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Velocity Study
Hi all,
I just finished reading the Optimization of the Injection Phase - Rheology Study and found myself confused
The procedure is to establish a 95-98% filled shot at close to the machines maximum. Record the data and reduce the injection velocity by 10% until producing parts at the slowest injection velocity possible.
I completed my study and found that the viscosity stays fairly constant at about 50% of the machines maximum velocity.
Now here is where I get confused...The procedure doesn't exactly spell out what I am to do next...unless I overlooked it in the text.
I set the machine to around 60% of the machines maximum to ensure that the process will stay consistent with slight viscosity variations. At 60% of the injection velocity, the parts appear to be 70% filled.
I was inclined to adjust the transfer position such that the parts were filled 95-98% at this speed. But then questioned myself because for process development activities, I was asked to get a High and Low value for injection speeds to see the effect injection speed has on part dimensions. If I were to choose 60-70% injection velocity for the test, would I have to adjust the transfer position for both during the study?
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1 Attachment(s)
Re: Velocity Study
Here is an example of a rheology study and the parts made at each speed.
Attachment 407
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Re: Velocity Study
If you want to make full and packed parts to determine the effect of injection speed on part dimensions I would adjust the transfer to 95-98% filled parts for each injection speed tested.
For the general rheology study the example you posted is how I've always done it.
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Re: Velocity Study
Thanks for the input.
I just looked at several process sheets for our current machines running and we have fill time as a critical to quality validated parameter.
Plenty of times I have talked to technicians about troubleshooting issues and they throw around changing the Injection fill time...I ask if that is all they changed, and they said yes.
If they had a 95-98% filled part at say 0.50 seconds fill time and now are filling slower at 0.75 seconds, shouldn’t they have changed the transfer position to achieve 95-98%?
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Re: Velocity Study
I'd agree with your statement. For parts with tight tolerances I will get my fill only shot back to the same weight as the qualified process if I make a change to injection speed.