A new twist on multimaterial molding

Multimaterial applications are, well, multiplying. Fast, too. Companies like being able to combine functional and aesthetic features like protection, sealing, grip, and color variations, not to mention a very high-tech modern look. Better still, the finished part is one piece and won't separate unless you want it to. 

Power tools, sporting goods, and electronic gear like mobile phones already use multimaterial technology, and more products are en route. All that remains is for moldmakers and molders to gear up to meet the processing demands. Naturally, production will have to be fast, perfect, and above all, low cost. 

A Run Through 
Generally speaking, it is always better to have choices, and IMM recently came upon one for multicomponent molding, or MCM. Hekuma GmbH, located near Munich, Germany, has approached the MCM process from an altogether different angle. 

Its solution requires one molding machine and eliminates the need for rotating platens or mold components, complicated molds, and complex mold temperature controls that often accompany such systems. Hekuma's specialty is high-performance, purpose-built automated handling systems with ultrafast takeout robots, which is exactly how the company has approached MCM. 

The resulting system is a simplified solution to a complex task. Destined for The Tech Group Ireland, the system uses a two-component Netstal press, a standard stack mold, and Hekuma robotics to manipulate parts. Basic operation follows these steps (see diagram): 

1. At the end of the cycle, the U-shaped robot enters both openings in the stack mold. 

2. The EOAT on the first arm removes single-shot parts from the mold to a transfer station. 

3. That arm then moves to a ready position for the next cycle, which clears the way for the transfer station robot to move single-shot parts to the second arm of that U-shaped robot. 

4. Single-shot parts are transferred to the EOAT on the second arm, which places them in the second half of the stack mold at the end of the next cycle. 

5. While single-shot parts are being inserted into the mold, a set of EOAT on the opposite side of that second arm removes completed two-component parts to a second transfer station. 

6. The second transfer station moves the completed parts out of the MCM system toward downstream operations. 

The benefits of this system can be sorted into two categories: what you avoid and what you can do. 

What You Avoid 
For starters, Hekuma's solution, which is patented, avoids the need for two presses and relies instead on a standard two-component machine. Most multimolding systems on the market offer a variety of options for delivering the second material to the mold. Indeed, there are already many one-machine MCM solutions on the market. Hekuma's system, however, avoids the complexities of platen or mold rotation that are normally employed. 

Rotating plates, says Hekuma, are a wear factor, and all the more so when the machine is cycling quickly. At the same time, the core/cavity alignment of the rotating platens or mold plates must remain virtually perfect. Rotation, whether of platen or mold plate, takes time, and that time adds to the cycle and reduces output. 

Another factor is that rotating molds almost always need more space between tiebars than if they were stationary. This means that MCM jobs may have to run on a larger, more costly machine than actually needed just to get the tiebar space. 

Also, many MCM applications use materials from two different categories. A large number of automotive parts, for example, use a PA substrate with integral LSR gaskets or seals. The mold temperature requirements of these materials can vary greatly, creating a challenge. 

Hekuma says making such cooling and heating combinations work in one mold is not only complicated but also expensive. Moving the cooling/heating fluids or gases into and out of a mold piece that has to rotate freely only adds to the complexity. Hekuma says that it is only logical that moving mold pieces and temperature apparatus are more likely to malfunction than stationary molds. 

Under its solution, Hekuma says molders can avoid the challenge associated with running different materials in the same mold. With the stack mold configuration, mold design and temperature control are segregated. Temperature control in particular can be easily customized for each material. 

What You Can Do 
Hekuma says its solution is worth considering solely for the cost savings, enhanced productivity, and elimination of problems, but if that's not enough, look at the processing flexibility it offers. 

For example, it might appear at first that the movement time of the transfer stations in the Hekuma system is wasted. Yet, because transfer occurs during mold-closed time, it actually adds nothing to the cycle. 

The transfer stations offer other options as well. Parts on either of the stations can receive a variety of intermediate processing. The single-shot parts, for instance, can be cooled, heated, roughed up, or a binder can be applied to increase the adhesion of the second material. 

Also, EOAT can be added to the robotic arms at intermediate points to perform surface treatments or to insert inmold labels. The parts from the first shot can also be held in a buffer and thus not go immediately into the next shot. Finally, you can make this a three-component process using a three-stack mold. 

In Hekuma's plant, IMM saw most of the automation for the second of two production cells using this new multicomponent solution. Full system testing is being performed by Netstal. The cells eventually will be delivered to The Tech Group Ireland, just outside Dublin. That company's general manager, David Moffett, says each cell will ultimately retire two older systems producing a close-tolerance, high-volume part for an undisclosed computer-related application (see image above). The materials are a high-temperature thermoplastic and an elastomer with very different mold temperature requirements. The Tech Group will use 16+16 stack molds in the system and initial cycle times are expected to be about 18 seconds. 

Custom-built automated handling systems, like the one shown here, allow multicomponent molding with one molding machine and eliminate the need for rotating platens and other complex additions such as elaborate temperature controls. A U-shaped side-entry robot enters both openings of a stack mold (see detail in inset), removing single-shot parts from the mold to a transfer station for placement in the second half of the mold. Simultaneously, two-component parts are removed to a second transfer station, which sends them on to downstream operations.