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The below article can be used for machine setters and machine operators of injection moulding machines.
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View our other articles form our setter and operators guide for injection moulders. Taken from our moulders catalogue (Toolbox Edition)
How to calculate the Plasticising Rate in injection moulding.
Given the following data the plasticising rate can be calculated as:
- Material ABS
- Screw recovery time 7.2 sec
- Total shot weight 13.2 g
- No of impressions Single
Plasticising rate = Total shot weight of mould tool (grammes) / Screw recovery time (seconds)
= 132/7.2 = 18.33 g/sec
= 18.33 grammes per second in ABS
Given the following data calculate the plasticising rate
- Material POM
- Screw recovery time 5.02 sec
- Total shot weight 6.42 g
- No of impressions 16
- Weight of sprue & runner 8.68 g
Plasticising rate = Total shot weight in mould tool (grammes) / Screw recovery time (seconds)
Number of impressions 16 x Weight of one impression 6.42g = Total weight of 16 impressions = 102.72g
Total shot weight including feed system 102.72 + 8.68 = 111.4g
Plasticising rate 111.4/5.02 = 22.19 g/sec
Is the moulding machine capable of maintaining a 14 second cycle?
Let us assume the following
- The cycle time for component manufacture is 14 seconds, of which cooling time is 8 seconds.
- Total shot weight in mould tool in Nylon 66 is 128 grammes.
- Plasticising capacity of moulding machine when processing Nylon 66 is 15.60 g/sec.
- The mould tool will not open until the screw has fully returned to its stop position.
Due to sequential operation of the moulding machine, ie screw recovery only takes place during the cooling time:
Then: the total shot in mould tool is 128 g, the cooling time is 8 seconds, therefore the plasticising rate = 128/8 = 16 g/sec
As the machine can only plasticise Nylon 66 at a rate of 15.2 g/sec then the screw recovery time will be 182/15.2 = 8.42 seconds
This means that the cooling time will have to be extended to 8.42 seconds to accommodate the longer screw recovery time, hence a cycle time of 14 seconds with a cooling time of 8 seconds will be impossible.
NB: If the moulding machine was capable of parallel functions instead of sequential, then the cycle time of 14 seconds would be possible as the additional screw recovery time would take place during the opening of the mould tool and
ejection of parts.
Parallel functions allow the machine to continue to rotate the screw and return to its stop position after the cooling time has elapsed.