The formation of punch pin cracks is affected by many factors such as, but not limited to material quality, design defect, processing method, use environment, and operation mode. The following is an analysis of the most common causes of punch pin breakage based on the different positions.

Causes of Punch Head Fracture

(1) Material Issues

The punch head/beater absorbs a lot of impact energy. If the material hardness is too high and toughness is poor, it is easy to cause brittle fracture.

Materials that are of low quality or unfit for purpose, such as standard high-speed steel (HSS) rather than impact-resistant tungsten carbide.

(2) Heat Treatment Issues

If the punch head is quenched, poorly hardened or made too brittle, the punch head is not containing the high-frequency impact resistance required.

Poor tempering will lead to retained internal stress which lead to cracking of the head.

(3) Excessive Impact Load

Too much punching pressure, above the punch overload, can lead to sudden fracture.

Using it incorrectly, like punching high-hardness stuff (high-strength steel, stainless steel) too much.

(4) Poor Mold Assembly

The push pin contact with the die is very uneven as a result of tight fit.

Mold design which is unreasonable, causes great lateral force on punch head.

Punch midsection fracture causes

(1) Excessive Bending Stress

The punch pin is subject to lateral forces or eccentric forces that concentrate stress in the middle and gradually produce fatigue fracture.

Reduced lateral force due to misalignment from improper mold installation

(2) Internal Material Defects

Estimated tensile stress decreased strain along the midsection due to undeformed punch pin inserters, both with inclusions, air pockets, and cracks.

Low or no anneal or stress in the material during manufacturing can lead to break under impact.

(3) Poor Lubrication

Punching without adequate lubrication increases friction, introducing additional stress and reducing the midsection's resistance to breakage.

Causes of Punch Tail Fracture

(1) Improper Clamping Method

Improper clamping can create too much localized stress at the tail end, causing cracks as time passes.

(2) Tail Section Design Defects

Stress concentration can happen where design is poor, for example, in multiple steps or sharp transitions.

This may cause the force to be unevenly distributed across the tail again, if the tail shape does not meet the mold's requirement construction.

(3) Overuse and Fatigue Failure

This leads to material fatigue in long-term use, with fractures developing at the tail end, particularly under high-frequency stamping operations.

Preventive Measures

(1) Material Selection Optimization

High-toughness, wear-resistant materials, such as ASP60,ASP23, SKH-51, SKH-55,SKH59, etc.

Use coatings such as TiN, TiCN, CrN to improve wear resistance and impact resistance.

(2) Optimize Heat Treatment Processes

A properly quenched and tempered alloy provides a moderate hardness (HRC58-62 in most cases).

Low-temperature tempering can be used to decrease internal residual stress and increase toughness.

(3) Optimize Mold Design

The gap between the punch pin and the mold is correct, if the force is uneven, it will result in bending and deformation of the punch.

Reduce stress concentration and prevent punch fracture by increasing transition fillets.

(4) Enhance Precision of Processing

Keep punch surfaces consistently smooth to minimize machining marks that result in stress concentration.

Apply methods of high-precision grinding and polishing to increase fatigue resistance.

(5) Undermine lubrication as well as usage approaches

Lube finish during punching to keep friction and heat build up down.

Do not exceed punch pin load and adjust press stroke and pressure to be within safe limits.