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Experimental Study of Surface Roughness and Micro-Hardness Obtained by Cutting Carbon Steel with Abrasive WaterJet and Laser Beam Technologies

Mohammad S. Alsoufi*, Dhia K. Suker, Abdulaziz S. Alsabban, Sufyan Azam

Mechanical Engineering Department, College of Engineering and Islamic Architecture, Umm Al-Qura University, Makkah, KSA

Abstract: This paper presents a study conducted to determine the effect of abrasive waterjet (AWJ) and laser beam (LB) cutting technologies on surface roughness, Ra, and micro-hardness, µ-HV of the carbon steel samples. In this article, there is a brief discussion of the different ways of cutting carbon steel, such as AWJ cutting, as well as LB cutting. These techniques and their comparisons are illustrated in tables to highlight the differences between them regarding technical parameters, equipment, tools and economic performance and to select the best technology for cutting carbon steel. The results indicated that the average value of the surface roughness for the carbon steel sample was Ra = 7.54 µm, ±SD = 2.52 µm (for LB) and it was Ra = 6.34 µm, ±SD = 2.67 µm (for AWJ), for which the thickness was 6 mm. The difference was 1.2 µm. Also, the skewness, Rsk, and kurtosis, Rku, of the carbon steel sample after cutting by laser beam were 0.05 and 2.51, respectively. Whereas, Rsk and Rku of the carbon steel sample after cutting by abrasive waterjet were -0.04 and 2.69, respectively. Besides, the average value of micro-hardness for a carbon steel sample was HV = 548.82, ±SD = 72.4 (for LB) and it was HV = 525.70, ±SD = 72.5 (for AWJ). Surprisingly, the micro-hardness value for both cutting methods start roughly at the same value around 450 HV and then start to increase until the end of the cutting distance is reached. The difference was 23.12 HV. It also should be noted that, the effective case depth was about ~330 µm at 549 HV (for LB), and was about ~320 µm at 525 HV (for AWJ).

Keywords: surface roughness, micro-hardness, abrasive waterjet, laser beam

Citation: Mohammad S. Alsoufi, Dhia K. Suker, Abdulaziz S. Alsabban, Sufyan Azam, Experimental Study of Surface Roughness and Micro-Hardness Obtained by Cutting Carbon Steel with Abrasive WaterJet and Laser Beam Technologies. American Journal of Mechanical Engineering, 4 (5). 173-181. January 2016. doi:10.12691/ajme-4-5-2

1. Introduction

In today’s competitive business environment, things are entirely diverse. Surface finishing (as the final appearance of the product in several areas of modern engineering business, such as aerospace, automotive, construction engineering, environmental technology, industrial maintenance and chemical process engineering) is the last phase of stone processing and it does play a significant role in determining the high-quality of manufacturing components [1]. Nowadays, a huge number of technologies are available in the market for high-quality surface finishing. Fundamentally, they differ as regards the kind of action applied by the tool to the stone, with the consequence that the resulting high-quality of the surface finishing, which is required by the consumer, is also somewhat affected [2]. Abrasive waterjet (AWJ) cutting method and laser beam (LB) cutting process are two major cutting processes, which can maintain good quality even after the cutting method [3]. In this context, these technologies have been paid a great deal of interest due to their advantages when compared with other non-traditional techniques. So, this paper focused attention on two ways of shaping the workpiece materials, namely: abrasive waterjet cutting technology and laser beam cutting technology. These methods will be compared only regarding cutting metals (i.e., carbon steel), which meaningfully limits the scope of argument and at the same time determines their respective degree of precision.

