tailieunhanh - 21st Century Manufacturing Episode 1 Part 9

Tham khảo tài liệu '21st century manufacturing episode 1 part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 154 Solid Freeform Fabrication SFF and Rapid Prototyping Chap. 4 Comparison of Approximate Accuracy of Rapid Prototyping Processes Accuracy inches per inch Note that the machine suppliers quote in thou and that one thou 25 microns Figure Comparison of accuracy as of March 2000 . CASTING METHODS FOR RAPID PROTOTYPING Introduction The classic manufacturing texts by DeGarmo and associates 1997 Kalpakjian 1997 Schey 1999 and Groover 1999 are remarkably comprehensive in their coverage of the casting process. The several methods of casting include Lost-wax investment casting Ceramic-mold investment casting Shell molding Conventional sand molding Diecasting Rather than duplicate the material found in other books this section focuses on casting as it is done by rapid prototyping companies. Batch sizes from 50 to 500 are typical. The key market strategy is that casting is cheap and fast. However jt may not be the choice for the final product because of its tolerances. Depending on the type of casting chosen the tolerances vary from - 75 microns inch for lost- Casting Methods for Rapid Prototyping 155 wax processes to - 375 microns inch for standard sand castings also see Chapter 2 . Lost-Wax Investment Casting As mentioned in Chapter 1 the fundamentals of casting were invented by Korean and Egyptian artists many centuries ago. The following steps are known as the lost-wax investment casting process Figure a-c a master pattern of an engineering or art object is first carved from wax d-f it is surrounded by a ceramic slurry that soon sets into solid around the wax g the wax is melted out through a hole in the bottom leaving a hollow cavity h this hole is plugged and liquid metal is poured into the open cavity from the top i after a while the metal solidifies and the ceramic shell can be broken away to get the part j some cleaning deburring and polishing are needed before the object is finished. The process was greatly improved and .