How to select the best IML press

Are you planning to shop for a molding machine to run IML products? If so, have a read as four experts from leading IML machinery makers lay out their advice for making a savvy selection.

IML has potential in auto parts, toys, and lawn and garden products, and most of all in consumer packaging. But to be successful, an IML system, especially for packaging, needs properly prepared labels, proper molds, a proper product handling system, and most of all an accurate, high-speed molding machine, according to Michael Sansoucy, national sales manager at Netstal Machinery Inc. (Devens, MA), a company that’s supplied IML molding systems for more than 20 years.
“Less is best” is the rule in consumer packaging, Sansoucy says, namely, less material, part weight, cycle time, and most of all, less wall thickness.

Although less of those may be best for the end product, he says thinner walls mean you’ll need more injection capacity, more clamping force, and more plasticating capacity than you’d expect in general-purpose jobs. You’ll also encounter more in loads and strains, and you’ll need heavyweight molds. It all adds up to a very narrow process control window.

Sansoucy says you’ll have to consider how the clamping and injection unit, the IML handling system, and the press control each factor into your ability to obtain that necessarily narrow process window.

Injection unit selection

When it comes to the shooter, Sansoucy says IML consumer packaging requires injection units that can deliver the goods when it comes to these three criteria: consistent filling of very thin walls; repeatability; and high recovery rates for high-speed cycles with polypropylene.

To meet the first requirement, an injection unit has to deliver high system pressure and instantaneously deliver injection pressure for the entire stroke. Sansoucy says this means that for thin-wall packaging applications, an accumulator is a must, although, according to Joachim Kragl, manager of processing technology at Engel Canada Inc. (Guelph, ON), it should be noted that this is a requirement of the part itself and not because a label is being inserted.

For ensuring the necessary process repeatability, your screw stroke has to be within ±0.005-mm resolution and ±0.015-mm repeatability. And a barrier screw optimized for PP with an L/D ratio of, at the very least, 24:1 is necessary to provide the high recovery rates required.

In addition to stressing the positive impact of the ability of longer screws to provide plasticating rates necessary for thin-wall IML packaging, Sansoucy says barrier screws are equally important for five key benefits they provide: higher throughput; lower melt temperature; less torque requirement; improved melt quality; and excellent color mixing.

Kragl adds that, similar to the need for accumulators, barrier screws are necessary for the thin-wall part and not because there is a label to backmold. “It also helps a great deal if the melt is prepared perfectly, homogeneously, since nonhomogeneous melt can cause problems [label damage] when trying to backmold the label. If the melt is not homogeneous, you will see different flow characteristics, which can heavily influence the process, causing marks (such as halos) on the label, or, in an extreme case, the label may wash out or experience a change in color.”

A standard closed-loop control system provides closed-loop control only of the oil pump. The central accumulator-based type of injection system Sansoucy recommends provides sensor-managed, servodriven, closed-loop control at the injection unit as well as in the pump. This, he says, will ensure you’ll get the precise amount of pressure you need, when you need it, without wasting any time waiting for the pump to build pressure.

Clamping unit and control requirements

You’ll need a smooth clamp motion to ensure accurate label placement, so Sansoucy says you’ll need a clamping system that can provide both smooth acceleration and smooth lockup. The clamp-open position has to be maintained shot after shot—right around ±0.1 mm—to make it a robot-friendly molding system.

Kragl adds, “If the clamp does not stop on a dime, so to speak, you will face problems with label placement into the mold, and possibly part removal problems, which is dependent on the ejection method used. Some clamp designs incorporate a mechanical stroke limiter, for example, to repeatedly stop at the very same position—a real necessity in IML.”

For applications like thicker-walled containers—for example, a 5-gal bucket—huge daylight between the platens is critical because you have to reach in the clamp with a label, says Robert Hare, GM of Europe/USA sales and service for Ferromatik Milacron (Batavia, OH). “Daylight and clamp stroke in such applications are much more important than they are with thin-wall packaging,” he explains.

For thin-wall packaging apps, your molding machine’s clamp also has to be quite robust, providing either low or zero flexing. That’s because IML molds are usually pretty heavy. Many of them are big stack molds—hardly featherweights.

And your clamping system has to be engineered and built for speed to maximize productivity. Extremely fast dry cycles are a must, Sansoucy says, to ensure that cycle time goals are met. What’s needed are sturdy tiebars and platens, rock-solid support for the moving platen, and a reinforced frame in the part drop area, both for the moving platen and, if required, for the stack mold carriers.

A quick, smooth, profiled clamp motion control is another reported necessity. And your IML machine’s clamp has to provide mold-open position accuracy, because you’re going to have some rather speedy parts handling systems moving around in there.

Just how fast is fast? Sansoucy points to the Euromap 6 Standard as a good gauge. It sums up the time that it takes to open and close the clamp, sure, but it also includes lockup. It factors in clamp stroke set to 70% of the horizontal tiebar spacing and tonnage set to 70% of maximum.

He dismisses the alternative, commonly used “cycle contribution” method—i.e., dry cycle minus locking and unlocking—as being a less accurate speedometer. Successful packaging, he says, is all about output, not just how fast a clamp opens and closes—and output definitely includes locking and unlocking.

Paul Caprio, president of Krauss-Maffei Corp. (Florence, KY), says the Euromap 6 standard ensures that all machinery makers are measured in an identical manner so that a molder can compare dry cycle times. “Krauss-Maffei will quote a cycle time . . . based on the part’s cooling time in the mold. Everything else is simply a calculation of machine movements and the robot’s takeout time.”

Accurate, fast, and repeatable process control is vital to providing consistent labeling quality. Sansoucy also says the control system has to be responsive enough to match the fast cycles required to maximize productivity. “Poor injection control has resulted in label distortion and burn-through, making a very nice graphic look inferior,” he says. “Superior injection control leaves no gate witness mark.”

Efficiency is another factor in selecting the right control. “The molding machine control has to be able to interface with the IML automation equipment as much as possible to reduce the communication time between the machine and the robot, since cycle times are typically very short. Less time lost in communication results in a faster overall cycle,” Kragl says.

The whole enchilada

Although the focus to this point has been on the molding machine, the entire cell must be considered. “At the end of the day, the crux of a successful IML cell isn’t so much the molding machine as it is the IML device,” Hare says. “For those going down this road for first time, I would strongly recommend getting the whole IML package tested at one of three suppliers of your system. The labeling automation, molding machine, and the mold—the entire system—should be fully integrated and running to your acceptance. You don’t want to have to debug the system—you just want it up and running.”

Caprio contends that robotics are just as important to the IML process as is the molding machine. “Picking up the labels, delivering them to the mold, and taking out the finished product is every bit as critical,” he says.

“And what about the mold?” he adds. “Not every moldmaker knows how to handle the IML process, and such process-specific experience can be the difference between success and failure. This is why, when we are involved with an IML application, automation must be handled with a proven supplier as well as with a moldmaker with proven skills in this specific arena. Fortunately, most customers are buying production cells with all three components (machine, mold, automation) single-sourced, taking any finger pointing out of the equation.”

Another important issue Sansoucy raises is that if you’re shopping for an IML molding machine supplier, be sure to investigate its experience in delivering successful IML systems. It’s definitely not, he says, like buying a GP press. Your supplier should be able to supply the R&D, presale consultation, project engineering, training, and postsale services to ensure your productivity in a field where repeatable cycling in seconds and tenths of a second are critical. “IML costs can be reduced with good planning and a well-thought-out approach to a system,” he concludes.