Bong-Kee LeeSchool of Mechanical Engineering

Chonnam National University

Mold Design

5. Mold Structure

School of Mechanical EngineeringMold Design

Two-Plate Mold

Two-Plate Mold– the simplest and most reliable design– has the fewest number of moving parts and is more

straightforward to manufacture and run in production– is usually cheaper to manufacture

School of Mechanical EngineeringMold Design

Two-Plate Mold

Basic Two-Plate Construction

School of Mechanical EngineeringMold Design

Two-Plate Mold

Basic Two-Plate Mold General Arrangement

School of Mechanical EngineeringMold Design

Two-Plate Mold

Components– locating or register ring

• circular ring, screwed to the front clamping plate• enables the mold to be centered on the injection cylinder axis

by locating it into a machined hole in the stationary platen• good-quality low-carbon steel

School of Mechanical EngineeringMold Design

Two-Plate Mold

Components– top plate

• or, front plate, fixed half front plate, fixed half clamping plate• allows the mold to be secured to the fixed platen with cap

screws to hole it in position• low-carbon steel or alloy tool steel for very long-running jobs

School of Mechanical EngineeringMold Design

Two-Plate Mold

Components– split line

• or, parting line• plane or position at which the mold separates into two distinct

parts – stationary and moving platens• after the mold has split at this point, space is created for the

molded parts to be pushed or ejected from the mold

School of Mechanical EngineeringMold Design

Two-Plate Mold

Components– cavity insert

• or, mold insert, insert core• circular or rectangular piece of alloy tool steel that carried the

form of the molded part in it• more convenient machining and prevention of distortion from

the hardening

School of Mechanical EngineeringMold Design

Two-Plate Mold

Components– front cavity plate

• or, fixed half cavity plate• to hold the front half cavity inserts in position in the stationary

platen of the mold• low-carbon steel or alloy steel for very long-running jobs

– rear cavity plate• the same function and material as the front cavity plate• makes the rear half inserts captive between it and the cavity

support plate

School of Mechanical EngineeringMold Design

Two-Plate Mold

Components– cavity support plate

• to withstand the force generated by the injection pressure of the melt that is exerted on the actual cavity parts

• alloy tool steel to resist the cavity inserts being embedded (or hobbed) into it

• must be of sufficient depth (or thickness) to prevent excessive plate deflection taking place

School of Mechanical EngineeringMold Design

Two-Plate Mold

Components– ejection system

• carries a number of ejection pins that push or eject the parts from the cavities

• as well as ejector pins, it may use sleeve ejectors and blade ejectors or may also operate stripper plates, double ejection systems, collapsible cores or other more complex devices

School of Mechanical EngineeringMold Design

Two-Plate Mold

Components– ejection gap

• the amount that the ejector system can move towards the cavity support plate from its rest position

– support blocks• or, risers• connects the cavity support plate to the rear clamping plate or

back plate• good-quality low-carbon steel

School of Mechanical EngineeringMold Design

Two-Plate Mold

Components– guide pillar

• accurately align the front and rear platens of the mold• hardened alloy tool steel

School of Mechanical EngineeringMold Design

Two-Plate Mold

Components– return pins

• or, push backs• to return the ejection system to its initial or rest position when

the tool closes• to prevent any damage to the more fragile ejector pins through

contact with the front platen of the mold• hardened silver steel or hardened alloy steel

School of Mechanical EngineeringMold Design

Two-Plate Mold

Detailed Design

School of Mechanical EngineeringMold Design

Two-Plate Mold

Detailed Design– additional features

• clearances around the ejection pins, ejector return pins and ejector bar

• bushes on guide pillars and return pins– wears between the mold plates of soft mild or alloy steel and the

repeated sliding of hardened components

• screws to hole the tool together• support pillars• taper tapped holes on water cooling channels• stand-off buttons beneath the ejector system• chamfers on rectangular cavity insert• guide pillar and bush system completely aligns the mold

School of Mechanical EngineeringMold Design

Multi-Plate Mold

Three-Plate Mold– when an over feed gate is necessary, either for

multipoint feeding parts or for gating parts to achieve balanced flow

School of Mechanical EngineeringMold Design

Multi-Plate Mold

Three-Plate Mold– operation stages

• gate breaking or de-gating stage

School of Mechanical EngineeringMold Design

Multi-Plate Mold

Three-Plate Mold– operation stages

School of Mechanical EngineeringMold Design

Multi-Plate Mold

Three-Plate Mold– operation stages

School of Mechanical EngineeringMold Design

Multi-Plate Mold

Three-Plate Mold– disadvantages

• long opening stroke is necessary to accommodate all the different openings

• both the speed and accuracy of the mold open stop must be good as variations in either can results in the failure of the mold to operate or, worse, in a breakage

• the limiting factor on most molds is nearly always the length of opening stroke required

School of Mechanical EngineeringMold Design

Multi-Plate Mold

Three-Plate Mold– incorrect opening sequence

School of Mechanical EngineeringMold Design

Multi-Plate Mold

Three-Plate Mold– main requirements

• it must open in such a way that all possibilities of the molded parts sticking in the cavities are avoided

• the openings must be sufficient to ensure the runner, sprue, and the parts have sufficient room to fall freely from the mold

• the molding machine must have an accurate opening stroke, otherwise the pull rods and limit bolts may be broken or the parts and the runner system may not be stripped and ejected properly

School of Mechanical EngineeringMold Design

Multi-Plate Mold

Three-Plate Mold– comparison with hot runner systems

• suitable for medium-length production runs, where the relatively higher cost of the hot runner mold would not be economic

• often more reliable owing to simpler nature and does not require expensive heating and control systems

• changing material and/or color is easier since this type of mold clears its complete feed system every shot

• thermal sensitivity of certain material such as PVC or acetalsmay prohibit the use of hot runner systems

School of Mechanical EngineeringMold Design

Multi-Plate Mold

Three-Plate Mold for Drive Gear

School of Mechanical EngineeringMold Design

Multi-Plate Mold

Multi-Plate Undercut Molds– injection mold for valvehousings

School of Mechanical EngineeringMold Design

Multi-Plate Mold

Multi-Plate Undercut Molds

School of Mechanical EngineeringMold Design

Multi-Plate Mold

Stack Molds– highly efficient, cost-effective production method of

large projected areas• shallow boxes, cassette cases, video cases, and Petri dishes

– alignment of projected areas in stack molds

School of Mechanical EngineeringMold Design

Multi-Plate Mold

Stack Molds– simple design of stack molds