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ACIS – ACIS stands for “Andy, Charles and Ian’s System”.  Auto CAD programs are usually exchanged from CAD data using this computer file format.

A-Side – The A-Side is often referred to as the cavity part of the mold.  It is the half of the mold that mounts to the stationary side of the injection molding press. The resin is then injected in the cavity through the sprue. The A-side lacks ejector pins, which results in the production the cosmetic side of the part.


Barrel – The resin is melted in this part of the molding press.

Bead Blasting – Using an air blaster along with pressurized abrasives to achieve a surface texture.

Bevel – See “chamfer”.

Blush – The blemish in the finished portion of the injection.

Boss – Designed to allow fasteners, it is a barrel protrusion in a part.

Bridge Tool – Purposed for making production parts, it’s a provisional or temporary mold used until a high-volume production mold is available.

B-Side – Often called the core side of the mold, it is the mold half that is attached to the moving side of the injection molding press. It has ejector pins to push the portion of the open mold.

Bumpoff – This piece possesses an undercut. In order to expel the part, it must maneuver around the undercut.


CAD – Stands for “computer aided design”.

Cam – See “side action”

Cavity – The void in between the core and cavity is where the resin attaches to the part and hardens. It is the sunken feature on either side of the mold. The opposite core and the cavity interconnect when the mold is closed. The cavity side is often referred to as the cavity. In the example of a cup the whole A-side will be a cavity.

Chamfer – A flat corner which is truncated. Sometimes referred to as a bevel.

Clamp Force – The strength required, measured in tons, to hold the mold shut. It needs to be held shut so, during injection, resin can not escape.

Contoured Pins – Ejector pins with either end matched to the sloping outside on the part.

Core – The area between the core and cavity is where the resin will harden to form the part. It is a concaved area on each side of the mold, which will enter the opposite cavity when closed. The area between the core and cavity is where the resin will harden to form the part. The B-side of the mold is known as the core side. In the example of a drinking cup the B side would be the core.

Core-cavity – The purpose of a mold in which the A-side creates the outside of the part and the B-side creates the inside. The idea for this is that the part will decrease onto the B-side. This will then be ejected and when the outside and inside are composed with opposite and equal, also the thickness of the wall will be constant throughout. A little or thin core could be made using a steel pin.

Cycle Time – The time that is needed to complete a single part. This includes the hardening of the part, the mouth of the mold, the closing of the mold, the injection resin and the ejection of the part.


Direction of Pull – This is determined when the mold ejects the part or the mold opens. It is way that the mold moves when maneuvering away from the part surfaces.

Draft – It helps parts let go from the mold during ejection. It is also the way the features taper in the direction of pull. Then deeper features will be made in three-axis milling machines.

Drying of Plastics – The plastics must be dried before injection molding because many of them absorb water. Drying of the plastics guarantees great cosmetic and material turnout.

Durometer – This is how to measure the hardness of a resin. This is done on a scale of numbers ranging from lower to higher, or softer to harder.


Edge Gate – An injection molding that usually leaves a vestige on the outside of the part. This typically uses a gate that is referred to as a tab gate.

EDM – A method for making a mold, this can create thinner and taller ribs than milling. It makes square outside edges and text on the top ribs.

Ejection – The act of pushing the finished part out of the mold.

Ejector Pins – Pins made of steel that push the plastic part, they are associated with the B-side.

End Mill – Used to machine a mold, this is the cutting tool that is used.

ESD – An electrical effect that may need protecting in some applications. This stands for “electro static discharge”. Often certain types of plastics dissipate and prevent ESD or might conduct electricity.


Family Mold – A mold that possess two or more different parts.

Flame Retardant – An adhesive that is resistant to catching fire.

Flash – A sheet-like bulge that is created when the extra plastic flows into the parting line of the mold and beyond and freezes.

Flow Marks – Wear lines on the finished part that tell you the flow of plastic, in the mold, prior to hardening.

Food Grade – Resins or molds let off that will come in contact with food when applying, these are approved for making of parts.


Gate – The area where the plastic is inserted into the part. When the gate is taken away there is a visible groove.

GF – Known as a resin that has glass fibers mixed into it. It stands for “glass filled”. Resins that are glass filled are so much more rigid and stronger than one that is not. They also maybe more brittle and may tend to warp. Also resins can be filled with several things, such as stainless steel, carbon fiber, etc.

Gusset – Used as a triangular support. Such as a boss to a floor or a wall to a floor.


Hot Tip Gate – This injection molding method typically uses a hot gate on A-side of the part. This is used to take out the making of any sprue or runner. The gate vestige will be a sharp bump, if necessary this can be cut.


IGES – “Initial Graphics Exchange Specification”. Protomold may use IGES or surface files to make molded parts. It is a commonly used file format for sharing CAD data.

Injection – Act of guiding melted resin into the mold.


Jetting – Current marks made by the resin going into the mold, usually occurring near a gate and traveling at high speed.


Knit Lines – In a finished part there are visible indications, always created downstream, these are formed by intersections of two plastic flow fronts. They are also known as weld lines, these are formed through holes and between many gates.


Living Hinge – This thin piece of plastic connects two parts and keeps them connected while still being able to open and close. It takes precise gate placement and design.


Medical Grade – A resin has been deemed suitable for some medical uses.

Metal-safe – Removal of metal which changes the part design. It is removed from the mold to achieve a desired shape. The mold can be changed versus completely reconstructed after the mold has been manufactured, if the part design is changed after the fact.

Mold Release Spray – To start the extraction of parts from B-side, a liquid is added to the mold . When parts are sticking to the mold and are difficult to take out, this process is used.

