Plastics Training & Technology Blog

Understanding Jetting...

By Andy Routsis on May 14, 2012 3:45 PM 0 Vote 0 Votes

I was asked this question the other day when discussing molding defects...

Student

What actually causes Jetting?

My Response

This defect occurs when the polymer shoots into the mold and does not create a smooth laminar, or fountain, flow as it first enters the mold cavity. A laminar flow occurs when the polymer enters the mold cavity from the center, spreads out to the edges of the mold surface to allow more material to enter through the center. In the case of jetting, the polymer streams into the mold cavity and shoots forward like a cylinder of polymer with the first polymer to enter the mold continuing towards the opposite wall rather than spread to the nearest wall.

Additional Thoughts

Jetting, non-laminar flow, can be caused by one of three major factors:

• Low Material Temperature

• High 1st Stage Injection

• Poor Mold Design

-Andy

What is Micro-Molding...?

By Andy Routsis on May 10, 2012 3:40 PM 0 Vote 0 Votes

I was asked this question by a student the other day...

Bob

Can you please define Micro-Molding?

My Response

I have seen this defined as small parts around 1 milligram or less. In practice, I have seen it refer to parts much larger than that... The aspect that seems to differentiate micro molding vs. small commodity molding is the tolerance, application, and fine detail. For example, a gear or motor housing with extremely tight tolerances might be considered 'micro-molding' even if it significantly heavier than 1 milligram.

-Andy

Radii in Runners...

By Andy Routsis on May 8, 2012 9:55 AM 0 Vote 0 Votes

I was asked this during NPE...

Manager

My guys want me to look into the 'shear balancing' runner technology while I am here... Is this stuff worth it, or do radiused runners work just as well?

My Response

Runner technologies which balance the shear imbalance within the runner system and are invaluable in helping to minimize cavity imbalances. Tricks such as radii runner intersections might improve the imbalance, but I have seen enough proof to know that shear balancing is the most effective method of correcting for runner imbalance.

-Andy

Robotics at NPE...

By Andy Routsis on May 2, 2012 10:05 AM 0 Vote 0 Votes

At the recent NPE I noticed an emphasis on robotics...

Simplifying Robotics

There were many great advances to the programming and interface systems for robotics. Each advancement in simplifying the programming of robotics will improve the learning curve for a setup technician. One manufacturer even demonstrated the ability to have the robot mimic manual physical movements of the operator in real time.

Multi-Function Robotics

With the extensive advances in the speed of robotics, there is a large amount of time that exists between the moment the robot removes the part from the mold and when it is needed again. At this NPE, there was a strong emphasis on multi-function robots which take advantage of their speed by performing multiple trimming, inspecting, and assembly tasks in between cycles. Molders who can take advantage of their robots capabilities between cycles will save time and money over the log time.

-Andy

Verifying a Consistent Silicone Process...

By Andy Routsis on April 27, 2012 1:12 PM 0 Vote 0 Votes

I was asked this question the other day...

Quality Manager

What is a good way to ensure a silicone molding process is consistent?

My Response

One good way to check the consistency of the process is to routinely measure the part weight. A consistent part weight indicates the same amount of material is injected and packed each cycle. This wont necessary tell you what is wrong or has changed, but will be a good indicator of process shift.

-Andy

Differential Cooling...

By Andy Routsis on April 25, 2012 4:40 PM 0 Vote 0 Votes

I was recently in a discussion with someone who was heavily involved in a molding trial...

Engineer

We just went through a series of trials to reach the correct molded part dimensions on a part, and it turned out we needed to use four different temperatures to achieve this. What mold cooling information should we be documenting for this?

My Response

Regarding the mold cooling, you should first have a detailed diagram of the cooling line/themolator layout. This diagram should document the coolant temperature entering and leaving the mold for each temperature profile. Over time, you should consider adjusting the tooling to accommodate these complications.

-Andy

Spiral Flow Test for PP...

By Andy Routsis on April 23, 2012 11:45 AM 0 Vote 0 Votes

I received this question as a follow-up to a previous blog posting...

YM

Is there any standard (ISO or ASTM) that can be reference for a polypropylene spiral flow test?

My Response

Yes, there is a standard for this within ASTM D-4101. If you are looking to publish the results, then this can be very helpful. Unfortunately, the conditions, flow rates, and pressures used may not directly replicate your processing conditions. In practice, most of the companies I have dealt with create their own procedure based on the conditions of their process.

For example, if they are looking to compare the viscosity of two grades of material. they might replicate the melt temperatures and flow rates of the actual product, and measure the difference in pressure at transfer to represent viscosity.

Another company I have worked with uses many older, pressure-controlled, molding machines. This company uses a constant pressure with position transfer. The change in injection time and flow distance provides excellent information for comparing one material grade to another.

