Understanding Key Terms Used in the World of Injection Molding Manufacturing
At Form Manufacturing, we collaborate closely with our clients to ensure the highest quality injection molded parts and products as well as an optimal customer experience. To more effectively communicate with them about their projects, it helps for them to have a basic understanding of the key terms used in the injection molding industry which can be found in the following glossary:
Additives/Fillers
Substances added to plastic materials to achieve certain desired material properties that enhance performance and/or reduce costs, including flame retardants, lubricants, UV stabilizers, anti-aging, and colorants.
Aging
The undesirable, gradual change in the properties of the plastic material or mold, leading to reduced performance, brittleness, and failures over time.
Barrel
The cylindrical part of the molding press where resin is melted by heater bands before it’s injected into a mold.
Boss
Often designed for fasteners, a round protrusion on a plastic part designed to provide a mounting point, attachment point or structural reinforcement for assembly or functionality.
Bubbles
Defects in which air pockets form inside a molded component, often caused by rapid mold filling, poor venting, or inadequate material handling.
Cam Pin
A common type of mechanical actuator used to move a slide mechanism on an automatic injection mold, allowing for the creation of undercuts and complex geometries in molded parts. Also known as a horn pin, angle pin, or actuator pin.
Cavity or Die Cavity
The concave, or negative, space in a mold which is filled with plastic, or other molten material, to form the outer surface of the molded part. Molds are designated as a single cavity or multi-cavity, depending on the number of such depressions. Also known as the “A-side” of the mold.
Clamp Force
The amount of pressure used by the injection molding machine to hold a mold closed during the injection molding process, preventing the mold halves from separating under the high pressures from the molten plastic. It is usually referred to in tonnage and is a defining characteristic of the injection molding press size.
CMF
An acronym for Color, Material, & Finish, this is the aesthetic and tactile aspects of a product which impact how it looks and feels.
Cold Runner
A runner system using unheated channels (runners) to transport molten plastic from the machine nozzle to fill the mold cavities.
Core or Coring
The convex half or “B-side” of the injection mold tool that usually forms the internal features of a part.
Core Outs
The portions of a molded part that are gutted out in order to maintain uniform wall thickness, lighten the part, and reduce warp.
Cycle
The complete sequence of operations in a process and the time it takes to complete one set of moldings. The molding cycle follows the sequence: mold closing, filling, packing, holding, cooling (which typically accounts for half the cycle time), mold opening, and part ejection.
Daylight
Clearance dimensions between two platens of a press in the open position, determining the maximum mold size a press can properly operate.
Design for Manufacturing (DFM)
A review, including 2D drawings for characteristics to be controlled in production, that evaluates all design changes that need to be made and the proposed molding strategy. CMF is finalized along with the production schedule.
Draft or Draft Angle
The degree of taper of a cold mold-cavity sidewall or the angle of clearance designed to allow for easier removal of parts from a mold during the ejection process.
Durometer
The hardness of a material as measured by the Shore Durometer.
Ejector Pins
Slender rods used to push the molded part out of the cavity after it has cooled and solidified. Also called knockout pins.
Electric Discharge Machining (EDM)
A non-traditional machining process used in injection molding to create complex shapes and cavities in conductive materials by using electrical discharges to erode material. Also referred to as spark machining, spark eroding, wire erosion, burning, or die sinking.
Engineering Change Notice (ECN)
A document which describes, approves, and tracks changes made to a product or process. Used by all key stakeholders, including engineers, quality control, procurement, manufacturing, and supply chain partners.
Family Mold
A multi-cavity mold where each of the cavities forms one of the component parts of an assembled finished part. Used to create an assembly, balance part quantities, and save on tooling cost and piece price.
Filled Resins
A mechanical property-improving combination of materials, such as glass and carbon, with either thermoplastic or thermosetting polymers (commonly nylon).
First Articles
The first parts molded from a new mold used for customer approval and retention. First articles are molded in the specified resin, color, decoration and texture(s).
Flash
Excess molding material that is formed along a seam or mold parting line and is still attached to the part.
Flow Line
A common defect caused by improper flow of the melt into the mold, visible wavy lines or streaks that appear on the surface of a finished part. Also known as flow marks.
