Night moves

Courtesy of Morsch Machine

The lights are on but nobody’s around at Morsch Machine, which employs lights-out machining to run 24/7. Here, a pallet changer (left) feeds a machine tool (right). 

Five shops use different lights-out machining strategies, but all are focused on creating stable processes.

If you ask five machinists how they make a part, they’ll have six ways of doing it. The same appears to be true with lights-out machining. While the shops interviewed for this article take different routes to the goal of unattended operations, they all agree the foundation of the process is to have a stable, repeatable process.

Fully Developed

The rule at L&S Machine Co., Latrobe, Pa., is a process must be fully developed before any lights-out job is run. For example, an ongoing job at L&S involves machining an 8½ "×8½ "×0.600 " stainless steel adapter plate. Lights-out processes performed on a Haas vertical machining center include drilling more than 600 holes 0.192 " and 0.221 " in diameter using solid-carbide, through-coolant drills from OSG. The holes and the edge of the plate are chamfered. The shop fixtures parts in the machine in groups of five, and it takes about 6½ hours to process each set. 

L&S Machine’s operation in Marion Center, Pa., makes prototype and production parts, with an emphasis on the nuclear power industry. “We run them from 6 a.m. until 10 p.m. manned, then for 3 to 5 hours lights out,” said Foreman Dave Smathers. L&S fine-tuned the process at its main shop in Latrobe before committing to lights-out production. “We took our time,” he said. “We didn’t go unmanned until we knew we had problems like drill breakage solved. It didn’t go unmanned until about a year ago. We started running it without anybody here, then moved it to Marion Center.” 

Courtesy of B. Kennedy

Copious coolant flow aids consistency of drill life in lights-out machining at L&S Machine. 

Process monitoring helps maintain reliability. After each plate is drilled, the VMC’s spindle moves to a Renishaw OTS tool-length sensor, which confirms a drill is intact. If the sensor detects a broken drill, the machine stops. A drop in coolant pressure below a predetermined level will also halt machining. 

L&S prefers not to use load-monitoring technology. “We know the drills run anywhere between 30 and 36 percent on the spindle load meter. You can set the monitor to stop drilling any time load spikes up. That way, you won’t break a drill,” Smathers said. But the shop found that even minor variances in the work material triggered a machine stoppage. “It’s easier to just probe between parts. If a drill breaks, it usually shatters, so we don’t really lose a part over a broken drill,” Smathers said. 

However, drill breakage is essentially nonexistent because the process has been thoroughly proven and the drills have consistent life. “We know our drills last for 15 pieces,” Smathers said. The shop doesn’t baby the drills. “We run them as hard as we can,” he said. “We found a sweet spot of speed and feed at which the drills are really consistent.” 

Copious through-the-spindle coolant flow at 1,000 psi aids that consistency. “The coolant keeps the end of that tool nice and cool and assists in chip evacuation,” Smathers said. At the same time, coolant from multiple external nozzles floods the face of the plate to help evacuate chips. Then, between the drilling and hole-chamfering operations, the shop employs a Clean-Tec fan from Lang Technik to blow away any remaining chips that might damage the chamfering tool that follows the drill. The fan has a tapered-flange shank that enables it to be stored in the machine’s tool magazine, and its spring-loaded polymer blades deploy via centrifugal force when it makes two passes over the plates at 5,000 to 8,000 rpm. The combination of thorough process development and machining technology permits shop staff “to shut the lights out, leave and let it go,” Smathers said.

The Long Grind

Lights-out tool grinding involves many of the same issues as other metal-removal processes. Professional Tool Grinding Inc., South Easton, Mass., manufactures specials for the aircraft, aerospace, automotive and medical fields. PTG may run six or fewer prototype tools for customer tests, but according to Mike Hilbert, tool design and production engineer, production runs “get into the hundreds, even thousands,” which provides an incentive to reduce labor costs by running lights out. 

Courtesy of B. Kennedy

After drilling a stainless steel adapter plate at L&S Machine, the Haas VMC spindle moves to a Renishaw OTS tool-length sensor, which confirms the drill is intact. If not, the machine stops.

