leometwu的部落格

極短命的熱鍛模. A die that failed prematurely.  This tooling broke into 6 pieces. All cracks started from the entrance of ejector pin holes or threaded holes. 破成6塊, 破裂皆起始於底部頂出銷孔口.

 Compound nitride layer at the entrance of  ejector pin holes. Compound layer is hard and brittle and it cracks readily. Cracks then extended into matrix (and led to the fracture) when the impact stress   applied is large enough.
 

上: 熱鍛模 頂出孔 孔口未倒角. 轉角處(氣体)氮化白層會特別嚴重

氮化後,  孔口另以手提砂輪機大量磨去孔口白層(先除去引發微裂之禍首) 就可免除這一類破裂.  沒有白層, SKD61強韌的基地, 要萌生微裂 (initiate  microcracks) 是有相當的難度的.

Above: sharp corner + nitriding is always a formula for disaster when impact   loading is involved.
 
 
 

水準很低的模具廠: 孔口都不倒角. 一點應力集中的觀念都沒有. 沒受過機械設計的訓練?