Injection Molding Overview 250

acrylonitrile butadiene styrene

ABS. A thermoplastic material with good heat, chemical, and impact resistance. Acrylonitrile butadiene styrene is commonly used to manufacture medical equipment housings.

additives

A substance added to a plastic during manufacturing in order to improve or alter its properties. Additives can help add strength, ultraviolet resistance, and color to a plastic.

burn marks

A blemish on a plastic part caused by heated gas becoming trapped in plastic melt. Burn marks affect color, surface finish, and in some cases, strength and hardness of a plastic part.

carbon black

A soot-like additive that is used as a colorant and/or a protector against ultraviolet radiation in polymers. Carbon black is a type of light stabilizer.

ceramics

A hard, brittle material that can withstand high temperatures and resist corrosion. Ceramics include traditional materials such as brick, clay, and glass, as well as more advanced materials.

clamping unit

The component of an injection molding machine that secures the mold while resin is injected and cooled. The clamping unit opens and closes the mold to eject the solidified part.

cooling channels

A passage through which a cooling fluid is circulated to maintain the desired mold temperature. Cooling channels may run uniformly through the mold, or they may vary the amount of fluid that reaches different parts.

cycle

The time during which a machine works on a single part. The cycle includes the time it takes for the melt to enter the mold, cool, and be ejected.

cycle time

The amount of time required to complete one manufacturing process from its beginning to its end. Cycle times for molding processes include the time it takes to close a mold, fill a cavity with molten material, cool the material, open the mold, and release the final part.

ejector pins

A long pin that extends and retracts to force a solid, molded part out of a mold cavity. To prevent part deformation, the part must be completely cooled before ejector pins are activated.

epoxy resin

A tough, heat-resistant, dielectric resin used in advanced composites. Epoxy resin is used to make packages for integrated circuits.

family mold

A mold that makes multiple pieces of the same product at the same time. Family molds are suitable for producing multiple distinct parts per cycle but require careful balancing of cavity fill rates to ensure consistent part quality.

feed barrel

The holding chamber of an extrusion or injection molding machine in which material is melted and mixed. The feed barrel is typically heated and contains a reciprocating screw that moves material through the barrel.

feed throat

The component on an extruder or injection molding machine where resin granules enter the feed barrel. The feed throat connects the hopper and the feed barrel.

flashing

Excess material that has become trapped between mold shells. Flashing occurs when too much material is injected into a mold.

flow rate

The speed at which molten plastic travels into a mold. Flow rate is affected by the viscosity of the melt, the size of the runners, and the size of the gates leading to a mold cavity.

foaming agent

A substance that creates pockets of gas inside of melt in injection molding. Foaming agents lead to parts with a lower density than completely solid parts.

formaldehyde

A colorless chemical that is used to create some plastics. Formaldehyde, when mixed with phenol, can create phenolic.

gas-assisted injection molding

An injection molding process in which an inert gas, typically nitrogen, is forced into a mold to push the plastic against the walls of the mold and improve wall thickness uniformity. Gas-assisted injection molding also helps to prevent sink marks and voids.

gates

An opening at the end of a runner, which directs the flow of molten material into the mold cavity. Gates control the speed at which melt flows into the mold cavity.

granules

Small particles of material. Granules of raw materials are melted to form plastic parts in injection molding.

hopper

A large, funnel-shaped device located on top of the feed barrel on extrusion and injection molding machines. The hopper serves as the entryway for pellets of composite material into the feed barrel.

injection molding

A molding process in which liquid resin is heated in a barrel and deposited into a mold by a reciprocating screw. Injection molding is a polymer shaping process used in traditional manufacturing.

injection molding machines

A machine used in plastics injection molding to produce plastic components. Injection molding machines use a reciprocating screw to melt, homogenize, and inject plastic resin into a mold cavity under controlled pressure and temperature.

insert molding

An injection molding process in which components made of a material other than plastic, such as metal, are inserted into a mold before the melt is injected. Insert molding creates complex parts made of differing materials.

melt

Liquified plastic material. Melt is produced when the injection molding machine heats resin granules and pushes the material down the barrel.

metals

A naturally occurring material with high electrical and thermal conductivity, luster, density, and strength. Metals include copper, iron, nickel, steel, and lead.

mold

A device with a hollow cavity that holds heated liquid material and imparts its shape on the material as it cools. Molds are used in injection molding to give plastic parts their final shape.

mold cavities

Hollow voids in a mold that contain the shape of a part to be molded. Mold cavities fill with melt that becomes a part when it cools.

mold unit

The part of an injection molding machine that contains the mold and the clamps. The melt enters the mold unit through the sprue, which connects to runners that direct flow into cavities that give plastic its final shape.

molded

Formed by injecting molten plastic into cavities that have the imprint of the desired final shape of a plastic part. Molded plastic is used in a variety of products.

molecular orientation

The direction that polymer crystals harden in. The molecular orientation of a plastic affects its shear and tensile strength.

