ABSTRACT
The field of metal-forming processes is large and covers processes such as wire drawing, rolling, deep drawing, forging, extrusion, hydroforming, and rubber pad forming. Metalforming processes are all designed to mechanically deform metal into a shape without material removal, in contrast with manufacturing processes such as machining or punching. Each forming process has its own characteristic features in terms of the material flow and in terms of the basic operating variables (Sec. II.A), as shown in Fig. 1. A common classification method is to distinguish bulk-forming processes, where material is plastically deformed in three dimensions, and sheet metal forming (SMF), where sheet material is plastically deformed in two dimensions (the thickness of the sheet is more or less constant). As an example, the setup for a commonly applied SMF process is shown in Fig. 2. Thin, initially flat, sheet material is clamped between a blankholder and a forming die. The punch moves in the direction indicated by the arrow and forces the sheet material to flow into the forming die. In this way, the metal sheet is formed into a cup. Usually the sheet material is precoated with a metal-forming lubricant to control friction and wear that arises because of sliding between the metal sheet and the blankholder and the forming die. The application of tribology-the science and technology of interacting surfaces in relative motion-to metalforming processes often raises questions such as: how can a micro-oriented approach solve problems related to a 2800-ton transfer press 33 m long with metal-forming tools up to 30 tons, making millions of pressing operations each year? An answer to this question is given by looking at a general aim of the manufacturing industry, i.e., to make products of constant (high) quality in an increasingly competitive way. Control of friction and wear contributes to this aim by eliminating uncertainty in production and by reduction of the amount of waste. In general, it can be stated that control of friction and wear in the interface between tooling and processed material will make production equipment more stable, which in turn guarantees the required constant process output. Tool wear, in particular, has a direct negative influence on the product's dimensions and on the surface quality. Because metalforming tools represent high economical value and because change of tooling causes
standstill in production, it is clear that improvement and prediction of tool life is of high industrial importance.
