A Look at Plastic Injection Molding in the Modern Age | Manufacturing Engineering | advancedmanufacturing.org

Contributing Editor

Five-axis machining is a critical capability for any moldmaking facility today.

Look around. Plastic clothes hangers. Disposable cutlery. Bottle caps and syringes. Red Solo cups. It’s ironic that many of the lowest cost, highest quantity and most disposed of consumer products require one of the industry’s most complex and expensive mechanical assemblies—a plastic injection mold—to produce. They’ re filled with precision-machined parts that only a master craftsperson operating advanced CNC machinery can make, often in single-digits.

One well-known example is a children’s toy invented shortly after World War II. “The molds used to make LEGOs are the most accurate in the world,” says Tom Houle, director of the LUMEX line of hybrid additive machining centers at St. Paul, Minn.-based Matsuura Machinery USA Inc., and someone with decades in the plastic injection-molding trenches.

According to the toymaker’s website, Houle is right: Injection-molded LEGO bricks boast an accuracy of 0.005 mm. As a result, one made in 1958 will mate perfectly with today’s units, just as it will with any of the hundreds of billions of bricks made in between. And, due to a tooling technique that Houle has plenty to say about—conformal cooling channels—molded bricks go from injection to pack out (molten to hard) in 10 seconds. These impressive numbers are true whether the plastic parts came from the LEGO Group’s headquarters in Denmark or one of its newer manufacturing sites in Hungary, Mexico, the Czech Republic or China.

Mentioning this last country to many in the industry raises a contentious point: Given that it’s a highly automated process and labor costs shouldn’t be a concern—particularly at these volumes—why is so much of it performed outside of the United States? After all, America is the birthplace of plastics, including the acrylonitrile butadiene styrene (ABS) from which LEGO bricks are made, as well as the extrusion screw machine that helped this toymaker and countless other manufacturers become so successful. So what happened?

This isn’t a dig against LEGO. Far from it. The brand has a well-earned reputation for making kids smile—the author, his children and grandchildren among them. Who cares where those iconic plastic playthings were produced? Nor is it meant to criticize the many companies that made what must have been a difficult decision to pull up stakes and move their manufacturing operations to countries with lower labor costs and fewer regulations, especially in light of the favorable trade agreements constructed during the Bush and Clinton years. That’s all water under the bridge, right?

Maybe so, but as with so many other aspects of manufacturing, the proverbial chickens have since come home to roost. “I’m 43 years old, and it seems like everyone I work with is near retirement age, with no younger workers coming to take their place. Because of this, I’m fearful that within the next decade, everyone will be asking the same question: where the hell can I find an American-made mold?”

This sad statement comes from a business development manager with a Midwestern automotive supplier, one that decided to offshore its toolmaking operations to Asia more than two decades ago. The fortysomething (who has since left the company) was quick to add that there are some great mold-and-die shops in the U.S., Canada and Mexico, but they’re finding it increasingly difficult to compete with the large offshore conglomerates that employ hundreds or perhaps thousands of skilled workers, entire teams of mold engineers, and every software design and simulation tool imaginable. “The Chinese have gotten very good at it, and have greater resources besides.”

As suggested earlier, offshore manufacturers also have strong support in the form of lax workplace and environmental regulations, together with generous government subsidies. For instance, the Kiel Institute for the World Economy states in a recent report that “China’s overall subsidies range between three to nine times that of other OECD countries such as the USA or Germany.”

And a 2023 press release from the National Association of Manufacturers (NAM) noted that federal regulations cost the manufacturing sector about $350 billion a year, an amount equal to 12% of our gross domestic product. “Unbalanced federal regulations make it challenging to grow manufacturing in America by siphoning resources away from job creation and our communities,” adds NAM president and CEO Jay Timmons.

The Trump administration attempted to offset some of this imbalance with 25% tariffs on Chinese-made molds, a policy President Biden retained and that the American Mold Builders Association heartily supports. The organization announced earlier this year that “the Section 301 trade action is a significant tool to ensure that the U.S. mold-manufacturing industry remains healthy and globally competitive,” and by increasing the tariff, “American mold builders can continue to provide thousands of jobs across this country – supplying plastic injection molds for decades to come.”

And yet, tariffs are only a partial, temporary fix. Setting aside the discussion of who actually pays the cost delta (the consumer), eventually another administration comes along and changes trade policies, or the offshore moldmaker decides to set up shop in a tariff-free country, thereby avoiding the penalty altogether. The best solution is for domestic moldmakers (and, for that matter, any other manufacturing sector) is to adopt the U.S. Army slogan and “be all that you can be.”

One way to begin is with vertical integration, notes Matsuura’s Houle. “When I started in the business, every plastic injection molder had a tool shop and most of them made their own molds—in other words, they were responsible for the final product and the tooling needed to make it. Over time, though, many of these companies began to cut expenses by divesting themselves of their moldmaking capabilities, relying instead on external providers for build and repair.”

