Basic Mold Design

    Before an Injection Mold Design can be started the following criteria must be known, to enable a proper design.

Part
    Size 
    Function
    Acceptable Witness Marks for Parting Line, Method of Ejection, and Gate    
    Material Type, and Processing Characteristics, Shrink, Draft Requirements
    Production Required, Time Frame and Life of Mold
    Tolerance Considerations 
    Runner 
    Finish Specification, Data Inserts

Machine 
    Type
    Knock out Bar,  Size and spacing
    Tonnage
    Platen size 
    Shot size
    Locating Ring hole size
    Nozzle Spherical Radius, and 'O' Dimension
    Coolant Connector Type and Size

Processing  Capacity Study 
    Cycle time
    Number of Cavities Required Per Mold
    Possible Types of Moldbases
    Number of Molds to be Ordered, 
    Spare Cavity Steels Required

General
    What is the Timing of the Design/Mold Delivery?

If the above is known or specified, a mold design can be started.

A GENERAL APPROACH MAY FOLLOW THE FOLLOWING STEPS:
(INJECTION MOLD DESIGN REQUIRES SYNTHESIS OF MANY REQUIREMENTS AT THE SAME TIME )

Start at the part and work your way out.
Determine the best gate location. 
    CAE (Flow Analysis) is a superior tool to help determine a proper gate location.

Determine the appropriate Possible Parting Lines.
    The location of an acceptable parting line will provide for proper ejection of the part from                 the mold.
    A  correct parting line will ensure that the part 'Sticks' to the ejection (core) side of the mold.

Determine a Runner Layout that suits the number of cavities needed for the mold and incorporate Cold Slug Wells into the layout.

The next three items need to be 'Juggled" at the same time. Ejection, Coolant lines, Cavity steel sizes.

Determine Cavity steel sizes (you should have and idea of cooling layout too, at this point).  Will coolant holes be needed in the cavity steels? 

Determine the Ejection method, and location of the ejector contact area.

Determine Cooling Line location per coolant line placement rules.

Select a possible Moldbase (may change later) that suits the design requirements (Ejection travel, coolant connectors counterbored?, general size.  Make sure that the Knock-out bars will actuate the ejection system.  

Determine the number and size of Support Pillars needed  for the mold.  Extend the Ejector Bar if Necessary

Select a Sprue Bushing, and Locating Ring based of the Machine specified for producing parts.