Injection Molding (12)
Topics pertaining to the process of plastic injection molding and valuable insight gained from the use of various techniques. Contributed by various employees of Matrix Tooling, Inc. & Matrix Plastic Products.
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
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
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
Service and Sales in the Injection Molding Business
Written by John KellyKnowledge of the product and process is important in any business, none more so than injection molding. The business is quite complex and a good sales or customer service person often must be able to guide a customer with little or no knowledge through the intricacies of managing the molding project.
The sales/customer service person should have knowledge not only of the quoting/costing process, but also of design, mold building and production of the molded part. He or she must either be able to answer all of the customer’s questions or know where to obtain the answers.
In addition to technical knowledge, the sales/service person must be patient and understanding, as often a customer, especially one who is under pressure can be very nervous, even “cranky.” Here the sales/service person acts as a counselor and a buffer for not only the customer, but also for the molding company.
The sales/customer service person is a person of many talents and is key for the success of not only the injection molding company but for the customer’s success as well.
At Matrix Tooling, we design and build injection molds for a wide variety of advanced materials and processes, including metal injection molding (MIM.) While it is possible to build a very accurate injection mold, getting the actual molded part to meet the print specifications often requires more.
Resins with predictable shrinkage rates allow you to confidently machine details to a specific size without having to invest additional time "sneaking up" on them after processing. However, when working with MIM tools, not only are the shrinkage rates significantly higher (often representing a large percentage of the part size) but they are also less predictable. Subjecting the molded MIM pieces to the next required stage of heat treating further complicates things. Re-compounding the feedstock to adjust the "green" part is a common method used to achieve the required shrinkage and physical properties. But because each round of sampling entails the secondary processes of debinding and sintering, qualifying a MIM part can be time consuming.
While our industry's conscious efforts to reduce lead times have benefited the development of medical devices, certain parts are proving more difficult to qualify quickly. MIM parts seem to be among them. In order to address this challenge, Matrix has worked with our customers to develop "breadboard" parts: small quantities of machined finished parts, made to the database using conventional machining technologies, and made from the same raw material. This approach has numerous benefits. Since the initial test launch of a device may require as few as 3-6 units, machining breadboard parts is a more timely way to sample components that are destined to be produced using MIM. Any problems that crop up during the testing of the breadboard prototypes can be remedied prior to cutting any steel in the MIM tool, saving both time and money. Being able to prove out the concept more quickly and inexpensively with breadboard parts results in a faster release of MIM tooling for production and a smoother debugging and qualification process.
Written By:
Paul Ziegenhorn
President
My favorite part about working on R&D projects is that they tend to challenge you to think outside the box, try new things, and learn about the latest technologies. One of our recent development projects involved injection molding a long, thin-walled tube (picture a miniature drinking straw) with a wall thickness that shrinks down to .0035” over its nearly half-inch length. By comparison, that’s roughly the same thickness as a human hair. Even after running dozens of Moldflow® studies for gating locations and flow analysis, the only thing we were confident of was that it was going to be a challenge to fill the parts out completely.
After struggling on our first sampling, the instinct was to look for higher flowing materials to help make the distance more manageable. We started with a PE material with a
Melt Flow
Rating (MFR) around 50 g/10min and then moved on to a similar material with a MFR of 110. We were expecting to see a noticeable improvement in the 110, but what we found was no appreciable difference on the fill. It was determined that this was primarily due to leakage at the check ring / non-return valve, common to all traditional, reciprocating screw injection machines.
This brought us to one of the more interesting suggestions on the project. We decided to sample the tool in one of Sodick-Plustech’s (SPT) micro injection machines. This machine piqued our interests initially because of its two-stage (plunger-style) injection approach, but as we found is well-suited for this type of application for several reasons.
Like a traditional, reciprocating screw machine, Sodick’s two-stage injection technology (shown here) utilizes a small screw to melt and convey material. But unlike traditional machines the screw is not responsible for injecting plastic into the mold (or any high speed lateral movements). It feeds a second chamber, which is metered precisely, and then injected into the mold via a high-speed piston. The feed screw shuts off after material is loaded into the chamber, which eliminates back-flow without the use of a check ring / non-return valve.
On this particular machine, the piston is capable of reaching injection speeds of 450 mm/s, which isn’t particularly impressive by today’s standards. Many other press manufacturers tout injection speeds well past 1,000 mm/s. Sodick, too, offers a high-speed/high-pressure line that boasts an impressive 1,500 mm/s injection speed, but their selling point is based more on acceleration than on speed alone. The Sodick machine utilizes an accumulator that works with the main piston to reach maximum speed almost immediately upon injection.
The next selling point is the consistent shot sizes due to the tightly metered second chamber. For our application, this is critical because an inconsistent fill could cause a
short shot
, which would be nearly impossible to detect with the human eye or a vision system during production. On a project that could expand to a 16 or 32 cavity tool, this becomes increasingly critical to maintain good production parts.