This divestiture created a disconnect, Houle asserts, explaining that the buyers procuring the molds gradually became more concerned with price instead of mold performance, which helped to further open the door to offshore moldmaking. It also led to the current workforce situation: Most of the country’s moldmakers today have gray hair and are thinking about what fishing boat or motorcycle they’re going to buy after retirement. Again, there aren’t nearly enough in the pipeline to replace them.

Another hit to the domestic moldmaking industry came from an unlikely direction: electronics.

“To me, that was really the impetus behind the molding industry moving to China,” Houle laments. “The tooling needed to make consumer electronics is such a small percentage of the sales revenue that offshore manufacturers will often provide dies and molds for free just to gain market share. If we start building circuit boards here in the U.S. again, the domestic molding industry will have a much stronger position.”

That brings us back to the LEGO block and its 10-second cycle time. Without vertical integration, a moldmaker might say to its customer, “Hey, we have this new technology called conformal cooling. It’s going to make better parts more quickly and save you thousands and thousands of dollars in molding costs, but the mold will cost 50% more to make.” Unless the company measures itself on product quality, manufacturing efficiency and total cost of ownership—in that order—the response will likely be “Thanks, but no thanks.”

However, the plastic-injection-molding industry is coming full circle as more and more large contract houses take complete control of the molding process, Houle notes, from part design and simulation all the way through to packaging and validation of the final product.

In some cases, OEMs will acquire small mold shops they once relied on; in others, they’ll establish strong partnerships with these firms. Either way, there’s more money available to invest in automation and the development of lights-out manufacturing capabilities, not to mention another great equalizer: the metal-3D printing that makes conformal cooling possible.

“Before starting at Matsuura, I worked on a project with a manufacturing director of a large medical company who had the foresight to invest in a conformally cooled mold,” Houle says. “It saved the company over $5 million. Unfortunately, I would estimate that fewer than 10% of injection molders recognize the benefits.”

Makino Corp. doesn’t make metal 3D printers, but the Mason, Ohio-based CNC machine builder does have a very strong following among toolmakers. Senior Applications Engineer Michael Fecteau works out of the company’s Die/Mold Technology Center in Auburn Hills, Mich., and echoes what others have said.

“Offshore suppliers have really stepped up their game,” Fecteau attests. “For decades, shops in this area were making a lot of money reworking molds purchased from Asia. Not anymore. We’re seeing OEMs in the U.S. and Canada purchasing these overseas manufacturing companies, sometimes for tax breaks but also as an extension or replacement of their domestic capabilities. As a result, the reshoring trend that was going strong for quite a while has largely dried up as China’s quality improves and they keep their prices down to the point that it’s quite challenging for shops in North America to compete.”

Even with tariffs, offshore molds are generally less expensive than the domestic equivalent, notes Sean Shafer, Makino’s segment manager for the die and mold market. “Customers in the Windsor (Ontario) area have told us they’re able to procure completed inserts and other mold components from China for less than the cost of the raw material in Canada.”

So what’s the solution? Given the ongoing labor shortage everywhere in manufacturing, it’s a word you’ve likely heard a great deal lately—automation. But as Fecteau explains, this isn’t as simple as placing a robotic arm in front of a five-axis machining center or investing in one of Makino’s linear pallet pools (although that’s some of it). The automation he’s referring to is software-based, and it’s still very much in its infancy.

“Moldmaking is low quantity work, so if you want to automate it, you have to keep the machines continuously fed with reliable, efficient NC programs that will run without any issues,” Fecteau says. “The tricky part for most shops is gaining enough confidence in the cutting conditions and the machine setup to program a job, send it off to the cell controller and know that you won’t break a tool or scrap an expensive mold component. There are many variables involved, and the majority of moldmakers haven’t dialed in their processes to the point that they can machine the hardened steel parts used here without human interaction on the shop floor.”

It’s fair to make a similar statement about the aerospace and medical industries, both of which machine difficult materials to tight tolerances. In each case, Makino addresses concerns over unattended operation in several ways. “The first step is to generate accurate toolpaths from the CAM system,” Fecteau says. “Once these toolpaths are verified and post-processed, we utilize tools in (CGTech Inc.’s) VERICUT to confirm there are no collisions and for further optimization of the G-code. Once on the machine we use a Makino tool—Collision Safe Guard—to confirm there won’t be any collisions while the machine is running. This three-step process allows the customer to run unattended with confidence.”

But the manufacturing industry also has a pernicious skills gap, and, here again, it extends beyond mold and die to aerospace, medical and elsewhere. As many have found out the hard way, any attempt at automation will not be successful without robust, predictable processes and—perhaps most importantly—skilled workers.

The answer, of course, is training. “We offer a high-performance machining class in our Auburn Hills facility, where we go through everything needed to create predictable cutting processes,” Shafer says. “This includes the basics like toolholder, cutting tool and feed and speed selection, as well as topics like tool life monitoring and advanced control features. Only after you’ve established that baseline and gone on to develop sound internal machining standards should you take the next step into automation. There’s no easy button.”

