Pilot at BMW Munich plant evaluating use in vehicle assembly of custom orthotic devices produced by 3D printing
A pilot project in BMW’s Munich vehicle assembly plan is exploring the benefits of a new and innovative ergonomic tool—a flexible finger cot, which protects workers against excess strains on the thumb joints while carrying out certain assembly activities. The project is part of a dissertation in cooperation with the Department of Ergonomics at the Technical University of Munich.
Each of the flexible assembly aids is a unique piece, customized to the match the form and size of a worker’s hand. The BMW Group makes these orthotic devices in-house, using additive production procedures—i.e., “3D printing”.
The innovative orthotic devices are applied as part of a pilot project in an assembly area where rubber plugs are fitted. These have to be pressed in with the thumb and close, among other things, the drain holes for the paint coat. Even for people with strong hand muscles, this movement requires a certain effort.
|The orthotic device. Click to enlarge.||In application. Click to enlarge.|
In order to prevent the unnecessary overstretching of the thumb joint, the finger cots made of thermoplastic polyurethane are put over the thumb like a second skin. Right at the thumb joints, the assembly aid is open to allow the thumb to move without restriction. At the back of the thumb, though, the plastic material is reinforced. If the thumb is stretched, as in a ‘like it’ gesture, the reinforced elements collide, forming a stable splint. This way, the effort needed to press in the plug is spread across the entire thumb, down to the carpus.
In initial practical tests, the feedback of workers was very positive. It is currently being evaluated how the assembly aids can be applied as standard tools in further production areas.
Each of these finger cots is made specifically for its user. To this end, the worker’s thumb is measured with a mobile 3D hand scanner. Based on a standard production layout, the future orthotic devise is then computed and divided virtually into individual layers. Layer by layer, each of them about as thick as a human hair, the tool is then manufactured in a selective laser sintering process.
Based on the layer data, a plastic powder is selectively fused by a CO2 laser in a pre-heated construction chamber. This way, the plastic does not only mold into the layer presently created, but also merges with the previously formed one.
Thermoplastic polyurethane, the material used, is perfectly suited to making flexible orthotic devices. As a rule, it is elastic, but forms solid and rigid combinations at higher material strengths. The mechanical tensile strength is high, ensuring that the material can resist also strong, continuous strains without tearing. The BMW Group has been involved in research projects that have recently resulted in the market maturity of the highly innovative material, following several years of development.
A major benefit of the material is that the mechanical component properties can be customized for the respective application via a combination of different process parameters.
The BMW Group has applied additive production procedures for rapid prototyping in concept prototyping since 1989 and has developed the process further ever since. Depending on the specific component requirements, the BMW Group uses different procedures and materials. Besides selective laser sintering, these include stereo-lithography, polyjet printing, fused deposition modeling, and stream smelting of metals.
The Rapid Technologies Center at the BMW Group’s Research and Innovation Center (FIZ) in Munich produces close to 100,000 components a year using these methods. The range includes anything from small plastics holders to design patterns and vehicle components for functional tests. Depending on the procedure and the size of the component, components might be available within only a few days.
They are applied in vehicle development and testing, as individual provisions in production or in high-strain sections in the BMW Group’s DTM (German Touring Car Masters) vehicles. It is low volumes in particular that can be made at economic costs using additive production procedures as these do not require any forming tools.