Plastic Injection Molding Defect Guide

The Plastic Injection Molder’s Guide to Defect-Free Parts

Plastic injection molders – whether lacking the experience, adept knowledge or proper equipment – can produce defective products that don’t stand up to industry regulations, appearance requirements, and/or general client expectations.

Below, we outline the most common plastic injection molding problems and the causes behind them.

Mold Warpage

When it comes to plastic injection mold warpage, defects can be caused by several factors including:

  • Inadequate Injection Pressure or Time
  • Inadequate Residence Time
  • Barrel Temperature Too Low
  • Mold Temperature Too Low
  • Uneven Mold Temperatures
  • Nozzle Temperature Too Low
  • Improper Flow Rate
  • Inconsistent Process Cycle
  • Inadequate Gate Size
  • Incorrect Gate Location
  • Lack of Ejection Uniformity
  • Part Geometry

Mold Burns

There are several factors that contribute to plastic injection mold burns, such as:

  • Injection Speed Too High
  • Resin Temperature Too High or Too Low
  • Improper Venting
  • Trapped Air in Injection Cavities or Pockets
  • Inadequate Gate Size
  • Inadequate Nozzle Size
  • Part Geometry

Cold Flow Marks and Voids

In plastic injection molding cold flow marks & voids can occur due to:

  • Inadequate Water Cooling
  • Absence of Flow Dividers in Water Channels
  • Inadequate Cooling
  • Inadequate Cavity Pressure
  • Improper Injection Speed
  • Improper Melt Temperature
  • Incorrect Gate Style or Location

Part Self-Destruction

There are a variety of reasons for plastic injection molded parts destructing, such as:

  • Using Commodity Resins when Engineering Resins are Required
  • Resins Not Processed to Exact Requirements of Manufacturer’s Manual
  • Unreliable or Inconsistent Cavity Pressure
  • Uncalibrated or Incorrect Transducer
  • Inadequate Gate Size
  • Incorrect Gate Location
  • Water or Foreign Matter Contamination
  • Inconsistent or Incorrect Melt Temperature
  • Non-Homogenous Melt Temperature
  • Inconsistent or Incorrect Mold Temperature
  • Mold Temperature Non-Uniform to Part Cavity Proximity
  • Inadequate Cooling Rate
  • Inconsistent Overall Cycle Time of Molding Process
  • Part Produced Out of Tolerance
  • Part Geometry
  • Inconsistent Cavity Pressures Between Cavities in Multi-Cavity Molds

Black Specs & Splay

In plastic injection molding black specs and splay is usually caused by:

  • Resin Contamination (non-compatible resins, dirt, etc.)
  • Inadequate Resin Dry Time
  • Improper Melt Temperature
  • Injection Speed Too High
  • Improper Gate Style

U.S. Plastic Injection Molder Specializing in Engineering Resins

Plastic Molded Concepts is a U.S based company that uniquely specializes in molding with engineered resins. We have been thriving in the plastic molding business for 45 years. We have the experience and certified in-house Master Molders, allowing us to take on projects of any complexity.

PMC specializes in solving complex molding issues. If you’re a plastic injection molder or a customer of a molder that’s producing defective parts, reach out to PMC to request our expertise. Whether you need plastic injection molding, overmolding, insert molding, product design assistance, troubleshooting assistance or a combination of services, we’re here to help. Request a quote today for your next project.

Have questions about our process?

Contact us today