A mould is a complex machine that needs to be well designed to optimize the process and the production. The main and the most important parts of a mould are its core and cavity that will provide the plastic part after the filling process. This filling process poses a lot of constraints to the mould maker. One of the biggest and more complex constraints is the thermal regulation of the mould. Depending on this thermal regulation we can obtain a bad plastic part with a lot of default.
The traditional way to manufacture the cooling system by using standard drilling operations results in the coolant being too far or too near the cavity. This increases the difficulties and makes the injection process more complicated to remove the default on the plastic part. A mould maker has to try the mould on a press machine many times and to check the result of the injection, applying some modifications on the cavity or the mould to compensate these defaults. The Additive Manufacturing process permits a better definition of this cooling system. It can be generated by an offset surface based on the definition of the external or internal patches of the surfaces which define the plastic part. This cooling system can be continuous and perfectly paralleled to the cavity and not only straight obtained from a drill operation. The efficiency of this type of thermal regulation is optimal, and allows a reduction of the necessary tests on a press machine. The thermal analysis tools developed will allow checking the design of this cooling system and its efficiency.
Other quite important issues are the weight and the size of the mould that can be optimised by the Additive Manufacturing process. The core and the cavity are manufactured by removing matter by a traditional milling machine, according to the plastic part definition and the cooling system in a block. The Additive Manufacturing process allows using less matter and can be optimised by creating a dedicated “structural mesh” where the material is not necessary. This structure has to be strong enough due to the high level of pressure induced by the injection process. It is necessary to have no deformation in the core and the cavity during the injection. The stress analysis tools developed in WP4 together with the optimization tools provided by WP2 will be used to optimize the mould shape and to test its mechanical properties.
The Additive Manufacturing process will improve the mould but it is still necessary to mill the surfaces in contact with the plastic and the parting surfaces of the mould in the traditional way. The quality of the surfaces will not be fine enough to have no default on the part. The parting surfaces have to be perfectly joined to ensure the plastic is not leaking.
Dr. Tor Dokken
0314 Oslo Norwegen
P.O.Box 124 Blindern