According to the process model based on product model, the design of EPC mold needs to get mold cavity, core, movable block, inlay block, etc. through parting, then assemble through various standard parts and non-standard parts, and carry out structure, motion, interference inspection, etc., finally get the mold through manufacturing. After the EPS process model of the product is obtained, it can not be directly used for mold setting up, but also needs to be processed to some extent, usually including the following four steps:
(1) Shrinkage
Due to the shrinkage of the foam model and the shrinkage of the molten metal, volume zoom in is needed to compensate the shrinkage. Generally, the zoom ratio of the three dimensional model is 1.013 for the foam model using EPS beads as raw material and the casting with HT250 as raw material. Shrinkage can be placed at any stage of product design stage, process model design stage and mold design stage, and only once. Considering that accurate model is needed to simulate in product design stage, and shrinkage of mold placement in mold design stage will affect the size change of interface between mold and equipment, resulting in installation failure, so shrinkage is generally placed in process design stage for comparison Reasonable.
(2) Increase machining allowance
In some parts that need to be processed during the processing of products, the increase of machining allowance can make the blank still get qualified products through machining even if there is a certain error in casting. The upper and lower end faces of the motor shell shall have a margin of 4mm, and the single side and end faces of all kinds of Lappers shall be corrected by 3mm. The “offset” function of UG can easily add machining allowance to the model.
(3) Draft processing
The lost foam casting process has no draft requirement for foam model, but in order to facilitate the foam model to be removed from the mold, draft treatment is still needed on the lost foam mold. In the design of EPC mold, the draft processing should follow the principle of “increase machining allowance”, that is, when drawing with the direction of demoulding as the vector, it should be ensured that the model after draft can include the model before draft, and the model after draft is larger than the model before draft, so that the casting blank will be slightly larger than the three-dimensional product, which is equivalent to the increase of machining allowance. The advantage of this treatment is that there may be a large machining allowance in some parts of the casting during machining, but the theoretical products can still be obtained through machining. If the machining allowance becomes small, there is a risk that the casting will not be machined during machining, and the consequence of this kind of casting is generally scrap.
