Tool wear

The main advantages of ECM are that the rate of metal machining does not depend on the hardness of the material, compHcated shapes can be machined on hard metals, and there is no tool wear. 

Platiaum jewelry alloys are easily worked and readily melted and cast. However, they are difficult to machine, resultiag ia severe tool wear. Pure platiaum (99.95%) ia the form of coias and iagots is used as an investment metal. 

Machining of metals involves extensive plastic deformation (shear strain of ca 2—8) of the work material in a narrow region ahead of the tool. High tool temperatures (ca 1000°C) and freshly generated, chemically active surfaces (underside of the chip and the machined surface) that interact extensively with the tool material, result in tool wear. There are also high mechanical and thermal stresses (often cycHc) on the tool (3). 

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.

Fillers (calcium carbonate, calcium sulfate, aluminum oxide, bentonites, wood flour) increase the solid content of the dispersion. They are added up to 50%, based on PVAc. The purpose of the addition is the reduction of the penetration depth, provision of thixotropic behavior of the adhesive, gap filling properties and the reduction of the costs. Disadvantage can be the increase of the white point and a possible higher tool wear. 

Coatings are used on a large scale in many production applications in optics, electronics, optoelectronics, tools, wear, and erosion and others. In the case of electronics and optoelectronics, practically all CVD applications are in the form of coatings. 

Diamond-like CH4-H2 300 cutting tools wear, erosion, semi-... 

The nitrides reviewed here are those which are commonly produced by CVD. They are similar in many respects to the carbides reviewed in Ch. 9. They are hard and wear-resistant and have high melting points and good chemical resistance. They include several of the refractory-metal (interstitial) nitrides and three covalent nitrides those of aluminum, boron, and silicon. Most are important industrial materials and have a number of major applications in cutting and grinding tools, wear surfaces, semiconductors, and others. Their development is proceeding at a rapid pace and CVD is a major factor in their growth. 

Good lubrication is proved by several indications. First, all build-up is eliminated, indicating a wetted tool, so that welding does not occur. Secondly, the tool nose is last to fail, and finish roughness decreases from 200 to 50 microinches (practically a finish cut, ready for grinding) lubrication is evidently now supplied. Thirdly, the work diameter does not change more than 0.001 to 0.002 on 2.5 to 4 inch diameter, until an inch or so from failure. There is almost no tool wear. 

In addition, waxy additi ves also reduce die wall friction during both the compaction and pellet ejection phases. This of course results in a reduction in tool wear... 

Applications Wear parts, precision parts Cutting tools, wear parts, ball bearings, seals, engine parts (valves, turbo charger rotors) Mainly used for evaluation of materials, prototypes with simple geometries, cutting tools... 

Although hot-pressing is usually regarded as an expensive process and only simple shapes with a wide tolerance on dimensions can be made, it provides the only route for several valuable materials. Continuous hot-pressing methods have been developed for some magnetic ferrites and piezoelectric niobates. They olfer higher production rates but tool wear is very severe. 

Tool materials3 Work materials Machining operation and cutting-speed range Modes of tool wear or failure Limitations... 

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