How to Choose Between Single and Multi-Spindle | Manufacturing Engineering | advancedmanufacturing.org

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Automatic lathes with multiple spindles have evolved into today’s multi-spindle machines with powerful numeric controls and individually programmable spindle speeds to rapidly produce small, high-value parts.

Working view of INDEX MS 32 displays its variable tool carriers. INDEX says its core is composed of six fluid-cooled motor spindles integrated in the spindle drum. The machine incorporates infinitely variable speed range, high tractive force, compact design, low maintenance and the latest synchronous drive technology.

We asked experts about purchase decision-making, improvements to machine flexibility, new challenges and even the feasibility of retrofitting older machines (spoiler: It’s seldom cost-effective).

Contemporary multi-spindle CNC machines retain their well-known advantages, including:

Production facilities facing cost and volume challenges when replacing or upgrading single-spindle machines need accurate metrics. When it comes to choosing single- or multi-spindle systems, is it simply a matter of part production numbers, individual piece cost or other factors?

There are often overlooked factors when deciding whether to replace a single-spindle or purchase a multi-spindle machine, according to Jeffrey Reinert, president and CEO of Schütte Corp., Jackson, Mich.

“Generally, I think we find that people don’t consider their overhead costs,” Reinert says. “They look at the cost of the equipment, solely, and they calculate that out and divide it by the cycle time and the output.”

Platinum Tooling in North America distributes QUICK cut knurling tool for a machining process that uses cutting to remove material while being supplied at an axial feed rate. This process can therefore also be used for thin-walled or soft materials, as well as hard-to-machine materials.

Shops often have five to 10 (or more) Swiss-type machines running a given part, in, for example, a 100,000-sq-ft (9,290-sq-m) manufacturing facility. That determines shop output; if the total overhead is 999 of 1,000 parts produced per hour, then profit comes down to that single part. Replacement with multi-spindle machines capable of three to four times as many parts per hour means output would be greater and profits higher, while floor space is freed up and overhead covered.

“There’s a calculation required,” Reinert explains. “The cost of [any new] equipment is factored into the cost per piece, but the cost per piece is lower when you go to [more efficient] equipment, be it a multi-spindle or otherwise. So briefly, when your volumes go up, you should look at a multi-spindle rather than multiple machines of the same type.”

Index Corp., Noblesville, Ind., provides some concrete metrics. There are three general criteria for a shop to be successful with a CNC multi-spindle, Tyler Economan, the company’s technical sales manager, says, noting that:

1) Parts should be 52 mm or smaller in diameter.

2) Between 60% to 80% of a part’s features should be on either its front or back.

3) Lot sizes should be at a minimum of 5,000 for individual parts or families of very similar parts.

“If these three conditions are met, there is a very good chance a shop would benefit from investing in multi-spindle technology,” Economan says. “Shops that are facing constraints in terms of labor or floorspace stand to experience the most significant gains.”

Platinum Tooling Technologies, Inc., the exclusive importer of Heimatec tools, shows its 1:4 speed increasers for the most current Citizen machine models. Designed to optimize the machine’s parameters, these precision tools are efficient and cost effective.

Meanwhile, Preben Hansen, president of Platinum Tooling Technologies Inc., Prospect Heights, Illinois, contends that the work piece and volume are the basis for change. “It’s a very application-driven thing, but I think it really depends on the quantities that the customer’s doing,” Hansen says. “We often are supplying tooling for all kinds of machines where changeover is important and the quickness of how you can change and how you can get a new cutting tool into the machine and not spending a lot of machine time in changeover. That’s pretty critical in these applications.”

Today’s machines , while not radically different from their predecessors, are unlike those of the 1980s.

“Typically, they’re all CNC,” Reinert says. “If you consider the general consensus 20 or 30 years ago, you may have a negative opinion about multi-spindles. Back then they were somewhat difficult to handle, and it remains difficult to find operators that can run that type of equipment. Today’s multi-spindles are completely different and can do very complex work. We presently have [facilities] that change over the multi-spindles at 5,000 or 10,000 pieces.”

