Process chains for Advanced Tooling based on Additive Manufacturing

The purpose of this thesis is the establishment of new process chains for production of moulds for use in injection moulding. The whole manufacturing process chain is the object of the investigation and particular emphasis is given to two main aspects: the ex-ploitation of additive manufacturing techniques and the achievement of mould surfaces with optical or near-optical quality.
The state of art of additive manufacturing and polishing techniques for superfinishing of moulds surfaces are analyzed. Two fundamental issues of the two processes are pointed out, namely the insufficient surface quality of additively manufactured parts and the lack of automated and reproducible polishing processes for complex and free form surfaces such as those encountered in moulds for parts with aesthetic function.
Combinations of suitable process chains for delivering high performance moulds with optical surface quality and enhanced heat evacuation features are proposed. Common links between these process chains are the presence of additive manufacturing techniques in some stages of the process chain and the achievement of optical surfaces by means of controllable and reliable processes.
Two process chains for mould inserts production were developed from the design phase to preliminary injection moulding trials. Furthermore, a predictive model for surface roughness for ball nose end milling finishing processes is proposed as valuable tool for tool path planning, tool and process parameters selection.
The first process chain is based on the choice of suitable diamond machinable materi-als to be used in additive manufacturing. Extensive work was carried out in assessing diamond machinability performance of the selected alloys. Mould inserts, using the identified alloys, were produced by means of SLM, heat treated, diamond machined to nanometric surface roughness and tested in an injection moulding setup. Optical sur-face quality was achieved on the diamond machined insert surfaces and was also retained during the injection moulding tests with no measurable wear.
The second process chain is based on indirect tooling. The diamond machining process was exploited for the production of a copper master with the opposite shape of the mould cavity. The master was electroplated with nickel, and SLM was used to produce a bulk structure strongly attached to the electroplated coating. The master was chem-ically dissolved to reveal the nickel surface which became the mould insert functional surface. After minor machining operations the part was inserted in a mould and tested in injection moulding. Preliminary moulding tests showed no sign of degradation of the mould surface characteristics.
In order to facilitate the decision of the CAM specialist in tool path generation for finishing operations of mould surfaces, a comprehensive model for surface roughness prediction was developed for ball nose end milling. The model was able to take into account several contributions to the surface generation process such as the cutting edge micro geometry, the smearing of the workpiece material and errors in radial position of the cutting edges of the tool. Through experimental tests on hardened tool steel the model predictions were validated and its applicability in industrial context was demon-strated.