Aug. 06, 2024
As a job shop, Mitotec Precision continues to identify ways to speed changeovers for jobs that run across its two CNC multi-spindle machines for operators such as apprentice-now-employee Trevor Hutchins. Batch sizes of 20,000 parts is its sweet spot for these machines. (Photo Credit: Mitotec Precision)
Mitotec Precision is no stranger to multi-spindle cam automatics, but is new to CNC multi-spindles having purchased its first one in (added a second in the spring of ). What&#;s interesting is the Necedah, Wisconsin, company has never used its traditional cam or more recent CNC multi-spindles as one might expect for these types of high-production machine tools.
&#;We&#;re a job shop,&#; explains Clinton Pouillie, general manager. &#;Although a multi-spindle machine conventionally might be dedicated solely to running one part or a family of like parts, we&#;ve found a way to make 20,000 parts per run work for us despite the changeover times.
&#;In considering this, we first asked what we are as a company,&#; Pouillie explains. &#;If we are a multi-spindle company, then that&#;s where we need to make our capital investments. We also considered how this could help mitigate the challenge of finding new team members as the machines can match the output of four single-spindle machines that might require multiple operations as well as boost overall production compared to those machines.&#;
But even beyond the higher production capabilities, a CNC multi-spindle would offer the opportunity to respond faster to customers&#; shrinking lead times/hot jobs that might be challenging to deliver on multiple single-spindle machines. In addition, it would create a single quality stream of machined parts to inspect rather than many streams from different machines.
I learned more about this during a recent visit to the 80-person, ISO--certified shop that is now working to speed setups to minimize changeover times for its now two CNC multi-spindles, while facing a good challenge to have: endeavoring to keep them fed with new work given they might produce completed parts every 8 seconds.
The first CNC multi-spindle purchase was on the heels of a business rebranding. Until late , the company was known as Necedah Screw Machine Products. The name change to Mitotec Precision was made to demonstrate to customers and potential new employees its move away from mechanical machines to new CNC technology such as Swiss-types and turn-mills. (The company says the prefix &#;mito&#; means &#;threadlike&#; or precise and its pronunciation implies strength and might. The second half of its name represents the technical aptitude of its team.)
The shop chose 8-spindle machines with 26-mm barstock capacity believing this configuration offered the right combination of size and speed for the complex parts it would run across them. It is also in the process of eliminating external coolant lines, instead running oil through the tooling to further speed changeovers.
The CNC multi-spindle platform was the next logical step in terms of multitasking machining technology. After considering a few builders, the shop chose an 8 × 26 MultiSwiss from Tornos Technologies U.S. Corp.
Pouillie notes that Tornos offers its multi-spindle machines in a few different configurations. The shop decided that an 8-spindle machine with 26-mm barstock capacity offered the optimal combination of size, spindle speed (6,000 rpm) and spindle capacity to facilitate a broad range of complex parts and part sizes.
He also appreciates the machine&#;s hydrostatic spindle bearing design. &#;What impresses me is that the machine can be running eight 1-inch-diameter steel bars at 5,000 rpm and you hear the sound of the mist collector over any spindles noise,&#; Pouillie says, &#;We don&#;t hear vibration or rattling which leads to higher tool life, improved surface finishes and overall process stability.&#; Oil temperature control also contributes to process stability, while high-pressure oil delivery (the machine features 20-, 40- and 80-bar high-pressure coolant pumps) is very helpful in breaking chips and evacuating them from the cutting zone.
Pouillie says the shop uses TB Deco programming software from Tornos which he feels is particularly valuable for the multi-spindle platform. &#;The programming isn't as hard as one might think as each spindle has its own program, but it can be a challenge to coordinate wait codes without the software,&#; he explains. &#;Plus, it also automatically simulates a part run to reveal any error codes or overtravel conditions prior to running a job. In addition, it calculates the cycle time extremely precisely as it proves out a job.&#;
The TB Deco software also automatically adjusts an entire part program as a programmer makes changes to perhaps move operations from the spindle that has the longest cycle time (which on a multi-spindle is the true cycle time for the part) to another spindle(s). Mitotec Precision has an offline seat and its engineering team uses it to create all programs for the two CNC multi-spindles.
