Experimental study on CNC engraving parameters of Afghan white jade

Abstract

The CNC machining of nephrite is increasingly used in the jade engraving industry. As the most important standard for quality evaluation, surface roughness is influenced by cutting parameters. In this paper, taking the Buddha head as the machining object, the influence of cutting parameters on the surface quality of was studied by SYIL S7 CNC milling machine. The grooving experiment was carried out at spindle speed of 24,000 rpm, then the CAXA manufacturing engineer and JDpiant software were comparatively applied in machining. Furtherly, the influence of the spindle speed on the roughness was investigated. The research results were summarized as follows: (1) No edge breakage appeared when feed speed lower than 300 mm/min with the maximum depth of cut of 0.1 mm. In this case, when the jade is machined with the spindle speed range of 16,000–24,000 rpm, the mean roughness $R_{a}$ was in the range of 1,496.111–891.842 nm. (2) JDpiant software is more suitable for CNC jade engraving than CAXA manufacturing engineer. (3) In roughing stage, only the high-speed grinding contdition is satisfied, the integrity of side profile could be guaranteed. The higher spindle speed was conducive to achieve the fine surface quality. (4) The tungsten steel cutter in finish machining stage shows better grinding ability than diamond cutter used in rough machining stage. In order to formulate an economic spindle speed, the finishing surface roughness should be considered in conjunction with the requirement of polishing.

Keywords

Jade engraving CNC cutting parameters surface roughness

1. Introduction

In recent years, jade engraving equipment has been developed rapidly, including carving system, processing method, dust removal device, optimizing system of spindle and cutters, etc. Especially, the five axis CNC carving desktop machine makes the trend of the jade engraving by CNC machining [1, 2, 3, 4]. At present, almost all the plane engraving products were processed by CNC machine in the market, no matter nephrite type and the carved pattern [5, 6].

CAXA manufacturing engineer and JDpiant software are domestic 3D CAD/CAM software for the 2–5 axis CNC engraving, which were developed by Beihang haier software co., LTD and Beijing JINGDIAO group, respectively. Relief processing function of CAXA manufacturing engineer mainly applies for black and white image, capture image and curved surface image [7]. Meanwhile, JDpiant software uses vector pictures for engraving. Although both can convert graphics into G code for NC machining, which of more advantageous in the jade engraving needs to be tested.

Afghan jade is a generic term for colored carbonate jade, mainly composed of calcite and dolomite. It is traditionally considered as nephrite. Its Mohs hardness is below 6.5, generally between 4.5 and 5.0. In production, the cutting parameters are basically same as other nephrite. Due to the low price, fine and even luster, Afghan jade is well popular with the consumers. In 2018, the Chinese standard file ‘Process quality evaluation of carved jade products’ was officially implemented in the market. In terms of quality, surface roughness is the primary consideration. No chipping or breaking is the basic requirement of desirable machining quality. Although, it has been reported better surface quality could be obtained in brittle-ductile transition processing than traditional processing [8], the long processing time limits the former’s application in jade engraving. Therefore, the traditional cutting method is still widely used in industrial production.

The depth of cut ( $a_{p}$ ), feed speed ( $f$ ) and cutting speed ( $v_{c}$ ) are key factors in cutting process [9]. Reasonable cutting parameters could reduce shock and vibration, improve the rigidity of the process system and ensure the tool durability. When processing hard and brittle materials, coordinating $a_{p}$ , $f$ and spindle speed is of great importance [10].

Zhenping County, Henan Province is one of the three major jade production and trading centers in China. The field survey on the jade engraving process was conducted in enterprises. According to the survey, economic fine engraving machine are general used in production. They have repeat positioning accuracy of less than 0.05 mm and the speed range of 5,000–24,000 rpm. High-end fine engraving is not usually selected, unless the processing quality requirements are particularly high. The production process flow is shown as follows: first, rough machining the side profile and surface by diamond tool, then refining by tungsten steel tool, and finally polishing. Although, the spindle speed of 22,000–24,000 rpm, $f$ of 300 mm/min and $a_{p}$ of 0.1 mm are the commonly used cutting parameters in production, it is necessary to test that whether the empirical cutting parameters can be further optimized.

