materials Article
Applying Low-Frequency Vibration for the Experimental Investigation of Clutch Hub Forming De’an Meng 1,2, *, Chengcheng Zhu 1,3, *, Xuzhe Zhao 4 and Shengdun Zhao 1 1 2 3 4
*
School of Mechanical Engineering, Xi’an Jiaotong University, Xi’an 710049, China;
[email protected] School of Mechanical Engineering, Northwest Polytechnical University, Xi’an 710072, China Department of Mechanical Engineering, National University of Singapore, Singapore 119260, Singapore School of Engineering Technology, Purdue University, 401 N. Grant Street, West Lafayette, IN 47906, USA;
[email protected] Correspondence:
[email protected] (D.M.);
[email protected] (C.Z.); Tel.: +86-029-8266-8607 (D.M.)
Received: 4 May 2018; Accepted: 28 May 2018; Published: 30 May 2018
Abstract: A vibration-assisted plastic-forming method was proposed, and its influence on clutch hub forming process was investigated. The experiments were conducted on a vibration-assisted hydraulic extrusion press with adjustable frequency and amplitude. Vibration frequency and amplitude were considered in investigating the effect of vibration on forming load and surface quality. Results showed that applying vibration can effectively reduce forming force and improve surface quality. The drop in forming load was proportional to the vibration frequency and amplitude, and the load decreased by up to 25%. Such reduction in forming load raised with amplitude increase because the increase in amplitude would accelerate punch relative speed, which then weakened the adhesion between workpiece and dies. By increasing the vibration frequency, the punch movement was enhanced, and the number of attempts to drag the lubricant out of the pits was increased. In this manner, the lubrication condition was improved greatly. The 3D surface topography testing confirmed the assumption. Moreover, vibration frequency exerted a more significant effect on the forming load reduction than vibration amplitude. Keywords: clutch hub; vibration-assisted forming; load reduction; lubrication; surface quality
1. Introduction Clutch hub is an important torque transmission component, which is widely used in automatic transmission. However, its complex shape and highly precise dimensions make it one of the most complicated parts in automobile manufacturing. The conventional forming method for clutch hub forming mainly focuses on hobbing [1] and hot forging [2–4]. Hobbing usually cuts the workpiece, which is time consumption. Hot forging needs to heat the materials, which has bad performance in cost and precision. For the production of lightweight, high-strength, and low-cost parts in the automobile industry, sheet–bulk forming, which combines sheet and bulk forming, has been proposed for shortening the process chain and achieving high-performance products [5–8]. Many researchers have attempted to apply sheet–bulk forming in clutch metal forming by experimental or numerical methods. Ko et al. [9] introduced a roll die forming method to improve the dimensional accuracy in manufacturing a clutch hub. An optimal clearance between the punch and the roll was determined by the finite-element method and experiments. Zhuang et al. [10] proposed a method that combines deep drawing and extrusion process for the production of parts, such as the geared drum, on a servo press. In his study, several slide motions, such as speed motion, oscillation motion, and step motion, were considered, and results showed that step motion positively affected the surface quality and thickness reduction. Meanwhile, Mori et al. [11,12] presented a
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resistance heating method for clutch hub forming to improve the formability of ultra-high-strength steel. By resistance heating, the fracture was prevented, and the clutch hub was produced successfully. Sun et al. [13] investigated the clutch hub extrusion processes with various extrusion ratios and preformed shapes through the AFDEX software (Metal Forming Research Corporation, Jinju, Korea). Their simulation results revealed that stress state is the main determinant of local material flowing behavior and can be used for improving the degree of tooth filling. Wu et al. [14] also used the finite-element method to analyze flanging and coining operations during clutch1 hub forming. Several experimental and simulation works have been conducted for the control of local thickness and prevention of cracks at selected process conditions. Park et al. [15] utilized the commercial finite-element software DEFORM-2D (Scientific Forming Technologies Corporation, Columbus, IN, USA) to optimize preformed shapes and tooling geometries in order to prevent excessive thinning and crack formation. And experiments for clutch hub forming processes were also carried out for the verification of analytical models. Lee et al. [16] described a 3D finite-element method involving nine deep drawing processes and three ironing processes for forming a clutch drum. They found that the punch shape, punch angle, and thickness reduction ratio influences ironing dimensional accuracy and forming load. From the above descriptions, we learned that gear tooth formation undergoes an ironing process, and severe plastic deformation occurs during this procedure. The clutch hub is a thin-walled component, and large forming loads easily lead to damage on the surface and in internal parts. Owing to the development of servo press and hydraulic press [17,18], superimposing vibration to forming dies or workpieces during plastic processes has become a reality. Many scholars have devoted considerable effort for the development of vibration-assisted forming techniques, which enables the generation of good-quality products at a small forming load. Maeno et al. [19] applied pulsation to the forging process of stainless steel by using a servo press. Given the vibration, the elastic recovery between the die and the plate causes the liquid lubricant to automatically be fed into the gap, thereby greatly improving lubrication. Kriechenbauer et al. [20] described a novel technology for deep drawing on a servo press by superimposing low-frequency vibration between 10 and 50 Hz at a cushion and a press ram. Products with increased drawing ratios and no wrinkle were obtained through this technology. Matsumoto et al. [21] proposed a method for enhancing the friction condition in deep hole forming by controlling punch movement in pulsed and stepwise modes. Through this method, deep holes with high accuracy were produced. In these works, the most common effects induced by vibration were load reduction and surface quality improvement because of volume and surface effects. Travieso-Rodríguez et al. [22] proposed a vibration-assisted ball-burnishing process by attaching a vibrating module to a classical burnishing tool. The surface quality and process efficiency have been significantly improved with the assistance of external vibration energy. In the meanwhile, Jerez-Mesa et al. [23] also designed a ultrasonic vibration-assisted ball-burnishing tool for surface treatment of material Ti-6Al-4V. The vibration-assisted ball-burnishing technique showed a good performance both in surface quality and hardness improvements compared with traditional burnishing. Moreover, vibration also can affect the material property greatly. Liu et al. [24,25] presented a new method to produce ultrafine copper materials by using the ultrasonic. By applying ultrasonic vibration during upsetting procedure, the initial grain size drops from 50 µm to 100 nm. The statements above show vibration both has a significant effect on the interior and surface of the material, which is named volume effect and surface effect, respectively. The volume effect is manifested by the vibration-induced enhancements in dislocation movements and decreased flow stress levels [26,27]. The surface effect is attributed to the effect of vibration on friction condition in the interface between a workpiece and dies [28,29]. The volume and surface effects greatly influence forming load reduction. However, not all vibration-assisted plastic forming processes exert volume and surface effects. The result depends on the vibration frequency and amplitude [30]. To reduce the forming load and improve the quality of the clutch hub, we proposed a novel method for the application of vibration during traditional sheet–bulk forming. We developed a specialized
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device for vibration-assisted extrusion to investigate the effects of vibration on the clutch hub. Then, 11, x FOR PEER REVIEW and vibration amplitude on forming load were experimentally 3 of 13 the Materials effects2018, of vibration frequency investigated. The clutch hub surface was also examined with a 3D microscope. Based on the results, experimentally investigated. The clutch hub surface was also examined with a 3D microscope. Based we propose a basic explanation for load reduction due to vibration. on the results, we propose a basic explanation for load reduction due to vibration.
