While molds are precision machines for molding plastic, it is necessary to acquire appropriate strength in order to maintain its functions. In addition, since a mold becomes a heavy load when carrying out the operations of installing it or removing it, sufficient strength has to be acquired so that accidents causing injury to humans is not caused due to sudden problems such as the mold getting deformed or damaged due to its own weight while it is being carried.

In order to do this, it is not sufficient to ensure the strength based merely on experience or intuition, but it is important to carry out mold design using strength calculations based on the mechanics of materials.

In the design of plastic injection mold, it is necessary to utilize the data of the following experiments based on the mechanics of materials.

■ Static strength tests

• Tension test
• Bending test
• Shear test
• Compression test
• Buckling test
• Torsion test

■ Dynamic strength tests

• Impact test
• Charpy impact test
• Izod impact test
• Fatigue test

■ Industrial tests

• Creep test
• Wear test, etc.

Empirical formulae that have been technically established should be used for the calculations related to the strength of materials, and it is necessary to use a safety margin factor regarding the results of calculations.

Further, although it goes without saying, the results of calculations should strictly follow the "ethics of engineers", and it is necessary to take decisions based on good intents.

Since the prevention of mold damage accidents and acquisition of safety depend upon the judgment by the designing engineer, one should always be strict with oneself so that too much weight is not given to designs for cost reduction thereby blunting one's own most important decisions. This is something a mold design engineer should always remember.