Glossary

To help you gain a better understanding of our processes we’ve compiled a glossary of terms that we commonly use in our industry.

A
ACIS
A standard computer file format for exchanging CAD data, typically from AutoCAD programs. ACIS is an acronym that originally stood for “Andy, Charles and Ian's System.”

Additive manufacturing/ 3D printing
Commonly used interchangably, additive manufacturing (3D printing) involves a CAD model or scan of an object that is reproduced, layer by layer, as a physical three-dimensional object. Stereolithography, selective laser sintering, fused deposition modeling and direct metal laser sintering are some of the commonly employed additive processes.

A-Side
Sometimes called the “cavity,” it is the half of the mold that usually creates the exterior of a cosmetic part. The A-side usually does not have moving parts built into it.

Axial hole
This is a hole that is parallel to the axis of revolution of a turned part, but does not need to be concentric to it.
B
Barrel
A component of the injection-molding machine wherein the resin pellets are melted, compressed and injected into the mold’s runner system.

Bead blasting
Using abrasives in a pressurized air blast to create a surface texture on the part.

Bevel
Also known as a “chamfer,” it is a flat truncated corner.

Blush
A cosmetic imperfection that is created where the resin is injected into the part, usually visible as a blotchy discoloration on the finished part at the site of the gate.

Boss
A raised stud feature that is used to engage fasteners or support features of other parts passing through them.

Bridge tool
A temporary or interim mold made for the purpose of making production parts until a high-volume production mold is ready.

B-Side
Sometimes called the “core,” it is the half of the mold where ejectors, side-action cams and other complex components are located. On a cosmetic part, the B-side usually creates the inside of the part.

Build platform
The support base on an additive machine where parts are built. The maximum build size of a part is dependent on the size of a machine’s build platform. Many times a build platform will house a number of different parts of varying geometries.

Bumpoff
A feature in the mold with an undercut. To eject the part, it must bend or stretch around the undercut.
C
CAD
Computer-aided design.

Cam
A portion of the mold that is pushed into place as the mold closes, using a cam-actuated slide. Typically, side actions are used to resolve an undercut, or sometimes to allow an undrafted outside wall. As the mold opens, the side action pulls away from the part, allowing the part to be ejected. Also called a “side-action.”

Cavity
The void between the A-side and B-side that is filled to create the injection-molded part. The A-side of the mold is also sometimes called the cavity.

Chamfer
Also known as a “bevel,” it is a flat truncated corner.

Clamp force
The force required to hold the mold shut so resin cannot escape during injection. Measured in tons, as in “we have a 700 ton press”

Contoured pins
Ejector pins with the ends shaped to match a sloping surface on the part.

Core
A portion of the mold that goes inside a cavity to form the interior of a hollow part. Cores are normally found on the B-side of a mold, thus, the B-side is sometimes called the core.

Core pin
A fixed element in the mold that creates a void in the part. It is often easier to machine a core pin as a separate element and add it to the A-side or B-side as needed. Steel core pins are sometimes used in aluminum molds to create tall, thin cores that might be too fragile if machined out of the bulk aluminum of the mold.

Core-cavity
A term used to describe a mold created by mating A-side and B-side mold halves.

Cycle time
The time it takes to make one part including the closing of the mold, the injection of the resin, the solidification of the part, the opening of the mold and the ejection of the part.
D
Direct metal laser sintering (DMLS)
DMLS employs a fiber laser system that draws onto a surface of atomized metal powder, welding the powder into a solid. After each layer, a blade adds a fresh layer of powder and repeats the process until a final metal part is formed.

Direction of pull
The direction the mold surfaces move when they are moving away from the part surfaces, either when the mold opens or when the part ejects

Draft
A taper applied to the faces of the part that prevent them from being parallel to the motion of the mold opening. This keeps the part from being damaged due to the scraping as the part is ejected out of the mold.

Drying of plastics
Many plastics absorb water and must be dried prior to injection molding to ensure good cosmetics and material characteristics.

Durometer
A measure of a material's hardness. It is measured on a numeric scale ranging from lower (softer) to higher (harder).
E
Edge gate
An opening aligned with the parting line of the mold where resin flows into the cavity. Edge gates are typically placed on an outside edge of the part.

