How to Reduce Plastic Part Costs

Most plastic parts are designed with good intentions—extra strength, tighter tolerances, or higher-grade materials to reduce risk.

But in practice, these decisions often lead to overengineered components that increase cost without improving performance.

In injection molding, small design choices—like wall thickness, material selection, and geometry—can significantly impact:

• Material usage
• Cycle time
• Tooling complexity
• Production consistency

The result is often the same:
20–40% higher costs than necessary

This article breaks down the key cost drivers and how to optimize them before production begins.

The Hidden Cost of “Playing It Safe”

Overengineering typically comes from:

• Adding extra material “just in case”
• Tightening tolerances beyond functional requirements
• Selecting high-performance resins unnecessarily

While these decisions may reduce perceived risk, they introduce real manufacturing inefficiencies:

• Increased material consumption
• Longer cooling and cycle times
• More complex tooling
• Higher risk of defects (warping, sink, inconsistency)

In many cases, these tradeoffs provide little to no functional benefit

The Top Drivers of Plastic Part Cost

1. Wall Thickness – the biggest driver of cycle time and material cost

Cooling time increases sharply with thicker sections. Because cooling is one of the longest phases in injection molding, even small increases in wall thickness can significantly impact total production time.

Impact:

+10–30% material cost
+20–50% cycle time

What to do:

• Target the minimum wall needed for strength
• Keep wall thickness as uniform as possible
• Avoid thick clusters that extend cooling time

2. Material Selection

Often over-specified without performance benefit

Using engineering-grade or specialty resins when they are not required increases cost and can accelerate mold wear.

Impact:

• +15–60% material cost
• +10–25% tooling wear

What to do:

• Match material to actual performance requirements
• Avoid paying for properties you don’t need
• Select the lowest-cost material that meets function

3. Tool Complexity

Primary driver of tooling cost and lead time

Features like undercuts, slides, and lifters add components, setup complexity, and maintenance risk.

Impact:

• +20–100% tooling cost
• +10–30% longer lead time

What to do:

• Simplify geometry where possible
• Eliminate unnecessary undercuts
• Reduce moving components in tooling

4. Secondary Operations

Hidden cost multiplier in production

Machining, assembly, and finishing steps increase labor, handling, and variability.

Impact:

• +15–40% total part cost
• +10–25% production time

What to do:

• Design features to be molded-in when feasible
• Reduce post-machining and manual assembly
• Account for handling and inspection in total cost

5. Tolerance Requirements

Major driver of scrap and precision cost

Overly tight tolerances increase tooling precision requirements and raise rejection rates.

Impact:

• +10–50% production cost
• +5–20% scrap risk

What to do:

• Specify tolerances based on function, not habit
• Tighten only the dimensions that truly matter
• Balance precision with manufacturability

Example: Manufacturer Reducing Cost

A manufacturer with a molded component experiencing higher-than-expected costs.

Issues:

• Excess wall thickness
• Over-specified material
• Features requiring secondary machining

After optimization:

• Wall thickness reduced and standardized
• Material downgraded to a cost-effective alternative
• Secondary operations eliminated

Result:

• 32% reduction in per-part cost
• Faster cycle time
• Improved production consistency

Working with an experienced plastics supplier can help ensure the correct grade and formulation is selected.

Design for Manufacturability (DFM): What Most Teams Miss

DFM is not just about making a part manufacturable—it’s about making it efficient to produce at scale.

Common gaps:

• Late involvement of manufacturing partners
• Designing without tooling constraints in mind
• Over-prioritizing theoretical performance

Effective DFM requires:

• Early collaboration with your manufacturing partner
• Iteration before tooling is finalized
• Clear tradeoffs between cost, durability, and performance

DFM Checklist: Reduce Cost Before Tooling Begins

Use this as a quick evaluation before moving to production:

• Can we reduce wall thickness without sacrificing function?
• Are we paying for material properties we don’t need?
• Can we eliminate undercuts or simplify geometry?
• Can features be molded instead of machined?
• Are tolerances tighter than the application requires?

The Result

When parts are optimized for manufacturability:

20–40% Cost Reduction

Most visible in overengineered parts

Faster Production

Shorter cycle times and reduced lead times

Higher Consistency

Fewer defects, less rework, improved yield

Work With Sterling Plastics

Sterling Plastics helps companies optimize part design — reducing cost, improving manufacturability, and ensuring consistent production outcomes.

Contact us to review your part design and identify optimization opportunities.