Judgment and preventive measures of common defects in stamping parts

For the outer plate parts processed by stamping, the requirements are high, and there should be no obvious defects; for the inner plate parts, it is mainly required that there should be no cracks or dark cracks. For deep-drawn parts, first check whether the pressure point is clear, and then check whether there is any dark for cracks, use hand touch and whetstone to check fine lines.

1. Causes of nonconforming products:

A. Poor; quality of raw materials 

B. Improper installation and adjustment of punching die and improper use;

C. The operator did not feed the strips correctly along the positioning or did not guarantee that the strips were fed in a certain gap;

D Due to long-term use, the gap of the die changes or the wear of working parts and guide parts of the machine tool;

E. Due to the long time for impact and vibration of the die, the loosening of the fastening parts causes relative changes in the mounting positions of the die;

F. The operator was negligent in his work and did not follow the operating procedures.

2. The main measures to prevent nonconforming products:

A. The raw materials must conform the specified technical conditions (strictly check the specifications and grades of the raw materials, and conduct laboratory inspections on the workpieces with high dimensional accuracy and surface quality requirements under conditions).

B. All links specified in the process regulations shall be fully controlled and strictly followed.

C. It should be ensured that the tooling equipment used such as presses and dies are working in normal working conditions.

D. A strict inspection system is established during the production process. The first stamping parts must be fully inspected and can only be put into production after the inspection is qualified. At the same time, the inspection is strengthened. In case of accidents, they should be dealt with in time.

E Adhere to a civilized production system, such as the transmission of workpieces and billets, must use appropriate working position apparatus, otherwise it will crush and scratch the surface of the workpiece, which affect the surface quality of the workpiece.

F. During the stamping process, ensure that the cavity of the mold is clean, the workplace must be tidy and organized, and the processed workpieces must be placed neatly.

3. Common defects and solutions

1) Unevenness

Determination method: touch with hands, push with oilstone, and visual inspection.

It is recommended to use oilstone to push, the bright spots are raised up and the dark spots are sunken. 

Cause: the workpiece surface is not set up, should check whether there are foreign objects such as sand particles in the mold.

Solution: Use abrasive papers to polish the mold, if there are sands, to remove them and wipe cleanly.

2) Cracking (dark cracking)

Determination method: visual inspect the corners of the drawn parts and other places where the material is deformed. The front and back sides should be checked.

Cause: It may be due to mold strain and large blank holder force.

Solution: Check whether the workpiece is severely strained, and appropriately reduce the blank holder force.

3) Wrinkle

Judgment method: check the surface by visual inspection   

Cause: small blank holder force

Solution: appropriately increase the blank holder force.

4) Burr

Determination method: visual inspection s

Cause: The gap between the convex and concave molds is large.

Solution: trim the mold

5) Deviation hole

Determination method: check with standard measuring tools and compare with samples.

Cause: The workpiece is not placed properly, and there is a problem with the mold positioning device.

Solution: Correct the alignment. If you find that there is still a partial hole after the workpiece is aligned, you should report it and notify the mold repair.

6) Lack of holes

Determination method: compare with sample.

Cause: The punch is broken. 

Solution: Immediately stop production, report to the monitor, and inform the mold to repair the punch.

7) Hole deformation

Determination method: visual inspection.

Cause: the punch is worn.

Treatment: light abrasion need oiling, serious wore should inform.to repair the mold

8) The deep drawing is not in place

Judgment method: Check whether the pressure point is clear.

Reason: The main pressure is too small.

Solution: increase the main pressure appropriately.

9) Misfolded edges

Judgment method: compare with sample

Reason: The workpiece is not placed properly, and there is a problem with the positioning device.

Solution: Put the workpiece in place. If there are still irregularities, report it and notify the maintenance personnel to repair the mold.

10) Imprint

Judgment method: visual inspection

Reason: There are granular impurities on the working surface of the upper mold. 

Solution: Wipe the mold to keep its surface clean.

11) Strain

Judgment method: see with eyes

Reason: The working surface of the mold is worn and the mold hardness is not enough.

Solution: Modification.

12) Sand

Judgment method: push with oilstone

Reason: The material or mold surface is not clean.

Solution: Check the material or wipe the mold surface clean.

13) Bruises, scratches

Judgment method: visual inspection

Reason: The incoming or outgoing material hits hard objects such as molds. 

Solution: Be careful when feeding and discharging materials, handle the product gently, and increase the closing height of the mold if necessary.