Scientific Micro Injection Molding: Is It Possible?
Written by Brent BorgersonIn my previous micromolding blog , entitled “Micro Molds, One Key to Success as a Micromolder, I mentioned “Scientific Molding,” a methodology that is also sometimes referred to as “systematic molding” or “scientific processing.” Many molders who still harken back to the early days, when injection molding was more art than science, think it is impossible to scientifically micromold.
The chief reason for this thinking is the overwhelming popularity of Decoupled MoldingSM, a method first popularized by RJG Inc. founder, Rod Groleau. This technique, which has since evolved into three distinct types, has been a major influence in the application of scientific principles to the process of injection molding.
Decoupled MoldingSM (and other “scientific methods”) breaks the molding process down into specific fill, pack and hold portions. A key principle is how the injection of the melt is separated into fill (1st stage injection) and pack (2nd stage injection) portions of the stroke. In later versions of the method, the injection portion of the cycle is divided even further. But a major tenet of all these scientific methods is transferring the fill at about 95% of a volumetrically filled part. It is this premise which leads many molders to believe they cannot apply these methods to the molding of micro parts, many of which cannot be seen without the aid of a microscope.
Scientific Molding is much more than just separation of the injection phase though; it is all the steps taken when molding a part with best end properties, using a robust and repeatable process. These steps rely on the following prerequisites:
· A properly designed and constructed mold.
Without a robust mold, a robust process is next to impossible.
· A properly selected, sized and maintained molding press.
If the mold is great but the machine poor, you get a poor process. Barrel size must not be too small or too big for the intended shot size, and the press must possess abundant injection pressure to avoid a possible pressure limited condition.
· Carefully chosen and handled resin .
Handling includes properly drying (neither over- nor under-drying the resin) and researching the resin to be used.
· Molding the resin at the correct parameters.
Do your research, and set the mold as well as the melt temps correctly. It is usually best to begin mid-range, but much depends on the part geometry and wall thicknesses. Also use suggested pressures and speeds. This includes screw rotation speeds and back pressures.
Once the above prerequisites have been met, the initial sampling of the micro tool is done. And if the mold functions properly and produces visually acceptable parts, the optimization and validation of the scientific molding process is performed. This is usually comprised of of 6 steps: [i]
1. Viscosity study (or melt rheology study):
Usually cannot be done with micro parts.
2. Cavity balance:
This can be done on a multi-cavity micro mold.
3. Pressure drop study
This usually cannot be done completely on a micro mold, but watch your injection pressure so that you are not nearing the maximum.
4. Process window:
This study can and should be done for micro parts. Both the aesthetic and dimensional portions should be done. The result is also known as the MAD or Molding Area Diagram, and it illustrates how robust the process is.
5. Gate Seal (freeze):
On a micro part, this can be a bit hard to do and requires a very accurate gram scale (which is a prerequisite in micromolding.) Remember that you pay a lot for each place to the right of the decimal. If you have a lost weight moisture analyzer, remember that it has a super sensitive scale.
6. Cooling Study:
Many times in molding, the sprue / runner set up determines the cycle time. Nowhere is this more evident than in micromolding. Chances are the parts will have achieved optimum ejection temperature long before the sprue/runner will. Of course, in the case of a hot sprue/runner, a molder can do the cooling study.
At Matrix Tooling, Inc. /Matrix Plastic Products, we don’t accept that scientific molding cannot be applied to micromolded thermoplastic parts. In fact, we apply these proven techniques to develop robust processes every day, regardless of whether we are running large parts, small parts, or micro molded parts.
I’d like to thank my friend, Suhas Kulkkarni, Molding and DOE expert, author, teacher, consultant and Principal of FIMMTECH Inc. Suhas offered me advice and let me post questions about this topic on his Injection Molding Online forum, where other molders also offered greatly appreciated input.
Brent Borgerson
Senior Process Engineer (Older Molder)
Matrix Tooling Inc./ Matrix Plastic Products
Wood Dale IL
[i] Robust Process Development and Scientific Molding, by Suhas Kulkarni (published by Hanser) is a good reference for the details in performing the 6 step optimization process.
3D Printer Provides Multiple Benefits
Recently, Matrix purchased a 3D printer for our mold design & engineering department. One main reason we did this was to offer in-house rapid prototyping services to our customers, 70% of whom are medical device OEM’s who rely on us to help bring their cutting-edge products from concept to reality. Being able to take their data model and provide them with physical part samples they can hold in their hand is a value-added service that is especially helpful during the R&D phase of a new project.
