Manufacturing Processes, Fabrication, and Welding
Domain scope
This domain tests casting, forming, machining, joining, welding processes, weld defects, heat-affected zones, and fabrication tolerances. The exam favors process selection and calculation of cutting parameters.
Core rules
- Cutting speed is surface speed; spindle speed n = 1000V/(πD) with V in m/min and D in mm.
- Feed is expressed per revolution or per tooth; feed rate = feed per tooth × teeth × rpm.
- Welding creates a heat-affected zone whose properties differ from the base metal.
- Common weld defects include porosity, slag inclusion, lack of fusion, undercut, and cracking.
- Preheat and interpass temperature control help prevent hydrogen cracking in high-carbon or thick steel.
- Brazing and soldering melt filler but not the base metal; welding melts the base metal.
- Distortion is managed by balanced sequences, fixtures, and restraint.
Worked example
A 50 mm diameter cutter is used at 100 m/min cutting speed. n = 1000×100/(π×50) = 100,000/157.08 ≈ 637 rpm. If the feed is 0.1 mm per tooth and the cutter has 4 teeth, the table feed is 0.1×4×637 ≈ 255 mm/min. Check that the machine can achieve the required spindle speed before setting the feed.
Traps
- Using diameter in metres in the rpm formula without converting.
- Confusing cutting speed with feed rate.
- Assuming a weld is stronger than the base metal without qualification.
- Ignoring preheat requirements for thick or crack-sensitive steel.
- Treating brazing as a welding process that melts the base metal.