Additional Thoughts

Basically, I recommend you review the standard procedures for the spiral flow test, but adjust the test parameters to meet the specific needs of your production facility. The key factor is to perform a test which provides information which helps the production department.

-Andy

Restarting Your Training...

By Andy Routsis on April 19, 2012 12:25 PM 0 Vote 0 Votes

I was approached during NPE the other week by a manager...

Manager

We used to do On the Job training, but now we do nothing for our employees. How do we get started again?

My Response

The first step is to start training, even if it is something as simple as cross training. For example, you could have a technician assist in some mold PM's to learn more about tooling.

Your employees will never get into the mindset if you never do any training. Employees want to do a good job, but they need the necessary intellectual tools to succeed.

Additional Thoughts

I understand that there is much more to effective plant-wide employee development than this, but any training is better than no training at all... and you have to start somewhere.

-Andy

Part Sticking and Machine-Independent Documentation...

By Andy Routsis on April 16, 2012 11:00 AM 0 Vote 0 Votes

I received a detailed request for help from a blog reader last month. Below if a distilled rendition of the discussion...

Issue

The mold has run without issues for years. Now the parts stick in the mold almost every shot, there is more flash, and the cushion is much lower than recollection. All the machine and temperature settings are the same, but the result is much different. Could this be a check ring issue?

My Response

The check ring is more commonly an issue if the sticking is intermittent… which this seems not to be the case. My initial suspicion is that there is too much material being injected or packed into the mold. Second, the mold or melt temperature might be higher than usual. There are a wide host of items which could contribute to this problem... but investigating these first might give a good idea as to the cause of the defect.

Additional Thoughts

This could also be chalked up as a documentation issue. Since we don't know the melt temperature, 1st stage fill time, part weight, or other machine-independent parameters during the good runs, we cannot quickly identify 'what changed' between then and now.

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

Rule of Thumb for Packing...

By Andy Routsis on April 11, 2012 9:10 AM 0 Vote 0 Votes

I am often asked the following question...

JH

What is a good rule of thumb for second stage packing?

My Response

In the old days of pressure-controlled injection molding machines, the first stage pressure was used to completely fill the mold slowly while a lower pressure (approx. 40-60%) was used to compensate for shrinkage while waiting for the gate to freeze.In the newer machines, if the mold is completely filled during first stage, then the old 40-60% rule of thumb is often applicable.

If a scientific or decoupled type of process is being used, where the mold is not completely filled during first stage, then there are many factors which play into the final second stage packing pressure. Essentially, the only rule of thumb is to select a pressure which produces an acceptable part. The first stage injection pressure should have no bearing on the second stage packing pressure. I have seen thick parts using second stage packing pressures as low as 25% of the pressure at transfer, and I have seen thin-walled parts use as much as 125%.

Additional Thoughts

The fundamental underlying basis of good injection molding is to separate mold filling from mold packing. This means you should first establish a good fill, and then establish your part packing.

-Andy

Training Certificates...

By Andy Routsis on April 9, 2012 1:25 PM 0 Vote 0 Votes

I received this comment the other day regarding a recent post...

Manager

Two of our techs recently received training certification, but I don't see any real change between them and the other technicians.

My Response

Most certifications are based on the participants ability to pass some tests in a class setting. This process is beneficial in introducing new techniques and ideas to the employees, but seldom helps in changing the employees behavior. Most experts believe it can take many months to effectively change behavior. As a result, you must implement a broad reaching approach to training which not only teaches the new concepts, but reinforces the correct behavior over time.

Additional Thoughts

In the case of plastics processing, the employee needs to know how to process, practice the knowledge, and have the right processing and troubleshooting techniques reinforced by those in the workplace.

-Andy

NPE 2012 Passes...

By Andy Routsis on March 29, 2012 9:50 AM 0 Vote 0 Votes

If you are visiting NPE this April, I recommend you take advantage of our free passes (a $120 value): http://www.npe2012guest.org/?e=314

For more about NPE2012, please visit: http://www.npe.org/

-Andy

MFI and Regrind...

By Andy Routsis on March 28, 2012 9:25 AM 0 Vote 0 Votes

This question arrived as a follow-up question to a recent post...

NM

I am new to the business and an independent broker. In automobile parts (I deal with travel trailers, RV's, automotive and such) does MFI make a difference? Recycled or virgin? We are trying to cut costs, and it seems a lower MFI and recycled product is cheaper.

Regrading MFI

MFI is essentially a measurement of how much of a particular material flows through a capillary under a given load during the course of 10 minutes. The stresses and shear rates present in this test are not indicative of most plastics processes. If you want more comparative data you can acquire rheological data from the manufacturers... or request samples and actually preform some comparative rheological tests using your actual production equipment.

Regarding Regrind

You always need to first determine whether the use of regrind poses a liability issue with your customers. You should determine the relative quality of the regrind. Depending on the application, you can choose from a wide range of Rheological, physical property, and performance testing methods.

