【机械类文献翻译】冲压模具的受力分析

1、机械专业中英文文献翻译英文原文 stress analysis of stamping dies j. mater. shaping technoi. (1990) 8:17-22 9 1990 springer-verlag new york inc. r . s . r a oabstract: experimental and computational procedures for studying deflections, flit, andalignment characteristics of a sequence of stamping dies, housed in a tr

2、ansfer press, are pre-sented. die loads are actually measured at all the 12 die stations using new load monitors and used as input to the computational procedure. a typical stamping die is analyzed using a computational code, msc/nastran, based on finite element method. the analysis is then extended

3、 to the other dies, especially the ones where the loads are high. stresses and deflections are evaluated in the dies for the symmetric and asymmetric loading conditions. based on our independent die analysis, stresses and deflections are found to be reasonably well within the tolerable limits. howev

4、er, this situation could change when the stamping dies are eventually integrated with the press as a total system which is the ultimate goal of this broad research program. introduction sheet metal parts require a series of operations such as shearing , drawing , stretching , bending , and squeezing

5、. all these operations are carried out at once while the double slide mechanism descends to work on the parts in the die stations, housed in a transfer press 1. material is fed to the press as blanks from a stock feeder. in operation the stock is moved from one station to the next by a mechanism syn

6、chronized with the motion of the slide. each die is a separate unit which may be independently adjusted from the main slide. an automotive part stamped from a hot rolled steel blank in 12 steps without any intermediate anneals is shown in figure 1. transfer presses are mainly used to produce differe

7、nt types of automotive and aircraft parts and home appliances. the economic use of transfer presses depends upon quantity production as their usual production rate is 500 to 1500 parts per hour 2. although production is rapid in this way, close tolerances are often difficult to achieve. moreover, th

8、e presses produce a set of conditions for off-center loads owing to the different operations being performed simultaneously in several dies during each stroke. thus, the forming load applied at one station can affect the alignment and general accuracy of the operation being performed at adjacent sta

9、tions. another practical problem is the significant amount of set-up time involved to bring all the dies into proper operation. hence, the broad goal of this research is to study the structural characteristics of press and dies combination as a total system. in this paper, experimental and computati

10、onal procedures for investigating die problems are presented. the analysis of structural characteristics of the transfer press was pursued separately 3. a transfer press consisting of 12 die stations was chosen for analysis. typical die problems are excessive deflections, tilt, and misalignment of t

11、he upperand lower die halves. inadequate cushioning and offcenter loading may cause tilt and misalignment of the dies. tilt and excessive deflections may also be caused by the lack of stiffness of the die bolster and the die itself. part quality can be greatly affected by these die problems. there a

12、re a lot of other parameters such as the die design, friction and lubrication along the die work interface, speed, etc. that play a great role in producing consistently good parts. realistically, the analysis should be carded out by incorporating the die design and the deforming characteristics of t

13、he work material such as the elastic-plastic work hardening properties. in this preliminary study, the large plastic deformation of the workpiece was not considered for the reasons mentioned below. large deformation modeling of a sheet stretching process was carded out using the computational code b

14、ased on an elastic-plastic work hardening model of the deformation process 4. laboratory experiments were conducted on various commercial materials using a hemispherical punch. the coefficient of friction along the punch-sheet interface was actually measured in the experiment and used as a prescribe

15、d boundary to the numerical model. although a good solution was obtained, it was realized that the numerical analysis was very sensitive to the frictional conditions along the interface. in the most recent work, a new friction model based on the micromechanics of the asperity contact was developed 5

16、. in the present problem, there are several operations such as deep drawing, several reduction drawing operations, and coining, which are performed using complex die geometries. the resources and the duration of time were not adequate to study these nonlinear problems. hence,the preliminary study wa

17、s limited to die problems basedon linear stress analysis. a detailed die analysis was carried out by using msc /nastran code based on finite ele mentmethod. die loads were.measured at all the stations using new load monitors. such measured data were used in the numerical model to evaluate stresses a

18、nd deflections in the dies for normal operating conditions and for asymmetric loading conditions. asymmetric loading conditions were created in the analysis by tilting the dies. in real practice, it is customary to pursue trial-and-error procedures such as placing shims under the die or by adjusting

19、 the cushion pressure to correct the die alignment problems. such time consuming tasks can be reduced or even eliminated using the computational and experimental procedures presented here. die geometry and materials the design of metal stamping dies is an inexact process. there are considerable tria

20、l-and-error adjustments during die tryout that are often required to finish the fabrication of a die that will produce acceptable parts. it involves not only the proper selection of die materials, but also dimensions. in order to withstand the pressure, a die must have proper cross-sectional area an

21、d clearances. sharp comers, radii, fillets, and sudden changes in the cross section can have deleterious effects on the die life. in this work, the analysis was done on the existing set of dies. the dies were made of high carbon, high chromium tool steel. the hardness of this tool steel material is

