Projection nut welding is an important process within the resistance welding community. Many different segments of industry use this process in the fabrication of their products. Automotive, appliance and aircraft are examples of a few.
ASSORTED WELD NUTS
Ironically, with millions of nuts being projection welded there is very little data published on the process. In another article in this blog:
"WHAT ARE THE QUALITY STANDARDS FOR NUT PROJECTION WELDING?"
The lack of data was addressed. Two published articles were referenced:
AWS WELDING JOURNAL: RWMA Q & A JANUARY & MARCH 2011 – “QUALITY OF FORGED PROJECTION WELD NUTS”
Ring projections can be a round radius faced annular ring on one face of the part. Frequently the ring is a “V” shaped ring on the face of the part. Be it a ring or individual projections the process is the same. The projection design concentrates the force and heat on the part and heat will generate there when current is applied. The connection on the top of a water heater is an example we are all familiar with. This annular projection prevents the connection from leaking water during use.
TYPICAL RING PROJECTIONS
To develop the process to make this type of weld, some starting information is helpful. There is not much available. THE WELDING INSTITUTE in the UK “TWI” does have some basic data available.
They offered some information on general design considerations. Most importantly they offered estimated values of force, time and current.
Cross wire welding is a form of projection welding. When two wires are crossed that is a point contact. The heat and force are concentrated at that point contact. Even welding a wire to a sheet is a projection weld concentrated in a line point contact. Weld schedules are available in the literature for this type of operation.
The American Wire Gage Chart:
Knowing the wire size one can look up a possible weld schedule in:
AWS Standard C1.1 Recommended Practices For Resistance Welding
Assorted projection welding nuts are shown below. They are being welded in industry every day for cars, appliances, office equipment and many other products. Proper welding is imperative since many important items are being fastened to these nuts.
ASSORTED WELD NUTS
There is very little published data available on the subject of nut welding fasteners. A few articles have been written. Some data is available on the website of fastener manufacturers.
Two articles can be found in:
WELDING JOURNAL: RWMA Q & A JANUARY & MARCH 2011 – “QUALITY OF FORGED PROJECTION WELD NUTS”
This could be rephrased to be - What are the parameters of a projection welding process? In this case what parameters should be checked besides pressure, current and time when projection welding (PCT)? Before we move on, these three cannot be passed over. If the control or force application is not functioning properly the projection weld will not meet specification. The appropriate components must be part of the regular preventive maintenance list and checked daily, weekly, monthly as prescribed. A guide to machine and equipment maintenance can be found in:
AWS J1.2 GUIDE TO INSTALLATION AND MAINTENANCE OF RESISTANCE WELDIGN MACHINES
The next areas to address is the condition of:
FORCE APPLICATION AND FOLLOW-UP
PROJECTION SHAPE, SIZE & CONSISTENCY
ELECTRODE MATERIAL AND CONFIGURATION
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