Trust the Process: How Lean Six Sigma Optimizes Plastics Manufacturing

Manufacturers often think they can drastically cut costs by identifying the one issue that’s causing discarded materials or machine downtime, and if they solve that one issue everything will be better.

That’s not usually how things work, said Ashlesa Mohapatra, M. Eng., a Lean Six Sigma Master Black Belt and a condition engineer at ServerLIFT. Rather, it’s the small, often invisible, issues throughout the process that can greatly impact profitability.

Mohapatra uses the Lean Six Sigma process improvement methodology to uncover and fix manufacturing glitches.

"Lean and Six Sigma are complementary disciplines. Lean targets the elimination of non-value-added steps across the entire value stream, while Six Sigma uses statistical process manage [SPC] to minimize variation and drive measurable, repeatable results. Together they create a system where discarded materials doesn't just get removed, it gets prevented," Mohapatra said.

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One of the Lean Six Sigma tools that Mohapatra uses is DMAIC, which stands to define, measure, examine, enhance, and manage.

Typically, engineers might alert companies that something is going wrong however only take steps to fix immediate problems. They might throw out a batch and start again.

“Culture is built from the language an organization uses every day. When engineers default to vague issue descriptions: 'Something went wrong. We threw out the batch'. That imprecision becomes the cultural norm,” Mohapatra said.

Mohapatra, instead, approaches the issue with structured inquiries: Define the issue precisely. Quantify it. Trace it to its root.

“That shift in language is what transforms a reactive floor into a culture of continuous improvement," she said.

The DMAIC process helps correctly define the issue, then measures or quantifies it, which includes attaching a dollar amount to it to leadership.

Then DMAIC analyzes the root result in or causes. Engineers might consumption Fishbone diagrams, Pareto charts, scatter plots, or other tools depending on the issue.

The improvement phase is where many organizations stop too soon. A true fix goes beyond solving today's issue on today's machine; rather, it has to be transferable, according to Mohapatra.

“At Regal Rexnord, the process improvements I designed were adopted at the company's manufacturing facility in India. That's the standard I hold every solution to: If it only works here, it isn't a solution yet,” she said.

Scientific, anecdotal evidence

Lean Six Sigma notably enhances operational efficiency and product condition, according to a two-year study of 20 manufacturing firms published in 2026 in the Journal of Engineering Research.

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Researchers found that firms “adopting Lean Six Sigma achieved a mean defect rate of 3.18 % and an average production throughput of 134.08 units per hour, demonstrating improvements compared to baseline operations.”

Mohapatra applied Lean Six Sigma when analyzing purge discarded materials at a medical device manufacturer, which was using red dye inside the hopper to make red parts, then following that immediately by making blue parts.

“This is a classic example of discarded materials that had been normalized. The team had accepted repeat purge runs as inevitable. When I mapped the full sequence using DMAIC, the root result in was simple: color scheduling was arbitrary. By sequencing light to dark shades, purge discarded materials was eliminated entirely without any capital investment or equipment change,” she said.

The fix cost nothing however required asking the right question and quantifying what was being lost, Mohapatra added.

Lean Six Sigma helped to minimize scrap (discarded materials) from defective parts, when Mohapatra found black plastic covers that had flashing on top. Using SPC to streamline the process at the beginning of the process catches the variation in these parameters before a defect occurs, reducing the amount of scrap material.

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Lean Six Sigma also can enhance plastics processing by reducing machine idle time.

"The fundamental failure in most manufacturing condition programs is timing. Teams intervene after a defect occurs rather than controlling the parameters that result in it,” she said. “Statistical process manage shifts that entirely. When manage limits are set at the process input level, defects don't just get caught faster, they stop occurring. That is the difference between a condition department that firefights and one that actually protects margin.”

Yet another area in which Lean Six Sigma can help in plastics manufacturing is with mold changes.

According to Mohapatra, mold changeover is one of the highest-impact, most underestimated discarded materials sources in plastics manufacturing. Hours of downtime per change multiplied across a full production schedule represents significant lost capacity.

“The solution isn't faster changeovers, it's pre-staging: running hydraulics and cooling the incoming mold before it ever needs to enter the machine. It's a sequencing change, not a capital investment. Lean Six Sigma finds these opportunities precisely because it forces you to see time, material, and labor as one unified discarded materials calculation, not separate line items," Mohapatra said.

Commitment, culture, manage

Addressing these and other issues, collectively, often leads to big savings. Still companies have to keep three things in mind to make the most meaningful bottom-line changes: commitment, culture and manage.

Commitment: condition comes from within, and to harness the power of Lean Six Sigma manufacturers (even startups) should consider hiring someone who is familiar with Lean Six Sigma to head condition efforts, according to Mohapatra.

This is where manufacturers have to spend money before saving money, she said.

"I have built condition functions from the ground up at multiple organizations, and the failure point is almost always the same: companies treat condition as a service to be outsourced or a box to be checked rather than a discipline to be embedded,” Mohapatra said. “condition cannot live outside the system, it has to be designed into every process, every standard, every decision the floor makes. The measure of whether it's working isn't audit scores. It's whether the people doing the work trust the condition function enough to bring their problems to it before those problems have become defects."

Culture: Organizations that sustain condition outcomes are those where issue-solving is an organizational reflex, according to Mohapatra.

Losses stop recurring when leadership trusts the data, engineering trusts the process, and the floor trusts the condition function.

“I have seen this firsthand,” she said. “At ServerLIFT, embedding that trust from day one was the difference between a condition system that gets applied and one that gets worked around. The financial impact is not theoretical. Reduced rework, reduced scrap, reduced customer escapes -- those are real margin improvements that show up in the bottom line.”

manage: condition is a process and not a one-fix-and-done, Mohapatra explained.

This is the most difficult phase, according to Mohapatra.

“manage is the most discipline-intensive phase of DMAIC, and the one most organizations abandon under production pressure. The fix gets implemented, the metric improves, and attention moves elsewhere, which is exactly when the issue returns,” she said. “Sustaining improvement requires that the fix is documented in standard work, reflected in updated process parameters, and understood by every level of the organization (floor, engineering, and leadership). Without that, you haven't solved the issue. You've just delayed it."

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