An Electrothermal Model Based Adaptive Control of Resistance Spot Welding Process

Ziyad Kas,Manohar Das

doi:10.4236/ica.2015.62014

Abstract

Resistance Spot Welding (RSW) is a process commonly used for joining a stack of two or three metal sheets at desired spots. The weld is accomplished by holding the metallic workpieces together by applying pressure through the tips of a pair of electrodes and then passing a strong electric current for a short duration. Inconsistent weld and insufficient nugget size are some of the common problems associated with RSW. To overcome these problems, a new adaptive control scheme is proposed in this paper. It is based on an electrothermal dynamical model of the RSW process, and utilizes the principle of adaptive one-step-ahead control. It is basically a tracking controller that adjusts the weld current continuously to make sure that the temperature of the workpieces or the weld nugget tracks a desired reference temperature profile. The proposed control scheme is expected to reduce energy consumption by 5% or more per weld, which can result in significant energy savings for any application requiring a high volume of spot welds. The design steps are discussed in details. Also, results of some simulation studies are presented.

Highlights

In resistance spot welding, the welding process begins by applying pressure on a stack of metal sheets, held together between a pair of electrodes
To develop a control scheme for controlling the nugget temperature of the Resistance Spot Welding (RSW) model presented by Equation (8a), we realize that it presents a bilinear system characterized by some unknown parameters
Such a curve is characterized by a fast rise of temperature to melting point, melting of the workpieces at the faying surface area which causes a slight drop in temperature, followed by a cooling zone that results from removal of weld current

Summary

Introduction

The welding process begins by applying pressure on a stack of metal sheets, held together between a pair of electrodes. The formation of a weld nugget strongly depends on the electrical and thermal properties of the sheet and coating materials [1]. Since the contact resistance near the faying surface is much higher than the resistance of the sheets and electrodes, most of the heating is concentrated near the faying surface, causing melting and formation of a nugget. How to cite this paper: Kas, Z. and Das, M. (2015) An Electrothermal Model Based Adaptive Control of Resistance Spot Welding Process. Depending on the thickness and type of material, welding current ranges from 1,000 to 20,000 amperes or more, while the voltage typically is between 1 and 30 volts [2]

Methods

Results

Conclusion