Currently, the shop is devising ways to reduce changeover times which for now stands at under 8 hours. Although that can be twice as long as setting up a single-spindle for a new job, the production speed of an 8-spindle machine makes up for that.
For example, it is machining channels on the side of its Goeltenbodt toolholders that mate with a ground stop to enable fast changeover with high positioning repeatability. In doing this, each tool becomes dedicated to a specific spindle and there is no need to touch off cutters. The shop is also in the process of eliminating external coolant lines and instead running oil through the tooling to further speed changeovers by eliminating the need for operators such as Trevor Hutchins, shown in the lead photo, to remove and reclamp coolant hoses. Pouillie notes that the open design of the MultiSwiss provides Hutchins with easy access to the toolholders &#;without getting drenched in oil,&#; he quips.
Mitotec Precision has run a number of jobs across its MultiSwiss machines and has been able to more quickly respond to customers&#; hot jobs. &#;A customer might call needing 20,000 pieces of a complex part in a month, Pouillie explains. &#;Normally, this means we&#;d need open capacity on multiple machines, which we might or might not have. A multi-spindle gets us the ability to respond with one machine and one quality value stream for us to control.
Mitotec Precision reconfigured its floor space to leave room on either side of its two CNC multi-spindles because it envisions adding more of these high-production machines as part of its business model moving forward.
The MultiSwiss also offers a safer chance to take on more work from one customer because the shop won&#;t have to tie up multiple single-spindle machines for just one customer. That doesn&#;t make good business sense. And now that the shop has two CNC multi-spindles, customers with jobs running on one won&#;t have to worry about their work not being completed on time if that machine goes down because the job could be easily transferred to the other.
Although Mitotec Precision has benefited from the boosted machined parts production and other advantages the CNC multi-spindles offer, that higher production from two individual machines has caused bottlenecks with regard to part inspection and cleaning that it has worked to open.
Automated vision inspection systems such as this help alleviate measurement bottlenecks created when CNC multi-spindles significantly increase production volumes the shop must handle.
Per the former, the shop&#;s automated vision systems from Oasis Inspection Systems have proven valuable in speeding part inspection. &#;We certainly don&#;t want to have to halt production on a CNC multi-spindle that might be dropping completed parts every 8 seconds to manually inspect them at specific intervals throughout a job,&#; Pouillie notes. &#;Fast, automated inspection processes enable us to satisfy quality reporting requirements while keeping these machines up and running.&#;
Like part inspection, part cleaning can become a bottleneck when production volumes increase. This is one reason why Mitotec Precision added a single-chamber, solvent parts washer with automated loading/unloading system.
Per the latter, Mitotec Precision added a single-chamber, vacuum-solvent parts washer with automated loading/unloading system from JCOM Imports. Like part inspection, parts cleaning can become a bottleneck given the CNC multi-spindles are producing complex parts (sometimes having features such as blind holes) so fast. In addition, part cleanliness regulations continue to become more stringent.
Parts are cleaned by flooding the unit&#;s drum (with the option to swivel or tumble parts as well as use ultrasonics) to clean them to medical-grade standards (50 different cleaning programs/recipes are available). It is also operated under vacuum for energy efficiency and to help protect the machine components. Mitotec Precision is integrating a bar code system for each parts basket with the proper cleaning &#;recipe&#; to simplify the process for employees.
The CNC multi-spindles opened time on Mitotec Precision&#;s four VMCs that previously were used primarily for second-op work. Now, the shop is using machines such as this Brother VMC with pallet changer and hydraulic workholding for production work.