Some related posts on rheology and physical properties:

MFI for Different Materials...

Spiral Flow Test...

The Uses of MFI...

Explaining Melt Flow Index

Attribute Data vs. Variables Data...

Using Processing Aides with PP...

Calculating Apparent Shear Rate...

Crystallinity In Layman's Terms

Same Supplier... Same Grade... Bigger Dimensions...

In-Mold Rheology Test...

-Andy

Create a Training Portfolio...

By Andy Routsis on March 26, 2012 10:10 AM 0 Vote 0 Votes

I am often asked whether or not it is important to provide employees with printed certificates once they complete their training. As a result, I want to use this post to discuss the importance of creating a training portfolio for your employees.

Building a Training Portfolio

Every time your employees complete a step in their training plan or make an advance in competency, it should be documented and retained by the employee. We suggest that you create a personalized binder that the employee can use to store items such as training certificates, worksheets, training aides, photographs, and documents. The intent is to create a personal portfolio which the employee can use to demonstrate not only what they learned, but what they have applied.

-Andy

NPE 2012 West Hall, Booth #472...

By Andy Routsis on March 22, 2012 9:15 AM 0 Vote 0 Votes

For all those attending NPE 2012, please visit us at Booth #472 in the West Hall.

Stop by to discuss training, technology, plastics, or anything else you wish to review.

At our booth, you can also pick up your free copy of our new pocket guide entitled:

'The Injection Molding Reference Guide'

I also recommend you take advantage of our free passes (a $120 value): http://www.npe2012guest.org/?e=314

-Andy

MFI for Different Materials...

By Andy Routsis on March 19, 2012 4:25 PM 2 Vote 0 Votes

I received this question last week...

ATR

I am trying to find out why the injection pressure of PP is lower than the injection pressure of PC in terms of its MFI. But the MFI for PC is at a different temperature and for PP is at a different temperature.

My Response

Essentially, Melt Flow Index (MFI) is not an objective test. MFI uses different specifications for testing different materials. The pressures and shear rates are different than those encountered in production, and the temperatures are typically not the same either.

The benefit to this test is that it is easy for anyone to conduct, and it provides a single number result.

Additional Thoughts

The most effective use of the MFI test, I have encountered, is to compare different batches of the same material grade for material scheduling.

Objective testing such as capillary rheometry or spiral flow are much more involved, but can provide much more comprehensive results.

I discuss this in more detail in these posts:

The Uses of MFI...

Explaining Melt Flow Index

Spiral Flow Test...

-Andy

Processing Rule #1...

By Andy Routsis on March 16, 2012 3:40 PM 0 Vote 0 Votes

There are many rules to good processing, but this one is paramount...

Manager

What is the most important thing to look for when evaluating a technicians ability to process?

My Response

The most important factor in good processing is 'Rule #1 - Make One Process Change at a Time'. When a change is made, it’s imperative to wait for the results to take place before making another process adjustment. This rule ensures you know the specific cause and effect of any change made to the injection molding process.

For example, if you increase both the injection speed and packing pressure at the same time, you may eliminate a short shot, but while doing so - you’ve created flash, part sticking, burning, and cracking. Because you changed two parameters at the same time, you don’t know which change corrected the short shot and which parameter resulted in causing each of the new defects.

Anyone changing more than one parameter at a time is not approaching the process systematically.

-Andy

Two Plateaus During Gate Seal Determination...

By Andy Routsis on March 12, 2012 9:35 AM 0 Vote 0 Votes

Recently a technicians asked me this question...

Tech

During a gate seal determination (part weight vs. second stage time), we saw the part weight almost stabilize and then it shot up until it finally leveled out. What might have caused this?

My Response

When doing a gate seal determination, you might see this two-plateau result. Essentially, this is causes by material shrinkage in the gate area allowing more material to flow through the gate before the gate finally freezes.

The material can either flow through the center of the gate as the material shrinks around itself, or the material can flow around the gate as it shrinks away from the mold surface.This is most common when you are molding parts with thick gates or materials with especially high melt flow rates.

Additional Thoughts

Since the first plateau is caused by stagnation of flow before a second flow of material into the mold cavity, it is always good to verify that such a process does not result in delamination, brittleness, or low mechanical strength.

-Andy

High Back Pressure...

By Andy Routsis on March 9, 2012 9:40 AM 0 Vote 0 Votes

This question arrived as a follow-up to a previous post: More About Back Pressure...

Saylan

If I have to work with an odd back pressure like 250 bar, does it create any damage to the equipment or machine?

My Response

Assuming this is the plastic pressure, this would not necessarily cause machine damage. This will consume a large amount of energy and create a large amount of shear during recovery. The potential for material and additive degradation may be high depending on the material being processed.

You may wish to consider a new screw designed specifically to address the complication you are encountering during recovery. For instance you may need a longer transition zone if the shear is necessary for melting, or you may need a mixing element in the metering zone if the back pressure is used for additive mixing.

