Advanced Thermoforming, 2nd Edition

Chapter 30Steel Rule Die Punching

Written in cooperation with Dieter Kamml, Kiefel GmbH, Freilassing, Germany

30.1 BASICS

The purpose of punching is to separate the formed parts from the film web. In conventional thermoforming with roll‐fed machines, there is a distinction between matched metal punching and steel rule die punching. Lately, ultrasonic systems are also being used for punching out thermoformed parts. In this chapter we focus on steel rule die punching.

Band steel, milled, or forged cutting lines are used for steel rule die punching.¹ Band steel cutting lines can be purchased in trimmed, sharpened, and polished versions. Trimmed band steel has many applications. Sharpened band steel can be ground and used to cut hard and coated materials. Polished band steel cutting lines tend to have very smooth surfaces on the cutting edges, and provide very good punching and bending behavior. The low friction of the smooth surfaces at the cutting edges enable the punching to be precise.

30.2 SHAPES OF CUTTING EDGES

Steel rule die knifes can be supplied in a variety of cutting edge shapes. They can be worked one‐sided, double‐sided, with one‐sided or double‐side facet. For special applications there are cutting edges that are offset or centered with different cutting angles. There are even linear and concave cutting edges.

Steel rule dies are subject to wear. The width of a new knife is about 0.001 mm. Higher punching pressure is needed and bad cutting occurs in some applications ...