Two halves make
the part.
From the backplate to the last ejector pin. Take an injection mould apart, discover what each component does, and see how it all works together.
Start exploringInside the mould.
The mould, component by component
16 narrated chapters · about 9 minutes · pause and inspect any part
Explore the component guide.
The 3D view could not start on this device. All component explanations, diagrams and sources remain available below.
Scrub the cycle to inspect a precise position.
The same two-cavity mould is mounted between the platens.
A mould is a system of systems.
Follow the forces, the material and the heat. The individual parts begin to make sense together.
Built to hold together.
Clamping plates, support plates and spacers carry different loads. Follow the path back to the machine platen.
From pellet to part.
See how the sprue, runner and gate deliver melt to a cavity, and why their geometry matters.
Cooling is part of the tool.
Connect cooling circuits to cycle time, temperature distribution and the shape of the final part.
A role for every detail.
Functions, interfaces and clues to investigate. Open an entry to go deeper into the source material.
Moving-side backplate
The mounting face between the mould and moving machine platen. Carries the ejector housing and transfers its reaction into the platen. Here, backplate means rear clamping plate; some workshops use the word for a backing plate, so check the drawing.
Interfaces
Moving platen · Spacer rails and fastening screws · Machine ejector access
What to investigate
- Damaged mounting faces or loose fastening can disturb support and alignment.
Fixed-side clamping plate
Mounts the injection-side half to the stationary platen. Provides the front mounting interface and usually carries the locating-ring recess. Its mounting pattern must suit the machine and the complete mould stack.
Interfaces
Stationary platen · Locating ring · Cavity-side stack
What to investigate
- Burrs or trapped debris can prevent full seating.
Locating ring
Centres the mould inlet on the machine nozzle axis. Its outside diameter registers in the fixed platen. The ring locates the assembly during installation; mould clamps or the mounting system retain the mould.
Interfaces
Fixed-platen register · Front clamping plate · Sprue bushing
What to investigate
- An incorrect register or damaged ring can leave the nozzle off-centre.
Sprue bushing
Connects the machine nozzle to the mould's melt passage. A replaceable bushing provides the nozzle seat and directs melt into the runner. Seat geometry, alignment and fit require coordinated design; the cold sprue must release when the mould opens.
Interfaces
Machine nozzle · Locating ring · Cold runner or downstream melt path
What to investigate
- Leakage at the seat, sticking sprue or flash around the bushing merits inspection.
Cavity-side plate
Houses or directly forms the cavity-side tooling. Supports the cavity geometry and integrates alignment, fastening and thermal passages. The cavity may be machined into the plate or made as a separate insert.
Interfaces
Cavity insert · Guide bushes · Fixed-side stack
What to investigate
- Damage at the parting surface can create a repeatable flash location.
Core-side plate
Carries the core-side geometry and ejector passages. Supports core tooling while allowing ejectors to pass through. In the illustrated conventional arrangement it travels with the moving half.
Interfaces
Core insert · Support plate · Ejector pins
What to investigate
- Misaligned ejector bores or uneven support may produce wear and marking.
Core and cavity inserts
The shaped steel surfaces that define the plastic part. For a cup-like part, the core forms the inside and the cavity forms the outside. Part retention is designed so the moulding stays on the side equipped to eject it.
Interfaces
Parting line · Gate · Ejection and cooling
What to investigate
- Sticking on the wrong half suggests retention, draft or surface-condition issues.
Cold runner
Distributes melt from the sprue towards the gates. A cold runner fills and freezes each cycle, then leaves with the moulding or is separately removed. Its layout influences cavity balance and adds material to the shot.
Interfaces
Sprue · Gates · Runner ejection
What to investigate
- Unequal filling can involve runner balance, gates or thermal conditions.
Gate
The controlled entry from the feed system into a cavity. Gate type and location affect filling, packing and the mark left after separation. A gate is a feature in the melt path, not necessarily a separate replaceable part.
Interfaces
Runner or hot nozzle · Cavity · Gate vestige on part
What to investigate
- Jetting, blush, premature freeze-off or a large vestige are clues, not unique diagnoses.
Guide pillars
Bring the two mould halves into alignment as they close. Pillars enter corresponding bushes before vulnerable forming features meet. Their role differs from machine tie bars and from precision interlocks near the cavity.
Interfaces
Guide bushes · Core and cavity plates
What to investigate
- Scoring or galling can indicate contamination, poor alignment or inadequate lubrication.
Guide bushes
Provide the mating bearing surfaces for guide pillars. Replaceable bushes guide closure and limit wear in the mould plates. Thermal conditions, mould weight and required accuracy influence the alignment arrangement.
Interfaces
Guide pillars · Plate bores
What to investigate
- Wear, looseness or binding can degrade repeatable closure.
