Plastics: Injection Molding Basics 2: Process

The second of a three part training series, this course provides a general understanding of the injection molding process, using 3D animation to demonstrate parts of the process that easily convey otherwise complex concepts. Specific content discusses polymers and the three criteria used to classify them, covers some of the more common procedures for material preparation, introduces the three phases of the molding process, explains the need for maintaining an accurate process log, and defines common injection molded part defects and explains their causes.

Anyone working or planning to work with injection molding within the plastics industry. While the basic injection molding series is ideal for new hires, it also serves as an excellent refresher course for anyone involved in plastics processing.

• Be aware of the major processes that are used to make plastic parts.
  • State that injection molding is the world's most widely used plastics process.
  • Recall that there are other major plastics processes
  • Explain that Injection Molding can be a one step process.
• Know the different criteria by which plastic materials are classified.
  • List other references of pellets.
  • List different criteria used for classifying polymers.
  • Recall that thermoplastic materials can be reprocessed and recycled easily.
  • Explain that amorphous polymers melt quickly when heated.
• Describe how plastic resins are handled before being processed.
  • Explain that resins often require preparation before processing.
  • Identify that the lot number should be clearly marked on all stored material.
  • Recall that moisture in the polymer can cause defects.
• Know the three main phases of the injection molding process.
  • List processes of the injection phase.
  • Explain how the sprue works.
• Understand when the filling phase of the process begins and ends.
  • Describe how filling can be adjusted.
  • Identify when filling ends.
• Know why and when packing takes place.
  • Name packing as the additional material to compensate for shrinkage.
  • Identify when material shrinkage takes place.
  • Describe the result of insufficient packing pressure.
• Know why and at what stage during the process holding takes place.
  • Name the final stage of injection.
  • Agree that excessive hold time has little effect on the part quality.
  • Select the two parameters that affect hold.
• Understand when cooling takes place and how it works.
  • Define cooling as the second stage of the molding process.
  • Identify how much of the overal cycle time is typically consumed by cooling.
  • Identify when screw recovery takes place.
  • Recall that friction accounts for seventy to ninety percent of the heat required.
• Describe the different parameters used to control screw recovery.
  • Recall that Screw Recovery has four different parameters.
  • Identify the barrel's heater bands as providing ten to thirty percent of the heat.
  • Agree that the barrel temperatures should be set to the lowest recommended settings.
• Be aware of the many different methods used to eject parts from the mold.
  • Name the third phase of the molding process.
  • Explain when the ejection phase starts.
  • Recall that the mold should open as fast as possible without risking damage.
  • Identify how stripper plates push on the entire perimeter of the part.
  • Describe the danger of excessive tonnage.
  • Describe what should happen if the mold tries to close on a stuck part.
• Know how to help ensure that the process is consistent and repeatable.
  • Identify the General Processing Guidelines to follow.
  • Choose part weight measurements to verify a consistent process.
  • Select items that should be at inspection stations.
• Understand the importance of a process log.
  • Explain the importance of documenting all changes in a process log.
  • List items that must be included in the process log.
• Take a systematic approach when troubleshooting part defects.
  • Agree that a particular defect can have a variety of causes.
  • Choose to make only one adjustment at a time.
  • Agree to change temperature as a last resort when making adjustments.
• Recognize common molding defects, their causes, and their remedies.
  • Identify production personnel as those who must be able to recognize common defects.
  • Choose how Flash most commonly occurs.
  • Select the reason Sinks most often occur.