A novel ultrasonic vibration-assisted structure for radial milling is proposed, and the ultrasonic vibration-assisted radial milling (UVARM) is further studied in terms of theoretical model and milling experiment. The motion and feed characteristics of UVARM are also analyzed. A special fixture is designed to construct the experimental platform of UVARM, in which the vibration is applied to the workpiece along the radial direction. The preliminary results show that with the increase of spindle speed, the milling force in both conventional cutting (CC) and UVARM experiments tends to increase. In addition, when the feed per tooth increased, the milling force increased. With the involvement of ultrasonic vibration, the milling force is significantly reduced, with the maximum reduction reaching 20%. The comprehensive analysis showed that there was a decrease of about 10% to 25% in the ultrasonic case compared with the conventional method. It is also found that UVARM can inhibit the production of a built-up edge. With the ultrasonic vibration, the burrs on the processed surface are also reduced, and the grooves left by tool traces are shallower. Compared with conventional milling, the roughness value of the machined surface obtained by UVARM is reduced by 10% to 32%. The experimental results also show that UVARM can effectively improve the dimensional accuracy of the workpiece.
An ultrasonic vibration-assisted cutting (UVAC) is a kind of compound machining method which combines ultrasonic vibration with conventional machining. Compared with conventional machining (CM), UVAC can effectively improve the dimension precision, surface quality, and stability of the processing system. In the UVAC process, the tool and the workpiece have periodic contact and separation. The experimental results show that applying ultrasonic vibration is helpful to improve the cutting force, tool life, and machining accuracy for hard brittle materials machining [
However, few works have been focused on the study of that when the vibration is applied to the workpiece along radial direction during ultrasonic vibration-assisted machining. The proposed work is to impose a vibration to the workpiece in the feeding direction, which makes the device a compact structure. A novel ultrasonic vibration-assisted structure for radial milling is proposed, with a special clamping device designed to set up the experimental stage for UVARM. The motion mechanism of the cutting edge of the UVARM is studied. Further investigation is also conducted to analyze the cutting tool and chip separation with different process parameters. The influence of each feed per tooth, spindle speed, vibration amplitude, and other process parameters on UVARM force, dimension precision, and surface quality was studied through a single-factor experiment. It is verified that the UVARM can effectively solve the disadvantages of ultraprecision machining such as difficulty in chip removal, severe tool wear, and high processing cost.
As shown in Figure
Main vibration direction in the UVARM process.
Path of single edge milling cutter in 1.5 cycles.
In Figure
The trajectory equation of the milling cutter center is [
The trajectory equation of the
A 3-edge type milling cutter is taken into consideration; therefore,
In addition, the trajectory equation of the milling cutter center is
The trajectory equation of the
The vibration-assisted milling trajectory of one of the single tool tip is simulated using MatLab as shown in Figure
UVARM path diagram of the single blade.
The ultrasonic generator used in this study is a 2000b/BDC power generator (BRANSON, USA). Its maximum output power is 1100 W and the output frequency is 20 kHz. The ultrasonic vibrator produced by BRANSON is selected in this project. The ultrasonic vibrator is a combination of the ultrasonic transducer and ultrasonic amplitude converter, which can transform electric vibration signals more efficiently. This work applies ultrasonic vibration along the feed direction to the workpiece. The UVARM system studied in this paper is built on the TH5650 type vertical machining center. The ultrasonic vibration device can be firmly fixed on the milling machine workbench, so as to perform the UVARM. In this part, the designed UVARM system is used to carry out the comparison experiment with conventional milling of 6061-T6 aluminum alloy. The UVARM system is shown in Figure
Schematic diagram of the ultrasonic vibration system.
Ultrasonic vibration system is mainly composed of an ultrasonic generator, ultrasonic transducer, ultrasonic amplitude, and tools. The ultrasonic vibration device can be firmly fixed on the milling machine tool and follow the workbench to implement horizontal and vertical movement, so as to perform the UVARM. The clamping system consists of four parts: front pressure plate, back pressure plate, beam, and bracket. In order to ensure machining accuracy and reduce costs, the front and rear pressure plates are divided into two parts: upper and lower pressure plates. The front and rear pressure plates are connected to the supports through a set of screws. The ultrasonic vibration clamping system is shown in Figure
Special fixture structure for ultrasonic vibration system.