2. Materials and Methods
2. Materials and Methods
2.1. Material Properties
2.1. Material Properties
Low-carbon sheet steel DC04 (produced by baosteel, Shanghai, China) was used, which is Low-carbon sheet steel DC04 (produced by baosteel, Shanghai, China) was used, which is widely used in automobile manufacturing because of its good performance in stamping and drawing. widely used in automobile manufacturing because of its good performance in stamping and Thedrawing. DC04 sheet’s thickness 1.5 mm, with an average sizegrain of about 20about µm. 20 Theμm. chemical The DC04 sheet’swas thickness was 1.5 mm, with angrain average size of The composition of the material is shown in Table 1. chemical composition of the material is shown in Table 1. Table DC04 steel. steel. Table1.1.Chemical Chemicalcomposition composition of of DC04 C% 0.07
C% Al% Mn% Mn% Al% 0.07 0.3 0.02 0.3 0.02
P% P% S% 0.02 0.025 0.02
S% 0.025
2.2. Process of Vibration-Assisted Clutch Hub Forming
2.2. Process of Vibration-Assisted Clutch Hub Forming
The clutch hub studied in this paper was a periodic and symmetric cylindrical part with 18 The that clutch studied in this paper was a periodic andclutch symmetric 18 an teeth teeth arehub aligned circumferentially (Figure 1). The hub iscylindrical a key partpart andwith plays thatimportant are aligned circumferentially (Figure in 1). automotive The clutch hub is a key part and plays an important role role in power transmission transmission systems. The outer and inner diameters of the drum are 64 and 58.8 mm, respectively. The tooth length was 22.5 mm. The in power transmission in automotive transmission systems. The outer and inner diameters oftop theand drum thicknesses the tooth were 1.1tooth and 0.9 mm. was Moreover, the maximal and side minimal corner radii are side 64 and 58.8 mm,ofrespectively. The length 22.5 mm. The top and thicknesses of the were 0.6 and 0.4 mm. tooth were 1.1 and 0.9 mm. Moreover, the maximal and minimal corner radii were 0.6 and 0.4 mm.
Figure Clutchhub hubgeometry geometry dimensions dimensions (unit: Figure 1.1.Clutch (unit:mm). mm).
Figure 2 shows the vibration-assisted clutch hub forming process and includes five steps. The Figure 2 shows the vibration-assisted clutch hub forming process and five The workpiece was a drawn cup with 1.3mm thickness and the sidewall was cutincludes to a height ofsteps. 20 mm. workpiece was a drawn cup with 1.3mm thickness and the sidewall was cut to a height of 20 mm. The first step was workpiece clamping, in which a workpiece was clamped by a holder and Thepunched. first stepThen, was workpiece which a down workpiece was clamped a holdermanner. and punched. the punch clamping, carried the in workpiece the die inside in an by oscillating The Then, the was punch carried thewith workpiece down the die inside in clutch an oscillating manner. The punch punch superimposed low-frequency vibration during hub forming. Its movement wascurve superimposed low-frequency hub forming. Its movement curve is shown inwith Figure 2f. This feedvibration mode wasduring namedclutch “forward-one-backward-half”. When the is shown in Figure 2f. Thisthe feed modereverted was named When the forming was forming was ended, punch to its“forward-one-backward-half”. original state, and the workpiece returned with the punch of friction. the workpiece ejected by returned the ejector. During the forming ended, thebecause punch reverted to Lastly, its original state, and was the workpiece with the punch because procedure, the die superimposed at a reciprocating motion. In the contrast to conventional colddie of friction. Lastly, the was workpiece was ejected by the ejector. During forming procedure, the forming processes, vibration-assisted forming decreases forming force and thereby improves was superimposed at a reciprocating motion. In contrast to conventional cold forming processes, product quality.forming Given the rebuilding of lubricating film during the reciprocating motion, thethe vibration-assisted decreases forming force and thereby improves product quality. Given friction condition was improved. rebuilding of lubricating film during the reciprocating motion, the friction condition was improved.
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Figure 2. Procedure of clutch hub forming processing.