The majority of our work is in developing and producing complex components, so we needed a unit that would be capable of printing the high-quality, finely detailed models we work with every day. We selected the Objet30 which features a range of 5 printing materials, varying in physical and mechanical properties (strength and flexibility), and available in a choice of 4 colors. With this new capability, our designers can test out customers’ concepts before time and money are invested in production tooling.
But there is another significant benefit to having this additive technology under our roof.
Matrix is very fortunate to have a group of very creative people working here, in many areas and levels of the company. Those people will use a tool like this to experiment and develop unique ways of making things. With their talent and this technology, the possibilities are endless and exciting!
Micro molds one key to success as a Micromolder
Written by Brent Borgerson
Matrix Plastic Products has been micromolding plastic parts since the mid-1990's, long before it was in vogue. This pusher (shown) for a micro linear cutter cartridge is .031" x .040" x .040" and weighs just .0008 grams. Most of our micro projects are for the medical industry, for minimally invasive surgical applications in particular, but we also provide micro components used in the electronics industry. Weighing just fractions of a gram, some of these parts are smaller than a pellet of resin , with tolerances of five ten thousandths of an inch (0.0127 mm) or less.
I believe one of the main reasons we are not intimidated by projects like these is that we also have Matrix Tooling, Inc. under the same roof. The close-tolerance and high precision of our molded products is rooted in our long history as a designer and builder of close-tolerance and high precision molds. Our strength in specialty tooling has proven to be a key factor in our evolution into the successful micromolder we are today.
Matrix Tooling builds most of our micro molds with cold runners and low cavitations (8 or fewer) because that combination makes it easier to maintain tight specifications. While mini hot runners are available, many of the resins we use in micromolding do not lend themselves to hot runner molding.
While almost any thermoplastic resin can be used in micromolding, Matrix Plastic Products commonly uses high-flow, high-temp grades such as LCP, PEEK and PEI. These materials have predictable shrink, and the high mold temps involved help flow, especially in very thin-walled parts. They also exhibit superior end use properties such as strength, stress crack resistance, thermal stability and dimensional stability.
Yes, much of our success in micromolding can be ascribed to our mold construction which must be tight and precise, well supported and robust. I asked Steve, one of our experienced moldmakers at Matrix Tooling (but who was new to micro moldmaking) what the key to his first successful micro mold was. “Trusting our equipment,” he replied. Matrix Tooling employs only state-of-the-art CNC moldmaking technology.
However, we also subscribe to scientific molding practices. With a part that you can barely see, it is next to impossible to fill to 95% before transferring; but many other aspects of systematic/scientific molding are rigorously applied here at Matrix. I will discuss “Scientific Micromolding” in a subsequent blog.
Matrix Plastic Products operates both hydraulic and electric presses in the smaller size ranges, and it is essential that the molding machine be sized according to the job at hand. But for micromolding, we prefer the electric machines with their inherent precision and repeatability.
On jobs where the actual finished part is barely much more than an add-on to the sprue and runner, not only is the tooling critical, but the Quality Assurance can also be very demanding. Here again, Matrix meets the challenge with such equipment as OGP vision systems, Vision Engineering video microscopes, and a CGI cross-sectional scanner for First Article inspections. Microscopes are a common sight at Matrix: not only in QA, but in the molding, clean room and tooling areas as well!
We don’t “sweat the small stuff.” Matrix Tooling, Inc. and Matrix Plastic Products has the equipment, know-how and experience to successfully handle any micromolded project. We’re always happy to offer our insight into yours.
Brent Borgerson
Senior Process Engineer (Older Molder)
Matrix Plastic Products
Wood Dale, IL
In addition to building injection molds for medical applications, Matrix specializes in injection molding with a wide range of medical grade polymers. Among these materials are bioabsorbable resins for surgical implants which we process in our ISO -8 / Class 100,000 cleanroom. Examples include PLA, PLG, PLC, PDO, PDLG, and PG. These dissolving resins have very unique (and sometimes challenging) requirements, and several years of experience have taught us how to process them successfully. These bioabsorbable materials represent the majority of our cleanroom production at Matrix.
Recently we were awarded a medical program that involved processing an implantable-grade PEEK polymer . Due to its high-strength, biocompatibility, and high temperature & chemical resistance, PEEK is being specified for an increasing variety of long-term implantable medical device applications. While Matrix has been building PEEK tooling and molding PEEK in production for many years, this was the first time we would be processing PEEK in our cleanroom.
