CRCA / mild steel welding

Cold reduced sheet is thin and heat-sensitive relative to plate, so weld sequence and fixture restraint control distortion more than amperage does. Galvanised or pre-coated CRCA should not be confused with bare CRCA: zinc fume and coating damage change the process, the ventilation and the post-weld treatment.

The commercial consequence is that CRCA 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 CRCA 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. Hot-rolled IS 2062 E250 plate above 6 mm is cut and formed, not pressed, on Ganesh's route: the 12 kW fibre laser cuts to 20 mm and the 200 T brake forms to 10 mm. 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 joining method where the customer needs a flat, paintable panel with no heat marking, or where the assembly must be disassembled for shipping. In those cases a folded and riveted or bolted construction is better.

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.

• Genset base frames
• Elevator counterweight frames
• Rack frames
• Forklift guards

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 CRCA the practical constraint is rust: cut, formed and coated parts should not sit unprotected in a humid shop, and the route is sequenced so pretreatment follows fabrication within the same production window. CRCA is also the easiest material to change late: a grade swap from CR1 to CR4, or a 0.2 mm thickness change, can be made without retooling in many cases, which keeps the decision reversible while volumes are still uncertain.

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 CRCA / mild steel, 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.