1 Introduction

Titanium alloys have outstanding mechanical and chemical qualities, such as high tensile strength and toughness, excellent corrosion and oxidation resistance, lightweight, extreme temperature resistance, and high strength-to-weight ratio [1, 2]. Due to their wide commercial availability and economic feasibility, titanium alloys are expected to be the most widely used in the coming years. Although several titanium alloys have been produced, they are rarely useful for large-scale commercial use. In the meanwhile, some compositions such as Ti–8Mn, Ti–7Al–4MO, and Ti–4Al–3Mo–1 V have only observed brief applications. Ti–6Al–4 V is the most often used alloy and has the highest demand of all 20th-century alloys. What distinguishes Ti–6Al–4 V is several good qualities that make it essential for commercial use in numerous industries such as aerospace, automotive, and biomedical. Because of higher performance and fatigue characteristics, as well as functionality improvement of the parts, which depend on titanium alloys especially Ti–6Al–4 V, titanium alloys are utilized in jet engine parts, engine compartments, fan blades, fuel tanks, and airplane hulls. In biomedical applications, Ti-alloys have excellent mix of corrosion-resistance and antibacterial characteristics. These properties allow for a wide range of applications in orthodontics, dental implants, artificial joints, and surgical equipment [3].

However, Ti-alloys offer good qualities, they are difficult to be machined using conventional methods because of their high mechanical characteristics [4, 5]. The machinability characteristics suggest many challenges for the machining, such as increased machining force, irregular size, increased machining temperature, reduced tool life because of tool wear [6], and low surface quality. So, it is considered a problem for cutting efficiency [5, 7], However, some studies try to help in cutting titanium alloys by preheating the alloy before cutting, which helps in decreasing cutting problems and time [8]. Then, studies started to use the laser source as a heat source to increase tool cutting quality and life by decreasing the cutting force [9, 10].

Then, some studies presented a comparison between conventional and laser-assisted machining, which added more assurance that laser-assisted machining is better than conventional methods [11, 12]. As a result, some studies focused only on using nontraditional machining methods such as laser machining (LM) [13], abrasive water jet machining (AWJM) [14], ultrasonic machining (USM) [15], and abrasive water jet-assisted laser machining (AWJALM) [16], which are examples of alternative machining processes that are more efficient and faster than conventional methods. But, laser cutting machining is preferred over abrasive water jet machining and plasma machining with many advantages, such as low operation time and low operation energy, and there is no need to harden the metal before cutting [17].

The laser cutting method is classified as a thermal-cutting process that uses a laser beam source to machine such types of materials and is extensively utilized in the manufacturing industry [18], which is achieved by directing and focusing a high-power, coherent, monochromatic laser beam onto the surface of a workpiece with wavelengths ranging from ultraviolet to infrared. The workpiece absorbs the high value of laser beam energy, and a high rise in temperature happens at the focused area of the machined material. The material melts or vaporizes because of the elevated temperature and may undergo chemical changes before being evacuated using a high-pressure support gas, depending on the substance's characteristics and the intensity of the beam [19]. In addition, laser beam machining has some techniques of cutting [13], which can be mentioned as laser beam sources, which are Co2, fiber laser, and ND: YAG pulsed laser [20, 21].

The laser cutting process has parameters that affect the cut surface and kerf profile quality, which are important to define well to get the best quality of cut surface for the intended applications. Those factors are laser beam power, cutting velocity, focal position, focus position, standoff distance, nozzle type, nozzle diameter, material type, material thickness, pulse width, frequency, type, and pressure of the assist gas. So, it is necessary to detect the right conditions of the cutting process to get the best surface quality. It is hard to use all the factors as variable factors because it will require such huge and complicated work. So, the researchers used to make some variables fixed parameters and others variable parameters; the most used set of parameters as variable parameters is laser power, cutting velocity, and assist gas pressure [22,23,24,25,26].