Over the years, we have designed our PEEK tooling to utilize either hot oil circulation or electric cartridge heat. In our experience we have found that hot oil provides more consistent heating than electric heaters; and while some PEEK parts can be processed using either heat source, many critical parts definitely require hot oil. In the past, we always had the flexibility to pick and choose where to run these jobs: on our main floor or in the cleanroom. Now, however, we had an implant that, due to customer requirements, had to be processed in the cleanroom. At the same time, it required hot oil heating. We had a dilemma: “how do we use hot oil in our cleanroom?”
Those responsible for overseeing our cleanroom operations would not consider using oil in the room, so we began our search for temperature control alternatives. The solution was the purchase of a Single Temperature Controls high-pressure hot water thermolator capable of reaching 430° F. We're in the process of making a few design tweaks to strengthen the final part which is still being qualified, but the thermolator has been tested several times in samplings and we are prepared for the production phase of this project.
As an “Older Molder,” I recall the days of frugality when anything that could be cleaned and/or sterilized, from soda bottles to surgical implements, was re-used. About the only “disposable” medical devices were bandages, Q-Tips and tongue depressors. Of course, health & safety regulations have increased dramatically since then. With infection control a top priority, and given the high cost of labor to disinfect and re-sterilize medical devices, many more are now designed for “single-use.”
Matrix Tooling, Inc. and Matrix Plastic Products has extensive processing experience with the broad range of materials, from commodity to engineering grades, which are used to produce medical disposables.
Commodity Resin Applications: Items previously made of glass and steel are now injection molded using inexpensive commodity resins such as polystyrene, polypropylene, and polyethylene. Examples include Petri dishes, pipettes, test tubes, beakers, centrifuge containers, vials, thermometer probes, IV and other tubing connectors and, yes, the ubiquitous bed pans and tongue depressors. Although they are produced from relatively low-cost resins, they are produced in huge volumes. Designing them to be as thin-walled as possible allows for shorter cycle times and ultimately lower overall costs.
Matrix produces a variety of thin-walled devices, such as sharps containers,
syringes and mouth guards, from commodity resins.
The equipment used to produce these parts is much like that used to mold thin-walled packaging: presses (hydraulic or electric) with thick robust platens, rapid injection rates, high available injection pressures, and precise controls. Toggle machines are favored for deep drawn parts due to higher available clamp opening pressure. High water flow is required, especially when using polyolefin resins. Large horsepower water temperature control pumps and large coolant lines, both to and in the molds, are required. Turbulent coolant flow is essential to the quality, as well as the economical production, of these parts.
Engineering Resin Applications: While commodity resins often make up the largest volume of a medical molder’s physical output, engineering resins can easily make up a majority of the molder’s product value output.
Various factors including strength, temperature, chemical resistance and initial sterilization requirements determine the need to use an engineering grade. For example, devices requiring intense initial sterilization (via such methods as autoclave, chemical, Ethylene Oxide (ETO or EO), and gamma ray or electron beam radiation) require a specialty grade resin that can withstand the sterilization process.
Engineering materials such as PEEK , Polycarbonate, Nylon, PEI, and LCP - in both filled and non-filled varieties - can be quite expensive. Matrix works hard to mitigate these costs by consistently maintaining a scrap rate well below 1% through efficient mold design and, of course, efficient processing.
This multi-component surgical device, tooled & molded by Matrix, features GF nylon and PC.
Matrix has produced a variety of surgical stapler cartridges using LCP.
Brent Borgerson
Senior Process Engineer (Older Molder)
Matrix Tooling Inc. /Matrix Plastic Products
Problem Solving in Injection Molding - Part 3
Written by Brent Borgerson
In my previous post on structured problem solving, I discussed the “5 Whys” technique. Although it is a very useful method, it can potentially lead you astray as a problem becomes increasingly complex and an intuitive answer (often guided by experience) is not apparent.
In these cases, it may be more beneficial to use a Cause and Effect, or Ishikawa Fishbone Diagram. Karou Ishikawa (1915-1990) was a Japanese industrialist and statistician, whom we will meet again later when discussing other problem solving tools. He was a contemporary and disciple of Dr. Deming (1900-1993.) He also shared great friendships with other North American quality notables such as Joseph Juran (1904-2008.)
