OPS 330 Week 5 Quality and Continuous Improvement Example

Porosity in the Welds and Paint That Peels: Quality Improvement and a Continuous Improvement System for a Trailer Plant

[Student Name]

University of Phoenix

OPS/330: Strategic Operations and Logistics

Week 5 Assignment

[Instructor Name]

[Date]

Red Dirt Trailer Works, its defect data, costs and results are composites written for a model paper.

Over this course, Red Dirt Trailer Works, the composite livestock and horse trailer builder in Ada, Oklahoma, has found its welding bottleneck, planned an integrated system, set inventory policies and forecast demand. One part of its reputation remains at risk: dealers report more paint problems and weld repairs than they did five years ago. This paper measures the cost of quality problems, runs an improvement project on the largest one and builds a system for continuous improvement.

The Cost of Poor Quality

The team estimated costs from six months of rework logs, scrap tickets and warranty claims, then annualized them: weld rework about $150,000, paint touch-ups and repainting about $110,000, scrap of cut and welded parts about $60,000 and warranty claims from dealers about $90,000. Total internal and external failure cost is about $410,000 a year, roughly 2 percent of sales. Prevention and appraisal, mostly final inspection, cost about $120,000. The balance shows a plant spending far more fixing problems than preventing them.

Where the Problems Are

A Pareto chart of 1,240 recorded defects ranked by count showed weld porosity at 38 percent, paint adhesion failures at 27 percent, wiring faults at 12 percent, misaligned doors at 9 percent and others at 14 percent. Porosity and paint together make up about two-thirds of defects. Porosity matters most because it occurs at welding, the bottleneck: every hour spent grinding out and rewelding a joint is a trailer-hour the whole plant never gets back.

A DMAIC Project on Weld Porosity

Schroeder et al. (2008) described Six Sigma as a way of organizing improvement that runs alongside the regular hierarchy, with trained project leaders, a fixed sequence of steps and numerical targets, and argued that this structure is what separates it from earlier quality programs. Red Dirt applied the method's five phases with a small team: a welding lead, a quality technician, a maintenance mechanic and the operations manager.

Define: reduce porosity defects in frame and floor welds, which force rework at the bottleneck and cause cracked joints in the field.

Measure: inspectors checked 50 weld joints a day by visual and dye penetrant inspection for four weeks. The average proportion defective was 6 percent.

Analyze: a cause-and-effect session and tests pointed to three causes. Aluminum filler wire stored in an unheated cage absorbed moisture and surface oxide; joints were not always cleaned with a stainless brush and solvent before welding; and on windy days, drafts through open bay doors disturbed the shielding gas. Porosity was about three times higher on windy days and with wire from the cage than with fresh wire.

Improve: wire moved to a heated, sealed cabinet with first-in, first-out rotation; a cleaning station and checklist were added at each bay; and portable weld screens and strip curtains were installed at bay doors. Over the next four weeks, the defect rate fell to about 2 percent.

The most expensive defect in the plant was caused by a cold cage of welding wire and a south wind.

Holding the Gain

A p-chart now tracks the daily proportion of defective joints in a sample of 50. Using the improved average of 0.02 as the center line, the distance from the center to each limit is three standard errors, and the standard error is √(0.02 × 0.98 ÷ 50). That square root is about 0.0198, and three times it is about 0.059. The upper control limit is therefore about 0.079, and the lower limit is zero. A point above the upper limit, or seven days in a row sitting higher than the average, triggers an investigation the same day. The wire cabinet and cleaning checklist become standard work, audited weekly.

What the Welders Thought

The welders were skeptical at first; several believed porosity came from the alloy itself and could not be fixed. Running the comparison of fresh and caged wire in front of them, with dye penetrant results laid side by side, changed minds faster than any presentation. Two welders proposed the weld screens after noticing that the worst joints came from the bay nearest the north door. Their names went on the improvement board, and both joined the paint adhesion team.

Paint Adhesion Next

The second project, on paint adhesion, will follow the same method. Early data suggest inconsistent surface preparation on aluminum, the same root theme of cleanliness that drove porosity.

A Continuous Improvement System

Single projects fade without a system. Bessant et al. (2001) described continuous improvement as a set of behaviors that organizations develop in stages, from occasional problem solving to embedded routines in which improvement is part of everyone's work. Shah and Ward (2003) found that bundles of lean practices, implemented together, were associated with better operational performance. Red Dirt's system has three parts. Daily problem boards at each work area record problems, owners and actions, reviewed in a ten-minute stand-up at the start of each shift. A kaizen event each month brings a cross-functional team together for three days on one process, starting with wiring faults and door alignment. A suggestion process promises a response within five working days and recognizes adopted ideas at the monthly plant meeting.

Measures

The plant will track cost of poor quality quarterly, aiming to cut it from about $410,000 to under $200,000 within two years; first-pass yield at final inspection; warranty claims per hundred trailers; weld defect proportion on the p-chart; and the number of suggestions implemented per month.

Quality and Strategy

Quality supports all of Red Dirt's competitive priorities. Durability, one of the reasons customers buy, depends on sound welds and lasting paint. Dependable delivery, the priority dealers stressed, depends on not losing bottleneck hours to rework. Reducing porosity alone returns roughly 12 welding hours a week to production.

Conclusion

Red Dirt spends about $410,000 a year on failures, concentrated in weld porosity and paint adhesion. A DMAIC project traced porosity to wire storage, cleaning and drafts and cut it from 6 to about 2 percent, held by a calculated p-chart and standard work. Daily boards, monthly kaizen and fast responses to suggestions turn that first success into a system for continuous improvement that supports durability and dependable delivery.

References

Bessant, J., Caffyn, S., & Gallagher, M. (2001). An evolutionary model of continuous improvement behaviour. Technovation, 21(2), 67-77. https://doi.org/10.1016/S0166-4972(00)00023-7

Schroeder, R. G., Linderman, K., Liedtke, C., & Choo, A. S. (2008). Six Sigma: Definition and underlying theory. Journal of Operations Management, 26(4), 536-554. https://doi.org/10.1016/j.jom.2007.06.007

Shah, R., & Ward, P. T. (2003). Lean manufacturing: Context, practice bundles, and performance. Journal of Operations Management, 21(2), 129-149. https://doi.org/10.1016/S0272-6963(02)00108-0