Multi-cavity Mold – In order to reduce piece-part pricing, multiple copies of the same part will be run in high volumes.


Nozzle – At the end of the barrel, this tapered fit of the injection molding press is where the resin enters the sprue.



Packing – Using higher pressure when injecting a part, this forces more plastic into the mold. This increases the probability of flash and may cause the part to adhere to the mold. It is often used for fill problems or to combat sink.

Parasolid – A file format used to exchange CAD data.

Parting Line – Usually a thin line is created on the part, after the pieces of mold come together.

Pickout – Metal placed into the mold to make an undercut. It is ejected with that part followed by being taken out by the user and re-inserted into the mold.

Post Gate – Injects plastic through a pin hole in the in the ejector. This is a gating technique which leaves a gate area on the B-side of the part. Opposite a post gate there is usually a blush gate.

Press – This injection molding machine makes parts out of plastic. It holds the mold closed, liquefies the resin, injects it into the mold, opens the mold and ejects the part.

Process – Consisting of input variables, this is referring to the injection molding environment, such as pressure, injection rates, temperature, and time. These are controlled to fill the mold while improving the tradeoffs between dimensional accuracy and cosmetics.



Radiused – A rounded edge which usually occurs due to part geometries. In the Protomold milling process, this is a natural outcome. A filet is when the radius is purposely added to an edge.

Recess – Caused by the impact of the ejector pins, this often seen as a dent in the plastic part.

Reinforced Resin – With filters added for strength these base resins are very prone to warp. The reason being the fiber orientation usually follows flow lines in turn resulting in asymmetric stresses. These resins are typically less tough but stronger and harder.

Resin – When talking about injection molding it is synonymous with plastic.

Rib – A member of a molded part, which serves the purpose of reinforcement.

Runner – Machined into the mold, this acts as a channel that directs the resin from the sprue to the gate.


Screw – Inside the barrel, this mechanical part forces the resin out the nozzle.

Shear – As they slide against one another or slide against the forces of the mold, this is referred to as the force between layers of the resin. The friction that results causes the resin to heat some.

Short shot – This is when the part is not completely filled with resin, causing missing or short characteristics.

Shrink – During solidification this is referred to as the change in the size of the part, typically based on written material property data. It is built prior to machining into the mold design.

Shutoff – Where the A-side and B-side contact on the mold surface. The parting line is where the shutoff meets the part.

Side action – A setup within the mold where the sliding cam allows for the molding of parts with undercuts. The undercut-creating mold face is held in place during the injection process. It moves out of the way prior to ejection.

Sink – Unwelcomed depressions in the surface of the part which are created by the shrinking of resin when it hardens. Sink is most prevelant in thick sections of the part.

Splay – Visible, discolored streaks in the part, which is caused by the moisture in the resin.

Sprue – The resin takes this route from the point where it begins in the mold until it reaches the runner(s). It solidifies and remains attached to the part via one or more runners and is typically taken away in finishing.

Stack Molds – Several similar molds positioned behind each other in order to allow extra parts to be produced during one cycle.

Stationary Platen – A large plate that is located on the front of an injection molding press which does not move during operation.

Stress Cracking – Three types: 1. Thermal stress cracking caused by over-exposure to high temperatures. 2. Physical stress cracking which occurs in the crystalline structure of the part and is the result of internal or external strain. 3. Chemical stress cracking which is caused by a liquid or gas penetrating the surface.

Striations – Marks due to the direction of melt flow on the surface.

Strings – Excess material in the form of a string due to the gate not being cut off properly.

Stripper Plate – A plate that is used to strip a piece of mod from core pins and force plugs.

Structural Foam Molding – A process used to make parts that are comprised of a solid skin with a foam core.

Submarine Gate – A gate located below the parting line from the runner to the mold cavity.

Suck-back – A term used when the pressure is not held constant while the melt cools before the screw returns, often resulting in some melt flowing back and creating sink marks on the surface of the part produced.


Tab Gate – A small tab located perpendicular to the mold, roughly the same thickness as the part that can be removed.

Thermoplastic – A polymer that flows when heated up to a specific temperature.

Thermoset – A polymer that is resistant to flow when exposed to high temperatures. The material is “set” during the original molding process and will only decompose under extreme temperatures.

Tie-Bar Spacing – A measurement that limits the size of molds that are able to be put between the tie-bars, it is the area between the tie-bars on the injection molding mechanism.

Toggle – A clamping mechanism that applies pressure through the use of a knee joint. It is used to exert pressure on the mold.

Tonnage – A system that categorizes injection molding machines by the clamping force of each machine.

Tunnel Gate – Refer to Submarine Gate.


Undercut – A protuberance or indentation that resists the removal of the part from a two-piece mold.


Valve Gating – A gate type that uses spring tension to hold a pin in the gate. This gate is then used to compress the plastic in the runner. Once the pressure exceeds the spring tension, the pin is released and melt fills the cavity.

Vent – An opening in the cavity that allows gases to escape the cavity as it is filled with melt.

Vented Barrel – A plasticator piece designed with a vent port positioned over the compression portion of the screw to allow the escape of gases prior to the injection process.

Vertical Flash Ring – The space or area between the force plug and the wall of the cavity.

Voids – Areas in the part that filled with air that were not filled with material.


Warpage – Structural distortion to the molded part typically caused by an uneven flow, cooling and compression.

Weld Line – Weak areas in the finished part due to material flowing from two directions and meeting together to form a line.

Wisps – A smaller version of stringing often due to over packing the mold.




Contact us at 847-695-9700 or to have us quote this option for your next custom molding project!