To date, there has been rarely reports on the influence of cutting parameters on the jade surface quality. In this study, to explore the possibility of the higher machining efficiency and lower spindle speed, the influence of the expanded ranges of $a_{p}$ and $f$ on processing quality were firstly applied to grooving experiments. Moreover, to evaluate the more suitable software for jade engraving, the trials processing of CAXA manufacturing engineer and JDpiant software were expeerimented. Furtherly, the performance of expanded spindle speed on surface roughness was studied. This study will provide a basis for further optimization of cutting parameters in jade engraving.

2. Materials and methods

2.1 Materials and instruments

Afghan white jade was purchased from Shifosi Jade Article Factory in Zhenping county, Nanyang city, China. 5A wear-resistant cutting tool with carved embossed electroplated conical grinding head for jade engraving (YU3020 4 $\times$ 30 ${}^{\circ}$ $\times$ 1, emery material) and tungsten steel triangular pyramid flat cutting tool (3J3.1503, 4 $\times$ 15 ${}^{\circ}$ $\times$ 3, cone low radius 0.3 mm) from WeiTol were shown in Table 1. CNC milling machine (SYIL S7, spindle speed of 5,000–24,000 rpm, repeat positioning accuracy $\leqslant$ 0.02 mm), Metallographic microscope (LEICA DM 2500, accuracy $\leqslant$ 1 $\mu$ m), 3D surface profiler (Bruker, Contour GT-K, minimum RMS $\leqslant$ 0.1 nm) were shown in Fig. 1. Honor V10 mobile phone (20 million pixels) was used to take pictures. The minimum engraving accuracy setting of CAXA manufacturing engineer (Version 2013) and JDpiant (Version 5.5) are 1 $\mu$ m and 0.1 $\mu$ m, respectively.

Table 1
Types and paramaters of cutting tools

Type

Sketch

Parameter

WeiTol YU30204

\times

{}^{\circ}

\times

Shank length is 43 mm, shank diameter is 3.175 mm, nose angle is 30

{}^{\circ}

and the bottom diameter is 1.0 mm.

WeiTol 3J3.1503

Shank length is 33 mm, shank diameter is 3.175 mm, nose angle is 15

{}^{\circ}

and the bottom diameter is 0.3 mm.

Figure 1.

Experimental setup and test equipment.

2.2 Experimental method

2.2.1 The grooving experiment

As well known, $a_{p}$ and $f$ are the important parameters for cutting, and have a great impact on cutting force and efficiency. To explore the maximum values of $a_{p}$ and $f$ , grooving experiments were carried out with diamond carving cutting tool at the maximum spindle speed of 24,000 rpm. For the increment of $a_{p}$ is generally 0.1 mm in traditional machining, $a_{p}$ was set to 0.1 and 0.2 mm, and the $f$ was set to 300, 600 and 900 mm/min. By observing the quality of the bottoms and edges of the grooves with metallographic microscope, the influence of $f$ and $a_{p}$ on the processing were obtained. In the whole machine processes, workpieces were glued to the substitute board, and were rinsed and cooled with water.

2.2.2 The experiment of software comparison

Based on maximal $f$ and $a_{p}$ obtained by grooving experiment, CAXA manufacturing engineer and JDpiant were used to model, simulate and machine the Buddha’s head (Fig. 2) at the maximal spindle speed of 24,000 rpm. For the processing method, the former adopted contour processing scheme, the later used the Z-direction gathering scheme. The expected software would correspond to the better machined surface quality. Figure 2 shows the jdp vector format containing path information of with 51.2 MB memory and 24 bit depth. The same cutting parameters were used in roughing and finishing process.

Figure 2.

Image of the Buddha’s head.

Figure 3.

Grooving experiment with different $f$ and $a_{p}$ . From top to bottom, $a_{p}$ is 0.1 mm ( $f$ are 600, 300, 900 mm/min) and 0.2 mm ( $f$ are 900, 600 and 300 mm/min).

