Sumitomo Electric Co., Ltd. has developed a GS coated carbide ball end mill for machining high hardness (≥60HRC) molds, which is characterized by ultra-fine particle cemented carbide with excellent hardness and toughness. The base of the knife is coated with a coating material with excellent heat resistance and lubricity on the surface of the substrate by a new coating technique; the ball-end cutting edge is processed by high-precision technology. 
It is well known that the hardness of a cutting tool should be more than three times the hardness of the workpiece. However, when the hardness of the tool is increased, the toughness naturally decreases, which causes the tool to be easily chipped. Especially, the end milling of the high hardness material is interrupted cutting, and the impact is large, and the chipping is more likely to occur. In order to optimize the cutting performance of the GS ball end mill, the hardness and toughness of the cemented carbide substrate must be balanced and optimized at a high level. Sumitomo Electric Co., Ltd. improves the hardness of the cemented carbide matrix by reducing the content of the Co binder phase, and improves the toughness of the cemented carbide matrix by making the grain size of the hard alloy main component tungsten carbide fine. Through the matching optimization study of the two, an ultrafine particle cemented carbide substrate with excellent hardness and toughness was developed. 
For the tool coating material, in order to meet the needs of high-hardness material end-milling, it should not only have excellent heat resistance, but also have a high level of lubrication to reduce cutting resistance.
Improve anti-adhesive wear and surface quality. When the coating friction coefficient is less than 0.3, it can have excellent lubricating properties. The friction coefficient of a widely used TiAlN coating is about 0.5; in recent years, the TiSiN coating has a friction coefficient of about 0.6; the TiCN coating has a friction coefficient of 0.3, but its heat resistance is too Low, can not be used to process high hardness die steel. The GS ball end mill uses a coating with a very low coefficient of friction of only 0.2 and a heat resistance comparable to that of a TiSiN coating. Its hardness Hv = 5100, which is 30% higher than the TiAIN coating (Hv = 3500). the above. Therefore, the GS ball end mill can significantly reduce the frictional resistance, suppress the cutting resistance and the increase of the cutting heat, and prolong the life of the tool, suppress the occurrence of the chip sticking phenomenon, and improve the surface quality and cutting efficiency. 
In the design and processing of the tool, the machining tolerance of the ball nose radius R is +3 to -7 μm. When the ball head R is machined with high precision, excessive grinding is prevented, and R and straight line processing is completed continuously and smoothly. A high quality end mill ball head forming surface. 
The above characteristics make GS coated carbide tip end mills have good wear resistance, rigidity, toughness, heat resistance, lubricity and high precision, which is very suitable for rough and fine milling of mold cavities. It can also perform higher performance when processing mold materials such as hard steel with a slightly lower hardness.
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