Additional Thoughts

This may be great application for a shot-pot style of molding machine. This would allow a properly designed material-specific screw to be used to melt and convey the material while a plunger is used to inject the melted polymer.

-Andy

Maximum Pressure Setting During Injection...

By Andy Routsis on March 6, 2012 12:15 PM 0 Vote 0 Votes

This question was received earlier this week...

CD

What should be the minimum pressure during switch over time of injection?

My Response

If you are switching over through the use of screw position, then you should ensure the maximum pressure setting is significantly higher than injection pressure at transfer.

Additional Thoughts

It is critical that you have enough pressure available to maintain the desired injection speed.

More about this can be found here:

Identifying A Pressure Limited Process...

-Andy

The Best Training Method...

By Andy Routsis on March 2, 2012 8:25 AM 0 Vote 0 Votes

I received this question via email yesterday...

NG

Which is the best type of training?

My Response

No single method of training can meet each of the success factors necessary to teach all your employees. For this reason, it is important to use a training plan comprised of multiple training methods targeted to teach your employees the knowledge and skills they need to succeed.

Additional Thoughts

Our approach to employee training most often includes factors such as focused on-the-job instruction, interactive online training, and skill development exercises.

-Andy

Complications from 1st to 2nd Stage Transfer...

By Andy Routsis on February 27, 2012 1:00 PM 0 0 Vote 0 Votes

In a comment thread in a previous blog entry, a reader had some questions about how to handle the transfer from 1st to 2nd stage transfer. The basic focus of the discussion both in the comments as well as private were about a general approach to establishing the transfer, yet they have many different types and brands of machines.

My Comments

Unfortunately, here is no standard for machine response from fill to pack. I have seen some machines stop the screw immediately when 2nd stage is turned off, yet allow extensive overshoot once it is turned on. Other machines have different settings for how over or under-damped you want the machine to behave. You should determine the behavior of your actual machines and then make a procedure specific for those machines so everyone can setup a process the same way.

-Andy

More About Back Pressure...

By Andy Routsis on February 23, 2012 9:50 AM 2 Vote 0 Votes

I was recently asked about back pressure...

GG

My employees were asking me to explain the following statement 'Back pressure causes additional material to flow over the flights of the screw'. I wanted to hear your explanation before discussing it with them.

My Response

During screw recovery, the screw is pumping material forward down the flights of the screw. If unhindered, the material will flow to the front of the screw, thus pushing the screw backward to build the next shot. Back pressure provides resistance to the backward movement of the screw, causing some of the material pumped forward to either 1) flow back within the screw channels or 2) flow back over the flights of the screw between the flights and the barrel.

Additional Thoughts

There will always be some degree of backflow within the channels and over the flights, but increased back pressure will significant increase this effect.

-Andy

Differential Cooling for Warpage...

By Andy Routsis on February 20, 2012 1:45 PM 0 Vote 0 Votes

I was recently at a molder's facility who was having a complication with one part...

Molder

Even though this polypropylene part has a curve, we have a problem with it curving too much thus causing a complication with assembly.

note: when discussing the troubleshooting process, they have investigated most aspects of the process, but it turns out they never considered trying differential mold temperatures.

My Suggestion

Although I try to avoid using differential coolant temperatures when possible, it would be a good option to investigate for this mold/process combination. Since PP has a high degree of crystallinity, decreasing the temperature of one side will cause a tendency to bow towards the opposite side due to differential shrinkage. In this case, the coolant temperature differential between one side and the other might only be 5 or 10 degrees, but it might be enough to counteract the bowing.

Additional Thoughts

Before using differential heats, it would be beneficial to measure both the coolant temperature entering and exiting the mold as well as the temperature of the mold steel. In many cases, you may be using differential coolant temperature, but the result may be similar mold surface temperatures.

-Andy

Appreciating Other Job Functions...

By Andy Routsis on February 15, 2012 3:50 PM 0 Vote 0 Votes

I recently encountered this common issue...

Tooling Manager

The techs don't seem to appreciate the effort the tooling department makes to keep the molds operating. They don't take good care of the tools.

My Suggestion

It would be beneficial to have the technicians and die setters participate in a few mold PMs. This would give them a first-hand view of the maintenance required and an appreciation of how much effort is required to care for the tools.

Additional Thoughts

We recommend a small amount of cross training for most of your employees in the roles of those around them including quality, material handling, and even maintenance. This will give them an appreciation of the roles of those working around them.

-Andy

A Few Older Posts About Training Your Employees...

By Andy Routsis on February 13, 2012 9:45 AM 0 Vote 0 Votes

I often get asked "Why should we train", so I went through some older posts and found a few of my favorite posts on this topic...

If You Teach a Man to Fish...

When It Comes to Training...

Should Quality Learn About Processing...

