INJECTION MOULDING DESIGN CONSIDERATIONS

INJECTION MOULDING DESIGN CONSIDERATIONS 

In the design of injection mold, the following machine specifications are to be considered.

1. Locking or clamping force:

          This is the maximum force with which the two die halves are kept closed to resist the injection pressure. The clamping force required to keep the mold closed during injection must exceed the force given by the product of the opening pressure in the cavity and the total projected area of all impressions and runners. Thin sections need a high injection pressure to fill the impression completely and therefore require more clamping force.

2. Injection pressure: 

          This is the pressure under which the molten material is forced inside the cavity (up to 1800 kg/cm²). This pressure is set in the machine according to the plastic material to be molded, component thickness, etc.,

3. Shot weight: 

         The shot weight is the weight of the component including the feed system. Calculated shot weight should be less than the machine shot weight.

4. Distance between Tie bars:

          It is the minimum distance between the edges of the tie bars that guides the moving platens. This measurement limits the size of molds that can be placed between the tie-bars and into the molding machine. Tie bars are used in molding machine to hold the platens. It also guides the moving platen during closing and opening of the mold.

5. Minimum and Maximum Mold Height: 

          It is the minimum and maximum distance that can be adjusted between the stationary and moving platens. The mold shut height should always lie in between the maximum and minimum mold height.

6. Ejection force: 

          The force required to eject the component after cooling of the plastic material in the impression. It is about 3-5% of the locking force.

7. Maximum Ejection Stroke: 
          This is the maximum distance through which the component can be ejected during the open condition. The ejection stroke to be adjusted on the machine depends on the component depth.