Custom sheet metal fabricator, Perfo AB, Mariestad, Sweden, manufactures bar code plates punched of sheet metal using a Murata Wiedemann Centrum 2000 turret punch press and a guided tool system from Mate Punch and Die (Anoka, Minnesota) that dramatically increases part accuracy and reliability. The bar code plates contain critical specification information for the manufacture and assembly of specific automobile models.
A single plate identifies the car to be made, its components and the team of workers who will make it. The team stays with the car from the beginning and relies on the bar code as its master reference point to coordinate all assembly materials and activities. The completed plate requires a series of closely located, rectangular-shaped holes separated by narrow strips of material, some as narrow as 1 mm and as long as 20 mm. Perfo tried using standard 114 tooling in its Centrum 2000 but ran into two problems.
According to Ove Persson, manager of Perfo's punching operations, "Conventional tooling failed to strip the punch cleanly. On tight corners, urethane strippers didn't have the force and rigidity to hold the part flat. When the punch withdrew, the webbing clung to the punch and rolled over."
There was a second problem. "Occasionally, slugs came free only partially from the flat part," he said. "Some went into the part webbing, irreparably distorting the webbing across the panel surface."
Trying to solve the problem, Mr. Persson sharpened the press tools and lowered the turret punch press speed, but these steps didn't help. After contacting Mate, a specially designed, one-hit, two-hole Mate Marathon cluster tool was designed with Slug Free dies to handle the two different hole sizes.
The Mate Marathon punch holder, stripper and die were designed to provide control over both material and scrap as the punch penetrates and retracts. The self-contained stripping action features disk springs, while the dies are designed to avoid any tendency for slug pulling by stripping the slug off the retracting punch. The length adjustment allows the punch to be resharpened without using shims. The punch holder contains the punch and stripper as an integral unit, while the lower unit combines die, die shims, and die holder in a single assembly for easy placement into the machine station.
Additional design features contribute to precision punching and clean stripping. The punch holders are fully hardened, precision ground and feature built-in lubrication and cooling vents to maximize service life. The punches are made of premium high speed steel which provide high abrasion and galling resistance, making them especially good for punching stainless steel.
The bar code plates were produced at 200 and 400 hits per minute, depending on sheet thickness, material type and distance between the webs. Production time for a complete bar code plate was approximately eight to ten seconds. The bar code plates were punched out of mild steel, stainless steel and plastic in sheet thicknesses from 0.5 to 0.8 mm.
Mr. Persson also said no tool resharp-ening was needed for the entire path run of several hundred different bar code plates with a total quality of 500,000 pieces for a total of 10 million hits without web rollover or slug pulling problems. MMS