Typically, unattended production takes place for 4 hours on weeknights and over the weekend. Hilbert agreed that establishing a sound process before running lights out is critical. “We wouldn’t do a setup piece and then leave. For a job running over the weekend, we set it up Friday afternoon and run it for a couple hours to make sure everything is leveled out and on the right path.” 

Tolerance requirements help determine if a job is right for lights out. Tools ground unattended are still precise, but tolerances are ±0.001 " rather than ±0.0005 ", for example. “Over the weekends, we will find jobs with more open tolerances,” Hilbert said.

Tools that require less operator intervention are also logical choices for lights-out operation. Hilbert said the shop’s Walter grinding machines produce consistent work whether attended or not, but grinding wheel wear is a consideration. In some cases, Hilbert noted, PTG employs software that measures parts while the machine is running and makes adjustments for wheel wear.

Grinding speed and feed rates do not change for unmanned operation, Hilbert said, “but for lights-out operation over the weekend, we might slow the rapid movements of the machine to 80 percent to minimize wear and tear on the machine.”

A Flexible Schedule

Joe Salontai, CEO of Morsch Machine Inc., Chandler, Ariz., said his shop “absolutely” determines a machining process is stable before running it lights out. “We make sure that a part is running well, and then we will commit it to overnight production. We are rambunctious but not foolhardy!” 

Another word to describe Morsch Machine is ambitious, in regard to its approach to flexible production scheduling and lights-out operation. The company machines, assembles and finishes enclosures, support components and chassis—most from aluminum—for the electronics and avionics industries. 

The facility runs 24/7, operating four machining cells with a focus on flexible automation. One large cell includes three Hitachi Seiki horizontal machining centers, two with 120-tool magazines and one with 210 tools, serviced by a rail-guided vehicle shuttling 44 pallets. The plant’s newest cell features a Toyoda HMC with 494 tools and 18 pallets, also with an RGV. 

Morsch Machine uses the flexibility of cellular production in both manned and lights-out scenarios. Salontai said the shop developed its own Excel spreadsheet-based scheduling system that multiplies the cycle time for each part by the volume required to determine total machining time for a job. Earlier this year, the system was changed to enable machining time data to be apportioned to the day, night and lights-out shifts. 

Every Friday morning, a group meets to devise a production schedule for the upcoming week. “We focus on unused minutes,” Salontai said. “There is always going to be downtime. The goal is always zero, but we never get there. We usually are able to limit downtime to 400 to 600 minutes a week.”

Using cellular manufacturing helps minimize downtime. “That’s the neat thing about the flexibility of a cell,” Salontai said. “You can put parts into reserve in the cells so they will run at specific times, or you can line them up by pallet so that they will run one after another. We have the flexibility to pull a pallet into a machine that needs a little extra time.”

Morsch produces its parts in small runs, typically 100 per week at most. The flexibility of the cells and creative scheduling can enable economic production, in some cases, of as few as one part per day, Salontai said. 

A key element of automation and effective lights-out operation is consistency among machining processes, which Salontai said is facilitated by the company’s Zoller heat-shrink and presetting system. The rigid toolholding method minimizes runout and enables tool lengths to be set within 0.0001 ". “That plays into lights-out operation,” he said. “We can replicate the tools very well in the cells. Sometimes, one tool running lights out will machine seven or 10 different part numbers, and we want to make sure it produces the same results on each part.”

The facility does have stand-alone VMCs available for quick-response jobs, but the shop wants to move more work into the automated cells to maximize productivity and minimize labor. “To compete with offshore entities, you are trying to minimize labor input” with lights-out machining, Salontai said. 

The shop’s 24/7 schedule includes running through the weekend on a modified lights-out basis. Both Saturday and Sunday, two-person work teams come in for 2 hours in the morning and return for 2 hours late in the day. “We have about eight people who arrange the schedule among themselves and share the weekend responsibility,” Salontai said. Their tasks include monitoring machine health, fixing machine problems, unloading completed parts and loading new workpieces. “It gives them the opportunity to get some overtime, and gives us the peace of mind that we are still producing throughout a weekend.” 

