Huang Naiyu

A note on rapid manufacturing process of metallic parts based on SLS plastic prototype

Abstract The polystyrene prototypes were produced by selective laser sintering (SLS) rapid prototyping process. According to properties of thermal depolymerisation of prototype material, the rapid manufacturing process for metallic parts was worked out through the combination of rapid prototypes and precise casting technology. After prototypes burned out in precision shell moulds, a series of complicate thin walled Al-alloy parts have been successfully made by vacuum differential pressure casting (VDPC) process. Accuracy of parts and influencing factors were investigated and discussed. The process combines the advantages of producing high-qualified metallic parts with shortening the period of production cycle.

Process optimization for AZ91 Mg-alloy low-pressure EPC process

The influence of a key process variable on the mold filling characteristics of AZ91 Mg-alloy was studied in the low pressure EPC process. The applied flow quantity of insert gas from 1 to 5 m3/h associated with the pressurizing rate in the low pressure EPC casting process was considered for rectangle and Lr shape plate casting. The experimental results show that there is an optimal flow quantity of insert gas for good mold filling characteristics in AZ91 Mg-alloy low-pressure EPC process. The optimal flow quantity of insert gas for the specimens is 3 to 4 m3/h. Either less or higher than the optimal flow quantity of insert gas would lead to misrun defects or folds, blisters and porosity defects. The practice of hub casting confirmed that the low-pressure EPC process with an optimal processing variable exemplified as 4 m3/h gas flow quantity was capable of producing complicated magnesium castings without misrun defects.

Complexation between borate ion and hydroxyl groups of phenol-formaldehyde resol resin

The complexation reaction between borate ions and phenol-formaldehyde resol resin in aqueous solution was studied by pH measurement, small model molecules and infrared spectroscopy. The results show that the complexation can proceed completely and rapidly at room temperature. Borate ion attacks phenol hydroxyl groups and adjacent position hydroxymethyl groups on the phenol ring of the resin, and forms the coordinate bond between boron atom in borate ion and oxygen atom in the hydroxyl groups. The complexation is a quantitative reaction. The complex is a six member ring containing two oxygens and one boron. The complexation can release hydrogen ions resulting in the decreasing pH in the resin solution.