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Thread: Velocity Study

  1. #1
    Join Date
    Mar 2019
    Location
    Nebraska
    Posts
    23

    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?

  2. #2
    Join Date
    Mar 2019
    Location
    Nebraska
    Posts
    23

    Re: Velocity Study

    Here is an example of a rheology study and the parts made at each speed.

    Click image for larger version. 

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  3. #3
    Join Date
    Sep 2018
    Location
    Portland, OR
    Posts
    20

    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.

  4. #4
    Join Date
    Mar 2019
    Location
    Nebraska
    Posts
    23

    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%?
    Last edited by The Rookie; 13th October 2019 at 04:27 PM. Reason: Wording

  5. #5
    Join Date
    Sep 2018
    Location
    Portland, OR
    Posts
    20

    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.

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