Common Metal Stamping Part Quality Defects and Solutions: A Comprehensive Guide

The current metal stamping market is highly competitive both at China and abroad. When consumers choose related metal stamping hardware products, they are not only limited to the reasonable price, but also pay more attention to the quality of related products. The quality problems of stamping parts not only affect the appearance of related device products, but also reduce the anti-corrosion and lifespan of the products. However, in the process of netal stamping, it is inevitable that various quality defects will occur. As a professional metal stamping manufacturer since 2007, we would like to describe in detail the quality common defects, the causes and solutions as below for checking.

Part 1 ： Common metal stamping quality defect and causes  

1.1  Dimension and tolerance  

The dimensional of the metal stamping part have the hole dimension and position and shape deviation, uneven thickness and tolerance not meeting specification requirements.

Cause analysis: The actual size of the stamped part deviates from the design drawing , exceeding the specified tolerance range. Excessive mold production, stamping die wear or inaccurate positioning, material rebound (especially high-strength steel, aluminum alloy); Insufficient rigidity of the stamping machine or poor parallelism of the slide. This may be caused by insufficient mold manufacturing accuracy, mold wear, material thickness deviation, improper stamping process parameters, etc. For example, after long-term use of the mold, the cavity size may become larger due to wear, resulting in out-of-tolerance size of the stamped part.

1.2:  Surface defects  

Some main defects have the scratches, bruises, burrs, and orange peel patterns.

Causes: The stamping die surface is rough or the cutting edge is blunt;  Insufficient lubrication or impurities mixed in;  The surface coating of the material falls off (such as the zinc layer).

 Scratches: Scratches appear on the surface of stamped parts, which is mainly caused by foreign matter on the mold surface, the mold surface roughness does not meet the requirements, or friction caused by relative sliding between the material and the mold during the stamping process.

Cracks: Cracks appear on the surface or inside of stamped parts. This may cause by insufficient toughness of the material itself, improper stamping process (such as too fast stamping speed, too many stamping times), too small radius of the mold corner, etc. When the material is subjected to excessive stress during the stamping process, exceeding its strength limit, cracks will occur.

Burrs: Burrs appear on the edge of stamped parts, which is usually caused by the wear of the cutting edge of the die, too large or too small cutting edge gap. When the cutting edge is worn, the cutting edge is no longer sharp, and burrs will be generated during stamping; and if the cutting edge gap is not appropriate, the material will not break normally during the shearing process, thus forming burrs.

1.3. Surface deformation  (warping, distortion)

There is some flatness tolerance, wavy edges, warped corners. The shape of the stamped parts does not match the designed shape, and there are distortions, warping, and deformation. The reasons include unreasonable mold design, uneven material properties, inappropriate stamping process parameters, and improper stamping sequence. If the material is subjected to uneven force during the stamping process, it is easy to cause warping and deformation.

Causes:   Uneven stress release in the material;   Unreasonable distribution of the clamping force, etc.; Improper process arrangement leading to accumulated stress.

1.4. Surface cracking and wrinkling of stamped parts 

There is some Cracks at the bottom of the drawn parts and wrinkles at the flange edges.Related reasons: Insufficient elongation or poor fluidity of the material; Too large a drawing ratio (such as a depth/diameter ratio of > 2.5);  Too small a blank holder force (wrinkling) or too large (cracking). The shape of the stamped parts does not match the designed shape, and distortion, warping, and deformation occur. The reasons include unreasonable mold design, uneven material properties, inappropriate stamping process parameters, and improper stamping sequence.

 If the material is subjected to uneven force during the stamping process, it is easy to cause warping and deformation.

1.5. Burrs 

  The burr height of the punching edge exceeds the tolerance (＞0.1mm).  Causes:  The gap between the punch and the die is unreasonable (too large or too small);

The cutting edge is worn or chipped. Burrs appear on the edge of the stamped part, which is usually caused by the wear of the cutting edge of the die, too large or too small cutting edge gap.

After the cutting edge is worn, the cutting edge is no longer sharp, and burrs will be generated during stamping; and if the cutting edge gap is not appropriate, the material will not break normally during the shearing process, thus forming burrs.

1.6.  Uneven thickness :  

 The thickness or the thinning rate of the side wall or corner of the drawn part is greater than 30%.

It may Causes by material flow is blocked (the mold radius is too small) and Poor lubrication leads to excessive friction.

