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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.

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Always Get Mold Prints…

I was recently involved in a consulting job and was asked the following question…

Project Manager
The tooling vendor is charging extra for the mold prints and CAD drawings. Should we purchase these?

My Response
You should always obtain prints and CAD files from your tooling vendor… even if you plan on using this vendor for molding your parts, tooling repairs, design modifications, and regular maintenance. Basically, anything can happen, the vendor can go out of business, management could change their practices, ownership can change, or leaking roof could wipe out the data and leave you with a mess.
Just as you have a backup of your computer’s critical data… you must obtain prints and files of your molds to serve as a backup of your mold. 
Additional Thoughts
The best approach is to ensure that costs associated with prints and digital files are included in the original quotation. Always spell these specifics out in detail so that there is no confusion.
-Andy

Selecting Your Training Metrics

In a recent webinar, I received a common question…

Mark
When tracking the improvements of training, what should I monitor?
My Response
I will answer this is a few parts…
1) Choose from the data that is already available – Do not create new metrics to monitor… if it was important to the management, someone would already be monitoring the parameters.
2) Select 3-4 parameters – Choose a few important parameters… monitoring too many parameters will become overwhelming.
3) Gather data form the last 6-12 months – Without a good baseline for comparison… you will not know how much things have improved.
Additional Thoughts
Don’t be afraid to share the credit with other initiatives. In many cases, another improvement initiative will take place while the training is going on. For example, the die setters and technicians could be implementing 5S at the same time you are training them on processing. In such a case, the reduction in downtime and changeover time will most likely be a cumulative result from both initiatives… especially when the initiative is integrated into the training through tasks and customization.
-Andy

Teaching The Exceptions To The Rule…

A colleague of mine were recently discussing employee training, and the conversation moved towards this question…

George
I understand that there are general rules that can be taught, but how do you handle the exceptions that come up from time to time?
My Response
There are always exceptions to the rule, but it is more important to teach your employees the fundamentals first… and then explain the exceptions that might apply to your application.
When you handle the teaching of an exception, it is most important that you explain why this exception occurs. 
Additional Thoughts
In most cases, an exception occurs as a result of factors such as a shortcoming in the mold or part design or possibly a need to overcome a deficiency in the processing equipment.
-Andy

Understanding Back-Flow Within the Barrel…

I received an interesting follow-up question regarding one of my earlier posts…

Steve
One of our techs stated that there is back-flow in the barrel. Is this true? How does this happen?

My Response
Yes, back flow does occur within the barrel in three ways:
1) Material will flow back over the check ring – During injection, all check rings will leak a little, causing some back-flow along the screw.
2) Material will flow back down the screw – During injection the material that leaks around the check ring will push polymer back down the screw channel.
3) Material will flow over the screw flights – During screw recovery, polymer will pass over the flights of the screw. This mixing will increase with an increase of back pressure.
Additional Thoughts
All this back-flow exists in virtually all reciprocating-screw molding machines. If you are processing a heat sensitive material… you need to do your best to minimize these affects by maximizing the efficiency of your screw recovery, and monitor the performance of your check ring.
-Andy

Assisting Part Ejection From Long Cores

I received this e-mail from a molder overseas…

Nathan
We are molding PS 750 (NL)  tubes in an eight cavity mold. When we use a higher mold temperature, part ejection is good, but the parts display sinks near the slides. With a lower temperature, we can mold parts which look good, but are difficult to eject. We believe we have enough draft on the part and extensive polishing has been done to assist part ejection, yet the parts is hard to eject. If we spray mold release, the part will release from the mold, but this is not a good long term solution. Do you believe the fault is in the material?
Note: Nathan also provided many photos and specifications for both the tool and parts which we will avoid displaying these to protect his customers.
My Response
The three biggest factors that hinder part ejection and hold the core to the part are: the force holding the part to the core, the vaccuum forces holding the part to the core, and the coefficient of friction between the core and the part.
First, the hoop stresses due to shrinkage causes the part to contact the core even after it begins moving off the core. The warmer the part is during the time of ejection, the less this stress will hinder part ejection.
Second, highly polished surface of the core can create such a good seal with the core, it can help to maintain the vacuum seal during part ejection. Applying a very slight texture or surface treatment to the core surface can often reduce this seal and help gas get under the part, thus reducing these vacuum forces. Many molders will also use porous steel and air poppet valves to help facilitate this removal process.
Third, the coefficient of friction for most tool steels can be improved significantly through the use of dry lubricating surface treatments such as dicronite. This is one of quickest ways to overcome friction and improve part ejection.
Additional Thoughts
One great benefit to surface treatments such as dicronite, you can see the coating on the core, so any wear or damage to that coating can be easily tracked and monitored.
-Andy

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