OPS 385 Week 5 Improving and Sustaining the Process Example

From 7.4 to 2.1 Percent and Holding: Improving and Sustaining the Alternator Rebuild Process

[Student Name]

University of Phoenix

OPS/385: Lean Six Sigma and Process Management

Week 5 Assignment

[Instructor Name]

[Date]

Delta Rebuild Industries, its improvements, results and figures are composites written for a model paper.

In Week 3 the alternator project at Delta Rebuild Industries, an invented remanufacturer in Memphis, Tennessee, verified two causes of bench test failures: regulators from a newer, cheaper supplier, linked to high voltage, and slip rings that passed a visual check despite exceeding runout specification, linked to low output at idle. Week 4 measured voltage capability at a Cpk of 0.60. This paper completes the improve and control phases.

Generating and Selecting Solutions

For each cause, the team brainstormed options with rebuilders, the buyer and the test technician, then scored them on expected effect, cost and time to implement.

Regulators: options included returning fully to supplier A, requiring supplier B to complete corrective action, adding incoming inspection of supplier B regulators or splitting volume. The team chose to return to supplier A immediately, at about $6 more per unit, while supplier B completes a corrective action plan; if supplier B's parts pass a 200-unit incoming test with failures under 1 percent, it can regain a share of volume.

Slip rings: options included machining every slip ring, training rebuilders to judge more strictly or measuring runout on every ring. Machining all rings would add about 4 minutes per unit and remove material from rings that did not need it; stricter visual judgment would not fix a problem that eyes cannot see. The team chose measurement: a dial indicator fixture that checks runout in about 30 seconds, with a simple rule to machine any ring above the specification.

The Pilot

Both changes ran for four weeks on all heavy-duty alternators. Of 840 units tested, 18 failed, a rate of about 2.1 percent, against the 7.4 percent baseline. High-voltage failures fell from 23 percent of failures to almost none, and low output failures fell by about three-quarters. Over the same period, first-week warranty returns showed no early field failures among pilot units, though warranty effects will take months to confirm. A two-proportion test comparing the pilot and baseline failure rates gave a p-value well below 0.001.

Capability After Improvement

With supplier A regulators, the voltage mean moved to about 14.20 volts and the standard deviation fell to about 0.11. Cp is (14.6 minus 13.8) / (6 × 0.11) = 0.8 / 0.66 = 1.21, and with the mean centered, Cpk is also about 1.21. That falls short of the 1.33 often targeted for mature processes but is a large gain from 0.60; the team noted that further reduction in spread would require work with the regulator supplier on its own process.

A dial indicator costing less than a day's rework replaced a judgment no eye could make.

Mistake-Proofing and Standard Work

The runout fixture was designed so that a rebuilder cannot place the armature in the rebuild stand until it has passed through the fixture and a green light shows. This applies the mistake-proofing idea that Shingo (1986) promoted: build checks into the process so errors are caught at the source rather than found later. Standard work for teardown and rebuild was rewritten with photographs and the new runout step, and all rebuilders were trained and signed off in the first two weeks.

The Control Plan

Regulated voltage: X-bar and R chart, five units a day at test; owner, test technician; reaction, check regulator lot and bench calibration the same day.

Test failures: p-chart, daily; owner, rebuild supervisor; reaction, review failure modes and stop for a team huddle if a point exceeds the limit.

Slip ring runout fixture: daily check with a master armature; owner, rebuild lead; reaction, remove the fixture from service and recalibrate.

Regulator incoming quality: lot sampling of 20 units per shipment; owner, receiving inspector; reaction, quarantine the lot and notify purchasing.

Warranty returns: monthly; owner, quality engineer; reaction, teardown analysis of every alternator returned within 90 days.

How the Rebuilders Responded

The runout fixture met some resistance at first. Two senior rebuilders felt that measuring every ring implied their judgment was not trusted. The team showed them the data from Week 3, where a third of rings that looked fine were out of specification, and asked them to help design the fixture's layout. Within a week they were pointing out rings they would have passed that the gauge rejected, and one suggested a color-coded tag for machined armatures so that machining could prioritize them.

Handoff

The black belt handed the process to the rebuild supervisor, the process owner, at a short meeting with the plant manager. The handoff included the control plan, the charts, standard work, training records and the project's data. The project closes after three months of stable control charts.

Results and Lessons

At the pilot rate, rework drops from about 15 units a week to about 4, saving about $40,000 a year, and the warranty effect, if confirmed, adds about $40,000 more, against an added regulator cost of about $63,000 a year at 10,500 units. The regulator choice therefore roughly pays for itself through warranty and rework savings, while the slip ring change saves money outright. Zu et al. (2008) studied quality management practices and found that Six Sigma's structured approach, role structure and focus on metrics added to traditional quality management practices in improving performance. Delta's lessons: verify the measuring instrument first, test cheaper parts before switching fully and replace visual judgment with measurement where it matters.

Lean and Six Sigma Together

The Week 1 lean changes, smaller batches and a pull signal at test, cut alternator lead time from eleven days toward five. Fewer test failures support that flow: each failure used to send a unit back through rebuild and test, adding a day. Hines et al. (2004) described how lean thinking evolved from a focus on shop-floor tools toward a broader approach that integrates with other improvement methods to deliver customer value. At Delta, lean shortened the wait and Six Sigma removed the rework that kept interrupting the flow.

Conclusion

Two verified causes received targeted solutions: a return to the reliable regulator supplier with a path for the other, and measured rather than judged slip rings. A pilot cut failures from 7.4 to 2.1 percent and raised voltage capability from 0.60 to about 1.21. Mistake-proofing, standard work, a control plan with owners and reactions and a formal handoff are designed to keep those gains, while the combination with lean flow brings Delta closer to the fast, reliable rebuilds its fleet customers value.

References

Hines, P., Holweg, M., & Rich, N. (2004). Learning to evolve: A review of contemporary lean thinking. International Journal of Operations & Production Management, 24(10), 994-1011. https://doi.org/10.1108/01443570410558049

Shingo, S. (1986). Zero quality control: Source inspection and the poka-yoke system. Productivity Press.

Zu, X., Fredendall, L. D., & Douglas, T. J. (2008). The evolving theory of quality management: The role of Six Sigma. Journal of Operations Management, 26(5), 630-650. https://doi.org/10.1016/j.jom.2008.02.001