Most of the previous studies discussed the influence of those three parameters on the surface and kerf quality of titanium alloys. Most of them have revealed that the laser power is the most important factor, followed by cutting velocity and assist gas pressure, such as cutting 2 mm Ti–6Al–4 V alloy with nitrogen as an assist gas [27], cutting 3 mm Ti–6Al–4 V alloy with azote as an assist gas pressure [25], and cutting 3 mm pure titanium and Ti–6Al–4 V alloy with nitrogen as an assist gas [28].

However, some of them found that cutting velocity is the key factor, followed by laser power and assist gas pressure, such as when cutting 2 mm pure titanium with nitrogen as an assist gas [29]. But, if one of the cutting velocities or the laser power has been set as a fixed parameter in the cutting parameters, the other one will be the dominant parameter.

When the laser power was a fixed parameter, the cutting velocity was the dominant parameter, such as when cutting 1.4 mm Ti–6Al–4 V alloy with nitrogen as an assist gas [30], cutting 1.6 mm Ti–6Al–4 V alloy with air as an assist gas [31], and cutting 5 mm Ti–6Al–4 V alloy with nitrogen as an assist gas [32]. When cutting velocity was a fixed parameter, the laser power was the dominant parameter when cutting 3 mm Ti–6Al–4 V alloy with oxygen gas as an assist [33].

Many studies have investigated the effect of laser power, cutting velocity, and assist gas pressure on cut-edge surface quality for a thickness range of 1–3 mm. However, there is not enough research on the laser machining of Ti–6Al–4 V alloys with a thickness greater than 3 mm due to the difficulties of cutting higher thicknesses.

Therefore, the objective of the current study is to produce high-quality cuts of thick Ti–6Al–4 V alloy sheets using nitrogen as an assist gas to optimize the efficiency of the prementioned applications. The combination of laser beam power, cutting velocity, and assist gas pressure were used as the input cutting parameters. Efficient cut trials have been selected based on Taguchi method which led to L9 orthogonal arrays. The cut surface quality, kerf width, kerf taper, and dross height of 4 mm Ti–6Al–4 V alloy sheet were investigated as performance parameters as they affect the quality of the mentioned applications. A 3D plot of input versus output parameters was employed using Minitab software. The most effective cutting parameters on surface roughness, upper kef width, kerf taper, and dross height were discussed.

2 Experimental Work and Methodology

2.1 Laser Cutting Machine and Material Description

2.1.1 Laser Cutting Machine

To investigate surface and kerf qualities, a CE Mark fiber laser machine (Central wavelength equals 1080 ± 5 nm, the maximum modulation frequency is 5 kHz and the power instability is ± 1.5%), which is shown in Fig. 1 (OR_p4020 t3 3 kW raycus), was used to cut a 4-mm thick sheet of Ti–6Al–4 V alloy. Nitrogen was used as an assist gas for different cut trials, and cutting parameters were laser beam power, velocity of cut, and assist gas pressure. Figure 2 shows schematic of laser cutting process which indicates the different parameters of the process.

Fig. 1
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Laser machine and samples setup for cutting

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Fig. 2
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Schematic of laser cutting process

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2.1.2 Material Properties and Sample Preparation

Table 1 shows chemical composition and mechanical properties of Ti–6Al-4 V alloy, which was supplied by Baoji Lida New Materials Co.Ltd. The received samples were dimensioned as 120 × 80 × 4 mm,Query; then, they were divided into small pieces of 80 × 10 × 4 mm using a wire-cutting machine, which is shown in Fig. 3. These samples were fixed by glue to a plate to ensure stability during cutting process as shown in Fig. 4.

Table 1 The chemical composition and mechanical properties of Ti–6Al–4 V alloy
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Fig. 3
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Wire cut machine

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Fig. 4
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Samples preparation for cutting

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2.2 Cut Trials

Since there are not enough previous studies of laser cutting of Ti6Al4V alloy, many experiments were done to get the closest set of parameters using cutting parameters, which were used for 3-mm sheet thickness [25, 33], then changing these parameters by increasing or lowering laser power, cutting velocity, and assist gas pressure values. Even after obtaining the right set and when cutting was done, two samples were not cut completely; therefore, they were excluded from studied output values to not affect the experimental results.