How Much Re-Training...

Feel free to forward these to anyone who might be interested.

-Andy

2012 NPE - Don't Miss It...

By Andy Routsis on February 9, 2012 10:40 AM 0 Vote 0 Votes

Hi Everyone,

Try not to miss the 2012 NPE in Orlando. For information, visit the website at www.npe.org.

-Andy

Put the Tonnage on the Mold Base...

By Andy Routsis on February 6, 2012 12:10 PM 0 Vote 0 Votes

I was at a molder the other week who had this common issue...

Engineer

Our technicians always change the clamp tonnage and it seems to cause problems with venting, actions, and wear. Even the setup guys mess it up.

My Response

Once you have determined the tonnage that should be used on a tool, I recommend you put a plaque on the side of the mold stating the tonnage to be used. If the recommended tonnage is stamped right on each tool, it is hard for a technician or setup person to miss it.

Additional Thoughts

If you are having a problem with a specific issue, such as tonnage, always look for a simplistic way to draw attention to it.

-Andy

Don't Forget the Fundamentals...

By Andy Routsis on February 3, 2012 10:00 AM 0 Vote 1 Vote

I received this comment the other day...

Manager

I understand my technicians have not had any formal process training, but what they really need is advanced training.

My Thoughts

It is common to believe that advanced training will automatically cause your employees to function at a higher level. Unfortunately, advanced training does little to change behavior if your employees lack a good understanding of the fundamentals. A great example of this is the decoupling of 1st stage filling from 2nd stage packing.

Let's presume you have a technician who has been filling the mold completely during 1st stage fill for the past 15 years. Now you send this person to a class focused on the finer points of optimizing filling and packing based on the foundation of a short shot during first stage fill. This employee would learn very little which is directly applicable to his job since he still believes filing the mold completely during 1st stage fill is the best way to process.

-Andy

Coloring Water Line Connections...

By Andy Routsis on February 1, 2012 12:25 PM 0 Vote 0 Votes

One molder asked me this question the other day...

Manager

Our setup techs always seem to connect the water lines incorrectly. We have diagrams to show the setup, but they seem to mess it up anyways.

My Response

Companies who use individual water lines rather than a manifold should color-code everything using blue lines for incoming water, red lines for outgoing water, and extra colors such as yellow for line which exit and re-enter the mold.

Once you have this established, place colored plaques on each connection of the mold. This will ensure that your employees cannot accidentally connect an in-line to an out connector.

-Andy

Setting Final Cushion...

By Andy Routsis on January 25, 2012 10:10 PM 0 Vote 0 Votes

During some classroom training the other week, a student asked me the following question...

John

What value should you set the cushion at?

My Response

A good rule of thumb is 10% of the initial shot size. For example, if the overall shot size is 100mm, then the cushion should be about 10mm. This avoids pressure losses from too much material in front of the screw, yet provides enough room in front of the screw for normal variability.

The Purpose of Cushion

Targeting Cushion Size vs. Transfer Position

-Andy

Teaching Tolerances...

By Andy Routsis on January 23, 2012 7:00 AM 0 Vote 0 Votes

I was asked this question during a recent on-site visit...

QA Manager

What is an easy was to explain tolerances to new employees?

My Response

Focus on the fact that tolerances are commonly expressed in a way which can be easily broken up into simple math equations.

Dimension: 1.00 ± 0.01

Upper Limit: 1.00 + 0.01 = 1.01

Lower Limit: 1.00 - 0.01 = 0.99

Additional Thoughts

When possible break ideas into their simplest form such as an equation or concept. Keep in mind the issue is very often math not tolerances. In this case, focus the attention on basic math and calculator usage first before moving on to part tolerances.

-Andy

How Much Training a Week...

By Andy Routsis on January 18, 2012 7:20 AM 0 Vote 0 Votes

As a trainer, this is one of the more common questions I receive...

Manager

How much training a week should I give my employees?

My Response

We typically recommend between 1 and 2 hours a week. It is always much better to provide your employees a slow, steady, & consistent stream of information over an extended period of time. One hour a week for 40 weeks can be much more effective than one 40-hour week in altering the behavior and improving the skills of your employees.

Additional Thoughts

There is always a place for multi-day training sessions, but they are most effective in teaching a specific skill rather than relaying general knowledge.

-Andy

PBT in Hot Runner Systems...

By Andy Routsis on January 16, 2012 8:55 PM 0 0 Vote 0 Votes

I was asked this question by a molder who was having trouble balancing a hot runner system...

Bob

We have this new mold which is running 16 cavities in PBT. Usually we can balance the mold using the drop temperatures, but that does not seem to work on this mold. Any thoughts?

My Response

Essentially, semi-crystalline polymers with a high degree of crystallinity such as PBT and nylon are not highly affected by temperature. In such a case, you will have to adjust the gates or the hot runner system itself to balance the shear of the mold.

