Application of modified FMEA approach for iron foundry's product defects reduction

Abstract

To reduce defects in cast iron products and to evaluate the return on quality investment. The selected product is an automotive part, Fly wheel ZEI, which is the most volume production of the case study company. The defect symptom of interest is blowholes or pinholes defect (B111) which is the highest defect found in production. There are many possible causes of B111 defect. The defect is as high as to lower the production yield and also ruin the company's reputation from customer complain. Primarily, the team benchmarks on the production control with the first tier company who is producing the fly wheel ZEI. It is found that there are two different controlled factors which are brand of coal dust and present of corn starch in mould sand. The case company is using coal dust brand A and corn starch addition with ratio per sand 1:8 while the benchmarked company using coal dust brand B and not using corn starch any more. Brainstorming other related factors to B111 defect and applying cause and effect matrix, why-why analysis, and FMEA, relevant factors with more than 100 RPN in FMEA table found which are high % sulphur in coal dust due to the present coal dust brand "A", ash content in mould sand due to the present coal dust brand "A", sand low permeability due to too much water absorption by present of corn starch, sand low compactability due to fine substance from present of corn starch, and hot sand stick to the pattern due to using up high temperature mould sand. Coal dust B and absent of corn starch are factors of interest in B111 defect reduction. Factors screening is done by one-factor-at a-time (OFAT) to the 168 specimens. It is found that using coal dust B and absent of corn starch can significantly reduce the B111 defect with 95% confidence. The findings are confirmed by casting the F/W ZEI for 6,000 units. The B111 defect exists at 1.7% which is acceptable. Return on quality investment (ROQI) is defined based on the 6,000 cast units. The company can reduce the unit cost 0.52 baht from switching to coal dust B and stop using corn starch. Apart from that, the company can significantly save the damage cost due to the B111 defect. The company can gain the advantages of ROQI from casting the first 6,381 units Fly Wheel ZEI. To draw the conclusion that coal dust A and corn starch are main effects to B111 defect on fly wheel ZEI of the case company. Thus, the appropriate control is using coal dust B : bentonite at ratio 1:4 and stop using corn starch in sand moulding