Figure 2. Procedure of clutch hub forming processing. 2.3. Experiments
2.3. Experiments
Figure 2. Procedure of clutch hub forming processing. Vibration-assisted clutch hub forming was conducted with the setup shown in Figure 3. The setup was composed of the control system, system, ejector cylinder, Vibration-assisted clutch hub forming washydraulic conducted with vibration the setupcylinder, shown in Figure 3. The setup 2.3. Experiments servo value, displacement sensor, force sensor, and forming dies. The hydraulic system supplied a value, was composed of the control system, hydraulic system, vibration cylinder, ejector cylinder, servo pressure range of 0–15clutch MPa, hub providing a maximum force ofwith 300 kN. control system can alter Vibration-assisted forming was conducted the The setup shown in Figure 3. The displacement sensor, force sensor, and forming dies. The hydraulic system supplied a pressure range of the was vibration frequency and amplitude by changing servo vibration value’s switching and setup composed of the control system, hydraulicthe system, cylinder,frequency ejector cylinder, 0–15 MPa, providingservo a maximum force of 300 kN. The control system canthe alter the vibration frequency interval. value’s response was less than 10 ms,The and maximum servo value,The displacement sensor, force time sensor, and forming dies. hydraulic systemvibration supplied a and pressure amplitude by changing the servo value’s switching frequency and interval. The servo value’s frequency of the vibrating wasa 50 Hz. The mover of 300 the kN. displacement sensor was can fixedalter range of 0–15 MPa,cylinder providing maximum force of The control system the slider, andthan its motion precision was ±10 μm. The force sensor was installed between the die response time wasfrequency less 10 ms, and the maximum vibration frequency of the vibrating cylinder thewith vibration and amplitude by changing the servo value’s switching frequency and frame for recording forming force in the axial direction. To investigate the influence of was interval. 50 and Hz. body The mover of the displacement sensor was fixed with the slider, and its motion precision The servo value’s response time was less than 10 ms, and the maximum vibration vibration frequency on the was forming force, we set the the vibration frequency to 30, 20, or 10 Hz. The was frequency ±10 µm. The force sensor installed die of and frame forsensor recording forming of the vibrating cylinder was 50between Hz. The mover thebody displacement was fixed average velocity of the punch was 5 mm/s. The lubricant used in the forming experiment was liquid theaxial slider,direction. and its motion precision was μm. The sensorfrequency was installed the die forcewith in the To investigate the ±10 influence offorce vibration on between the forming force, lubricant, and the parameter was 0.485 PaS. To investigate the influence of amplitude on the andthe body frame for recordingtoforming force in theThe axial direction. To investigate the influence of we set vibration frequency 30, 20, or 10 Hz. average velocity of the punch was 5 mm/s. forming force, we set the vibration amplitude to 0.2, 0.4, or 0.6 mm, where the vibration frequency vibration frequency on the the forming force, we setliquid the frequency toparameter 30, 20, or 10 ThePaS. The lubricant used inHz. the forming experiment was lubricant, and the was 0.485 was fixed at 20 After forming experiments, thevibration surface quality and 3D morphology ofHz. the average velocity of the punch was 5 mm/s. The lubricant used in the forming experiment was liquid formed parts were further by aon color laser microscope Osaka, Japan). To investigate the influence ofanalyzed amplitude the3D forming force, we(VK9710K, set the vibration amplitude to 0.2,
lubricant, the parameter wasfrequency 0.485 PaS. was To investigate amplitude on the 0.4, or 0.6 mm,and where the vibration fixed at 20 the Hz.influence After theofforming experiments, forming force, we set the vibration amplitude to 0.2, 0.4, or 0.6 mm, where the vibration frequency the surface quality and 3D morphology of the formed parts were further analyzed by a color 3D laser was fixed at 20 Hz. After the forming experiments, the surface quality and 3D morphology of the microscope (VK9710K, Osaka, Japan). formed parts were further analyzed by a color 3D laser microscope (VK9710K, Osaka, Japan).
Figure 3. Schematic of a vibration-assisted hydraulic extrusion press.
Figure 3. Schematic of a vibration-assisted hydraulic extrusion press.
Figure 3. Schematic of a vibration-assisted hydraulic extrusion press.
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3.1. Microstructure
3. Results 3.1. Microstructure
The material used in this study is a typical commercial sheet metal DC04. Figure 4a shows the 3D The material used insteel. this study a typical commercial metal DC04. Figuregrains 4a shows therolled 3.1. Microstructure microstructure of the DC04 Givenis the multiple rollingsheet processes, the coarse were 3D microstructure of the and DC04showed steel. Given the multiple rolling processes, the coarse grains were (TD) and deformed into ellipsoids long strip shapes, as viewed from transversal direction The material used in this study is a typical commercial sheet metal DC04. Figure 4a shows the rolled and deformed into ellipsoids and showed long strip shapes, as viewed from transversal and rolling direction (RD). grainsthe were produced during the severe plastic deformation 3D microstructure of theMany DC04 small steel. Given multiple rolling processes, the coarse grains were direction (TD) and rolling direction (RD). Many small grains were produced during the severe rolled and into ellipsoidsbehavior and showed long is strip shapes, as viewed 4b. from transversal processing. Thedeformed tension deformation of DC04 displayed in Figure The result shows plastic deformation processing. The tension deformation behavior of DC04 is displayed in Figure 4b. direction (TD) andstress rolling direction (RD). small with grains were produced during theMPa severe that the average yield 0.2% offset wasMany 220 MPa, an220 ultimate strength of 320 The result shows that theataverage yield stress at 0.2% offset was MPa, with an ultimate strengthand an plastic deformation processing. The tension deformation behavior of DC04 is displayed in Figure 4b. elongation 46.8%. of 320of MPa and an elongation of 46.8%. The result shows that the average yield stress at 0.2% offset was 220 MPa, with an ultimate strength of 320 MPa and an elongation of 46.8%.