Additional Thoughts

Cold runner systems are the best for these materials. I know many molders who use a press-side low-RPM grinder to effectively grind up the material and re-introduce PBT back into the process.

-Andy

Documentation Takes Too Long...

By Andy Routsis on January 13, 2012 9:38 AM 0 Vote 0 Votes

I was in a discussion recently with a GM and he had this problem...

Manager

My technicians are not willing to take the time to document their changes. They claim it takes too long?

My Response

The issue here is not time, but education. If your employees are not taking time to document, it is likely that they do not fully understand the importance and benefits of good documentation. If they understand the ways it can simplify their job and improve their effectiveness, they would be more interested in compliance. Unfortunately, this is not a simple fix... it require the employees to not only understand the benefits, but also know what to do with the information they are given.

-Andy

Creating a Training Plan...

By Andy Routsis on January 11, 2012 9:10 AM 0 Vote 0 Votes

I was recently at a company who purchased some training a while back from a different provider under the guise of having a 'resource' for all their employees to use...

My Comments

Training is good, but it is critical that you tie the training to each job function through the use of a training plan. Without a structured training plan focused on job title you will not be able to make a change to your workforce. In general, your employees will not go and train unless there is a structure to show them what they are supposed to do when they train.

-Andy

The Best Way to Process...

By Andy Routsis on January 9, 2012 9:20 AM 0 0 Vote 0 Votes

I was recently at a molding facility during a training implementation was in need of some training due to a lack of fundamentals among the employees...

Company President

What is the best way to process, and why don't we just have everybody process that way starting tomorrow?

My Response

I told her that there were ways that there are many ways to process, and there are a few methods which are far superior to others. Unfortunately without a strong background in processing knowledge your employees will have no reason to understand why this method is better.

Essentially, people who have been making a living molding a particular way do not just change their entire approach to processing because someone tells them it is better. You need to educate them on plastics, machinery, materials, processing, and tooling to ensure that they know why it is a better way.

Additional Thoughts

There are always steps which your employees can take to improve the process. As they see the success they will continue to employ more cost saving, and process improving techniques. This is one of the reasons why it can be easier to teach someone who has never processed that to teach someone who has processed for years.

-Andy

Melt Temperature and Density...

By Andy Routsis on January 5, 2012 9:05 AM 0 Vote 0 Votes

I received this excellent question last week...

Saeed

In one of your videos, you state that higher melt temperatures will increase part weight. To my understanding, a less viscous material is pumped in the cavity with a relative ease thus increasing the part weight. Could you please guide me as to whether or not a decrease in density negates the above?

My Response

You are correct that you will be injecting a less dense material in this scenario… but the higher melt temperature causes many things to occur, but the 2 major factors increasing the part weight and density are listed below:

1) There will be a higher amount of material flow and in-mold pressure during packing resulting in more material entering the mold during both 1st and 2nd stage.

2) A higher melt temperature promotes an increase in part shrinkage resulting in a higher overall part density.

Additional Thoughts

This question points out how complex the interactions between the mold, machine, material, and injection molding process can become.

-Andy

Follow-Up on Increasing Injection Velocity...

By Andy Routsis on January 1, 2012 5:15 PM 0 0 Vote 0 Votes

I received an email from a blog reader about another benefit to increasing injection velocity...

Harry

Another reason we use a higher injection velocity in our facility is to increase the amount of packing that is possible.

My Comments

This is correct because of two reasons. First, the gate begins to freeze the moment the material enters the gate. The shorter time required to fill the mold allows more time for packing. The second reason is because the pressure loss within the mold cavity is decreased, allowing more packing pressure to reach the extremities of the mold during packing.

-Andy

Decreasing Energy Consumption during Injection...

By Andy Routsis on December 27, 2011 12:05 PM 0 Vote 0 Votes

I was at a company recently and the engineer was confused about how to reduce energy consumption during injection...

Engineer

I know higher injection velocities reduce variability, but a lower injection speed uses less pressure and thus reduces the overall energy consumption... right?

My Response

Actually, a higher velocity reduces overall energy consumption during injection even though the injection pressure is increased. Increasing the injection velocity decreases the material viscosity through shear thinning. As a result, the overall energy required to push the final volume of polymer necessary to fill the mold is decreased.

In an actual example performed by one of our trainers, the data from a molding process which was filled at two different times is shown below:

Slow Fill:

Fill time = 3.15sec

Transfer Pressure = 10,460psi

Fast Fill:

Fill time = 0.83sec

Transfer Pressure = 11,910psi

Although the faster fill time has a higher pressure at transfer, the molding machine applied the injection pressure for 27% of the time necessary to fill the mold at the slower speed. When you multiply the fill time by the transfer pressure you get the following effective (or relative) viscosity:

Effective Viscosity = t x psi

Slow Fill = 32,950 psi-s

Fast Fill = 9,890 psi-s

Assuming the pressure profiles are similar in shape, it can be reasonably proposed that the faster fill consumed approximately 30% of the energy necessary to fill the mold at the slower speed.

