Effect of TiN Coating on Punch Wear in Combined Forward and Backward Extrusion

• Main Authors: ZHI-JIANG,HUANG, 黃智強
• Other Authors: Chao-Cheng Chang
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/59430083984051542132

碩士 === 國立高雄應用科技大學 === 模具工程系碩士班 === 101 === Die wear causes poor product quality, die life reduction and cost increase. It is a key factor influencing the forming processes. Therefore, understanding the characteristics of die wear can help die design and process planning, improve die life, and increase economical benefit. This study used a precision micro forging press to conduct micro combined forward and backward extrusion processes in order to investigate the characteristics of punch wear. The study considered two types of punch surfaces from different treatments. One was the high speed steel (SKH9) surface with polishing treatment. The other was the TiN coating surface of the punch with the same treatment as the previous one. The punches diameter were 0.9 mm in diameter and their shapes were spherical faces. The product rate were set as 50 pcs/min. In the experiments, the variations in surface texture, roughness and dimensions of the extruded products were carefully examined in both types of punch surfaces in order to understand the wear processes during the production runs. The observations of the wear were mainly divided into two stages. The first stage considered one examination per 100 pcs up to 1000 pcs. The rest runs up to 10000 pcs were examined every 1000 pcs. This study also used a finite element package DEFORM-2D and the Archard’s wear model to predict the punch wear. The predicted results were then used to identify severe wear locations which were selected for the observations. The experimental results show that the wear characteristic of the punch without coating is clearly different from the one with TiN coating, and the severe wear occurs in the first and second stages, respectively. Between the production runs from 6000 pcs to 8000 pcs, the surface texture of the punches have significant change. The wear on the TiN coated punch is mainly caused by fatigue wear. The wear on the punch without coating mostly results from abrasive wear. Moreover, the wear in both types of punches includes adhesive wear. After 6000 pcs, the thickness of the TiN coated layer on the punch gradually decreases and its surface texture becomes the same as the one of the punch without coating. The results show that the TiN coated layer clearly improves punch life.