Additive manufacturing by multi-axis robotic wire deposition – Optimization of the deposition trajectories and robot control

Maxime CHALVIN (Sept. 2017)

Funding : CDSN (Specific Doctoral Contract for Normalien)

Partner company : Poly-Shape

Supervision : Vincent HUGEL and Sébastien CAMPOCASSO

For several years, additive manufacturing has been booming in the industrial sector for the direct production of small series of functional metal parts. However, powder bed technologies currently have high manufacturing costs and dimensional limits (about 600 mm) that hinder their diffusion in certain industrial sectors such as aeronautics or naval. Multi-axis direct deposit techniques are currently in strong development because they offer larger working dimensions, possibilities of recovery on parts (repair, addition of entities…) and can be combined with machining processes to lead to so-called hybrid manufacturing processes.

Additive manufacturing by wire deposition is a process that many manufacturers are relying on to reduce part manufacturing costs in the future. Indeed, this highly flexible technology has many advantages over other additive manufacturing processes: low investment (around €100 to 500k, compared to €600k to €1.5m for powder bed processes and €800k to €2m for powder spraying), large workspace (several metres), high productivity (several kg/h compared to a few g/h), good metallurgical quality (defects similar to welding, no porosity, etc.), low downtime and material loss, low cost and rapid material change, reduced HSE risks compared to metal powders, etc.

Wire deposition using industrial robots is therefore a process that could improve the competitiveness of the aeronautics industry and appears ideal for manufacturing applications in the naval industry given the small series and large dimensions of the parts produced. These two target sectors are major economic players in the PACA region.

Currently, the additive manufacturing machines on the market offer few possibilities for adjustment and modification due to the locks imposed by the manufacturers. The possibilities of research work on these means are thus limited. The use of industrial robots coupled with direct deposit systems makes it possible to obtain large and more “open” manufacturing facilities. Specific developments can thus be carried out in order to optimize a targeted manufacturing process. This optimization requires simultaneous control of the parameters of the deposition process (energy, yarn feed rate, etc.), but also of the trajectory and feed rate of the “depositing point”. It is also possible in some cases to vary the deposition orientation, and thus to remove the manufacturing supports. Nevertheless, successful manufacturing requires the ability to generate complex three-dimensional deposition trajectories that allow the part to be “filled” correctly according to its geometry and that of the bead deposited. However, the bead and part geometries can vary depending on process parameters, part temperature or deposition orientation with respect to gravity.

The generation of trajectories is a common problem for all Direct Energy Deposition processes on multi-axis machines, whether they use powder spraying or wire deposition regardless of the fusion technology (arc with coated electrode, MIG-MAG, TIG, plasma, laser, or even electron beam). The consideration of thermal problems when generating trajectories is also a research area that is the subject of some work recently initiated for powder bed processes. The proposed thesis topic therefore aims to complement the current work on trajectory optimization in the case of the wire deposition process.