1.1. Abrasive WaterJet Cutting Technology

Abrasive waterjet (AWJ) cutting technology is an extended version of waterjet cutting. Abrasive waterjet is the method of cutting the material by the use of a thin waterjet under high-pressure with added abrasive slurry used in order to cut the target material through erosion [4]. The waterjet technique using water (H₂O) with high-pressure was patented originally in the late 60’s by a scientist in the United States. However, the rapid development of the waterjet process gained momentum in the early 80’s as a revolutionary breakthrough in the area of non-conventional processing technologies [5]. Currently, it is a rapidly developing technology, which is used in the modern engineering industry for processing a diversity of engineering materials at macro-, micro- and nano-scales. It is an emerging know-how, which has a large number of compensations over other non-conventional cutting techniques, for instance, no thermal distortion effect, high flexibility, high machining versatility, minimum stresses on the affected zone and small cutting forces [6]. Often, with the intention of improving the repeatability performance of the procedure, an additive is used in the form of abrasive garnet grains materials, which allows the cutting of very hard/thick materials efficiently, such as stainless steel or even carbon steel. The precise name of this hydro-abrasive treatment is “abrasive waterjet”. Figure 1 shows the schematic diagram of abrasive waterjet (AWJ) and the quality zones. Briefly, the abrasive waterjet cutting process can be described as follows [7]: (1) The water (H₂O) is fed by a pump under high-pressure system, after passing through the water causes the suction nozzle to attach to the abrasive mixing chamber; (2) A mixture of water (H₂O) and abrasive (composed of natural almandine garnet grains) is directed to the AWJ nozzle in order to form and stabilize; (3) The final result, is a stream of hydro-abrasive, which has sufficient power to cut through even the toughest materials. Typically, the possible working spaces of the abrasive waterjet technology are available from a few sq ft to hundreds of sq ft and high-pressure water pumps are available from 276 MPa up to 689 MPa [8].

Figure 1. Schematic diagram of abrasive waterjet and quality zones

1.2. Laser Beam Cutting Technology

Laser beam (LB) cutting technology is another promising non-contact method for machining. The first trial in laser beam cutting was done in 1967, when oxygen (O₂) assist gas was used to cut a steel sample with a focused CO₂ laser beam. Laser beam cutting technology is one of the industrial thermal cutting processes, which uses a high-point of the cutting jet by introducing energy and high purity gas [9]. Moreover, the laser beam is based on a gas mixture where the light is amplified by carbon dioxide (CO₂), nitrogen (N₂) and helium (H₂) molecules. Furthermore, the laser beam is focused onto the material surface to be cut, and it heats up the target and causes high-melting point capillary formation passing through a material surface. The power of a laser beam is used to cut various thicknesses of materials, even the toughest surfaces. The laser beams are broadly used to cut and weld most metals, for example, carbon steel, stainless steel, aluminum, copper, etc. Indeed, the laser beam cutting process is fully automated by a CNC system [10,11]. Advantages of laser beam cutting technology are narrow kerf widths, high repeatability and minimal material distortion [12,13]. Figure 2 demonstrations the schematic diagram of the laser beam and the quality zones.

Figure 2. Schematic diagram of laser beam and quality zones

2. Experimental Set-up

Following this introduction, the main objective of the investigation is to derive conclusions based on the measured surface roughness, Ra, and micro-hardness, µ-HV, and determine in which manner precise cutting machining methods affect surface roughness and micro-hardness of the workpiece. Figure 3 shows the schematic plan of the direction for cutting samples by AWJ and LB and the measuring zone. Also, it demonstrates the area of the surface roughness and hardness measurements. Experimental cutting conditions are summarized in Table 1 and Table 2 for both abrasive waterjet and laser beam technologies, respectively.

Figure 3. Schematic plan of cutting samples by AWJ and LB

Table 1. Experimental conditions of AWJ cutting

Table 2. Experimental conditions LB cutting

2.1. Materials Selection

In general, the primary objective of the research is to derive conclusions based on measuring the surface roughness, Ra, and micro-hardness, µ-HV for certain material using advanced technologies, i.e. abrasive waterjet and laser beam methods. To do that, two carbon steel samples at considerable cost savings with a size of 50 mm × 30 mm × 6 mm were cut out of boards of greater dimensions and prepared for cutting by abrasive waterjet and laser beam techniques. Table 3 shows the chemical composition elements of the carbon steel samples. Also, Figure 4 illustrates the photographs of carbon steel surface after cutting by abrasive waterjet and laser beam methods with a close-up view of the cutting process.

Figure 4. (a) top view of carbon steel after cutting with the cutting direction and side view for (b) AWJ (c) LB. A close-up view after the cutting process (d) AWJ and (e) LB

