Design and Development of Sheet Metal Draw Component Using CAE Technology

Transcription

1 Design and Development of Sheet Metal Draw Component Using CAE Technology Y. N. Dhulugade 1, P. N. Gore 2 1 PG Student, Mechanical Dept. DKTE Society s Textile and Engineering institute, Ichalkaranji. India. 1 Senior Engineer Design & Development, Dies and fixtures, Adventtooltech Pvt. Ltd. Pune, India. 2 Associate Professor, Dept. of Mechanical Engineering, DKTE Society s Textile and Engineering institute, Ichalkaranji. India Abstract Achieving high standard quality products in almost no time with great economy in industry demands for a technology that helps exceed the engineering requirement of products. This paper highlights development of draw component and the changes made in product design due to manufacturing and assembly reasons considering the design intent; and also the advantages of using various CAE softwares used in designing draw tools. It helps reducing the complete product development cycle as compared to what happens with conventional methods. Lesser effort and ease to model the complete setup and important features with different design parameters, improved the product development without compromising quality. Thorough attempt is aimed for design sheet metal draw die using the latest technology to make it time and cost effective, identifying the problem areas through analysis results and Based on the analysis prepare the query report and suggest revisions/ modifications in the product design. Finally, work out the best die design to produce defect-free components based on the inputs received. Thus using the CAE software one can design economical die because the design changes, modifications and challenges can be observed and solved in the initial phase of the design only. Otherwise without these efforts the die design and the processing could end up as a costly and complicated assignment. Keywords- Design Intent, economy, FEM simulation, Product Design, sheet metal draw die. I. INTRODUCTION The sheet metal deep drawn technology is one of the most challenging processes in manufacturing. Drawing operation is the process forming a flat piece of material into a hollow shape by means of punch which causes the blank to flow into the die cavity (refer figure 1). The depth of the draw may be shallow, moderate or deep, various geometries and sizes are made by drawing operation, two extreme examples being bottle caps and automobile panels. Typical defects that occur due to incorrect flow of material into the die during the stamping process are wrinkling caused by excessive compression, tearing or splitting caused by excessive tension, and spring back caused by elastic recovery of the material. [6, 7] Fig.1(a) Schematic illustration of the deep drawing process on a circular sheet-metal blank. (b) Variables in deep drawing of a cylindrical cup [10]. II. WHAT IS THE PROBLEM? Tool development for form component is very costly process and it will take lot of time if we go conventionally. So we can use latest technology such as crash analysis during the design phase so that problem areas in forming can be easily pointed out through analysis results which will make our work, time and cost effective. And based on analysis report tool designer can suggest revisions/ modifications in the product design which will help tool designer to design a tool which will produce defect free components based on the inputs received. Without these efforts the die design and the processing could end up as costly and complicated assignment. [1, 5] As shown in fig. 2, draw Component may face challenges such as, Wrinkling, Tearing, Thinning, Springback. Fig.2 Draw component challenges 30

