Spot Welding
Questions and Answers
Aluminum is very conductive and therefore Has a very small resistance. To make up for this a very high current is required to generate heat per JOULES LAW.
If your equipment has the capability to deliver enough amperage and force then it can be used to weld aluminum.
Resistance welding requirements run:
• Amperages of 30,000 – 50,000 amperes would be common power requirements for aluminum using AC equipment.
• Additionally relatively high forces are required to contain the weld and forge the weld nugget. Forces of 5kn (1150 lb.) force up to 20 kn. (4500 lb.) can be expected.
• Weld times can run from 8 to 30 cycles.
This data is for:
Alloy 2024 Thickness from 0.64 mm (0.025 in) to 3.18 mm (0.1.2 in)
If your welder has the power and duty cycle capability to perform the above then you can weld aluminum. Your local machine distributors will be able to help you make this determination.
Different values are available for midfrequency powered systems. They will be similarly higher than the normal steel values.
Reference: AWS Standard C1.1 - Recommended Practices for Resistance Welding
RWMA – RWMA Resistance Welding Manual 4th Edition
The answer to this question can be found in this blog and in many available references. References are listed below and an abbreviated table is listed here. You and your customer must decide upon the acceptable specification and then produce the product accordingly. The data provided here is a guide that does work but can vary from machine to machine. The exact settings must be determined by trial and error.
Slight modifications of these values will work for bare non coated steel.
A full list of materials and thicknesses and associated weld schedules can be obtained in AWS Standard C1.1. The RWMA Manual offers a full background in Resistance Welding including Machinery, Electrical and all components. The Tuffaloy Products Catalog offers weld schedules.
Related Article:
What are the typical resistance weld schedule settings to weld 1mm to 2mm low carbon steel?
References: AWS Standard C1.1 - Recommended Practices for Resistance Welding
RWMA – Resistance Welding Manual 4th Edition
Tuffaloy Products Catalog
As stated in other articles in this blog copper is a very conductive material and has little resistance and will not heat up very much. Copper electrodes are not used. RWMA Class 13 or 14 refractory materials are used. They heat up and transfer heat into the copper. In many applications the copper is coated with a low melting material, which will melt and act as a brazing agent and bond the surfaces together. This joint can only be as strong as the interface material. Zinc and Tin are commonly used but are not very strong. This limits their effectiveness.
A better joint can be formed if a true resistance braze is performed by placing actual braze material in the joint. Heat this joint using the same resistance method until the braze material melts and fills the joint and is allowed to solidify under very modest pressure. Don’t squeeze the molten braze material out of the joint. This braze joint will be strong and durable.
Low Force Adjustable Holder
The following articles in this blog will further explain resistance brazing.
How do resistance brazing schedules vary from spot welds?
Resistance brazing is used regularly in the electrical industry to make attachments in their highly conductive copper and silver products.
References:
CMW Products Inc. Catalog
Tuffaloy Products Catalog
RWMA, Resistance Welding Manual, Section 6
Welding a ferrule on the end of braided wire is done frequently to reduce the cost of assembly of electrical devices. Unfortunately, published process are not available.
The ferrule and the wire are copper or copper alloy. They may be coated with a plate or a varnish. Since heat in resistance welding is generated by resistance, resistance welding copper does not generate heat readily. People that perform ferrule welding generate the heat by using a hot electrode like RWMA Class 14 – Molybdenum.
REFRACTORY FACED ELECTRODES
The heat is generated in the electrode, which then is transmitted into the ferrule and the wires. As they heat up the ferrule plate and wire varnish is melted or burned away and the wires and ferrule begin to bond under the pressure of the welder.
The actual weld conditions/schedule will have to be developed by trial and error.
Reference: RWMA Resistance Welding Manual 4th Edition
Burnout is a term that I am not familiar with. This term implies two possible events:
• Expulsion at the electrodes
• Transformer Failure
I will look at each of these individually.
EXPULSION
This refers to expulsion of hot material from the weld face area. Numerous articles have been written on this subject in this blog:
WHY DO I HAVE EXPULSION AT THE WELD INTERFACE?
WHY DO I HAVE SURFACE EXPULSION?
Each of these articles list many reasons for expulsion. Each of those reasons has it’s own article in this blog explaining how it affects the weld and expulsion.
Do a search for the individual listed reasons and read the articles.
Expulsion leads to severe/accelerated electrode wear and is dangerous for personnel nearby. It also can coat machine parts and the product being welded with weld flash.
TRANSFORMER FAILURE
The other definition of BURNOUT could be failure of the transformer. There are only two general concerns for transformer users:
• Overheating
• Drawing more power than the rating for the transformer.
The fix for this is ensure that the transformer has the proper water flow as required by the manufacturer. Secondly confirm that the transformers are operating within the rating limits litsted on the manufacturers attached label.
Beyond this transformer issues and testing need to be addressed with the manufacturer of the equipment. Equipment design and maintenance is not in the realm of this blog.
References: RWMA – RWMA Resistance Welding Manual 4th Edition
AWS – AWS Standard J1.2 Guide to Installation and Maintenance of resistance Welding Machines
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