TRAJECTRORY CONTROL FOR AN INCREMENTAL FORMING PROCESS USING AN INDUSTRIAL ROBOT IN DELMIA

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1 TRAJECTRORY CONTROL FOR AN INCREMENTAL FORMING PROCESS USING AN INDUSTRIAL ROBOT IN DELMIA Ionuţ CHERA 1, Octavian BOLOGA 1, Gabriel RACZ 1 and Radu BREAZ 1 ABSTRACT: The goal of this research is to display the necessary steps needed to build, simulate and obtain the toolpath of a punch used for a robot assisted asymmetric single point incremental forming process. The system used for the simulation of a robot assisted incremental forming process was built and tested with the help of DELMIA software package. The programming code needed to control the industrial robot for the actual forming process was obtained through an internal compiler from DELMIA software. An experimental study was also presented for the manufacturing of a truncated pyramid shaped sheet metal part. KEY WORDS: incremental forming, sheet metal, industrial robot, tool path 1 INTRODUCTION In recent years new methods in sheet metal manufacturing needed to be developed and researched because traditional techniques lack flexibility and require a considerably high investment costs. As technology progresses, new solutions emerge, lowering the production costs and time. Asymmetric single point incremental forming is such a solution, best suited for the production of low cost prototypes and pre-series components (Jeswiet et al, 2008, Sasso et al, 2008, Vihtonen et al, 2008, Meier et al, 2009). Incremental forming caught the interest of scientific research groups very early on and now more and more manufacturers are using this method to create their own prototypes. Promising results were also reported in manufacturing medical implants by means of asymmetric single point incremental forming (Ambrogio et al, 2005, Oleksik et al, 2009). Unlike traditional metal forming processes, performing fast production changes are possible due to easy configuration of the forming machines such as CNC milling machines. Although the time required to make a sheet metal part is longer than on a traditional forming press, the time spent on tool design and prototype production is significantly shorter. The use of modern industrial robots to perform asymmetric single point incremental forming can further increase the flexibility of the process (Sasso et al, 2008). 1 Lucian Blaga University of Sibiu, Engineering Faculty, Emil Cioran 4, Sibiu, Romania ionut.chera@ulbsibiu.ro, octavian.bologa@ulbsibiu.ro, gabriel.racz@ulbsibiu.ro, radu.breaz@ulbsibiu.ro 32 Figure 1. Process principle of asymmetric single point incremental forming (ASPIF) 1.1 Asymmetric single point incremental forming A brief description of the ASPIF process principle is presented in figure 1. The blank (2) is fixed by mean of the blank holder (3). In order to shape the sheet metal part, the punch (1) has an axial feed movement on vertical direction, continuous or in steps s (incremental), while the other element, the active plate (4) carries out a plane horizontal movement. However, in spite of its great potential, the industry is still reluctant to apply the ASPIF process on a large scale, due to two major drawbacks: low shape and dimensional accuracy of the parts and sheet metal integrity (Rauch et al, 2009). A large number of papers about incremental forming have been presented in recent years, aiming to find what machine is best suited for this process and of course what are the most influential process parameters both in running experiments and for production (Callegari et al, 2004, Katajarinne et al, 2008). ACADEMIC JOURNAL OF MANUFACTURING ENGINEERING, VOL. 11, ISSUE 1/2013

2 Also many authors published articles regarding incremental forming in which they conducted experiments by means of industrial robots. of an incremental forming robotized system with an optical measurement device, held by another robot, Figure 2. Roboforming, Meier (2009) Figure 3. Principle of roboforming, Meier (2009) 1.2 Robot forming Meier proposed the concept of roboforming as a dieless, incremental, robot-based sheet metal forming process for cost-effective manufacture of prototype parts and small batch sizes. Its principle is based on flexible shaping by means of a freely programmable path-synchronous movement of two industrial robots driving workpiece-independent forming tools, (Meier et al, 2009). The principle of roboforming is presented in figure 3. The setup the authors used which is presented in figure 2, consists of two KUKA KR360 serial robots and a blank holder which is positioned on a vertical plane between the two robots. One of the robots holds the forming tool which is moved in increments perpendicularly on the blank and along the lateral direction either on parallel layers