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A Typical Injection Mold Design Guide



This checklist can be used as a general reference guide for injection mold design

engineers. It is divided into 3 parts of a mold design process.

Part 1 - Requirements to start your mold design:

Check the injection machine where the mold is to be mounted. This will help you

decide the size and structure of the mold. for ease of installation and other factors.

Important notes:

Locating ring size (or other positioning method)

Nozzle size

Method of clamping (Auto or manual)

Temperature control system

Determine the number of cavities and volume requirements. This will help you

decide the material that you are going to use and other mold components that you will

choose for cost effective design.

Determine the gate location and size.

Determine the location where ejector pin marks are prohibited.

Part 2 - Mold base layout:

Place cavities close to the center of the mold to minimize base size and runner

length.

Ensure that the molded part remains on the movable half (ejector half) upon

opening of PL to facilitate proper ejection.

Waterlines should be placed as evenly as possible to the contours of the cavity.

Use support pillars underneath the cavity pockets.

Use ejector guides for molds with small ejector pins and rectangular ejector pins.

Provide eye-bolt hole for ease of mounting and dismounting.

Install mold opening prevention locks on the operator side.

Establish pry bar groove on the corners of the mold parting line to facilitate ease of

mold opening during assembly and maintenance.

By this time you may ask for the mold layout approval from the customer.

Part 3 - Cavity/core details:

Check material shrinkage. Locate portions (corners) for possible significant

deflection and deformation.

Maintain uniform wall thickness.

Draft angle should be within dimension tolerance.

Divide core blocks to simplify machining and provide gas vent path.

Gate, small cores, and cores with shut-off fittings are better designed as insertable

components for easy modification and repair.

Watch out for possible deformation of core pins.

Position the ejector pins on the ribs and other high strength locations. Ensure

ejector balance.

Detailing/part drawing: Include all parameters needed for processing -material,

quantity, surface finish/texture, dimensions, tolerances and many more. Do not

assume the machinist understands everything.


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Any design change and amendments to the mold must be re-approved by the

customer or mold owner.



Standard horizontal clamp presses deliver molten resin to the mold through a hole in

the center of the stationary press platen. A material-delivery system — usually

consisting of a sprue, runners, and gates — then leads the resin through the mold and

into the cavity. These components of the material delivery system are discussed in this

section.



Sprues



The sprue, oriented parallel to the press injection unit, delivers resin to the desired

depth into the mold, usually the parting line. Though they can be cut directly into the

mold, sprue bushings are usually purchased as off-the-shelf items and inserted into the

mold (see figure 7-18). The head end of the sprue bushing comes premachined with a

spherical recess — typically 0.5- or 0.75-inch radius — to receive and seal off against

the rounded tip of the press injection nozzle. The sprue bushing flow-channel

diameter typically tapers larger toward the parting line at a rate of 0.5 inch per foot.

This eases removal of the molded sprue. The sprue orifice size, the diameter at the

small end, comes standard in odd 1/32s from 5/32 to 11/32 inch. Sprue design can

affect molding efficiency and ease of processing. In many molds, the greatest

restriction to material flow occurs at the press nozzle tip and sprue orifice. These areas

see the highest volumetric flow rate of the entire system. An excessively small

sprue orifice can g..