Plastic Pipes Continuous Improvement

Plastic Pipes Continuous Improvement

A Lean/Continuous Improvement (CI) culture in the manufacturing industry of plastics pipes leads to the achievement of strategic goals by means of a serious commitment to excellence in quality, customer satisfaction, increased revenues and cost reductions.

The implementation of a Lean/CI culture in the manufacturing industry of plastics pipes provides tangible results while addressing and focusing on the improvement of specific and well determined key performance indicators (KPIs) in order to enhance operational efficiency as for instance eliminating bottlenecks in a plant/office workflow so that cycle times can be reduced and provide more value to customers in a shorter period of time. A few examples of KPIs are listed below.

Quality KPIs

Coloring/pigmentation defects: quantifies the number of defects due to pigmentation issues (i.e. color matching, discoloration spots, etc.)

Scrap rates: quantifies amount of WIP/finish product disposed due to non-conformance.

# of defects/part: quantifies the number of defects per part (not matching tolerances, shrinkages, warps, knit lines, etc.)

Revenue KPIs

Profit margin: it can be used per business units (plants) or by product type. Low profit margins are indicators that cost reductions must be addressed.

Quote to close ratio: measures the number of close sales relative to the number of quotes.

Sales Cycle time: depending on each organization, it normally measures the time elapsed from the generation of a lead to closing a sale.

HR/Team Strength KPIs

Average time to achieve goals: measures the efficiency of employees to evaluate how long it takes them to achieve specific goals.

Employee training: courses provided to employees. This KPI is meant to impact employees productivity, loyalty & satisfaction.

Employee retention rate: measures staff turnover. Poor talent retention is associated to high costs.

Case Study HDPE Pipes

A manufacturer of extruded HDPE pipes experienced high scrap rates due to non-conformant pipes caused by multiple defects (i.e. surface defects, wall thickness, length, density, pigmentation, etc.). As a result, the company decided to implement Lean to address this issue.

For the initial investigation the overall weight of pipes was selected as a comprehensive variable for wall thickness, length and density (pigmentation influencing density as per blending method). After analysing 25 samples from production it was found that the process capability was in the order of 1.5 sigma (Cpk = 0.02) with a defect rate of 59.96% and a cost of poor quality (COPQ) in the order of 37.5% of the company revenue.

Making use of a Lean tool called Pareto rule (aka rule of the 20/80) the company determined that 80% of most influential defects were caused by only 20% of the root causes identified during the root cause analysis (fishbone diagram). It was observed that that the standard operating procedure (SOP) for the test of pigments was not being followed and many pipes came off the process with color defects. It was also found that variations in HDPE viscosity were caused by variations in density originated in the blending process (resin, additives, pigments, slipping agents, etc.). Higher viscosities would lead to poor flow, surface defects, higher shrinkage rates and warps delivering additional problems with maintaining a constant diameter. Conversely, low viscosities would deliver thinner walls under specified tolerances.

After a correlation analysis between blend density and viscosity, the company was able to determine the desired MFI (melt flow index) to obtain an extrusion process within specification. Following this initial implementation the company was able to reduce the defect rate to 5% and the cost of poor quality plummeted to 15% of revenue.

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