During stating trials, some defect has been found because of the higher values of cutting velocities or lower values of the laser beam power as it is shown in Fig. 5. Table 2 shows a number of cut trials and the different sets of parameters which were used to get the right set of cutting parameters. The evaluation method to those trials was to check if the full cut happened through the range of the nine trials or to check the height of the drosses or by seeing the bottom kerf width quality.

Fig. 5
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Defects of some starting trials

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Table 2 Different sets of parameters which are used for cut trials
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2.3 Design of Experiment

A well-planned experiment can significantly decrease overall number of cutting trials without reducing the accuracy of any experimental study. Because many studies were made by using the most basic L9 OA [34,35,36,37,38]. Therefore, Taguchi was used to make the cutting process robust and effective by eliminating the unnecessary cutting trials. In this study, three control parameters with three levels for each were investigated, and the set of fixed and variable parameters is shown in Tables 3 and 4.

Table 3 Fixed parameters of cutting
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Table 4 Variable parameters of cutting and their levels
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Table 5 illustrates the nine experiments which made to investigate the influence of laser cutting conditions on surface and kerf quality, as well as dross height. It also shows the state of cut.

Table 5 Taguchi arrays L9 (3 × 3)
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2.4 Measurements

2.4.1 Methods and Devices Used for Measurement

Laser-cut samples were divided into small specimens to be used in measuring the output performance parameters. Surface roughness values were measured by Mitutoyo device, (The Surftest SJ-210), which measures the average values for each line of the three measured places as shown in Fig. 6.

Fig. 6
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Place of measurement of surface roughness

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SEM images were taken for all the cut samples by using (JEOL, JSM IT 100) device. Then, UKW, LKW, and drosses height were measured using ImageJ program by taking around three to five measures to each line of cut path and taking the average value of them for UKW and LKW. But for the dross height, it has only one measure which is the height value, which is represented in Fig. 7. Furthermore, kerf taper angle was calculated by using Eq. (1) [39] based on the average values of UKW and LKW as shown in Fig. 8, but for very small angles, equation 1 can be reduced to be more applicable [40].

$$\mathrm{KT }\left(^\circ \right)={\text{arctan}}\left(\frac{\left({\text{UKW}}-{\text{LKW}}\right)}{2{\text{t}}}\right)$$
(1)

where UKW and LKW represent values of upper and lower kerf widths and (t) represent the thickness of Ti–6Al–4 V alloy.

Fig. 7
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Representation of unremoved drosses of laser cut path

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Fig. 8
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Representation of UKW, LKW, and KT

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2.4.2 The Measurements of Performance Parameters

Tables 6, 7, 8, and 9 illustrate the measurements of performance parameters (surface roughness, upper and lower kerf widths, kerf taper, and dross height).

Table 6 Surface roughness measurements
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Table 7 Kerf width measurements
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Table 8 Kerf taper measurements
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Table 9 Dross height measurements
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3 Results and Discussion

3.1 Surface Roughness

Figure 9 shows the values of surface roughness at three places (1, 2, and 3 mm) with different input parameters for cutting process. Seven samples were cut, while two samples (sample No. 3 and sample No. 6) were not cut because of lack of power in sample No. 3 and high cutting velocity in sample No. 6.

Fig. 9
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Surface roughness values at the different input parameters

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For sample no. 1, it was observed that the surface roughness values were high in all zones, which are 10.87 ± 0.54 µm, 12.34 ± 0.62 µm, and 16.26 ± 0.81 µm, respectively, as the low cutting velocity led to a higher value of the heat concentrated without removal because the assist gas pressure is also low.

For sample no. 2, surface roughness values were improved at the beginning of the cut due to increasing velocity but were still high at the end of the cut as the assist gas pressure was not enough to remove them. For sample no. 3, the used cutting conditions did not lead to a full cut of the sample because of the high value of velocity against the low value of laser power, which does not give enough heat to cut the sample.

