Consideration on Surface Modification of Steel Dies to Reducing the Plastic Sticking in the Forming Process

Abstract

Plastic parts such as syringe, phone cases, containers, etc. are formed in the mold under the molten temperature and with the high pressure. Plastic sticking to the mold surface during forming process is a serious practical problem for the manufacturing. The sticking limits mold lifetime, reduces production speed and degrades product surface quality. Mold material, surface condition, plastic chemical properties and molding parameters effect on the sticking. In this work, the effectiveness of surface treatments including mechanical polishing, plasma nitriding, hard DLC coating and TiB 2 ion implantation were investigated in regards to reducing the plastic sticking on the steels -SKD61, HPM38 and PX5 surface. The surface finishing was characterized with surface roughness, hardness, friction coefficients and wettability. Adhesion strength of the steel -plastic interface for the plastic materials: polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET), poly-butylene terephthalate (PBT) were measured with the developed method, with the concept of real surface area. It was shown that, for the different plastics, the appropriate die material and die finishing must be chosen to provide the lowest plastic sticking.