3D assembly effect drawing of UVARM system.
In the figure, 1 is the cushion block, 2 is the guide rail, 3 is the slide block, 4 is the workpiece, 5 is the cover plate, 6 is the stud, 7 is the front support column, 8 is the swing rod, 9 is the ultrasonic transducer, 10 is the back support frame, 11 is the beam, 12 is the fixed block, 13 is the back support block, 14 is the bottom plate, and 15 is the front support block. The experimental setup is shown in Figure
General assembly diagram of the UVARM system.
The vibration device is analyzed using the FEA method with Abaqus software. In this analysis, the material properties of each part are set as Table
Material properties.
Material | Density (kg/m3) | Young’s modulus (GPa) | Poisson ratio | |
---|---|---|---|---|
Piezo | PZT-4 | 7.45·10−9 | 76.5 | 0.3 |
Amplitude-changing bar | Titanium alloy | 4.43·10−9 | 113.8 | 0.34 |
Stud | #45 | 7.85·10−9 | 206 | 0.25 |
Workpiece | 6061-T6 | 2.80·10−9 | 70 | 0.33 |
Natural frequency of vibration device model.
Order | Frequency | Order | Frequency | Order | Frequency | Order | Frequency |
---|---|---|---|---|---|---|---|
1 | 1127.7 | 11 | 9921.3 | 21 | 22956 | 31 | 40708 |
2 | 1128.8 | 12 | 9926.6 | 22 | 27107 | 32 | 40732 |
3 | 2271.6 | 13 | 15986 | 23 | 27208 | 33 | 41868 |
4 | 2287.2 | 14 | 16026 | 24 | 28262 | 34 | 43379 |
5 | 4275.3 | 15 | 16174 | 25 | 30318 | 35 | 44612 |
6 | 4280.6 | 16 | 16608 | 26 | 30346 | 36 | 44622 |
7 | 4789.1 | 17 | 18411 | 27 | 31124 | 37 | 46079 |
8 | 5241.8 | 18 | 18432 | 28 | 36878 | 38 | 46102 |
9 | 8305.8 | 19 | 19995 | 29 | 39241 | 39 | 46554 |
10 | 9594.6 | 20 | 22949 | 30 | 39243 | 40 | 46652 |
The 40th-order vibration mode of the vibration device model is presented in the form of a color cloud diagram. For the convenience of comparative study, the typical 6th-order vibration mode of the 40th-order vibration mode is extracted, and its form is shown in Figure
Vibration pattern diagram of the vibration device model. (a) 1st order. (b) 6th order. (c) 9th order. (d) 16th order. (e) 19th order. (f) 30th order.
Through a comparative study on the 40th-order vibration mode diagram of the vibration device, it is found that the vibration mode of the vibration device model in the 16th and 19th orders is relatively ideal; that is, the vibration corresponding to the 16th and 19th orders has radial vibration but no unnecessary vibration in other directions. It can be seen from Table
This study uses the Kistler9257B type quartz piezoelectric dynamometer (Alpine Instrument, Swiss), the model of the charge amplifier is Kistler5070A multichannel amplifier, data acquisition system is a USB Kistler 5697A type high-speed acquisition system, and the data analysis system is type Kistler2825A DynoWare software. In order to measure the surface roughness of the workpiece, a Micromeasure 3D profiler was used. The sampling area of this 3D contour instrument is flexible. It can analyze areas of 0.1 × 0.1 mm, 0.2 × 0.2 mm, and 0.3 × 0.3 mm. In the actual measurement, the measurement area should be set according to the actual situation. The measured surface in this test is flat and the machining area is large. 0.2 × 0.2 mm of the processed surface is selected for sampling analysis in this survey. In order to observe the surface morphology of the workpiece, this experiment also adopted a VHX-1000e ultrasonic depth of 3D display system imported from Japan.
