Processor Tips


A Molder’s Plea: Let’s Standardize Controllers

By: Robert Gattshall 27. September 2016 18:08

When choosing a new press molders must take into account several factors, including training from the supplier. Choosing a machine that your technical staff is familiar with is obviously important, because the learning curve on a new controller can sometimes be significant. But why is that, exactly? When you rent a car you don’t need to spend much time getting familiar with it. P,R,N,D is a standard for any automatic-transmission vehicle, regardless of who makes it. It isn’t so simple when it comes to injection molding machines. There seems to be no standardization from manufacturer to manufacturer with regards to controller layout, icons, or even terminology. (John Bozzelli wrote a great article a few years back that points out the multiple phrases used to describe “cushion” and it is worth a read. See May’12 Injection Molding Know How; short.ptonline.com/Bozzelli.) 

SCRAMBLING THE KEYBOARD
One of my favorite analogies to show how subtle changes in layout and icons can have a big impact is the standard QWERTY computer keyboard, shown in Fig. 1 (p. 54). We are all very familiar with this layout (some of us learned it on typewriters), and many of us are extremely efficient using it, even your hunt-and-peck, two-finger typists.

Imagine if you bought a new laptop, and when you opened it up, you had the layout in Fig. 2 in front of you. Not a big change from what you know, as far as changes go. Just a single row of keys is reversed, although many would point out that the alteration affects the most important row of keys. Frankly, it would take a lot of time to get accustomed to this new layout, and we would make many mistakes trying to figure it out, even those of us who are 60+ words/minute typists on the original QWERTY keyboard. 

Now, what if the change was a bit more complex? What would our learning curve look like with the kind of alteration in Fig. 3? Keep in mind that none of the key symbols has changed, only the order in which they appear. I don’t know about you, but my emails would be a nightmare.

So, I hope we can all agree that most of us would make some mistakes while trying figure out these new layouts, even if they could be easily corrected with a “DELETE” or “BACKSPACE” key.

Well, injection molding machine controllers don’t allow us to fix mistakes with a keystroke. Pressing the mold-close button, because you confused it with the ejector-forward button could cost you a mold. Think about that—something as simple as confusing an icon can cost your company hundreds of thousands of dollars! 

To avoid this, some molders decide to stick with one machine manufacturer across the board. There are pros and cons to this approach, and I think the benefits are obvious, but what about the drawbacks? What keeps your machine manufacturer competitive from both a cost and technology standpoint if it knows it has no competitors for your business? What if your current preferred machine supplier doesn’t offer the technology you need for newly awarded business? There is a very plausible scenario in which you would have no choice but to introduce a new controller into your facility, even if you use a single source for machines. 

Standards for machine controller layouts would ensure that when your single machine source decides to upgrade its controller, the layout, icons, and terminology don’t get scrambled. This is not a “What if?” circumstance—that very sort of scramble has happened on almost every machine on the market. Upgrades are expected—technology keeps changing—but that doesn’t mean that we can’t maintain standards.

This also doesn’t mean that machine manufacturers can’t set themselves apart with additional options or technologies. There will obviously still be unique features that are proprietary to their brand. With today’s technology and the operating systems that the machine manufacturers use, a standard screen layout could be agreed upon and made available. This doesn’t mean that this is the only interface option the manufacturers would offer. It just means that there would be a standard available if the end user wishes to use it. There are machines on the market right now that allow the end user to set up custom screen layouts; why not have a standard layout be one of the options as well? 

There are many examples that demonstrate why a standard layout would be a good idea. There are machine controllers, for example, that depict screen-access buttons for mold close and open, but the action buttons (which actually move the mold) are depicted in the opposite order. Not a big deal, right? They have arrows on them, so they should be perfectly clear to the operator, right?

Not necessarily; especially in the 5S manufacturing world we live in today. How easy would it be to hit that mold-close button thinking you were hitting the mold-open button? Especially considering you might have just pressed the button to access the mold-open screen. The correct layout for both sets of buttons should mimic the movement of the mold from the operator side of the machine. Keeping a controller well organized is important: a place for everything, and everything in its place. 

STANDARDIZED LAYOUT, ICONS & TERMINOLOGY
Screen layout is important, and so are the icons that machine manufacturers use. It’s hard to understand why we don’t have a stan- dard layout, icons, and terminology for basic functions of an injection molding machine. It has been 144 years since John Wesley Hyatt invented the first injection molding machine in 1872, and we still can’t agree on how to label fill time.