Gas-Assisted Molding
A low-pressure injection molding process where pressurized nitrogen gas is injected into the mold during cooling, pushing the plastic into the mold extremities and hollowing out thicker sections in the part. Typically used to mitigate the chance of sink marks.
Gate
The orifice through which the molten material flows from the runner into the cavity. Types of gates include sub, edge, fan, and cashew.
Gate Trim
Material left over from cutting the component from the runner or sprue, usually cut flush with the edge of the component.
Gibbs
The portion of the custom injection mold that holds the slide down so the cam can actuate it.
Hand Load
Removable inserts that are manually placed into the mold and removed after molding to create features like undercuts or threads. Often used in low-volume production or when complex geometries are difficult to achieve with automated mechanisms.
Heel Block
A structural component within the mold assembly that supports and aligns the ejector system, keeping the slide in the forward position when the machine is closed on the mold, ensuring smooth and controlled movement of ejector plates or pins during the ejection phase.
Hot Runner
A waste-mitigating runner system in which the sprue and runners are heated in a manifold so the material can flow through them to the cavity in a molten state.
Injection Molding
A complex manufacturing process that involves injecting molten materials, typically thermoplastic pellets, into a mold where it cools and hardens into a desired shape. Perfect for the creation of precise, durable parts quickly and in large volumes, the injection molding process offers a number of advantages.
Insert Molding
The process of molding an insert (e.g. a small piece of threaded metal) directly into a plastic part by loading it into a molding machine before the injection molding process.
Jetting
A turbulent flow, or jet, as the melt enters the mold cavity, often resulting in an undesirable snake-like pattern on the part’s surface. Caused by an undersized gate or where a thin section rapidly becomes thicker.
Knit Lines
Where melted material flows together to form a line or lines that may cause weakening or breaking of the component.
Living Hinge
A flexible hinge made from the same material as the two rigid pieces it connects. Typically thinned to allow the rigid pieces to bend along the hinge line to allow for opening and closing.
Melt Flow Index (MFR)
A measure of how easily a plastic flows at its melting point. The higher the MFR, the lower the viscosity. Best used when comparing materials in the same class.
Mold Frame
A series of steel plates that support and align all the mold components, ensuring stability and accuracy during the molding process. It includes cavities, cores, runner system, cooling system, and ejection system.
Moldflow or Moldflow Analysis
Simulation software for injection molding used to predict and optimize the flow of molten plastic within a mold, helping engineers identify potential issues and optimize the molding process before production.
Multi-Cavity Mold
A mold having two or more impressions for forming finished items in one machine cycle. Results in shorter lead time per batch and faster production.
Nozzle
The end of the barrel where plastic flows in and out the mold. Often interchanged between projects to match the material and mold.
Overmolding
A process of molding a polymer over a plastic or other type of substrate by partially filling a mold cavity with one plastic and injecting a second shot to encapsulate the first shot. Overmolding is used for creating desirable ergonomic and cosmetic features as well as added durability and longevity.
Packing
The filling of the mold cavity or cavities to full capacity without causing added stress on the molds or causing flash on the finished parts.
Parts Approval
Conducted prior to a part going into mass production, the Part Approval Process (PPAP) ensures a supplier’s production process consistently yields parts meeting the client’s requirements. It involves the verification of design, process capability, and quality control measures.
Parting Line
A small line on a finished part that shows where the two mold halves came together when closed.
Piece Price
The cost of each individual plastic part produced in the injection molding process.
Platen
The base plate surfaces on an injection molding machine onto which the mold plates are mounted. One side is considered a moving side, back half, or ejection side, while the other side is considered the stationary side or front half.
Polymer
The molecular designation of long, repeated, linked chains. Includes resins used in injection molding.
Purging
The forcing of one molding material out of the nozzle tip with another material to clean the nozzle tip prior to molding a new material. Special purging compounds are often used.
Resin
The raw plastic material heated and injected into a mold in order to create a component in the desired shape. Often a thermoplastic polymer in pellet form.
Reverse Engineering
The process of analyzing the design of an existing component without access to the original design documentation. It involves studying and deconstructing the part to understand its manufacturing process, material composition, and functional specifications in an effort to faithfully reproduce the component.