Additional Thoughts

The additional benefit to filling faster is that the polymer fills the mold and begins to cool faster. In this case the overall cycle time could drop as much as 2 seconds due to the higher injection viscosity.

-Andy

Don't Forget to Move the Temperature Probe...

By Andy Routsis on December 22, 2011 11:00 AM 0 Vote 0 Votes

I was discussing the measurement of the polymer temperature with an engineer and he explained a problem he is encountering...

Joe

Each of our technicians are getting different results when we they measure the melt temperature... especially when we measure high temperature materials like polysulfone.

note: I asked one of their techs to demonstrate how they measure the melt temperature and he purged the material, inserted a thin-style probe, and recorded the highest temperature reading. I then asked the technician to repeat the process, but when he inserted the probe I asked him to move is around slowly. The result was a temperature which was 15 degrees higher than his previous measurement.

My Response

When measuring a melt temperature, it is important to move the probe around a little. When the probe is inserted into the melt, a skin of cooled polymer forms around the probe. To ensure you are getting the temperature of the melt, you need to use the surrounding material to soften this skin and get some of the interior polymer melt in contact with the probe.

-Andy

Making Significant Changes...

By Andy Routsis on December 19, 2011 10:15 AM 0 Vote 0 Votes

As a follow-up to a previous post, I was asked to expand in the second rule of processing...

The 5 Basic Rules of Processing (from before):

Rule 1 - Make one process change at a time

Rule 2 - Make significant changes

Rule 3 - If a change does not help, change it back

Rule 4 - Document the process

Rule 5 - Document all changes to the process

Rule #2

The idea behind this is that you always want to know you are making a change which is important. Too often people will tweak different parameters without any direct knowledge as to the effectiveness of the change.

When you make a change, you want to ensure it is large enough to make a difference. Remember any change to the process can be reversed either completely or partially.

Additional Thoughts

I have seen many molders who make small adjustments with the belief it will improve the situation. A symptom of this behavior is a control panel with a large amount of numbers which do not end in either 5 or 0. For instance, if the injection profile looks like the following... V1=11.1 mm/s, V2=30.3 mm/s, V3=23.4 mm/s, V4=28.4 mm/s, and V5=12.7 mm/s. It is very unlikely that each of those velocities have been optimized and each speed in the profile can be properly justified. This type of profile is almost always the result of someone tinkering with the process until a good part came out of the machine.

-Andy

PPE for Purging...

By Andy Routsis on December 15, 2011 11:15 AM 0 Vote 0 Votes

I have seen many variations on this principle...

Steve

Here we only require our employees to wear safety glasses when purging... is that fine?

My Response

Purged plastics can cause some of the most debilitating injuries because they have a tendency to not only burn, but stick to or inject under your skin as well. When purging goes well, the conditions are relatively safe, but it is not uncommon for a explosive discharge to occur as a result of nozzle blockage or gas buildup.

If you are not wearing a face shield, heat resistant gloves, and long sleeves while purging; you are opening yourself up for serious injury.

Additional Thoughts

In all our training courses, we stress the same PPE recommended by most machine manufacturers which includes the wearing of the following when purging:

Face Shield
Heat Resistant Gloves
Long Sleeves (Cotton)

-Andy

5 Basic Rules of Processing...

By Andy Routsis on December 12, 2011 7:05 AM 0 Vote 0 Votes

I was asked this question yesterday via email...

Manager

What should I be looking for when my guys process?

My Response

There the 5 things that I always look for:

Rule 1 - Make one process change at a time

Rule 2 - Make significant changes

Rule 3 - If a change does not help, change it back

Rule 4 - Document the process

Rule 5 - Document all changes to the process

These rules apply to injection molding, extrusion, and blow molding alike.

Additional Thoughts

This list seems pretty simple, but I have found that most molders skip at least one or two of these steps whenever they process.

-Andy

More on Robots vs. Automation...

By Andy Routsis on December 9, 2011 9:55 AM 0 Vote 0 Votes

This question came up as a follow-up question to a recent blog about robotics and automation...

GH

Would a part diverter be classified as robotics or automation?

My Response

The general rule I always follow is: If it is programmable, it is a robot... if not, it is automation.

Therefore, if the diverter acted as a sort device where acceptable parts were sent one way, while defective or questionable parts were sent another way based on process or inspection data, then it could be considered robotics. If a sensor was just placed on a conveyor to sense different parts and automatically divert of orient parts in a specific manner, then it might be considered automation.

Additional Thougths

Under such a definition, a simple device such as a sprue picker which needs to be mechanically adjusted to alter the speed, length, and movement of the arm might be considered automation.

-Andy

Automation vs. Robotics...

