**1. Introduction**

102 Tungsten Carbide – Processing and Applications

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Machinability can be defined as the relative susceptibility of the work material to the decohesion phenomenon and chip formation, during cutting and grinding. This feature depends on work and tool's material physic-chemical properties and condition, method of machining, as well as cutting conditions [1]. Therefore, there is no unique and unambiguous meaning to the term machinability. This feature, can be described by many various indicators. Each one of them carries out a wide variety of operations, each with a different criteria of machinability. A material may have good machinability by one criterion, but poor machinability by another [2].

To deal with this complex situation, the approach adopted in this chapter is to divide machinability indicators into two groups, namely: physical and technological indicators. Physical machinability indicators include i.a. temperatures, cutting forces, vibrations and residual stresses generated during machining process, because their value have the direct influence on the ensemble of the remaining machining effects. Technological indicators include mainly machined surface texture and tool's life (relatively tool wear).

The most popular method for producing tungsten carbide components is by powder metallurgy technology. Nonetheless, for individual, small quantity production or product prototyping this method is too costly and time consuming. The alternative to powder metallurgy is Direct Laser Deposition (DLD) technology, which can be used to quickly produce metallic powder prototypes by a layer manufacturing method [3, 4] – Figure 1. The primary objective of DLD technology is the regeneration of machine parts or machine parts manufacturing with the improved surface layer properties, e.g. higher corrosion, erosion and abrasion resistance. Direct Laser Deposition is an extension of the laser cladding process, which enables three dimensional fully-dense prototype building by cladding consecutive layers on top of one another [6]. The DLD technology is increasingly being used

© 2012 Twardowski and Wojciechowski, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

in production of functional prototypes, modify or repair components which have excellent hardness, toughness, corrosion and abrasion wear-resistance, e.g. machine parts for the automotive industry – Figure 2. In the near future DLD technology will be used in manufacturing of spare parts in long term space missions [7] or submarines [8].

Machining Characteristics of Direct Laser Deposited Tungsten Carbide 105

Unfortunately, DLD technology has also significant disadvantage. Presently most components produced by DLD technology has an unsatisfactory geometric accuracy as well as surface roughness and requires some post-process machining to finish them to required tolerances [9]. Therefore, the machinability of DLD manufactured materials (e.g. tungsten

Tungsten carbide has excellent physicochemical properties such as, superior strength, high hardness, high fracture toughness, and high abrasion wear-resistance. These properties impinges wide application of tungsten carbide in industry for cutting tools, molds and dies. On the other hand, these unique properties can cause substantial difficulties during machining process, which can result in low machinability. Therefore, machining of tungsten carbide requires the knowledge about the physical effects of the process, as well as appropriate selection of machining method and cutting conditions, enabling desired technological effects. The primary objective of post-process machining of tungsten carbide is

The most popular finishing method of tungsten carbides applied in the tooling industry is grinding with the diamond and CBN (cubic boron nitride) wheels. However, in order to produce optical components made of cemented carbide (e.g. spherical mirrors) the profile quality requires a low surface roughness, a stringent form accuracy on the submicron scale, as well as a low amount of surface damage [10]. Traditional grinding with the diamond wheels can cause machining-induced cracks and damages to the material. To remove these cracks and damage and to obtain a mirror finish, lapping and polishing with fine diamond abrasives are usually employed. Nevertheless, these processes can cause the deterioration of

Recently, ultraprecision grinding has been developed that substantially decreases subsurface damage and can precisely control the geometry of the finished surface [11, 12]. This kind of process is conducted on the ultraprecision CNC grinding machines, with threeaxes movements, and micro-system to deterministically generate, fine, and pre-polish a plano or spherical surface. Very often these machines have motors with power exceeding 1kW and maximal rotational speeds above 80 000 rpm. The example of ultraprecision set-up

Tools applied in the ultraprecision grinding processes are usually selected as metal-bond diamond cup wheels (Figure 3b) with grit sizes between 15÷25 µm. The selected CNC grinding program includes two parts, i.e. stock removal and spark out. During the stock removal step, the grinding speed is selected in the range of 10÷15 m/s (for a small tool diameters it corresponds to rotational speeds up to 40 000 rpm). The vertical feed rates of the tool spindle are usually selected in the range of 0.05÷0.2 mm/min, and the workpiece spindle rotated at 1000 rpm. During the spark out phase, the workpiece is rotated with a 1000 rpm

to achieve satisfactory geometric and physical properties of its surface texture.

carbide), require further and extensive studies.

form accuracy and increase the machining cost.

is shown in Figure 3a.

for about 180 rotations.

**2. Machining of tungsten carbide** 

**Figure 1.** Direct laser deposition technology (DLD): a) the scheme of process, b) the view of process [5]

**Figure 2.** The application of DLD technology for the crankshafts (a, b) and parts for the automotive industry (c) [5]

Unfortunately, DLD technology has also significant disadvantage. Presently most components produced by DLD technology has an unsatisfactory geometric accuracy as well as surface roughness and requires some post-process machining to finish them to required tolerances [9]. Therefore, the machinability of DLD manufactured materials (e.g. tungsten carbide), require further and extensive studies.
