Projection Welding

Questions and Answers

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.

Projection Weld Parts

                                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”

The author of these articles has offered the following insight and test data for push-off testing:

The evaluation of a coined/forged projection nut by means of a destructive push-off test is a viable means of determining the integrity of the weld. With the aforementioned in mind, a few beneficial items to keep in mind while performing this type of test would include:

How consistent and repeatable is the push-off test
      • Rate of force being applied
      • Normality of parts in fixture
      • Ability of test apparatus to withstand the ‘shock’ of a potential instantaneous unloading when the weld nut separates from the            base material

How consistent and repeatable is the welding process
      • Part presentation to welder(s)
      • Weld projection geometry consistency

The following test data demonstrates the potential variability with the push-off test and the nut weld process. The nut welds were considered to be acceptable. The four nut weld tests were not run under production optimized conditions. As they say, there is always room for improvement.

Nut Weld push off test results

As shown, variation exists on what are considered good product. This variation exists due to the elements noted above. The most notable are the weld nut projections, nut placement and the robustness and repeatability of the testing process.

As exhibited by the data, push-off tests can be used to evaluate nut welds. The amount of variation will depend upon the control of the variables on the input side. The important result is to meet a minimum value.

References: References: AWS Welding Journal: January & March 2011
                                        Q & A “Quality of Forged Projection Weld Nuts” by DONALD F. MAATZ JR.
                                       AWS Standard C1.1 Recommended Practices for Resistance Welding
                                       Technical Input by - DONALD F. MAATZ Jr.

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.

Ring Projections

             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.

 

Electrode Force             18-24      kg per mm of projection length (circumference)

Weld Time                      7 – 10    cycles

Welding Current             470-630 amp per mm of projection length

 

This information can be used for estimating the weld schedule conditions. Using these values some heating will occur. Always start at modest values and be careful until initial results have been evaluated.

These values do not state what material is being welded. Adjustments will be required to account for this. That is why there is a range. At the start of testing expect to use the full range and maybe more.

 

Reference: The Welding Institute, TWI – Recommendations For Resistance Welding Annular Projections

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:

American Wire Gauge

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.

Projection Weld Parts

                                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

ALIGNMENT

PROJECTION SHAPE, SIZE & CONSISTENCY

ELECTRODE MATERIAL AND CONFIGURATION

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