For sample no. 4, it has the same quality as sample No. 1 because of the small cutting velocity, which leads to the same result. Sample no. 5 has better quality than sample no. 4, which reaches 7.01 ± 0.35 µm at the start of the cut, as shown in Fig. 10b, because of increasing velocity to 1500 mm/min and assist gas pressure to 10 bar, but it is still higher at the end of the cut. For sample no. 6, the cut did not occur because of the high increase in velocity, as it did with sample no. 3.

Fig. 10
figure 10

SEM of laser cut surface of: a sample no. 1 (Pu = 2 kW, V = 1000 mm/min, P = 6 bar), b sample no. 5 (Pu = 2.5 kW, V = 1500 mm/min, P = 10 bar), and c sample no. 9 (Pu = 3 kW, V = 1000 mm/min, P = 8 bar)

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For sample no. 7, despite the lower cutting velocity of 1000 mm/min, good face quality is observed at the beginning of the cut due to the high pressure of the auxiliary gas, which is 10 bar, while in the middle and end of the cut, inadequate quality is observed due to the low value of cutting velocity. For sample no. 8, the start cut quality is good because of the increasing velocity to 1500 mm/min, but it is moderate at the middle and end of the cut because of the low pressure, which is 8 bar.

For sample no. 9, it was noticed that the quality of the start and middle of the cut is good, which are 2.34 ± 0.12 µm and 6.41 ± 0.32 µm, respectively, as shown in Fig. 10c, because of increasing velocity to 2000 mm/min, and moderate at the end of the cut. Some SEM images have been taken at the end of the cut surface. It was also observed that the pressure used was not enough to remove all the melted metal, which led to some voids and a high value of resolidified metal at the end of the cut, as shown in Fig. 10a, as the maximum value that could be used by the machine was 10 bar, while it showed excellent quality at the start and middle of the cut.

Figure 11 shows the measured values of the surface roughness profile for samples 1 and 7. So, to get the best quality of cut, the cutting conditions should be moderate in laser power, high in cutting velocity, and high in assist gas pressure.

Fig. 11
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Measured values of surface roughness profile for a sample no. 1 and b sample no.7

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3.2 Kerf Width

SEM was taken to the cut line from the upper and lower sides, as shown in Fig. 14. The upper and lower values of kerf width are shown in Fig. 12. It shows excellent quality on the upper side of the cut but also shows more molten metal on the lower side of the cut because of a lack of pressure.

Fig. 12
figure 12

Kerf width of upper and lower values at the different input parameters

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Seven of the nine samples were cut as shown in Fig. 13 based on the parameters used during laser cutting, and the results were as follows: For sample no. 1, it was noticed that kerf width values are small at the beginning and the end of the cut as the low cutting velocity value of 1000 mm/min led to a high value of concentrated heat without removal as the assist gas pressure value is 6 bar, which is also low.

Fig. 13
figure 13

Cut samples from the upper and lower sides

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For sample no. 2, the kerf width value at the beginning of cutting increases because of an increase in the value of the cutting velocity to 1500 mm/min and an increase in the value of the assist gas pressure to 8 bar, but the value of the kerf width at the end of the cut is small because of a lack of power, which is 2 kW.

For sample no. 3, the used cutting conditions did not lead to a full cut of the sample because of the high value of velocity against the low value of laser power, which did not produce enough heat to cut the sample. For sample no. 4, there has been a noticeable increase in the value of the kerf width for the upper face to 0.896 ± 0.004 mm as the laser power has increased to 2.5 kW, but it is still low at the end of the cut as the pressure cannot remove the whole melted metal.

For sample No. 5, the kerf width values at the upper and lower sides decrease to 0.774 ± 0.016 mm and 0.408 ± 0.039 mm, respectively, as shown in Fig. 14a, d, because of the increasing cutting velocity value to 1500 mm/min at the same power value of 2.5 kW as in sample no. 4. For sample no. 6, the cut did not happen because of the high increase in velocity, as happened with sample no. 3.

