軸承保持架零件的沖壓模具設(shè)計（含CAD圖紙和說明書）
軸承保持架零件的沖壓模具設(shè)計（含CAD圖紙和說明書）,軸承,保持,維持,零件,沖壓,模具設(shè)計,cad,圖紙,以及,說明書,仿單
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 Technol,(1990)8:17-22
1990施普林格出版社紐約公司
文章摘要：我們用一臺多工位自動壓力機來研究沖壓模具的變形過程，其中包括突然換位，校準特征等一系列的過程。模具載荷實驗實際上是對12個工位使用新的負載監(jiān)控后的測量（其測量的數(shù)值將會輸入計算程序）。再基于有限元法對沖壓模具進行分析（其中有限元法需要用到一個計算代碼和MSC/NASTRAN分析軟件）。這樣后再將分析擴展到其他的模具，特別是那些高負載的沖模。應(yīng)力和變形是用來評估模具載荷對稱還是非對稱的條件，根據(jù)我們對模具獨立的分析發(fā)現(xiàn)在模具的應(yīng)力和變形只要是輕度的那這個模具還是好的。然而這種情況在當沖壓模具最終和壓力機成為一個整體后也是可能會變化的。
簡介：
鈑金零件需要拉伸，剪切，彎曲，和擠壓等一系列的操作，所有這些操作的進行都會被安置在多工位自動壓力機上。材料是通過給料機送入壓坯，在操作中材料通過同步機制的滑塊運動從一個位置運動到下一個位置。在生產(chǎn)中每一個模具都是一個獨立的單位，其都可以在主滑動上進行單個調(diào)整。如圖1所示一個用熱軋鋼板做的汽車零件其不需要退火的12個加工步驟。
圖1：一個沖壓零件
壓力機主要用于生產(chǎn)不同類型的汽車和飛機零部件和家電，不同的多工位自動壓力機其生產(chǎn)速率大約在500到1500每小時。雖然以這種速度生產(chǎn)是快速的，但往往緊密的公差尺寸很難實現(xiàn)。此外，機器在每個沖程中在偏心載荷的作用下同時在幾個模具上進行不同的操作，因此，在某一個位置上的沖壓載荷會影響工作線上其他操作的執(zhí)行。另外一個實踐問題就是把所有的模具正確的安裝到壓力機上的大量的時間問題。因此，本研究的目標是研究當壓力機和模具聯(lián)合作為一個整體時結(jié)構(gòu)特點。在本文中，將會展示那些研究模具問題的實驗和計算過程，還有單獨對壓力機結(jié)構(gòu)特點的分析。
我們將會用一種由12個工位組成的壓力機來分析。一般典型的模具問題有過度變形，傾斜，和上下半模錯位，不適當?shù)木彌_和偏心載荷會引起模具的傾斜和錯位。傾斜和過度變形也可能是由模套與模具本身的剛度不足而造成的。這些模具問題將會對所生產(chǎn)的部分產(chǎn)品有很大的影響。還有很多其他的參數(shù)，如模具設(shè)計，摩擦與潤滑沿模具的工作界面的摩擦，速度，等等。這些問題的解決將會在生產(chǎn)中發(fā)揮很大的作用。實際上，分析應(yīng)在結(jié)合模具設(shè)計及工作材料的變形特性下進行，譬如彈塑性的硬化加工。在這個研究中，工件的大面積塑性變形不作考慮。
大面積的拉伸變形過程是由于對建模過程的彈塑性硬化的計算代碼的錯誤。實驗室實驗進行的各種商業(yè)材料使用的半球形沖頭。沿穿孔板的界面摩擦系數(shù)實際上是在實驗測量和作為邊界的數(shù)值模型。雖然得到了很好的解決方案，實現(xiàn)了數(shù)值分析是沿界面摩擦條件非常敏感。在最近的工作中，一種新的基于細觀接觸摩擦模型被發(fā)明[ 5 ]。在目前的問題，在使用復(fù)雜的幾何結(jié)構(gòu)的模具，有幾個操作如拉深，少數(shù)減少的繪圖操作，和模壓。資源的持續(xù)時間都不足以研究這些非線性問題。因此，初步的研究僅限于模具基于線性應(yīng)力分析問題。
