Automation, Manufacturing and Professional Practice
Automation, manufacturing and professional practice tests PLC operation, sensors and actuators, production metrics, CNC and manufacturing tolerances, safety, standards and engineering ethics. Questions often use a plant scenario and ask for the best engineering judgement, not just a formula.
Core rules
- A PLC repeats input scan, program execution and output update. Ladder logic is evaluated rung by rung; use fail-safe wiring so loss of power stops hazardous motion.
- OEE=Availability×Performance×Quality. Availability=run time/planned production time; performance=(ideal cycle time×count)/run time; quality=good count/total count.
- CNC tolerances depend on machine rigidity, tool wear, thermal growth and fixture rigidity; do not promise a tolerance tighter than the process capability.
- Safety systems are independent of normal control; e-stops are hardwired and reset must not restart motion automatically.
- Professional practice requires competence, honesty, confidentiality, conflict-of-interest disclosure and protection of public safety.
Worked example
A cell is planned for 480 min; downtime is 48 min, so availability=432/480=0.90. It makes 540 parts with an ideal cycle of 0.7 min: performance=(0.7×540)/432=378/432=0.875. Good parts are 529, so quality=529/540=0.980. OEE=0.90×0.875×0.980=0.772, or 77.2%.
Traps
- Adding OEE factors instead of multiplying them.
- Using total time instead of planned production time for availability.
- Assuming a PLC output changes instantly within the same scan.
- Treating a software interlock as a substitute for a hardwired safety circuit.
- Signing off a design outside your competence or hiding a known safety risk.