GB527 Unit 4 Quality Improvement Memo Example

Inspect After Machining or Seal the Castings: A Unit 4 Quality Improvement Memo for an Irrigation Valve Plant

[Student Name]

Purdue University Global

GB527: Global Operations

Unit 4 Quality Improvement Memo

[Instructor Name]

[Date]

The plant, its foundry and every figure are composite and illustrative; the sources cited are real.

To: Plant Manager, Platte Valve Works

From: Quality Engineer

Subject: Reducing pressure-test leaks

Recommendation

Ask our foundry to vacuum-impregnate every valve body casting, at $1.20 a casting, and start a weekly chart of the pressure-test leak rate. This should cut total leak-related costs from about $221,600 a year to about $89,900. An inspector after machining would cost more than it saves.

The Problem

We build about 24,000 valve assemblies a year. At the end-of-line pressure test, 3.1 percent leak. Each is torn down, the body replaced or repaired, and the valve rebuilt, at about $72 each, or about $53,600 a year. Another 0.5 percent leak after installation in the field, often during the first weeks of the irrigation season. Each field failure costs about $1,400 in warranty parts, a dealer's labor charge and freight, or about $168,000 a year. Total failure cost is about $221,600, before counting the dealers' frustration in the busiest weeks of their year.

We sectioned 40 leaking valve bodies last quarter. In 32 of them, the leak path was porosity in the casting: small voids from the casting process that machining opened into a passage between the water chamber and the outside. The other eight leaked at seals or threads.

Four of every five leaks come from voids that were in the casting before we touched it, yet we find them only after machining, assembly and testing.

Option A: An Inspector After Machining

A dedicated inspector could pressure-test machined bodies before assembly. The inspector would cost about $68,000 a year, including equipment. If the inspection caught about 70 percent of porosity leaks before assembly, those bodies would be scrapped at about $18 each rather than $72, saving about $28,100 a year in rework. A small share of borderline porosity would still pass and leak in the field, so field failures might fall only about 15 percent, saving about $25,200. Total cost under this option would be about $236,200 a year, more than today.

Inspection finds defects; it does not prevent them. Juran and Godfrey (1999) describe the costs of quality as prevention, appraisal, internal failure and external failure, and note that spending on appraisal alone rarely lowers total cost when defects are created upstream.

Option B: Seal the Castings

Vacuum impregnation fills casting porosity with a sealant before machining. Our foundry offers it for $1.20 a casting, about $28,800 a year. Based on the foundry's results with other customers and our sectioning, it should prevent about 80 percent of porosity leaks. Rework would fall to about $10,700 a year and field failures to about $50,400, for a total of about $89,900 including the impregnation charge, a saving of about $131,700 a year.

This is prevention spending: it removes the cause before value is added. Heizer et al. (2020) describe the same principle as building quality at the source, so that defects are stopped where they arise instead of being sorted out later. The remaining leaks, at seals and threads, should be addressed separately through assembly torque checks.

Monitoring: A Weekly Leak Chart

To confirm the result and catch any return of the problem, we should chart the pressure-test leak rate weekly on a p-chart, which tracks the proportion of defective units against control limits. With about 480 valves tested a week and a current rate of 3.1 percent, the control limits would be about 0.7 and 5.5 percent. After impregnation begins, the chart should show a shift downward, and the limits should then be recalculated. Montgomery (2020) recommends this kind of attribute chart for monitoring the fraction of nonconforming units in a process.

A point above the upper limit would signal a change, such as a new casting pattern or a lapse in impregnation at the foundry, and would trigger sectioning of the next leaking bodies.

Costs and Timing

The foundry can begin impregnation within three weeks. The p-chart requires about an hour a week of the quality technician's time. Both should start before the January peak, so that the improvement reaches dealers in the season when field failures cost us most.

Risks

Impregnation may not reach all porosity in the thickest sections, so we should section a sample of leakers after two months. The foundry's charge may rise; at more than about $6.70 a casting, the saving would disappear. Finally, if porosity is rising because of a change at the foundry, impregnation would hide the cause, so we should ask the foundry for its own porosity data each month.

References

Heizer, J., Render, B., & Munson, C. (2020). Operations management: Sustainability and supply chain management (13th ed.). Pearson.

Juran, J. M., & Godfrey, A. B. (Eds.). (1999). Juran's quality handbook (5th ed.). McGraw-Hill.

Montgomery, D. C. (2020). Introduction to statistical quality control (8th ed.). Wiley.