Table 3. Chemical compositions of carbon steel

2.2. Measurement Scheme of Surface Roughness

Surface roughness, Ra, [14] is considered as one of the utmost significant issues that affect product quality in the abrasive waterjet (AWJ) cutting process, similar to the case in the laser beam (LB) cutting process. This fact is due to some critical applications needing a specific high-quality level to finish the product or complete a central part of an extremely sensitive product [15]. In this paper, the surface profile of the carbon steel samples was analyzed in order to determine the statistical standard parameters and the most efficient parameters to be applied to perform are (surface roughness, Ra, root mean square, Rq, ten-point height, Rz, total profile depth, Rt, skewness, Rsk, and kurtosis, Rku) by using Taly-surf® (Taylor Hobson Precision, Inc.). In the current situation, the test-rig can deliver up to 0.8 nm resolution over a measuring range of 12.5 mm including 0.125 µm horizontal data spacing. A nominal 2 µm stylus was used with an average applied load of 0.7 mN and traverse speed down to 0.5 mm/s. The traces were auto-levelled to a linear least-squares regression straight line fit. Then, the data was filtered with a standard value of 0.8 mm cut-off. Each test was repeated at fresh/new locations at least three times on the surface area to ensure the reproducibility of the results. In each case, the fresh/new site was at least ±0.5 mm from the previous one. Indeed, this approach should have avoided any alteration of the counter-body surface, e.g. due to micro-friction or micro-wear, which might happen during the test and indeed would affect the measurements in the following tests. All trials were achieved with a typical “ball-on-flat” arrangement applying a linear sliding contact at constant velocity over a particular distance. Tests were carried out by using a single scan approach “forwards motion” and the profiler had a scan length of 10 mm. More technical details, see [16].

Regular calibration had to be performed. So, before running the exercise, a standard calibration ball radius with D = 22.0161 mm and serial no. 639-506-B (112/1844) (Taylor Hobson Precision, Ltd.) was used to calibrate the precision test-rig. Calibration presented the cantilever was a linear spring system (R² > 0.99), under operating and normal atmospheric pressure typical for this type of machine, with absolute uncertainties of less than 1 % of reading data and the measurement resolution down to at worst 50 nm. Also, the calibration results confirm that the gauge travels through (and therefore, is calibrated over) most of its range.

2.3. Measurement Scheme of Micro-Hardness

The micro-hardness values of the carbon steel samples were measured using a Vickers diamond (Microhardness, Zwick Roell Indentec ZHV1-AFC, Germany). Each sample with a different method of cutting technique (abrasive waterjet and laser beam) was impressed with loads of 50 grams (0.4903 N) for only 15 seconds. Noticeably, there were no cracks on the surface of the material, thereby providing a size of the Vickers diamond indentation that allowed measurement of the surface hardness of this material. This instrument is designed for rapid micro-hardness tests of all types and shapes of metallic and non-metallic materials. Each test condition with the same normal load and time was conducted three times. An average of three readings for each test condition was recorded as the HV and HRC value of a specimen. The result of applying the normal load with a penetrator is an indent or permanent deformation of the material surface affected by the indenter. Mean hardness values were then calculated for each of the sample surfaces. Standard calibration was used to calibrate the test-rig providing approximately 95 % level of confidence. The uncertainty estimation has been carried out accordance to United Kingdom Accreditation Services (UKAS) requirements. Table 4 shows the force verification results. Whereas, Table 5 shows the indentation information type and calibration results. Finally, Figure 5 shows the indentation image of the calibration results on the stainless steel standard block.

Table 4. Force verification results

Table 5. Indentation information type and average calibration results

Figure 5. Image of the calibration results

3. Experimental Results and Discussions

3.1. Surface Roughness Performance

The repeatability performance of the average value of the surface roughness, Ra, of the carbon steel sample is higher in the laser beam cutting technology than in the case of abrasive waterjet cutting technology. The average value of the surface roughness for carbon steel was Ra = 7.54 µm, ±SD = 2.52 µm (for laser beam) and it was, Ra = 6.34 µm, ±SD = 2.67 µm (for abrasive waterjet), for which the thickness is 6 mm. The difference was 1.2 µm. Figure 6 shows the 3-points of the Ra performance on the carbon steel samples after cutting by AWJ and LB technologies. The surface roughness, Ra, measurements are from the top, middle and bottom section of the specimen. Each data point of the Ra is the average value of three measurements. Figure 7 shows the surface roughness performance of 6 mm thickness carbon steel for abrasive waterjet and laser beam cutting methods. Besides, both cutting methods represent very low value of the surface roughness, Ra, at the beginning of the cutting process and after that start to rise until the high value of the surface roughness is reached at the end of the cutting process. This is due to the fact that as the particles move down during the cutting process, they lose their cutting ability and kinetic energy. In the upper corner (Kerf taper geometry) of the cut surface sample, there is a small curve caused by the hitting particles departing from the jet (nozzle). Generally, this section is accepted as an ignorable edge impact. Then, the smoother surface section is located under the first section. A little heat generated by the abrasive waterjet (AWJ) process is absorbed by the water and carried into the catch tank. The material surface itself experiences almost no alteration in temperature during the machining processes. Only the waterjet nozzle has a high temperature. In the point of passage of the abrasive stream through the material surface, there is no dross. However, it was observed that there was a small loss of material to be tested. On the other hand, the laser beam emits heat, which deforms the material. Re-melting zones are visible in the corners and dross occurs. The biggest deformation takes place at the point of passage of the beam through the material, which reaches a few sub-millimetres in size. Table 6 shows the average value of the statistical analysis of the carbon steel surface profile. Hence, surface roughness distribution parameters of skewness, Rsk, and kurtosis, Rku, were calculated. The skewness, Rsk, is a measure of the asymmetric spread of the surface height, whereas the kurtosis, Rku, represents the peakedness of the surface roughness distribution. A Gaussian surface has a skewness of 0.0 and a kurtosis of 3.0 with an equal number of valleys and peaks at a certain profile of the surface height. The skewness and kurtosis of the carbon steel sample after cutting samples by laser beam were 0.05 and 2.51, respectively. Moreover, the skewness and kurtosis of the carbon steel sample after cutting samples by abrasive waterjet were -0.04 and 2.69, respectively.

