Semi-solid forming applications: high volume automotive products

Abstract

Efforts to improve fuel efficiency by the transportation industry have been directed in recent years toward the use of mass production capable, low-cost, aluminum castings as part of a weight reduction strategy. Die casting and permanent mold methods have been used extensively in the manufacture of light-weight castings to satisfy the need. However, quality limitations imposed by these casting methods such as porosity and the need for impregnation, trapped gas and the ability to heat treat the parts for improved strength, and non-uniform mechanical properties have restricted the range of applications available. In the last six years, a semi-solid forming (SSF) process has developed into a mature, high volume production method for light-weight, aluminum parts.

The development of the SSF process depended upon the resolution of a number of critical technical issues: i) a reliable source of feedstock, ii) a robust forming technology capable of producing light-weight products capable of meeting automotive specifications, iii) alloys suitable for the SSF process of rapid cycling/high productivity manufacture, and iv) a joint customer/supplier ‘design for manufacture’ capability to enable the production of low-cost, functionally innovative products. In this paper, the products and mass production process used for high volume automotive applications will be described.
The manufacturing experience described illustrates the benefits of joint supplier/customer development in the design and manufacture of critical parts. Tailoring of alloy, semi-solid viscosity, tool lubricants, press dynamics, and part design in order to optimize process/product characterize the engineering collaboration that took place.
The advantages of the SSF process are described in terms of fundamentals of the forming process and the microstructural characteristics of the product. Robust methodology has been used throughout the development process and is currently being used in broadening SSF technology to include a semi-solid on demand process and a wider range of alloys.