Figure (a) The microstructureand and(b) (b) stress stress and curve of the DC04 steel.steel. Figure 4. (a)4.The 3D 3D microstructure andstrain strain curve of the DC04
To investigate theThe vibration on the material the formed partssteel. were cut along Figure 4. (a) 3D microstructure and (b)microstructure, stress and strain curve of the DC04
Tothe investigate thecases vibration on theinto material microstructure, thevibration; formed (b) parts werevibration cut along the section. Four were taken consideration: (a) without applied section. Four cases were taken intoon consideration: (a) without applied vibration with 10 the Hz; (c) applied vibration withmicrostructure, frequency 20 vibration; Hz (d) (b) applied vibration with with Tofrequency investigate vibration the material theand formed parts were cut along frequency 30 Hz.applied The sections wereinto polished with sand paper to mirror surfacevibration and etched withfrequency 4% frequency 10 Hz; (c) vibration with frequency 20(a) Hzwithout and (d)vibration; applied with the section. Four cases were taken consideration: (b) applied vibration nitric acid alcohol solution to reveal their Then, metallographical observation was with frequency 10 Hz; (c) applied vibration with frequency 20surface Hz andand (d) etched applied vibration with acid 30 Hz. The sections were polished with sandmicrostructure. paper to mirror with 4% nitric conducted a Nikon (Nikon Tokyo, Japan). microscope frequency 30using Hz.reveal The sections weremicroscope polished with sandCorporation, paper to mirror surface andThe etched with 4% alcohol solution to theirLV150 microstructure. Then, metallographical observation was conducted image results were shown to in reveal Figure their 5. Then, the images were analyzed by the software Image was Pro nitric acid alcohol solution microstructure. Then, metallographical observation using a Nikon LV150 microscope (Nikon Corporation, Tokyo, Japan). The microscope image results Plus (V6.0,using Media Cybernetics Rockville,(Nikon USA) Corporation, and the average grainJapan). size was as conducted a Nikon LV150Inc., microscope Tokyo, Theobtained, microscope were shown in Figure 5. Then, the images were analyzed by the software Image Pro Plus (V6.0, Media shown in Table 2. There noFigure significant change grain size theby four image results were shownis in 5. Then, theinimages werebetween analyzed thecases. software Image Pro Cybernetics Inc., Rockville, USA) and the average grain size was obtained, as shown in Table 2. There Plus (V6.0, Media Cybernetics Inc., Rockville, USA) and the average grain size was obtained, as is no shown significant change in grain size between theinfour cases. in Table 2. There is no significant change grain size between the four cases.
Figure 5. Cross-section microstructure applied different vibration frequencies: (a) Without vibration; (b) Applied vibration with frequency 10 Hz; (c) Applied vibration with frequency 20 Hz; (d) Applied vibration with frequency 30 Hz. Figure 5. Cross-section microstructure applied different vibration frequencies: (a) Without vibration; Figure 5. Cross-section microstructure applied different vibration frequencies: (a) Without vibration; (b) Applied vibration with frequency 10 Hz; (c) Applied vibration with frequency 20 Hz; (d) Applied (b) Applied vibration with frequency 10 Hz; (c) Applied vibration with frequency 20 Hz; (d) Applied vibration with frequency 30 Hz.
vibration with frequency 30 Hz.
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Table 2. REVIEW Average Materials 2018, 11, x FOR PEER Without Vibration
grain size with different vibration frequencies.
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Table 2. Average grain size with Vibration different Frequency vibration frequencies. Vibration Frequency 10 Hz 10 Hz Vibration Frequency 10 Hz
24.3 µm
Without Vibration 24.3 μm 3.2. Forming Force along with
25.2 µm Vibration
Frequency 10 Hz 25.2 μm Punch Displacement
24.1 µm Vibration Frequency 10 Hz 24.1 μm
Vibration 25.6 µm Frequency 10 Hz 25.6 μm
Figure 6 reveals the load–displacement curve without vibration. On the basis of the characteristics 3.2. Forming Force along with Punch Displacement of the clutch hub, the load curve can be classified into three stages [10]: (1)On elastic and microplastic Figure 6 reveals the load–displacement curve without vibration. the basis of the deformation; (2) severe plastic deformation; and (3) gear tooth deformation. During characteristics of the clutch hub, the load curve can be classified into three stages [10]: (1) elastic stage and (1), the workpiece contacted with the andplastic begandeformation; to move inside material underwent microplastic deformation; (2) die severe andthe (3) die. gear The tooth deformation. Duringelastic stage (1), the workpiece contacted with the dieincrease and began to mainly move inside theby die. The material and microplastic deformation. The forming force was caused elastic deformation elastic and microplastic deformation. forming increase was mainly caused by duringunderwent this period. In stage (2), the material began toThe flow insideforce the die, and severe plastic deformation elastic deformation during this period. In stage (2), the material began to flow inside the die, and occurred. Plastic deformation was the main reason for the increased load. In stage (3), the gear severe plastic deformation occurred. Plastic deformation was the main reason for the increased load. tooth was gradually deformed. The contact area between the workpiece and die increased as the In stage (3), the gear tooth was gradually deformed. The contact area between the workpiece and die displacement The friction force The wasfriction proportional the contacttoarea; thus, area; the increase in increasedincreased. as the displacement increased. force wastoproportional the contact thus, forming force at this stage was mainly due to increased friction. The maximum load of clutch hub the increase in forming force at this stage was mainly due to increased friction. The maximum load forming of was clutch60.1 hubkN. forming was 60.1 kN.
Figure 6. Load–displacement curve of clutch hub forming without vibration. Figure 6. Load–displacement curve of clutch hub forming without vibration.