Table 6. Statistical analysis of the carbon steel surface profile

Figure 6. 3-points Ra performance

Figure 7. Surface roughness performance of 6 mm thickness carbon steel for abrasive waterjet and laser beam cutting methods

Kerf taper (upper edge and lower edge) is the most significant parameter to be mentioned after surface roughness, Ra, which is produced due to the variation in the jet velocities and energy from the “jet-wall” to “jet-center”, where the maximum velocity takes place [17]. This performance criterion is a critical factor during assembly operation as the taper of the surface may cause some difficulties during the process and lead to the failure of a collection of the two parts together. Figure 8 shows the schematic illustration of the upper and lower edge of the surface before and after the cutting method. It is clearly observed that the top kerf width during the cutting process is considerably different from the bottom kerf width due to the expansion of the jet. Kerf taper ratio is well-defined as the ratio between the top and the bottom of the Kerf width, see Equation (1) [18].

[picture] | (1)

Wang, J., in [17] used scanning electron microscopy (SEM) in order to investigate the Kerf geometry (the upper and the lower edges) and taper angle which results from different machining parameters. It was determined that impact angle of 80° will achieve the greatest depth of cut and have less effect on other characteristics. Additionally, different studies were conducted on various material surfaces to examine which machining parameters have the most significant impact on the performance. Glass epoxy composite laminate was used to investigate the effect of abrasive type and hydraulic-pressure on Kerf ratio. It was concluded that increasing hydraulic-pressure and mass flow rate enhances the cutting process and reduces the Kerf taper ratio, in addition to the harder, more abrasive material providing better cutting and smooth surfaces [19]. Meanwhile, the Kerf widths (top, bottom, and ratio) were investigated for Al material by three single mesh sizes for garnet abrasive waterjet which reveals different behavior in terms of multi-mesh size [20]. Also, various types of abrasive material, for instance, garnet (X₃Y₂(SiO₄)₃), silica sand (SiO₂), silicon carbide (SiC) and olivine (Mg, Fe)₂SiO₄, were used to study the impact of abrasive type on the Kerf width of cutting surface. Using silicon carbide (SiC) produced greater width of cut than garnet due to its hardness and the Kerf width decreased by high feed rate [21]. Recently, colemanite powder (CaB₃O₄(OH)₃·H₂O) was used as abrasive material compared with a garnet type which is the whole common type of abrasive used in waterjet cutting technology. The study was conducted on different kinds of materials such as aluminum 7075 alloy, marble (CaCO₃), titanium alloys (Ti₆Al₄V) Grade 5, glass and a composite material. The results showed that the amount of colemanite powder (CaB₃O₄(OH)₃·H₂O) used is higher than garnet (X₃Y₂(SiO₄)₃) to give same action [22].

Figure 8. schematic illustration of the upper and lower edge of the surface before and after the cutting

3.2. Micro-Hardness Performance

Figure 9 shows some random surface topography images of the micro-hardness test for both methods. Also, Figure 10 illustrates the micro-hardness performance of a 6 mm thickness steel plate for abrasive waterjet and laser beam cutting methods. Clearly, it can be seen that the average value of the micro-hardness of carbon steel sample was HV = 548.82, ±SD = 72.4 (for laser beam) and it was HV = 525.70, ±SD = 72.5 (for abrasive waterjet). Surprisingly, the micro-hardness value for both cutting methods start roughly speaking at the same value around 450 HV and then start to increase until the end of the cutting distance is reached. The difference was 23.12 HV. Generally, it shows a markedly similar trend to the previous case for the surface roughness trend where the Ra increases gradually from the surface.