Another positive about the machine is a more consistent melt and material residence time. Again, the lack of a check ring helps by allowing for a more reliable first-in/first-out material path. And since the feed screw isn’t creating excess heat via shear, the material is subject to more uniform heat profiles as it moves through the processing stages.
One last positive about the machine is the capability to swap out injection units (smaller or larger) and match them with differently-sized platen and tie bar configurations. Matrix is running quite a few bioresorbable/bioabsorbable polymers lately which require minimal shot sizes due to the extremely high material costs. However the molds associated with these projects are often complicated and require multiple side actions, slides, and/or lifters, so running them in a traditional micro-molding machine with a 4-inch max opening and similar small distances between the tie bars doesn’t always lend itself to the mold design.
Written By:
Andy Ziegenhorn
Insulated Runner Molds: Old Technology, but Not Entirely Obsolete
Written by John KellyEarly in the history of injection molding, molders realized the problems inherent in producing high volume, fast cycling parts of commodity resins with cold runners, especially in high-cavitation molds. Cold runners can stick or hang in the mold and interrupt or extend the cycle; and often the cold runner being the last part of the shot to set up, can dictate the overall cycle.
It soon became obvious that “runnerless” molding was the way to go. Early hot runners were of the internally heated (torpedo) type or the externally heated manifold hot runner. Both were prone to leakage and hard to (especially the torpedo type) change colors with. Predating these systems were a type of runnerless mold called an Insulated Runner .
Insulated Runners had an oversized internal runner cut into both the top clamp plate and the “A” plate. This runner was very thick and relied on the thickness of this runner-cull to keep the plastic in a molten state as long as the molding machine was cycling. The walls of the runner were solid with only a molten center core providing melt delivery. These led to cylindrical drops (also very thick) and generally to top-center-gated parts.
This system needed fast, uninterrupted cycles to keep the gates open and even momentary interruption caused one or more gates to freeze off.
Startup was also tricky with these molds. Methods included hand injection of multiple shots into the mold before going to auto, making one big shot and going to auto, or boosting the back pressure way up and extrusion filling the runner cull.
Later the gate drops were heated with a probe which made startup easier and also made keeping the gates open easier, even allowing a brief disruption the the cycle. With very fast cycles (3 to 6 second range) the heated probe insulated runner can have a fairly small thickness and in some cases, be reground and re-used in the product.
Though sometimes a bit tricky to startup and keep running, these systems could offer advantages over not only cold runners, but hot runners as well. These include:
- Quick cycles
- Less regrind and scrap , though the thick cull wasn’t generally used back in molding
- The tool was less expensive to build and maintain
- Less chance for melt leakage.
- Color changes were very fast compared to hot runners, as the whole colored cull was pulled after the molding machine’s barrel was cleaned. Often color changes can be preformed in 5 minutes with less than 5 pounds of scrap
- Even if heated gate drops were employed, fewer and less sophisticated controllers were needed.
Yes, the insulated runner is an old technology, but if you have a multi-cavity, fast-cycling job using a commodity resin like PP or PE with frequent color changes, and want a more economical tool that is easier to maintain, then consider insulated runner tools.
Drying engineering resins is crucial to obtaining desirable end products with these high–performance and often expensive resins. Thermoplastic resins are being called on to be as strong as metal and to survive in harsh environments. To achieve these end properties, a resin must be processed correctly, and one area of proper processing is to ensure that the resin is molded at or under the manufacturer’s specified maximum moisture content (%).
At Matrix Plastics Products, we are very careful (almost to the point of being neurotic) about our resin drying and dryness assurance procedures. We take a multi-pronged approach to these issues including some of the techniques and procedures as follows:
- • Drying Time: We follow the manufacturers’ recommendations as a minimum for drying time before beginning molding as well as residence time in the dryer. These steps are carefully documented for accountability.
- • Drying Temperature: Again, resin makers’ guidelines are strictly followed.
- • Dew Point Monitoring of the Dryer: Our dryers feature dew point monitors and alarms which are consistently observed. The dew point on a dryer is the best indication of the proper function of the dryer, which allows us to foresee many impending problems.
- • Moisture Analyzer: Our Quality Inspection lab features an OMNIMARK Mark IV moisture analyzer which can be used to test and verify results. This is the last line of defense and is used whenever there is any doubt about the dryness of a resin. In the case of sensitive jobs, moisture analyzing test are routinely used and documented.
A part molded with wet resin (moisture content above the manufacturer’s suggested max percentage) may not be a cosmetically unappealing part, but it is almost always a structurally weak part. Hydrolysis – the result of heating moist resin – produces an action in the resin that is essentially akin to thermal degradation. The molecular structure and integrity are affected, and a weak and/or brittle part is the result. Some of these problems are not always readily detectable, especially during the early life of the product, but premature and unexpected failures can result from molding with “less-than-dry” resin. We try our best to avoid this situation.
Written By:
Brent Borgerson
Senior Process Engineer (Older Molder)
Pat Collins
Molding Operations Manager