The workpiece used in this experiment is the 6061-T6 aluminum alloy block of 25 × 25 × 30 mm. In order to reduce the material waste and ensure the convenience of clamping, a 9 mm through-hole is generated at the end of the workpiece and different workpieces are numbered. Then, the workpiece is connected with the amplitude-changing rod by a double-headed bolt. The 3-tooth ultrahard straight shank end mill with a diameter of 8 mm was selected in this experiment. The specific parameters are shown in Table
Tool parameters.
Cutter material | Diameter (mm) | Spiral angle of the cutter (°) | Cutter tooth no. |
---|---|---|---|
High-speed steel | 8 | 45 | 3 |
Generally, the milling force acting on the milling cutter can be divided into circular force, feed resistance, and depth of cut resistance. According to the feed characteristics analysis in the second section, the parameter selection should meet
Level of experimental factors.
Case | Amplitude ( | Spindle speed (min−1) | Feed per tooth ( |
---|---|---|---|
1 | 0 | 800 | 2 |
2 | 10 | 1000 | 4 |
3 | 15 | 1500 | 6 |
4 | 20 | 2000 | 8 |
5 | 25 | 2500 | 10 |
The effect of ultrasonic amplitude, spindle speed, and feed per tooth on milling force was studied by a single-factor experiment. The experiment can be divided into three steps. (1) The ultrasonic amplitude and the feed per tooth remain unchanged, and the influence of spindle speed on the milling force is explored. (2) The ultrasonic amplitude and spindle speed remain unchanged, and the influence of the feed per tooth on the milling force is explored. (3) The spindle speed and feed per tooth remain unchanged, and the influence of ultrasonic amplitude on milling force is explored. The specific experimental scheme is shown in Table
Single-factor experimental set.
Case | Feed per tooth ( | Feed rate (mm/min) | Spindle speed (min−1) | Depth of cut (mm) | Amplitude ( |
---|---|---|---|---|---|
1 | 6 | 36 | 2000 | 0.3 | 0 |
2 | 6 | 36 | 2000 | 0.3 | 10 |
3 | 6 | 36 | 2000 | 0.3 | 15 |
4 | 6 | 36 | 2000 | 0.3 | 20 |
5 | 6 | 36 | 2000 | 0.3 | 25 |
6 | 6 | 14.4 | 800 | 0.3 | 0 |
7 | 6 | 18 | 1000 | 0.3 | 0 |
8 | 6 | 27 | 1500 | 0.3 | 0 |
9 | 6 | 45 | 2500 | 0.3 | 0 |
10 | 6 | 14.4 | 800 | 0.3 | 15 |
11 | 6 | 18 | 1000 | 0.3 | 15 |
12 | 6 | 27 | 1500 | 0.3 | 15 |
13 | 6 | 45 | 2500 | 0.3 | 15 |
14 | 2 | 12 | 2000 | 0.3 | 0 |
15 | 4 | 24 | 2000 | 0.3 | 0 |
16 | 8 | 48 | 2000 | 0.3 | 0 |
17 | 10 | 60 | 2000 | 0.3 | 0 |
18 | 2 | 12 | 2000 | 0.3 | 15 |
19 | 4 | 24 | 2000 | 0.3 | 15 |
20 | 8 | 48 | 2000 | 0.3 | 15 |
21 | 10 | 60 | 2000 | 0.3 | 15 |
The process parameters are set as spindle speed 2000 min−1, depth of cut is 0.3 mm, different amplitudes are 0 and 15
In this section, the influence of spindle speed on milling force during processing is analyzed and studied by selecting different spindle speeds. In the experiment, the feed per tooth was 6
It can be found that the component force in
In this section, the influence of feed per tooth on milling force during the processing is analyzed by selecting different types of feed per tooth. Among them, 2000 min−1 of spindle speed was selected in the experiment, the ultrasonic amplitude was selected as 15
In this section, different ultrasonic amplitudes are selected to analyze the influence of ultrasonic amplitudes on the milling force during processing. In the experiment, the feed per tooth was 6
To sum up, under the assisted effect of ultrasonic vibration, the milling force in
In this section, groove milling experiments are conducted to study the surface roughness of the bottom surface of the groove formed by the bottom milling edge of the milling cutter and to compare the surface roughness Sa formed by the UVARM. The main research object is 6061-T6 aluminum alloy milling surface roughness, and the ultrasonic vibration-assisted radial milling work stage is independently designed. By single-factor experiment, the comparison of ultrasonic vibration-assisted radial milling with conventional milling under the same processing conditions was investigated. The effect of spindle rotation, feed per tooth, and ultrasonic amplitude on the surface roughness of the machined surface is analyzed, which accordingly verified the superiority of ultrasonic vibration-assisted radial milling.