or on a helical patch. The other KUKA robot is equipped with the supporting tool which holds the sheet on the backside, by moving synchronously along the outer contour, constantly on the same level or directly opposed to the forming tool (Meier et al, 2009). Another example of research done in this area is the work of Sasso, which proposes the integration Figure 4. Hibrid robot Tricept H1, Sasso (2008) developed for quality control purposes of processes and products, (Sasso et al, 2008). The robotized system consists of two robots that perform two different tasks. The first robot that is used for the actual forming of the parts is six degrees of freedom robot with hybrid kinematics, the Comau Tricept H1, figure 4. This robot has three parallel and three serial kinematics joints and is able to support up to 15 KN loads on the main axial direction. The Comau Tricept H1 robot moves a spherical punch according to a predefined path, deforming a gridded sheet metal that is scanned by a couple of cameras mounted on six degrees of freedom anthropomorphic robot (Comau Smart S4). Although the second robot does not support such high loads as the first one, it has a much higher dexterity, permitting to move and orientate the acquisition head mounted on the wrist in the correct position. The system that the authors use is completed by a projector and four fixed cameras, that permit the evaluation of the final shape of the formed parts by means of fringe projection and phase shift techniques. As a result of the postprocessing of the acquired images, according to the so called grid method, the strain distribution was computed, and the quality of the forming process was assessed, (Sasso et al, 2008). An alternative robot forming method was developed by Schafer, in which a hammering tool is moved by an industrial robot over a sheet metal fixed by a frame, figure 5. The forming is executed by successively punching the sheet metal by the hammering tool. The robot moves the hammering tool along calculated path. Compared to other incremental forming processes in which the deformation of the sheet metal is done locally by a static force, the hammering principle has some ACADEMIC JOURNAL OF MANUFACTURING ENGINEERING, VOL. 11, ISSUE 1/

3 advantages: small reaction forces affect the robot because the deformation forces are generated by the application like 3D model design, process planning, resources planning, discrete and continuous event Figure 5. Robot hammering, Schafer (2004) inertia forces of the punch and not by the robot itself. Another two advantages of the hammering process is the small area of deformation and the lack of friction forces in the feed direction. The main disadvantage of the hammering principle is the appearance of the vibrations in the sheet metal and for this reason the high sonic emission. If the experiments are done in a confined space with sound insulation, the sonic emission can be significantly reduced, (Schafer et al, 2005). 2 THE ROBOTIC SYSTEM The system used for the simulation and for the incremental forming experiments consists of a six degrees of freedom anthropomorphic robot, KUKA KR 6, figure 11, a custom blank holder, a custom tool holding unit and the forming tool. The KUKA KR6 robot has great flexibility and is suitable for both point-to-point and continuous-path controlled tasks, (KUKA KR6 robot manual). The tridimensional models of the robotized system components that were designed in CATIA V5 are presented in figure 6. Using DELMIA software package, an accurate tridimensional model for the KUKA KR 6 robot was imported in the simulation environment. DELMIA is one of the most powerful virtual prototyping applications in manufacturing. DELMIA is part of the product lifecycle management applications for addressing requirements from design to production and maintenance (Pratt et al, 1995, Xiang et al, 2004). The core of DELMIA is a product, process and resources model that link up with various Figure 6. Tridimensional model of the robotic system used for the simulation Figure 7. Detail from the working area simulation, 3D visualization, layout planning and virtual reality, all in the same platform, (Shen et al, 2005, Huang et al, 2007). A detailed view from the working area of the robotic system used for the simulation in DELMIA software is presented in figure 7. 3 THE STAGES OF THE SIMULATION The basic steps needed in order to simulate the movement of the tool along a predefined toolpath for an asymmetric single point incremental forming process done with the help of an industrial robot is presented in figure 8. The first step of the process is designing the robotic system components and the tool path in CATIA V5. After the components have been modeled, they will be assembled in the Assembly module in CATIA V5. Using Catalog Browser function from DELMIA software package, an accurate tridimensional model of the KUKA KR ACADEMIC JOURNAL OF MANUFACTURING ENGINEERING, VOL. 11, ISSUE 1/2013

