Quick-Change Shot Sizes for Injection Molding

Installed on a 110-ton MD-S8000 all-electric injection molding machine, the Shot Maker will allow Niigata to change the shot sizes its running at the show from 2.75 to 4.37 to 6.53 oz. Niigata will be demonstrating the Shot Maker by molding a foldable phone holder from a family tool. The 6-cavity tool makes three different sizes of the phone holders, with two cavities forming one holder. The smallest shot size can make one holder, with the medium making four and the largest able to fill all six cavities. The tool was built to show off the both the Shot Maker and Niigata’s Constant Pressure Flow (CPF) mode, which automatically compensates for the unbalanced tool.

A patented option that is only available on a Niigata machine, the Shot Maker works by swapping out the end section of the barrel, while the screw and the barrel’s main section remain in place. Changeable by hand in approximately 15 minutes, the Shot Maker is roughly the size of a large end cap, with the three units currently available measuring approximately 6, 8 and 10 in. in length.

Encompassing the stroke section of the barrel from stroke forward, Shot Maker allows molders to alter that portion of the barrel’s diameter. Steve Cunningham, general manager Niigata USA Injection Molding Div., told Plastics Technology that the machine at PTXPO will have a 30-mm standard barrel, which is also the size of the screw. When the forward stroke section is changed via the Shot Maker, the barrel diameter is altered to either 35 or 40 mm.

More Flexibility for More Jobs
Cunningham says Shot Maker targets the molder who can tackle most jobs with a specific tonnage of machine but has some outlier molds that would require a different injection unit or an entirely new press. “I’ve sold machines for many, many years,” Cunningham says, “and I’d sit down with an owner and he’d say, “I want to buy a 110-ton machine, and 80% of my work can be done with smallest screw and barrel, but I do have a few jobs that need the bigger shot size.’”

Facing this situation, molders often choose to buy the larger injection unit and subsequently have too big a shot capacity for 80% of their work, which makes it difficult to optimize their processes. Doing so accommodates all the tools that are going to run on the machine, but it often pushes the press out of its “sweet spot”, Cunningham notes.

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