Economan suggests that as manufacturers butt up against growth constraints—frequently in the form of an inability to hire enough skilled operators as well as floorspace capacity—many must choose to forgo work or invest in building or expand a facility,” he says. “These manufacturers turn to multi-spindles because they are able to produce far greater quantities of parts without increasing their square footage or number of employees.”

Additionally, there is a trend of manufacturers seeking out machine tool partners that can provide true turnkey solutions. Rather than simply an advanced machine, they are looking for a package that includes all of the technology needed to make a part, as well as full process development and training for their staff to ensure efficient knowledge transfer.

As an alternative to purchasing new and costly machinery, there may be a temptation to upgrade or retrofit existing machines’ control systems. But this typically isn’t recommended.

“Retrofitting a control system would require exhaustive adaptations to either change the kinematics of the older machine or put safety measures into place on the control,” Economan says. “With the time and associated costs of these actions, it is nearly always more cost effective to simply invest in a new machine.”

Platinum Tooling imports Rineck shrink fit tooling and shrink fit machine technology which equips a wide range of standard shrink fit tool holders as well as custom tooling. In addition to standard 4.5° taper tools, 3° slim and extra slim tools are available. Most holders come standard with length adjusting screws. Coolant delivery to the cutting tool can be achieved either through the center or flange of the tool holder utilizing coolant jets or slots.

Schütte’s Reinert agrees that any turning machine, milling machine or multi-spindle would theoretically benefit from changing the control system after 20-25 years of use. Today’s machines deliver improved performance in drives and computers, better dynamics in speeds and feeds, and, therefore, higher outputs, better finishes and greater production.

The exception, according to Reinert, is “a part process so specific that it makes sense. Some processes are so stable and so defined that there is not a benefit to going to a brand-new piece of equipment, and then it is worth expending resources on a retrofit.

“We have an order to rebuild, from the ground up, multiple machines and add as many new features as feasible,” he continues. “The customer loves it but, at the end of the day, the cost is about 65% of a new machine.”

So, what guides capital expenditure? According to Index, the evaluation of changeover speeds is one aspect based upon the industry axiom that “you’re only making money when you’re making chips.”

Economan explains that “an hour of a multi-spindle sitting idle represents far more parts not being made than an hour of a traditional single-spindle sitting idle. In the past, changeovers required enough machine downtime that shops could only afford to run large part runs on them,” he adds. “By streamlining the changeover process, we have changed that cost-benefit balance so that far smaller lot sizes can be run.”

Tool supplier Platinum takes a more agnostic view, with retrofits benefiting high-volume, dedicated production machines.

“Newer machines certainly are more capable,” Platinum’s Hansen says. “The controls have more features, they run faster and produce more torque. So, I think as machines develop, they become more capable of giving customers greater flexibility and address a different level of production.”

In today’s environment, there is no industry segment with an overabundance of qualified operators. Thus, a machine’s ease of use is critical. To this end, while CNC multi-spindles may look incredibly complex when running, they are not significantly more difficult to program than single-spindle machines.

“We emphasize to new users that they are essentially six or eight small traditional lathes,” Economan says. “One of the biggest challenges in terms of application development is learning how to balance production across the available spindle stations, as the longest cycle time for an individual station becomes the de facto cycle time for the part,” Economan asserts.

Like others, Index trains customers on general machine operation “and use of our Virtual Machine, which provides a digital twin to the physical machine,” he says.

Platinum’s Hansen notes that machine manufacturers are keenly aware of education, “but you need to start with someone that’s willing, their brain’s got to be like a sponge to absorb all of that [knowledge] if you haven’t worked [in the industry].”

Manufacturers tend to provide good general training, Hansen notes. However, he says it can be difficult to get people who actually know something about specific types of tooling. “In our experience, pretty much everybody we have hired has no background.”

