Turning On To Compact Bar Feeders
Compact bar feeders deliver the performance and capacity needed for this turning cell to run in a largely unattended mode.
Sometimes smaller is better. S&C Electric Co. (Chicago, Illinois) manufactures more than 16,000 components for fuses, switches, metal enclosed gear and other parts for the electric power industry. Many of its parts are turned, and the firm recently expanded its in-house turning capacity by adding a pair of compact, two-axis, CNC turning centers. When it came time to choose the best bar feeder for its new compact machines, the firm selected equally compact 6-foot magazine bar feeders instead of the 12-foot “Gatling gun” tube feeders used on some of the plant’s older CNC lathes. The combination of compact lathe and compact bar feeder has met the company’s needs so well that it has become the model for the company’s future equipment purchases.
S&C was founded in Chicago in 1911. The firm occupies a 1.3 million-square-foot engineering, manufacturing, R&D and headquarters complex—including a recently completed 300,000-square-foot addition—on a 46-acre campus on the city’s far north side, close to Lake Michigan. Although the firm has numerous standard products, it is basically a job shop whose business consists largely of low-volume and special orders. And like any job shop, the firm was faced with the need to improve productivity and increase efficiency. Some of S&C’s older two-axis CNC lathes, which are equipped with 12-foot bar feeders, have problems with vibration, which happens when a bar that is not sufficiently straight is made to rotate at high rpm. To prevent the vibration, the operators must run the machines at less than optimum speeds.
The 12-foot bar feeders pose additional problems. First, they take up considerable space, which is always at a premium in S&C’s busy production department. They are also labor intensive: The operator must always be available to load bars one at a time into the bar feeder, and he or she must remove the remnant of the last bar before loading the next one.
Some of the company’s newer CNC lathes have spindle-length bar loaders, which avoid many of the problems of the older 12-foot bar feeders. Unlike 12-foot tube feeders, which support the bar along its full length as it rotates, the spindle-length bar loader inserts the entire bar segment into the lathe spindle. This bar length cannot exceed the length of the lathe’s headstock. Once inserted, a spindle liner supports the bar as it rotates.
Lathes equipped with spindle-length bar loaders usually have spindle lengths of about 4 feet, which means that S&C must cut the 12-foot-long bars delivered by the supplier into 4-foot lengths. That reduces material usage efficiency: Instead of just one remnant per 12-foot bar, there are now three (one per 4-foot length). Compounding the problem, modern lathes are more compact than their predecessors, and they have shorter spindles. That means that the 12-foot bars must be cut into even shorter lengths to completely fit the spindle, worsening bar usage efficiency.
Because S&C’s existing turning equipment was operating at capacity, the firm looked to new CNC lathes to provide not only additional capacity but also a higher level of efficiency than was possible with the existing equipment—particularly in the area of faster change-overs. There was an additional incentive: The company was outsourcing the machining of some parts, and studies showed that it could save enough by bringing some of those jobs in-house to further justify the purchase of new turning equipment.
Accordingly, the company turned to Ellison Machine Tools and Robotics (Warrenville, Illinois), a machine tool distributor with whom it had a long-standing relationship, with some ideas for a turning center that would fit its needs. Ellison provided two Captain L370, compact (6.5 feet overall length), two-axis CNC lathes made by Okuma America Corp. (Charlotte, North Carolina). Each lathe is equipped with an equally compact (8.5 feet overall length) Prodigy bar feeder made to feed 6-foot bars by Iemca Advanced Feeding Systems.
New Thinking About Machine Tools
The two-axis CNC lathes represent a significant departure from traditional thinking at S&C. “In the past, when we needed a new turning center, we would buy one that offered the greatest flexibility—a machine that could produce any part that we make,” explains Phillip Olson, associate senior engineer, operations support, at S&C. “That thinking prized flexibility above every other consideration. Today, we have refocused our manufacturing processes and employ a strategy called Advanced Manufacturing Process, or AMP. Our shop floor is now arranged into mini factories, with parts running from one machining area to another in a specific path from start to finish and flowing in one direction only. This allowed us to move away from specifying turning centers capable of machining any part, to choosing turning centers for specific types of parts.”
The new two-axis turning centers incorporate features that their older counterparts simply do not have. For example, the machines incorporate a teach function, in which the first few pieces of a job are run and the machine “memorizes” the horsepower required for a particular cut. Once the norm for that cut is established, upper and lower limits can be set. When these are exceeded because of a worn or broken tool, the machine will stop. The condition triggers an alarm that alerts the operator to the problem. S&C’s Mr. Olson stresses that features such as this help make it possible to run the machines—safely—in an unattended mode. If a tool breaks or an insert chips, the machine stops before it or the tooling can be damaged.
No Channel Changing
Two essential characteristics of the turning cell, namely fast change-over from one job to the next and the ability to run unattended for long periods, could not have been realized without the lathes’ new 6-foot magazine bar feeders. “Typically, a bar feeder’s guide channel must be changed when the next job involves a significant change in bar diameters,” Mr. Olson explains. “The Prodigy helps us hold down change-over times because we don’t have to change the channels in the bar feeders. One was fitted with a guide channel capable of running bars from ½- to 1 ¼-inch diameter; the other [was fitted] with a guide channel to accommodate bars from 1 ¼ to 2 inches in diameter.