2 While the die designer attempts to design a draw die, the process for drawing entails the use of hydraulic press since the rate of deformation has to be controlled throughout the operation of draw. The draw die should be built to tackle the problem of wrinkling especially prominent at the top corners; tearing along the sides of the corner and the bottom area; while thinning is associated along the corner edges prone to uneven flow. And the problem of spring back may occur due to elastic recovery of material. The rejection amounts to a loss of man hours of the hydraulic press, skilled labor, special material (DD or EDD quality for draw) and other resources directly or indirectly associated with the process. A. Necking Failures Necking failures such as shown in Figure 3 are preceded by localized thinning that may not be visible in the part. [6] B. Material Quality Issues Fig.3 Necking failure of component When drawing operations fail, often the material is immediately blamed. The logic is that if the vendor can supply some material that will run it should be possible to do so consistently. Material formability properties do vary from lot-to-lot, and even within the same coil. Proper deep drawing material should be selected while going for good quality products and error free deep drawing operation. [6] 1. Why The Problem Is So Important Stamping industry applies CAD techniques both in the process planning and die design already for many years. After determining process sequences and process parameters the forming dies are designed using sophisticated CAD systems. However still we don t have any evidence whether the designed tool will provide the right component and as it is die goes for tri-out and automatically it consumes time and cost and it will effects on the final cost of the die. If the die tri-out goes well and component received matching to the requirements, the die will go for production, on the other hand if die tri-out fails and component showing some splitting and wrinkles, die set needs to be reworked. It means firstly rework the die construction by changing the die parameters such as draw radii drawing clearance etc. even if the problem not solved we have to think for new die design and process planning. In some of the cases the development team goes to the product design stage to modify the product parameters so more we go back the design and development costs are increasing indirectly. [5] 2. Conventional Practices for die design and development As shown in following schematic (diagram 4) in previous days the method used for process planning and die designing will becoming costly due to some reasons. Initially the process planning is done when the final product design received from the product designer and after that tool is designed, die construction is made and finally tool is shifted for tri-out this is what conventional method of die design for a particular product. If everything goes well and if the drawn parts matching to the required part then the die is sent to production. On the other hand if triout fails and part showing undesirable results then development team goes for die reworking and if problem not solved after die rework, new die design or new process planning is required, in some cases product design is also changed and in all this activities the lead time go on increasing as well as cost and time. All this happens because problem observed at the last stage of the development. [5] 31

3 Schematic diag.4 3. Solution for the problem: Decreasing the lead time for product development along with the cost and time is the real challenge to the industry but it can be achieved with the latest CAE techniques such as simulation. The schematic diagram for process planning and die design using these techniques is shown below in schematic diag. 5 Efficient use of simulation techniques from the earliest stage of product development to give feedback from each step to make the necessary corrections and improvement when it takes the least cost, with this approach stamping defects can be minimized or eliminated before die construction and try-out. If any correction or redesign is needed it can be done immediately, in very short time, thus it lead to a much smoother die try-out and to shorter lead times with less development costs. [5] Schematic diag.5 4. Areas To Check The areas where a necking failure or fracture is occur on a stamping can be predicted with analysis during the development and die tryout period for new stampings [6]. Once the areas found to thin leading to failure are identified, regular checks should be made, this permits corrective action to be taken before a necking failure becomes visible. Causal factors for a pronounced increase in thinning include: 1. Excessive blank holder force. 2. Material problems such as a lack of draw ability. 3. Material too thin. 4. Scored die surfaces. 5. Die Tryout Procedure A skilled die tri-out technician will optimize the metal flow by making a series of trial parts and reworking the blank holder as needed. In some cases, it is necessary to increase punch radii with the approval of the product designer. [6] 6. Benefit of Minor Product Changes Minor product changes are often highly beneficial to reduce or eliminate the occurrence of fractures. The corner is the usual location of a fracture in a rectangular drawn shell. 32

4 Fig.6 rectangular drawn shell having a corner fracture Refer fig. 6 typical fracture caused by the metal flow at the corners locking due to circumferential compression is shown. B. Drawing force: Fig.8 As the drawing process progresses the force increase and reaches to peak and begins to drop until it reaches the fracture point. It is observed from the curve (Fig.9) that the fracture point is not at the maximum load condition but it is after that. The maximum principle stresses occur at fracture rather than at point of maximum load, material fails after the maximum load due to its ductile properties. [11] Fig.7 Rectangular box draw with large outboard tab. The tab may severely restrict metal movement into the draw cavity and result in a fracture. [6] 6. Effect of various parameters on drawing process observed by CAE techniques A. Blank holding force: Drawing process is greatly influenced by blank holding force. It is seen that deep drawn part quality is affected significantly by flow of metal into die cavity. The force exerted by blank holder on the sheet provides restraining force which controls the metal flow. Excessive flow may lead to wrinkles, while insufficient flow can result in tearing. Curve shows (Fig.8) that larger blank holding force requires more forming load. [11] Fig.9 C. Effect of clearance between punch and die: As shown in the curve (Fig.10) it is clear that large value of clearance between punch and die would require effective forming load more to form the component. Required effective forming load decreases as the clearance between punch and die decreased. [8, 11] 33

