**2. Ignition risk in conventional machining of Mg-based materials**

Even though Mg-based materials are considered to be the easiest materials to machine due to their low cutting forces, well-formed chips, and good surface finish, they are highly inflammable. The risk of ignition rises when process temperature crosses 450°C, which is close to the melting temperature of Mg [2, 3]. In spite of advantages such as 50% lesser cutting forces compared to aluminum in turning operations and cutting tools retaining sharp edges for a long period, Mg possess high affinity to oxygen at higher temperatures (>450°C). Mg is also reactive in nitrogen and carbon dioxide atmosphere even in the absence of oxygen. Ignition temperature of Mg can be controlled by adding alloying elements such as calcium and beryllium and rare earth metals such as cerium, lanthanum, or yttrium but cannot be avoided [4–6]. Ignition of chips occurs during high-speed machining especially during finishing operations, i.e., chips in the form of powder (<500 μm) tend to explode. These powders not only create safety hazard but can also damage the machine tool components [7].

Weinert et al. [2] highlighted the importance of removing the chips from the workspace of the machine tool during machining. It was reported that the hot chips generated during machining contains up to 90% of the heat generated at the cutting zone, which can significantly affect the workpiece and machine components by transferring the heat. Thermal expansion of both machine tool and workpiece thus required to be identified. The risk of fire and potential damages to the workpiece as well as the machine tool can be significantly controlled by fast and reliable removal of the chips. Controlling the temperature during machining is therefore crucial in preventing the ignition. Ning Zhao et al. [8] reported three types of ignition that occurs during face milling of AM50A magnesium alloy which includes sparks, flares, and continuous flares. Among three types of ignitions, it was reported that flares and continuous flares are dangerous for safe production. Therefore in order to reduce the temperature of chips and powder-type dust generated during machining, many researchers have used cutting fluids during machining process [9–13]. The use of cutting fluids also resulted in reaction with magnesium which forms hydrogen, a highly explosive and flammable gas. For this reactivity issue, mineralbased oils are recommended during machining of Mg-based materials by selecting appropriate process variables. However, it is necessary to take proper care at higher cutting speeds to prevent flank buildup (FBU) on tools while using mineral-based oils because formation of flank BUE and burrs creates another problem in machining Mg-based materials due to high thermal expansion coefficient, and this may further lead to decreased accuracy of machined surfaces. The presence of FBU increases cutting forces and affects surface quality [14].

On the other hand, conventional machining of Mg-MMC is also challenging. In addition to ignition risk, the presence of harder ceramic particles in MMC causes serious abrasion of the tool, which shortens the tool life, and increasing volume fraction of ceramic particles leads to increased cutting forces [15, 16]. This in turn, increases the manufacturing cost. Tonshoff et al. [7] investigated tool wear in turning Mg-MMC containing SiC particle reinforcement (MELRAM 072TS) using

**63**

*Abrasive Water Jet Cutting: A Risk-Free Technology for Machining Mg-Based Materials*

polycrystalline diamond (PCD) tool and PCD, TiN-coated tools. The tin-coated tool was destroyed immediately due to the impact of SiC particles. Chipping off the layer was observed in PCD tool. Furthermore, molten material was observed on edges of all tool materials. This adhesive effect between work and tool material not only creates a negative influence on machining forces but also leads to creating poor

Xiangyu Teng et al. [17] studied micro machinability of Mg-MMC containing titanium (Ti) and titanium diboride (TiB2) nanoparticles. AlTiN-coated tungsten carbide micro-end mills were used to machine Mg-MMNC. Machined surface was characterized by surface morphology and surface roughness. Investigations revealed cutting tool was affected by chip adhesion. This chip adhesion found more in machining Mg-MMC containing nano-sized Ti particles compared to Mg-MMC containing TiB2 nanoparticles. Further it was reported that cutting forces while machining Mg/Ti MMC found nearly two times compared to Mg/ TiB2 nanocomposites. Increase in cutting forces increased the roughness of surfaces and also induced burrs on slot edges of cutting tool. The surface of cutting tool was also affected by coating peeling off while machining Mg/TiB2 nanocomposites.

