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Hyrum
5th December 2011, 11:45 PM
I am building an injection molding control right now to control an old Arburg injection molder I have. It is coming along very nicely although I am new to injection molding. I have owned 3 injection molders but they were all small and had plunger style injection units. (one was a Morgan)

I have a few questions on what parameters need to be considered and a little about the process. If you can give any help please comment.

Below is what I gather from what the cycle and the questions I have:

1 Clamp- From what I see there is a low pressure for the first part of the stroke and then high pressure once the mold is nearly closed. The only parameter I plan on having in the control is an alarm if the clamp doesn't close after a specified time.

2 Inject- Plastic flows into the mold and pressure is held for a specified time.

3 Extrude- All I know is the screw rotates for a specified amount of time. Is the hold pressure maintained? Does the injection unit retract after this? Please give detail.

4 Open- The only parameter I plan on having in the control is an alarm if the clamp doesn't open after a specified time.

5 Eject- Is there any reason to have the ejector knock more than once? I seem to remember a machine on youtube knock twice.


In case you are interested in my machine:
Its an Arburg Allrounder 300 it has a hydraulic system that powers all the cylinders and the screw. Position is monitored by 9 limit switches

Toggle open
Toggle High pressure
Toggle closed
Knock out in
Knock out out
4 switches on the injection unit

I'm documenting the process of getting this machine going on www.allrounder300.blogspot.com (http://www.allrounder300.blogspot.com)

Thanks!

Suhas
6th December 2011, 06:57 PM
Hello Hyrum,
There are a lot of factors and alarms to consider - but they all depend on what is the end product you will mold and also what is the plastic you will mold. There are several times, speeds, pressure and temperatures used in the molding process that should be monitored and should have alarms.
Sometimes you do need two ejection strokes and with some problem molds more than two - I have seen up to even five - ridiculous!
I am not sure if I answered any of your questions, if not let me know. Your blogspot looks good! Is this a hobby? profession? Are you retired? a young Steve Jobs? :)
Regards,
Suhas

brentb
7th December 2011, 01:02 AM
Many times multiple ejector strokes are needed due to mold or part design. The design is not necessarily faulty, it may just "have" to be that way.
Some parts don't eject until the reverse stroke and need 2 pulses.
People (especially mold makers) hate multiple strokes as it adds double (or more) the wear on the moving mold parts without doubling the output. It is better than crunching the mold on a part though!
Molders in the past used mold sweeps and air blasts to help eliminate multiple strokes, and now, robots.

I remember the original Paulson training videos (Beta Max Format). They opened with a molding machine ejecting parts with about 5 quick pulses. We laughed, as we would get in big trouble if we did something like that, and it was on a training film on the "correct" way to mold.
This was back when Don Paulson and Rod Groleau were partners. Paulson later branched out into training only, and Rod became RJG. They were originally CPI or Control Process Incorporated


Keep on Molding!

brent

pjhall
7th December 2011, 08:12 PM
Hyrum,

What year is that beast? Looks like a nice project. I've molded on Arburgs for many years. They are good presses, although some of the older controls took a bit getting used to. The switches on the injection unit were fun to deal with. I can still here that alarm when B26 is not made....

GTRules
12th December 2011, 06:35 PM
What are using to control the process? PLC?