor stripping action.Too much shear.Excessive clearance.RemedyUse return-type die.Keep shear equal to metal thickness or less.

11. Blanks or holes not to specified sizeCause Worn punch or die.Incorrect punch or die.Material characteristics.Material not lying flat during operationRemedyReplace punch and/or die.Sharpen punch and die.Align the die and press properly Optimum stripping force

12. Slug pulling Cause Incorrect clearance.Excessive lubricant.Magnetize punch.Not enough punch penetration through dieRemedyReplace punch or die. Keep lubricant to a minimum.Check magnetization. Consider shedder pins in punches.

13. Miscuts Cause Poor feedingImproper stock locationPoor knockout action.Careless operator.Broken shedder pins.RemedyCheck setup of knockout for depth. Observe and assist operator. Proper pilotingProper material guidingProper strippingClean die surface

14. Misfeeds Cause Feed line not set properly Burr and scrap on die surface Press speed too fastNo proper stoppersRemedyUse misfeed detector Use proper lubricant Proper pilotingProper material guidingClean die surface

1. Spring Back CauseIn bending operation the elastic limit of the metal in process is exceeded, but its UTS is not. Therefore some of the original elasticity of the material will be present on itRaw material is not flatRaw material thickness variationIncorrect punch and die clearancePunch is not heeled properlyPunch is too thin and weakRemedyOver bendingProper bottoming Offset on punchUse effective coining pressure on metal flow area FORMING &DRAWING DIES

2. Earing (Or) Rugged Edge CauseWhen sheet metal is rolled at the mill, a fiber structure is formed in the direction of rollingImpurities in materialEaring becomes Severity when the sheet metal is cold workedNon uniform blank holding forceRemedyUse good materialsMake uniform blank holding force Give more trimming allowanceTool to be aligned properly

3. Wrinkling Cause Insufficient the blank holding force (mostly in flanges). Too large area of unsupported metal between punch and draw ringBroken spring behind blank holder RemedyIncrease spring pressure Redesign punch and dieUse draw beadsUse homogeneous material

4. Puckering CauseWrinkling is called as puckers if they appear in any other part of the cup like sidewall. It may be due the improper clearance between punch and die. In addition, it will occur when the die radius is too large. RemedyReset correct clearanceUse optimum die radiusProper blank holding force

5. Tearing Cause Too much blanking holding pressureToo severe a reduction in areaRough spots on draw ring, punch, blank holderPoor draw ability of materialRemedyReduce spring pressureLarge radius is neededAdd stages in drawAnneal the part before drawAll friction surface are polishedUse lubricant

6. Fracturing Cause Too thin sheets Starts from the cleavage fracture and grow bigExcessive blank holding pressureDie radius too smallPress speed is too largeBlank too largeRemedyUse polyurethane sheets for lubricantDie surface to be cleaned properlyUse smooth corner for smooth material flowReduction percentage should be optimum

7. Orange PeelCause When metal is stretched, it loses the shiny surface produced by rolling. Stretching causes the surface to become dull and in severe cases quite rough. Large grain size means more possibility of getting orange peel-effect.Most frequently occurs on the lower cylindrical wall where tension is high. RemedyExpensive polishing or buffing could be used to compensate this kind of defectsOther alternatives would be to use metal having smaller grain size

8. Thinning Cause Insufficient metal flowInsufficient clearance RemedyUse flat draw beadsReduce blank holding forceUse proper lubricant

9. Burnish MarksCauseWhen the top of the cylindrical cup wall is highly polishedInsufficient clearance The metal has been burnished or ironed. RemedyLarger clearance would eliminate this conditionOptimum polish

11. NeckingCause Strain ratio is more on stock materialNon uniform forceBlank development is too small RemedyUse draw beadsAnneal the part before drawUse homogenous material Proper punch and die radius

12. Stretcher Strains CauseNon-uniform yielding of the metal due to trapped gases within the metal. Rim steels are responsible for this defect The lines in figure may disappear as drawing continues RemedyAluminum killed steels are free of this defect

13. Pitting CauseDue to Scales on the sheetsPoor quality of sheetRemedyClean stock materialClean die surfaceClean lubricant

14. Scratching CauseTool fails to keep the blank with contacting the die surfaceSmall particles of sheet metal become welded to the dieRaw material is too hard or inconsistent RemedyGive proper clearanceBetter or higher-pressure lubricantsQuality steels should be punchesMore frequent polishing of the die will prevent severe

THANK YOU