4 robot needs to be imported in Device Task Definition module. commands, Device Task Definition contains analysis tools. Figure 8. The basic steps needed for the simulation of the toolpath Device Task Definition provides tools for 3D modeling at the work cell level. Device Task Definition provides all the tools required to perform robotic feasibility studies and programming in an environment where product data and manufacturing resources can be integrated into a single 3D model. This model performs the basis for the development of robotic processes. Device Task Definition allows you to test for robot reach and access in a complex manufacturing work cell. It provides tools for the development of robot programs and facilities to test those programs while checking for interferences. The output of Device Task Definition is a work cell model that is ready for the next step: development of a complete manufacturing simulation with synchronization of all resources. Robot tasks and tag definitions for robot motion are integral to Device Task Definition. Users can create tags and add them to tasks or can create tags in free space for clearance moves. Device Task Definition provides interactive jogging and robot teaching capabilities to develop and test robot tasks. These tasks can be simulated, one at a time. In addition to the basic setup Figure 9. Set Tool window setup from DELMIA These tools add the following capabilities: basic measuring of distances and angles, collision and band width analysis. ( Next step in the simulation process is to insert the rest of the robotic system components in Device Task Definition module, then attach the forming tool to the robot with the help of the Set Tool function, figure 9. The position of the components needs to be adjusted in order to optimize the simulation process. A new task is assigned to the robot, and then the continuous trajectory of the tool attached to the robot is defined. The path points are automatically generated on the trajectory previously defined. After obtaining the standard tool path, in which we cannot modify the orientation of the tool, we need to create a secondary tool path in order to have the freedom to change the working angle of the tool. For the purpose of simulating an asymmetrical single point incremental process, we need to have the axis of the tool perpendicular to the sheet metal. The secondary tool path is created by using Create new robot task function on the primary path. After creating the secondary tool path, the path points appear under the form of tags. Now we can modify the orientation for each individual tag to best suit our needs. To make our work much easier we only need to modify the angles of the first and the last tag from the secondary tool path, then use Interpolate function to align all the tags in the desired orientation. The next step in the process is to teach our robot in which configuration to run using the Teach a device function, figure 10. After checking for collisions, robot joint limitations and singularity problems, we can now proceed to simulate the movement of the robot following the secondary tool path. Once we are ACADEMIC JOURNAL OF MANUFACTURING ENGINEERING, VOL. 11, ISSUE 1/

5 satisfied with the simulation we can generate the program code with the Create Program function. finished sheet metal part is presented in figure 15. The forming process lasted approximately 5 minutes. Figure 10. Teach a device window from DELMIA Figure 11. Custom stand and KUKA KR 6 robot DELMIA uses an internal compiler and depending on your version of DELMIA, it needs a particular version of java installed on your PC. For our version V5R20, we used j2sdk-14107, with good results. The compiler creates two files and both have to be transferred to the KUKA controller in order to use the robot properly. 4 EXPERIMENTAL STUDY Figure 12. Dimensions of the test part In order to demonstrate the capabilities of the method described above, a truncated pyramid sheet metal part was manufactured using a custom made stand and with the help of a KUKA KR6 anthropomorphic robot, figure 11. The sheet metal part can be produced directly from the CAD model without the need of a die plate. The dimensions of the desired sheet metal part are presented in figure 12. The material used for the sheet metal part is a St 14 mark of steel with a thinness of 0.4 millimeters. The forming tool used in this experiment is a hemispherical head punch with a diameter of 6 millimeters. The first step in the manufacturing process is to design the part itself in a CAD environment. We chose to use CATIA V5 for our experiment. A tridimensional model of the truncated pyramid is presented in figure 13. The second step is to construct the tool path needed for the experiment in CATIA. The tool path required to produce the truncated pyramid is presented in figure 14. Following the necessary steps described in the Stages of the Simulation chapter, a program code was generated by means of a specific DELMIA function. After transferring the necessary files to the robot controller, the experiment can begin. The 36 Figure 13. Tridimensional model of the test part Figure 14. Tool path for the test part Figure 15. Finished sheet metal part ACADEMIC JOURNAL OF MANUFACTURING ENGINEERING, VOL. 11, ISSUE 1/2013

