FRACTURE TYPES AND THICKNESS DISTRIBUTION IN SUPERPLASTIC SHEETS FORMED WITH PLASTIC INJECTION MOLDING

This paper investigated the fracture types and thickness ratio distribution in superplastic Zn-22% Al sheets formed during a hybrid process combining superplastic forming with plastic injection molding. Three types of sheet fractures (edge crack, central crack, and combined crack) were observed. The effects of using this approach on sheet molding and fracture window for various parameters, including melt temperature, injection pressure, and mold temperature, were investigated. They are presented and discussed as they relate to molding area and various fracture types. Central cracks occurred when superplastic sheets were formed by injection molding at higher melt temperature, whereas edge cracks occurred at higher injection pressure. When melt flow was parallel to the sheet rolling direction, areas of edge crack were enlarged. The sheet thickness ratio distribution was obtained for various injection parameters and rib depths. Observation of sheet thickness distribution for variation parameters, and the tendency for fracture can be generalized.     

The application of surface demoldability and moldability to side-core design in die and mold CAD

In casting, molding and forming processes, the surface geometries of the fabricated products are formed/molded by different functional components of tooling. In plastic injection molding, they are molded by core, cavity or side-cores. In die and mold CAD, how to identify the product surfaces formed/molded by the corresponding tool components for a given product CAD model is critical, as it affects the determination of parting directions, parting lines and parting surfaces, the generation of core and cavity blocks, and finally the design of side-cores and their actuating mechanisms. In this paper, the concepts of surface visibility, demoldability, and moldability are first presented and formulated. The surfaces formed/molded by core, cavity and side-cores are then defined based on the plastic injection molding process. The methodology to identifying and classifying them is further developed. By employing the proposed notions of the demoldability map of surfaces and undercut features, the most preferred demolding direction, the grouping of undercut features, and how to conduct the side-core design is articulated succinctly, and the detailed procedures and processes are presented. Through an industrial case study, the developed methodology for side-core design is systematically presented and the feasibility of the developed approaches is verified.     

The application of surface visibility and moldability to parting line generation

In molding, casting or forging processes, part surfaces are formed by the core, cavity and local tools in molding/casting or by the upper and lower dies and local tools in forging. In computer-aided design of dies and molds, automatic identification of surfaces molded/formed by these different tooling components is critical since the generation of parting lines depends on these surfaces, which would further influence the determination of parting surfaces, the creation of core and cavity blocks and the entire mold structure. In this paper, the surface partability and visibility are first proposed and its moldability is next presented. Considering the molding process as an instance, the concepts of core-, cavity- and the local tool-molded surfaces are defined. A methodology based on surface visibility and moldability to determine the potentially and actually moldable surfaces of these groups is developed. Since the generation of parting lines is a crucial preliminary design step in mold/die design life cycle, a new approach to determining the parting lines based on the proposed methodology is presented. A case study is used to test the methodology and approach, and to validate the efficiency in parting line generation of molded parts.     

Experimental study on moldability and segregation of Inconel 718 feedstocks used in low-pressure powder injection molding

Moldability and segregation of feedstock are linked to the rheological behavior of the powder-binder mixture. In this study, the impact of binders on viscosity and segregation of feedstocks was investigated. The experiments were conducted on several feedstocks obtained by mixing Inconel 718 powder with paraffin wax-based binder systems. The viscosity of feedstocks was measured by a rotational rheometer while the segregation within green parts was evaluated using a thermogravimetric analyzer. It was demonstrated that the variation in solid loading within a molded part can be measured with a sensitivity of at least ±0.25?vol% of powder. The results indicated that the predominant powder-binder separation appears clearly at the top and the bottom of the molded part. It was also shown that the viscosity profiles of feedstocks and the intensity of segregation depends significantly on the binder constituents used in feedstock formulation. The mixture containing only paraffin wax produced the best trade-off between high moldability and low segregation for an injection process requiring an extended time range between injection and solidification of the part (e.g. up to 10?min). For a short processing time (e.g. <1?min spent in molten state), the feedstocks containing paraffin wax with stearic acid or small amount of ethylene vinyl acetate can be also considered as good candidates for LPIM process because their viscosity and segregation potential are relatively low.