22、in the range of rockwell c 57 to 60. resistance to wear and galling was greatly improved by coating the dies with titanium nitride and titanium carbide. the dies were supported by several other steel holders made of alloy steels such as sae 4140. the geometry of a typical stamping die is axisymmetri

23、c but it varies slightly from die to die depending on the operation. detailed information about geometry andmaterials of a reduction drawing die (station number 4) was gathered from blueprints. it was reproducedin three-dimensional geometry using a preprocessor, patran. one quadrant of the die is sh

24、own in figure2. the data including geometry and elastic properties of the die material were fed to the numerical model. the work material used was hot rolled aluminumkilled steel, sae 1008 a-k steel and the blank thickness was about 4.5 ram. stampings used in unexposed places or as parts of some dei

25、sgn where fine finish is not essential are usually made from hot rolled steel. the automotive part produced in this die set is a cover for a torque converter. a principal advantage of aluminum-killed steel is its minimum strain aging.experimental procedures as mentioned earlier, this research involv

26、ed monitoting of die loads which were to be used in the numerical model to staldy the structural characteristicsof dies. the other advantage is to avoid overloadingthe dies in practice. off-center loading can be detected and also set-up time can be reduced. thus, any changes in the thickness of stoc

27、k, dulling of the die,unbalanced loads, or overloadings can be detected using die load monitors. strain gage based fiat load cells made of high grade tool steel material were fabricated and supplied by idc corporation. four identical load cells were embedded in a thick rectangular plate as shown in

28、figure 3. they were calibrated both in the laboratory and in the plant.the plate was placed on the top of the die. the knockout pin slips through the hole in the plate. six such plates were placed on each of six dies. in this way,24 readings can be obtained at a given time. then they were shifted to

29、 the other six dies for complete data. all the 12 die loads are presented in table 1.computational procedures linear static analysis using finite element method wasused to study the effect of symmetric and asymmetric loading for this problem. a finite element model of die station 4 was created using

30、 the graphical preprocessor, patran, and the analysis was carried outusing the code msc/nastra n . the code has a wide t a b l e i. die loadsdie station loadnumber (kn)1 3562 6413 2144 3565 8546 7127 2858 32o9 234910 113911 21412 2100spectrum of capabilities, of which linear static analysis is discu

31、ssed here. the nastran code initially generates a structural matrix and then the stiffness and the mass matrices from the data in the input file. the theoretical formulations of a static structural problem by the displacement method can be obtained from the references 6. the unknowns are displacemen

32、ts and are solved for the appropriate boundary conditions. strains are obtained from displacements. then they are converted into stresses by using elastic stress-strain relationships of the die material. the solution procedure began with the creation of die geometry using the graphical preprocessor,

33、 patran. the solution domain was divided into appropriate hyper-patches. this was followed by the generation of nodes, which were then connected by elements. solid hexa elements with eight nodes were used for this problem. the nodes and elements were distributed in such a way that a finer mesh was c

34、reated at the critical region of the die-sheet metal interface and a coarser mesh elsewhere. the model was then optimized by deleting the unwanted nodes. the element connectivities were checked. by taking advantage of the symmetry, only one quarter of the die was analyzed. in the asymmetric case, ha

35、lf of the die was considered for analysis. although, in practice, the load is applied at the top of the die, for the purpose of proper representation of the boundary conditions to the computational code, reaction forces were considered for analysis. the displacement and force boundary conditions are

36、 shown for the two cases infigure 4.as mentioned earlier, sheet metal was not modeled in this preliminary research. as shown in figure 4(a),the nodes on the top surface of the die were constrained (stationary surface) and the measured load of 356 kn was equally distributed on the contact nodes at th

37、e workpiece die interface. similar boundary conditions for the punch are shown in figure 4(b). it is noticeable that fewer nodes are in contact with the sheet metal due to the die tilt for the asymmetric loading case as shown in figure 4(c). in real practice, the pressure actually varies along the d

38、ie contact surface. since the actual distribution was not known, uniform distribution was considered in the present analysis.discussion of results as described in the earlier section, the numerical analysis of die station 4 (both the die and punch) was performed using the code msc/nastran . two case

39、s were considered, namely: (a) symmetric loading and (b) asymmetric loading fig. 4. boundary conditions. (a) symmetric case (onequadrant of the die). (b) symmetric case (one quadrant ofnthe punch). (c) asymmetric case (half of the die).symmetric loading numerical analysis of the die was carried out

40、for a measured load o f 356 kn as distributed equally in figure 4(a). the major displacements in the loading direction are shown in figure 5(a). these displacement contours can be shown in various colors to represent different magnitudes. the m aximum displacement value is 0.01 m m for a uniformly d

