What causes burrs in seam welding?

Burrs in seam welding might be describing weld flash or material that escaped from under the weld wheel during the weld and forms an irregular ridge along the length of the seam weld. All resistance welds seam or spot can leave some deformed material around the periphery of the weld zone. Generally this is not enough to be called a burr but in some cases the indentation would be cosmetically offensive if the surface were to be subsequently painted or were in a very visible location like the hood of a car. Product designers avoid welds in these locations.

Where seam welds generate visible indentations or slight raised areas which are not desired they can be treated as cosmetic welds. The weld schedule and electrodes, in this case weld wheels are selected to reduce the amount of heating and expulsion on the side of the part where the burr condition is not wanted. The wheel weld face might be increased. The force may be increased. This reduces contact resistance and surface heating. Adjustments to current and weld speed can be made. All of these would be made with the intent of reducing the surface heat and amount of material being expelled or pushed out during the welding process.

 A1 178b inclined seam weld wheels

Seam Welder with Knurled Drive Wheels

A second source of burrs in seam welding is potentially from the drive mechanism. Some seam welding wheels are driven by a small wheel which rides on the periphery and turns the seam welding wheel. This drive wheel is frequently knurled to prevent slippage. In addition the drive wheel is frequently used to dress the weld wheel as it turns. Some minimal amount of wheel material is cut to maintain the face shape of the driven wheel. Some copper flakes will be generated and they could be rolled into surface of the weld as the wheel travels. These flakes would be small and do not interfere with the weld integrity but could be visible and not desired in cosmetic locations.  Minimixing this knurling might need to be addressed in this situation.  Build in secondary operations might be considered, inline immediately after welding to smooth the burr or remove the flakes from the knurl drive.

Reference: RWMA – Resistance Welding Manual Section 4


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