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Meeting Moldmaking Challenges

Kip Hanson
By Kip Hanson Contributing Editor, SME Media

Designing and manufacturing plastic injection molds is a difficult way to earn a living. Here’s what the industry is doing to make it a little easier.

Mastercam’s Dynamic Motion engine is material-aware, constantly adjusting the vector of the cutter path to maintain a consistent chip size. (Provided by CNC Software Inc.)

Of all the different manufacturing disciplines, plastic injection moldmaking is perhaps the most challenging. Part accuracies are best measured in microns. Surface finishes often approach optical levels. The metals used in mold production are both tough and exceedingly hard, while the machined surfaces found in a typical mold cavity are quite complex, with intersecting curves and angles that would stump a mathematics major.

Worse, each mold might contain several of these cavities—or several dozen—with hundreds or even thousands of mating components that must be painstakingly assembled before the mold will actually produce a perfectly-formed Yoda doll or plastic tackle box. Again, moldmaking is difficult work.

The good news is help is here. In some respects, however, manufacturing the mold is the easier part. Mold design carries its own set of unique challenges. There’s unrelenting pressure to deliver a cost-effective design that performs as expected, with tight timelines and competition both domestic and abroad. Fortunately, there are a fair number of companies that recognize this, supporting moldmakers with tactics and technologies that make this vital industry a little easier to navigate.

One of these is San Rafael, Calif.-based Autodesk Inc., suppliers of design and manufacturing software products including PowerMill, Moldflow, and Fusion 360. Marketing Manager Clinton Perry suggested that moldmakers face many of the same challenges found in any manufacturing sector, but thanks to a higher level of complexity, the stakes are somewhat higher with moldmaking.

“Speed to market is a major focus in the industry, a factor that’s exacerbated by the many months it might take to design, build, and test a production-grade mold,” he said. “Just as there’s massive pressure on moldmakers to ensure they can deliver on time, it’s also crucial that they’re able to deliver high-quality components. Anything that we as suppliers can do to ensure that mold components come off of CNC machine tools mostly ready to go, with a minimum of post-processing, addresses both of these considerations.”

One of the tools to accomplish this is computer-aided design and manufacturing software designed specifically for moldmakers, he noted. This means functions such as plastic flow and cooling analyses, molded part optimization, shrinkage and warpage compensation, and other design-related activities. Further, because moldmaking is often a collaborative effort, the ability to share information via
the cloud is an increasingly popular request from customers and manufacturers alike.

On the manufacturing side, robust simulation and verification capabilities validate that the NC code used to drive machinery will not only be completely accurate, but safe, with no chance of collision, gouging, or uncut material. “Even an entry-level CNC machine tool can be expensive, but the ones used by moldmakers cost far more,” he said. “Our job is to make sure that no equipment or tooling gets damaged during the machining process, and that shops can get the most out of their hard-earned investment.

“Take machine collisions as an example,” Perry continued. “It’s essential that CAM software can identify hazardous motion before anyone goes near the actual machine, but it’s more advantageous if the CAM software can go further and automatically modify the program to avoid the collision completely. Crucially, all of this must be achievable without the CAM programmer needing to be a software Jedi master.”

Bridging the Gap

Perry’s last comment raises another big concern for the industry: people. Where finding a skilled machine operator is difficult for any shop, recruiting one who can successfully machine a mold that may cost as much as the machine tool itself can be a real challenge. Brian Pfluger, EDM product line manager for Makino Inc., Mason, Ohio, agreed, adding that humans are needed to make parts, no matter how automated the manufacturing.

“And that’s a bit of a problem right now, since the skills gap has yet to be rectified,” he said. “The good news is that machine controls are getting smarter, as are the software systems needed to program them. The machine tools themselves are also far more capable than in the past, so much of the hand fitting and benchwork that has long been a staple of tool and die manufacturing is, in many cases, unnecessary. This changes the role of moldmaker into more of a project engineer than skilled craftsman, a role that is in some ways easier to fill.”

Fast, accurate machine controls such as the Heidenhain TNC 640 shown here are a prerequisite for any successful moldmaking endeavor. (Provided by Heidenhain)

As with most of manufacturing, Industry 4.0 is also changing the face of moldmaking. Makino is one of several machine tool builders to offer advanced connectivity options and remote monitoring tools. Assuming they have the necessary permissions, operators can use CNC-based systems to access the company’s CAD/CAM software, the corporate ERP system, or surf a vendor’s website for troubleshooting support, all from the shop floor.

