Hot platen brazing to produce laminated steel tooling

Abstract

The market demand for reduced product lead times coupled with increases in product iterations have driven the need to produce tooling as quickly as possible. Advances made in the rapid prototyping field have aided these lead time reductions considerably. The next logical step in reducing product lead times further is to actually apply the lessons learned in rapid prototyping to the manufacture of rapid tools, tools which are robust enough for production purposes. This paper outlines a method of sequentially joining steel sheets together using high strength brazed joints to produce laminated tools. Individual joints were produced by using a heated platen, rather than a furnace. One of the potential problems with this method is the heat from the platen re-heating previously brazed laminates during tool build. Heat flow trials were conducted to determine process operating windows for brazing so that the heated platen was in contact with the top laminate long enough to melt the braze alloy, but not so long that previously brazed layers were re-melted. Lap shear test samples were used to evaluate the tensile strengths of bonded laminates. Constants for the trials were, platen temperature, laminate material and its thickness, braze material, joint area and joining pressure. At optimum conditions, i.e. the least time taken to obtain the highest tensile strength, 1.6 mm laminate joints averaged 9.3 kN lap shear fracture loads after 210 s heating time. An operating window of 40 s was established for brazing two laminate interfaces without excessive heating occurring at the third interface.