Fig. 14
figure 14

SEM of the UKW and LKW of: a, d sample no. 5 (Pu = 2.5 kW, V = 1500 mm/min, P = 10 bar), b, e sample no. 7 (Pu = 3 kW, V = 1000 mm/min, P = 10 bar), and c, f sample no. 9 (Pu = 3 kW, V = 2000 mm/min, P = 8 bar)

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For sample no. 7, the kerf width values increase again to 1.377 ± 0.015 mm and 0.439 ± 0.017 mm in the upper and lower sides, respectively, as shown in Fig. 14b, e, because of an increase in power value to 3 kW at a small cutting velocity of 1000 mm/min. For sample no. 8, the kerf width values decrease again because of an increase in cutting velocity to 1500 mm/min at the same power as sample no. 7.

For sample no. 9, the upper kerf width value continues to decrease as shown in Fig. 14c, reaching a value of 1.043 ± 0.021 mm in the upper side because of the cutting velocity value increasing to 2000 mm/min and increasing to 0.640 ± 0.029 mm on the lower sides as shown in Fig. 14f because of the medium value of pressure, which is 8 bar. To sum up, the values of the kerf width were affected most by laser power and cutting velocity values.

3.3 Kerf Taper

The results of kerf angle are presented in Fig. 15. Thick materials with high mechanical properties will lead to an increase in the taper angle.

Fig. 15
figure 15

Kerf taper values at the different input parameters

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For sample no. 1, it was noticed that the kerf taper value is small as the low value of cutting velocity of 1000 mm/min leads to a high value of concentrated heat without removal as the assist gas pressure value is 6 bar, which is also low, but it was removed from the figures as it represents unfamiliar case as the LKW was bigger than the UKW.

For sample no. 2, the kerf taper increased to 1.89 ± 0.61° because the cutting velocity value was increased to 1500 mm/min with an increase in the assist gas pressure value to 8 bar. For sample no. 3, the cutting conditions used did not lead to full cutting of the sample, as shown in Fig. 16a, because of the high-velocity value of 2000 mm/min against the low laser power value of 2 kW, which does not produce enough heat required to cut the sample.

Fig. 16
figure 16

Cross-section view of kerf taper of: a sample no.3 (Pu = 2 kW, V = 2000 mm/min, P = 10 bar), b sample no.4 (Pu = 2.5 kW, V = 1000 mm/min, P = 8 bar), c sample no.6 (Pu = 2.5 kW, V = 2000 mm/min, P = 6 bar), d sample no.7 (Pu = 3 kW, V = 1000 mm/min, P = 10 bar), e sample no.8 (Pu = 3 kW, V = 1500 mm/min, P = 6 bar), and f sample no. 9 (Pu = 3 kW, V = 2000 mm/min, P = 8 bar)

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For sample no. 4, the increase in the kerf taper value continues to reach 3.18 ± 0.3° as shown in Fig. 16b, because of an increase in laser power to 2.5 kW. For sample no. 5, the kerf taper value decreases slightly because of increasing the cutting velocity value to 1500 mm/min with an increase in the assist gas pressure value to 10 bar, which helped in removing the molten metal and refining the cutting surface.

For sample no. 6, as shown in Fig. 16c, the cutting process did not occur due to a high increase in velocity as it did with sample three. For sample no. 7, the kerf taper increases with a noticeable value of 6.68 ± 0.22°, as shown in Fig. 16d, because of an increase in power to 3 kW at a small cutting velocity of 1000 mm/min, but even though using a high-pressure value of 10 bar, it did not influence the kerf taper value.

For sample no. 8, the kerf taper values decrease again to 4.55 ± 0.24°, as shown in Fig. 16e, because of the increase in the cutting velocity value to 1500 mm/min at the same power value of 2.5 kW for sample no. 7. For sample no. 9, the kerf taper values continue to decrease to reach 2.88 ± 0.35°, as shown in Fig. 16f, due to the increase of the cutting velocity value to 2000 mm/min. To sum up, kerf taper values are affected by laser beam power more than the other parameters.