3.3. Influence of Vibration Frequency and Amplitude on Forming Force
3.3. Influence of Vibration Frequency and Amplitude on Forming Force
The experiment results of vibration frequency on forming force are shown in Figure 7. Three
The experiment of vibration frequency on forming force10are shown in Figure Three kind kind values of results frequency were considered, namely, 30, 20, and Hz. The clutch hub 7. forming was separated into three stages, as described in 10 Figure In clutch stages (1) and (2), we process clearly was valuesprocess of frequency were considered, namely, 30, 20, and Hz. 6. The hub forming observed vibration fluctuations in the forming force, but maximum formingobserved force did that separated into that three stages,causes as described in Figure 6. In stages (1) the and (2), we clearly not decrease. However, in stage (3), with the application of low-frequency vibration, an obvious load vibration causes fluctuations in the forming force, but the maximum forming force did not decrease. reduction occurred as the forming force fluctuated. The maximum load at the frequencies of 30, 20, However, in stage (3), with the application of low-frequency vibration, an obvious load reduction and 10 Hz were 45, 51.4, and 55 kN, respectively. The corresponding load drop rates were 25%, occurred as the force the fluctuated. The maximum load at the frequencies of an 30,open-loop 20, and 10 Hz 14.3%, andforming 8.3%. Because servo valve used in this experiment was controlled in were 45, 51.4, and 55 kN, respectively. The corresponding load drop rates were 25%, 14.3%, and 8.3%. method, the vibration amplitude was not well coupled with the frequency. When the vibration Because the servo valve used in this experiment was controlled in an open-loop method, the vibration frequency increased, the commutation time of the servo valve was reduced and the amplitude subsequently On the basis the displacement records obtained from theincreased, position the amplitude was notdecreased. well coupled with theoffrequency. When the vibration frequency transducer, theof amplitude values were obtained, and the the amplitudes at thesubsequently frequencies of 30, 20, and On commutation time the servo valve was reduced and amplitude decreased. 10 Hz were 0.16, 0.22, and 0.39 mm, respectively. the basis of the displacement records obtained from the position transducer, the amplitude values To investigate the influence of amplitude on the forming force separately, the vibration were obtained, and the amplitudes at the frequencies of 30, 20, and 10 Hz were 0.16, 0.22, and 0.39 frequency was fixed at 20 Hz and three amplitudes, 0.2, 0.4, and 0.6 mm, were considered. The load– mm, respectively. To investigate the influence of amplitude on the forming force separately, the vibration frequency was fixed at 20 Hz and three amplitudes, 0.2, 0.4, and 0.6 mm, were considered. The load–displacement
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Materials 2018,forming 11, x FOR PEER REVIEW curves of clutch hub with different vibration amplitudes are shown in Figure 8.7 ofIn13the forming Materials 2018, 11, forming x FOR PEER REVIEW of 13upper limit stages (1) and (2), the force oscillated with the displacement increase and 7the displacement curves of clutch hub forming with different vibration amplitudes are shown in Figure of load diddisplacement show anstages obvious decrease. When the forming process moved intoand the stage (3), 8.not In the forming (1) andhub (2),forming the forming oscillated withamplitudes the displacement increase curves of clutch with force different vibration are shown in Figure the limit load ofstages loadreduction did an obvious decrease. When the forming process intoand the an obvious8. maximum was attained. The maximum load atmoved the amplitudes of 0.2, Inupper the forming (1)not andshow (2), the forming force oscillated with the displacement increase stage (3), an obvious maximum loadan reduction was attained. The maximum load at moved the amplitudes upper limit of load did not show decrease. When the forming the and 17%, 0.4, and 0.6the mm were 53.8, 51.8, and 49.8 obvious kN, and the load drop rates process were 10.3%,into 13.6%, of 0.2,(3), 0.4,an and 0.6 mmmaximum were 53.8,load 51.8,reduction and 49.8 was kN, and the load rates were 13.6%, and stage obvious attained. Thedrop maximum load 10.3%, at the amplitudes accordingly.17%, Anaccordingly. increase in also positively caused the informing forming load. Anamplitude increase in amplitude also positively caused thedrop drop in load.
of 0.2, 0.4, and 0.6 mm were 53.8, 51.8, and 49.8 kN, and the load drop rates were 10.3%, 13.6%, and 17%, accordingly. An increase in amplitude also positively caused the drop in forming load.
Figure 7. Comparison of load–displacement curves of clutch hub forming with different vibration
Figure 7. frequencies. Comparison of load–displacement curves of clutch hub forming with different Figure 7. Comparison of load–displacement curves of clutch hub forming with different vibration vibration frequencies. frequencies.
Figure 8. Comparison of load–displacement curves of clutch hub forming with different vibration amplitudes. Figure 8. Comparison of load–displacement curves of clutch hub forming with different vibration Comparison of load–displacement curves of clutch hub forming with amplitudes.
Figure 8. vibration amplitudes.
different
3.4. Influence of Vibration Frequency and Amplitude on Surface Quality Figure 9 shows the surface appearance of a clutch drum before and after the gear forming process. Before the gear forming process, the workpiece was a 1.3 mm-thick cylindrical part. After gear forming, the thickness of the workpiece wall was reduced to 1.1 mm. The gear tooth underwent severe plastic deformation, and obvious scratches appeared on the gear tooth surface, as shown by the red rectangle of Figure 9b.
the Frequency surface appearance of on a clutch 3.4. Figure Influence9 ofshows Vibration and Amplitude Surface drum Qualitybefore and after the gear forming process. Before the gear forming process, the workpiece was a 1.3 mm-thick cylindrical part. After Figure 9 shows the surface appearance of a clutch drum before and after the gear forming gear forming, the thickness of the workpiece wall was reduced to 1.1 mm. The gear tooth underwent process. Before the gear forming process, the workpiece was a 1.3 mm-thick cylindrical part. After severe plastic deformation, obvious scratches appeared toothgear surface, shown by gear forming, the thickness and of the workpiece wall was reducedon tothe 1.1 gear mm. The tooth as underwent Materials 2018, 11, 928 8 of 14 the red rectangle of Figure 9b. severe plastic deformation, and obvious scratches appeared on the gear tooth surface, as shown by the red rectangle of Figure 9b.
Figure 9. 9. Surface Surfaceappearance appearancebefore before and after clutch forming process without vibration: (a) and after the the clutch forming process without vibration: (a) Before Before (b)forming. After forming. forming; After Figureforming; 9.(b)Surface appearance before and after the clutch forming process without vibration: (a) Before forming; (b) After forming.
