Cemented carbide is an alloy material made of hard alloy of refractory metal and bonding metal by powder metallurgy process. It has high hardness, wear resistance, good strength and toughness, heat resistance and corrosion resistance. The properties, in particular its high hardness and wear resistance, remain substantially unchanged even at temperatures of 500 ° C and still have high hardness at 1000 ° C.

 

Cemented carbide has high hardness, strength, wear resistance and corrosion resistance. It is known as “industrial teeth” and is used in the manufacture of cutting tools, knives, cobalt tools and wear-resistant parts. The market demand for quality alloys continues to increase. The future of high-tech weaponry equipment manufacturing, advances in cutting-edge science and technology, and the rapid development of nuclear energy will greatly increase the demand for high-tech content and high-quality stability of cemented carbide products.

 

Cemented Carbide Processing Problems

 

Due to the high melting point and brittleness of cemented carbide, sufficient pulse current density is required for processing, but it is not possible to use coarser processing standards. When using the medium and fine gauges of the pulse width of the existing pulse power supply, the electrode materials such as copper and graphite are greatly depleted.

 

According to the qualitative theory of the existing low-loss processing, the ratio of the peak current to the pulse width should be ≤A (A is a constant, such as copper processing steel, A ≤ 0.1A / μs), but the electric pulse of this parameter is used to process the hard Metal alloys often lack practical significance due to low productivity.

 

Cemented Carbide Processing Strategy

 

From the principle of EDM, any conductive material can be processed, and it is also possible to achieve low loss processing. Hard alloy is no exception. However, according to the low-loss qualitative theory, when ≤0.01 A/μs is selected, it has the phenomenon of adsorbing carbon, and the effect of low-loss processing can be obtained. In order to improve the processing productivity, the increase of the no-load voltage amplitude can be used to expand the spark gap value under a given processing surface roughness condition, improve the chip evacuation condition, and correspondingly reduce the pulse stop time.

 

Tips for Reducing Surface Cracks

 

The thermal conductivity of cemented carbide is small. For example, the thermal conductivity of tungsten carbide cemented carbide is 58.62~87.92W/(m•K), and the thermal conductivity of tungsten cobalt titanium alloy is generally 16.75~62.8W/(m• K). In order to avoid cracking, the processing standard of large pulse width cannot be selected. For example, a transistor pulse power supply has been used to process cemented carbide, and a pulse width of 800 μs and a peak current of 1.5 A have been selected, resulting in severe network cracks on the machined surface.

 

Therefore, in the roughing process, a relatively small pulse width (for example, 100 μs or less) and a high peak current are used, so that the heat-affected layer of the so-called electric discharge machining is thin. Even if there is a crack, its depth is shallow. Then, when finishing, the small pulse width and the higher peak current are also selected, and the shallow cracks generated by the roughing can be almost completely removed. Selecting the standard in this way not only avoids cracks, but also has a good surface roughness.

 

The crack has a great influence on the service life of the cold forging die. Therefore, the cold forging die after the EDM finishing must be further polished to completely remove the heat-affected layer generated by the electric discharge machining, otherwise the mold may crack when used.