Mistake proofing concepts and case studies John Holmes

Mistake proofing concepts and case studies John Holmes

Mistake proofing • “The basic principle of mistake proofing is that a defective component will not be manufactured – and if by some chance it is, it will be noticed by the operator before the next operation is carried out” [Mc. Kellen 2004].

Mistake proofing levels Judgment inspections >0 absolute defect rate Informative inspections SQCS Su. CS Se. CS Increasing timeliness of feedback Inspections closer to source Source inspections + Poka-yoke Zero QC (0 absolute defect rate)

Poke yoke classification: Regulatory Level of Regulatory function Definition Example Warning Device uses audio or Buzzer activated by visual queue to alert optical sensor when sophistication Level 1 wrong part bin selected Level 2 (best) Control Device shuts down Barcode scan of machines or lock wrong product shuts clamps to halt down line [TLC] operations [Shingo 99]

Poke yoke classification: Setting function Contact Definition Example “sensing device detect abnormalities in Vending machine rejecting foreign product shape or dimension by coins whether or not contact is made between the products and the sensing devices” Fixed-value “abnormalities are detected by checking for the specified number of motions in cases where operations must be repeated a predetermined number of times” [Shingo] Motion step “abnormalities are detected by Airplane takeoff checklist [Mc. Kellen] checking for errors in standard motions in cases where operations must be carried out with predetermined motions” [Shingo] Filling an egg carton [Mc. Kellen]

Case study: Toyota Camry Headrest Adding a poke yoke Use halfcircle to prevent insertion error Regulato Setting Simple and Error ry functio inexpensive? condition function n Control Contac Yes -Headrest (Car will t does not start (shape prevent until must removal and limit fit) allows switch backwards detects installation. headrest -Can cause installed) whiplash injuries [NHSTA].

Case study: Kel-Tech Engineering Source inspection + poke yoke Poke yoke jig to detect weld nut at source workstation Visual queue Air gun turned off (cannot proceed with assembly)

Case study: Kel-Tech Engineering Source inspection + poke yoke Poka-yoke type? Inspection Error condition Improvement type Contact (jig senses all 4 weld nuts are present) and control (air gun disengaged to prevent further operations) Source Missing weld nut None