Conversely, the CNC multi-spindles have opened time on the shop&#;s four VMCs that previously were used primarily for secondary operations. Now, it uses these machines for production work. One example I saw during my visit was a small casting for a medical application run across a Brother VMC with pallet changer using hydraulic vises and Paws Workholding system on a rotary table.
The shop has taken further strides along the CNC multi-spindle path by altering the layout of its shop floor &#; not only to accommodate its second MultiSwiss, but additional CNC multi-spindles on either side of the current pair. One challenge for Sales Manager Warren Schoenborn, however, is finding new work to both generate a backlog on those machines while maintaining availability to work in a high-volume job when a customer needs it. Per the former, he&#;s eyeing new markets for the shop, such as medical and optics.
Regardless, this falls in line with Mitotec Precision&#;s mantra of thinking differently and creatively. This is an example of shops with which I enjoy staying in touch. Who knows what new process or technology a subsequent visit at some point might reveal.
I started writing about machining and manufacturing businesses 25 years ago. (Time flies.) Anyway, how such companies now present themselves in terms of their brick and mortar operation (and online, too) is drastically different from years ago. Note the look of Mitotec Precision&#;s foyer. Does it look like the entrance to a &#;machine shop?&#; It does not. And that&#;s a good thing in terms of helping change the perception of what a business that focuses on machining &#; or more appropriately serving its manufacturing customers &#; is all about.
This projectile is one of several air bag components made on Tornos multispindle automatics at the rate of 300 per hour. When previously made on a two-axis CNC single-spindle with a secondary operation, the rate was 50 parts per hour.
Fig. 2&#;The step-by-step production of the stainless steel demonstration part, completed in 17 seconds each. A single-spindle would run a minute or more.
One bank of Har Technologies' multispindle units and automatic bar loaders. The new technology has enabled Har to increase both business volume and profitability.
Fig. 1&#;This chart illustrates the relative productivity difference between single-spindle turning and multispindles. The comparison is based on cycle time and parts per cycle.
The basic look of the multispindle has changed little over the years. How it works, though, has undergone a veritable revolution with the implementation of CNC and the increasingly effective use of singlepoint cutting tools.
Multispindle manufacturing for small parts looks, at first glance, like a breakthrough in production output. It seems logical that a six-spindle machine should outperform single spindle units by producing five times the parts per minute. And, when multispindle machines are totally dedicated to production of a single part, multispindle units often have time left over to further increase their profitability by taking on more business without additional investment in equipment or operation-related costs. In these cases, the benefits that CNC technology brings to faster job changeover are significant.
Discussion should start with an examination of the principle and operation of multispindle machines. Then we can explore the potential for increases in profitability as we climb the evolutionary ladder from single-spindle, cam-driven machines to investment in CNC-controlled multispindle screw machines.
In a very rough analogy, the multispindle gains its speed in very much the same way the old Gatling gun was able to increase its firing time. There's even a rough physical similarity. A multispindle machine subdivides the typical single-spindle operation cycle into more individually controllable segments.
In both multis and single spindles, tool movement and timing are controlled by a system of cams, a stored CNC program that actuates servomotors, or by a parallel operating system that is effectivly a blend of the first two. In this parallel mode, movement of tools is controlled by a central clock that electronically emulates the mechanical function of the main camshft and actuates the tool slides individually through servomotors.
In the single-spindle setup, one tool moves to the stock, completes its operation, returns to its home position, and the remaining operations are carried out in the same way, one step at a time. Some systems allow up to four tools to cut simultaneously&#;two turning tools and an endworking tool at the main spindle, and a back-working tool at the subspindle.
Still, on a single spindle machine only one part is being worked on per cycle. Cycle time might easily be 15 seconds per part, or just under four parts per minute&#;factoring in the time to feed new stock for the next cycle. While providing the flexibility of comparatively lightning fast changeovers, in general, cycle times for a CNC machine are slower than cams.
