Overmolding Overhaul

Inject a substrate, insert it into a different tool and overmold—lather, rinse, repeat. For most of its 25 years, that’s how Innotech Precision Inc. in Toronto handled overmolding, using a transfer method requiring two molds, two machines and a good bit of labor input.

When a class A trim-component program for full-sized GM trucks came up in 2018, the job was not unlike many other multi-material jobs Innotech had fulfilled with transfer molding. This time, however, an advanced tool technology from a Quebec-based moldmaker and the potential to apply an e-Multi auxiliary injection unit from Mold-Masters led the company to a new overmolding strategy.
 

Future Flexibility

Rudy Koehler, Innotech president, considered the project at hand as he weighed what technology the company would utilize, including the alternatives of new two-shot molding machine or a standard press with an auxiliary injection unit. “Let’s say we have a two-shot application seven years from now, and the one that we have now goes away,” Koehler says, “and we don’t know if we’ve got the replacement work. We can take the e-Multi off; we can sell it; or we can put it on another machine.”

The bigger investment and lead time on a dedicated two-shot machine would be a different story. “Maybe a pure two-shot machine has some features that we’re giving up on,” Koehler says, “but there’s enough pros to the approach we took that with 20/20 hindsight I’m still pretty comfortable with the decision.”

“Buying a pure two-barrel or two-shot machine, you’re getting into a very specific, very custom piece of equipment that might not have the versatility to run another mold in the future or be able to be reconfigured,” adds Scott Jones, Innotech’s v.p. of engineering.

The approach Innotech took was to purchase an e-Multi and a new 500-ton all-electric Toshiba press (now supplied by Shibaura Machine Co.), pairing them with a specialized multi-material mold that puts a spin on traditional 2K designs that use a rotary table.

Class A Trim

The class A trim component Innotech has been molding since mid-2020 is positioned at the front edge of the truck’s front door. Apart from the molded plastic, it comprises a stamped decorative metal element and a steel reinforcement.

In the Innotech molding cell, a six-axis Kuka robot inserts the metal components to be overmolded using electromagnets in the robot tooling—in the mold, pins hold them in place. Before the mold closes, cameras inspect the inserts, ensuring they’re in position and halting the cycle if they’re not.
 

The first shot of talc-filled PP from the main barrel encases the inserted steel reinforcement, which is located in a high-stress area of the assembly. Next, instead of a rotary table spinning the mold for the second shot, the mold has a rotating core built into it. When the platens open, the mold’s core rises out of the base and rotates 180°. The trim parts are right- and left-hand, and in the four cavity mold, the two lower cavities are filled with the first PP shot, and spun into the upper position, where the TPV seal is overmolded using the e-Multi mounted on the stationary platen.

Innotech’s goal was to automate the cell as much as possible, with one operator loading metal inserts into a nest for the robot. That same operator inspects and packs good parts within the cycle time with ample time for all three tasks.

The new process has led to lower inventory, less labor, lower scrap and greater product quality. “When we do insert transfer molding,” Jones says, “we create work in process, and this totally eliminates that. The quality is a lot better. With transfer, you get into mold-fit issues with first shot into the second shot, and a lot of quality concerns. So there’s a lot of advantages to doing it this way in one machine.”