SPC and Injection Moulding

[bobdoering]

I think you hit the nail on the head when you contrast the usage of SPC in plastic injection molding versus metal machining. Although I may not necessarily buy the comment on machine complexity - having worked in both industries - the material variation and process parameter variety is more significant in injection molding. Other factors I have run into is seasonality of cooling water temperature (when a cooler is not used), cooling (or heating) variation across the tool, frequency of injection (tools have a long time to cool during breaks if the machine is shut down - lose steady state), flow variation from cavity to cavity based on runner system design, humidity (serious issues for some polymers), etc. Weight can be a lousy measure because of the variation of density from the injection pressure drop across the runners and cavities. The point is plastic injection molding is "organic" in many different ways - and it as readily SPC'ed as the height of mushrooms in a forest. Best of luck!!

 

[Przemek]

Dear All, I read this subject and I have a fiew question. Let me introduce my self. My name Przemek Im from Poland; 2 months ago I was promoted on Quality Manager position in medium moulding company. We have 25 moulding machines and 10 semi-automatics.
What is more important in quality improvement plan in mould company?
How to do this - what is the best way?

Please help me start with this all we have really poor quality -over 130 customer complains per year, problem with people fluctuation. How to start the best? Thanks for all help

 

[BradM]

Dear All, I read this subject and I have a fiew question. Let me introduce my self. My name Przemek Im from Poland; 2 months ago I was promoted on Quality Manager position in medium moulding company. We have 25 moulding machines and 10 semi-automatics.
What is more important in quality improvement plan in mould company?
How to do this - what is the best way?

Please help me start with this all we have really poor quality -over 130 customer complains per year, problem with people fluctuation. How to start the best? Thanks for all help

Hello!

We're all about helping!

I do have some general questions. Do you currently utilize SPC? Do you have a quality management system in-place? How are you tracking customer complaints? Are you tracking other measures such as scrap rate? Do you have dedicated inspectors, or who is doing the inspections?

What percent of total product shipped does your complaints represent?

If you were to pick two areas in your process and focus your efforts for improving your quality, what would they be?

Getting a little better feel of your situation will allow us to offer up a bit more specific suggestions. Too, your question may be ideally located here, or it may do better in another forum.

Anyway, when you get a chance, repost with a bit more information, and we'll do our best to assist!

 

[Przemek]

Hello. Many thanks for your quick answer.
I try to answer on all your questions.
In 2007 we have 47 complaints in 2006-107. I did a Pareto and more then 60 percentage its problems with flashing, short shots, or burrs, 25-30% dimensional problems, rest its packing and logistics,we use SPC for 30-40 type of details (producing over700) only when customers wants. Im also a Management Representative for ISO system, but how i wrote in previous post i starting my new position.
for customer complaints I start use 8D report standards. . I started work in april and we received customer complaints but for parts produced before April. to this time i dont have any complaints for parts produced after 01-April 2007
I analyzed and 62-70% our shipments is OK.
2 areas in my process which Ishould improve are mould quality and people.

 

[BradM]

Great reply. Thank you.

I am intrigued that you identify people as a problem. Do you feel there is too much inconsistency in their approaches? How many shifts are you operating? What are the actions that people are doing inconsistently to create the issues? Can you see the problems during production?

Do you have standardized procedures in place people are following?

When you state you analyzed shipping, did you perform random sampling, or 100% inspection?

Are you utilizing control charts? How many process variables are you looking at?

I will take by the use of your tools that you have at least some basic skill set in quality. I hope my questions do not seem insulting or basic. You will need to be our eyes and ears of your situation, as we cannot be there.

It looks like you've done a fairly adequate job of locating the failures. Now, figuring out the root cause will get you down the path a bit further.

 

[fireonce]

Even if after more than one year, your infomation is still worth to be learnt yet.

 

[Przemek]

Hello. I have one more question. I read all posts in this subject and I try found the best method for "on-line alarm" when something wrong doing with process. Currently we measured dimensions of parts after process (reactive way) but how to controll process during cycle (preventive).i read in one book then weight should be controlled 16 hours after infection. Its true? I dont have a visual systems, but all my machines are from 2000 year (new). What kind of paremeters should be during controll? Thanks for help

 

[Howard Atkins]

As was seen by my article, I recommended weight, but that is also reactive and the wait for 16-24 hours is necessary with such materials as PA66 as the weight changes rapidly.

Cycle time is a very basic parameter that gives an idea of the complete process.
If your machines have the ability to use tolerances then this is a simpler and more effective method as you have a 100% check of each shot.
This does not have the glamour of SPC but controls the parameters, such as plastification time etc

 

[Bill Ryan - 2007]

I have very limited experience with injection moulding but would it be possible to set up a simple study? Weigh product as it is ejected and reweigh it after the 16-24 hours?

My background is in aluminum and zinc die casting. Weight was used on most product as it was ejected from the die and this type of study is what we did to be able to know product would be acceptable after the "creep" phenomenon (especially with zinc) was complete. We had very good success once the relationship was established. But I'm the first to admit I have no knowledge of plastic aging properties.

 

[Howard Atkins]

You are right, but for some polymers you must weigh at the same time interval from ejection to keep the study straight.
Another difference is the density for each commercial polymer changes from lot to lot, so that the same grade of POM can vary between 1.39-1.41 g/cc.