No abstract

Failure analysis investigates the causes of a product's destruction. Its final objective is to suggest measures that can be taken in order to prevent or minimize the chance of failure in the most economical way. This paper studies the failure of a rotary cold working die. The tool was manufactured from AISI D2 tool steel and it was intended for cutting paper 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 process was initiated by a crack that began at the point of a diameter change of the tool body in the attachment part, where the tool was fastened to the rest of the machine. This paper presents the first results of the die failure study. Historical data were 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 and macroscopic analysis of fracture surfaces. The paper presents conclusions on the fracture mechanism and form and suggests the first probable causes leading to die failure. The results could be useful for industry as regards the avoidance of such failures in the production process.

The study examines the dramatic drop in the efficiency of a cutting tool. The specific tool is part of machine used for cutting envelopes of paper for medical products packaging. Two similar pieces, selected after breaking down in service, were examined in depth. Historical data was collected. The tool temperature range during operation and the material hardness were measured. The fracture surfaces as well as the surrounding areas were carefully inspected. Chemical analysis was performed in order to identify the tool and coating materials. Results showed that components were made of different steels: D2 and Vanadis 6. The coating material also differs. Samples were selected and prepared for optical and electron microscopy. The condition of the cutting edges and the heat-treated microstructure were considered. Thickness, quality and homogeneity of the coatings were also inspected. Both tools failed by fatigue mode under different conditions. The fracture mechanism and its principal causes are discussed. The reasons of failure for both cutting tools are examined and compared. Poor designs associated with improper handling have led to the components breakage. Appropriate recommendations are given in order to eliminate similar situations and to improve the cutting performance.

No abstract