EDM
Electric Discharge Machining. A moldmaking method which can create taller, thinner ribs than milling, text on top of ribs and square outside edges on parts.

Ejection
The final stage of the injection-molding process where the completed part is pushed from the mold using pins or other mechanisms.

Ejector pins
Pins installed in the B-side of the mold that push the part out of the mold when the part has cooled sufficiently.

Elongation at break
How much the material can stretch or deform before breaking. This property of LSR allows for some difficult parts to be surprisingly removed from molds. For example, LR 3003/50 has an elongation at break of 480 percent.

End mill
A cutting tool that is used to machine a mold.

ESD
Stands for “electro static discharge,” an electrical effect that may necessitate shielding in some applications. Some special grades of plastic are electrically conductive or dissipative and help prevent ESD.
F
Family mold
A mold where more than one cavity is cut into the mold to allow for multiple parts made of the same material to be formed in one cycle. Typically, each cavity forms a different part number. See also “multi-cavity mold.”

Fillet
A curved face where a rib meets a wall, intended to improve the flow of material and eliminate mechanical stress concentrations on the finished part.

Finish
A specific type of surface treatment applied to some or all faces of the part. This treatment can range from a smooth, polished finish to a highly contoured pattern that can obscure surface imperfections and create a better looking or better feeling part.

Flame retardant
A resin formulated to resist burning

Flash
Resin that leaks into a fine gap in the parting lines of the mold to create an undesired thin layer of plastic or liquid silicone rubber.

Flow marks
Visible indications on the finished part that show the flow of plastic within the mold prior to solidification.

Food grade
Resins or mold release spray that are approved for use in the manufacture of parts that will contact food in their application.

Fused deposition modeling (FDM)
With FDM, a wire coil of material is extruded from a print head into successive cross-sectional layers that harden into three-dimensional shapes.
G
Gate
The generic term for the portion of the mold where resin enters the mold cavity.

GF
Glass-filled. This refers to a resin with glass fibers mixed into it. Glass-filled resins are much stronger and more rigid than the corresponding unfilled resin, but are also more brittle.

Gusset
A triangular rib that reinforces areas such as a wall to a floor or a boss to a floor.
H
Hot tip gate
A specialized gate that injects the resin into a face on the A-side of the mold. This type of gate doesn’t require a runner or sprue.
I
IGES
Initial Graphics Exchange Specification. It is a common file format for exchanging CAD data. Protomold can use IGES solid or surface files to create molded parts.

Injection
The act of forcing molten resin into the mold to form the part.

Insert
A portion of the mold that is installed permanently after machining the mold base, or temporarily between mold cycles.
J
Jetting
Flow marks caused by the resin entering a mold at high speed, typically occurring near a gate.
K
Knit lines
Also known as “stitch lines” or “weld lines,” and when multiple gates are present, “meld lines.” These are imperfections in the part where separated flows of cooling material meet and rejoin, often resulting in incomplete bonds and/or a visible line.
L
Layer thickness
The precise thickness of a single additive layer that can reach as small as microns thin. Often, parts will contain thousands of layers.

LIM™
Liquid injection molding, which is the process used in the molding of liquid silicone rubber.

Live tooling
Mill-like machining actions in a lathe where a rotating tool removes material from stock. This allows for the creation of features like flats, grooves, slots, and axial or radial holes to be created within the lathe.

Living hinge
Very thin section of plastic used to connect two parts and keep them together while allowing them to open and close. They require careful design and gate placement. A typical application would be the top and bottom of a box.

LSR
Liquid silicone rubber.
M
Medical grade
Resin that may be suitable for use in certain medical applications.

Meld lines
Occurs when multiple gates are present. These are imperfections in the part where separated flows of cooling material meet and rejoin, often resulting in incomplete bonds and/or a visible line.

Metal safe
A change to the part design that requires only the removal of metal from the mold to produce the desired geometry. Typically most important when a part design is changed after the mold has been manufactured, because then the mold can be modified rather than entirely re-machined. It is also commonly called “steel safe.”