Figure 9. Topography images of the micro-hardness test

Figure 10. Micro-hardness performance of 6 mm thickness carbon steel for waterjet and laser cutting methods

Figure 11. Variation of micro-hardness performance at different depth below the surface

Figure 11 demonstrates the variation of µ-hardness at a different depth below the surface. In the meantime, the effective case depth was about ~330 µm at 549 HV (for laser beam), and it was about ~320 µm at 525 HV (for abrasive waterjet). Each hardness value in the figures represents an average value of 10 measurements in order to ensure the repeatability and the reproducibility of the results. It is evident from the repeatability performance of the micro-hardness figure that the hardness increased gradually away from the upper edge surface. There is about ~20 % increase in hardness of the surface as compared to the hardness of the starting point about ~1 mm from the upper edge surface. It is believed that the observed rise in hardness closer to the surface is due to the effect of hardening as a result of high-impact.

3.3. Visualization Analysis

Two carbon steel samples were processed by abrasive waterjet (AWJ) and laser beam (LB) cutting methods when the target surfaces were positioned at z = 1.5 mm (standoff distance). In this paper, the surface topography is visualized through a scanning electron microscope (SEM), which has been performed as a useful and advanced technique in describing the small-scale structures on the cut surface materials at different magnification factors. Figure 12 demonstrates the SEM images of the carbon steel samples after the cutting processes by using abrasive waterjet and laser beam methods. From those images acquired by using such a method, five typical images for each cutting processes representing the results.

In AWJ process images, apparent traces created by high-pressure abrasive particles can be found and distributions of marks are quite uniform. Besides, there are few grooves in the AWJ images that terminates its progress with a truncation at the end, which is one of the most distinct features on the surface topography being exposed to AWJ cutting method. Indeed, the amount of kinetic energy is not enough for the abrasive particles to cut through the 6 mm thickness of the carbon steel sample and the abrasive particles might deviate from the original track and/or embed themselves directly in the sample to be tested. From another perspective, the development of the radial velocity component in the jet stream is prompted by the vertical expansion of the jet stream. Consequently, it improves to some degree the possibility of the embedment of abrasive particles. Such a remarkable phenomenon has been observed in the literature review [23]. Also, it should be noted that in this connection the physical properties of abrasive particles cannot be neglected. By examining the surface roughness profile, it was found that the AWJ cut surface of carbon steel is negatively-skewed. The ratio of the two surface roughness profile parameters Rq/Ra is approximately 1.22.

In LB method images, during the process, a thin layer of melt flows down the cut front and it becomes unstable and generates slow waves at the melt surface area. Tani, G., et al. [24] clarifies that the creation of the dross at the lower edge of the Kerf taper and the scratch on the cut edge (surface roughness profile, Ra) depend on the melt film properties (~20 µm) condition throughout the Kerf taper. Wolfgang, S., et al. [25] describes that dross formation is related to the melt film properties, for instance its thickness and velocity. He also related this outcome to the experimental remarks of viscous free surface flows around an edge and the separation of the melt flow from the solid surface. From another perspective, the delay of the viscous melt film streamlines during laser beam cutting of a 6 mm thickness of carbon steel sample can result in flow separation as the melt layer thickens quickly with the intention of satisfying continuity within the boundary layer. BLS also known as boundary layer separation is the point along the cut edge where the flow separation occurs. Downstream the BLS line, there is a backflow of the melt film next to the Kerf taper wall and the boundary layer flow changes from “laminar flow (beginning-of-the-cut)” into “turbulent flow (Ending-of-the-cut)” in which the melt film particles move in uninformed tracks. The change to turbulent boundary layer flow can also be caused by the disturbances in the laser beam cutting method, for instance, fluctuations in processing parameters, which may become amplified until turbulence is developed [26]. By examining the surface roughness profile, it was found that the laser beam cut surface of the carbon steel is positively-skewed and the ratio of the two surface roughness profile parameters Rq/Ra is around 1.21.

