Multitasking Lathe Speeds Production of Complex Mold Parts

Originally titled 'Multitasking Lathe Speeds Production of Complex Mold Components'

An Okuma machine helped this Ohio moldmaker boost a segment of its business.

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Last year, Trifecta Tool and Engineering in Dayton, Ohio, had its best year ever, according to co-founder Bret West. That was because the company purchased a multi-axis, multitasking Okuma LB3000 MYW lathe and saw its orders for caps and closure molds almost triple, from 5 percent of its business to about 15 percent.

Trifecta has built molds for caps and closures since West and four partners founded the company in 2004. It also builds molds for automotive and consumer products, including plastic-injection and rubber-injection tooling for automotive, plus compression tools for the oil and gas industry. A specialty is high-temperature tools for molding parts in materials like Torlon, polyetheretherketone (PEEK), Amodel, Ultem and polyphenylene sulfide (PPS) plastics. But West says the company plans to focus on continued growth in molds for caps and closures, and the Okuma’s ability to cut machining time and eliminate some machining functions will play a key role. 

“Components for caps and closure tools need to be 100-percent interchangeable so that if you have a 32-cavity mold and a problem arises with one of the cavities, you can interchange any part in any cavity,” West says. “The challenge for us is to lower costs by being able to machine hardened, close-tolerance injection mold components that have complex shapes like threads and gears, and do it accurately and efficiently. By having this multitasking capability using the
Okuma, we probably cut 30 percent to 50 percent of machining
time out of each job while still maintaining tight tolerances and the correct stack heights in order to achieve precise interchangeability.”

Multitasking in One Setup
The Okuma LB3000 MYW is a “live-tool lathe,” meaning it is a CNC turning center that also has milling capability, allowing machinists to hard-turn components and eliminate most grinding operations. For example, each cavity stack within Trifecta’s closure molds typically consists of three to five parts (the core, cavity and other components). Before purchasing the Okuma, the company’s machinists would first have to turn the round parts, then grind inner and outer diameters, and then mill water lines using one of the company’s Hurco CNC mills. The grinding process alone could take an extra hour to two hours per part within each cavity stack, depending on the complexity of the part, West says. 

“A time-savings aspect for us is the ability to eliminate the OD/ID grinding process and instead hard-turn cores as much as possible,” he says. “You cannot turn everything, but we have been able to reduce grinding by 90 percent on a lot of the parts we make, and we are still able to hold close tolerances.”

An additional assembly from WTO GmbH also enables the Okuma to perform gear-hobbing functions to machine unscrewing core details and other components. “The gear-hobbing ability allows us to completely finish most parts in one setup,” West says. “Previously, unscrewing spindles used to have gears that were inserted, or they had to be sent out to be gear-hobbed. When these gears were needed, the hobbing process was usually outsourced, and it could take two to three weeks before the parts came back. We save a tremendous amount of time over the course of such a project by being able to hob the gears right on the spindles in house now.”

The Okuma-designed, high-torque PREX synchronous motor also enables the machine to make heavy cuts in difficult-to-machine materials, including tool steels like stainless, hardened and high-carbon. This, combined with Y-axis-offset turning and a main spindle and live subspindle located within a double toolholder, enable the completion of both rough and finish turning within one tool station.For instance, if a workpiece is being turned with the main spindle and a secondary operation has been programmed into the job, the subspindle can run at the same synchronized speed as the main spindle and, using its jaws, pull the workpiece over in order to thread, mill, drill or hob on the back of the same workpiece. This functionality eliminates the need for indexing tools and reduces cycle times, West says.

Thermal Stability 
Another key feature of the lathe is its built-in thermal stability. “It helps us maintain dimensional stability of the machine, even when we have long-running jobs, and saves a lot of time because we no longer have to stop mid-stream to make manual adjustments to the workpiece to compensate for temperature changes,” West says.

According to Okuma USA’s David Fischer, this built-in thermal stability is a result of the company’s thermal compensation software, which it calls Thermal Active Stabilizer, or TAS. “Basically it is an algorithm that runs continuously in the background and, based on temperature-sensor readings, it adjusts the machine to compensate for growth,” he says. “This produces a machine that will hold very tight tolerances in environments that are not tightly controlled temperature-wise.” 

More specifically, he says, the machine is designed to remove as much heat as possible from the main components (base and bed castings, headstock, saddle, turret and tailstock) in order to minimize growth, thereby ensuring that the machine remains more dimensionally stable. 

West says Trifecta is already looking at buying a second Okuma LB3000 MYW lathe to continue growing its caps and closure mold business. “We plan to stay very diversified in the markets we serve. It’s important to us to have a balance of capability and income sources, and the Okuma lathe has definitely contributed to our continued success.” 

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