1、Procedia Engineering 29 (2012) 1486 1491 1877-7058 2011 Published by Elsevier Ltd. doi:10.1016/eng.2012.01.160 Available online at 2012 International Workshop on Information and Electronics Engineering (IWIEE) An Investigation on the Impact Noise of a Six-Bar Linkage Mechanical Press Yanxin Luo

2、a*, Ruxu Dub a State Key Lab of Mechanical Transmission, Chongqing University, Chongqing, 400044, China. b The Institute of Precision Engineering, The Chinese University of Hong Kong, Shatin, N. T., Hong Kong Abstract Conventional mechanical press consisted of crack and slider is one of the most com

3、monly used for stamping. But it cannot satisfy deep drawing operations, in which long dwelling time in the BDC is desirable to avoid crack or wrinkle. This motives the design of a six-bar linkage for the mechanical press. However, the working noise is introduced by the new mechanism. This paper pres

4、ents a systematics study on the noise of the mechanical press. A combination of noise signature analysis, rigid body dynamics analysis and finite element method (FEM) are adopted to investigate the root cause of the noise. It is found that the noise is caused by the collation of the gears. Finally,

5、an improved design is then proposed and some suggestions are given to reduce the noise. 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Harbin University of Science and Technology Keywords: Six-bar mechanical press, Signature analysis, Impact noise, Finite elemen

6、t method (FEM) 1. Introduction Conventional mechanical press consisted of crack and slider is one of the most commonly used for stamping. Its trajectory is not controllable at the bottom dead centre (BDC), and hence it cannot satisfy the diverse needs 1. For example, long dwelling time in the BDC is

7、 desirable to avoid crack or wrinkle for deep drawing operations 2. This motives the design of the five-, six-, nine- bar linkage for the * Corresponding author. Tel.: +86-23-65106999; fax: +86-23-65105795 E-mail address: 1487Yanxin Luo and Ruxu Du / Procedia Engineering 29 (2012) 1486 1491 mechanic

8、al press 3, 4. In general, in the design of a mechanical metal forming press, designers concern mostly the kinematics 5. Few have studied the dynamics of the press, though it is very important its performance 6. When a commercial press is designed and built, its necessary to investigate its performa

9、nce and make continuous improvements. In this research, a six-bar linkage (including a four-bar linkage and a crank-slider mechanism) has been adopted to build a commercial mechanical press with the capability of max loading of 300ton. Design engineers had carefully checked the kinematics of the pre

10、ss and the manufacturing and assemblies were done within the design specification and therefore the press works fine. Though, the press generates loud noise with and without loading. The sound intensity is higher than 90db, which causes various concerns, such as the reliability of the machine and th

11、e safety of the operator. The mechanism of the driveline is illustrated in Fig. 1 (a), and its CAD model is shown in Figure 1(b). It consists of seven parts: a motor (not shown in the figure) that connects to the flywheel through the high speed shaft, a reduction gear set (which includes the high sp

12、eed gear and the low speed gear), a coupler that controls the engagement of the gear set and the crank, a crank-slider mechanism, and a four bar mechanism that connects to the slider. Among them, the four bar mechanism is the key as it doctrines the dynamic performance of the press. L1=45mm L2= 165m

13、m L3=208mm L4= 260mm L5=80010000mm e=80mm Fig. 1. (a) Illustration of the six-bar linkage mechanism; (b) the physical model of the mechanism This paper aims to find the root cause(s) of the noise. The presented research will investigate the noise from various aspects and provide improvement solution

14、s. The rest of this paper is organized as follows. The signature analysis of noise is presented in Section 2. In Section 3, the dynamics of the system is studied by rigid-body dynamics analysis and FEM. In Section 4, an improved design is proposed to reduce the impact noise. Finally, conclusions are

15、 given in Section 5. 2. Signature analysis of noise signal 2.1. Experimental setup As mentioned earlier, the noise is the major concern of the design. The first step is to analyze the noise signal. The sound signal was measured using a microphone placed closely to the press. Figure 2 shows the exper

16、imental setup, the main apparatuses include a microphone (Manufacturer: Brel and (c) the impact frequency is 23 Hz. It is necessary to analyze the dynamics of the drive system to find the root cause of the noise. 3. Dynamics analysis 3.1. Impact force analysis To investigate the sources of the noise

17、, the dynamic model of the system is necessary for further investigation of mechanical, which may reflect real working conditions, should be constructed for an accurate loading analysis. In this research, the dynamic analysis of the press is carried using a commercial software system RecurDyn. All j