With 48 or more tools operating in a six- to eight-axis multi-spindle machine, operators often need to program “wait marks” to prevent collisions. Compared to single-spindle machines, Reinert says, “you have to have an operator who’s able to visualize, because you need them to know what could be done on station one and two, and three, four and five. They need to be able to visualize and think, ‘If I move this feature, this operation from position four to position three, or from position three to position five, I can make this whole operation more efficient.’ On a single-spindle machine, you don’t.”

Schütte’s in-depth training provides up to seven weeks of instruction at its facility in Cologne, Germany. However, there’s a natural reluctance for this expensive training beyond one to two weeks.

“Are you going to have an operator that could be creating revenue on a single-spindle machine because it’s easier to comprehend, train for three to five days and then generate revenue, or send them to school for three or four weeks?” Reinert wonders aloud.

His question is honest: Should facilities invest in operational efficiency of a more complex machine delivering greater revenue?

“Sometimes we just want the fast buck, and the fast buck is the easier way,” Reinert says. Thus, a dilemma: an easily trained single-spindle operator and less revenue, or costly training but higher revenue? “I guess we have to start thinking longer term, and start investing in our people and training them more thoroughly,” he says.

Back working with one or three spindles.

As tools and tooling have evolved, so have capabilities. Driven tools with improved coatings and materials together with high-pressure cooling fosters significantly improved high-speed milling and high-speed drilling in exotic metals.

“It opens the door to virtually every industry and delivers flexibility when you can cut at these high speeds nowadays,” Reinert says.

Index established iX4.0, an Internet of Things (IoT) platform for its machines, and has developed several production apps:

They include a new IoT connection to allow older models and non-Index machines to connect to the iX4.0 platform. The product, which has already launched in Germany, will debut in North America at IMTS in September.

While gathering data has become increasingly easy, collating and effectively using it is another story.

“How to make that information beneficial to the whole machining process is the difficult part, and where you need to collaborate with the people that are building machines and the control manufacturers,” Hansen stresses. “Owning one part of the equation doesn’t work, you need all parts to make it happen.”

For Platinum, it’s helping to achieve the proper speeds and feeds needed to utilize its cutting tools in the machine tools.

New methods, greater speeds and torque create challenges, particularly when producing smaller parts. Platinum provides speed enhancers that can multiply the rpm of some machine three- to fourfold. Together with small tools that perform better, finishes may not need secondary work.

“They can get more accomplished with the machines by having the optimum rpm or the optimal cutting tools to perform,” Hansen says.

At Index, a focus on reducing setup and changeover times “has made multi-spindles viable for manufacturers who produce smaller lot sizes and made the technology flexible for a wider range of job shops and companies that require a higher level of agility and responsiveness,” Economan adds.

Another interesting development, Reinert notes, is the ability to form spherical parts from stainless steel. “With ball-turning type attachments—not on our machines exclusively—manufacturers are able to make balls out of stainless steel rather than brass, which requires chrome plate,” he says. “This eliminates multiple operations, and at the end of the day, is more cost effective.”

In general, as machining requirements become more evenly split between the front and back of a part, it becomes very challenging to effectively produce on a multi-spindle.

“We introduced double synchronous spindles for backworking, which allows for the efficient processing of parts that are more balanced, but the technology simply is not designed for truly balanced parts,” Economan says. “That is a consequence of having four stations available for frontworking and only two for backworking.” He points out that parts exceeding a 4:1 length-to-diameter ratio may be more suited to traditional Swiss-type machines.

With multi-spindle machines expanding into aerospace, medical, dental and electronics, the challenge of recruiting and training, adoption of advanced Industry 4.0 and 5.0 tools, as well as better data collection and use, multi-spindle machines create new opportunities. Agility and responsiveness are required.

Index Corp.

317-770-6300 | www.index-group.com

Schutte Corp.

517-782-3600 | www.schutteusa.com

Platinum Tooling Technologies Inc.

847-749-0633 | www.platinumtooling.com

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Contributing Editor