Mold release spray
A liquid applied to the mold as a spray to facilitate the ejection of parts from the B-side. It is typically used when the parts are difficult to eject because they are sticking to the mold.

Multi-cavity mold
A mold where more than one cavity is cut into the mold to allow for multiple parts to be formed in one cycle. Typically, if a mold is called “multi-cavity,” the cavities are all the same part number. See also “family mold.”
N
Net shape
The final desired shape of a part; or a shape that does not require additional shaping operations before use.

Nozzle
The tapered fitting on the end of the barrel of the injection-molding press where the resin enters the sprue.
O
On-axis hole
This is a hole that is concentric to the axis of revolution of the turned part. It is simply a hole on the end of a part and in the center.

Overflow
A mass of material away from the part, typically at the end of fill, connected by a thin cross-section. The overflow is added to improve part quality and is removed as a secondary operation.
P
Packing
The practice of using increased pressure when injecting a part to force more plastic into the mold. This is often used to combat sink or fill problems, but also increases the likelihood of flash and may cause the part to stick in to the mold.

Parasolid
A file format for exchanging CAD data.

Part A/Part B
LSR is a two-part compound; these components are kept separate until the LSR molding process begins.

Parting line
The edge of a part where the mold separates.

Pickouts
A mold insert that remains stuck to the ejected part and has to be pulled out of the part and placed back into the mold before the next cycle.

Porosity
Undesired voids included in a part. Porosity can manifest in many sizes and shapes from many causes. Generally, a porous part will be less strong than a fully dense part.

Post gate
A specialized gate that uses a hole that an ejector pin passes through to inject resin into the mold cavity. This leaves a post vestige that usually needs to be trimmed.

Press
An injection molding machine.
R
Radial hole
This is a hole formed by live tooling that is perpendicular to the axis of revolution of a turned part, and could be considered a side hole. The center line of these holes are not required to intersect the axis of revolution.

Radiused
An edge or vertex that has been rounded. Typically, this occurs on part geometries as a natural result of the Protomold milling process. When a radius is intentionally added to an edge on a part, it is referred to as a fillet.

Ram
A hydraulic mechanism that pushes the screw forward in the barrel and forces resin into the mold.

Recess
An indentation in the plastic part caused by the impact of the ejector pins.

Reinforced resin
Refers to base resins with fillers added for strength. They are particularly susceptible to warp because the fiber orientation tends to follow flow lines, resulting in asymmetric stresses. These resins are typically harder and stronger but also more brittle (i.e. less tough).

Resin
A generic name for chemical compounds that, when injected, form a plastic part. Sometimes just called “plastic.”

Resolution
The level of printed detail achieved on parts built through additive manufacturing. Processes like stereolithography and direct metal laser sintering allow for extremely fine resolutions with the smallest of features.

Rib
A thin, wall-like feature parallel to the mold opening direction, common on plastic parts and used to add support to walls or bosses.

Runner
A channel that resin passes through from the sprue to the gate/s. Typically, runners are parallel to, and contained within, the parting surfaces of the mold.
S
Screw
A device in the barrel that compacts resin pellets to pressurize and melt them prior to injection.

Selective laser sintering (SLS)
During the SLS process, a CO2 laser draws onto a hot bed of thermoplastic powder, where it lightly sinters (fuses) the powder into a solid. After each layer, a roller lays a fresh layer of powder on top of the bed and the process repeats.

Shear
The force between layers of resin as they slide against each other or the surface of the mold. The resulting friction causes some heating of the resin.

Short shot
A part that wasn't completely filled with resin, causing short or missing features.

Shrink
The change in part size as it cools during the molding process. This is anticipated based on material manufacturer recommendations and built into the mold design before manufacturing.

Shutoff
A feature that forms an internal through-hole in a part by bringing the A-side and B-side in contact, preventing the flow of resin into the through-hole.

Side-action
A portion of the mold that is pushed into place as the mold closes, using a cam-actuated slide. Typically, side-actions are used to resolve an undercut, or sometimes to allow an undrafted outside wall. As the mold opens, the side action pulls away from the part, allowing the part to be ejected. Also called a “cam.”