Salontai pointed out that such an arrangement is not practical on a daily basis. “You are running almost 24 hours a day, and you can’t do that,” he said, because regular manned shifts include process monitoring, inspection, toolsetting and maintenance, as well as machining parts requiring operator attention.

Although Morsch’s machines can send alarms via telephone, the shop doesn’t use that capability. “We tried that originally; we had a paging system. If a machine were to stop for some reason and there was an alarm, the problem was that somebody would get a page at 1 a.m. People get tired of that,” Salontai said.

However, Morsch does employ touch- and laser-based broken tool detection systems to avoid what Salontai calls “a cascade effect. If you break one tool, it might come along and break another and another.” Tool probing is selective, focusing on tools that have a tendency to break or on a specific job or a job series.

“We have minimized problems that way. If a broken tool is detected, the machine stops and won’t run that job or any job with that tool,” Salontai said. Several of the shop’s machines can stop one job if a tool breaks and then move on to another job that doesn’t require that tool. 

Night Vision

In addition to making parts on screw and CNC machines, Wolverine Machine Products Co., Holly, Mich., has two waterjets, the larger of which is a WardJet RX-3013 unit with a 156 "×360 "×10 " work envelope. (For a detailed description of waterjet strategies and problem solving at Wolverine, see Part Time on page 30.) 

The shop ventured into lights-out operation for a time-sensitive job involving large parts used in tooling for aerospace composite parts because the customer “needed the parts and we were trying to get ahead of their schedule,” said Blaine Walker, special projects manager.

On the first day of the job, the shop continued machining a 9 '-long rail-like Invar part to completion unattended to “get a jump; it gave us a half a day buffer,” Walker said. The 8-hour cut began early in the afternoon and extended until about 9 p.m.

Key to making the decision was the nature of the cut. “We would not have attempted this with the waterjet if any of the factors had been different,” Walker said. The waterjet in this case was used basically as a saw, and the cutting speed was slow enough to reduce the chances of problems such as garnet clogs or improper abrasive flow to the cutting head. During the long cut there was no on-and-off cycling of the garnet flow, which might produce clogs.

Courtesy of Wolverine Machine

For a time-sensitive job that involved cutting large Invar parts used in tooling for aerospace composite parts, Wolverine Machine ventured into lights-out waterjet cutting.

Relaxed tolerances were also a factor; the parts were to be machined later to a mirror finish for use as composite molds, and the waterjet-cut specifications required leaving ¼ " of stock for finishing. Unlike parts that Wolverine waterjet cuts for a Stirling heat engine used to generate solar power, the big tooling parts required no in-process inspection.

Although the cut had run throughout the day and appeared to be stable, Walker set up a video system to monitor the job after hours. Describing the system as “essentially a computer on a cart,” Walker said the shop had used it to communicate with the manufacturer after buying its first waterjet. 

The computer was fitted with a video capture card and software that enabled Walker to access the shop network from home and view the machine’s cutting head. In addition to seeing the cutting action, Walker could also view and operate the WardJet machine’s Windows-based control using virtual network software from RealVNC, Cambridgeshire, U.K. The software permits one PC to remotely control another. The software allowed Walker to stop the waterjet if a problem occurred.

Avoiding Entropy

Swiss-style machines feature multiple side- and end-working tools and receive a continuous flow of workpieces from a bar magazine, making them excellent tools for lights-out machining. Mark Stipo, president of High Point Precision Products Inc., Sussex, N.J., agrees with that statement, as long as the application is correct. However, he said achieving “correctness” includes a number of considerations. 

“The first thing we look at are part tolerances,” he said. “A general rule is that a part where the tightest tolerance dimension is greater than ±0.0015 " or ±0.002 " lends itself to running all night, because the chances a part will go out of spec during an overnight run are minimal.”