multi-cavity molds

A mold that makes multiple copies of the same part at the same time. Multi-cavity molds are ideal for high-volume production runs.

overmolding

An injection molding process in which a part is molded in one type of plastic and then coated with another plastic. Overmolding bonds the plastics together.

phenol

A chemical that is used to create some plastics. Phenol, when mixed with formaldehyde, can create phenolic.

phenolic

A type of thermoset made from phenol and formaldehyde that is used to create some plastics. Phenolics are often used with binder agents in additive manufacturing.

pigments

A powdered coloring agent mixed with resin. Pigments are an additive used to color the surface of a plastic product.

plastics

A lightweight material that is corrosion resistant and easily shaped. Plastics, or polymers, are some of the most common manufacturing materials.

polycarbonate

PC. A transparent thermoplastic that is used for items that require high heat resistance. Polycarbonate is a common polymer that is used for safety glasses and other welding PPE.

polyethylene

PE. A thermoplastic in the polyester family that is highly resistant to electricity and heat. Polyethylene is often used to manufacture tough plastic bags and beverage containers.

polypropylene

PP. A polymer that is tough, flexible, and resistant to fatigue. Polypropylene is commonly used to make translucent products such as food packaging.

polystyrene

PS. A thermoplastic that is transparent and easily shaped. Polystyrene has elastic qualities.

polyurethane

A thermoset polymer that is versatile and wear resistant. Polyurethane is used in resins for adhesives, elastomers, and fillers.

production runs

The collective processes that are necessary to manufacture a group of similar or related parts. Production runs are measured by the total number of a product that must be produced.

resin

A raw polymer, usually in the form of beads or pellets, that is not yet molded into its final shape. Resin is melted to form plastic parts.

runners

A channel in a mold that provides a path for the melt and delivers it to the mold cavities. Runners connect to mold cavities via gates.

rutile titanium dioxide

A white, powdered additive that is used as a colorant and/or protector against ultraviolet radiation in polymers. Rutile titanium dioxide is a type of light stabilizer.

scorching

A plastic defect caused when too much heat is used to melt a resin, or when the material stays in the feed barrel too long. Scorching affects color, surface finish, and in some cases, strength and hardness of a plastic part.

screw

A component of an injection molding machine that mixes and compresses the resin. Screws push melted resin down the feed barrel into the mold unit.

shear strength

The ability of a material to resist forces that attempt to cause the internal structure to slide against itself and separate. Shear strength is the amount of shear force a material can withstand before fracturing.

shells

Components of a mold unit with hollow cavities that form a mold when pressed together. Shells are often made of steel or aluminum.

short shot

An incomplete load of material in a mold. Short shots cause shrinkage and sink marks in plastic parts.

shrinkage

The reduction in size of a part as it contracts while cooling within a mold. Shrinkage of a plastic can be offset by adding more melt in future runs.

silicone casting

The process of creating a part by pouring liquid silicone into a mold. Silicone casting molds can be made from polycarbonate.

silicone rubber

A rubber-like material composed of a silicone polymer that is used to create flexible parts. Silicon rubber has good strength and resistance to heat.

sink marks

A defect in a plastic part where a thicker wall has cooled at a different rate than a thinner part. Sink marks are prevented by cooling channels and gas-assisted injection molding.

sprue channel

Part of a mold that connects the injection nozzle to the runners. Sprue channels typically run perpendicular to runners.

structural foam molding

An injection molding process in which a foaming agent is mixed with the melt. Structural foam molding creates plastic parts that are less dense than completely solid parts.

synthetic

Manufactured or produced through deliberate processes rather than having a natural origin. Plastics are synthetic polymers.

tensile strength

The ability of a material to resist forces that attempt to pull apart or stretch it. Tensile strength is the amount of tensile stress a material can withstand before fracturing.

thermoplastics

A grouping of plastics that can be repeatedly reheated and re-shaped. Thermoplastics are the most commonly used plastics.

thermosets

A grouping of plastics that, once cooled, can never be reheated and reshaped. Thermosets will char or burn if heated after they have been hardened.

tolerance

An acceptable deviation from a desired dimension that still meets part specifications. Tolerances indicate the allowable difference between a physical feature and its intended design.

ultraviolet radiation

UV radiation. Energy transmitted as invisible wavelengths. Ultraviolet radiation can damage some materials over time.

ultraviolet stabilizers

An additive that protects plastic resin from ultraviolet radiation. Ultraviolet stabilizers include carbon black and rutile titanium oxide.

viscousity

Resistance to flow. Viscosity increases as a plastic part cools.

voids

A tiny air pocket that has been trapped in the composite material during molding. Voids are undesirable because they compromise the integrity of the finished product.

warpage

The twisting and deformation of a plastic part. Warpage occurs when a part does not cool properly.

warped

Physically twisted or deformed. Warped parts are often a result of internal stress within a material caused by uneven cooling.

weld lines

A plastic defect caused by melt separating and then recombining while cooling. Weld lines cause cosmetic defects and can lower the tensile strength of a part.