Plastic Injection molding machine: Terms, Terminology, Glossary, Vocabulary List.

Injection molding machine terms or glossary which are frequently used to describe a certain process or part of the injection molding. Many terms or words used in the industry for injection molding. If you are from the plastic field or studied plastic engineering then probably you know what all these terms mean and why these terms or words used for injection molding machines.

Injection molding machine glossary or terms

You may know only these terms or words related to injection molding when you are from the field of plastic or studied plastic but what about the other who are geek to know the meaning of these words so we brought the injection molding vocabulary or terms list.

Injection molding terms or vocabulary list

Support Pillar – A circular rod mould component used to support the ejector hall of the mould. It is required because of the tremendous amount of pressure exerted against the “B” plate by the injection phase of the moulding process.

Thermocouple – A device made of two dissimilar metals that are used to measure the temperature of a heated area such as a barrel or nozzle. It sends a signal to a controller which then turns off or on to control the temperature of that area.

Thermoplastic – A plastic material which, when heated, undergoes a physical change. It can be reheated, thus reformed, over and over again. See THERMOSET.

Thermoset – A plastic material which, when heated, undergoes a chemical change and cures. it cannot be reformed, and reheating only degrades it. 

Tie Bars – Large diameter rods that connect stationary platen “A” to stationary.platen 3″. The moving platen contains bushings that are used for sliding over the tie bars, allowing the moving platen to travel between the 2 stationary plates.

Toggle Clamp – A term used to describe the use of a mechanical scissors action system.12 open and close the clamp unit o! a molding machine. It is operated by a relatively small hydraulic cylinder.

Transition Zone – That area in the center of the screw (between the feed zone and metering zone) This section has a tapering flight depth condition that compresses the plastic material in preparation for injection.

Undercut – A recess or extension on the molded part, located in such a way as to prevent or impede ejection of the part by normal molding machine operation.

Vent – A shallow groove machined into the parting line surface of a mold in order to allow air and gases to escape from the cavity, or runner, as the molten plastic is filling the mold. Sometimes also located on ejector and core pins.

Vented Barrel – A heating barrel designed with an automatic venting port which allows moisture · and gases to escape from molten plastic prior to being injected into a mould.

Nozzle – A device mounted at the end of the heating barrel which focuses plastic material to flow from the machine into the mould.

Non-Return Valve – A Mechanism mounted in (or a!) the nozzle of the injection machine, Which operates to shut off injection flow at the end of the injection cycle. This eliminates material from the upcoming shot from drooling out of the nozzle when the mold opens to eject parts from the previous shot.

Parting Line – A plane at which two halves of a mould meet. Also applies to any other plane where two moving sections come together and form a surface of a molded part.

 Plastic – A complex organic compound (usually polymerized) that is capable of being shaped or formed.

Platens – The flat surfaces of a moulding machine onto which the two halves of the mould are mounted. One is stationary and the other travels. There is a third platen (stationary) at the clamp end of the machine which serves as an anchoring point for the clamp unit.

Plunger – The injecting member of a non-screw design moulding machine. Plungers do not rotate, (auger) to bring material forward in preparation for the next cycle. Nor do they blend the material as a screw does.

Polymer – A group of long chains of monomers, bonded together in a chemical reaction to form a solid. This term is often used interchangeably with PLASTIC, but there can be a difference. 

Purging – A process of injecting unwanted plastic material from the injection cylinder into the atmosphere for the purpose of changing materials, changing colors, or removing degraded material. Also, the name was given to the mass of material that is purged.

Reciprocating Screw – A helical flighted, metal shaft which rotates within the heating cylinder of a moulding machine, shearing, blending, and advancing the plastic material. After rotating, the screw is pushed forward which injects the plastic into the mould. Also, simply referred to as “the Screw”.

Moving Platen – The platen of a moulding machine that travels (opens and closes). It is the con to the clamp unit and is the mounting location for the “B”, or traveling, half of the mold.

Mold – The term is given to the entire tool (cavity, core, ejectors, etc.) needed to produce parts from the molten plastic material.

Monomer – A molecular unit of an organic substance, usually in the form of a liquid or gas. POLYMER.

Melt – A term given to describe the condition of molten plastic prior to injection into a mould. A proper melt has the consistency of warm honey.

Metering Zone – That area of the screw at the front end which contains properly melted plastic that is ready to inject.

Regrind – Plastic material formed by granulating pre-moulded material. Regrind virgin material has been exposed to at least one heating cycle.

Runner – Grooves or channels cut into either one or both halves of the injection moulded to provide a path for the molten plastic material to be carried from the sprue to the gates of the cavity.

Screw speed – The rotating speed of the screw as it augers new metering zones. It is expressed in RPM (revolutions per minute).

Secondary Operation – Any activity performed after the moulding process required to produce a finished product suitable for its designed purpose. 

Semi-Automatic Operation – The term used to define the mode in which a moulding machine is operating when there is a need for an operator to start each cycle.

Shot – A term given to the total amount of plastic material is injected into a mould in a single cycle.

Shutoff Land – A raised area of the mould surface surrounding the cavity image. This area is usually between 0.002 and 0.003 inch high, approximately 1/2 inch wide and is used to focus clamping pressure on the mould. The use of a shutoff land reduces the amount of tonnage required to keep a mould closed against injection pressure.