5 If we compare the experimental results with the simulation results it showed the validity of simulation to predict where the damaged zones will appear in the part during deformation and it is an accurate simulation technology to achieve precise prediction of quality defects in initial phase of design only so need for costly experiments will be eliminated. In this way great time and cost can be saved. [3, 4] Fig.10 I. Simulation Validity: Different blank holder forces selected for evaluating the effect of BHF, on the other hand parameters such as drawing speed, blank dimensions etc. are kept constant. Refer fig.11, if we apply 350 KN BHF the wrinkling is more & risk of crack is less, on the other hand if we increase the BHF to 800KN the crack area is visible, thinning and tearing is also increased at this BHF. A. Benefits of simulation: It is used as try-out tool to shorten production die try-out and thus to reduce the die cost and lead time. It is used as production tool to provide production stamping conditions. It is used as guide to use simulation output to drive consistency among die engineering &construction etc. Stamping simulation may be used as learning tool to explore and gain new knowledge and application guidance for new forming techniques. [5] III. CASE STUDY- DESIGN AND DEVELOPMENT OF OIL PAN A. What is oil Pan: An oil pan is a component that typically seals the bottom side of four-stroke (Refer fig.12), internal combustion engines in automotive and other similar applications. Its main purpose is to form the bottommost part of the crankcase and to contain the engine oil before and after it has been circulated through the engine. During normal engine operation, an oil pump will draw oil from the pan and circulate it through the engine, where it is used to lubricate all the various components. After the oil has passed through the engine, it is allowed to return to the oil pan. Fig.11 Simulation of drawn component at different BHFs According to the results of these simulations a wrinkle has been observed at 350 KN BHF, increase in thinning and fracture has been observed at 800KN. It also shows that wall thickness of component becomes thinner from the edges. Finally 600 KN BHF is selected which gives desirable results. Fig.12. Oil pan assembly. 34

6 B. Methodology: Analysis for the given configuration of the component under `draw (Method CAE analysis using Auto- Form). Evaluate the `design intent of the features on the component. Document the query report and discuss with the concerned Product designer for his comments/ explanation/ views. Based upon the analysis, suggest revisions/ modifications in the product design for ease of `flow of the sheet-metal material in the die cavity. Determination of blank size. Calculate ejection force required. Material selection for die and other auxiliary items for the process of stamping. Selection of configuration for the die set. Press machine selection based on the type of press, tonnage required. Detailed Design for the Draw Die. Manufacturing of the die as per the 3D data. Assembly of various components of the die together to make it ready for tri-out. Take the tri-out on suitable no of components, note down problems occurred during the tryouts. Do inspection of suitable no of components and see whether they are matching with cad data received (CMM- Inspection). C. Oil Pan Simulation: While the die is being considered for design, the blank development is inferred from the Draw Analysis using software depicting crash- as in Hyper-Form or Auto-Form where nature and extent of deformation resulting in the formed component is analyzed. This method of finding the blank development is deployed using the software interface and later fine-tuned during trials and experimentation. For the study we have used Auto-form software for simulation purpose. Auto-form can address these issues very well as it gives various forming plots and thickness plots at different loading conditions Refer fig.13. Fig13. Oil Pan simulation at different loading conditions D. Design Intent of oil pan The oil pan should contain sufficient amount of oil that can be used for lubrication purpose of the engine. Design should be such that it will provide lubrication oil to all engine parts that require the lubrication. Drain plug should be provided to change the oil and located at lowest point. During drainage of used oil, all the oil should collect at one point so that it will be easy to remove it out. There should not be any oil leakages in the oil pan after fitment. The shape of the oil pan should be such that it will not foul with the other parts below the engine. Design Iteration 1: During development stage initially one simple design is made taking the reference from same oil pan designs and keeping in mind the functions of oil pan. After studying the component data decision is made to make the forming tool for the component. But the side walls of the oil pan are having the straight walls having 90 deg. Angle with the horizontal plane. As far as sheet metal forming is concerned it is not possible to press such component without any draft angle for good effect. So tool designer has requested to product designer to change the design on the basis of analysis results received. The holes provided on the oil pan for assembly purpose are less and it can lead to leakages, so no of holes are added and emboss is provided to avoid any leakages (Refer fig.14). 35

