Abstract:

Mechanical failure may be defined as any change in the size, shape, or material properties of a machine or machine part that renders it incapable of satisfactorily performing its intended function. Failure analysis investigates the causes of the products destruction. Final objective of failure investigation is to suggest measures to be taken so as to prevent or minimize the failure in the most economical way. The performance of a tool, or the tool lifetime, depends on the tool design, the material selection, the tool manufacturing, the heat treatments, the production conditions and the tool maintenance. Failures can be attributed to any one or a combination of these factors.
The design of a tool steel is the first step in the toll technology. Is the primary responsibility of any mechanical designer to ensure that his design functions as intended for the prescribed design lifetime and at the same time, it is competitive in the market [1]. Success in designing competitive products while averting premature mechanical failures can be consistently achieved only by recognizing and evaluating all potential modes of failure that might govern the design.
This paper studies two cases of failure. The first one was constructed following AISI H13 steel and was intended for the production of 60.000Kg of aluminium profile. The die consisted of two parts, male and female. The male part fractured during operation after the production of only 500Kg of profile.
The second case analyses a rotary cold working die. The tool was manufactured following AISI D2 tool steel and it was intended for cutting paper envelops at room temperature. The tool failed during the setup process on the machine it was designed for, thus failing to commence the manufacturing process.
The paper presents the results of the die failure study. Historical data was collected: operating conditions, lifetime, restitution of sound operation, collection of recorded history, measurement of operating temperatures and hardness control. This was followed by optical inspection, selection and preparation of samples for macroscopic and microscopic analysis of fracture surfaces. The paper presents the role of design in the causes leading to die failure. The results could be useful for industry as regards the avoidance of such situations in the production process.

References:
[1]J.A. Collins,» Failure of Materials in Mechanical Design: Analysis, Prediction, Prevention”, Wiley-Interscience Publication, U.S.A., 1993, pp1-15.

Keywords:

failure analysis, tool design, tool lifetime, cutting tool, extrusion.