Brass welding

Brazing with a silver-based filler keeps the joint below the melting range of the brass and limits zinc fume. Welding brass directly causes zinc evaporation, porosity and a colour mismatch that is hard to hide. On assemblies that will be polished, the joint and the heat-affected zone need to be planned into the finish.

The commercial consequence is that brass is priced on its own material line, not blended into a steel rate. Material grade, thickness, tolerance and finish are quoted separately from conversion, so a change of specification is visible in the price.

Ganesh quotes to the drawing first and to ISO 2768 general tolerances where the drawing is silent. For brass welding, the practical starting points are in the table below. They are starting points, not a guarantee: the part geometry, thickness and fixturing decide what can actually be held, and the quotation states the tolerance offered.

Welding fixtures are designed and built in the Ganesh tool room, which is why assembly geometry is controlled by steel, not by a welder's eye. Lead-bearing CuZn39Pb2 machines and shears more freely but is restricted in some markets under RoHS and REACH, so the grade has to be chosen against the destination market, not only the drawing. The route is quoted as one sequence so the customer does not have to coordinate a cutter, a former, a welder and a coater.

Welding is the wrong route for most brass assemblies; a folded, riveted or brazed joint is usually better. If the design needs a structural joint, consider changing the material.

A manufacturability review before quotation is the cheapest place to find this out. Send the drawing, material, finish and annual quantity and the review comes back in writing.

• Decorative frames
• Instrument housings
• Electrical assemblies
• Hardware

Weld when the assembly cannot be formed as one part or must be shipped knocked down. Robotic MIG pays back on repeat assemblies where the fixture holds the joint in the same place every cycle; below a few hundred identical assemblies a year, a fixture and manual MIG are usually more economic. Do not weld where the customer needs a flat, unmarked panel or where the assembly must be disassembled for service. For brass the practical constraint is alloy restriction and tarnish: the grade has to satisfy the destination market's substance rules, and the surface needs protection if it must stay bright. Brass is usually a volume material by nature, so the process decision is often already made by the part family; the real choice is the alloy and the temper, and whether the destination market permits the lead content.

State the weld symbol or size, whether welds are structural or sealing, the finish requirement on the weld (dressed or as-welded), and the dimensional tolerance on the assembled frame rather than on the individual parts. Say whether the assembly is coated after welding, because that changes the access and the masking plan.

Inspection covers weld size and length, visual defects, distortion against the assembly drawing and, where specified, penetration or leak testing. Fixtures are maintained in the tool room. Weld and dimensional records are kept with the batch, and material is traceable to mill certificates.

Cost splits into fixture amortisation, fit-up, weld time, cleaning and inspection. Fit-up is usually the largest labour element: a part that locates itself in the fixture takes a fraction of the time of one that has to be measured and clamped. Distortion correction, if it is needed, is pure rework cost. On brass, material is quoted as its own line at the prevailing rate for the grade and thickness, so a change of specification is visible rather than hidden in a blended rate.