That’s not the only term without a consensus. If you look at four different machine manufacturers, you’re going to find four different terms to describe ejectors, fill time, fill speed, cushion, decompression, screw rotation, and so on. Those of us that have been in the industry long enough are more than likely familiar with most of these, but even today I discover new ways machine manufacturers label the basic functions and outputs of an injection machine. How much time and money would the industry save us all if standards were required from machine manufacturers for the basic functions of the machines we run? In an industry where the tooling costs can often reach hundreds of thousands of dollars, standardization could represent a significant savings or cost avoidance. A technician simply confusing an icon or the order of its placement could be catastrophic to a program and your customers.

Once again, this does not hinder the machine manufacturers from standing out and offering options that other machine manufacturers don’t have. It just provides the end user with a consistent platform that would reduce the learning curve on new equipment. It would also ensure that updates or upgrades to controllers retain the standard as well.

Maybe machinery manufacturers are avoiding standards in an attempt to lock a customer into using their equipment to save training time. But machine manufacturers need to stand out from competitors on the basis of their machine performance and customer service. They should set themselves apart with their will- ingness to stay competitive via new technologies, repeatability, and economy. It should not be dependent on the time it will take to train your staff to use their controls.

Remember—our job as processers is to reduce the effects of variation on our process. Variation comes from all angles of an injection molding process: the material, the mold, the machine, and the processor. Standardized machine controls would be one way to reduce the effects of human error and variation coming from the processors themselves.

ANOTHER THING: INJECTION STAGES
For the last several years, machine manufacturers have been touting the number of injection or hold stages they offer. One manufacturer offers the option to set 10 stages, and the next manufacturer outdoes them with 12. I am not going to argue whether or not we should ever be using a 12-stage injection profile; I am just going to ask that the machine manufacturers give me the option to set one stage.

You can offer 12, that’s fine, but let me be able to select a single stage. One through 12 should be my options, not two through 12. It seems like a simple thing, but trust me, requiring two stages can increase the risk of a technician making a mistake. If I need to change my fill time from 2.0 to 1.95 seconds to better center it within my upper and lower control limits, I have to change two setpoints on my machine, rather than one. So in order for me to use a single stage of injection, I have to set two setpoints at the exact same number. I don’t care if you want to “upgrade” to 50 stages, allow the molder to set them from one through 50. 

ABOUT THE AUTHOR: Robert P. Gattshall is currently engineering manager at the Richmond, Mo., Adhesive Technologies operation of German conglomerate Henkel AG. He has worked 20 years in automotive and medical injection molding, including 17 years in process engineering and process development. Certified in John Bozzelli’s Scientific Injection Molding, Gattshall has developed more than 1000 processes using its principles. Contact: 262-909-5648; rgattshall@gmail.com. 

Know Your Mold-Building Terminology

By: Robert Beard, P.E., Honored Fellow SPE 12. August 2013 21:53

For many years I held a seminar called Purchasing & Quoting of Plastic Parts aimed at OEM purchasing and molding personnel.  Attendance has waned during the recession, but the need for knowledge is still there, especially where conformal-cooled molds are concerned. 

I have seen many purchase orders over the years worded only  “Build a 4-cavity mold to produce ABC,” and nothing else. So it continues with conformal-cooled molds:  “Build a 4 cavity conformal cooled mold to produce ABC”.  People who purchase conformal-cooled molds need to understand the technology so that they know how to specify a conformal-mold in a P.O.

So what questions should OEMS or injection molders be asking their moldmaker? My list:

1. Who is designing the mold?  

2. What analyses will be done?  (You’re paying for these; put it in the P.O.)

3. How much experience do they have with each of the software packages?

4. Who is building the conformal inserts and what are they responsible for?

5. Who has the responsibility for the whole mold?

You have to have an understanding of the technology in order to write a good P.O., whether you are an OEM or a molder.

About the Author

Robert A. Beard is president of Robert A. Beard & Associates, Inc. which was formed in 1984. He has more than 40 years of experience in plastics. He presents seminars nationally and internationally entitled: Purchasing & Quoting of Plastic Parts, and Virtual Workshop On Trouble Shooting The Injection Molding Process. He has been elected to the prestigious grade of Fellow and is a Honored Service Member in the Society of Plastics Engineers, and has served as the Chairman of the Fellows Selection Committee. Contact: (262) 658-1778; email: rabeard@plastic-solvers.com; website: plastic-solvers.com

Busting the Conformal Cooling Myths

By: Robert Beard, P.E., Honored Fellow SPE 8. August 2013 16:43

Conformal cooling is opening up new ways of doing things with new tools to solve problems. As cooling lines get smaller and closer to the core and cavity wall, and take a torturous path through the mold, the hydraulic resistance is increasing for each channel. There is a myth, at the floor level, that if the main water inlet to the mold is connected to say a 12-port manifold, that the manifold splits the water into 12 equal parts. This is not true. Hydraulic resistance determines that. The higher the hydraulic resistance is in each channel, the less water that goes into the channel.