7 Design Iteration 2: Fig.14 As shown in fig.15. some draft angle is given as shown and emboss added and as mentioned earlier the oil should be collect at one point after it is used for lubrication purpose so taper is given to front side of the oil pan as shown so that all the oil is collected at one corner and it will be drained out from drain plug easily. Design iteration 4: Fig.16 In this iteration(fig.17), the depth of second chamber is decreased and depth of first chamber is increased somewhat, Due to Engine block assembly is fouling with the oil pan hump shape is given as shown to center of oil pan. But such revert draw is not possible and design is changed again. Design Iteration 3: Fig.15 Some design changes were done in the lower side of the engine assembly so automatically the shape of the oil pan is changed and is made as shown in fig.16, the depth of first chamber is decreased and depth of second chamber is increased so that it will not affect the volume of the oil. But in this design the depth of second chamber is very deep and is not possible to form the components with this depth. To give technical support to this statement we have done simulation of the same design and in that we see due to extra deep material gets cracks due to thinning and some wrinkles are also observed. So design is changed. Design iteration 5: Fig.17 In this design depth of second chamber is decreased so that it will be possible to form the component and depth of first chamber is increased somewhat. The sharp corners provided in the earlier designs are given fillets so that there should not be any problem of cracking of material at the corners. After such changes the design is finalized and approved (Fig.18). [1, 2] 36

8 Fig.18 E. Blank Development using CAE Techniques: Blank is developed from available cad data using forming suite software. Initially the component is imported into the software. Then the software will create meshing using available skin.then the tipping direction is given to the software, tipping direction is the direction in which forming has to be done. Then give input of material used for forming and its thickness. Finally the software will give the developed blank data and forming area along with scrap layout (Refer fig.19). [3] Fig.19 Blank development using CAE software F. Tool Design for oil pan: Forming tool is designed for oil pan considering draw depth of oil pan the decision is made to make two dies for drawing and one die for restrike and flanging. Oil pan quantity required is only 100 no. of batch so decision is made to not go for blanking tool and trimming and holes are going to made on five axis laser cut machine Following fig.20 will show the process sheet for oil pan development. Fig.20 Process sheet for oil pan development 37

9 G. Experimentation: The experimentation will be carried out over a suitable press machine (Refer photographs 21)based on the tonnage requirement for the subject component and requisite raw material identical with the specifications on the drawing of the Die/ Component will be provided for the trials. The parameters such as blank size, blank holding pressure, die block radius, drawing speed (rate of deformation) etc. are varied looking towards the problems like wrinkling, thinning, tearing etc. these parameters will be changed one at a time and also in combination of two or three. The simulation and analysis software provides sufficient information regarding above problems. The component will be tried out for a batch quantity for checking the consistency of the draw operation over the given lot. Record the necessary parameters on the machine while a satisfactory lot of the desired component quality is produced. Fig22. Cmm report H. Validation Fig. 21. Oil Pan-Tool tri-out photographs The components received as a consequence of the above trial are referred to as the sample pieces exhibiting the test results. The die validation process would be said as complete while the sample component received from the Die over the test run matches the requirements specified over the drawing by using the CMM, following figures 22 will show some of the snaps of the CMM report. IV. CONCLUSION The problem areas such as wrinkling, thinning, spring back are the biggest challenges to the industry now a days but these problems can be tackled and sorted out in the initial phases of the design by using simulation techniques. While designing new product for a particular requirement, the product designer and tool designer should have good communication between them and each of them should share their thoughts and queries in front of development team and final product should validate all the functional and manufacturing requirements. Decreasing the lead time for product development along with the cost and time is the real challenge to the industry. It can be achieved with latest CAE techniques such as simulation, efficient use of simulation method at the earliest stages of design can help to make necessary corrections and improvement when it takes least cost. Defects can be minimized or eliminated before try-out. So that lead time along with time and cost can be minimized. 38