As shown in Figure
Comparison of workpiece surface topography with 20 times magnification. (a) UVARM. (b) CC.
The area of 0.2 × 0.2 mm was selected as the scanning area on the processed workpiece surface. MICROMEASURE2 3D profiler was used to observe the 3D surface topography of the area and the image is taken as shown in Figure
3D topography contrast of workpiece surface. (a) UVARM. (b) CC.
It can be intuitively found from the observation above that the height of the peak valley fluctuation range of conventional milling surface is among −6∼6
In this section, on the premise of fixing other experimental parameters, the influence of spindle speed on milling force during processing is analyzed and studied by selecting different spindle speeds. The specific experimental scheme and the final experimental data measured are shown in Table
Experimental data (sequel).
Case | Feed per tooth ( | Feed rate (mm/min) | Spindle speed (min−1) | Milling depth (mm) | Vibration amplitude ( | Surface roughness Sa ( |
---|---|---|---|---|---|---|
9 | 6 | 45 | 2500 | 0.3 | 0 | 1.90 |
10 | 6 | 14.4 | 800 | 0.3 | 15 | 1.87 |
According to the experimental data obtained in Table
The behavior of surface roughness with the spindle speed.
As shown in Figure
The behavior of surface roughness with the change of feed per tooth.
As shown in Figure
Surface roughness behavior with ultrasonic amplitude.
In this section, the influence of ultrasonic amplitude on machining dimension precision during UVARM was studied by a single-factor experiment. Three repetitions of the milling process for groove generation are conducted in each group of the processing set. The workpiece is inspected using a VHX-1000E microscope. In order to avoid the effect of the accidental error on the experimental results, five times of measurements are conducted on each machined workpiece. The average value of the measurement results is regarded as the groove dimension. The groove width and the ultrasonic vibration are plotted in Figure
Dimensional accuracy of grooves under different amplitude conditions.
In this paper, the UVA milling experiment setup is constructed. The material 6061-T6 is taken as the object to study the effect of cutting parameters on the experiment output, e.g., cutting force, workpiece surface roughness, and dimensional accuracy. The preliminary results can be summarized as follows. On the basis of the TH5650 type vertical machining center, the UVARM experimental setup is built by combining a special clamping device with the existing ultrasonic equipment. The experimental results also show that, with the increase of spindle speed, the milling force in both the CC and UVC experiments tends to increase. When the feed per tooth increased, the milling force isncreased. With the involvement of ultrasonic vibration, the milling force is significantly reduced, with the maximum reduction reaching 20%. The comprehensive analysis showed that there was a decrease of about 10% to 25% in the ultrasonic case compared with the conventional method. Through a comparative study on the surface morphology of the 2D and 3D images of the processed surface, it is found that UVARM can inhibit the production of a built-up edge. With the ultrasonic vibration, the burrs on the processed surface are also reduced, and the grooves left by tool traces are shallower. Compared with conventional milling, the roughness value of the machined surface obtained by UVARM is reduced by 10% to 32%. The experimental results also show that UVARM can effectively improve the dimensional accuracy of the workpiece. When ultrasonic amplitude increases from 0 to 10
The raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.
The authors declare that they have no conflicts of interest.
The authors acknowledge the financial aid and support from the National Natural Science Foundation of China (Grant no. 51875097).