Sink
Dimples or other distortion in the surface of the part as different areas of the part cool at different rates. These are most commonly caused by excessive material thickness.

Splay
Discolored, visible streaks in the part, typically caused by moisture in the resin.

Sprue
The first stage in the resin distribution system, where the resin enters the mold. The sprue is perpendicular to the parting faces of the mold and brings resin to the runners, which are typically in the parting surfaces of the mold.

Steel pins
A cylindrical pin for formatting high-aspect-ratio, small-diameter holes in a part. A steel pin is strong enough to handle the stress of ejection and its surface is smooth enough to release cleanly from the part without draft.

Steel safe
Also known as “metal safe” (which is the preferred term when working with aluminum molds). This refers to a change to the part design that requires only the removal of metal from the mold to produce the desired geometry. Typically most important when a part design is changed after the mold has been manufactured, because then the mold can be modified rather than entirely re-machined.

STEP
Stands for “Standard for the Exchange of Product Model Data.” It is a common format for exchanging CAD data.

Stereolithography (SL)
SL uses an ultraviolet laser focused to a small point to draw on the surface of a liquid thermoset resin. Where it draws, the liquid turns to solid. This is repeated in thin, two-dimensional cross-sections that are layered to form complex three-dimensional parts.

Sticking
A problem during the ejection phase of molding, where a part becomes lodged in one or the other half of the mold, making removal difficult. This is a common issue when the part is not designed with sufficient draft.

Stitch lines
Also known as “weld lines” or “knit lines,” and when multiple gates are present, “meld lines.” These are imperfections in the part where separated flows of cooling material meet and rejoin, often resulting in incomplete bonds and/or a visible line.

STL
Originally stood for “STereoLithography.” It is a common format for transmitting CAD data to rapid prototyping machines and is not suitable for injection molding.

Straight-pull mold
A mold that uses only two halves to form a cavity that resin is injected into. Generally, this term refers to molds with no side-actions or other special features used to resolve undercuts.
T
Tab gate
An opening aligned with the parting line of the mold where resin flows into the cavity. These are also referred to as “edge-gates” and are typically placed on an outside edge of the part.

Tear Strip
A feature added to the mold that will be removed from the part after molding to aid in creating a crisp end on the part. This is often done in conjunction with an overflow to improve the final part quality.

Texture
A specific type of surface treatment applied to some or all faces of the part. This treatment can range from a smooth, polished finish to a highly contoured pattern that can obscure surface imperfections and create a better looking or better feeling part.

Tunnel gate
A gate that is cut through the body of one side of the mold to create a gate that does not leave a mark on the exterior face of the part.

Turning
During the turning process, rod stock is rotated in a lathe machine while a tool is held against the stock to remove material and create a cylindrical part.
U
Undercut
A portion of the part that shadows another portion of the part, creating an interlock between the part and one or both of the mold halves. An example is a hole perpendicular to the mold opening direction bored into the side of a part. An undercut prevents the part from being ejected, or the mold from opening, or both.
V
Vent
A very small (0.001 in. to 0.005 in.) opening in the mold cavity, typically at the shutoff surface or via an ejector pin tunnel, that is used to let air escape from a mold while the resin is injected.

Vestige
After molding, the plastic runner system (or in the case of a hot tip gate, a small dimple of plastic) will remain connected to the part at the location of the gate/s. After the runner is trimmed off (or the hot tip dimple is trimmed), a small imperfection called a “vestige” remains on the part.
W
Wall
A common term for the faces of a hollow part. Consistency in wall thickness is important.

Warp
The curving or bending of a part as it cools that results from stresses as different portions of the part cool and shrink at different rates. Parts made using filled resins may also warp due to the way the fillers align during resin flow. Fillers often shrink at different rates than the matrix resin, and aligned fibers can introduce anisotropic stresses.

Weld lines
Also known as “stitch lines” or “knit lines,” and when multiple gates are present, “meld lines.” These are imperfections in the part where separated flows of cooling material meet and rejoin, often resulting in incomplete bonds and/or a visible line.

Wireframe
A type of CAD model consisting only of lines and curves, in 2D or 3D. Wirefame models are not suitable for rapid-injection molding.
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