Common injection molding defects

Automated Vision Inspection

Common Injection-Molding Defects and How Automated Vision Inspection Can Help

Learn how the SORSYS RT-Series vision inspection system can detect flash, short shots, sink marks, warpage, weld lines, burn marks, contamination, damaged features, ejector pin marks, and other molding defects on every part, every cycle.

Request an Inspection Review

Why It Matters

Small Process Changes Can Create Significant Quality Risks

Injection molding produces plastic components quickly and consistently. However, changes in material, mold condition, temperature, pressure, cooling time, or part design can create defects that affect appearance, dimensions, assembly, and product performance.

In high-volume production, relying only on manual sampling may allow defective parts to continue through packaging or assembly. The SORSYS RT-306 automated vision inspection system can be configured to inspect every part from multiple angles and automatically separate accepted and rejected components.

Common Quality Problems

Injection-Molding Defects the RT-306 Can Inspect

Flash

Flash is unwanted excess plastic that forms around parting lines, mold edges, holes, openings, or other features. It may be caused by mold wear, excessive injection pressure, insufficient clamping force, or poor mold alignment.

How the RT-306 can inspect flash

Cameras examine the outside profile, edges, openings, and parting-line areas of each component and compare the observed shape with an approved part.

Excess material around outside edges
Flash around holes and openings
Irregular part profiles
Material extending from the parting line
Small burr-like plastic projections

Short Shots and Incomplete Features

A short shot occurs when molten plastic does not completely fill the mold cavity. The finished part may have a missing section, incomplete rib, unfinished edge, partially formed hole, or another incomplete feature.

How the RT-306 can inspect short shots

Using top, bottom, front, side, angled, or internal views, the system verifies that critical features are present and fully formed.

Missing corners or edges
Incomplete ribs, tabs, clips, or bosses
Partially formed holes
Incorrect outside profiles
Missing molded details
Areas with insufficient material

Sink Marks

Sink marks are shallow depressions that commonly appear near thick sections, ribs, bosses, or areas that cool unevenly. They are generally associated with material shrinkage during cooling.

How the RT-306 can inspect sink marks

With suitable lighting and camera positioning, visible sink marks can appear as changes in surface shape, reflection, contrast, or shadow.

Surface depressions
Irregular reflections near ribs or bosses
Localized contour changes
Cosmetic surface inconsistencies

Detection capability depends on the defect depth, location, part color, and surface finish.

Warpage and Dimensional Distortion

Warpage occurs when a molded component cools or shrinks unevenly, causing it to bend, twist, bow, or move outside its dimensional tolerance.

How the RT-306 can inspect warpage

The system measures visible profiles, feature locations, diameters, widths, lengths, and alignment against programmed tolerances.

Bent or bowed components
Incorrect outside dimensions
Misaligned features
Out-of-round openings
Incorrect spacing between molded features
Parts that do not match the approved profile

Weld Lines and Flow Marks

Weld lines form where separate flows of molten material meet inside the mold. Flow marks, jetting, and similar defects may appear as lines, waves, streaks, or irregular surface patterns.

How the RT-306 can inspect surface defects

Vision tools inspect selected cosmetic or functional surfaces for changes in texture, contrast, intensity, and pattern.

Unusual surface lines and streaks
Flow patterns near the gate
Jetting marks
Visible weld lines
Localized changes in surface appearance

These applications require controlled lighting and validation using actual part samples.

Burn Marks and Discoloration

Burn marks can appear as dark, brown, or black areas caused by excessive heat, trapped air, or inadequate mold venting.

How the RT-306 can inspect discoloration

Color and grayscale inspection tools identify visible areas that fall outside an approved appearance range.

Dark or burned regions
Unexpected color variations
Black spots
Localized discoloration
Surface staining

Performance depends on the visual contrast between the defect and the surrounding surface.

Contamination and Foreign Material

Dust, grease, degraded resin, mixed material, or other foreign particles may become visible on the surface of an injection-molded component.

How the RT-306 can inspect contamination

High-resolution cameras examine designated surfaces for unexpected spots, particles, residue, and color differences.

Unexpected spots and particles
Grease or surface residue
Color differences
Chips and burrs
Surface damage
Missing features

Damaged Features and Scratches

Parts may become scratched, chipped, cracked, dented, or damaged during molding, ejection, handling, trimming, or transportation. Insufficient draft may also contribute to scraping or drag marks during ejection.

How the RT-306 can inspect physical damage

The system examines critical surfaces and molded features for a wide range of visible defects.

Chips and visible cracks
Scratches and drag marks
Damaged edges
Broken clips or tabs
Deformed threads and gate areas
Missing or partially damaged features

Ejector Pin Marks

Ejector pin marks are witness marks, indentations, raised impressions, or discoloration left where ejector pins push a molded component out of the mold cavity.

These marks may be caused by pin wear, misalignment, uneven ejection force, or ejector pins positioned in cosmetic areas.

How the RT-306 can inspect ejector pin marks

Cameras inspect designated ejector-pin zones for visible witness rings, protrusions, impressions, and shading differences.

Visible witness rings or circular marks
Raised or recessed pin impressions
Discoloration or shine differences
Marks extending above the approved surface plane
Pin marks outside the approved inspection zone

Inspection Coverage

Multi-Angle Inspection for Better Defect Detection

A defect may be visible from one side of a molded component but hidden from another. The SORSYS RT-Series can be customized with multiple cameras and inspection stations to examine components from top, bottom, front, inside, outside, side, and angled views.

The system can also be configured with automatic, robotic, vibratory, or manual feeding. After inspection, accepted and rejected components are automatically separated.

up to, 3,600 Parts per hour

up to, 3 Inspection stations

up to, 8 Cameras,

Built Around Your Part

Customized Inspection for Each Plastic Component

Injection-molded components vary in shape, material, color, surface finish, tolerance, and production speed. An automated inspection system should therefore be designed around the actual component and its known quality risks.

Presence and absence checks

Profile comparison

Dimensional measurement

Surface-defect inspection

Color and contrast verification

Hole and opening inspection

Feature-position verification

Good-part and reject sorting

Inspection-data collection and reporting

Camera resolution, lens selection, field of view, lighting, part orientation, feeding method, and cycle time are selected according to the smallest defect that must be identified.

Quality Improvement

Improve Injection-Molded Part Quality with the RT-306

By inspecting every component for visible surface, feature, profile, and dimensional defects, the SORSYS RT-306 helps manufacturers improve inspection consistency and reduce the risk of defective parts reaching customers.

Reduce the risk of defective parts reaching customers
Identify molding problems earlier
Reduce manual sorting requirements
Improve inspection consistency
Protect downstream assembly processes
Maintain traceable quality standards

Discuss Your Application

Do You Need to Inspect an Injection-Molded Component?

SORSYS can evaluate your component, review the defects you need to detect, and configure the cameras, lighting, feeding system, and inspection stations around your specific production requirements.

Contact SORSYS