Auto Spot Weld FE Connection Using TCL Script For Process Automation

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1 Auto Spot Weld FE Connection Using TCL Script For Process Automation Vishal Gole Technical lead-cae Vishal.G.Gole Sagar J Patel CAE engineer Sagar.J.Patel Pravinkumar Sonavane Technical lead-cae Pravinkumar.Sonavane Satish Sahu Senior Engineer-CAE Satish.Sahu Abbreviations: BIW Body in White, TCL Tool Command Language. Keywords: BIW, Spots, CAE, FEA, TCL program Abstract Computer Aided Engineering (CAE) is the used to accurately simulate engineering problems across wide spectrum of domains such as automotive, biomedical, civil industries etc. The accuracy of CAE simulation depends on various input parameters like geometry, material properties, details of joineries etc. There are various modeling techniques used in CAE for correct representation of joineries such as bolts, laser welds, adhesives and most importantly spot welds. One of the most crucial phase in CAE modelling of a vehicle is spot welding for BIW, closures and sheet metal components. Ordinarily, an entire vehicle consists of spot welds. Typically, it takes about 20 hours to complete the entire process with existing method. Moreover, this approach is susceptible to human errors and can only be rectified with additional efforts. Missing or changing the location of spots may lead to inaccurate results when performing CAE analysis. To overcome these inaccuracies and to reduce the time, a customized tool for Hypermesh is developed which completes the task in just 15 minutes with great accuracy. Introduction CAE tools are widely used in automotive industry. It has allowed automakers to predict the safety, comfort and durability behavior of the vehicle using computer simulations rather than physical prototype testing each time. The accuracy of CAE results depends on the correct representation of complex geometry with finite elements, material properties and various connections including spots, bolts and seam welding etc. Creation of spot welds is a time consuming and repetitive task. Also, manually connecting the spots can cause inaccuracy and even missing of spots in some locations. This may result in to erroneous results. In order to avoid inaccuracies in the results, one needs to capture the repetitive tasks, standardize and automate them. In the current paper, the process of automating the spot welds in BIW using tcl script is discussed in detail. 1

2 Process Methodology A tcl/tk script is written for hypermesh to develop an interactive GUI that automates the process of spot creation right from the beginning, given that spot geometry data and finite element model is available. Spot geometry data is usually an iges/step file. Fig. 1 shows a graphical representation of a single spot geometry. It consists of 2 discs as shown in the figure. The space between the discs is where the panel lies which have to be connected by spots. Typically 3 types of spots are used to connect panels in BIW, trim and closures: 2T, 3T, 4T, which connects 2, 3 and 4 panel respectively. Different types of spots have different representation. Green color represents 2T spots, yellow represents 3T and red color represents 4T spots. The salient feature of this script is that it will identify these different types of spots and create corresponding FE spots. There are different techniques to represent spot welds in FEA to obtain accurate results for Safety, Durability and NVH. Some of the popular techniques include use of 1D bar elements, 0D rigid elements and the most widely used method of RBE3-hexa-RBE3. In the present study the spot welds are represented using RBE3-hexa-RBE3 method. The tcl script can also be easily modified to simulate spot using another technique. The GUI is user friendly, interactive and easily comprehensible even for the naive users. The layout of the GUI is as shown in Fig. 2. The geometry file has other many data apart from spot data. To segregate the spot geometry, the GUI gives an option to input the volume of a single spot geometry. Using this value, the script will isolate all the spots geometry from other geometry (PS: All the spots will have the same volume). After specifying the range of spot geometry volume, click on Separate Spots to isolate the spot geometry. User can then review if everything is correct and no unnecessary geometry data has been combined with spot data on the Hypermesh screen. Once the review is complete, click on Create Points. This button is used to create points at the center of each spot geometry as shown in Fig. 1. These points are necessary input to create spots. This step will also classify different types of spots and put them in different collectors of 2T, 3T and 4T spots. The final step is to create FE-spots after specifying value for Spot Diameter and Tolerance in the space provided for them in the GUI. Create Spots will create 2T, 3T and 4T FE-spots depending on the color of the spots and organize them into different collectors for the convenience of the CAE analyst. FE spots created is as shown in Fig. 3. Figure 1 Spot Geometry with Points Figure 2 Spot Automation GUI Layout 2

