Welcome!

This informative blog allows plastics professionals to discuss plastics training and technology. Brought to you by Routsis Training: the plastic industry's premiere training provider.

VISIT OUR STORE
VISIT OUR WEBSITE

The Symptoms Of Machine Dependant Documentation

In a recent discussion with a brand new customer, when discussing common defects he posed this query…
Steve K.
Although we don’t really have one or two defects we get all the time, but we get a lot of different defects all the time. We run a lot of different molds, machines, and materials… and we change a lot of molds. Do you think that might have anything to do with it?
My Response
After a few pointed questions, Steve explained that his employees only documented the machine settings during start-up. Although this is very common in the injeciton molding industry, the process settings of one machine provide virtually no guidance when the mold is hung in a different machine. Even using the same barrel temperatures can result in melt tempertaure differences in excess of 50ºF! 
We went on to discuss the importance of machine independent documentation that includes part specific data such as part weight, fill time, coolant and melt tempertaures as well as the actual pressures applied to the polymer. We also strategized methods to get Steve’s employees to adjust their behaviors over the long term.
Additional Thoughts
Even though Steve had some good employee working for him, every time they put a mold into a machine, they put the data into the machine. When the part does not magically come out right… the have to process without a set of machine independant targets to aim for.
If the mold ran great in machine #4 last week you need to know specific details such as: Fill Time = 3.2 seconds, Melt Temperature = 427ºF, Final Part Weight = 23.5 grams. This information is invaluable when you put the mold in machine #3 next week.
If you or anyone you work with would like to learn more about process documentation… we have some FREE multimedia webinars on scientific molding which can be viewed at http://www.traininteractive.com/free/webinar/player/
-Andy

Scientific Molding For High Speed Applications

In a recent webinar regarding Scientific Molding, I received this question…
Ralph
Is scientific molding applicable to high speed packaging machine where injection fill time and hold time are around 0.5s with an overall cycle time of 3sec?
My Response
Yes, you should always approach processing logically and document the process by its outputs… especially in your case, where any change in your process is virtually imperceptible to the human eye. Such changes can only be identified through the accurate measurement and proper documentation.
Additional Thoughts
Although every process seems unique, all injection molding processes operate under similar principles. There is a 1st stage fill time, 2nd stage pack time, final part weight, melt temperature, etc. All these factors are imperative in ensuring a process can be consistently repeated. For free multimedia presentations on scientific molding, please visit: http://www.traininteractive.com/free/webinar/player/
-Andy

1st to 2nd Stage Response Time

I was asked this great question the other day…

eMailer
I heard something about machine response (reaction time during switching from fill to hold).

How does this response influence my process?
My Response
There are many aspects which must be considered when reviewing the transfer from 1st to 2nd stage. Most of these can be seen on your machine’s pressure curve.
Under-Damping:
– As the injection pressure graph transitions from first to second stage, the curve should not dip far below the specified packing pressure. If this occurs, the molding machine is ‘under damped’ and is not capable of transferring from velocity control to pressure control without losing significant pressure. Under damping often results in sinks and short shots due to insufficient packing pressure. This only occurs when molding with hydraulic machines, and indicates a faulty hydraulic valve.
Over Damping:
– If the pressure curve transfers between stages gradually, the molding machine is ‘over damped’. This indicates that additional material is being forced into the mold at a pressure higher than the set point. An ‘over damped’ molding machine will often result in flash or overpacking due to the fact that the hydraulic valve can not transition into pressure control adequately. The controller may need to reprogrammed or a hydraulic valve may need replacement to resolve ‘over damping’.
Overshoot:
– Similar to over-damping, many machines have heavy injection units which are difficult to slow down when the machine transfers from 1st to 2nd stage. This can often cause inconsistent fill. Although most electric molding machines have accurate servo motor controls which prevent this, many hydraulic molding machines are very susceptible to this situation. On these machines, it is a great idea to use one or two transitional speeds to prevent this condition.
Fluttering:
– Fluttering or erratic changes within the injection pressure curve during transfer indicate faulty hydraulic valves or electric servo motors. These fluctuations, as with the other conditions above, affect shot-to-shot consistency and should be improved to the best of the machine’s capabilities.
Additional Thoughts
You should always evaluate the capabilities of your molding machines with rigorous testing. This is another reason why machine-independent process documentation is so important… process outputs tend to ignore the idiosyncratic behavior of any individual machine.
-Andy

Reading Materials are Not Training Materials

I was recently asked about the effectiveness of reading materials…

Chris
We receive several monthly periodicals at our plant, and my manager asked me why these cannot be used for training… I know this won’t work, but I don’t know how to explain this to him.

Can you help me understand why this is so?

My Response
Just because something provides good information does not always mean it is an effective training method. Reading does not provide particularly high retention rates: meaning that you’re likely to forget most of what you’ve read!
Studies have shown that most people can only remember about 20% of what they read. This retention drops even lower when the reader is unfamiliar with the topic, making it particularly ineffective when training new hires or inexperienced personnel.
Certain factors can increase retention of what’s being read, such as an emotional connection with the information. As much as we’d all like employees to be passionate about plastics, it is unrealistic to expect them to react emotionally to what is usually pretty dry reading material.
Additional Thoughts
I always recommend plants have such periodicals to their employees since these periodicals can be great tools when trying to introduce someone to a new featured technology.
-Andy

Process Inputs vs. Process Outputs

In a recent webinar on the topic of Scientific Molding, I received this question regarding process outputs…
Vishu
In a scientific injection molding process, can we change process inputs while maintaining the same outputs?
My Response
There are many cases where a change in the inputs may have little or no affect on the actual process… For example, if the process was pressure limited, a change in the injection speed will have no affect on the process. This is why the process inputs are significantly less important than the resulting process outputs.
Additional Thoughts
To illustrate this with another example… if your process has too much screw speed and back pressure, a ten degree drop in barrel temperature may not have the desired effect on the melt temperature. If you concentrated on the melt tempertaure instead, you would know how each change directly affects the melt temperature.  
Both of these scenerios relate specifically to why documentation of process outputs is critical. For free multimedia presentations on scientific molding, please visit: http://www.traininteractive.com/free/webinar/player/
-Andy

  • Recent Posts

  • Recent Comments

  • Archives

  • Categories

    • © 2016 All Rights Reserved | Powered by Wordpress | Made with ❤ by Themely