A critical evaluation of a large number of injection molds for parts fulfilling a variety of applications results in the identification of certain classes and groups that differ from each other in their construction in some basic manner. Of course，for the sake of clarity such a classification cannot contain all combinations that are possible among the individual classes and groups.
It is also quite conceivable that new knowledge and experience will make an expansion necessary.Such a classification does，however, serve its purpose if it transmits the collected experience in mold design in detail and in the clearest manner possible. When faced with a new problem，the mold designer can then see how in similar cases such a mold was designed or has to be designed Moreover，there should also be an attempt to evaluate the collected experience and create something even better instead of simply following previous designs.
A basic requirement of any mold that is intended for use on an automatic injection molding machine is that the molded parts be automatically ejected from the mold without the necessity for secondary operations (degating，machining to specified dimensions，etc.).
From a practical standpoint，a classification of injection molds should be based on the main design features and manner of operation. These include:
- The type of gating and means of degating
- The type of ejection used for the molded parts
- The presence or absence of external or internal undercuts on the part to be molded
- The manner in which the part is released from the mold.
Methodical Mold Design
In general, the requirements and design possibilities are considered in relation to each other in a preliminary mold design. This initial design is intended to be corrected without a great deal of time and effort and provides a useful basis for discussion and further work in planning the production (e.g.，specification of the number of cavities and selection of the injection molding machine). It is not necessary that this initial design be complete to the last detail. In many cases，dimensioned hand sketches will already be satisfactory for practical purposes.
It is only after the part design has been completed and all requirements that affect the design of the mold have been clarified that the final mold design can be prepared. This design then serves as working instructions for the mold maker.