# Recent Progress Trend on Abrasive Waterjet Cutting of Metallic Materials: A Review
## 1 Introduction
### Abrasive Waterjet Machining Application  
In the past and recent years, AWJM has gained high interest amongst researchers, as it is a versatile tool that is used in almost all manufacturing processes and materials. Figure 2 presents the statistics of various workpieces utilized in AWJM applications, as established from several reviewed publications [25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 40; 41; 42; 43; 44; 45; 46; 47; 48; 49; 50; 51; 52; 53; 54; 55; 56; 57; 58; 59; 60; 61; 62; 63; 64; 65; 66]. The first chart (a) shows a generated summary of various workpieces that have been employed in AWJM applications, while the second chart (b) represents created synopsis material types for enhanced analysis based on several research studies used from the year 2017 to 2020. A number of studies in metal, composite, and natural materials discovered similar quality defects such as surface roughness, striation marks and kerr geometry inaccuracies [25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 40; 41; 42; 43; 44; 45; 46; 47; 48; 49; 50; 51; 52; 53; 54; 55; 56]. As shown in Figure 2a, aluminum alloy, which is a metallic material, has captured the highest value of twelve (12) research studies, whilst natural material, rock, has gained the least attention amongst these selected recent researches in AWJM application. As illustrated in Figure 2b, metal materials have received the highest attention, attaining 58% of the population of these selected latest studies in AWJM performance. These are difficult-to-cut materials that possess drawbacks related to their high alloying content (i.e., chromium and nickel), low thermal conductivity, high ductility, and low machinability level [67]. It was noted that the mentioned quality issues and defects are highly influenced by their material properties [68; 69]. Varied types of materials possess divergent machinability due to their different mechanical and chemical properties, and a number of metallic materials identified as one of the most hard-to-cut materials [28]. Figure 3 illustrates the typical machinability of several  
Figure 2: Statistics of (**a**) various workpieces employed in AWJM applications and (**b**) material type from 2017 to 2020 publications reviewed in this work. employed materials in abrasive waterjet (AWJ) cutting applications [69]. The machinability index indicates the speed of the machining process. Cutting machinability can be estimated by several indices such as the forces merging while cutting, cutting speed, surface quality of cut material, etc. [69]. Moreover, a higher machinability index denotes a faster cutting speed which has been established based on extensive cutting tests [69]. Figure 3 also demonstrates that tungsten carbide denotes the lowest level of machinability, subsequently followed by ceramics and metals such as stainless steel, Inconel and titanium; in this regard, these workpieces are the most difficult-to-machine materials. AWJM has also been recognized to be an effective technology in cutting non-conducting material with a low machinability index. Research to date has explored differing operating mechanisms of AWJM for various industrial conditions and applications. Table 2 enumerates AWJM applications in different industry sectors with regards to specific material usage [49; 70; 71; 72], which shows that AWJM applications cover a vast range of industrial domains. Figure 3: Machinability of frequently employed materials in AWJ cutting applications [69]. After expounding the machining mechanism and benchmarking performance against other non-conventional technologies, in addition to enumerating the advantages and applications of AWJM, it is essential to discern the technology's current conditions, limitations and process drawbacks that affect its technological effectiveness. A very high noise (approximately 80 to 100 Db) is produced by AWJM during the machining process, and acquisition costs are driven by the high-pressure pump, high volume of required water quality, and purity [3; 6; 15; 24].