Spot Welding
Questions and Answers
Water flow measurement is critical to ensure the components of the resistance welder and especially the electrodes are receiving the proper amount of cooling water during operation.
AWS J1.2 Guide to Installation and Maintenance of Resistance Welding Machines offers information about the setup and maintenance of resistance welders.
Glidcop is a tradename for a dispersion strengthened copper material classified by the RWMA. The most common form is RWMA Class 20. It is frequently used to resistance weld galvanized steel. There are other uses but this is a common usage and will be assumed the subject matter for this inquiry.
RWMA Class 20 is used in a manner similar to RWMA Class 1 and Class 2. It is most often used at or near expulsion levels of the weld lobe. It’s claims to fame are resistance to heat and anti-sticking. At various intervals during it use it is changed and dressed and reused. The other more common method in automation, the robot moves the electrodes periodically to a dressing station while the next part is loaded.
The question asked is: what is the life expectancy of RWMA Class 20? The answer depends upon what is being welded, how close is the weld schedule is to the high end of the weld lobe, how much expulsion is being experienced, how much material is being dress away?
To start this off “RO” stands for Reverse Osmosis. This is a filtration process that uses a semi permeable membrane to filter out larger particles in the water. It removes most minerals. “DM” stands for Demineralized Water. It is also called Deionized water. It also removes the minerals from the water. As the name implies the ions are removed. The pro for both is they produce pure water.
AWS has a standard for water used in resistance welding equipment:
AWS Standard J1.2M/J1.2:2016 Guide to the Installation and Maintenance of Resistance Welding Machines
Yes, upslope might help in the reduction of expulsion or spatter during resistance welding.
In another article: WHAT IS UPSLOPE IN RESISTANCE WELDING
It was described that the lower power applied during upslope gives the components a chance to anneal and relax and come into full contact before full power is applied. This reduces the possibility for material expulsion. An example is poor alignment or badly formed projections can sometimes be helped with upslope.
The answer is yes. MFDC can be used to heat 10 mm bars.
In this application the equipment could be running nearly continuously. In the design of the equipment care must be taken to make sure the equipment is cooled adequately to insure it does not overheat. Additionally the MFDC equipment must be sized properly.
Properly cooled and sized MFDC will handle this job nicely and perform well.
This is a classical application of Joules Law:
The heat is being generated by the resistance to the flow of current through the material.
Reference: RWMA, Resistance Welding Manual 4th Edition
Page 17 of 47
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.