41、istributed load of 356 kn. the corresponding critical stress is very small, 8.4 mpa in the y direction and 30 mpa in the x direction. the calculated displacements and stresses at the surrounding elements and nodes wereof the same order, but they decreased in magnitude at the nodes away from this cri

42、tical region. thus, the die was considered very rigid under this loading condition. symmetric loading was applied to the punch and the numerical analysis was carried out separately. the displacement values in the protruding region of the punch were high compared to the die. the maximum displacement

43、was 0.08 m m . it should be noted that the displacement values in this critical range of the punch were of the same order ranging from 0.05 mm to 0.08 ram. although the load acting on the punch (bottom half) was the same as the die (upper half), that is, 356 kn, the values of displacements and stres

44、ses were higher in the punch because of the differences in the geometry. this is especially true for the protruding part of the punch. the corresponding maxim u m stress was 232 mpa. this part of the punch is still in the elastic range as the yield strength of tool steel is approximately 1034 mpa. t

45、he critical stress value might be varied for different load distributions. since the actual distribution of the load was not known,the load was distributed equally on all nodes. as the die (upper half) is operating in a region which is extremely safe, a change in the load distribution may not produc

46、e any high critical stresses in the die. although higher loads are applied at other die stations(see table 1), it is concluded that the critical stresses are not going to be significantly higher due to the appropriate changes in the die geometries.asymmetric loading for the purpose of analysis, an a

47、symmetric loading situation was created by tilting the die. thus, only 15 nodes were in contact with the workpiece compared to 40 nodes for the symmetric loading case. as shown in figure 4(c), a 356 kn load was uniformly distributed over the 15 nodes that were in contact with the workpiece. although

48、 the pressure was high, because of the geometry at the location where the load was acting, the critical values of displacement and stress were found to be similar to the symmetric case. the predicted displacement and stress values were not significantly higher than the values predicted for the symme

49、tric case.fig. 5. displacement contours in the loading direction. (a) symmetric case (one quadrant of thedie). (b) symmetric case (one quadrant of the punch). (c)asymmetric case (half of the die).conclusions in this preliminary study, we have demonstrated the capabilities of the computational proced

50、ure, based on finite element method, to evaluate the stresses and deflections within the stamping dies for the measured loads. the dies were found to be within the tolerable elastic limits for both symmetric and asymmetric loading conditions. thus the computational procedure can be used to study the

51、 tilt and alignment characteristics of stamping dies. in general, the die load monitors are very useful not only for analysis but also for on-line tonnage control. future research involves theintegration of the structural analysis of stamping dies with that of the transfer press as a total system.ac

52、knowledgmentsprofessor j.g. eisley, w.j. anderson, and mr. d.londhe are thanked for their comments on this paper.references1. r.s. rao and a. bhattacharya, transfer process de-flection, parallelism, and alignment characteristics,technical report, january 1988, department of mechanical engineering an

53、d applied mechanics, the university of michigan, ann arbor.2. editors of american machinist, metalforming: modem machines, methods, and tooling for engineers and operating personnel, mcgraw-hill, inc., 1982, pp. 47-50.3. w.j. anderson, j.g. eisley, and m.a. tessmer,transfer press deflection, paralle

54、lism, and alignment characteristics, technical report, january 1988, department of aerospace engineering, the university of michigan, ann arbor.4. b.b. yoon, r.s. rao, and n. kikuchi, sheet stretching: a theoretical experimental comparison, international journal of mechanical sciences, vol. 31, no.8

55、, pp. 579-590, 1989.5. b.b. yoon, r.s. rao, and n. kikuchi, experimental and numerical comparisons of sheet stretching using a new friction model, asme journal of engineering materials and technology, in press.6. msx/nastran, mcneal schwendler corporation.22 9 j. materials shaping technology, vol. 8

56、, no. 1, 1990中文译文 冲压模具的受力分析 r.s.rao j.mater.shaping technol,(1990)8:17-22 1990施普林格出版社纽约公司 文章摘要：我们用一台多工位自动压力机来研究冲压模具的变形过程，其中包括突然换位，校准特征等一系列的过程。模具载荷实验实际上是对12个工位使用新的负载监控后的测量（其测量的数值将会输入计算程序）。再基于有限元法对冲压模具进行分析（其中有限元法需要用到一个计算代码和msc/nastran分析软件）。这样后再将分析扩展到其他的模具，特别是那些高负载的冲模。应力和变形是用来评估模具载荷对称还是非对称的条件，根据我们对模具独立的分析发现在模具的应力和变形只要是轻度的那这个模具还是好的。然而这种情况在当冲压模具最终和压力机成为一个整体后也是可能会变化的。简介： 钣金零件需要拉伸，剪切，弯曲，和挤压等一系列的操作，所有这些操作的进行都会被安置在多工位自动压力机上。材料是通过给料机送入压坯，在操作中材料通过同步机制的滑块运动从一个位置运动到下一个位置。在生产中每一个模具都是一个独