Automated robot-assisted methodology for manufacturing and post-processing of workpieces based on generative manufacturing processes© Steffen Wurm
Generative manufacturing has gained great importance for the manufacturing industry in recent years. The number of industrial systems for additive manufacturing tripled in Germany in the period from 2010 to 2014. For more than 15 years, additive manufacturing methods of plastic components have been used mainly in the field of rapid prototyping and single-part production. In recent years, the technology has evolved to the extent that it can already be used for small batches and series production. What all additive processes have in common is that they make a compromise between component quality and throughput time. The maximum speed of material application is limited by the performance of the extruder system, and the process time is significantly dependent on the selected layer thickness.
A low throughput time can only be achieved by a low layer resolution and induces the fact that, as a rule, post-machining is required for high-tolerance quality ranges. If a component also exhibits high complexity and strong geometric overhangs, a support structure is required to maintain component stability during the process. An extension of the machine kinematics used in the process offers the potential to reduce or even completely eliminate the amount of support materials. Additional degrees of freedom allow reorientation between the component and the extruder already during the process without having to rely on reclamping of the workpiece carrier.
As part of the "AuRoNa3D" research project, a hybrid process chain is being developed that contributes to increasing the degree of automation of additive manufacturing processes. For this purpose, conventional 3D printing is extended by additional degrees of freedom and machining is introduced to increase geometric dimensional accuracy.
Two programs for machine program and process management form the core of the hybrid process chain. The "Preperation and Simulation Tool" takes over the preparation and preprocessing of the process data. The program accesses the component information from the CAD/CAM system via an interface and supplies the machine program to the robot control for the cutting post-processing and optical measurement. A slicer is used to create the machine program for additive manufacturing. The individual machine programs can then be used for process simulation. Within the Preperation and Simulation Tool, all three program sections are aggregated to a common machine program (G-Code). This creates alternating control blocks for additive manufacturing, optical measurement and subtractive post-processing. During the program runtime, the "Control Tool" program monitors the manufacturing process. If insufficient quality is detected during optical measurement, the control block for clamping reworking is executed subsequently. In the case of functional surfaces, the machining post-processing is always executed. For quality monitoring, the additively manufactured component is guided under the sensor in defined poses and a 3D point cloud of the actual state is generated. The actual geometry is compared with the CAD data and potential violations of quality requirements are identified. If the quality of the additive manufacturing meets the specifications, the machine program block for subtractive finishing is not executed and the next additive manufacturing stage follows.