Multispindle machines begin with three, five, six or eight pieces of barstock, each secured in its own collet and mounted on an indexing headstock. With tools controlled at each index station in X and Y axes, and the provision for end working tools operating in conjunction with a subspindle, work progresses continually on parts in all spindles as they index from station to station.
As the cycle time is reduced, the number of parts produced per minute climbs. With the ability to attack the work multiple times per cycle, usually parts can be fully completed on a multispindle machine (see Figure 1).
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The option of mounting up to three tools at any one position, including one from the end, allows the programmer to break each operation into smaller components that may be carried out at different points in the multi-station cycle. A part might be drilled to an optimum depth to suit the timing of a parallel operation at that station, then drilled further at another station, and tapped at yet another point along the process.
As an example, we'll step through the 17-second cycle on the stainless steel part (see Figure 2). The cycle begins after the previous part is cut off at the sixth station. The machine is a Tornos MultiDECO 26/6, which is a six-spindle CNC machine.
The collet is opened and a new length of bar is fed in and locked; the entire barrel then indexes, in 0.8 second.
Position 1: A cross slide tool puts a chamfer on the back end of the part while a center drill, on the center slide, begins the drilling process with an oversize bit, just deep enough to create a chamfer at the beginning of what will be a threaded hole.
Position 2: The X2 cross slide, fitted with a turning tool, faces the part, then turns down a chamfer and three steps while the center slide, using a bit sized to the true hole diameter, feeds about two-thirds into the depth of the hole.
Position 3: The hole is drilled to its final depth and a turning tool finish-turns the two smaller diameters.
Position 4: The ID of the completed hole is now tapped and the slide moves a tool with an insert to single-point thread a portion of the OD of the first diameter.
Position 5: This position's tool finish-turns the largest of the three machined diameters and creates a radius on the original raw stock diameter, finishing it back to the largest diameter, leaving the appropriate length of the chamfer cut in position 1.
Position 6: The couterspindle collet grips the part as it is cut off from the bar, and the back end of the part is given its finish and a radius.
All of the cutters used in this cycle are standard insert tools. Part of the CNC multispindle economy derives from the ability to effectively use insert turning tools rather than form tooling.
Why not just consider a cam-driven multispindle machine? They're cheaper, for one. Or simply purchase additional single-spindle CNC or cam machines?
Operator familiarity with CNC programming for screw machines is a major consideration. If your shop operates exclusively mechanical equipment, who will program a new CNC machine? On the other hand, today's tech graduates are used to the laboratory-like cleanliness and programming-based nature of the CNC environment and generally are not trained in the old cam methods. It's a dilemma for shops. One thing is for sure, the skill sets needed for the operation and setup of cam-actuated machines are increasingly in short supply.
Arthur Mandell is the machine tool finance and leasing principal of Trans Capital Resources Limited (Carlstadt, New Jersey), which has 25 years invested in consultation with companies working to justify their major equipment purchases. He stands firm in the belief that the only true measure of a machine's profitability to a company is based on the cost per part and the number of the parts run. "Ultimately," he says, "the production of the parts is what's going to pay the bill, driven by the cost per part. The least important part of the formula is the cost of the equipment.
"In theory," says Mr. Mandell, "one hundred percent of the parts that are made on a multispindle machine could be made on some other machine&#;but it doesn't work in reverse. So, clearly, one kind of consideration is the types of parts you're making." He cites the example of male-female relationship parts, where multispindles outpace single-spindle machines in the ease and time of switching over from male to female for a partial run.
Even were there is no direct cost advantage per part produced, there would still be the time advantage, allowing the multispindle machine to begin to produce parts sooner than on a cam-operated multispindle. Certainly, when cam-driven multispindle machines were the only option, the time to set them up was rarely justified by their faster cycle time over single-spindle cam machines. And, as with most high technology-based products, the cost of multispindle centers has begun to decline somewhat.
