# Recent Progress Trend on Abrasive Waterjet Cutting of Metallic Materials: A Review
## 2 Abrasive Waterjet Cutting Application Limitations and Challenges  
AWJM is extensively used for cutting operations; hence, there is a necessity for enhancing its performance. AWJ cutting processes still face challenges in quality and productivity performance, mostly metallic material identified as one of the hard-to-cut material due to its low machinability. There have been reported cutting defects when using an abrasive waterjet machine. Damage may also vary depending on the material to be machined [73]. The issue of material response to AWJM in terms of its behavior, i.e., burr formation, high surface roughness, striation marks, distorted kerf geometry, and delamination, has been studied since the beginning of AWJM applications in the 1980s [74; 75]. Table 3 shows common AWJ cutting issues that have been restudied by researchers, particularly metallic materials.  
Table 3 details that previous works have encountered similar customary defects inherent in this machine's application for difficult-to-cut materials, particularly metals [15; 62; 76; 77; 78]. Several studies have shown that AWJ cutting has been broadly applied to metallic materials with varied thicknesses. The AWJ cutting process has also been revealed to contain similar defects, such as kerf taper, roughness and cracking of cutting metals regardless of the thickness. A summary of recent studies applying AWJ cutting of metals with varied thicknesses is itemized in Table 4.  
As shown in Table 4, the kerf taper angle and surface roughness are major quality issues identified in the AWJ cutting of metallic materials with varied thickness. Accordingly, a machinability study performed by [PERSON] et al. [79] detailed the AWJM performance in cutting low alloy steel of different thicknesses (5, 10, 15, 20 mm). Their experiments revealed that the material thickness impacts machine performance, such as the material removal rate, surface roughness, and kerf wall inclination. Hence, it is necessary to investigate the influence of material thickness for precise AWJM, as cutting operations involve various thicknesses of product formation in fabrication industries.  
The aforementioned issues are challenges to AWJ cutting performance. However, these issues have been recently reinvestigated and it was concluded that AWJM performance relies on its process parameters. Therefore, it is necessary to have a continuous comprehensive study of process parameters to improve AWJ cutting performance, which is discussed in the succeeding section.  
\begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{2}{c}{**Materials**} & \multicolumn{1}{c}{**Industrial Application**} \\ \hline
**Type** & **Workpiece** & \\ \hline Natural & Concrete, cement, ceramics, graphite, stone & Mining, manufacturing and processing of ceramics and graphite, building, construction, housing, and tile industry. \\ \hline Metals & Titanium, aluminium, stainless steel, and alloys. & Automotive, marine, aerospace, architecture and civil, medical, food industry, automotive, electronics industry. \\ \hline Composites & Wire glass, laminated glass, optic glass, composites, and magnetic materials. & Aerospace, automotive, electronics industry, Glass, decorations, promotional, optical fiber, and the medical industry. \\ \hline \hline \end{tabular}
\end{table}
Table 2: AWJM materials and areas of application [49; 70; 71; 72].