Injection Moulding Machines have become highly sophisticated, complex, computerized machines with many features that need to be considered when deciding which machine will be able to make a particular product.
In the design of injection mould, the following machine specifications are to be considered.
1. Injection pressure
This is the pressure in the barrel at the point of injection, expressed in kg/cm2 or kbar. A higher L/D ratio produces greater Injection Pressure. The greater the Injection Pressure the better the quality of product produced.
2. 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.
The shot weight of a machine does not tell us the maximum volume of part that that machine can produce, because the pressures for moulding are higher than for extruding. Typically, the maximum volume of a low quality part will be 85% of the Shot Weight, or around 75% for a high quality part.
Parts need to weigh between 35% and 85% of the Shot Weight of a machine, any lower and the machine may be damaged during production, any higher and the mould cavity or cavities will not be filled.
3. Clamp force
The melt is injected into the mould under very great pressure, which the mould halves, and any other components or cores, must be able to resist in order to maintain their shape and to avoid any seepage. The larger a component is, the greater the pressure and so, the greater the clamp force.
The clamping force required to keep the mould 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.
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 moulds that can be placed between the tie-bars and into the moulding machine. Tie bars are used in moulding machine to hold the platens. It also guides the moving platen during closing and opening of the mould.
5. Minimum and Maximum Mould Height
It is the minimum and maximum distance that can be adjusted between the stationary and moving platens. The mould shut height should always lie in between the maximum and minimum mould height.
6. Mould opening stroke
This is the distance that the moving mould half moves from mould closed to mould open. Because the injection moulded part has to clear the mould and have room to be removed from the machine, the Opening Stroke must be greater than:
7. 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.
8. 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.
0 comments:
Post a Comment