A Fishbone Diagram can help us to identify possible root causes, sort and relate possible root cause interactions, and present them in an organized manner. It works under the premise that all problems can be attributed to one of the following six causitive factors (or to a combination of these factors):
Manpower
Methods
Materials
Machinery
Measurements
Environment
Originally, only the first five factors were considered and were called the “Five Ms”, but environment was soon added to the list. Many variations of this “5 Ms and an E” list exist, including: 8 Ps, 8 Ms and 4 Ss. At the top of article is an example of a Fishbone Diagram using a short shot /small dimensional reject as the problem:
The above is a simplified Fishbone Diagram, but it shows how the main causes and subsequent sub-causes lead to the effect: in this case, a rejected shipment due to short shots and dimensionally small parts. This is why it is also known as a Cause and Effect Diagram. It is a visual analytical tool that is especially useful to the injection molder in solving complicated problems.
Brainstorming, the technique we used out on the floor to quickly and informally solve molding problems, is also key when constructing a Fishbone Diagram. Cross-functional problem solvers representing tooling, design, quality, maintenance, and molding gather around the conference table. Everybody offers their ideas, and if the group agrees that they are valid, the ideas are posted as “bones” or spines on the diagram as possible causes or factors. Later, the group decides which causes are critical factors and which are minor. In the above diagram, they may decide that a cold molding room is a minor factor not worthy of further investigation.
There are 3 main rules for Brainstorming:
Everybody contributes ideas.
There are no “crazy” ideas; even those that are seemingly “off-the-wall” can lead to other relevant concepts.
Do not criticize others’ ideas or get personal. This is the quickest way to shut off the flow of creativity and bring the brainstorming session to a screeching halt. The idea is to generate as many ideas as possible to write on the board and then to decide which ones to include on the Fishbone Diagram.
In subsequent blogs, I will examine other structured problem solving methods that should be in every molder’s toolbox.
Brent Borgerson
Senior Process Engineer (Older Molder)
Matrix Tooling Inc. /Matrix Plastic Products
Problem Solving in Injection Molding - Part 2
Written by Brent BorgersonStructured or Formal Problem Solving
There are times when informal or experienced-based problem solving alone may prove inadequate, a “band-aid” approach to a more complicated issue. Informal solutions that ignore the root cause of the problem are not likely to prevent it from rearing its ugly head again later.
Structured or formal problem solving methods and tools allow us to get to the root cause of the problem and solve it permanently. The myriad of analytical tools and structured methods available can befuddle even a trained statistician. A structured problem solving method can enable a molder to choose which problem solving tools best apply to a particular project. Many structured problem solving tools are also process improving tools. (I have always considered process improvement to be problem solving on a grander scale, but I will examine process improvement tools more specifically in a future blog entry.)
Almost all structured problem solving methods hark back to Drs. Deming’s and Shewhart’s PDCA (Plan – Do – Check – Act) Cycle, which can be traced back further to early 1600’s England and Francis Bacon’s Scientific Method. Today’s DMAIC (Define, Measure, Analyze, Improve, Control) from Six Sigma, and the various numbered (5-, 6- 7-) step methods of problem solving, all stem from Deming’s and Shewhart’s methods.
Before a problem can be solved, we must define and get to the root cause of the problem. A technique called The 5 Whys can be used. This technique was gleaned from the 1970’s Toyota Production System (TPS), and can be useful for quickly getting to the root of a problem.
For example, assume that a late delivery on a project has resulted in an unhappy customer.
Apply the 5 Why method:
1. Why is the customer unhappy? = Because the project didn’t get delivered as promised.
2. Why didn’t project get delivered as promised? = Because the job took longer than anticipated.
3. Why did it take longer than anticipated? = Because the complexity of project was underestimated.
4. Why was the complexity of the project underestimated? = Because we made a rough estimate, ignoring the complexity of separate stages of the project.
5. Why did we do this? = Because we were running late on other projects.
It is now apparent that we need to revise our time estimation methods.
We can also apply The 5 Whys to a more typical molding problem; say a reject from a good customer:
1. Why did the customer reject the shipment? = Because of short shots and small dimensions.
2. Why did we get small parts and shorts? = Because not enough plastic got packed into the mold cavities.
3. Why didn’t enough plastic get packed into the cavities? = Because the molding machine wasn’t capable of doing this.
4. Why wasn’t the machine capable of doing this? = Because the melt index of the resin lot in question was too low and the machine became pressure limited.
5. Why didn’t we know this? = Because we didn’t do incoming resin inspection and/or set process alarms on the molding machine.
Conclusion: We clearly need to revamp our incoming resin inspection procedures and assure that our process/machine is robust enough to avoid this mistake in the future.