基于有限元方法通過利用MSC／NASTRAN代碼對模具進行了一個詳細的分析。在所有使用新的負載監(jiān)控站對模具載荷進行了測定。這樣的測量數(shù)據(jù)運用在數(shù)值模型中來評估模具的正常工作條件下和非對稱載荷狀況的應(yīng)力和變形。在模具傾斜中非對稱載荷也是應(yīng)被分析的。在實踐中，人們習慣于追求的試驗和錯誤的程序，如放置墊片在模具或調(diào)整墊壓模對準正確的問題。這種耗時的任務(wù)，可以在這里提供的計算和實驗程序減少甚至消除使用。
模具的形狀和材料
金屬沖壓模具的設(shè)計是一個不精確的過程。在試模中有相當多的試驗和錯誤，往往需要進行可接受的零件調(diào)整來完成一個模具。它不僅涉及到模具材料的正確選擇，而且還有尺寸。為了能夠承受壓力，模具必須有適當?shù)臋M截面積與間隙，半徑，內(nèi)圓角，和橫截面的突變會對模具壽命產(chǎn)生有害的影響。在這項工作中，對模具的現(xiàn)有的設(shè)置進行了分析。
模具是用高碳，高鉻工具鋼做的。這個工具鋼材料的硬度在羅克韋爾C 57至60的范圍內(nèi)。通過涂層模具氮化鈦和碳化鈦大大提高耐磨性。模具的制成還有其他幾種合金鋼如SAE 4140。一個典型的沖壓模具的幾何形狀是軸對稱的但根據(jù)操作不同每個模具也是有略微不同的。關(guān)于減少拉深模具的幾何形狀和材料的詳細信息被收集于設(shè)計圖中。通過使用一個預(yù)處理程序轉(zhuǎn)載成3d幾何圖形，Patran。一個象限的模具，如圖2所示。數(shù)據(jù)包括模具材料的幾何形狀和模具的彈性性質(zhì)。
所使用的工作材料是鋁合金，SAE 1008，鋼的厚度約為4.5的RAM。沖壓件在陰暗的地方使用或一些不必要完好完成的部分通常是用熱軋鋼板來制作。該模具生產(chǎn)的汽車是一個變矩器蓋。鋁合金的主要優(yōu)勢是它的最小應(yīng)變時效。
實驗程序
如前所述，本研究涉及數(shù)值模型中使用的模具載荷的監(jiān)測，staldy模具的結(jié)構(gòu)特點。另一個優(yōu)點是避免模具在正式工作中超載。偏心加載可以被檢測到，并設(shè)置時間可以減少。因此材料厚度的變化，模具的鈍化，不平衡負載，或超載都可以使通過模具載荷監(jiān)控方法檢測。
IDC公司提供了基于應(yīng)變的菲亞特負載細胞制成優(yōu)質(zhì)工具鋼材料。四個相同的傳感器被嵌入在一個厚矩形板，如圖3所示。他們被校準在實驗室和工廠。板被放置在模具的頂端。敲出來的銷板中的孔滑過。六個這樣的板被放置在每個模具上。在這種方式中，24個讀數(shù)，可以在給定的時間內(nèi)得到。然后他們通過完整的數(shù)據(jù)被轉(zhuǎn)移到其他六個模具。所有12個模具載列于表1。
圖2：模具的幾何形狀（一個象限）
圖3：四個負載組鑲嵌于一個厚的板料中
計算程序
通過采用有限元方法的線性靜態(tài)分析的方法研究了對稱和非對稱載荷的影響這一問題。通過使用圖形處理器建立了模具站4有限元模型，Pa
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