Flow marks - A wavy pattern or discoloration caused by a slow injection speed which allows the material to cool too quickly.

Blow molding – The process follows the basic steps found in glass blowing. A parison (heated plastic mass, generally a tube) is inflated by air. The air pushes the plastic against the mold cavity to form the desired shape. Once cooled, the plastic is ejected.  This method is used to make plastic bottles.

China has a wide variety of skill sets available from high end to the lowest low. The culture is open to interpretation when the plastic injection mold shop decides how to design the cavitation structures. I suggest having your own injection mold tooling expert and engineering determine the way the cavities function. I also suggest having certifications on hand for all the steel used in the plastic injection molds. This would include all receipts and traceability documentation. There are different levels of quality in China for steel and you made have a variety of heat transfer issues associated with it.

Blister – As the name says, this is a part defect which appears as a small bubble or blister on the surface of a part and it generally created by gas or air bubbles.

Posted by Kyle Coblentz | 02 / 19 / 14 0 Comments

Flash or burrs – A thin lip or protrusion beyond the body of the part that is generally caused by poor clamping force, improper mold design and/or mold damage.

Polymer - A substance that has a molecular structure consisting chiefly or entirely of a large number of similar units bonded together, e.g., many synthetic organic materials used as plastics and resins.

Weld line - Also called a knit line, the juncture where two flow fronts meet and are unable to join together during the molding process. These lines usually occur around holes or obstructions and cause localized weak areas in the molded part.

Masterbatch – A solid or liquid additive for plastic used for coloring plastics or imparting other properties to plastics.

Alloy – A plastic alloy is a physical modification of an existing plastic to achieve higher performance and or functionality.  These alloys are often used in the automobile industry and to replace metal parts.

Additives – These compounds are added to resins to improve the overall performance and appearance of finished products.  A key trend in this area today is using additives that are made from organic materials such as eggshells, wood pulp, rice hulls or materials that improve the biodegradability of the plastic.

Core - A protrusion or set of matching protrusions, which form the inner surface of a plastic part. They are often considered they “male” side of the part.

Thermoplastic - A material that can be heated and cooled repeatedly without changing the material structure.  Highly recyclable.

Cold slug – A defect characterized by a small non-uniform area on the part caused by an improperly heated piece of plastic becoming attached to the part.

I suggest anyone sourcing plastic injection mold tooling in Low Cost Countries to make the visit, send a watch dog or anything else to mitigate potential issues. I sourced plenty of plastic injection mold tooling in Low Cost and High Cost countries in Asia during my career with a Japanese owned company.

Tie bars - Bars which provide structural support to the mold in the press.  The spacing between the tie bars dictates the size of the mold that can be placed into the injection machine. The mold opens and closes riding on the tie bars.

Bridge tool – An injection mold that makes parts until the final tool is completed.  These molds or tools are not meant to be production tools.

Vent – A channel from the mold cavity that allows gas and air to escape as resin is being injected into the cavity to prevent many types of defects from occurring.

Prototype tool – Also called a soft tool, a preliminary mold built to produce prototype parts and used to make adjustments to the final production tool.

Colorant – A pigment system, usually in pelletized form, powder or liquid, which is mixed with resin to produce the desired color.

Release agent – A compound, which is sprayed on the mold, or as an additive, molded into the part to help facilitate the release of the part.

Annealing - Annealing is the heating and slow cooling of a plastic part which allows the polymer chains to recoil and relieve internal stresses.

In short, the USA and others are leveraging the moment and getting some quality plastic injection molds out of China. Check the references and make sure you call non-competing companies to mitigate your risks. Also hire people that project managed these types of injection mold suppliers to deliver exactly what you ordered.

Compression molding - The name of this molding method says everything.  A heated plastic material is placed in a heated mold and is then compressed into shape. The plastic can be in bulk but often comes in sheets. The heating process, called curing, insures the final part will maintain its integrity. This molding method is often used to make large objects such as automobile components.

Delamination - This defect appears as a flaky surface layer on the part and is often caused by contamination or moisture in the resin pellets.

Only one thing made me sleep at night when I have millions of dollars and tight performance timelines. I made the circuit of visitations to the engineering groups, tooling fab shops (all of them including 3rd tier) and plastic molding shops. There is nothing worse than have a several hundred thousand dollar injection molds crash and burn passing the 1000 shot mark. It leaves a mental on you when it happens.

Flash gate – An alternative to a fan gate, which conveys the melted resins into a thinner gate section creating a linear melt flow into the cavity.

Undercut – Can be a design flaw that results in an indentation or protrusion that inhibits the ejection of the part from the mold.  Other times undercuts are designed into a mold to ensure a part holds onto the correct side of the mold.

EDM or electric discharge machining - A manufacturing process used to create molds, where the shape of the mold cavity is obtained by removing metal material using electrical discharges.

Degassing – Opening and closing of a mold to allow gas to escape.  Trapped gas and/or air can cause parts defects such as blistering and bubbles.

Thermoset – A material, which when heated, is pressed or molded into a shape.  The heating process changes the structure of these materials, and for this reason they cannot by re-heated.

Multi-shot molding – A process where two or more plastic substances are injected into the mold to form a part.  Toothbrushes are often manufactured using this technique.

Hot-runner mold – Hot runner molds consist of 2 plates that are heated with a manifold system.   The manifold sends the melted plastic to nozzles which fill the part cavities.

Over molding – A two-shot process, in which two plastic substances, are injected into a mold sequentially, usually a harder base material with a coating of softer material.