To investigate the To investigate the influence influence of of vibration vibration on on the the surface surface quality, quality, we we conducted conducted aa series series of of To investigate the influence of vibration on the surface quality, we gear conducted a series of microscopic experiments on a 3D laser microscope. The middle part of the tooth (red rectangle microscopic experiments on a 3D laser microscope. The middle part of the gear tooth (red rectangle area microscopic experiments on a 3Dcut laser microscope. The middle partthe of microscopic the gear toothobservation. (red rectangle area showed in Figure thepart formed part for The showed in Figure 9b) was9b) cutwas off fromoff thefrom formed for the microscopic observation. The topography area showed in Figure 9b) wasofcutthe offgear fromtooth the formed for the in microscopic The topography experiment results surface part are shown Figures 10observation. and 11. The 2D experiment results of the gear tooth surface are shown in Figures 10 and 11. The 2D mesoscopic topographytopography experimentresults resultsshowed of the gear toothscratches surface are shown on in Figures and surface 11. Thein2D mesoscopic obvious appearing the gear10tooth the topography results showed obvious scratches appearing on the gear tooth surface in the absence of mesoscopic topography results10, showed scratches gear tooth surfacewidth in theon absence of vibration. In Figure when obvious the vibration was appearing applied onon thethe punch, the scratch vibration. In Figure 10, when the vibration was applied on the punch, the scratch width on the gear absence of vibration. In Figure 10, when the vibration was applied on the punch, the scratch width on the gear tooth surface started to decrease. This result indicates that increase in vibration frequencies tooth surface started to decrease. This result indicates that increase in vibration frequencies results the gear tooth surface startedwidth. to decrease. result indicates that30increase vibrationtended frequencies results in decrease in scratch When This the frequency reached Hz, thein scratches to fade inresults decrease in scratch width. width. When the frequency reached 30 Hz,30the scratches tended to fade away. in decrease in scratch When the frequency reached Hz, the scratches tended to fadein away. 2D and 3D microtopography results showed that scratches achieved a similar microstructure 2D and 3D microtopography results showed that scratches achieved a similar microstructure in the away. 2D andand 3D microtopography resultsand showed scratches a similar of microstructure the presence absence of vibration withthat vibration at achieved the frequencies 10 and 20 in Hz. presence and absence of vibration and with at the frequencies of 10 and 2010Hz. the presence and were absence of vibration andvibration with at ofthe frequencies andNumerous 20 on Hz. Numerous grooves generated and revealed thevibration occurrence a severe plasticof deformation the grooves were generated and revealed the occurrence of a severe plastic deformation on the gear tooth Numerous grooves were generated and revealed the occurrence of a severe plastic deformation on the gear tooth surface. However, under the vibration frequency of 30 Hz, the gear tooth surface was much surface. However, under theunder vibration frequency of 30 Hz, gear tooth was much flatter gear tooth surface. However, the vibration frequency of the 30 Hz, the gear surface tooth surface was much flatter than in the other samples and did not retain a groove. 3D microtopography results showed that than in than the other and did a groove. 3D microtopography results showed that the flatter in thesamples other samples andnot didretain not retain a groove. 3D microtopography results showed that the asperities were flattened by the rigid tools, and many pits were retained on the surface. In Figure asperities were flattened by the rigid tools, and many pits were retained on the surface. In Figure the asperities were flattened by the rigid tools, and many pits were retained on the surface. In Figure11, 11, the vibration frequency was fixed at 20 Hz. Increasing vibration amplitude form 0.2 mm to 0.6 mm the frequency waswas fixed at 20atHz. Increasing vibration amplitude form 0.20.2 mm to to 0.60.6 mm has 11,vibration the vibration frequency fixed 20 Hz. Increasing vibration amplitude form mm mm has a positive effect on scratch width decrease. 2D and 3D microtopograpy results showed the surface ahas positive effect on scratch width decrease. 2D resultsshowed showedthe thesurface surface a positive effect on scratch width decrease. 2Dand and3D 3Dmicrotopograpy microtopograpy results roughness tends to become better as the amplitude increases. roughness better as asthe theamplitude amplitudeincreases. increases. roughnesstends tends to to become better
Figure 10. Comparison of the surface quality of clutch hubs formed under different vibration frequencies: (a) Without vibration; (b) With vibration at frequency 30 Hz; (c) With vibration at frequency 20 Hz; (d) With vibration at frequency 10 Hz.
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Figure 10. Comparison of the surface quality of clutch hubs formed under different vibration frequencies: (a) Without vibration; (b) With vibration at frequency 30 Hz; (c) With vibration at9 of 14 Materials 2018, 11, 928 frequency 20 Hz; (d) With vibration at frequency 10 Hz
Figure 11. Comparison of the surface quality of clutch hubs formed under different vibration Figure 11. Comparison of the surface quality of clutch hubs formed under different vibration amplitudes: (a) Without vibration; (b) With vibration at frequency 30 Hz; (c) With vibration at amplitudes: (a) Without vibration; (b) With vibration at frequency 30 Hz; (c) With vibration at frequency frequency 20 Hz; (d) With vibration at frequency 10 Hz 20 Hz; (d) With vibration at frequency 10 Hz.