6 5 CONCLUDING REMARKS Incremental forming of sheet metal parts can be a reasonable alternative to traditional methods especially for producing prototypes and small batches. These low volume production orders require an increased level of flexibility to minimize the costs. This leads to the use of CNC milling machines and industrial robots which meet the requirements for producing low cost prototypes. The use of a robotic system for incremental forming has several advantages such as high flexibility and relatively low costs. Allot more experiments need to be executed in order to completely assess the benefits of robots in this area on manufacturing. The aim of this research was to present an overview of the modeling and simulation capabilities of DELMIA software package. This software can be successfully used for creating, simulating and obtaining the tool path used for an asymmetric single point incremental forming process done by means of an industrial robot. DELMIA offers the possibility to export directly the necessary program code for a large number of robot models. The design of the robotic system proved to be efficient and reliable for our purpose, although it needs a bit of improvement. Future work will cover the testing of different materials with different thicknesses. Also we would like to test more complex geometries and different strategies regarding path planning. 6 REFERENCES Ambrogio, G., De Napoli, L., Filice, L., Gagliardi, F. (2005). Application of Incremental Forming process for high customized medical product manufacturing, Journal of Materials Processing Technology , Callegari, M., Amodio, D., Ceretti, E., Giardini, C. (2006). Sheet Incremental Forming: Advantages of Robotized Cells vs. CNC Machines, Industrial Robotics:Programming, Simulation and Application l, ISBN , pp Huang, T., Kong, C.W., Guo, H.L., Baldwin, A., Li, H. (2007). A virtual prototyping system for simulating construction processes, Automation in Construction,16, pp Jeswiet, J., Geiger, M., Engel, U., Kleiner, M., Schikorra, M., Duflou, J., Neugebauer, R., Bariani, P., Bruschi, S. (2008). Metal Forming Progress Since CIRP Journal of Manufacturing Science and Technology, 1(2-17):2 17. Katajarinne, T.,Vihtonen, L., Kivivuori, S. (2008). Incremental forming of colour-coated sheets, Int J Mater Form, Suppl 1, pp Meier, H., Buff, B., Laurischkat, R., Smukala, V. (2009). Increasing the part accuracy in dieless robot-based incremental sheet metal forming, CIRP Annals - Manufacturing Technology., 58, pp Oleksik,V., Pascu, A., Deac, C., Fleaca, R., Roman, M. (2009). Numerical Simulation of the Incremental Forming Process for Knee Implants, Proc. COMPLAS X, X International Conference on Computational Plasticity, Fundamental and Applications, eds. E. Oriate and D.R.J. Owen, Barcelona. Pratt, M.J., (2004). Virtual prototyping and product models in mechanical engineering, Virtual Prototyping -Virtual Environments and the Product Design Process, Chapman and Hall, London, 1995, pp Rauch, M., (2009). Tool path programming optimization for incremental sheet forming applications, Computer-Aided Design., 41, pp Sasso, M., Callegari, M., Amodio, D. (2008). Incremental forming: an integrated robotized cell for production and quality control, Meccanica, 43, pp Schafer, T., Schraft, R.D., (2005), Incremental sheet metal forming by industrial robots, Rapid Prototyping Journal 11/5 (2005), Shen, Q., Gausemeier, J., Bauch, J., Radkowski, R. (2005). A cooperative virtual prototyping system for mechatronic solution elements based assembly, Advanced Engineering Informatics,19,pp Vihtonen, L., Puzik, A.,Katajarinne, T. (2008). Comparing Two Robot Assisted Incremental Forming Methods: Incremental Forming by Pressing and Incremental Hammering, Int J Mater Form., Suppl 1, pp Xiang, W., Fok, S.C., Thimm, G. (2004). Agentbased composable simulation for virtual prototyping of fluid power system, Computers in Industry,54, pp Delmia Tutorial, viewed 25 September fault.htm. KUKA KR6 Robot Manual. ACADEMIC JOURNAL OF MANUFACTURING ENGINEERING, VOL. 11, ISSUE 1/