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Load Sensitivity Test On Electric Molding Machines…

I was asked this question the other day…

Milan
Does it make any sense to perform a load sensitivity test on a electric machine?. I did few tests, but results were very good, range 0,016% to 0,105%.
Note: The Dynamic Load Sensitivity Test measures how much the injection time shifts with a change in resistance.
My Response
Most all-electric molding machines perform very well in the Dynamic Load Sensitivity Test. In most cases, a variation over 1% is very uncommon in newer machines.
In general, load sensitivity is not a concern with all-electric injection molding machines. Such tests are helpful once or twice a year as part of the general machine maintenance program. This will help you maintain a record of the machine’s performance, and will help you monitor or detect any degradation in performance over time.
Additional Thoughts
for more about the benefits of all-electric molding machines, please review: Are Hydraulic Machines Going the Way of the Dinasour…?
-Andy

Transferring on End of Fill…

I received a blog response which highlights a growing trend in the molding industry…

Blogger
I am using a pressure sensor at the End of Fill on a new all-electric molding machine. With a DIII process, I am having good success in using the pressure at the end of fill for V/P transfer. This works well with a standard deviation of 0.07mm for cushion.

note: For more on a DIII process, please read: Rules for a DIII Process

Additional Thoughts
The advent of highly-responsive all-electric injection molding machines is allowing people to control the process in very unique ways to fit a specific situation. Using the cavity pressure at the end of fill to transfer from velocity control to pressure control can be a great way of controlling the amount of pressure which is received within the mold cavity during the mold cycle.
The biggest concern with this approach is the response of the machine. Most hydraulic molding machines lack the response time to facilitate the correctly use of an end of fill sensor. 
-Andy

Group Training In Different Facilities…

I was asked the following question the other day…

Don
In our main facility, we follow up our training with group discussions with some success. Unfortunately, in our facility overseas, these discussion groups don’t work at all. Do you have any ideas why this happens?

My Response
In group settings, there are typically a couple people who follow along with the discussion, while others often struggle to keep up. If the ones who are struggling are uncomfortable in speaking up, then the entire effort suffers.
Additionally, factors such as the company, management, or even culture can make it difficult for a participant to feel comfortable speak up. Overall, most employees prefer to learn at their own pace.
Additional Thoughts
When we establish training programs, we prefer structured self-paced training with focused one-on-one instruction which ensures that the employee learns. In such a setting, the employee does not feel any of the pressures that exist in a group format. This approach has proven successful in virtually all companies and cultures.
For a related discussion, please review this previous entry: Relying on On-The-Job Training Alone
-Andy

Results of Screw Wear…

I received this follow-up question in a recent blog and decided to answer it in more detail using the blog…

MJ
Which kind of process parameters vary when the screw becomes worn?

My Response
Basically, the most common affects that arise from screw wear relate to the increased back-flow over the flights of the screw. This back-flow increases mixing, but also lowers material conveyance and increases residence time distribution.
As the screw wear increases, the number of revolutions necessary to recover the shot will also increase… thus resulting in more shear heating, a higher melt temperature, and possible polymer degradation.
Additional Thoughts
Since the melting and conveying properties of the screw become compromised, excessive screw wear can also cause a significant increase in the amount of energy which is consumed during screw recovery.
For a related discussion: Tolerance For Screw Wear
-Andy

Understanding Voids…

I received this question today…

AJ
A co-worker told me voids are actually not filled with air or gas. Is this true? Could you explain what voids really are?

My Response
Your co-worker is correct. Voids are sections in the center of a part where material shrinks away from itself and leaves what appears like a small hole within the part.
Although they often appear to be air bubbles, they are actually vacuums within the part where no gas is present. An increase in packing or holding pressure usually corrects this.
Additional Thoughts
Keep in mind, gas entrapment can often be confused with the presence of voids.
-Andy

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