3 Figure 3 FE Spots Created Many times the spot geometry is faulty and it has more than 2 spots within 25mm radius, which are unnecessary and leads to error in CAE results. To address the issue, the script has an added feature that it deletes extra spots within 25mm radius and keeps only 1 spot. The algorithm is designed in such a way that while deleting redundant spots, it will take into consideration the priority of different types of spots. 4T spots have higher priority than 3T spots, which have greater priority than 2T spots. In case there are more than 2 types of spots within 25mm radius, the script will keep the spot with higher priority and delete the one with lower priority. In case of two spots of the same type, it deletes any one of them. Flow Chart 3

4 Results & Discussions Based on the type of spot geometry, (green for 2T; yellow for 3T; red for 4T) corresponding spots are created for the entire model, a portion of which is shown in Fig. 1. Redundant spots are deleted thus increasing the accuracy of FEA results. The spots are segregated into different collectors for user convenience. Substantial amount of FE modelling time and effort is reduced. Benefits Summary The present method discussed is highly accurate and speedy as compared to any other existing manual method. This script eliminates human intervention and thus increasing the accuracy of model setup. TABLE I TIME SAVED IN CREATING SPOTS FOR DIFFERENT COMPONENTS Sr. No Assemblies No of Spots (Approx.) Total Time (Manual) Total Time (Automated) 1. BIW Hrs 20 mins 2. DOORS Hrs 5 mins 3. TAILGATE Hrs 2 mins 4. HOOD Hrs 2 mins Total 39 Hrs 29 mins Challenges The script greatly depends upon the geometry of supplied spots. Any discrepancy between the spot data and the component geometry might lead to inaccurate spot creation. Future Plans The plan is to make a comprehensive tool for connections by extending similar approach for creation of other connections like adhesive, seam weld and bolt joints. Conclusions The spot welding of complete vehicle can be done with great accuracy and very less time. The script was used and the corresponding result was reduction in total spot creation time from from 39 hours to around 30 minutes, thus reducing the total time by approximately 98%. The manual procedure would have otherwise taken very large time. Human interaction is minimum hence probability of errors are very less. The GUI is user friendly and interactive. Model Checking time is reduced. Even a CAE engineer new to modelling process can easily follow the procedure and spot weld. ACKNOWLEDGEMENTS We are grateful to each and every individual who directly or indirectly supported us in accomplishing this paper. We express my sincere gratitude to Mr. Indranil Bhattacharyya for his encouragement, motivation and valuable inputs which made possible the successful completion of the paper. Moreover, we are extremely thankful to all the members of Durability and NVH team for their constant inputs and assistance towards the completion of this paper. REFERENCES Journal Papers: 1) M. Merkel, A. Schumacher, Automated Optimization Process for a CAE Driven Product Development, Journal of Mechanical Design, 125(4), 2004, ) Okba Hamri, Jean Claude Léon, Franca Giannini, Bianca Falcidieno, Computer Aided Design and Finite Element Simulation Consistency, Journal of Mechanical Engineering, 56(11), 2010, , 4

5 Chapters in Books: 1) Introduction to HM Customization Using Tcl to Control the Hypermesh Session (Altair Engineering, Inc 2013) 2) Brent Welch, Ken Johns, Jeffery Hobbs, Practical Programming in Tcl and Tk (Upper Saddle River, NJ07458, Prentice Hall,2003) 3) Ibrahim Zeid, CAD/CAM Theory and Practice (McGraw-Hill, 1991). 5