4. Discussion 4. Discussion Obvious load reduction was observed during the vibration-assisted clutch hub forming in a Obvious load reduction was observed during the vibration-assisted clutch hub forming in a wide wide range of frequency and amplitude. The reasons for load drop were classified into two types: range of frequency and amplitude. The reasons for load drop were classified into two types: volume volume and surface effects. In the volume effect, vibration is assumed to a kind of energy and can be and surface effects. In the volume effect, vibration is assumed to a kind of energy and can be absorbed absorbed by dislocations in the same manner as thermal energy. This effect reduces flow stress. In by dislocations in the same manner as thermal energy. This effect reduces flow stress. In the surface the surface effect, load reduction is attributed to the decrease in friction force caused by the relative effect, load reduction is attributed to the decrease in friction force caused by the relative motion in motion in an interface. an interface. As shown in Figure 6, clutch hub forming can be divided into three stages according to the As shown in Figure 6, clutch hub forming can be divided into three stages according to the curve’s curve’s local slope. In stages (1) and (2), the load fluctuated with the superposition of vibration, but local slope. In stages (1) and (2), the load fluctuated with the superposition of vibration, but the the maximum load did not decrease. Given that the contact area between the workpiece and the die maximum load did not decrease. Given that the contact area between the workpiece and the die at at the first two stages was small, the increase in forming force was mainly ascribed to elastic and the first two stages was small, the increase in forming force was mainly ascribed to elastic and plastic plastic deformation. This notion means that the vibration only causes elastic unloading on materials, deformation. This notion means that the vibration only causes elastic unloading on materials, and and vibration energy is not effectively transmitted to the interior of a material to cause flow stress vibration energy is not effectively transmitted to the interior of a material to cause flow stress reduction. reduction. In stage (3), the contact area between the workpiece and die gradually rises with the In stage (3), the contact area between the workpiece and die gradually rises with the formation of the formation of the gear tooth. Frictional force is proportional to the contact area; thus, the increase in gear tooth. Frictional force is proportional to the contact area; thus, the increase in forming force at this forming force at this stage was mainly due to the increase in friction. Figures 6 and 7 reveal that the stage was mainly due to the increase in friction. Figures 6 and 7 reveal that the load reduction caused load reduction caused by vibration only occurred in stage (3). This result suggests that the by vibration only occurred in stage (3). This result suggests that the phenomenon of forming force phenomenon of forming force reduction in the vibration-assisted clutch forming process was mainly reduction in the vibration-assisted clutch forming process was mainly due to the change in friction due to the change in friction condition and not the alteration of the material’s interior properties by condition and not the alteration of the material’s interior properties by the vibration. Additionally, the results in Figure 5 and Table 2 showed there was no significant change in grain size between
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the vibration. Additionally, the results in Figure 5 and Table 2 showed there was no significant the different vibration conditions, confirmed ourconditions, assumptionwhich that volume effect did not occur change in grain size between thewhich different vibration confirmed our assumption during vibration-assisted clutch hub forming process. that volume effect did not occur during vibration-assisted clutch hub forming process. Figures that thethe vibration frequency andand amplitude positively affectaffect the forming load Figures77and and8 8show show that vibration frequency amplitude positively the forming reduction. However, in the experiment on vibration frequency on forming force, vibration amplitude load reduction. However, in the experiment on vibration frequency on forming force, vibration isamplitude not a constant and declines as the frequency increases. Theincreases. load reduction phenomenon is notvalue a constant value and declines as the frequency The load reduction during this experiment suggests that vibration exertsfrequency a more pronounced impact on load phenomenon during this experiment suggestsfrequency that vibration exerts a more pronounced reduction than the vibration amplitude. Vibration frequency plays a more sensitive role in frictional impact on load reduction than the vibration amplitude. Vibration frequency plays a more sensitive force reduction the clutch during formingthe experiments. role in frictionalduring force reduction clutch forming experiments. By analyzing the present results in detail, By analyzing the present results in detail,the thereduction reductionin informing formingforce forcewith withthe thesimultaneous simultaneous application of vibration was found to be related with two factors, namely, the relative speed between the application of vibration was found to be related with two factors, namely, the relative speed workpiece andworkpiece die (related with and amplitude) reciprocation times of punch (related between the and diefrequency (related with frequency and and the amplitude) and the reciprocation times with frequency). Given the theoretical and experimental results reported in prior studies [31–34], of punch (related with frequency). Given the theoretical and experimental results reported in prior the relative speedthe significantly influences the frictional shearthe stress. Most of these works wereofbased studies [31–34], relative speed significantly influences frictional shear stress. Most these on the Stribeck curveon [35]. the friction regimes of the boundary mixed lubrication, works were based theInStribeck curve [35]. In frictionlubrication regimes ofand boundary lubricationhigh and sliding speed results in decreased friction coefficient. The punch speed during vibration-assisted clutch mixed lubrication, high sliding speed results in decreased friction coefficient. The punch speed hub forming can be decomposed constant can and a component can be represented by during vibration-assisted clutch into huba forming becosine decomposed intoand a constant and a cosine the following equation: component and can be represented by the following equation: v = v0 + 2π f Acos(2π f t), (1) 𝑣 = 𝑣0 + 2𝜋𝑓𝐴𝑐𝑜𝑠(2𝜋𝑓𝑡), (1) where v is the punch speed, v0 is the velocity without vibration and its value is 5 mm/s, A is the where v is the punch speed, v0 is the velocity without vibration and its value is 5 mm/s, A is the vibration amplitude, and f is the vibration frequency. During one oscillation cycle, the punch speed’s vibration amplitude, and f is the vibration frequency. During one oscillation cycle, the punch speed’s applied vibration is larger than that without vibration in some specified intervals. The effective average applied vibration is larger than that without vibration in some specified intervals. The effective speed can be used to evaluate the speed over a period of vibration and can be expressed as average speed can be used to evaluate the speed over a period of vibration and can be expressed as Z t Z t Z t 2𝑡 3𝑡 1𝑡1 𝑣 + |∫𝑡 v2 𝑣+| + ∫𝑡 v3 𝑣 )/T /𝑇, (2) (2) v =𝑣̅ = (∫0 v+ 1 t 2 0 t 1
2
where T is the vibration cycle, t1 and t3 are time intervals when the punch speed direction is positive, where T is the vibration cycle, t1 and t3 are time intervals when the punch speed direction is positive, and t2 is time interval when the punch speed direction is negative. By combining Equations (1) and and t2 is time interval when the punch speed direction is negative. By combining Equations (1) and (2), (2), the effective average speed 𝑣̅ can be obtained, and its diagram is shown in Figure 12. The the effective average speed v can be obtained, and its diagram is shown in Figure 12. The vibration vibration amplitude and frequency both positively affect the increase rate of average speed. The amplitude and frequency both positively affect the increase rate of average speed. The Stribeck curve Stribeck curve shows that the increase in average speed led to frictional stress reduction. This result shows that the increase in average speed led to frictional stress reduction. This result thoroughly thoroughly explains the findings in Figure 7. explains the findings in Figure 7.