2.2.3 The experiment on the influence of spindle speed

Using the better software and its engraving settings in Section 2.2.2, the cutting experiments were carried out under different spindle speed. In order to enhance the charm of the Buddha statue, the cheek should appear plump and smooth, which requires high-quality machining for portraying the image. Bruker’s 3D surface profilometer was used to measure the surface roughness of the cheek point on Buddha’s face. In consequence, the influence of the spindle speed on the surface roughness was obtained.

3. Results and discussion

3.1 Influence of $f$ and $a_{p}$ on machining quality

The results of grooving experiment are shown in Fig. 3. It is observed that (1) The white chip residue becomes more and more obvious as $a_{p}$ or $f$ increases; (2) When the $f$ is 900 mm/min, the white cutting residue is obviously observed, no matter the $a_{p}$ value is 0.1 mm or 0.2 mm; (3) When the $a_{p}$ is 0.2 mm, regardless of the $f$ , white cutting residue is generated at the bottom of the groove. It is proved that when machining the hard and brittle materials, $a_{p}$ is prior to the $f$ , which is consistent with the literature [11]. Under certain conditions of spindle speed and $f$ , the grinding force increases as $a_{p}$ raises, which causes the increasing vibration of the cutting system. Therefore, more discontinuous chips can be generated on the contact surface of jade and the cutter, which reduces the surface quality.

Figure 4.

Comparison of grooving quality at different $f$ ( $a_{p}$ : 0.1 mm).

The bottom and sides of the groove were observed by the metallographic microscope ( $a_{p}$ : 0.1 mm). And the upper or lower widths of the slots have been marked by blue lines, as shown in Fig. 4. When $f$ is 300 mm/min, the smooth bottom surface and neat side walls are presented, and the boundary lines between the bottom and the side walls are obvious. When $f$ is 600 mm/min, the bottom shows coarse particles and unevenness, the boundaries between bottom and side become blurred. When $f$ increases to 900 mm/min, the bottom surface flatness continues to deteriorate, the boundaries become more blurred and white discontinuous crushed chips residue and marginal fragmentation appear on the upper edge. The coarse particles at the bottom are the high hardness components such as tremolite, diopside, plagioclase, quartz, and periclase, etc. The Mohs hardness of these hard spots is usually more than 5.5, which is generally higher than calcite. Therefore, the surface quality of the grooving is mainly determined by the grinding process of the diamond cutter.

The above phenomena may be explained by the following points.

As $a_{p}$ becomes larger, the cross-sectional area of the cutting layer increases. The cutting force brought by the spindle and feed movement is gradually insufficient to overcome the cutting resistance, which lead to the appearance of unsteady cutting condition. At this time, $F_{x}$ and $F_{y}$ change greatly and are disorder, forming a self-excited oscillation at the end of the milling cutter (beating phenomenon), which induces the workpiece unevenly loaded and forms the crack and edge collapse [12, 13].

Increasing $f$ causes the grinding capacity reduction. As $f$ increases, the grinding time acting on the hard spot reduces, meanwhile, the decrease of the friction coefficient between tool and jade also reduces the grinding force [9]. Those are also the reasons for that the bottom grain size gradually becomes larger.

In the meantime, the cutting force toward the critical fracture depth increases, and the probability of brittle crack rises gradually. Thus, the staggered cracks easily form between the sidewall and the bottom, which is likely to cause local collapse.

The upper edge of the groove is affected by the unstable system vibratory shock, and marginal fragmentation is most likely to occur.

Therefore, the increase of $a_{p}$ and $f$ would be detrimental to the grinding-milling. When the maximum $a_{p}$ is 0.1 mm, $f\leqslant$ 300 mm/min is the product quality assurance in the CNC machining. Meanwhile, in order to minimize breakages, the feed speed should be reduced at the cut-in and cut-out stages [14].