In a conformal mold, it is important to measure the flow rate of each cooling line and calculate the Reynolds number to see that it is above 5000 for turbulent flow. This can be done by installing a flow meter with a metering valve on each cooling line on the return manifold so that each cooling line can be manually balanced.

If we continue to do what we have always done, we deserve to get what we’ve always gotten.

For more on the myths of conformal cooling, check out an upcoming new FastTrack training program on September 4th and 5th, near Toledo, OH, sponsored by Plastic Technologies, Inc. (PTI), which will feature two modules— Conformal Cooling for Injection Molding (September 4th) and Medical Plastics Design and Processing (September 5th).

Conformal Cooling Seminar Outline


1.) Understanding heat management

2.) How resin selection affects heat management.
How resins can be modified to cycle faster.

3.) Choosing the right mold metal.

4.) Understanding how Fluid Dynamics impacts Dynamic Heat Transfer.

5.) Alternative cooling technologies to be used with conformal cooling.

6.) Conforming Cooling Technologies, including a European technology
presentation not seen in North America.

7.) Examples why Moldflow and Computational Fluid Dynamics (CFD) are important,
if not necessary, tools for designing conformal cooling channels

 

_______________________________________________________________________________________

About the Author

 

Robert A. Beard is president of Robert A. Beard & Associates, Inc. which was formed in 1984.  He has more than 40 years of experience in plastics. He has been president of the Chicago and Philadelphia sections of the Society of Plastics Engineers, and has served as National Councilman for the Chicago Section.  He presents seminars nationally and internationally entitled: Purchasing & Quoting of Plastic Parts, and Virtual Workshop On Trouble Shooting The Injection Molding Process.  He has been elected to the prestigious grade of Fellow and is a Honored Service Member in the Society of Plastics Engineers, and has served as the Chairman of the Fellows Selection Committee. Contact: (262) 658-1778; email: rabeard@plastic-solvers.com; website: plastic-solvers.com

Calibrate Those Instruments

By: Timothy Womer 28. June 2013 09:37

I was recently asked to visit a sheet processor to determine the cause of a major screw design problem. So, as always, I started at the beginning to gather all of the technical information to determine the root cause. This facility had 5 large extrusion sheet lines, and they were issues with all 5 extruders.

With the extruder at room temperature, I set up three dial indicators on the discharge flange of the barrel in the X,Y and Z axis.  Then I turned on the barrel heaters to the standard zone setting to make sure that the barrel thermally expanded in the Z-axis direct as much as it should theoretically, and that the X and Y indicators move minimally.

 

The simple equation to determine the amount of expansion that a barrel should grow is:

 

ΔL=0.00000633 X ΔT X L

where:

                                             ΔL = The change in length

                                             ΔT = The change in temperature, in this case from room

                                                       temperature to the barrel zone setting

                                                     

                                               L =  The heated length of the barrel

 

Amazingly the barrel grew within about  0.030-in. of the theoretical change in length, which in this case was approximately 0.750 in.

 

Then I measured the flight OD on several of the screws for various designs to determine if there was a consistent wear pattern. There was, so that was noted.

 

Then I gathered all of the process data.  This is a very important part of doing a “CSI” on screws.  This is where you collect the given throughput rate at a given screw speed against the headpressure during that timed rate check, motor load and melt temperature.

 

The motor load reading is taken from ammeter on the control panel; the screw speed is taken from the tachometer.  If at all possible, it is best to have the customer’s plant manager to check the motor load with a hand held meter to verify that the ammeter on the control panel is reading correctly.  As for checking the screw speed, this typically can be done by using a stop watch and counting the rotation of the drive quill at the back of the gearbox.

 

In this case the control panel ammeter was reading correctly, but the screw speed was not.  The customer’s setup sheet showed that their standard setup was to have the extruder operating at 70 rpm, but when I counted the revolutions of the drive quill, I was getting 92 rpm.  This is an error of 24%! 

 

I then checked the tachometer on the line next to the one that I was gathering the process data from and the tachometer on it read 86 rpm but when I did the count, it was only rotating at 70 rpm. This meter was mis-calibrated by 23%!!!

 

So, the moral of the story is, the only thing worse than no data is BAD data.  In this case, the customer immediately had their maintenance people re-calibrate all of their control instruments.

