Projection Welding
Questions and Answers
Projection welding weld nuts is very common in industry. There is some data available on the subject. One source is AWS. The other is Ohio Nut and Bolt Company. Their site has schedules for many weld nuts and studs to choose from.
The answer to this question is maybe. It will depend upon several variables that were not supplied with this inquiry.
MATERIAL BEING WELDED – stainless steel, low carbon steel and aluminum have increasing current requirements.
MATERIAL THICKNESS – This will dictate the size of the projection. Projection size will dictate current amperage, time and force requirements.
PRODUCTION RATE – Number of welds per minute.
TYPE OF MACHINE/TRANSFORMER – Press welder, AC, DC, MFDC
With this information one can size the transformer needs and make an informed decision.
In projection, resistance brazing or spot welding, residue from the process eventually builds up on the face of the electrode.
CLEANING COPPER SPOT WELDING ELECTRODES:
In the case of spot welding mushrooming is also present. Spot welding electrodes are normally copper alloys making a machining process on or off the machine the most practical method of mushroom and residue removal.
CLEANING COPPER, COPPER TUNGSTEN (RWMA Class 11), MOLYBDENUM (RWMA CLASS 14) AND PURE TUNGSTEN (RWMA CLASS 13) PROJECTION & RESISTANCE BRAZING ELECTODES:
In projection welding and resistance brazing there can be some mechanical wear of the electrode face but frequently there is a buildup of fluze or foreign product generated from the weld, weld flash or???. At some point this buildup may interfere with part loading or locating. Cleaning becomes necessary. Depending upon the electrode material a simple machining process may be called for if it is a copper alloy.
In this scenario there are two possibilities:
1. The weld nut has come off.
2. The weld nut is still adhering the part.
In either case the weld nut projection geometry has been altered. The Question is what should be done to correct for this?
In Case # 1 the nut should be scrapped and new weld nuts welded to the part. This may require some refinishing of the weld blank at the weld location prior to rewelding. A clean smooth surface is desired prior to rewelding. Additionally, a process adjustment may be required to make an acceptable weld.
In Case # 2 this is a reprocess or repair. The only acceptable repair the Detroit-3 have ever considered is a form of arc weld to the exterior of the nut. This could be a MIG-braze if the metal is thin. If thicker a GMAW may be employed. A reweld would never be acceptable. There are too many variables to overcome to achieve an acceptable weld.
It is likely that a standard published 3 or 4 projection weld schedule does not exist in the literature. The options are start testing from scratch or look at spot welding data for the same material that may exist.
The best way is to use a known similar weld schedule to estimate for the initial test coupons.
Simply use the data for one spot weld and multiply current and force by three or four depending upon spot spacing. Time stays the same.
FOUR PROJECTION PART
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