10 A. Future scope Study can be done on increasing fatigue life of oil pan by modifying the oil pan structure & increasing frequency of natural vibration modes to a specified level.it can be done by developing a finite element model of existing pan and verifying it against experimental modal analysis results. Heavy steel oil pans can be replaced with thermoplastic polymer material as it provides high strength to weight ratio, long flow distances, short injection times and reliable molding of thin walled sections. Unlike with steel or aluminum, plastic oil pan can be molded with integrated valves or cooling channels. FEA simulation can be significantly used in plastic injection molded oil pans for positioning of ribs at edge of oil pan and to significantly improve the overall stiffness of the critical flat sections, yet with minimum height of design. FEA can also be used to simulate impact of wall thickness, number of gates and their positioning, weld line formation, warp age behavior and to optimize respective processing parameters. Acknowledgement Authors would like to take this opportunity to express sincere and whole hearted thanks to Mr. Shailesh Bhadade from Icon Technologies, Pune for giving the opportunity to work with the development of oil pan through-out the process. We would also thankful to Dr. V. R. Naik, Head, Department of Mechanical Engineering, DKTES, Textile & Engineering Institute, Ichalkaranji for continuous encouragement during this work. We are extremely thankful to Prof. Dr. P.V.KADOLE, Principal of DKTES, Textile & Engineering Institute, Ichalkaranji for his help provided during this work. REFERENCES [1] Ontology based design meta intent representation, Yingzhong Zhang, Xiaofang leo, school of mechanical engineering Dalan university of technology, China V /09/2009IEEE PP 2-6 [2] Behavior and design intent based product modeling, Laszlo Horwath & Imre J Rudas, Volume Hungary PP[10-25]. [3] Fuh-Kuo Chen, Yeu-Ching Liao Finite element analysis of drawwall wrinkling in a stamping die design VIII International Conference on Computational Plasticity COMPLAS VIII CIMNE, Barcelona, 2005 PP 2-4 [4] Yang Feng, Xiaochun Lu, Bing Gao Numerical Damage prediction and Experiments in Deep Drawing of Irregular Square Cup / IEEE DOI /ICICTA PP [5] Journal of achievements in material and manufacturing engineering, volume 24 issue 1 september2007 PP [6] International journal of Intelligent Computer-Aided Stamping System (ICASS), intellicass inc.pp-2-5 [7] Hitenkumar Patel optimization of an aerospace component die design using metal forming simulation capability of hyper-form Hyper-works Technology conference (HTC), PP 1-7 [8] S.J. Hu, Z. Marciniak, J.L. Duncan Text 0Book Of Mechanics of Sheet Metal Forming ISBN PP [9] Ninig-an Hu, Ning-yan Zhu Aid Design Die of Auto-Body Using Numerical Simulation of 3-D Sheet Metal Forming Processes SAE China (Society of Automotive Engineering of China) PP [10] Kalpakjian Manufacturing Processes for Engineering Materials, 5th ed. Schmid 2008, Pearson Education ISBN No PP [11] T.S. Yang, Finite element analysis of elliptic cup deep drawing of magnesium alloy sheet, VOL. 27, issue 2, April 2008, NSC E , pp