Reasons for Scrap Rebound of Pneumatic Punch Press Stamping Process

Discover the underlying factors that lead to the rebound of punching scrap of pneumatic punch press machine during stamping. This article explores the vacuum adsorption, oil film adhesion, magnetic adsorption, and punch passivation that contribute to this issue, emphasizing their impact on the quality of stamped parts and the service life of the die.

1. Vacuum Adsorption:

During stamping, the extrusion plastic deformation of soft materials creates a vacuum between the punch tip and the scrap. This vacuum state generates an adsorption force, pulling the punching scrap from the die's surface and resulting in scrap rebound.

2. Oil Film Adhesion:

To reduce metal adhesion of pneumatic punch press machine during high-speed stamping, lubricating oil is often applied to the friction area of the die. Whilst providing effective lubrication, the oil film can also lead to adhesion between the punch tip and the punching scrap, causing it to bounce back.

3. Magnetic Adsorption:

After sharpening the upper die, its die belt, lacking multiple demagnetization procedures, exhibits strong magnetic adsorption. When working with materials prone to magnetic adsorption, like silicon steel sheets, the magnetic force of the upper die pulls out the punching scrap, causing it to bounce back.

4. Scrap Package due to Punch Passivation:

With repeated use, the punch edge becomes passivated and loses its sharpness, forming a small R fillet. This passivation leads to the scrap wrapping phenomenon, where the scrap clamps onto the blunt punch during extrusion and deep drawing deformation. As a result, the punching scrap is brought out of the die's surface, causing it to rebound.