Industry Insights

During stamping die trials, the most troublesome issues are often not "big problems" like forming springback, but specific faults such as the strip not feeding smoothly, scrap not discharging, and positions not aligning. They may seem trivial, but they directly determine whether the trial can pass on the first attempt. Below, we break down the most common problems at the trial stage.

Jumping Scrap: Scrap Getting Carried Up by the Punch

During piercing, after the punch punches out the scrap, the scrap does not smoothly fall into the scrap hole but is carried up by the punch and bounces back onto the strip surface or into the die. The causes are usually improper clearance between the punch and the scrap hole, unreasonable scrap hole design (such as too long a straight wall or no taper), or the punch being magnetized. Jumping scrap can, at best, press scrap onto the product and cause marks, and at worst, damage the die. In one recorded case, jumping scrap occurred at piercing round hole 8 in section A—a typical scrap bounce-back problem.

Sticking: Scrap or Product Stuck in the Die and Unable to Come Out

Sticking often occurs in the die hole, stripper plate, or leveling mechanism. In the case, "the finished product stuck on the leveling insert" means the product did not strip smoothly and got stuck on the insert in the leveling station. Sticking can, at best, require stopping the machine for cleaning, and at worst, damage the die, greatly reducing trial efficiency.

Strip Interfering with the Stripper Plate: The Feeding Path Is Blocked

The stripper plate is responsible for pressing the strip and helping the punch strip the material. If the height-limiting position of the stripper plate inside the die is improperly designed, the strip will hit local structures of the stripper plate during feeding, causing poor feeding or strip deformation. In the case, "the height-limiting position of the stripper plate inside the die interfered with the strip"—the limiting structure of the stripper plate intruded into the strip feeding path.

Pilot and Pitch Accuracy: The Lifeline of Progressive Dies

Progressive dies rely on the strip feeding step by step, and the position of each station must be precise. Pilot pins insert into pilot holes pre-punched in the strip to "lock" the strip in the correct position. Export progressive dies are required to have pilot pin stations to prevent strip deviation. Pitch accuracy refers to the length accuracy of each feed: ±0.015 mm for ordinary parts and ±0.008 mm for precision electronic parts. If the pitch is inaccurate, all subsequent piercing and bending will be misaligned, and the product will be directly scrapped.

Misfeed Protection Sensor: Not Optional, but Standard

This is the "fuse" of a progressive die. The sensor detects whether the strip has been fed into position. Once the pitch is abnormal—fed too much, too little, or not at all—the machine must stop immediately. If it does not stop, the punch will press down at the wrong position, directly damaging the die edge or even scrapping the entire die. That is why export progressive dies list it as standard equipment.

Haina's View

Most of these stamping die trial problems are rooted in the mold design stage: insufficient scrap hole taper, inaccurate stripper plate height limits, misplaced pilot pins, improper sensor selection. In mold development, Haina confirms the strip feeding path, scrap discharge method, and misfeed protection logic one by one during the design review stage, and verifies them item by item during trial molding according to a checklist—rather than repeatedly disassembling and repairing the mold after problems arise. If you have stamping part development needs, you are welcome to communicate with us at the DFM stage to eliminate trial molding risks in advance.