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Rethinking the injection molding machine

Can one inventor change the way plastics is injection molded using a homemade machine from his basement? Rick Fitzpatrick, a molding veteran with tool design stints at the former Courtesy Corp. (now Rexam) and Capsonic, has long questioned the current molding model of large machines and large multicavity molds, and for the last 10 years, he has manifested those doubts in smaller machines that re-imagine the molding process. His goal: "getting to the size of a machine that actually prepares plastic economically."

Tony Deligio

February 28, 2011

3 Min Read
Rethinking the injection molding machine

"Why is it that an injection molding machine can cost $500,000," Fitzpatrick asked, "but I've got more control at my fingertip with a hot glue gun? Everyone looks at injection molding having to be all of these cavities, because everyone equates cheap parts with all these cavities, and they don't really understand the machine cost, the cost of floor space, the cost of labor to support that machine, so literally what you end up with are very high capital costs for marginal profits."

Fitzpatrick's answer has gone through number of iterations but boils down to small, table-top machines that combine a continuous extrusion screw with a plunger system running down its center to deliver plastic that's heated at the nozzle. In a 2004 video, he shows an early prototype based on a multipurpose machine purchased from discount hardware supplier, Harbor Freight. Using a lathe spindle to turn the screw, which is itself a modified wood auger, the small prototype, which is not running a mold, rapidly piles molten polypropylene on a table. Heating comes from two small 250W heaters, with the 200-rpm spindle running 110V and plugged into the wall.

"I thought, 'Man, if I can pump plastic like this, at these rates, what do I need a big machine for?'" Fitzpatrick recalls. In larger machines, Fitzpatrick notes shear heat is required to melt plastic, and to achieve shear heating large batches of resins must be prepared. To safely accommodate the melt stream, large barrels and machines are required. In his system, small batches of plastics are heated on an as-needed basis to specified temperatures, with the lower-pressure environment allowing barrel-wall thicknesses down to 1/8-inch.

As part of the paradox of large machines, Fitzpatrick points to hot runner systems. "If I've got a hot runner system and it's sitting there and can hold this polypropylene at 300°F or whatever," Fitzpatrick asked, "why do I need that whole machine to move it two inches across a plate? That's when I started playing with this idea of small machines."

Fitzpatrick says for the $22,000 to $24,000 you might pay for an eight-cavity mold, he can create a machine with a four-cavity mold for the same price. To promote the program, Fitzpatrick has joined the MYOS (make your own stuff) community online, and will use that platform to initially push the technology to do-it-yourselfers, inventors, and hobbyists. After a decade of work, Fitzpatrick is hopeful his concept can catch on.

"In all these years, it's really hard, it's like pushing everything up hill," Fitzpatrick says. "I go to plastics guys, and they'll agree with everything and then it will come down to: it's too high risk, if it were so good everyone would be doing it."

Because of that, Fitzpatrick is changing his target audience for the systems. "I've been a failure at trying to sell to the people who learned how to tame the big dinosaur, and I don't really want to go after them anymore because it's a losing proposition," Fitzpatrick says, "but there are a lot of little guys who need a lot of little parts. What was the first question in our target marketing meetings at Capsonic: What's the volume? If it's under 75,000 pieces/yr for insert molding, we ain't doing it, go away." 

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