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編號
無錫太湖學(xué)院
畢業(yè)設(shè)計(jì)（論文）
相關(guān)資料
題目： 軸承保持架沖壓模具設(shè)計(jì)
機(jī)電 系 機(jī)械工程及自動(dòng)化專業(yè)
學(xué) 號： 0923181
學(xué)生姓名： 呂金勇
指導(dǎo)教師： 黃敏（職稱：副教授）
2013年5月25日
無錫太湖學(xué)院
畢業(yè)設(shè)計(jì)（論文）
開題報(bào)告
題目： 軸承保持架沖壓模具設(shè)計(jì)
機(jī)電 系 機(jī)械工程及自動(dòng)化 專業(yè)
學(xué) 號： 0923181
學(xué)生姓名： 呂金勇
指導(dǎo)教師： 黃敏 （職稱：副教授）
2012年11月25日
課題來源
自擬。
科學(xué)依據(jù)（包括課題的科學(xué)意義；國內(nèi)外研究概況、水平和發(fā)展趨勢；應(yīng)用前景等）
（1）課題科學(xué)意義
隨著與國際接軌的腳步日益放慢,市場競爭的日益加劇,人們對模具的各種要求也不斷的加大.可以說模具制造技術(shù)是用來衡量一個(gè)國家工業(yè)發(fā)展水平的重要標(biāo)志。則現(xiàn)階段的工業(yè)生產(chǎn)中，模具是一種非常重要的工藝裝備。其在各個(gè)行業(yè)中也演繹著非常重要的角色，其運(yùn)用于汽車、機(jī)械、航天、航空、輕工、電子、電器、儀表等行業(yè)。在我國的模具行業(yè)中有50%的是沖壓模具，足以看出沖壓模具之重要。所以現(xiàn)階段對于沖壓模具的研究也是非常有必要的。
軸承保持架沖壓模具的研究狀況及其發(fā)展前景
隨著計(jì)算機(jī)技術(shù)的發(fā)展和普及，沖壓模具也基本實(shí)現(xiàn)了計(jì)算機(jī)化，其中使用最多的是cad軟件。抽高壓模具的計(jì)算機(jī)化也是日益發(fā)展趨勢下不可避免的。近些年來各種多軸數(shù)控機(jī)床，激光切割機(jī)床數(shù)控雕刻機(jī)床等等紛紛面世，這些設(shè)備在提高模具的數(shù)量，規(guī)模和制造能力上的作用是不可估量的。還有其中快速成形技術(shù)和快速模具技術(shù)這兩種先進(jìn)的制造技術(shù)也越來越廣泛的應(yīng)用于模具行業(yè)。
中國的模具行業(yè)每年都保持著25%的增長率，其行業(yè)的生產(chǎn)能力也僅次于美國日本，位列世界第三。其行業(yè)生產(chǎn)能力約占世界總量的10%。
然而, 與國際先進(jìn)水平相比, 中國的模具行業(yè)的差距不僅表現(xiàn)在精度差距大、 交貨周期長等方面, 模具壽命也只有國際先進(jìn)水平的 50% 左右。大型、精密、技術(shù)含量高的轎車覆蓋件沖壓模具和精密沖裁模具是現(xiàn)階段最需要解決的問題。綜上由于市場需求模具的現(xiàn)階段發(fā)展快速，應(yīng)用廣其前景也是也是非?？春玫摹?