Mr. Mandell, firm in his position that the cost per part tells all, regardless of machine cost, prepared a cost analysis to prove it. The equipment cost comparison chart (see Figure 3) shows not only the economy achieved by using a multispindle machine, it makes several points that go beyond economy to generate additional business and realize a disproportionately greater profit.
The premise of the chart is the difference between two single-spindle CNC-controlled machines and one CNC multispindle machine. While the multi costs $200,000 more and runs for the same number of production hours per week, the values begin to change when cycle times are compared. As the single turns out a part every 17.5 seconds, the six-spindle multi, because it performs at least six operations at a time, drops a part into the bin every 4 seconds; that's 3.43 parts per minute for a single, 15 for the multi.
Assuming a reasonable 85 percent efficiency for both types of machines, it will require two single-spindle machines to turn out the projected two million parts, versus 0.45 multispindle machines. Essentially, the multi is working less than half-time to produce the same as two singles. Remember that for later.
Mr. Mandell's example is based on 8 percent financing for a five-year period. While the monthly payment for the two singles is $.10 less than for the multi, a reduction of that cost to parts per minute, considering machine cost alone, puts the singles at $0.051, while the multi&#;working only half-time&#;came in at $. The additional profit realized from the reduced cycle time: $34,351.32.
The real bombshell comes in the "Other cost factors per machine per period," in this case, five years. Using a base overhead of $2.00 per machine, the doubling factor of the singles begins to add up already, and continues through labor, maintenance and repairs (which assumes a one-year manufacturer's warranty). Now, in addition to more than $34,000 of increased profit, our hypothetical shop owner saves $623,400 in additional expenses&#;plus $171,756.58 in potential additional profit from the other 55 percent of the multispindle machine's available production time.
Here's where a moderately aggressive shop owner can more than double profit from his or her investment in multispindle technology. Better yet, the shop can bid more aggressively, due to open time on a machine that's already turning a profit at 45 percent of capacity.
It takes little risk to grow business that way, yet many people still look at that big dollar-figure investment in a multispindle machine and fail to realize the cost-per-part savings that can accrue to those types of screw machine shop business styles that lend themselves to the multispindles' advantages.
Dividing screw machine shops into three categories can help that decision along. Consider the differences between a job shop, a multi-customer contract manufacturer, and a contract manufacturer whose output is dedicated to single-part production all year long.
The job shop owner responds to whatever variety of purchase orders cross his desk on any given day. He knows that he has a certain number of customers, but doesn't know what their parts requirements will be. This shop is not a likely candidate for multispindle operation. That said, it is possible that the shop specializes in parts particularly suited to multispindle manufacturing, as in the male/female example cited earlier. It would take a very sharp cost analysis to see whether the investment would turn a greater profit, but if it did, it would open a strong competitive advantage. Having a mixture of equipment to handle the next job coming in, cutting changeover time might help to expand the business, but there is greater risk here than in other situations.
The contract manufacturer knows that he already has orders for certain quantities of certain parts, so he will be making the same or similar parts over time. Making time for cost comparisons of multispindle machines against existing equipment is highly warranted in this scenario. The shop has already specialized in a line of parts, and the continuing business for the duration of the contracts allows for a much greater sense of security in making the multispindle change. Since the multispindle cost per part advantage almost automatically creates a greater profit with the machines running at only half capacity, this company can aggressively pursue more work&#;or simply purchase fewer CNC multispindle machines and reap the profit inherent in the faster cycle and changeover times.
Then there's the contract manufacturer whose equipment is at 100 percent capacity all year, making the same part, time after time, perhaps on a single-spindle CNC or a gang of cam-driven machines. If we're dealing in quantities of six million identical parts, it's even possible that a rotary transfer system has been set up. But, come the time that this company eyes a juicy order for a family of parts in the one to two million range each, get a cost comparison like our example, and strongly consider expanding beyond the single-part business with a CNC multispindle or two.