3.4 Dross Area

Measured dross values are illustrated in Fig. 17, and SEM images of the cut cross-section are shown in Fig. 18.

Fig. 17
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Dross height values at the different input parameters

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Fig. 18
figure 18

SEM of the drosses of: a sample no.1 (Pu = 2 kW, V = 1000 mm/min, P = 6 bar), b sample no. 3 (Pu = 2 kW, V = 2000 mm/min, P = 10 bar), c sample no. 4 (Pu = 2.5 kW, V = 1000 mm/min, P = 8 bar), d sample no. 5 (Pu = 2.5 kW, V = 1500 mm/min, P = 10 bar), e sample no. 8 (Pu = 3 kW, V = 1500 mm/min, P = 6 bar), and f sample no. 9 (Pu = 3 kW, V = 2000 mm/min, P = 8 bar)

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For sample no. 1, it is noticed that the dross height is large, as shown in Fig. 18a, as the low cutting velocity of 1000 mm/min resulted in a higher concentrated heat without removing the drosses as the assist gas pressure is 6 bar, which is also low. For sample no. 2, dross height decreases to reach 0.370 mm due to the increase in the cutting velocity to 1500 mm/min and the increase in the assist gas pressure value to 8 bar.

For sample no. 3, the cutting conditions used did not lead to a full cut of the sample, as shown in Fig. 18b, because of the high-velocity value of 2000 mm/min against the low laser power value of 2 kW, which did not give enough heat needed to cut the sample. For sample no. 4, the increase in the dross height value continued to reach 0.807 mm, as shown in Fig. 18c, because of the increase in the laser power value to 2.5 kW and the decrease in the cutting velocity to 1000 mm/min.

For sample no. 5, the dross height increased with a high value to reach 1.183 mm, as shown in Fig. 18d, because of increasing the cutting velocity value to 1500 mm/min, which resulted in a decrease in heat concentration, which led to difficulty removing the drosses before they became sticky. For sample no. 6, cutting did not occur because of the high increase in velocity, as happened with sample no. 3.

For sample no. 7, the dross height decreased by a noticeable value, reaching 0.546 mm, because of an increase in power value to 3 kW at a small cutting velocity of 1000 mm/min, which resulted in good melting of the metal and helped the pressure remove the majority of the formed drosses.

For sample no. 8, the dross height increases again to reach 0.719 mm, as shown in Fig. 18e, because of increasing cutting velocity to 1500 mm/min at the same power used in sample no. 7. For sample no. 9, the dross height continues to decrease to reach 0.270 mm, as shown in Fig. 18f, because of the increase in cutting velocity to 2000 mm/min. In summary, dross values were affected most by cutting velocity.

3.5 3D Plot of Laser Cutting Parameters Versus Output Performance Parameters

To detect the optimum input parameters of the laser cutting process versus the output performance of the cutting surface, a 3D plot of the input versus output parameters was employed using Minitab, which shows the effect of the input parameters on the output parameters as shown in Figs. 19, 20, and 21. It was observed that cutting velocity with laser power and assist gas pressure with cutting velocity have the most influence on surface quality, kerf width, and dross height, where surface roughness and UKW are small at higher values of cutting velocity and medium values of laser power, as shown in Fig. 19 and 20.

Fig. 19
figure 19

3D plot of input parameters versus output parameters for a SR at 1 mm, b SR at 2 mm, c SR at 1 mm, and d SR at 2 mm

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Fig. 20
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3D plot of input parameters versus output parameters for a SR at 3 mm, b SR at 3 mm, c UKW, and d UKW

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Fig. 21
figure 21

3D plot of input parameters versus output parameters for a LKW, b KT, c KT, and d dross height

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KT is small at minor values of power, as shown in Fig. 21c. Dross height is small at medium values of cutting velocity and assist gas pressure, as shown in Fig. 21d.

