The short service life of tools used to pierce advanced high-strength steel sheet (AHSS) is one of the primary concerns of the automotive industry. A high tool wear rate is expected due to high strength of the sheet to be pierced. This work investigated the effects of tool clearances on the quality of pierced holes, the piercing force, the piercing energy, and tool wear in piercing operations of AHSS and carbon steel sheet. The piercing energy was observed to be the major factor affecting tool wear. The energy was high when using a small tool clearance on AHSS. The tool with large clearance piercing AHSS exhibited a similar degree of wear as that piercing the low carbon sheet. A double shear zone on the cutting edge of AHSS was responsible for the high piercing energy, especially the energy required to push the slug through the die hole and that required for the return stroke, and the high wear rate of the piercing tool with small clearance.

The hole expansion process is a forming process that the fracture easily occurred on the hole edge. Therefore, many research papers presented various processes to make a precision pre-hole shearing to a hole expansion process such as wire cut, EDM, and laser cut. The purpose of this work is to increase a hole expansion ratio on the high strength steel sheet. The conventional piercing by piercing punch and piercing with a counter punch was used to make a pre-hole shearing process in this research paper. The high strength steel grade 590 and 980 MPa of 1.2 mm of thickness were used in the experiments. From experimental results, it was found that the pre-hole shearing by piercing with a counter punch can be increased a shear surface on cutting edge of workpiece. Moreover, the used piercing with counter punch can improve the hole expansion ratio more than the conventional piercing process because sheared surface around the hole edge was increased.

This paper aims to evaluate residual stress of coated film on cold work tool steel grade SKD11 (JIS) substrate. Four types of film coating were deposited on hardened SKD11 steel. Mechanical property of film coatings was examined by nano-indentation. The thickness of the films was analyzed by scanning electron microscopy (SEM). Residual stress of coated film was investigated by using curvature technique based on the Stoney equation. The results of them were compared and correlated to the bond strength of the films from scratch testing. The influences of residual stress on bond strength of the films were thoroughly discussed in details.

This work studied on the feasibility to produce agricultural bush parts using cold forging followed by machining to replace existing processes of piercing operation followed by shaving had been studied. Short tool life of the shaving punch is a major problem for existing processes. From this work, it was found that the maximum force required for cold forging operation is similar to that used on the existing process. Therefore same facility can be employed for a proposed method. A proper selection of billet size was necessary not only to obtain specific shape of final part, but also to yield maximum rate of material utilization. Another factor influencing the process was material flow constraint by cold forging die design. The design with highly constrained would lead to high stress introduced to the part. It is recommended to use forging die design with allow more of free material flow which is expected to improve tool life.

This work considers the influences of various types of die surface treatment, lubricants and temperature on friction for hot forging process of brass. Well-known ring compression test were carried out to evaluate friction coefficient for various conditions. Tool material was hot work tool steel H13 and workpiece material was brass C3771. Tool surface condition selected were normal hardening, treated by hard chrome, plasma nitriding and vacuum nitriding. Tests were conducted with and without lubricants at elevated temperature between 400–600°C. The results of experiments without lubricant show that friction coefficient is reduced when using die with treated surface regardless of working temperature. The influences of surface treated on die are not significant when forming under lubricated condition. In other word, lubricant has minor effect to reduce friction when the treated tools are employed. However, graphite in water was found to be almost compatible lubricant to graphite in oil when forming by tool which is treated by vacuum nitriding. The hardness and roughness of tool surfaces are found no relevance to friction coefficient in this work.