However, tolerances of ±0.0005 " or tighter bring workpiece material characteristics into the mix. With free-machining materials like aluminum or brass, “you can run ±0.0005 " all day and all night, all week. In 303 stainless, you might be able to; in 17-4 stainless, it’s not likely,” Stipo said. The shop doesn’t run potentially flammable titanium at night. If oil coolant flow were to stop, titanium chips can “catch fire, and set fire to the rest of the machine,” Stipo said. There are machine fire suppression systems available, he said, “but you don’t want to have to put out a fire.”

Courtesy of B. Kennedy

Mark Stipo of High Point Precision Products programs a part for lights-out production on one of the company’s Marubeni Citizen-Cincom Swiss-style machines.

About 90 percent of High Point’s work involves making microparts for dental implants and instruments. Machining small parts produces small chips, but “the bigger the parts, the bigger the chips,” Stipo said. “You worry about chips wrapping around the tool so you have to have a material conducive to (chip) breaking, or you use high-pressure coolant to make the chips come off.”

Although the shop’s Marubeni Citizen-Cincom machines can send telephone page messages when a machine alarm occurs, the shop doesn’t use that option. Stipo said such systems defeat the purpose of lights-out machining. “If you are at home and have to respond to an alarm, you’re still at work; it’s not lights out in your brain,” he said. 

For truly unattended operation, Stipo believes it is essential to first establish a stable process. He said: “When we find a candidate for lights out, we will hone the process and then run it a couple of times during the day without anybody touching the part. We just monitor the machine and tool wear. We bring parts off and measure them, but we won’t adjust the machine. We’ll do an SPC chart and see how the process is going. If it is stable, then we will run it all night.”

Cutting parameters are fine-tuned to maximize consistency and tool life. Initially, High Point runs the tools at the most aggressive parameters that will produce parts consistently. Then it backs off the feed rate to maximize tool life. The stable process that produced 1,000 parts per tool may then produce 4,000 to 5,000 parts before a tool change is needed. The price is a slightly longer cycle time. Optimally, every applied tool should last at least the length of the night shift. 

Courtesy of B. Kennedy

Swiss-style machines, like this Marubeni Citizen-Cincom unit in action at High Point Precision Products, feature multiple side- and end-working tools and receive a continuous flow of work material from a bar magazine, making them excellent candidates for lights-out machining.

Lights-out operations also involve economic risk, Stipo said. “You have to look at a worst-case scenario. You have to figure out how much raw material you’re willing to risk if, as soon as the person goes home, a tool breaks and the machine makes garbage parts. For many of the parts that we run all night, the material diameters are so small that if we were to scrap a whole run, it might be worth a couple hundred dollars worth of material.” Conversely, on larger-diameter parts where material might be worth $5.00 per part and a run consists of 500 units, “are you willing to scrap $2,500 worth of material?” Stipo asked. 

Lights-out machining is not simple. “You don’t put a bar in, press go and walk out the door,” Stipo said. “You have this thing called entropy; it’s Murphy’s way of trying to pull your part out of process into chaos.” The key to lights-out machining is to make sure “that entropy is not going to happen overnight. You have to ask, ‘What is my process going to look like at the end of 12 hours or 15 hours?’ It will degrade to some extent, but is it going to degrade to the point where it will go out of spec? However, there definitely are jobs that are just nuts and bolts and can run all night unattended,” he said. cte

About the Author: Bill Kennedy, based in Latrobe, Pa., is contributing editor for Cutting Tool Engineering. He has an extensive background as a technical writer. Contact him at (724) 537-6182 or by e-mail at billk@jwr.com.

Contributors

High Point Precision Products Inc.
(973) 875-6229
www.highpointprecision.com

L&S Machine Co.
(724) 837-5500
lsmco@comcast.net

Morsch Machine Inc.
www.morschmachine.com
(480) 961-7673

Professional Tool Grinding Inc.
(508) 230-3535
www.ptgspecials.com

Wolverine Machine Products Co.
(800) 397-8446 
www.wolverinemachine.com