Slide– A section of the mould which is made to travel at an angle to the normal movement of the mould. Used for providing undercuts, recesses, etc.

Sprue – The plastic material that connects the runner system to the nozzle of the heating cylinder of the moulding machine. It is formed by the internal surface of a bushing that joins the mould to the machine’s nozzle.

Sprue Bushing – A hardened bushing that connects the mould to the molding machine nozzle and allows molten plastic to enter the runner system.

Stationary Platen – The platen at the injection end of the moulding machine that does travel! It contains the “A” half of the mould and locates the mould to the nozzle of the injection unit. The moving platen travels between this platen and

Stress – A resistance to deformation from an applied force. Moulded plastic products tend to contain stresses moulded in as a result of forces applied during the injection process. These stresses may result in fractures, cracks, and breakage if they are released during use of the product.

Cycle– The total amount of time required for the completion of all operations needed to produce a moulded part. Sometimes referred to as the “gate-to-gate” time, meaning the time from when an operator first closes the gate until the time the operator closes the gate again for starting the next cycle.

Crystalline – A plastic material in which the molecular structure becomes mobile only after being heated above its melting point.

Decompression – A method of relieving pressure on the melt after preparing it for injection : during the upcoming cycle. This minimizes the drooling that occurs when a shutoff nozzle is not utilized 

Defect – An imperfection in a moulded part that results in the product not meeting original design specifications. These defects can be visual, physical, and/or hidden. 

Draft – An angle (or taper) provided on the mould to facilitate ejection of the moulded part.

Ejector Half – That half of the mould which is mounted to the moving platen of the injection machine. Sometimes called the “live” half or the “moveable” half because it moves. This hall of the mould usually contains the ejection system:

Ejector Pin – A pin, normally circular, placed in either half of the mould (usually the ejector haji) which pushes the finished moulded product, or runner system, out of a mould. Also referred to as a “knockout” pin, for obvious reasons.

Feed Throat – The area at the rear end of the injection unit that allows fresh plastic to fall from the hopper into the heating barrel.

Feed Zone – That area of the screw that is at the rear and receives fresh material from the feed throat.

Filler – Specific material added to the basic plastic resin to obtain particular chemical, electrical, physical, or thermal properties. 

Flash– A thin film of plastic that tends to form at parting line areas of a mould. May also be found in vent areas and around ejector pins. Flash is caused by too great a clearance between mating metal surfaces, which allows plastic material to enter. :

Flight – The helical metal thread structure of the injection screw.

Gate – An opening found at the entrance of a cavity (end of the runner system) which allows material to enter.

Granulator – Machine designed to grind up rejected pre-moulded plastic (products or runners). The material generated by this process is called regrind.

Anisotropic Shrinkage – Shrinkage that occurs more in one direction than another.

Automatic Operation – The term used to define the mode in which a moulding machine is operating when there is no need for an operator to start each cycle.

Barrel – A metallic cylinder in which the injection screw (or plunger) resides in the moulding machine. Also called CYLINDER.

Blend– A mixture of 2 or more plastics.

Boss – A projection of the plastic part, normally round, which is used to strengthen an area of a part; provide a source of fastening, or to provide an alignment mechanism during assembly.

Cartridge Heaters – Pencil-shaped electrical heater devices sometimes placed raise the temperature level of the mould. Especially beneficial when moulding high-temperature crystalline materials.

Cavity – A depression or female portion of the mould which creates the external plastics part of the surface.

Check Ring – A ring-shaped component that slides back and forth over the tip end of the screw. The check ring eliminates the flow of molten material backward over the screw during the injection process.

Clamp Force – The force, in tons, that the clamp unit of a moulding machine exerts to keep the mould closed during the injection process.

Clamp Unit – That section of the moulding machine containing the clamping mechanism. used to close the mould and keep it closed against injection pressure created by the injector process. The clamp unit also contains the ejection mechanism.

Cold Slug Well – A depression (normally circular) in the ejection half of an injection mould, opposite the sprue, designed to receive the first front, or “cold” portion, of molten plastic during the injection process.

Compression Ratio– A factor that determines the amount of shear that is imparted to plastic material as it travels through the barrel. It is determined by dividing the depth of the screw flight in the feed section by the depth of the screw flight in the metering section.

 Conditioning – Exposing a moulded part to a set of conditions (such as hot oil) which impart favorable characteristics to the product.

Cooling Channels – Drilled holes or channels machined into various plates or components of an injection mould providing a flow path for cooling medium in order to control the temperature of the mould.

Core –  An extended or male portion of the mould which creates the internal plastic part surface. [b] A pin or protrusion designed to produce a hole or depression in the plastic part.

 Counterbore – A recessed circular area. Commonly used to fit the head of an ejector pin [return pin, suck pin, etc.] in the ejector plate.


I hope you liked and got your query answered in above injection molding terms or glossary which is generally used and if you have any query or find useful this article then please let us know by leaving your comment in the below comment thread.

5 thoughts on “Plastic Injection molding machine: Terms, Terminology, Glossary, Vocabulary List.”

  1. Excellent stuff. I can not describe how much your blog has helped me in my academic research on the subject. I am now going to get top marks for sure. Thanks a million. I owe you one.


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