Figure 12. 12. Influence Influence of of amplitude amplitude and andfrequency frequencyon onthe theaverage averagevelocity. velocity. Figure
Similarly, in the corresponding experiments shown in Figures 7 and 8, the average speed of Similarly, in the corresponding experiments shown in Figures 7 and 8, the average speed of punch punch is shown in Figure 13. Figure 13a displays that although the amplitude declined with is shown in Figure 13. Figure 13a displays that although the amplitude declined with increasing increasing vibration frequency, the average velocity still increased. The amplitude exerted a more vibration frequency, the average velocity still increased. The amplitude exerted a more pronounced pronounced effect on the punch average velocity than that in the results in Figure 13a. However, the actual results shown in Figures 7 and 8 were the reverse, and this observation implies that vibration
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effect on the punch average velocity than that in the results in Figure 13a. However, the actual results frequency exerts an on frictional stress reduction rather average velocity. shown in Figures 7 additional and 8 wereeffect the reverse, and shear this observation implies thatthan vibration frequency Materials 2018, 11, x FOR PEER REVIEW 11 of 13 The surface morphology results shown in Figure 10 reveal that increasing vibration frequency exerts an additional effect on frictional shear stress reduction rather than average velocity. The reduces surface the number of surface scratches, indicating that the reciprocation movement between the workpiece morphology results shown in Figure 10 reveal that increasing vibration frequency reduces the number frequency exerts an additional effect on frictional shear stress reduction rather than average velocity. and die the indicating lubrication condition. Thus,10 the higher frequency is, the more obvious the of surface scratches, that the reciprocation movement between the workpiece andreduces die altered The altered surface morphology results shown in Figure reveal that the increasing vibration frequency effect is. This process is illustrated by Figure 14. Numerous asperities were randomly distributed the numbercondition. of surface Thus, scratches, the reciprocation movement theis. workpiece the lubrication the indicating higher thethat frequency is, the more obviousbetween the effect This process and die the altered the14. lubrication condition. Thus, the randomly higher the distributed frequency is,throughout the more obvious the tool throughout workpiece surface. During plastic deformation without vibration, the workpiece rigid is illustrated by Figure Numerous asperities were the effect is. This process is illustrated by Figure 14. Numerous asperities were randomly distributed compressed the workpiece and flattened the asperities. Lubricant oil was sealed in the pits andand an surface. During plastic deformation without vibration, the rigid tool compressed the workpiece throughout the workpiece surface.inDuring plastic deformation without vibration, forming the rigidprocess, tool extremely thin lubricant film formed the interface. During the vibration-assisted flattened the asperities. Lubricant oil was sealed in the pits and an extremely thin lubricant filma the and flattened the asperities. Lubricant oildirection was sealed in the pits and an rigid compressed tool inworkpiece an oscillation mode, and the relative velocity between workpiece formed in moved the interface. During the vibration-assisted forming process, a rigid toolthe moved in an extremely thin lubricant film formed in the interface. During the vibration-assisted forming process, a and die changed rapidly. The lubricant oil sealed in the microvalley was dragged out, and the oscillation mode, andinthe velocity between the workpiece and diethe changed rapidly. rigid tool moved anrelative oscillation mode, direction and the relative velocity direction between workpiece lubricant film oil in the interface increased because of the vibration. infilm vibration frequency The lubricant sealed in theThe microvalley was dragged andThe theincrease lubricant in the and die changed rapidly. lubricant oil sealed in theout, microvalley was dragged out, andinterface the raisedlubricant thebecause number of attempts for dragging out the lubricant oil from the pits. These notions explain increased of the vibration. The increase in vibration frequency raised the number of attempts film in the interface increased because of the vibration. The increase in vibration frequency why increase in frequency results in decreased load. for dragging the lubricant the pits. These notions explain why increase frequency raised theout number of attemptsoil forfrom dragging out the lubricant oil from the pits. These notionsinexplain why in frequency results in decreased load. results in increase decreased load.
Figure 13. Influence of vibration frequency (a) and vibration amplitude (b) on the punch average
Figure 13. 13. Influence of vibration vibration frequency (a) (a) and and vibration vibration amplitude amplitude (b) (b) on on the the punch punch average average Figure velocity during vibration-assisted clutch hub forming. velocity during vibration-assisted clutch hub forming. velocity during vibration-assisted clutch hub forming.
Figure 14. Comparison of lubrication during vibration-assisted forming with and without vibration: (a) Before forming; (b) Without vibration; (c) With vibration.
Figure 14. 14. Comparison Comparison of of lubrication lubrication during during vibration-assisted vibration-assisted forming with and without vibration: Figure (a) Before Beforeforming; forming;(b) (b)Without Withoutvibration; vibration;(c) (c)With Withvibration. vibration. (a)
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5. Conclusions An improved vibration-assisted clutch forming method was proposed. The effects of vibration frequency and vibration amplitude on forming load reduction and surface quality were investigated by experimental methods. The main conclusions of this study are as follows: (1) (2) (3)
(4)
Increases in vibration frequency and amplitude positively affect forming load reduction. The effect of vibration frequency on the load drop was greater than that of the vibration amplitude. The forming load decreased with increasing vibration amplitude because the increase in vibration amplitude improved the relative speed between the workpiece and the blank and weakened the adhesion in the interface. The increase in vibration frequency raises the number of attempts for dragging out lubricant oil from the pits and in turn greatly widens the lubricant film thickness. The 3D microscope results confirmed this notion.
The range of vibration frequency and amplitude during experimental study were 10~30 Hz and 0.2~0.6 mm, respectively. The validity of the conclusions obtained in this paper is limited to the above conditions. This paper presented a basic explanation for the load reduction during vibration-assisted clutch forming. Nevertheless, a more rigorous and theoretical model must be developed in future research. Author Contributions: D.M. and S.Z. conceived and designed the experiments; D.M. and C.Z. performed the experiments; D.M., X.Z., and S.Z. analyzed the data; S.Z. contributed reagents/analysis tools; and D.M. wrote the paper. Funding: This research was funded by the National Natural Science Foundation of China for Key Program (Grant No. 51335009), as well as the Natural Science Foundation of Jiangsu Province, China (Grant No. BK20140407). Conflicts of Interest: The authors declare no conflict of interest.
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