Microforming and ultrasonic forming

by 1968- Bunget, Cristina Janeta

BUNGET, CRISTINA JANETA. Microforming and Ultrasonic Forming. (Under the direction of Gracious Ngaile.) The production of micro-parts has become more important and necessary in more fields, from electronics, computers, and micro-motors to micro-surgical tools and devices. Traditionally these precision mechanical parts are fabricated by machining. The net shape or near net shape processes, such as metal forming processes, are best suited for miniaturization because of the higher productivity and accuracy. But there are some limitations imposed by producing the tools and equipment, handling the parts, and more importantly with miniaturization there are size effects, which slow down the application of this process on a larger scale. The implementation of the microforming in mass production depends on the understanding and overcoming these effects. This research covers the size effects and presents a method to reduce the effect of the miniaturization, by superimposing ultrasonic oscillations on the microforming processes, with focus on micro-extrusion processes. Although the technology of ultrasonic forming is already used at macro-scale and some benefits have been realized such as the reduction in the forming forces and reduction of the friction between the die and the workpiece, the mechanism that explain these benefits are not yet understood. The principal objectives of this work are to develop an analytical model to determine the influence of the ultrasonic oscillations on the micro-extrusion processes, to design a set of tooling capable to superimpose the oscillations on the microforming and to observe through experiments the influence of the ultrasonic oscillations on the micro-extrusion processes. In order to study the tribological effects in microforming, finite element method was used to simulate the extrusion processes, starting with macro-scale and going down to micro-scale. The results of the simulations didn’t show significant differences between the surface expansion distributions for different sizes of the specimen. This is due to the fact that, at present, finite element codes do not include the billet surface topography in the frictional model. But it could be concluded that severe tribological conditions should be expected with miniaturization. In order to gain better understanding of the influence of the ultrasonic oscillations on the microextrusion, an analytical model was developed. The model proposed assumes that asperities will be elastically and plastically deformed by ultrasonic oscillations. In the cause of oscillation heat will be generated due to plastic deformation and sliding friction at the tool-workpiece interface. The developed model was used to predict temperature induced during deformation for forward micro-extrusion processes. A maximum temperature of 600º C was predicted, which agrees well with previous experimental observation. In order to verify the benefits of the ultrasonic oscillations on microforming, a set of tooling was designed and built. Finite element method was used to assist the design. Static, modal and harmonic analyses were conducted. Also a parametric analysis was conducted, in order to optimize the tooling for the experiments. After building the tooling a series of micro-extrusion tests were first carried out to observe the size effect on the friction in microforming processes and to evaluate the behavior of three lubricants. In the evaluation of the lubricants, the forming load and the surface finish after deformation were the two aspects considered. It was found that Lubricant-1 exhibited smaller forming load, and Lubricant-3 exhibited a better surface finish. When ultrasonic oscillations were superimposed on the micro-extrusion processes, the forming load decreased. A reduction of the forming load between 10 and 25 % was recorded. Also an improvement in the surface quality was observed. Overall, based on the test results, the ultrasonic oscillations were proved to have beneficial effects on the micro-extrusion processes.