3.2 The pros and cons analysis of CAXA manufacturing engineer and JDpiant

3.2.1 Image processing

Once the grayscale image is imported by the image processing module in CAXA manufacturing engineer, no further modification can be made. Figure 5a shows the bmp format image converted from the jdp vector format with pixel size of 1,534 $\times$ 1,995. For the JDpiant software, the image editing task requires importing the original jdp or other vector images and intercepts the processing area. After selecting the graphics clustering scheme (Z direction in this paper), the graphics processing stage is completed. The sizes of the processed pictures were 44.93 $\times$ 33.32 mm (Fig. 5a and b).

3.2.2 Parameter settings

CAXA manufacturing engineer and JDpiant software were used to trial processing. The same cutting parameters were that the total depth of cut is 6 mm, the spindle speed is 24,000 rpm, $f$ is 300 mm/min, and the $a_{p}$ is 0.1 mm. The execution of CAXA manufacturing engineer only includes roughing and finishing. And other main machining settings are the line spacing (0.08 mm), allowance for finish (0.1 mm), the machining accuracy (0.001 mm), and completion of the surface roughing on nine layers. The product, machined by JDpiant software, experienced side profile machining, surface roughing and finishing process. The main machining parameters of JDpiant are listed in Table 2.

Table 2
Main parameters setting of JDpiant

Procedure	Tools and main parameters
Side profile machining	Tool: WeiTol YU3020 4 $\times$ 30 ${}^{\circ}$ $\times$ 1 (1) Slotting speed is 1.4 mm/s; plunge rate is 0.894 mm/s; jump speed is 2.5 mm/s; clearance height is 10 mm, position height is 2 mm; slow down distance is 10 mm, no drop delay. (2) Layered processing setting: $a_{p}$ is 0.1 mm, cutting along the side profile, the angle at which the tool first touches the workpiece is 0.5 ${}^{\circ}$ , and reserved surface height is 0.02 mm. (3) Machine precision is 0.02 mm, climb milling priority,adopting the arc transition mode, and the minimum sharp angle is 15 ${}^{\circ}$ .
Surface roughing	Tool: WeiTol YU3020 4 $\times$ 30 ${}^{\circ}$ $\times$ 1 (1) Surface fine engraving parameters setting: total depth of cut is 6 mm; reciprocating walking mode, default value of steep slope, path spacing is 0.2 mm. (2) Processing range setting: the engraving margin allowance is 0 mm; the surface allowance is 0.1 mm; the protective surface allowance is 0.06 mm, and the protective surface is raised by 0.12 mm. (3) Feed setting: the path spacing is 0.167 mm, the overlap ratio is 94.45 mm, the surface residual height is 0.003 mm, and surface residual height of 45 ${}^{\circ}$ direction is 0.005 mm, and the feed mode is closed. (4) Engraving accuracy: processing precision is 0.02 mm; flatness coefficient is 0.5; angle error is 10 ${}^{\circ}$ , climb milling priority; the contour processing sequence is from the inside to the outside, and the layering order is the region priority; adopts an arc-over mode with a minimum sharp angle of 15 ${}^{\circ}$ in the sharpe-angle form.
Finishing	Tool: WeiTol 3J3.1503 The path spacing is 0.035 mm, the margin allowance of the boundary is 0 mm, the allowance of the protective surface is $-$ 0.12 mm, and the protective surface is raised by 0.12 mm; the other parameters are the same as above.

Figure 5.

Images processed by software.

3.2.3 Comparasion of efficiency and surface quality

From Table 2, comparing with CAXA manufacturing engineer, the processing function setting of JDpiant are more specific. The best products of two trial processing can be seen in Fig. 6.

Figure 6.

Machining quality comparison at spindle speed of 24,000 rpm.

The program generated by CAXA manufacturing engineer has more than 500,000 lines with the machining time exceeding 10 h. The rough surface and the obvious knife marks of the product are observed (in Fig. 6a), which fail to meet the wearing requirements. Hence, extra work was required to remove the exceed material outside the Buddha’s head.