Similarly, management can remotely monitor CNC equipment to check on the status of a job, resolve an alarm, or collect real-time machine data and production information for analysis. “Each of these functions serves to increase machine utilization and make manufacturing processes of all kinds more efficient, moldmaking among them,” said Pfluger.

Keeping Control

To be competitive, moldmakers must fully utilize their machining assets. “Moldmaking success is, in large part, about taking full advantage of the machine tool and all of its control capabilities,” said Gisbert Ledvon, TNC business development manager for motion control and components manufacturer Heidenhain Corp., Schaumburg, Illinois. “This is why it’s so important for the industry overall to maintain tight relationships between the control builders, the machine tool companies, and the various suppliers of CAM software.”

The challenge, he said, is that technology is changing at such a rapid pace that moldmakers often struggle to keep up. Heidenhain or a competing control builder may introduce a new feature to improve part accuracy, for instance, but unless the CAM provider knows about it, the post-processors used to output the necessary machine code might not get updated until months later, if ever.

The solution is a tight network of partnerships between everyone involved, relationships that Heidenhain heavily promotes. Of course, customer involvement is also necessary, as is continuous training. One example of this was a special event hosted by tooling provider Seco Tools LLC, Troy, Mich., where Heidenhain and other suppliers joined representatives from dozens of mold and die companies to share information and introduce new metalworking techniques.

Ledvon was there. “Everyone’s busy, but it’s important to take time to attend these types of training events; if not, you’re going to be left behind,” he said. “Another example is a five-axis machining seminar we offered in January and again in June, during which we discussed the use of circle-segment end mills, also known as conical barrel cutters. Provided you have the right machine control and the CAM software to support it, barrel cutting can reduce finish machining times by 80 percent or more, and significantly improve surface finishes as well.”

Over a Barrel

The slightest mismatch between surfaces in a mold cavity will be mirrored in the plastic parts it produces. This image shows an exaggerated view of the hyperMILL smooth blending capability. (Provided by Open Mind Technologies)

Alan Levine offers such software. The managing director of Open Mind Technologies USA Inc., Needham, Mass., developer of hyperMILL CAM software, agreed that conical barrel cutting is an excellent way to improve moldmaking efficiency, but it’s far from the only such method.

“When we first introduced barrel cutting strategies, it was a real eye-opener for many in the industry,” Levine said. “But we’ve also developed numerous complementary, and in some cases quite similar toolpath technologies, including one we call prismatic fillet finishing. This uses a conical barrel or ball-shaped cutter with what is primarily an up-and-down stroking movement, avoiding most blending issues while also providing finer surfaces and reduced cycle times.”

Perfect blending is everything to a moldmaker, Levine pointed out. Using highly accurate CAM software and a rigid, accurate machine tool goes a long way towards achieving it, but that’s only part of the solution. A growing number of shops are moving towards hard milling, eschewing traditional moldmaking processes that use a sinker EDM to finish machine mold cavities; since much if not all of the mold is now milled in the hardened state, tool wear becomes more problematic.

“By using a high-performance milling approach, some of our customers see success with hardened tool steels up to 60 Rockwell as well as pre-hardened materials in the 35 to 40 Rc range,” Levine said. “Mold shops can realize outstanding dimensional accuracy, which then leads to better blending. And because fewer passes are needed to attain the necessary geometry and surface finish, tool life improves while cycle time falls. Each of these attributes is critical to achieving the most efficient moldmaking solution.”

Give Me Five

Perhaps the only downside to the high-performance milling strategies just mentioned is the need for a five-axis machining center. Of course, that’s okay—much of the moldmaking industry has already come to realize the many benefits of this machine tool technology, namely greater part accuracy, lower fixture costs, reduced WIP, and shorter product lead-times.

Ben Mund, senior market analyst for Mastercam developer CNC Software Inc., Tolland, Conn., agreed. “Granted, machine shops producing complex aerospace and medical components are just as likely to invest in a five-axis machining center,” he said. “But these capable machines are also quite attractive to mold shops, where it’s often necessary to reach deep into a mold cavity with a relatively small cutting tool; because it’s easier to minimize tool overhang in this situation, tool life and part quality are generally better on a five-axis.”