“We still must change the collet,” Mr. Olson continues. “Originally, setting up the bar feeder’s pusher to run a different bar diameter required unthreading the collet and removing some washers, a task that took several minutes. However, about the time that we bought the bar feeders, IEMCA introduced a quick-change system in which the collet is secured with a spring-loaded cross pin. Now, instead of having to use a wrench to remove the collet, you simply remove the pin, lift off the existing collet, insert the new collet and replace the cross pin. We have yet to perform time studies on the quick-change collet system, but we’re confident that it will reduce setup time by 3 to 5 minutes.
“Also, when we purchased the machines, we purchased an optional sliding track that allows us to retract the bar feeder from the lathe to provide room to work on the machine’s headstock,” Mr. Olson adds. “The sliding track enables our maintenance people to slide the bar feeder away from the lathe for servicing and then reposition it when they’re finished without having to realign the two, which can be a time-consuming task. Our operators use the sliding track to change the quick-change collets, eliminating the need to remove the pusher from the machine.”
Large Bar Capacity
Without the 6-foot bar feeders, S&C’s new turning cell would probably be unable to run unattended to the extent envisioned for it. The operator can load 6-foot bars side by side in the magazine-style bar feeder to make a 15-inch-wide carpet. While the operator is busy tending other machines, the bar feeder will automatically feed the bars one at a time to the lathe until they are all consumed, or until the required quantity of parts for the job is machined.
Automatic bar loading is also a feature of the short bar loader. However, where the short bar loader ejects the bar remnants to the bed of the lathe where they mix with the chips, the Prodigy 6-foot bar feeder retracts the remnant to the back of the bar feeder and ejects it into a separate scrap container. This remnant retraction feature eliminates possible damage to the chip conveyor, as well as tooling and way cover damage from falling remnants. (Remnants of large diameter bar can be heavy.)
Half An Operator
“Typically, we have one operator per machine,” Mr. Olson notes. “We justified the purchase of the 6-foot bar feeders on that basis. However, today we run both lathes with 0.5 operator. In the morning, you may see an operator at the turning centers loading bars, checking parts or setting up a job, but in the afternoon, both machines are usually running unattended.
S&C uses insert-type tooling extensively and has tried to take advantage of improved insert grades as they become available. Efforts in this area were frustrated in the past by the inability to run the CNC lathes at high speeds and feeds because of the limitations of the (12-foot) bar feeders. Bar vibration at high rotating speeds adversely affected machining results, and bent bars would jam in the bar feeders, resulting in work stoppages.
The 6-foot magazine bar feeders have virtually eliminated such problems. Now S&C is tooling the turning centers using the newest inserts and running at higher speeds. “With the 6-foot bar feeders, we can run at higher rpm,” Mr. Olson affirms. “We keep the machines running at the high end, particularly with smaller-diameter bar. A lot of our drills are insert drills that we use at the higher rpms to reduce cycle times.”
Cell Runs 24/7
S&C operates its turning centers on a 24/7 basis. The company refines the way it uses the machines on an ongoing basis to exploit their productivity potential. For example, it established a standard turret configuration—the Okumas have a 12-station turret—in an effort to reduce setup time when going from one job to the next. One station is the feedout and cutoff station; another is the rough turning station; one is the finish turning station; and so on. And where deburring operations are required for jobs running in the cell, portable drilling machines, buffing wheels, deburring wheels and similar light equipment mounted on carts with casters can be rolled up to the machines and stationed where they are most convenient for the operator.
There’s a strategic dimension to the new turning centers. At one time, S&C machined many of its parts from castings. The cell is helping the company to eliminate the use of castings and instead machine its parts from solid stock. In fact, a complete product line was designed to be produced from barstock machined on the Okuma turning centers. “We eliminated the cost and leadtime associated with castings,” Mr. Olson notes. “We can not only machine the parts from bar a lot faster than we can machine individual castings, but we can also accommodate design modifications faster. On the Okuma turning centers, design changes are frequently accommodated with a few minor changes to the machining program. With castings, we’d have to have changes made to the patterns, which could take weeks.”
The time it takes to fill the customer’s order is always an important gage of operating efficiency. S&C tracks jobs from the time the order is received to the time that finished parts are shipped, and the company has gone from more than a year for some parts, to 7 to 8 days for most parts today. It’s a safe bet that some of the latter parts were produced in the turning cell.
Model For Future Improvements
S&C’s production floor is best described as crowded. Mr. Olson recalls that people wondered where he was going to put the two new lathes. (In fact, they were installed in what had been a tub storage area.) The point is that the shop was able to accommodate the compact lathes and bar feeders where it would have been unable to find room for larger machines. The proof of the success of the turning cell is that S&C will soon be doubling the size of the cell with the addition of two more Okuma Captain CNC turning centers and IEMCA Prodigy 6-foot bar feeders. What’s more, Mr. Olson reports that the turning centers represent a model for the compact, more focused, highly efficient, solutions that S&C will use to address future machining requirements.
S&C Electric can be reached at (773) 338-1000.
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