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

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

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

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

*Magnesium - The Wonder Element for Engineering/Biomedical Applications*

applications through advanced machining technologies.

increases cutting forces and affects surface quality [14].

the machine tool components [7].

by 2023 at a compound annual growth rate (CAGR) of 12.7% during forecast period [1]. Extended applications in 3Cs (consumer electronics, computers, and cell phones) have enhanced the demand and growth of Mg-based materials in global markets. With this increase in demand, researchers and engineers are continuously focusing on machining aspects of Mg-based materials to expand the industrial

**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

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

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

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tool and work material. EDM is especially used in the production of die, mold, automotive, surgical, and aerospace components. EDM is most suitable for machining of geometries with high aspect ratio and microstructures. EDM can drill a hole of size 0.1 mm [19]. Ponappa et al. reported with high aspect ratio holes of ϕ 0.5 mm with 12 mm height drilled by EDM in Mg/Al2O3 nanocomposites. However, recast layer was observed at some portion of the cut zone due to a series of spark generation and generation of high temperatures between the tool and work [20]. Generation of high temperature during the process can alter the target material properties. The presence of reinforcement particles makes machining of MMC slower by creating difficulties due to the breakage of conductivity caused by non-conductive and high melting points of reinforcement particles. Breaking of wires in WEDM during the process is one of the major problems. Due to high temperature caused between tool and work interface, wire electrode breaks usually in the top edge of the machined surface. Another major limitation of EDM falls in its incapability in cutting nonconductive materials.

LBM uses thermal energy to remove the material using a laser beam by melting and vaporizing. Unlike EDM, LBM is not only limited to conductive materials; it can be applied for a wide range of materials [21]. The major advantage of LBM lies in its capability to produce geometrically complex shapes and miniature holes. LBM have the capability to make slot as low as 0.25 mm width. Generally, machining operations in LBM includes drilling and grooving. Mechanically induced material damage, cutting forces machine vibration, and tool wear are absent in LBM [22]. Machining speed and material removal rate can be increased in LAM. However, an increase in machining speed resulting in a rough surface that splits out into striations is caused by the unsteady motion of molten layer or repeated blockage of plasma. LAM is having its own limitations when machining Mg-based materials, the reflectivity of Mg can result in inadequate heating which limits the cutting capability, and also small chips produced during machining tend to ignite when in contact with the laser beam. Therefore, LBM of thermally sensitive Mg-based materials is risky. Melting of reinforcement material and chemical reactions were reported in LBM of MMC which also affects the microstructure.

AWJM technology is one of the leading and fastest growing NTM technologies for cutting a wide range of materials such as metals, stone, tiles, plastics, FRP, composites, food, ceramics, rubber, etc. In AWJ cutting the impact of solid particles at high velocity along with water at high pressure removes the target material by means of erosion [23]. AWJ uses cold water during the process that eliminates slag deformation and dross waste that is generally found in plasma and laser cutting processes. Additionally, both garnet (abrasive) and water used in the cutting process can be recycled [24]. The AWJM process is therefore environmentally friendly when compared to other cutting processes. The process is also clean and does not involve chips, chemical reactivity, and air pollution. Water jet eliminates dust by carrying away the eroded material and does not generate fumes which are generally present in other NTM processes [25]. In recent years AWJM has received tremendous attention especially in machining difficult to machine and thermally sensitive materials [26, 27]. Due to its versatility, ease of operations and extended capabilities, AWJM has become the hot choice among different machine tools for manufacturing industries. Application areas include automotive, aerospace, construction, medical industries, etc.

Unlike other NTM processes (EDM, LBM/LAM) AWJM does not include higher processing temperatures, and most importantly there is no HAZ [28]. Therefore machined surfaces are neither affected by remelting nor by recrystallization. Thus AWJ cutting technology offers risk-free machining of Mg-based materials by eliminating HAZ. The only drawback of AWJM is lesser efficiency in creating highquality surfaces which can be expected from the other two methods. Bimla Mardi

**65**

also highlighted.

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

et al. [29] investigated the surface integrity of Mg-based nanocomposites generated by AWJ. Feasibility of AWJ in machining Mg-based nanocomposites was reported. Experimental results were analyzed and compared under varied traverse speeds. It was concluded that lower traverse speeds give better surface finish and higher traverse speed results in the poor surface finish. Furthermore, it was concluded that for machining Mg-based MMC, AWJ machining is the most promising method with

Due to omnidirectional cutting capabilities of AWJM at higher feed rates, it is considered to be the fastest machining option for MMCs [30]. Based on available literature, it can be concluded that even though LAM/LBM and EDM can be efficiently used to machine Mg-based materials, the risk of ignition cannot be avoided. Therefore AWJM is the most suitable and risk-free machining technology for Mg-based materials. Below are some of the distinct advantages of AWJ machin-

• No microstructural and microhardness changes occur in the machined

• No thermal distortion, high machining versatility, and high flexibility [32].

