BLANKING CALLS FOR HIGH-PERFORMANCE STEELS

摘要

In blanking, as in other cold form mgprocesses, such as drawing, extrusion, Bending,coining, wire-drawing, etc.. both simple and compoundstresses may damage the dies after only a very short period in service.The most frequent causes of premature deterioration of a die are:- Wear- Splintering of the cutting-edge- Built-up edge (sticking)- Plastic shearingThese occurrences are first and foremost due toexcessive stressing of the die, more specifically of the punch and the matrix.Adhesive wear takes place, with a tendency to stick inthe case of low-hardness working material, such as copper and aluminium.With high thicknesses in the material to be blanked,such as tempered steel, there is a prevalence of abrasive wear.In the area of transition, both types (mixed wear) may be encountered.These types of wear may occur irrespective of thethickness of the material to be blanked. The conditionsrequired for achieving a high degree of resistance towear in the blanking parts include high hardness in thedie, low friction between the tool and the material tobe worked, and high form stability.Splintering of the cutting-edge takes place, on theother hand, due to high alternation of the stresses inthe die, which consequently lead to severe breakage ofthe latter caused by material fatigue. This dramaticoutcome is prevented by high compressive strength anda sufficiently high degree of hardness.The built-up edge occurs when the materials worked arevery pliable. Layers and fragments from the materialbeing cut are deposited on the tool, thus changing thestability of the cutting edge. A low frictioncoefficient and optimal choice of the tool will combatthe formation of the built-up edge (i.e., sticking).The cutting edges are plastically sheared due tooverloads. A high degree of hardness and compressivestrength are vital prerequisites for the stability of the cutting edge.To meet the requirements so far described, the steelstraditionally used in blanking work have been rich incarbide, due to their chemical composition.