Ribs or Ribbing
Thin, bladed support features on a part that are used to reinforce wall sections and bosses and minimize warp. Offering lower cycle times and cost, ribs or ribbing optimizes materials, weight, and use of plastic by creating thinner wall sections without sacrificing significant strength.
Runner
The channel cut into custom injection molds that connects the sprue with the gate for transferring the molten materials to the cavities, ultimately filling the part.
Screw
The rotating screw that transports and pressurizes molten material to fill the mold cavity.
Shear
Produced by speed and pressure, the friction needed to maintain the melt during injection molding. Too much shear causes material to burn while too little causes it to freeze off, resulting in a short shot.
Shore Durometer
A device for measuring the hardness of a material, typically of polymers. The term is also used to describe a material’s rating on the scale, as in an object having a “Shore durometer of 70.” Higher numbers on the scale indicate a greater resistance to indentation and thus harder materials. Lower numbers indicate less resistance and softer materials.
Short Shot
When a molded part does not completely fill the mold cavity during the injection molding process, resulting in an incomplete or defective product.
Shot/Shot Size
The yield or amount of material injected into a mold in one cycle, including the runner and sprue. Also known as the injection capacity or shot capacity.
Shrink Rate
Ranging from 0.001-0.060 per inch, the rate at which a specific injected plastic will shrink once it is cooled, causing dimensional differences between a molded part and the actual mold dimensions. Because of shrink rates, a mold cavity is designed bigger than the finished part, and as the part is cooled, a dimensionally correct part is created. Most shrink rates fall in between .004 and .021.
Side Action
A technique utilizing special inserts which allow for the creation of complex undercut geometries perpendicular to the main parting line, otherwise impossible to make with a standard straight-pull mold. Also known as side core-pulling.
Single-Cavity Mold
A mold having only one cavity and producing only one finished part per cycle.
Sink Mark
An area of the finished molded part where the plastic sinks below the surface creating a shallow depression or dimple due to factors such as shrinkage or low cavity fill.
Slide
A sliding steel mechanism that allows the mold to form complex geometries and release the part when the mold opens. Used for creating parts with undercuts or recesses that prevent a simple straight pull. Required for automatic injection molds. Also called slide action or slider.
Sprue
Perpendicular to the runner, the channel that connects the injection molding machine’s barrel and nozzle to the runner and the first area the plastic flows into from the molding machine barrel.
Steel Safe
A design technique that allows for material removal of metal from an injection mold to modify the part. Also called metal safe.
Straight Pull
A mold without any side-actions or special features that may be used to resolve undercuts.
T0, T1, T2 Shots
Different stages of mold trials which represent key steps in improving the mold and ensuring the final part meets quality and design requirements.
Thermoplastic
A classification of plastics that are moldable at elevated temperatures and solidify after cooling. Common thermoplastics include polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC).
Thermoset
A classification of plastics that undergo a permanent chemical change in composition when heated.
Thin Wall Molding
Thin wall molding is the molding of plastic parts with wall thicknesses .005 to .060.
Tonnage
The size of an injection molding machine in reference to how much force it can apply when closing a mold. The closing pressure is used to resist injection pressure and seal the mold. Higher tonnage machines also have larger barrel and screw assemblies for larger part volume.
Tooling
A specialized, complex, metal structure with a cavity that defines the shape of the final part. Commonly called a mold.
Undercut
Any indentation or protrusion of a molded part that impedes ejection from the mold. Categorized into internal and external undercuts, undercuts can still be molded, but require a side action or side pull.
Vent
A shallow channel or opening cut located at various points in the cavity that allow air to flow out as molten material flows in.
Vestige
A small and often unsightly mark or protrusion left on a molded part after the gate and runner are removed.
Wall Thickness
The thickness of the cross section of the plastic part.
Warp
Often caused by internal stresses via uneven material flow, cooling, and compression, an area of an injection molded part that has been dimensionally distorted during cooling or molding, causing undesired results in the finished product.
Weld Line
Usually occurring around holes or obstructions, a visible line where two flow fronts meet but fail to “knit” or “weld” together on a finished part after the molding process, resulting in locally weak or broken areas.