About the author: Ernie Grohs is a product manager for Tornos Technologies, U.S. Corporation (Brookfield, Connecticut).
Har Technologies, in Harwood Heights, Illinois, had a pretty good business going for 46 years using single-spindle lathes and in recent years, CNC turning centers. Why would CEO Jeffrey Lampert switch to multis? After calculating the risk, he thought the payoff would be worth it&#;the opportunity to enter a new market that Har could not possibly serve with single-spindle CNCs: manufacturing millions of small air bag components. With eight Tornos-Bechler multispindle automatics, Har manufactures about 600,000 air bag components each week. Har has experienced 50 percent compound growth in less than five years, thanks to the new niche market the company has carved out for itself.
One component Har makes is the projectile that triggers air bag inflation upon impact. The production rate was 50 parts per hour on two-axis CNC lathes with subspindles, followed by a secondary operation on a manual lathe to remove the cutoff. The multis raised that rate to 300 and Har currently ships about 170,000 projectiles each week.
In operation, the spindle carrier indexes to position 1 where a cross slide faces the workpiece and an end slide moves in from behind. Then the carrier indexes to position 2 for OD grooving from a cross slide and partial hole drilling from an end slide. At position 3, the hole is drilled to its final depth. At position 4, the pointed end is formed, the hole is reamed to its final diameter and then flat bottomed. At position 5, the point is finish turned from a cross slide. At the final position, the point is cut off, supported by a subspindle. As the piece is cut off, the subspindle retracts, a back finishing tool moves into position, the part is finalized and sent down the part chute.
In addition to the increased productivity, Har is able to charge a great deal less for their parts. They are able to meet the quantities required by the automotive industry without additional investment in space to house more single-spindle machines. And Har's multi team, after minimal training on machine operation, often earns bonuses tied to quality and productivity.
Alternative 1:
Alternative 2: Make
Single Spindle
Multispindle Autoloader
yes
yes Cost
$225,000
$650,000 Residual Percent
0.00%
0.00% Machines Required
2
1
Equipment Cost Each Machine Single Spindle
$225,000 Multi-
spindle
$650,000
Production Hours Per Week 120 120
Cycle Time Per Part (In Seconds) 17.50 4.00
Number of Parts Per Minute 3.43 15.00
Efficiency 85% 85%
Quantity of Parts Per Year 2,000,000 2,000,000
Number of Machines Required 1.99 0.45
Total Equipment Cost $450,000.00 $650,000.00
Financing Interest Rate* 8.00% 8.00%
Financing Term (Stated in Months) 60 60
Residual Amount: $- $-
Monthly Payment Amount Total: $9,124.38 $13,179.66 Residual value of equipment if lease financing is used
Cost Per Hour Per Machine $8.84 $25.54
Cost Per Minute Per Machine $0.17 $0.50 Calculated using efficiency factor stated above
Cost Per Part $0.051 $0.033
Additional Profit Realized From Reduced Cycle Time $- $34,351.32 Difference in cost per part x number of parts per year
--------------------------------------------------------------------------------
Other Cost Factors Per Machine Per Part
# of Years
5
Overhead Per Machine Per Hour $2.00 $115.200.00 $57,600.00
Labor Per machine Per Hour $19.00 $1,094,400.00 $547,200.00
Maint. Per Machine Per Year $120.00 $1,200.00 $600.00
Repair Per Machine Per Year $4,500.00 $36,000.00 +$18,000.00
Total Other Costs: $1,246,800.00 $623,400.00
--------------------------------------------------------------------------------
Cost Difference Over Life of Contract $ $623,400.00 Additional income realized from reduced expenses over life of contract
Savings Realized From Reduced Cycle Time + $171,756.58
--------------------------------------------------------------------------------
Additional profit realized from reduced cost per part x number of years for contract
Total Add'l Profit Realized Over Life of Contract $795,156.58
If you are looking for more details, kindly visit Multi-Spindles Hydraulic Drilling Machine.
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