Although the programs produced by JDpiant exceeds 780,000 lines, the machining time was less than 4 h. Importantly, the outline of the Buddha’s head is obvious fine, smooth with good feeling in touch (Fig. 6b).

It is well known that the fragmentation of brittle materials under compression is highly correlated with the very large initial compression deformations, especially during the cut in and cut off stages, the unevenly stressed force is the main reason for the jade’s collapsing [14, 15]. In these respects, JDpiant reveals attractive features and more details in parameters setting, and also results in the better efficiency and surface quality. Therefore, JDpiant as CNC program software is more suitable for jade engraving.

3.3 Influence of spindle speed on surface quality

JDpiant 5.5 was used to evaluate the influence of spindle speed change on surface quality, with $f$ 300 mm/min and $a_{p}$ 0.1 mm, respectively.

3.3.1 Side profile comparison

Figure 7 shows the back side-profile of the products at different spindle speed. The crack size decreases with the rising of spindle speed, which is conducive to the continuity of the surface contour [13, 16]. At the spindle speeds of 18,000 and 24,000 rpm, there is no significant difference on the side profiles. Both profiles are smooth and neat, and no material crack is observed on the edges. At the spindle speed of 12,000 rpm, the intermittent profile is seen from the shadow, which affects the esthetics of the finished product. Furthermore, at the spindle speed of 6,000 rpm, many chipping gaps appeared on the side profile, which may cause jade cracking during the subsequent processing.

Generally, high-speed grinding (HSG) can significantly improves surface finish and reduces damages [17] when $v_{c}$ lies in the range of 45–100 m/s. By calculation, the machining process follows the conventional grinding rules when the spindle speed is lower than 14,330 rpm. Therefore, it is normal for Afghan white jade to collapse when processed spindle speed less than 12,000 rpm. In contrast, in the HSG stage, when all other parameters are constant, not only increasing the spindle speed can cause decreasing of the unit cutting thickness, but also the cutting force acting on each abrasive particle can be correspondingly reduced [18].

Thus the supplementary experiments were carried out between 14,000–18,000 rpm (steps at 1,000 rpm). The results showed that edge collapse appeared successively when the spindle speed is lower than 16,000 rpm. Therefore, the spindle speed $\geqslant$ 16,000 rpm is recommended.

Table 3
Surface roughness after roughing at 24,000 rpm and finishing at different spindle speed (nm)

Roughness		Roughing stage	Finishing stage
indexes		24,000 (rpm)	16,000 (rpm)	18,000 (rpm)	24,000 (rpm)
$R_{a}$	1	3,217.089 ${}^{\text{a}}$	1,440.001 ${}^{\text{b}}$	1,202.095 ${}^{\text{c}}$	821.980 ${}^{\text{d}}$
	2	3,463.768	1,465.127	1,388.437	880.965
	3	3,678.572	1,443.300	1,296.015	972.580
$\bar{R}_{a}\pm$ SD		3,453.143 $\pm$ 230.925	1,449.476 $\pm$ 13.654	1,295.516 $\pm$ 93.172	891.842 $\pm$ 75.887
$R_{p}$	1	19,084.538 ${}^{\text{a}}$	6,443.338 ${}^{\text{b}}$	7,416.212 ${}^{\text{c}}$	7,973.833 ${}^{\text{d}}$
	2	16,782.624	5,770.735	10,196.566	8,072.526
	3	15,241.841	7,909.315	7,712.902	10,173.590
$\bar{R}_{p}\pm$ SD		17,036.334 $\pm$ 1,933.871	6,707.796 $\pm$ 1,093.542	8,441.893 $\pm$ 1,526.815	8,739.983 $\pm$ 1,242.520
$R_{q}$	1	4,125.027 ${}^{\text{a}}$	1,927.442 ${}^{\text{b}}$	1,575.465 ${}^{\text{c}}$	1,065.565 ${}^{\text{d}}$
	2	4,378.977	1,882.140	1,725.221	1,148.218
	3	4,737.617	1,735.616	1,747.238	1,270.577
$\bar{R}_{q}\pm$ SD		4,413.874 $\pm$ 307.782	1,848.399 $\pm$ 100.265	1,682.641 $\pm$ 93.468	1,161.450 $\pm$ 103.145
$R_{t}$	1	40,314.392 ${}^{\text{a}}$	30,286.326 ${}^{\text{b}}$	21,938.944 ${}^{\text{c}}$	20,103.896 ${}^{\text{d}}$
	2	37,206.504	20,557.320	22,431.460	20,700.804
	3	42,946.288	20,542.688	20,123.836	21,534.888
$\bar{R}_{t}\pm$ SD		40,155.728 $\pm$ 2,873.180	23,795.445 $\pm$ 5,621.273	21,498.080 $\pm$ 1,215.341	20,779.863 $\pm$ 718.764
$R_{v}$	1	$-$ 21,229.852 ${}^{\text{a}}$	$-$ 23,852.988 ${}^{\text{b}}$	$-$ 14,522.733 ${}^{\text{c}}$	$-$ 12,310.064 ${}^{\text{d}}$
	2	$-$ 20,423.876	$-$ 10,786.584	$-$ 12,234.893	$-$ 12,628.278
	3	$-$ 27,704.444	$-$ 12,633.374	$-$ 13,056.187	$-$ 11,361.299
$\bar{R}_{v}\pm$ SD		$-$ 23,119.391 $\pm$ 3,991.170	$-$ 15,757.649 $\pm$ 7,071.319	$-$ 13,056.187 $\pm$ 1,273.113	$-$ 12,099.880 $\pm$ 659.122