As with Open Mind and the majority of CAM developers, Mastercam has developed its own proprietary, high-performance metal removal routines “able to remove huge amounts of material quickly and accurately.” Yet Mund points to automation—the software kind—as another necessary step towards greater moldmaking efficiency.

“It’s not all about cycle time,” he said. “Consider something as simple as holemaking. A typical mold might have dozens and dozens of holes, and programming them one at a time can burn up a significant chunk of time. It can also lead to errors—missing just one of those holes might lead to days of downtime, or even a scrapped part. But by using feature recognition and other automated software functions, moldmakers can dramatically reduce this effort, and do so with less risk.”

Thinking Additively

This insert came off a LUMEX hybrid machine basically ready for assembly into a production mold. (Provided by Matsuura)

While traditional machining methods for moldmaking are evolving, there’s also an elephant in the moldmaking room. It’s called hybrid manufacturing, and if Tom Houle has anything to say about it, this novel approach to mold manufacturing will be coming soon to a shop near you (or perhaps your own).

The director of the LUMEX line of metal sintering equipment for Matsuura Machinery USA Inc., St. Paul, Minn., Houle is quick to tell you that in the two years since its introduction, this machine is already having a dramatic impact on the moldmaking industry.

How does it work? As with other metal powder bed 3D-printing technologies, the LUMEX uses a high-power laser to build parts one layer at a time, working its way from the bottom up until the workpiece is complete.

The LUMEX, however, is also equipped with a 45,000-rpm milling spindle, which is programmed every few layers or so to precisely machine away excess sintered material. The result is a mold (or most any other metal component) that’s every bit as accurate as those produced with traditional methods, but with far fewer design constraints.

“The return on investment is threefold,” he said. “Number one, our customers are seeing the value that comes with implementing additive manufacturing technology into their tools. These include conformal cooling channels, porous venting, and virtually no concerns over deep ribs. Secondly, it’s quick-turn manufacturing, which means the ability to build a production tool in days versus weeks or months, with reduced tooling costs. Finally, those toolmakers who are also injection molders are reaping the additional benefits of cycle time savings, thanks to an additively manufactured mold’s far greater cooling capabilities.”

This last part is the big kahuna. Houle offered multiple customer case studies, all showing 25-45 percent reductions in cycle time. For one large OEM in the St. Paul area, this adds up to a $5.5 million savings over the projected five-year molding life of a multi-part assembly.

The investment is significant. Houle said that a LUMEX will cost roughly the same amount as a high-quality machining center and a metal 3D printer combined, but considering the benefits, the cost should be easy to justify for many moldmakers.

Knocking Down Obstacles

Emuge Circle Segment end mills, also known as conical barrel cutters, feature unique forms with large radii in the cutting area of the mills, allowing a larger axial DOC during pre-finishing and finishing operations. (Provided by Emuge)

AM is not a slam dunk to implement. Learning all there is to know about additive will admittedly take some moldmakers far out of their comfort zone. And because there’s subtractive manufacturing thrown into the mix, the LUMEX carries its own distinct set of machining obstacles.

Dan Doiron, milling products manager for Emuge Corp., West Boylston, Mass., (the same company that manufactures the conical barrel cutters discussed earlier) can speak to one of these. He explained that, because the end mills used on the LUMEX are plowing through coarse, layered metal, Emuge has designed wear-resistant coatings and tool geometries specifically for this type of hybrid machining application.

“There is a significant abrasion factor when working in a powder bed environment, as well as some thermal considerations, but this is why there’s been such a high level of collaboration between our two companies,” he said.

Matsuura isn’t the only company offering hybrid machine tools, but at this point, the LUMEX is, perhaps, the only one designed with moldmaking in its sights. “I’ve been in the moldmaking business for most of my life, and I can tell you that additive and hybrid manufacturing are at the same place that wire EDM and sinker EDM were 25 years ago,” said Houle. “It was the early adopters of those technologies who were the most successful back then. The parts became better; labor costs dropped; throughput increased—it was just a huge jump in productivity, especially for small mold shops. That’s precisely what additive is poised to do, right now.”

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