Spot Welding

Questions and Answers


To answer this question, we need to start by defining some words. The question asked appears to be describing extending “HOLD TIME”. This is the time the electrodes remain on the parts exerting force while the part is cooling down.

The word “RETRACTION” is frequently used to describe a cylinder or servo function where the control asks the force device to only open partially to reduce the electrode travel time between welds. More welds can be performed in a short time.

For more information - In this BLOG See:

WHAT IS HOLD TIME IN RESISTANCE WELDING?

WHAT IS A RETRACTION FUNCTION?

A resistance welding schedule has three defined segments. They are:
                                                                                    SQUEEZE

                                                                                       WELD

                                                                                       HOLD

This question comes up frequently. Many look for a formula to set the squeeze and hold time for resistance welding.

Several articles have been written on this subject in this blog:

HOW DO YOU SET THE PROPERSQUEEZE TIME IN A RESISTANCE WEDING SCHEDULE?

IS THERE A FORMULA TO DETERMINE THE SQUEEZE TIME IN RESISTANCE WELDING?

IS SQUEEZE TIME IMPORTANT?

HOW WILL HOLD TIME CHANGE THE RESISTANCE WELD STRENGTH?

Resistance brazing is not spot welding so the electrode face geometry does not have to concentrate the heat into a small area. Frequently the electrode face is machined to conform to the surface that it is in contact with. Frequently the electrode will contact the entire work piece surface. In some cases the electrode faces is milled out. The work piece is nested into the face of the electrode in order to insure proper part placement and alignment. A small vacuum is sometimes pulled through the center of the electrode to hold the part in place before the electrode closes. This is very common for small part brazing.

The electrode material is frequently RWMA Class 2. It could be ETP copper and in many cases carbon electrodes are used.

Refractory faced electrodes2

When resistance brazing contact materials, refractory faced electrodes RWMA Class 11, 13 and 14 as well as Class 2 are commonly used.

Pressure, current and time (PCT) are the basic functions performed by the resistance welder. These functions are controlled or initiated by the weld controller. It initiates each step when told to start the weld process by input from the foot switch or automation PLC. The controller allows time for each step to operate and controls the current amplitude. In simplified form this is Squeeze, Weld and Hold. The squeeze sequence allows the pressure system to build up the force to contain the weld. The weld function is the actual current flow and is totally controlled by the weld controller. It regulates the amplitude and time of current flow. Hold is the period which allows the weld nugget to cool down and solidify under force. The controller regulates this time.

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