Figure 12. SEM images of the carbon steel samples after the cutting processes (a) laser beam and (b) abrasive waterjet

3.4. AWJ vs. LB Methods

The next issue in the article was to compare the abrasive waterjet (AWJ) and laser beam (LB) cutting technologies. Indeed, several studies examine the abrasive waterjet method alongside the laser beam method. Noticeably, the studies give different results due to different materials used and different parameters [7,27,28,29,30]. The abrasive waterjet cutting method is the generally accepted efficient technology for cutting various materials as of its advantages over other non-conventional techniques, for instance, no heat is generated in the cutting process, there is high machining versatility, minimum stresses on the affected zone, high flexibility, and small cutting forces. Also, the abrasives after cutting can be re-used which allows for possible reduction of the cutting cost of the process and machining can be easily automated. The process does, however, have some limitations and drawbacks. It may generate high noise and a disordered working environment; the machining is not applicable for machining a too thick workpiece, only a limited number of materials can be cut economically, taper cutting is also a problem with abrasive waterjet cutting in very thick materials [31].

Arola, D., et al., introduced compressive residual stresses in the metal surfaces for abrasive waterjet (AWJ) peening and the maximum compressive residual stress resulting around 400 MPa. He also pointed out that AWJ is peening and invoked a signiﬁcant increase in the surface roughness, Ra, which is consistent with the results obtained in this paper [32]. To sum up, Table 7 shows the comparison between abrasive waterjet cutting and laser cutting methods regarding different parameters. Moreover, Table 8 lists the effects of various machining methods on equipment and tooling, whereas Table 9 illustrates the economic performance of different machining methods.

Table 7. Comparison between abrasive waterjet (AWJ) cutting and laser beam (LB) cutting methods, adapted from [32,33,34]

Table 8. Effects of different machining methods on equipment and tooling, adapted from [32,33,34]

Table 9. Economic performance of different machining methods, adapted from [32,33,34]

4. Conclusions

The main purpose of the present investigation is to compare and contrast the two essential cutting techniques (abrasive waterjet and laser beam) in terms of the surface roughness, Ra, and micro-hardness and to select the finest technology for cutting metal thats available in the business environment. The effect of abrasive waterjet (AWJ) and laser beam (LB) cutting of carbon steel has been presented based on an experimental investigation. Experimental results indicate that better quality surface of final cutting process was reached by the use of abrasive waterjet (AWJ) technology for comparable working conditions regarding surface roughness, Ra, and micro-hardness in short-distance within 6 mm thickness of the carbon steel samples. These results are indeed as expected for the AWJ technology compared to the LB technology. Although nowadays the progressive technologies of AWJ and LB cutting are very well-known, a limited works have been done on the issue of comparison of these techniques from surface roughness as the final product quality and the micro-hardness of the cutting process.

Study of these interrelations was represented in this research and the analysis presented in this study can be summarized as follows for carbon steel materials:

• The average value of the surface roughness performance was Ra = 7.54 µm, ±SD = 2.52 µm (for laser beam) and it was Ra = 6.34 µm, ±SD = 2.67 µm (for abrasive waterjet), for which the thickness is 6 mm. The difference was 1.2 µm.

• The skewness, Rsk, and kurtosis, Rku, of the carbon steel sample after cutting by LB were 0.05 and 2.51, respectively. Whereas, the skewness, Rsk, and kurtosis, Rku, of the carbon steel sample after cutting by AWJ were -0.04 and 2.69, respectively.

• The average value of micro-hardness performance was HV = 548.82, ±SD = 72.4 (for laser beam) and it was HV = 525.70, ±SD = 72.5 (for abrasive waterjet). The difference was 23.12 HV.

• The micro-hardness value for both cutting methods start roughly speaking at the same value around 450 HV and then start to increase until the end of the cutting distance is reached.

• The effective case depth was about ~330 µm at 549 HV (for laser beam), and it was about ~320 µm at 525 HV (for abrasive waterjet).

The final observation is that abrasive waterjet (AWJ) cutting technology is not the fastest way to cut the materials especially if a high-quality product is required, and a long time spent cutting the samples will increase the overall cost. However, from these results, it is clear that AWJ cutting technology is the most suitable of those compared for cutting metals. Indeed, this report is consistent with the researchers mentioned in the literature review which is cited within and has been used as an investigation for the existing paper.

The future research has to contribute significantly to study the effect of different conditions of AWJ and LB cutting methods and to use the Taguchi-Grey Relation Analysis for assessing the optimal set of control factors in order to obtain high-quality surface finishing.

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