AWJ technology is being utilized by many modern industries such as automotive, aerospace, chemical processing, environmental engineering, construction engineering, medical, etc., for performing different operations such as industrial cleaning, surface preparation, paint, enamel and coating stripping, manufacturing operations, etc. Since this chapter is mainly focused on machining aspects, only linear cutting, drilling, turning, and milling machining operations are discussed. AWJM involves a number of process parameters to achieve qualitative and quantitative results. Geometry and quality of the machined surfaces depend mainly on the appropriate selection process parameters. **Table 1** shows detailed AWJ process

In the present chapter, in order to identify the machining capability of Mg-based

materials, experimental investigations on AWJ linear cutting and AWJ drilling operations were carried out. The effect of input parameters on the depth of penetration and surface integrity of AZ91 alloy and nanocomposites was analyzed. AWJ drilling of AZ91 Mg alloy was carried out and compared with conventional and jig boring processes. Overview of AWJ is turning, and AWJ milling operations were discussed. Further research possibilities in AWJ machining Mg-based materials are

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

ing over other methods:

• Lower setup time.

surfaces [31].

• High productivity.

• Elimination of dust.

• No heat affected zone.

• Simple programming methods.

• Higher feed rates can be achieved especially in MMC.

**4. AWJ machining operations and process parameters**

parameters for different machining operations.

good surface finish and minimum subsurface damage.

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

et al. [29] investigated the surface integrity of Mg-based nanocomposites generated by AWJ. Feasibility of AWJ in machining Mg-based nanocomposites was reported. Experimental results were analyzed and compared under varied traverse speeds. It was concluded that lower traverse speeds give better surface finish and higher traverse speed results in the poor surface finish. Furthermore, it was concluded that for machining Mg-based MMC, AWJ machining is the most promising method with good surface finish and minimum subsurface damage.

Due to omnidirectional cutting capabilities of AWJM at higher feed rates, it is considered to be the fastest machining option for MMCs [30]. Based on available literature, it can be concluded that even though LAM/LBM and EDM can be efficiently used to machine Mg-based materials, the risk of ignition cannot be avoided. Therefore AWJM is the most suitable and risk-free machining technology for Mg-based materials. Below are some of the distinct advantages of AWJ machining over other methods:


*Magnesium - The Wonder Element for Engineering/Biomedical Applications*

LBM of MMC which also affects the microstructure.

aerospace, construction, medical industries, etc.

conductive materials.

tool and work material. EDM is especially used in the production of die, mold, automotive, surgical, and aerospace components. EDM is most suitable for machining of geometries with high aspect ratio and microstructures. EDM can drill a hole of size 0.1 mm [19]. Ponappa et al. reported with high aspect ratio holes of ϕ 0.5 mm with 12 mm height drilled by EDM in Mg/Al2O3 nanocomposites. However, recast layer was observed at some portion of the cut zone due to a series of spark generation and generation of high temperatures between the tool and work [20]. Generation of high temperature during the process can alter the target material properties. The presence of reinforcement particles makes machining of MMC slower by creating difficulties due to the breakage of conductivity caused by non-conductive and high melting points of reinforcement particles. Breaking of wires in WEDM during the process is one of the major problems. Due to high temperature caused between tool and work interface, wire electrode breaks usually in the top edge of the machined surface. Another major limitation of EDM falls in its incapability in cutting non-

LBM uses thermal energy to remove the material using a laser beam by melting and vaporizing. Unlike EDM, LBM is not only limited to conductive materials; it can be applied for a wide range of materials [21]. The major advantage of LBM lies in its capability to produce geometrically complex shapes and miniature holes. LBM have the capability to make slot as low as 0.25 mm width. Generally, machining operations in LBM includes drilling and grooving. Mechanically induced material damage, cutting forces machine vibration, and tool wear are absent in LBM [22]. Machining speed and material removal rate can be increased in LAM. However, an increase in machining speed resulting in a rough surface that splits out into striations is caused by the unsteady motion of molten layer or repeated blockage of plasma. LAM is having its own limitations when machining Mg-based materials, the reflectivity of Mg can result in inadequate heating which limits the cutting capability, and also small chips produced during machining tend to ignite when in contact with the laser beam. Therefore, LBM of thermally sensitive Mg-based materials is risky. Melting of reinforcement material and chemical reactions were reported in

AWJM technology is one of the leading and fastest growing NTM technologies for cutting a wide range of materials such as metals, stone, tiles, plastics, FRP, composites, food, ceramics, rubber, etc. In AWJ cutting the impact of solid particles at high velocity along with water at high pressure removes the target material by means of erosion [23]. AWJ uses cold water during the process that eliminates slag deformation and dross waste that is generally found in plasma and laser cutting processes. Additionally, both garnet (abrasive) and water used in the cutting process can be recycled [24]. The AWJM process is therefore environmentally friendly when compared to other cutting processes. The process is also clean and does not involve chips, chemical reactivity, and air pollution. Water jet eliminates dust by carrying away the eroded material and does not generate fumes which are generally present in other NTM processes [25]. In recent years AWJM has received tremendous attention especially in machining difficult to machine and thermally sensitive materials [26, 27]. Due to its versatility, ease of operations and extended capabilities, AWJM has become the hot choice among different machine tools for manufacturing industries. Application areas include automotive,

Unlike other NTM processes (EDM, LBM/LAM) AWJM does not include higher processing temperatures, and most importantly there is no HAZ [28]. Therefore machined surfaces are neither affected by remelting nor by recrystallization. Thus AWJ cutting technology offers risk-free machining of Mg-based materials by eliminating HAZ. The only drawback of AWJM is lesser efficiency in creating highquality surfaces which can be expected from the other two methods. Bimla Mardi

**64**