 

NOTE: Sometimes the screw rotation is faster than what a person is able to visually observe. In these cases, I take the advice given to me when I was a kid by an old mechanic mentor of mine (who only had a 4th grade education)...I  “count the clicks.” I had no idea what he meant until he showed me.

Howard took this machinist scale (a pencil or pen will work) and turned on the chuck of the engine lathe in his shop, then took the scale and let it rub against the chuck. On an extruder it can be a small bolt in the back of the rotating drive quill or the drive key on the shank of the screw.  Then with your stopwatch in one hand the “clicker” in the other, you can count the number of times that bolt or key hits the end of the scale, pencil or pen...or the number of clicks.  “Count the clicks.”  Very simple but very effective.

 

Just make sure that your instruments are calibrated on a regular bases and also do a check and balance when gathering data.  Never trust what you think  you see the first time.

__________________________________________________________________________________


Tim Womer is a recognized authority in plastics processing and machinery with a career spanning more than 35 years. He has designed thousands of screws for all types of single-screw plasticating. He now runs his own consulting company, TWWomer & Associates LLC. Contact: (724) 355-3311; tim@twwomer.com; twwomer.com
 

Overhung Loads

By: Timothy Womer 10. June 2013 11:06

Recently a processor installed a new screw into its 6-in., 32:1 L/D extruder. Within a few weeks the hard facing that had been welded on the flight OD started to pop off. The flight failure was in an isolated area, so it was then assumed it was due to a poor weld bond. The screw was ultrasonically inspected and the remaining flights showed good bore, but the entire screw had to be rebuilt.
 
Within about 4 weeks after it was returned, the customer called and said that the flights had failed again in the same area, which was located about in the middle of the screw and within about a 12-in. length. The screw was returned to the manufacturer and repaired a second time, sent back to the customer and reinstalled.
 
Once again, in about another 4-5 weeks the customer called again to say the screw had been pulled and yet again the flights had failed in the same exact location. This was unbelievable! 
 
After much research and review of the screw design, it was considered that there was something wrong with the extruder—and not the screw—and most likely the problem  was due to thermal expansion.
 
It was time to make a plant visit.  The first thing I noticed was that the 900-lb, 6-in. screen changer—located approximately 36 in. in front of the front barrel support— had no support under it, causing a cantilevered overhung load.
 
So to determine if the barrel was expanding properly, the die and adapter were disconnected from the extruder. Then, three dial indicators were mounted so that they contacted with the screen changer. The indicators were mounted independent to the extruder at 12 o’clock, 3 o’clock, and also on the face of the extruder, so that the movement could be measured in the X, Y and Z axis. The die and cart had been pushed up close to the screen changer so that it could be used as the independent support for the indicators.
 
Also, a dial indicator was mounted independently near the middle of the barrel between the front barrel support and the face of the feed throat housing, at the 12 o’clock position. This was done to observe if the barrel would bow upwards, which be an indication that the barrel was not thermally expanding forward properly.
 
Calculations were made to determine the theoretical amount of thermal expansion that should be expected when the barrel zones were set at the processing temperatures of the extruder. The expected expansion was to be approximately 0.434 in. at an average barrel temperature of 410°F. Once all of the indicators had been properly “zeroed” on the “cold” extruder, the barrel zones were turned on and allowed to heat up.
 
Within an hour, the barrel only expanded forward approximately 0.400-in., but the screen changer had dropped 0.045-in. and the middle of the barrel had lifted 0.032-in. for a total deflection of 0.077 in. Also, it was evident and measured that the barrel had only moved forward at the front barrel support a distance of 0.253 in.
 
From all this it was concluded that the overhung load from the screen changer was causing a bind in the area of the front barrel support and not allowing for smooth and uniform expansion of the barrel in the axial direction. 
 
A support for the screen changer was fabricated and installed to eliminate the overhung load. Also, it confirmed by a major screen changer manufacturer that they recommend a screen changer cart for all screen changers 6-in. diameter and larger. and even for smaller extruders also.
 
Lesson learned: Excessive overhung loads and non-uniform thermal expansion will cause premature screw and barrel wear.
 
___________________________________________________________________________________
 
Tim Womer is a recognized authority in plastics processing and machinery with a career spanning more than 35 years. He has designed thousands of screws for all types of single-screw plasticating. He now runs his own consulting company, TWWomer & Associates LLC. Contact: (724) 355-3311; tim@twwomer.com; twwomer.com




« Prev | | Next »

RSS RSS  |  Atom Atom


All rights reserved. Copyright © Gardner Business Media, Inc. 2016 Cincinnati, Ohio 45244