# Spot Welding

## What is the best electrode material for spot welding galvanized steel?

In North America the most commonly used electrode materials for galvanized steel are RWMA Class 1, 2 and 20. By the quantity Class 1 and 2 are the most popular by far. Class 20 finds applications where the fabricator has weld schedules that make use of its unique properties – good conductivity and high heat resistance. Class 20 is sold at a premium for its higher heat properties.

In a previous article there is a complete discussion of this topic:
“WHY IS RWMA CLASS 20 USED FOR SPOT WELDING GALVANIZED STEEL?”

## What is the inductivity and voltages in the primary and secondary circuits and resistance in the weld area of a potential resistance weld of less than 15 milliseconds?

Answers to the questions asked do not exist in the literaturer.  This question has entered an area of academia and testing to reach definitive answers to the questions presented. This is beyond the scope of this blog.

Reference: RWMA - Resistance Welding Manual 4th Edition

## How much power is used resistance welding on a 150 KVA welder?

This question is asked often “How much power does my resistance welder use?” To answer this, we first need to calculate the Duty Cycle of the process. The formula for this is:

## What is a good way to align the top and bottom resistance welding electrode?

Proper alignment of the resistance welding electrodes is very important to insure proper force application and current flow through the electrode face. If not set up properly the part can be distorted and/or the electrode face can have exceedingly high current densities. This can result in distorted parts, expulsion and excessive electrode face wear.

## How do you prevent discoloration in two 1.2 mm (0.047”) plates tack welded for a subsequent braze joint?

This is the description of a typical cosmetic weld where one surface must be preserved as is. All heat and distortion must come from the other side, we will call it the back side. To do this a large “FLAT” faced RWMA “C” electrode is used on the good side. On the back side an RWMA “A” or pointed nose or in this specific case one with a face of 1.5 mm (0.060”).

The weld schedule should be designed to generate the heat from the back side and stop as the weld nugget just begins to grow into the top sheet. This will not be the best weld that could be produced. It will be a tack weld just good enough to hold the part together until the braze is made.

If discoloration is an issue water misting cooling, a gas shield or any other means could be used to prevent heat or oxidation on the one side.

COSMETIC WELD NUGGET MOSTLY IN ONE COMPONENT

Reference: RWMA - Resistance Welding Manual 4th Edition

### Have a Question?

Do you have a question that is not covered in our knowledgebase? Do you have questions regarding the above article? Click here to ask the professor.