Laura Griffiths speaks to Jens Ertel (JE), Head of BMW Additive Manufacturing, and Markus Lehmann (ML), Head of Installations Technique, Robotics, about BMW’s design and deployment of customised 3D printed robot grippers.
TCT: Tell us about that first iteration of the 3D printed robotic gripper. How did BMW identify this as a potential application for additive manufacturing?
JE: The BMW Group production system is constantly evolving, and there is always a drive to integrate new innovations, for example to optimise time, cost, and CO2 emissions. The example of the gripper for the CFRP roof handling in plant Landshut shows that for the very lightweight roof, a very heavy gripper was used. It was therefore clear that there was enormous potential to minimise the weight of the gripper. Of course, there are additional forces like the mass of the control units and actuators that the gripper must withstand. Nevertheless, we were very confident that we could achieve a significant weight reduction. After performing a topology optimisation, one of the most important tools for calculating lightweight designs, the result showed a rather complex shape. In recent years, new printing technologies have become increasingly available on a large scale, so that large, topologically optimised components like large grippers can now also be manufactured using additive manufacturing.
TCT: The gripper has been optimised with a new ‘bionic design.’ Can you talk us through the optimisation process?
JE: For the topology optimisation we first needed a so-called design space. This is the region or volume within which the optimisation algorithm is allowed to distribute material in order to find the optimal structural design. The design space represents the available physical space or domain where the structure can be placed. Additionally, the non- design spaces are defined. These are mostly mounting plates that are needed to later fasten add-on parts and to attach the gripper to the robot and that will be integrated in the bionic structure during the optimisation. After that, the forces and torsional moments acting on the gripper are estimated and the allowed deformation is defined. Also, the material properties and a minimum strut thickness are set. With all these values and some additional details the topology optimisation can be started. Through the clever combination of two different optimisation approaches, the resulting geometry of the optimisation is already of such high quality, that only minor manual editing of the design is necessary. The usually time intensive redesign of a topology optimisation result is replaced by an automised workflow, that accelerates the design process enormously. The optimisations of the bionic grippers were done in the software Synera.
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BMW Group
TCT: The gripper uses a mix of different forms of 3D printing. Why were each of these processes selected?
ML: The gripper for the CFRP roof production at the Landshut plant utilises a mix of different 3D printing processes to take advantage of the unique benefits that each technology offers. The selection of these processes was driven by the technical and economic considerations for the specific components of the gripper. The approach is not to simply ‘print everything’, but rather to use the 3D printing technology that provides the most benefits for each individual component. This strategic approach ensures that the overall gripper design is optimised for both technical performance and cost- effectiveness. For the vacuum grippers and the clamps of the needle gripper used to lift the CFRP raw material, the selective laser sintering (SLS) process was selected. SLS allows for the production of these intricate and complex parts with the required precision and durability.
On the other hand, the large roof shell and bearing structure of the gripper are manufactured using large-scale printing (LSP) technology. LSP is well-suited for producing large, stiff components in an economical and sustainable manner. Furthermore, in a subsequent optimisation step, the weight of the bearing structure was reduced even further. This was achieved by employing aluminium sand casting technology, where 3D printed shapes and cores were utilised. This approach allowed the full potential of topology optimisation to be exploited, leading to a significant reduction in the overall weight of the gripper.
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TCT: Why was weight optimisation such an important factor for this particular application?
ML: Basically, we want to reduce the weights of grippers in the production system, as this can reduce the moving masses and thus also the cycle times, energy consumption and CO2 emissions. In addition, the service life is increased and smaller robots can be used in the future. When optimising manufacturing processes, installation sequences can change so that higher loads must be moved with the existing setup. The reduction of the gripper weight also enables flexible adaptation here. In special cases, weight reduction isn't the only target, it can also be the increase of the stiffness of the gripper system.
TCT: This kind of application encapsulates how additive manufacturing doesn’t necessarily have to mean direct printing in a production environment. How does this gripper story demonstrate the potential for AM as an enabling technology?
ML: Essentially, we do not simply want to print everything, but rather utilise technology where it provides the greatest technical and economic benefits. 3D printing is another tool in the technology arsenal that complements and supports other technologies. Advancements in technology and materials open up new technological and economic applications. As seen in various exciting 3D printing projects at the BMW Group, 3D printing technology can be a key to success. In the case of bionic lightweight grippers, the full potential of topology optimisation can only be realised through the 3D printing technologies employed, allowing the maximum potential for weight savings to be exploited. Tool-free manufacturing enables rapid and economical deployment as well as accelerated iteration cycles.
BMW Group
TCT: What has been the impact of this bionic design and has it influenced any further developments along the production line?
ML: The use of additive manufacturing in the production system has been established for some time now. The first hybrid grippers, where, for example, only individual, smaller elements were printed, have also been in use for several years. This was also an initiator for the first trials with the printed large-format grippers. The CFRP roof grippers at the Landshut plant have now become a permanent part of the production, so that all CFRP roof grippers for this manufacturing step are produced exclusively by 3D printing. To fully exploit the potential of topology optimisation, there was a further development towards the bionic gripper, which is manufactured using sand casting and printed moulds. In addition to the Landshut plant, this type of gripper is now also used in the Munich plant for the production of the BMW i4. Further grippers are planned for additional plants.
TCT: Speaking more broadly about BMW Group’s deployment of AM - more than 400,000 parts were printed last year worldwide. How would you characterise 3D printing’s significance across the BMW Group production system?
JE: 3D printing has now become an essential and integral part of the product development process and the production environment of the BMW Group. The availability of 3D printers in the individual plants has significantly increased the creativity and innovative power on-site. Through the short distances and the fast, local production within a few hours or even minutes, customised solutions can be implemented quickly. The plants are connected in a tight network, in which applications and experiences with 3D printing are exchanged. This allows all locations to benefit from mutual support in terms of ideas, technologies and materials. Overall, 3D printing has become firmly established throughout the BMW Group. The number of applications and the penetration of the technology across all plants is steadily increasing. This way, 3D printing contributes decisively to the increase of efficiency, flexibility and innovative power in production.
This article originally appeared inside TCT Europe Edition Vol. 32 Issue 5 and TCT North American Edition Vol. 10 Issue 5. Subscribe here to receive your FREE print copy of TCT Magazine, delivered to your door six times a year.