Note: (1) The test data of a, b, c and d correspond to (a), (b), (c) and (d) in Fig. 9, respectively. (2) The horizontal line on the roughness indexes such as $R_{a}$ indicates the mean value. (3) SD is the abbreviation of standard deviation.

Figure 7.

Side profile comparison at different spindle speeds ( $f$ : 300 mm/min, $a_{p}$ : 0.1 mm).

3.3.2 Influence of spindle speed on surface roughness

The finish products were acquired with spindle speed of 16,000 rpm, 18,000 rpm and 24,000 rpm. All assays were performed in triplicate. Figures 8 and 6b are the best final products. The surface roughness of the Buddha was measured using Brooke 3D surface profiler (VSI mode, RMS repeatability $\leqslant$ 10 nm), where the test area is marked in the left cheek in Fig. 8b. The results of the test are shown in Table 3. The higher the spindle speed, the surface is more smoother and glossier after finishing.

Figure 8.

Surface quality comparison at different spindle speed ( $f$ : 300 mm/min, $a_{p}$ : 0.1 mm).

Figure 9.

3D surface contour test results at different spindle speeds and processing stages.

Firstly, the finishing stage plays an important role in reducing surface roughness. In jade appraisal, $R_{a}$ is used as the most common index on surface roughness evaluation. Taking the spindle speed of 24,000 rpm as an example, comparing the mean values of the various surface roughness indexes in the roughing and finishing stages, $\bar{R}_{a}$ is greatly reduced from 3,543.143 nm to 891.842 nm. In contrary to Fig. 9a, the surface in Fig. 9d is more flatter and uniform.

Secondly, increasing the spindle speed can promote the system stability. $R_{t}$ is defined as the largest vertical (peak-to-valley) distance in the assessment length range. From the Table 3, the $R_{t}$ distribution at the same spindle speed is more and more concentrated either from roughing to finishing, or from low to high spindle speed during finishing, indicating that the system becomes more stable as the increase of spindle speed. This is also consistent with the advantages of HSG discussed in Section 3.2.1.