(To be continued next month)
Brent Borgerson
Senior Process Engineer (Older Molder)
Matrix Tooling Inc. /Matrix Plastic Products
For anyone in manufacturing today, we have had the luxury of being handed a rich tradition in how to make things. For over 125-years, the United States has honed its skills as a manufacturing destination for making products sold world wide. Add in the knowledge gained by being thrown into two World Wars, where many businesses were asked to support the military effort. These wars required a rapid response and high volume production from our existing manufacturing plants, it was truly a national effort to support our military.
Today, we are faced with global competition that has a younger work force, one willing to work at greatly lower wages, and they are using the same equipment and software that we use. While this seems to be a competitive threat that would be tough to beat, we have one huge advantage over them. Our legacy of making world class products here is something significant, and not to be squandered. Much of China's manufacturing base in high end products is less than twenty years old. Having the latest and greatest equipment gets you just so far. The ability to win an endurance race such as the Indy 500 is more about the best and brightest technicians building an engine that not only performs well, but does it under the most grueling circumstances. While a stock engine might make it thru the race, someone committed to winning will only accept the best. And the fact remains that the best tooling comes from countries with long traditions of making things. Not the most populous regions with large groups of young people using the latest technology.
We have a duty to continue the legacy of manufacturing that was handed to us. What was passed on to us must be passed on to the next generation. We absolutely must invest in our youth, in our infrastructure and equipment. If not, the one huge advantage we currently enjoy will be gone. And once it's gone, playing catch up will be tougher than anything we've faced in the way of competition thus far.
Injection molding frequently involves problem solving. Many of the problems regularly faced by a molder are quality related problems including: short shots, flash , dimensional issues, warp, and cosmetic concerns. The molder is also frequently confronted with the need to reduce cycle times and/or increase yields.
Most problem solving in injection molding falls into two broad categories: structured (formal) and unstructured (informal). In a series of blog entries, we will discuss various problem solving tools used in injection molding.
First, let’s examine unstructured/informal problem solving.
Experience
The majority of everyday problem solving in molding relies heavily on experience as the problem solving tool. A good portion of this is the experience of the individual molder. There is an old molding tale that tells of “The World’s Greatest Molder” being interviewed for a trade journal. He was asked what the key to his success as a molder was. Being a man of few words, he replied, “Not making mistakes.” He was then asked how he avoided making mistakes. He answered, “Experience.” He was further interrogated as to how he obtained experience. “Making mistakes,” he replied.
Yes, one of the most often used problem solving tools in injection molding is based upon making mistakes… but learning from those mistakes!
The cumulative experience of a truly cross-functional team is powerful as both an informal and formal problem solving tool. When tackling a complex molding problem, it is a good practice to involve personnel from molding, tooling, design, and quality. This can be done in an informal shop floor setting or in a conference room. A group of technical people getting together to share their experiences in solving a problem is a technique called “brainstorming” which leads into our next blog discussion of structured or formal problem solving tools.
Written by:
Brent Borgerson
Senior Process Engineer (Older Molder)
Matrix Tooling Inc. /Matrix Plastic Products
Can Corrosion in a Mold Cavity be Transferred to a Molded Part?
Written by Paul ZiegenhornAs an ISO 13485 certified manufacturer, managing risk is always a priority. And the most basic concept of that management process is first understanding what those risks are.
Recently, the question was raised: "Can any trace mold corrosion be transferred to the final molded product?" This opened a spirited discussion because, while we've been building injection molds for over thirty years, nobody here had a definitive answer.
After consulting with others in the industry, as well as a metallurgist at our steel supplier, we came to the conclusion that while it's theoretically possible to transfer any contaminant from one surface to another, having a problem with bio-burden testing or introducing a contaminant into a product during plastic injection molding production is highly unlikely.
We are involved in a program that overmolds stainless steel with plastic. A stamped steel piece and a metal injected piece are both loaded into a tool steel mold, then overmolded with a high temperature nylon. The stamped piece is passivated; the MIM piece is as-molded and sintered. In speaking with our metallurgist, we learned that the main sources of corrosion on the mold cavities would be degraded resin coupled with high mold temperatures. Fortunately, as we are the molder on this program, we have control over both of these issues. Our processing and mold temperatures are both within manufacturers' specifications, so that helps control a major source of any corrosion. The metallurgist also explained that any corrosion sufficient enough to create a transfer problem would be visible to the naked eye.
The material we chose for this program was a high hardness, general purpose tool steel. We did this due to the fact that two metal inserts are being inserted into the mold cavity for overmolding . There are other grades with similar hardness and stainless properties available, but based on what we learned we do not feel it is necessary to change steel grades at this time. However, we have decided to add a visual check to our regular preventive maintenance plan for this job, a solution we now feel is sufficient to catch a problem before it occurs.