1.7 Material performance specification issues

 Hardness does not meet requirements: The hardness of the stamped parts exceeds or falls below the specified range. This may be because the hardness of the material itself is unqualified, or the work hardening phenomenon during the stamping process has not been effectively controlled. For example, during the cold stamping process, the material will undergo work hardening due to plastic deformation. If the degree of work hardening is too high, the hardness of the stamped parts will increase and the toughness will decrease. ◦ Insufficient material toughness: Stamped parts are prone to brittle fracture during use. This may be because the material is not tough enough, or the stamping process causes the material's toughness to decrease. For example, excessive cold stamping processing will change the material's crystal structure, resulting in reduced toughness.

1.8: Internal Dia/mould quality issues

 Internal structural defects: There may be structural defects such as pores, inclusions, segregation, etc. inside the stamping parts, which will affect the mechanical properties and reliability of the stamping parts. Porosity and inclusions are usually generated during the material smelting process, while segregation is caused by the uneven composition of the material during the solidification process. ◦ Residual stress: During the stamping process, residual stress will be generated inside the material. If the residual stress is too large, it will cause deformation, cracking and other problems in the stamping parts during subsequent processing or use. For example, when welding stamping parts with residual stress, the residual stress and welding stress are superimposed, which may cause cracks in the welding area.

Part 2 : Solutions for the comment defects :

2.1. Dimensional accuracy issues

 Add guide posts or precision positioning pins to the mold;  

Use springback compensation design (CAE simulation to optimize the profile)

Regularly check the parallelism and tonnage of the punch press.  

Cases Study : The hole position of the stainless steel bracket is offset → Use a carbide insert mold instead, and the service life is increased by 5 times.

2.2 Surface defects •

  Polish the mold to Ra0.2μm or less, chrome plate or TD treatment;

 Use volatile stamping oil (such as ester oil);

 Pre-clean the material (degrease, dust removal).

Case study: Aluminum parts scratched → Use nylon material pressure plate instead.

2.3 : Shape deformation  

Add shaping process (strong pressure 0.05~0.1mm);

 Use multi-point blank holding force control (such as servo hydraulic pad);

Optimize the layout direction (adjust along the material rolling direction).

 Case study: Warping of sheet metal → Add negative angle pre-bending structure to the mold.

2.4. Cracking and wrinkling

Check the Step-by-step of the drawing (e.g. 60% initial drawing, secondary shaping);

 Increase the radius of the die (R≥4t, t is the material thickness);

 Use hot forming (200~400℃) for high-strength steel.

 Case study: Cracks at the bottom of deep cylinder → Add an intermediate annealing process.

2.5. Burr Control

 Adjust the gap by 8%~12% of the material thickness (the smaller value is used for mild steel);

 Grind the die regularly (check every 50,000 punchings);

 Use fine blanking technology (V-shaped blank holder + anti-thrust force).

 Case: Burr on copper terminal → Use zero-gap blanking instead.

2.6. Part thinning

Optimize the layout of drawing ribs and balance the material flow;

 Locally spray high-viscosity lubricant (such as graphite paste);

 Use materials with better ductility (such as SPCC→SPCE).

2.7  Material performance issues:

Analyze the causes of related materials, replace different materials, and then find the causes.

2.8 : Internal quality issues: Check the specifications and standards of relevant molds.

Part 3 :  Defect Prevention

3.1 . Design stage:   Use CAE software (such as AutoForm) to simulate material flow, springback and stress distribution. Avoid sharp corners (it is recommended that the R angle should be 3 times the material thickness).

3.2. Process control: Develop a Standard Operating Procedure (SOP) to specify the range of parameters such as blank holder force and speed. ◦ First piece full-size inspection (using a 3D scanner to compare digital models).

3.3 Mold maintenance: Establish a mold life record and regularly replace wearing parts (such as punches and guide sleeves). Use coating technology (such as TiAlN coating to improve wear resistance).

3.4. Material management:Strictly inspect the performance of incoming materials (tensile test, thickness tolerance ±0.02mm). ◦ Store different batches of materials separately to avoid mixing.

Part 4  :   Quick troubleshooting table for typical problems  

Part 5 :  Conclusion

When metal stamping parts encounter quality problems and defects, we must first conduct an in-depth analysis of the causes of the issue, analyze related defected caused, and formulate practical solution. In addition, we need to keep good process records during the implementation of the plan, and feedback key issues to the previous items to prevent the same problems from happening again. This ensures that the product stamping process can be produced normally and improves production efficiency. This article explains the problems, causes, prevention and response measures of common quality defects in metal stamping. If you want to find an experienced hardware development factory to develop your metal stamping project, please contact our sales team now. Our team and engineers will provide detailed solutions and project schedules accordingly.