Therefore machining Mg-MMC with conventional methods is also associated with several problems such as increased cutting forces, surface roughness, and chip adhesion to tool material. It is really challenging to achieve a surface quality and accuracy MMC through conventional machining. Apart from these difficulties, conventional machining system for Mg-based material requires provision of storing chips in closed containers or the use of chip removal systems, protecting the machines using protection systems against explosions, adequate availability of class D fire extinguishers in the machine area, storage of dry sand in containers, and safeguarding the operators and installation of alarm systems in order to create the safest workplace [2, 18]. Indirectly these actions result in higher processing costs. Cost-effective processing of Mg-based materials is therefore an essential criterion to

**3. Overview of nontraditional machining of Mg-based materials**

on the suitability of NTM before being applied in practical fields.

machining (EDM), and AWJM are discussed in the present section.

Conventional machining demonstrated significant importance in machining Mg-based materials when compared to NTM over the years, despite serious problems such as ignition risk, tool wear, shorter tool life, and surface finish. Researchers are required to pay more attention to NTM processes to overcome difficulties of conventional machining. Literatures have witnessed the successful implementation of NTM processes in cutting a wide range of materials for different applications. Despite few limitations, nowadays NTM processes are having greater potential than conventional machining. However better understanding is required

During the past decades, numerous research efforts have been placed on NTM machining of different types of materials including MMCs. However, very limited studies are reported on machining of Mg-based materials and Mg-MMC through NTM techniques. Advantages and limitations of few NTM processes such as laser beam machining (LBM), laser-assisted machining (LAM), electric discharge

Nowadays EDM is extending its application areas by cutting a wide range of metals and MMC. EDM uses high thermal energy to remove the material by electric spark erosion. EDM regardless of the hardness of materials has typical advantages in cutting intricate and complex shapes. EDM eliminates mechanical stresses, vibration, and chatter during machining since there is no direct contact between

*DOI: http://dx.doi.org/10.5772/intechopen.85209*

surface quality.

expand the application areas.

#### *Abrasive Water Jet Cutting: A Risk-Free Technology for Machining Mg-Based Materials DOI: http://dx.doi.org/10.5772/intechopen.85209*

polycrystalline diamond (PCD) tool and PCD, TiN-coated tools. The tin-coated tool was destroyed immediately due to the impact of SiC particles. Chipping off the layer was observed in PCD tool. Furthermore, molten material was observed on edges of all tool materials. This adhesive effect between work and tool material not only creates a negative influence on machining forces but also leads to creating poor surface quality.

Xiangyu Teng et al. [17] studied micro machinability of Mg-MMC containing titanium (Ti) and titanium diboride (TiB2) nanoparticles. AlTiN-coated tungsten carbide micro-end mills were used to machine Mg-MMNC. Machined surface was characterized by surface morphology and surface roughness. Investigations revealed cutting tool was affected by chip adhesion. This chip adhesion found more in machining Mg-MMC containing nano-sized Ti particles compared to Mg-MMC containing TiB2 nanoparticles. Further it was reported that cutting forces while machining Mg/Ti MMC found nearly two times compared to Mg/ TiB2 nanocomposites. Increase in cutting forces increased the roughness of surfaces and also induced burrs on slot edges of cutting tool. The surface of cutting tool was also affected by coating peeling off while machining Mg/TiB2 nanocomposites.

Therefore machining Mg-MMC with conventional methods is also associated with several problems such as increased cutting forces, surface roughness, and chip adhesion to tool material. It is really challenging to achieve a surface quality and accuracy MMC through conventional machining. Apart from these difficulties, conventional machining system for Mg-based material requires provision of storing chips in closed containers or the use of chip removal systems, protecting the machines using protection systems against explosions, adequate availability of class D fire extinguishers in the machine area, storage of dry sand in containers, and safeguarding the operators and installation of alarm systems in order to create the safest workplace [2, 18]. Indirectly these actions result in higher processing costs. Cost-effective processing of Mg-based materials is therefore an essential criterion to expand the application areas.