3.6 The Main Effect of Laser Cutting Parameters on Studied Performance Parameters

To clarify the effect of laser cutting parameters related to each other, main effect plots of the variable cutting parameters on surface roughness, UKW, KT, and dross height were employed as shown in Figs. 22, 23, 24, 25, 26, and 27, which give a clear answer to the question of what are the parameters that affect the performance parameters more than others. Based on those plots, it is recommended to use high cutting velocity values at medium values of laser beam power and assist gas pressure to obtain the lowest values of surface roughness, which indicate high surface quality, as shown in Fig. 22 and 23. But for upper kerf width, it is recommended to concentrate on laser power to achieve the aimed values of UKW as it is proportional to laser beam power as shown in Fig. 24. Also, for kerf taper, it is recommended to use medium values of laser power with medium values of assist gas pressure to get acceptable values of KT, as it is proportional with laser power and inversely proportional with assist gas pressure, as shown in Fig. 26.

Fig. 22
figure 22

Main effect plot of cutting parameters on SR at 2 mm

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Fig. 23
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Main effect plot of cutting parameters on SR at 3 mm

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Fig. 24
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Main effect plot of cutting parameters on UKW

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Fig. 25
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Main effect plot of cutting parameters on LKW

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Fig. 26
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Main effect plot of cutting parameters on KT

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Fig. 27
figure 27

Main effect plot of cutting parameters on dross height

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For dross height values, it is recommended to use high values of cutting velocity with medium values of laser power and assist gas pressure, as shown in Fig. 27. To sum up, high values of cutting velocity with medium values of laser power and assist gas pressure will achieve the lowest values of cut surface roughness, kerf width, kerf taper, and dross height.

4 Conclusions

A fiber laser machine was used to cut a 4-mm-thick Ti–6Al–4 V alloy by using the most used set of cutting parameters, which were selected by Taguchi using Minitab program. The influence of laser power, cutting velocity, and assist gas pressure on Ti–6Al–4 V sheet surface and kerf quality was investigated. A 3D plots have been made to get the effect of input parameters on outputs. ANOVA method was applied to get the main effective parameter for each output performance parameters. The conclusion can be drawn as follows:

  1. 1.

    Cutting velocity was found to be the most significant control factors for surface roughness (at 1 mm and 2 mm) followed by laser power and assist gas pressure. But, laser power was the main effective parameter for surface roughness (at 3 mm) followed by cutting velocity and assist gas pressure.

  2. 2.

    The laser beam power was the effective parameters for the rest of output performance parameters, which are upper kerf width, lower kerf width, kerf taper, and dross height. The following parameter after laser power was differ from cutting velocity to assist gas pressure.

  3. 3.

    Assist gas pressure is not the most significant parameters of laser cutting process, but it helps in refining the surface by removing the cut metal which gives good surface quality also helps in decreasing the kerf angle by decreasing the amount of heat and removing the cut metals.

  4. 4.

    It was found that laser cutting power of 3 kW, cutting velocity of 2000 mm/min, and assist gas pressure of 8 bar were the optimized parameters to achieve the minimum surface roughness value of 2.34 ± 0.12 µm, minimum dross value of 0.270 mm due to high velocity.

  5. 5.

    The minimum value of kerf width was found to be 0.774 ± 0.016 mm at the upper surface of cut, and 0.408 ± 0.039 mm at the lower surface of cut at cutting conditions of Pu = 2.5 kW, V = 1500 mm/min, and assist gas pressure of 10 bar.

  6. 6.

    The minimum value of kerf taper was found to be 1.89 ± 0.61° the cutting conditions of Pu = 2 kW, V = 1500 mm/min, and assist gas pressure of 8 bar.

  7. 7.

    The higher values of surface roughness, kerf width, and kerf taper were found in conditions of trial 1 and 7 which happened because of using low cutting velocity values in both sides beside using high power in case of KW and KT.