Lecture 07: Injection Moulding Technology

Flashcards of key vocabulary terms and definitions from the lecture notes on Injection Moulding Technology.

Clamping unit

The part of the machine in which the mould is mounted. It provides both force and movement.

Daylight

The maximum distance between the stationary and moving platens.

Ejector

Ejects the moulded parts from the tool. The mechanism is activated through the clamping unit. The ejection force may be hydraulic, pneumatic or mechanical.

Fixed platen (stationary platen)

The inner face of the clamping unit that does not move during mould closing. It contains mould mounting holes.

(Full) hydraulic clamp

A clamping unit triggered by a hydraulic cylinder which is directly connected to the moving platen. The mould is opened and closed by application of direct hydraulic fluid pressure. This also provides the clamping force required to keep the mould closed during injection.

Injection cylinder

Part of the injection unit which includes the screw, nozzle, hopper, heaters.

Injection screw

Transports, mixes, plasticises and injects the material from the hopper to the machine nozzle.

Injection unit

The part of the machine which feeds, melts and injects the material into the mould.

Mould (tool)

Contains the cavity to inject into. Consists of two halves, a stationary and moving half which attach onto the platens. Halves are linked via the tie bars.

Moving platen

The inner face of the clamping unit that moves during mould closing. The moving half of the mould is bolted onto this platen. This platen also contains the ejection mechanism and mould mounting holes.

Plunger unit

Injects and plasticises material by heating it in a chamber between the mould and a plunger. The heating is done by conduction. The plunger forces material into the chamber which in turn forces the melt already there into the mould.

Tie bars (tie rods, tie beams)

Bars which link and align the stationary and moving platens together.

Toggle clamp

A clamping mechanism with a toggle directly connected to the moving platen.

Reciprocating screw

A screw which both plasticises, and injects material.

Component (part)

The final (end) moulded product.

Closing force

The force required to physically shut the tool.

Clamping force

The force required to hold the tool shut when the material is injected and is much higher than the closing force.

Flash

The swelling of the mould under the pressure during initial injection resulting in the melt polymer coming out of the mould cavity.

Three-Plate Mold

A mould with multiple plates that separates parts from the sprue and runner when the mold opens, allowing for automatic operation.

Clamping (Injection Moulding Cycle)

The clamping unit moves the moving half and closes the mould, maintaining the required force.

Injection (Injection Moulding Cycle)

The melted polymer is injected into the mould via injection nozzles.

Packing (Injection Moulding Cycle)

The mould cavity is filled completely with molten plastic and pressure is applied.

Cooling (Injection Moulding Cycle)

The mould is allowed to cool before the part is ejected.

Ejection (Injection Moulding Cycle)

The mould opens and the plastic part is ejected by the force of ejector pins.

Ejection temperature

The temperature at which the centre of the component is solidified.

Compensation for Shrinkage

The dimensions of the mold cavity must be larger than specified part dimensions to account for this.

Short shots

A short shot happens when the mould is not completely filled, leading to incomplete parts.

Sink marks

Sink marks occur when the surface of the moulded part sinks or dimples due to uneven cooling or inadequate packing.

Burning

Burning or discoloration of the plastic material can occur due to excessive melt temperature or residence time in the barrel.

Flash

Excess material that extends beyond the parting line of the mould.

Warping

Results in the deformation or twisting of the moulded part, often caused by non-uniform cooling or insufficient cooling time, leading to differential shrinkage.

Gas assisted injection moulding

A variation of traditional injection molding that involves using compressed gas to push molten plastic into remaining areas to create voids or thick-walled structures.

Conformal Cooling

Integration of cooling channels with complex, conformal shapes within a mould, allowing for more efficient and uniform cooling.

Micro injection moulding

A specialized form of injection moulding that is specifically designed to produce small, precise, and micro-sized plastic parts.