Thirdly, grinding effect of tungsten steel cutter in finishing is embodied. $R_{q}/R_{a}$ is usually used to characterize the grinding ability of the tool system. At the spindle speed of 16,000, 18,000 and 24,000 rpm, the values of $\bar{R}_{q}/\bar{R}_{a}$ are 1.275, 1.299, and 1.302, respectively, which are slightly higher than that of ordinary grinding (1.22–1.27). In the roughing process, the value of $\bar{R}_{q}/\bar{R}_{a}$ at the spindle speed of 24,000 rpm is only 1.278. However, there is no abrasive on tungsten steel blades, and its tip diameter is only 1/10 of that of diamond tools. It is fully confirmed that the surface finishing ability of tungsten steel knife exceeds that of ordinary grinding in jade engraving finishing. The possible reason is that the increase in spindle speed helps to reduce contact stress and avoid surface damage [13, 18, 19]. However, the detail mechanism needs further research.

Finally, the subsequent polishing is necessary. $R_{p}$ is the maximum peak height, representing the unprocessed raw material with micro dimension remaining on the surface, which is indicated in red in Fig. 9. In the finishing stage, although the flatness of the surface is getting better as the spindle speed increases, $R_{p}$ has been increasing. On the one hand, it shows that single long-time cutting is more effective than multiple short-time processing. On the other hand, system vibration increased, which is consistent with the report [20]. From Fig. 9b–d, it can be found that these residual area gradually decreases, so the area can be easily removed by the final polishing method.

When the maximum $a_{p}$ (0.1 mm) and $f$ (300 mm/min) used in rough and fine finishing stages, the $R_{a}$ of test area can preferably reach 821.980, 1,202.095 and 1,440.001 nm, corresponding to the spindle speed of 16,000, 18,000 and 24,000 rpm, respectively. And there are no obvious processing marks on the products. Therefore, jade engraving can be well performed in the spindle speed range of 16,000–24,000 rpm.

4. Conclusion

In this paper, the CNC expanded cutting parameters on engraving the Afghan white jade was researched. The main conclusions are as follows:

Compared with CAXA manufacturing engineer, JDpiant is more suitable for jade engraving, with better machining quality and shorter time cost.

When roughing the white jade of Afghanistan, as $f$ and $a_{p}$ increase, the efficiency can be promoted, but it can result poor machining surface and more breakage.

In the process of overall machining, HSG is the guarantee for the satisfying surface quality. The higher the spindle speed, the better surface roughness.

In conventional jade engraving machining, the empirical parameters $f$ and $a_{p}$ can reach the optimal process effect, only the spindle speed can be further optimized. The recommended cutting parameters are $f=$ 300 mm/min, $a_{p}=$ 0.1 mm, and the spindle speed $\geqslant$ 16,000 rpm. With those parameters, the mean $R_{a}$ of the test area would be lower than 1,449.476 nm.

From the practical point of view, this paper referenced the current mainstream machining methods, and used the same parameters in roughing and finishing stage. The surface roughness at the engraving stage has a certain impact on the efficiency or quality of final polishing stage. Therefore, the parameter optimization should be considered in conjunction with the subsequent polishing stage, which is our next research plan.

Footnotes

Acknowledgments

This work was financially supported by Scientific and Technological Research Projects of Henan Province (192102310250, 192102210215), Program for Innovative Research Team (in Science and Technology) in University of Henan Province (20IRTSTHN016), and Ph.D. start Foundation of Henan Institute of Science and Technology (203010616002).

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Experimental study on CNC engraving parameters of Afghan white jade

Abstract

Keywords

1. Introduction

2. Materials and methods

2.1 Materials and instruments

Table 1 Types and paramaters of cutting tools

2.2.1 The grooving experiment

2.2.2 The experiment of software comparison

3. Results and discussion

3.1 Influence of f and a p on machining quality

3.2.1 Image processing

3.2.2 Parameter settings

Table 2 Main parameters setting of JDpiant

3.3.1 Side profile comparison

Table 3 Surface roughness after roughing at 24,000 rpm and finishing at different spindle speed (nm)

Footnotes

Acknowledgments

References

Table 1
Types and paramaters of cutting tools

3.1 Influence of $f$ and $a_{p}$ on machining quality

Table 2
Main parameters setting of JDpiant

Table 3
Surface roughness after roughing at 24,000 rpm and finishing at different spindle speed (nm)