18、oint force between the linkages are obtained by this simulation, among which the contact force between the gears is attracted our interesting. Fig. 7 shows the contact force (in black) between the gears, and its differentiation (in orange). Examining the differentiation of the force, it is seen that

19、 the contact force quickly changes its direction twice, in A and B, when the punch is moving up. This is very likely to create two big shocks. Consequently, a loud noise will be generated. Differetiation (N/s) Punch position (mm) Gear Force(N) Fig.7. Impact force between the gears In order to furthe

20、r investigate the frequency components in the noise signal, though, Finite Element Analysis (FEA) is necessary. 3.2. Natural frequencies of the mechanical components Its well known that the vibration is usually caused by the vibration of structure, and therefore, its necessary to find the natural fr

21、equency of the structure. The analytical method can be used to find the natural frequency. However, it is not precise because of the assumptions. In practical, FEA is a variable method to find the precisely solution of differential equations for verifying the vibration of a structure. There is some

22、commercial software for FEA such as Abaqus, Ansys, Nastran, and etc7, 8. In this research, we used Abaqus to find the natural frequencies of the mechanical components as shown in Table 1. Also, the first mode shape of the high speed shaft is torsion, which is in the same direction of the torque. It

23、is believed that this mode is responsible for repetitive frequency of 23 Hz. And the fourth AB B A 1490 Yanxin Luo and Ruxu Du / Procedia Engineering 29 (2012) 1486 1491 natural frequency of high speed gear and the second natural of low speed gear are close to the mainly frequency of the noise. More

24、over, the corresponding mode shape is bending of the gear tooth. Therefore, the gear tooth should be further investigated. Fig. 8(a) shows the FEA model of the low speed gear. The loading is applied to one of the teeth. The applied loading is a normalized force of 1 unit, in the frequency range from

25、 1 Hz to 1,500 Hz. Fig. 8(b) shows results of the frequency response. From the figure, it is seen that the gear has three main frequencies at 480Hz, 740Hz, and 1,350 Hz respectively. The largest frequency component is at 740 Hz. It is believe that this frequency is responsible for the loud noise. Th

26、e discrepancies between the FEA frequency (740 Hz) and actual noise frequency (780 Hz) may be attributed to the simplification of the FEA model. In conclusions, we believe the loud noise is generated by the collision of the gears, and the noise can be reduced by eliminating of the gear clearance. Ta

27、ble 1. Modal frequencies of the main components of the press (Hz) Fig. 8 (a) FEM model of the gear pinion (b) frequency response 4. An improved design Based on the analysis result presented earlier, the length of the linkages should not be change as to keep the trajectory of the design. Also, the in

28、ertia of the flywheel and the stiffness of the high speed shaft etc., can also be fine-tuned to reduce the noise. However, these solution is not effective because of the mechanical components has small room for improving the design due to the strength constraints. Its an option to improve the design

29、 by eliminating the clearance between the gears. The proposed design is shown in Fig. 9. There are two gears mounted on the high speed shaft to eliminate the gear clearance. In this design, two set of gear pair are utilized and one spiral spring will mounted between the gears to eliminate the gear c

30、learance. The first set of gear pair will transmit the torque to the crank shaft for the case of the torque is in clockwise direction. When the torque changes its direction, the second set of gear pair works. Therefore, its believed that the design will reduce the noise effectively. However, the dyn

31、amics analysis is needed for the new design model in the future. Mode 1st 2nd 3rd 4th 5th 6th High speed shaft 24.2 29.7 54.8 285.3 581.0 1035.4 High speed gear 67.3 360.5 466.1 753.0 892.9 1189.0 Low speed gear 593.1 619.0 1147.8 1205.3 1278.0 1477.0 Upper linkage 67.0 74.7 80.5 102.6 185.2 282.4 1

32、491Yanxin Luo and Ruxu Du / Procedia Engineering 29 (2012) 1486 1491 Fig. 9. An improved design of the gear pair for eliminating the gear clearance 5. Conclusions This paper presents a study on the noise of a six-bar mechanical press. Based on the discussions above, following conclusions can be draw

33、n: The mechanical noise of the press contains a number of components corresponding to the natural frequencies of various components of the press. The noise is generated when the impact occurs. The impact is a result of the four bar mechanism that generates variable speed during the operation. The va

34、riable speed generates variable force, causing the gears impact on each other. Its an option to avoid the clearance between the gear pairs to reduce the noise. The combination of the signature analysis, mechanical dynamics analysis and FEM is effective method to analyze the root cause of machine faults. In addition to the application presented above, it can be used for many other applications that involve mechanical motion. Acknowledgements This research is partially supported by the Natural Science Foundat