Error processing SSI file

Error processing SSI file

The "Hydraw" Process for Ultrafine Gold Bond Wire


Overview

In a recent progress report to the National Science Foundation (NSF), the following progress report on the "Hydraw" process was forwarded:

Abstract:

This first semi-annual technical report covers the activities between October 1995 and March 1996. For wires below 1.5 mil, present day conventional drawing technology is limited to approximately 4% to 6% reduction in area per die. For smaller wire sizes both the reduction per die and speed become smaller, and the wire breaks more often. With "Augmented Hydrostatic Extrusion" (HYDRAW) Ref. [1] and Ref. [2], as described in the figure we are able to extend beyond some of present day limitations of the conventional processes. Reductions up to 25% are accomplished and wire breaks rarely occur. In this paper we will focus on the implementation of a concept that is essential to the success of the project. According to this concept we substitute a built-in automatic control system, to replace the more cumbersome closed loop sensor and control system.

The closed loop control system. In the original HYDRAW design (Ref. [2]) the pressure in the chamber supplies the bulk of the motivation power for the extrusion. The pressure is generated to a level below that required to push the wire out. While the pressure increases the liquid compresses and acts like a spring. The liquid in the chamber therefore cannot establish a positive speed control for the emerging wire.

The pick-up spool augmented the pressure with the required remaining minimal draw force that is essential to provide the speed control. The tension sensing device between the die and the pick-up spool (not shown here) provided the signal to the pressure pump. One option of the mode of this control is that if the tension rose, the pump was instructed to increase the pressure, and vise versa. In another mode the signal instructed a pressure control valve to respond.

The system works but it is sluggish. The response may be too slow or it may overshoot the target. Speed and tension fluctuate excessively and at higher and higher drawing speeds the wire breaks more and more often. The finer the wire is, the harder it becomes to control the system.

Built-In Clutch Control System. In the present design we introduced a clutch between the pick-up spool and the tension producing system. The characteristics of the clutch are such that when the difference between the speed of the emerging wire and the speed of the shaft increases the drawing force increases, and vice versa. Thus, for example, when the wire speed slows down, the differential speed rises, automatically providing the required increase in tension.

The clutch also provides the two required control limits on the emerging wire, i.e., tension and speed.

Tension. The wire can only sustain a drawing force that is below its strength. The motivation draw force is designed so that even when the wire is slowed down to a standstill, the tension will not reach the tensile strength of the wire. Thus wire break due to overload is deterred.

Speed. The pinch-off phenomena due to excessive speed is described in Ref. [2]. When control is maintained, the speed of the driving motor is the upper limit on the speed of the emerging wire. When the wire speed approaches that limit, the pulling force drops to zero before reaching the speed limit. Thus, run-out and pinch-off are prevented as long as the speed of the driving motor is maintained below the run-out speed.

References:

  1. Robertson, J., British Patent No. 19,356, October 14, 1893.
  2. Avitzur, B., Jin, J., and Simchon, M. "Augmented Hydrostatic Extrusion of Ultra-Fine Wire", Proceedings of the 1994 NSF Design and Manufacturing Grantees Conf. published by the Society of Manufacturing Engineers, One SME Drive, P.O.Box 930 Detroit, Michigan 48121. pp 405, 406.



Acknowledgement: This study is supported by NSF Phase II Grant #9321057
Error processing SSI file

 

Last Modified:
Monday April 26 2010

Error processing SSI file