By Andy Routsis on December 8, 2011 1:35 PM 0 Vote 0 Votes

I was asked the following question by a technician the other day...

Bob

What is the difference between automation and robotics?

My Response

Automation generally refers to any component which performs a basic repetitive task; such as conveying or sorting parts. In general, robotics are more complex devices which are programmed to perform advanced repetitive tasks; such as the removal, stacking, packaging, or assembly of parts.

Additional Thoughts

In the plastics industry, the terms automation and robotics both refer to mechanical pieces of equipment and are often used interchangeably.

-Andy

Broaden the Horizons of Your Employees, Part 2...

By Andy Routsis on December 1, 2011 1:20 PM 0 Vote 0 Votes

I recently received a request from a social-networking site to discuss the complications companies encounter in locating well-rounded employees. In this post, I want to address the underlying problem, which is the lack of comprehensive training for production employees.

Initial Concerns

The most effective training systems provide the employees with (1) the information and skills to work and make effective decisions in their job and (2) prepare them for new challenges and advancement opportunities.

Regarding the second goal, it is critical that you prepare your employees for professional growth and advancement. Once you train your employees enough to become competent and capable at their job, additional training should then be made available. Although some employees are content in their job, do not assume that your workforce is content to remain in the same job doing the same thing until the end of time. The best scenario is to have a cue of overqualified employees waiting for advancement. If a job is not currently available, many employers will offer them the opportunity to fill in (typically with the corresponding pay differential) when a higher job function calls in sick, goes on vacation, or takes an extended leave.

Additional Thoughts

Change is can be either slow and gradual, or quick and unexpected. Comprehensive employee training combined with effective advancement training will help you prepare your business for change, new markets, growth, and even downsizing.

-Andy

Broaden the Horizons of Your Employees, Part 1...

By Andy Routsis on November 29, 2011 9:25 AM 0 Vote 0 Votes

I recently received a request from a social-networking site to discuss the complications companies encounter in locating well-rounded employees. In this post, I want to address the underlying problem, which is the lack of comprehensive training for production employees.

My Thoughts

The most effective training systems provide the employees with (1) the information and skills to work and make effective decisions in their job and (2) prepare them for new challenges and advancement opportunities.

Regarding the first goal, the employees needs to know more that what is 'necessary' to do their job. For example, teaching the employee the basic steps in a die change is not effective long-term training. An effective die setter should have a fundamental understanding of many aspects including general safety, job-specific safety, tooling, machinery, processing, and the basic economics involved. Without this strong background, they lack the full knowledge and appreciation to bring true value to the company. Such a trained employee may be very helpful in identifying more efficient procedures, evaluating newer technologies, developing new solutions, and troubleshooting complications when they arise.

Additional Thoughts

It has been said that your workforce is your most valuable asset, yet this is only true when your employees are treated as more than simple robots. Robots who perform specific functions can be easily replaced... competent and capable employees, on the other hand, will help your company improve, grow, expand, and take on new challenges.

-Andy

More About Processing PVC...

By Andy Routsis on November 23, 2011 10:25 AM 0 0 Vote 0 Votes

I received this follow-up question regarding the processing of PVC...

MT

I would like to know if it is safe to mold parts in PVC and acetal in presses that are next to each other?

My Response

It should be safe to process, but it is critical that you vent the fumes from both machines to prevent corrosion of your equipment. You should also take the time to educate your employees on the dangers of combining these materials.

Additional Thoughts

It is critical that you create a system to prevent any chance of cross contamination. This may be as simple as a color-coded system so that the color of the container matches a panel next to the machine. Personally, I would create a fool-proof system where the container for VC is not compatible with the acetal material delivery system and vice-versa.

-Andy

Caveat Emptor: Selling Older Machines...

By Andy Routsis on November 21, 2011 10:20 AM 0 Vote 0 Votes

I was recently working with a company who had an interesting tale regarding the sale of one of their larger, older, hydraulic molding machines with a very large cylinder clamping unit and corresponding hydraulic reservoir...

Engineer

When we were trying to sell one of these pieces of junk, my recommendation was to drain the oil and sell it for scrap metal or parts. Purchasing then told me they had agreed to sell the machine for a few thousand dollars, hydraulic fluid and all.

note: After a quick calculation, he explained to them that they had just lost money since the value of the hydraulic fluid currently in the machine is worth almost twice the amount they are getting for the machine.

My Thoughts

Although complicated to quantify, most of these older machines are a real drag on the company and their resources. In this case, oil in the machine was more valuable than the machine itself. The machine was being sold because it was slow, unreliable, and wasting resources. It will provide the same drain of resources on the next molder who tries to operate it. Especially when your incorporate the expense of relocating, configuring, and hooking up the machine. In this case, I believe the engineer is right... the fluid should have been reclaimed and the machine should have been either scrapped or sold for parts rather than be brought back into service.

-Andy

-Andy

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