Erie Pa. — A low-pressure injection molding machine that can use multiple extruders that heat the melt in an electrically heated barrel, then pump the material into the mold gives low shear, lower pressure and better melt processing than standard high-pressure injection presses, according to Extrude To Fill LLC.
The preparation of the molten material is de-linked from the delivery of the melt into the mold, said Rick Fitzpatrick, chief technical officer of the company in Loveland, Colo., which goes by X2F. The machines use small extruders and thin-walled barrels designed to electrically conduct heat.
"It's a level of flexibility that you don't have with a machine that relies on a pressure-generated heat," he said.
X2F is different from conventional injection molding in many ways, Fitzpatrick said in a presentation at Penn State Erie's recent Innovation and Emerging Technologies Conference in Erie.
He said it's an output-based process that is controlled in real time using sensors. Resin viscosity is set and monitored using temperature readings and resistance to flow through motor torque data, screw back pressure and output of the extruder.
One big difference is pack and hold.
"So what we're doing, when we fill, is we build up to that final pack pressure. We begin extrusion. We build pack pressure as the mold cavity fills, and then we're able to go ahead and pack it out at whatever that set point is," he said.
Traditional injection molding uses high-velocity injection that creates a lot of shear. The machines must be large since they have to generate and contain the extreme pressures.
"You're coming in with stage one at a very high injection force. You're looking for a gate freeze-off and then you're trying to hold a second-stage pack and hold pressure," Fitzpatrick said. "And it's a difficult process to do because your pressure source is so far removed from where your pressure is actually needed, at the back of the screw."
X2F machines use much less tonnage and are lighter and cheaper than regular injection presses, he said. They can run traditional molds, but the low-pressure process also allows the use of aluminum molds.
Extrude To Fill claims its costs are more than 50 percent lower than those for conventional injection molding machines.
And the equipment is easy to use.
"Anyone in this room can be taught to run that in about 15 minutes, because the whole idea of using an output-based process means the control algorithm sets up the machine to run. You turn it on, it's going to warm up for five minutes. And it's ready to mold parts," he said at the Penn State Erie conference.
The X2F process is self-tuning, using precise controls.
"Screw speed is controlled by our machine algorithm," Fitzpatrick said. "Basically it's a self-diagnosing system where we understand material viscosity by the torsional load on the screw as well as the back pressure on the screw and other pressure sensors that we have buried in the system."
There is no gate freeze-off because X2F maintains a dynamic load at the gate, continuing to add material as it shrinks and fills the mold, he said, much like gas-assisted molding. "So it helps speed up your cooling because you're pushing it against the cavity wall so you get heat induction, but you pack out those parts," he said.
The equipment can bring material to a known viscosity without anything moving on the machine, he said.
"The whole process is based on our use of sensors, whether in the mold cavity or within the extruder," Fitzpatrick said.
The programmable logic controller handles the heater profiles so the machine can obtain the correct viscosity without overheating the material.