Backing / support plate
Supports forming steel behind the core or cavity plate. Spreads reaction load into rails and support pillars, reducing bending across the ejector space. It is an internal structural plate, distinct from the rear mounting backplate.
Interfaces
Core-side plate · Support pillars · Spacer rails
What to investigate
- Local flash can be a symptom of elastic deflection as well as a damaged parting line.
Spacer rails / risers
Create room for the ejector assembly to travel. Rails separate the rear mounting plate from the supported mould stack. They also transmit structural load around the moving ejector plates.
Interfaces
Backplate · Support plate · Ejector package
What to investigate
- Insufficient internal clearance can obstruct the intended ejector stroke.
Support pillars
Bridge open spaces in the mould support structure. Pillars add support beneath loaded regions while allowing the ejector plates to move around them. Placement depends on cavity load and clearance for the ejection system.
Interfaces
Backplate · Support plate · Ejector-plate clearance holes
What to investigate
- Inadequate support can allow plate deflection and flash.
Ejector retaining plate
Locates and retains ejector heads. Works with the ejector base plate as a moving package. Pin-head pockets and retaining details hold ejectors at the correct relative position.
Interfaces
Ejector pin heads · Ejector base plate · Ejector guidance
What to investigate
- Loose retention can produce irregular pin projection or return.
Ejector base plate
Receives the machine's ejector motion. Pushes the retained ejectors forward as a group and returns according to the tool's coupling and return design. Staged systems deliberately create more than one movement.
Interfaces
Machine ejector coupling · Retaining plate · Guide system
What to investigate
- Uneven travel or plate tilting points to guidance, loading or obstruction.
Ejector pins
Push the solidified part away from the mould steel. Pin faces contact selected part surfaces after the mould opens. Their position and supported area affect release and visible witness marks.
Interfaces
Retaining plate · Core-side bores · Plastic part
What to investigate
- Deep pin marks, whitening or distortion can indicate difficult release or premature ejection.
Ejector sleeve
An annular ejector surrounding a core pin. The sleeve advances around a central pin to apply force around features such as bosses. Pin and sleeve dimensions and materials must be specified as a compatible sliding pair.
Interfaces
Central core pin · Ejector package · Boss or circular feature
What to investigate
- Binding, scoring or flash at the sliding interface merits a fit and wear check.
Return pins and early return
Bring ejectors back before the mould closes fully. A conventional return pin acts through closure contact; some tools require a positive early-return mechanism so ejectors clear slides or other features earlier in the sequence.
Interfaces
Ejector package · Opposing mould half · Slide clearance
What to investigate
- Failure to retract can damage pins or collide with another moving feature.
Ejector guide pins and bushes
Keep the moving ejector package square. Guide components support the ejector assembly throughout its travel and reduce plate cocking. They are separate from the leaders aligning the mould halves.
Interfaces
Retainer and ejector plates · Ejector housing
What to investigate
- Uneven pin wear and skewed motion suggest a guidance problem.
Cooling channels
Carry temperature-controlled fluid near the forming surfaces. Heat passes from plastic into mould steel and then into the coolant. Channel layout, flow balance and deposits all affect thermal uniformity and cycle stability.
Interfaces
Temperature-control unit · Hoses and manifolds · Core and cavity steel
What to investigate
- A hot region, changing cycle or warpage may warrant flow and temperature checks.
Vents
Let displaced air and gases escape during filling. Shallow passages and other venting features provide an exit near trapped-gas locations. Their dimensions depend on the resin and tool design; excessive opening can admit melt.
Interfaces
Parting line · End-of-fill regions · Atmosphere or vacuum circuit
What to investigate
- A burn or short fill at a dead end may indicate inadequate or blocked venting.
Slide / side action
Retracts a forming feature sideways before ejection. In an angle-pin example, mould opening drives a carriage away from the part. The slide must clear the undercut before the ejectors advance.
Interfaces
Angle pin · Carriage guides · Undercut and ejector sequence
What to investigate
- Drag marks or damaged undercuts suggest incomplete clearance or timing problems.
Lifter
Combines ejection with sideways undercut release. An angled lifter moves through a guided arrangement as the ejector package advances. Its base needs freedom to accommodate the lateral movement.
Interfaces
Ejector package · Guide arrangement · Internal undercut
What to investigate
- Binding or witness marks can indicate poor guidance or insufficient release travel.
Hot-runner manifold and nozzles
Keep distribution passages hot between cycles. A heated manifold feeds mould-side nozzles. Thermal gates and actively driven valve gates are different arrangements; a valve-gate system adds pins and actuators.
Interfaces
Machine inlet · Temperature controller · Cavity gates
What to investigate
- Imbalanced filling, stringing or leakage require thermal, mechanical and process investigation.
What happens when you change a variable?
Try the engineering labs. Estimate clamping force, explore cooling time, and connect cycle time to output—with the assumptions in view.