Carbide tool

A wide apphcation of electrochemical grinding is the production of tungsten carbide [12070-12-1] cutting tools (see Carbides Tool materials). ECG is also useful in the grinding of fragile parts such as hypodermic needles and thinwaH tubes. 

Compacting tools must be propedy designed, constmcted, and fitted to the press. These maybe made of heat-treated steel or cemented carbide, depending on the economics and number of parts to be produced. Carbide tools are more expensive however, they can be used much longer than steel tools. 

Most cemented-carbide tools are WC-based and have Co as the binder. Other carbide tool materials based on TiC having a Ni—Mo binder were developed primarily for high (>300 500 m/min) speed finish machining of steels and gray cast irons for automotive appHcations. 

Table 7. Composition and Properties of Some Representative Grades of Cemented-Carbide Tools ...

Sometimes cemented carbide tools are used not only for hardness and wear resistance but also for high modulus or stiffness. For example, in end mills used in high speed machining of aluminum alloys, the deflection of the tool can affect the performance of the tool considerably. This includes chatter... 

Table 8. ISO Classification of Cemented Carbide Tools According to Use ...

Fig. 2. Tool wear mechanisms, (a) Crater wear on a cemented carbide tool produced during machining plain carbon steel, (b) Abrasive wear on the flank face of a cemented carbide tool produced during machining gray cast iron, (c) Built-up edge produced during low speed machining of a nickel-based alloy.

Thermal Fatigue. Cemented carbide tools sometimes exhibit a series of cracks perpendicular to the tool edge when appHed in intermpted cutting conditions such as milling. These thermal cracks are caused by the alternating expansion and contraction of the tool surface as it heats while cutting... 

The properties and performance of cemented carbide tools depend not only on the type and amount of carbide but also on carbide grain size and the amount of biader metal. Information on porosity, grain size and distribution of WC, soHd solution cubic carbides, and the metallic biader phase is obtained from metaHographicaHy poHshed samples. Optical microscopy and scanning and transmission electron microscopy are employed for microstmctural evaluation. Typical microstmctures of cemented carbides are shown ia Figure 3. 

Cemented carbide iaserts and tools for metal-cutting and metal-working have traditionally accounted for the largest percentage of carbide iadustry sales. However, carbide tool consumption ia nonmetal-working fields, notably ia the constmction and transportation iadustries, has grown rapidly. On the other hand, the demand for primary materials has been somewhat reduced by use of recycled cemented carbide scrap. 

Composites. Another type of electro deposit in commercial use is the composite form, in which insoluble materials are codeposited along with the electro-deposited metal or alloy to produce particular desirable properties. Polytetrafluoroethylene (PTFE) particles are codeposited with nickel to improve lubricity (see Lubrication and lubricants). SiHcon carbide and other hard particles including diamond are co-deposited with nickel to improve wear properties or to make cutting and grinding tools (see Carbides Tool materials). 

Titanium carbide and titanium nitride coatings for carbide tools that greatly outperform uncoated tools and are taking an increasing share of the market. 

CVD TiC coating on cemented carbide tools introduced and development of CVD tungsten. 

Coatings for carbide tools (usually with TiC and TiN underlayers). 

Oakes J., A Comparative Evaluation of HfN, AI2O3, TiC and TiN Coatings on Cemented Carbide Tools, Thin Solid Films, (107) 159-165(1983)... 

Coatings play a vital part in the cutting-tool industry and this is where CVD technology has made some of its most important gains. As an example, CVD films of titanium carbide on cemented carbide tools were first commercialized in the early 1960s and their use has continuously increased ever since. Today, the percentage of tools that are coated by either PVD or CVD depends on the type of tool as shown in Table 18.1 (in 1996). 

Other wear mechanisms are flank wear and crater wear which occur mostly with cemented-carbide tools. Flank wear refers to the depression that is formed below the cutting edge on the side of the tool caused by the abrasive wear of the cemented carbide. TiC is particularly effective in reducing it. Crater wear occurs in the form of small depressions on the rake face behind the point of contact of the tool with the workpiece. Diffusion of the cobalt binder into the cutting chip usually occurs with crater wear. TiN is effective in reducing both diffusion and crater wear.PI... 

Stjernberg, K., and Thelin, A., Wear Mechanisms of Coated Carbide Tools in Machining of Steel, Prac. ASM Int. Conf. on High Productivity Machining, Materials and Processing, Paper No. 8503-004, ASM, Metals Park, OH 44073 (May, 1985)... 

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