A successful custom plastic parts project starts long before production begins.
Many of the most expensive manufacturing problems can be traced back to decisions made early in the process. Unclear specifications, unrealistic tolerances, incorrect material choices, or incomplete production forecasts can lead to redesigns, tooling changes, delays, and unnecessary cost.
Before beginning a custom injection molding or thermoforming project, OEMs should answer several important questions.
1. What Does the Part Need to Do?
Start with the function of the component.
Before discussing tooling or manufacturing processes, define how the finished part will actually be used.
Consider factors such as:
- Mechanical loads
- Impact requirements
- Operating temperature
- Chemical exposure
- UV exposure
- Moisture
- Expected service life
- Cosmetic requirements
- Indoor or outdoor use
These requirements help guide decisions about material selection, part geometry, tolerances, and manufacturing process.
The more information a manufacturer has about the application, the better it can evaluate whether the design is appropriate for production.
2. What Material Should We Use?
Material selection is one of the most important decisions in custom plastic manufacturing.
Different thermoplastics offer different combinations of:
- Strength
- Flexibility
- Impact resistance
- Heat resistance
- Chemical resistance
- UV stability
- Dimensional stability
- Appearance
- Cost
An OEM may come into a project with a material already specified, but it is still worth discussing the application with the manufacturer.
At PDI, we work with customers to evaluate material options based on both part performance and manufacturability.
Choosing the right resin early can prevent performance problems and unnecessary design changes later.
3. Should the Part Be Injection Molded or Thermoformed?
Not every plastic component should be manufactured the same way.
Injection molding is often well suited for:
- Higher production volumes
- Complex geometry
- Tight tolerances
- Detailed features
- Repeatable production
Thermoforming may be better for:
- Larger components
- Covers and housings
- Panels and enclosures
- Lower to medium production volumes
- Projects requiring lower tooling investment
Because PDI offers both injection molding and thermoforming, we can evaluate the part based on its actual requirements rather than trying to fit every application into one process.
4. Is the Part Designed for Manufacturing?
A design may work perfectly in CAD but still create challenges in production.
Design for Manufacturability, or DFM, should be completed before tooling begins.
A DFM review may evaluate:
- Wall thickness
- Draft angles
- Ribs and bosses
- Undercuts
- Parting lines
- Shrinkage
- Warpage
- Material flow
- Ejection
- Tolerances
Making changes at the design stage is usually faster and less expensive than modifying a finished mold.
Early collaboration between the OEM and manufacturer can improve part quality while reducing tooling changes and production delays.
5. Which Dimensions Are Actually Critical?
Not every dimension needs an extremely tight tolerance.
Over-specifying tolerances can increase tooling complexity, inspection requirements, and production costs without improving the performance of the finished product.
OEMs should identify which dimensions directly affect:
- Fit
- Assembly
- Alignment
- Sealing
- Mechanical performance
- Safety
- Appearance
Those features can then receive the appropriate level of manufacturing and quality control.
A good plastic parts manufacturer should help distinguish between dimensions that truly require tight control and those that allow more flexibility.
6. How Many Parts Will We Need?
Production volume affects nearly every part of the manufacturing strategy.
Before starting the project, estimate:
- Initial production quantity
- Annual usage
- Expected growth
- Peak demand
- Product lifecycle
A program requiring several hundred parts per year may need a very different tooling strategy than one requiring hundreds of thousands or millions.
Understanding expected volume helps determine the appropriate tooling, equipment, cavity configuration, and manufacturing process.
7. What Should the Tooling Be Designed to Handle?
Tooling should be matched to the expected life of the program.
Important questions include:
- How many parts must the tool produce?
- Will production volume increase?
- Could the design change later?
- Should prototype or bridge tooling be considered?
- Will additional cavities eventually be needed?
- How will the tool be maintained?
The least expensive tooling option is not always the most economical over the full life of the project.
A properly designed tool should balance initial investment with production volume, part quality, maintenance requirements, and expected tool life.
8. Are Secondary Operations Required?
A molded or thermoformed component may require additional work before it is ready for assembly.
Secondary operations can include:
- CNC trimming
- Drilling
- Machining
- Assembly
- Hardware installation
- Finishing
- Inspection
- Packaging
These requirements should be identified early.
Designing a part without considering downstream operations can create additional labor or make assembly more complicated than necessary.
At PDI, our capabilities include molding, thermoforming, CNC machining, secondary operations, and inspection, allowing these requirements to be considered as part of the overall manufacturing process.
9. How Will the Part Be Inspected?
Quality requirements should be established before production begins.
Depending on the application, the inspection plan may include:
- First-article inspection
- Dimensional inspection
- In-process checks
- Custom inspection fixtures
- Visual standards
- Material verification
- Final inspection
OEMs should identify critical dimensions and performance requirements before tooling and production start.
This allows the manufacturer to build the appropriate quality controls into the process instead of determining them after parts are already being produced.
10. What Is the Real Project Timeline?
Manufacturing timelines involve more than molding cycle time.
A custom plastic parts project may include:
- Design review
- DFM analysis
- Material selection
- Tool design
- Tool construction
- Initial samples
- Testing and validation
- Tool adjustments
- Production approval
- Full production
OEMs should build time into the schedule for engineering review and validation rather than treating tooling completion as the start of finished production.
Planning these stages early helps reduce last-minute changes and unrealistic launch expectations.
What Information Should You Send With an RFQ?
A complete RFQ helps a manufacturer evaluate the project more accurately.
Whenever possible, provide:
- 3D CAD files
- 2D drawings
- Material requirements
- Critical tolerances
- Annual usage estimates
- Expected production volumes
- Cosmetic requirements
- Application details
- Quality requirements
- Target production dates
You do not need to have every detail finalized before contacting a manufacturer.
In fact, involving a manufacturing partner early can help identify potential improvements before design decisions become expensive to change.
Start With the Right Questions
Custom plastic manufacturing works best when engineering, tooling, production, and quality requirements are considered together.
Before starting a project, OEMs should understand what the part needs to accomplish, which material and process are appropriate, what production volume is expected, and how the component will be inspected and assembled.
At Plastic Designs, Inc., we work with customers from early design and DFM review through material selection, tooling, injection molding, thermoforming, machining, secondary operations, and final inspection.
The more we understand about the application at the beginning, the better we can develop a manufacturing strategy designed around performance, quality, production volume, and long-term cost.