Getting an injection mold built is a major step in bringing a packaging component into production. But before a new tool is approved for full-scale manufacturing, the parts it produces need to be carefully evaluated.
A part may look good at first glance and still have dimensional, functional, or cosmetic issues that could cause problems once production volumes increase. Performing the right quality checks before tool approval helps identify those issues early—when adjustments are typically easier to make.
Here are some of the key areas manufacturers and OEMs should evaluate before approving an injection mold for production.
1. Verify Critical Dimensions
One of the first steps is confirming that molded parts meet the dimensions specified on the drawing or CAD model.
Depending on the component, this may include:
- Overall length, width, and height
- Wall thickness
- Hole diameters and locations
- Snap-fit features
- Sealing surfaces
- Mating dimensions
- Critical tolerances
Some dimensions are more important to the performance of the part than others. Identifying critical dimensions early allows the molding and quality teams to focus on the features most likely to affect assembly or function.
2. Check for Warpage
Plastic parts can change shape as they cool after molding. Uneven cooling, material shrinkage, part geometry, and processing conditions can all contribute to warpage.
For packaging components, even relatively small amounts of warpage can affect how a part fits, closes, seals, stacks, or interacts with another component.
Parts should be evaluated after they have fully cooled to determine whether they maintain the intended shape and geometry.
3. Inspect for Sink Marks
Sink marks are depressions that can appear when thicker areas of a molded part cool and shrink differently than surrounding areas.
They are commonly associated with areas such as ribs, bosses, or thicker wall sections.
Depending on the packaging application, sink may be primarily cosmetic or it may indicate a design or processing condition that needs additional attention before the tool is approved.
4. Look for Flash
Flash occurs when a thin layer of plastic escapes between sections of the mold during injection.
Even small amounts of flash can create issues with appearance, assembly, sealing, or handling.
During tool qualification, parts should be inspected around the parting line, shutoffs, openings, and other areas where flash may develop.
5. Evaluate Short Shots and Incomplete Fill
A short shot occurs when molten plastic does not completely fill the mold cavity.
This can leave missing or incomplete features on the finished component. Thin walls, complex geometry, flow restrictions, venting, material selection, and processing conditions can all influence how well a cavity fills.
Trial runs help determine whether the tool can consistently produce a fully formed part within a stable processing window.
6. Review Gate Location and Appearance
The location and design of the gate can influence both the appearance and performance of a molded packaging component.
Quality teams should review the gate area for excessive vestige, deformation, stress, or other cosmetic concerns.
Gate location can also affect how material flows through the cavity, making it an important part of the overall tool evaluation.
7. Check Part Fit and Assembly
A component can meet its individual dimensional requirements and still create problems during assembly.
Whenever possible, molded samples should be tested with the actual mating components.
This may involve checking whether parts:
- Snap together correctly
- Align properly
- Open and close as intended
- Maintain the required clearance
- Assemble without excessive force
- Stay securely connected after assembly
Testing the complete assembly provides information that dimensional inspection alone may not reveal.
8. Evaluate Cosmetic Requirements
For visible packaging components, appearance can be just as important as dimensions.
Quality checks may include reviewing the part for:
- Flow lines
- Weld or knit lines
- Burn marks
- Discoloration
- Surface imperfections
- Gate marks
- Texture inconsistencies
Acceptable cosmetic standards should be established before production so that the customer and manufacturer have a clear understanding of what is considered acceptable.
9. Confirm Material Performance
The selected resin should also be evaluated under realistic molding conditions.
Different materials—and even different grades of the same material—can behave differently when it comes to shrinkage, flow, stiffness, impact resistance, and surface appearance.
Running the intended production material during qualification helps ensure the tool and process are evaluated under conditions that accurately represent future production.
10. Confirm Repeatability
A few good parts do not necessarily mean a tool is ready for production.
One of the most important parts of tool qualification is determining whether the molding process can repeatedly produce acceptable parts.
Instead of evaluating only the first samples from the press, parts should be reviewed across the production trial. This helps identify variation and determine whether critical dimensions, appearance, and function remain consistent.
Why These Checks Matter Before Tool Approval
Once a tool moves into full production, changes can become more complicated, expensive, and disruptive.
Identifying issues during qualification gives the tooling, engineering, molding, and quality teams an opportunity to make adjustments before production volumes increase.
The goal isn’t simply to produce one good part. It’s to establish a tool and process capable of producing good parts consistently.
Building Quality Into the Process
Successful injection molding programs depend on more than the mold itself. Part design, tooling, material selection, processing conditions, inspection, and communication all play a role in the final result.
At Marne Plastics, quality is built into the manufacturing process from initial qualification through ongoing production. Our team works with customers to evaluate molded components, identify potential issues, and establish repeatable processes before parts move into regular production.
Planning the right quality checks before tool approval can help reduce unexpected issues later—and create a stronger foundation for reliable production.