Leave Makino and head south for half an hour to Batavia, Ohio. There you’ll find Milacron LLC, an operating company of Hillenbrand Inc. and a leader in plastic extrusion and injection molding equipment. Andy Stirn, general manager of the company’s Advanced Systems Business, comes to the discussion with a slightly different viewpoint. He reiterates what Houle said about offshoring of the consumer electronics industry and its impact on North American molders, but notes that there’s still plenty of injection-molding activity in the U.S.

“With a few exceptions, most of the molding in China is done with one-, two- and four-cavity molds and uses human workers to handle the parts—simpler stuff, in other words,” Stirn says. “Compare that to North America, where you’re talking about 48- and 96-cavity molds and a process that’s highly automated.”

Much of this work is for the medical industry, where parts leave the molding machine and go through downstream processes like runner removal, sterilization and packaging, most likely without human hands touching them and often in a tightly controlled environment.

“That doesn’t mean we don’t have custom molders doing low-volume production in North America—we do—but generally speaking, the market is quite segmented,” Stirn continues. “Most of the medical stuff is here, and there’s still a fair amount of automotive, but yeah—when it comes to cell phones and computers, that’s almost exclusively done in China.”

It’s important to note that Milacron offers plastic injection-molding machines and auxiliary support equipment, not the CNC machine tools that Makino and Matsuura supply to toolmakers. Because of this, Stirn’s efforts are aimed more at the finished parts rather than the molds that make them. But if Houle is correct and vertical integration is the best path forward, these two groups—moldmakers and molders—will increasingly be one and the same. Regardless, automation in all its many forms will continue to play a significant role in molding success.

“A couple of years ago, labor was a huge factor,” Stirn says. “That’s beginning to change as more molders invest in robots. Once you grab a hold of the part, you can inspect it, place it in an assembly fixture, apply labels or stick it in a box or whatever. Automation offers significant benefits, so I think this trend among others will definitely continue to increase in North America.”

One final trend is sustainability. The molding process is growing more complex as molders respond to market and regulatory pressures by embracing greener materials. Consider co-molding. Stirn points to a cross-section of a plastic bucket as an example—here, the outer walls are made of virgin polymer that encapsulates a center section made of recycled material.

“From a sustainability perspective, co-injection is very significant,” Stirn says. “It’s a highly engineered solution that some pretty big brand owners are looking at, even though it’s more capital-intensive and the final product costs more. At the same time, there’s great interest in bio-based resins and polymers with greater recyclability, both of which will impact how molders and moldmakers everywhere move forward and adapt to changing requirements.”

Molding simulation software helps moldmakers design the most effective tools possible in less time.

“When we first launched SOLIDWORKS Plastics, surveys of 3D-CAD users involved in the design of plastic injection-molded parts and tooling indicated that 70% of them were not using any sort of simulation software. What’s even more amazing is that, 12 years later, we’re still seeing an unbelievable amount of trial and error in this industry.”

That’s according to Peter Rucinski, a SIMULIA industry senior director at Dassault Systèmes, Waltham, Mass. He goes on to say that there’s more to simulation than cool animations of melted plastic flowing into an injection mold.

The system allows moldmakers and product designers to virtually evaluate thousands of different feedstocks and resins (with more coming along each day). They can estimate molding times, understand and assess plastic flow, test various molding parameters like temperature and pressure, determine optimal gate, sprue and runner locations, and make numerous other crucial decisions long before the mold is made or the hopper filled with plastic pellets.

Simulation also helps avoid the manufacturing defects that can occur without an optimized design of both part and mold, followed by the molding process itself. Sink, flash, warping, short shots and voids—these are just a few of the trouble areas that plague plastic injection molders, all of which can be prevented or at least minimized by using molding simulation software.

“Simulation brings value no matter where you are in the process,” Rucinski says. “If you haven’t gone to tooling yet, the world is your oyster and you can easily make the part more manufacturable. But even if the part design is fixed, there are things you can do to minimize potential problems.

“It’s easy to simulate what would happen if you move a gate location, for example, or try a different material, increase hold time or any one of dozens of different scenarios,” he continues. “Simulation helps to eliminate the educated guesses and assumptions.”

This isn’t a commercial for SOLIDWORKS. As anyone who’s kicked the tires on modern design, programming and simulation tools knows, there are numerous high-quality options available. Instead, it’s a call for the U.S. manufacturing industry to invest in the advanced software needed to develop scientific processes, moldmaking among them.

Doing so will serve to capture some of the tribal knowledge hidden inside the brains of those who will retire at some point and give the next generation of workers a better chance of success in a rapidly changing and highly technical vocation.

And it will make manufacturing more efficient and free of costly errors, greatly improving a company’s bottom line. The result? More “Made in America” stickers everywhere you look.

Dassault Systèmes

781-810-3000 / www.3ds.com

Makino Inc.

513-573-7200 / www.makino.com

Matsuura Machinery USA Inc.

651-289-9700 / www.matsuurausa.com

Milacron LLC

513-536-2000 / www.milacron.com

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Contributing Editor