研究內(nèi)容
①了解沖壓加工的工作原理，國內(nèi)外的研究發(fā)展現(xiàn)狀；
②完成軸承保持架沖壓模具的總體方案設(shè)計(jì)；
③完成有關(guān)零部件的選型計(jì)算、結(jié)構(gòu)強(qiáng)度校核及液壓系統(tǒng)設(shè)計(jì)；
④熟練掌握有關(guān)計(jì)算機(jī)繪圖軟件，并繪制裝配圖和零件圖紙，折合A0紙不少于3張；
⑤完成設(shè)計(jì)說明書的撰寫，并翻譯外文資料1篇。
擬采取的研究方法、技術(shù)路線、實(shí)驗(yàn)方案及可行性分析
沖壓是一種利用壓力加工的方法，就是壓力機(jī)上裝上模具對材料施加壓力。使材料分離或者變形形成合格的所需產(chǎn)品。
沖壓模具材料的確定是一開始必須要確認(rèn)的，其次是沖壓模具的結(jié)構(gòu)設(shè)計(jì)分沖壓工藝的確定和模具結(jié)構(gòu)的設(shè)計(jì)兩個(gè)方面，則需從這兩個(gè)方面入手。最后是對模具的壓力計(jì)算還有軟件模擬。
研究計(jì)劃及預(yù)期成果
研究計(jì)劃：
2012年11月17日-2013年1月13日：按照任務(wù)書要求查閱論文相關(guān)參考資料，填寫畢業(yè)設(shè)計(jì)開題報(bào)告書,學(xué)習(xí)并翻譯一篇與畢業(yè)設(shè)計(jì)相關(guān)的英文材料。
2013年1月11日-2013年3月5日：指導(dǎo)員實(shí)訓(xùn)。
2013年3月8日-2013年3月14日：查閱與設(shè)計(jì)有關(guān)的參考資料不少于10篇，其中外文不少于5篇,翻譯機(jī)械方面的外文資料。
2013年3月15日-2013年3月21日：軸承保持架工藝分析。
2013年3月22日-2013年4月11日：初步繪制裝配圖和修改完成。
2013年4月12日-2013年4月25日：對凹凸模尺寸計(jì)算，繪制凹凸模及各零件。
2013年4月26日-2013年5月21日：繪制上下模及其各零件，完成設(shè)計(jì)說明書（論文）、摘要和小結(jié)，修改設(shè)計(jì)說明書開題報(bào)告格式，整理所有資料，打印后上交，準(zhǔn)備答辯。
預(yù)期成果。
特色或創(chuàng)新之處
① 沖模的使用便于生產(chǎn)自動(dòng)化，操作簡單，生產(chǎn)率提高。
② 減少制作軸承保持架的材料。
已具備的條件和尚需解決的問題
① 已找到大量相關(guān)資料文獻(xiàn)，對軸承保持架零件有相關(guān)認(rèn)識(shí)。
② 沖壓工藝的加工工序
指導(dǎo)教師意見
指導(dǎo)教師簽名：
年 月 日
教研室（學(xué)科組、研究所）意見
教研室主任簽名：
年 月 日
系意見
主管領(lǐng)導(dǎo)簽名：
年 月 日
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 o
Abstract:
Experimental and computational procedures for studying deflections, flit, andalignment characteristics of a sequence of stamping dies, housed in a transfer 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 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. However, 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. 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 synchronized 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 different 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, the 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 stations. 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 computational 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 the 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 are 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 the 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 based 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 prescribed 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]. 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 was 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 and 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 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 trial-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 and 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 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 axisymmetric 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 shown 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 deisgn 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 involved 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 stock, 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 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 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 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 Loads
Die Station Load
Number (kN)
1 356
2 641
3 214
4 356
5 854
6 712
7 285
8 32O
9 2349
10 1139
11 214
12 2100
spectrum of capabilities, of which linear static analysis is discussed 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 displacements 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, 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 created 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, half 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 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 the 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 die 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 cases 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 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 distributed 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 were
of the same order, but they decreased in magnitude at the nodes away from this critical 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 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 stresses 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. The 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 produce 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 asymmetric 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 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 symmetric case.
Fig. 5. Displacement contours in the loading direction. (A) Symmetric case (one quadrant of the
die). (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 procedure, 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 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 the
integration of the structural analysis of stamping dies with that of the transfer press as a total system.
ACKNOWLEDGMENTS
Professor J.G. Eisley, W.J. Anderson, and Mr. D.Londhe are thanked for their comments on this paper.
REFERENCES
1. R.S. Rao and A. Bhattacharya, "Transfer Process De-flection, Parallelism, and Alignment Characteristics,"Technical Report, January 1988, Department of Mechanical Engineering and 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, Parallelism, 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, 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, No. 1, 1990
中文譯文
沖壓模具的受力分析
R.S.Rao
J.Mater.Shaping Tec
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