Autoloading For Short Runs
Not too long ago, automatic load-unload was strictly for long production runs. Here is a system that makes it cost effective for short-run turning.
Some people consider short run automation a contradiction in terms. After all, automation means using mechanical devices, such as a robot, to perform repetitive, dangerous or physically taxing tasks that people would otherwise have to do. Automating a task is typically a costly undertaking. But when the task involves tens or hundreds of thousands or millions of parts, the cost of automation is amortized so that the cost of automation per part becomes insignificant—in fact, it usually provides a considerable savings over continuing to perform the task manually.
However, when the task is a short run, involving dozens or hundreds of parts, the cost per part of automating it becomes prohibitive. Thus, shops that produce parts in small quantities usually cannot justify the cost of automation and have been prevented from enjoying its labor-saving advantages. Until now, that is. Some new products have become available that are making short run automation an affordable reality, and shops have been quick to exploit them.
A case in point is Star S Mfg. Co., Inc., Thomaston, Connecticut, a third-generation precision turning shop. Star S began in 1944 as a Brown & Sharpe screw machine shop and did not change much until the mid-’80s, when brothers Roger and Robin Schrager took over the family business and began modernizing with computer-controlled machine tools.
The brothers bought a CNC lathe and then some machining centers. “We were still a Brown & Sharpe shop at the time,” explains Roger Schrager, the president of the firm. “Many of the parts produced on the screw machines needed multiple secondary operations. Instead of processing the parts over several secondary machines, each staffed by an operator who loaded the parts one at a time into his or her machine, which is the way we did it in the past, we switched to processing the parts on machining centers capable of performing multiple machining operations on multiple parts. The arrangement enabled us to hold down labor costs, because one operator could tend two or three machines.”
As the years passed, CNC machine tools became even more important to Star S as a means of satisfying customers’ demands for tighter tolerances, better surface finishes and more consistent parts. The shop replaced some of its screw machines with gang-tooled CNC lathes from OmniTurn (Farmingdale, New York). Two of these lathes are configured as bar machines, and because production frequently involves blanking parts on the shop’s remaining screw machines and finishing the blanks on the CNC lathes, two are chuckers.
When the time came for Star S to add more CNC turning capacity, it was ready to buy a fifth CNC lathe. The shop’s existing CNC chuckers required their operators to constantly be present to load and unload parts. This time, however, the shop wanted a chucker with an automatic load-unload device that would enable the operator to fill the loader and then go off to attend to other duties while the lathe automatically processed the blanks.
To satisfy Star S’s requirements, OmniTurn furnished its model GT-Jr. CNC lathe, equipped with an automatic part-loading device called a dial loader. The dial loader is one of several standard, off-the-shelf, automatic loaders developed by the builder for its CNC lathes. It automatically loads and unloads parts, allowing the lathe to operate unattended for extended intervals. It is relatively inexpensive compared to more traditional machine tool load-unload methods, and it mounts directly on the lathe, imposing no additional floor space requirements. Perhaps most important, the dial loader can be quickly and easily adjusted to load different parts, making it practical to use for short- and medium-run jobs.
One of the most impressive features of the dial loader is its simplicity. It consists of a round plate with a circular through-hole pattern drilled near its periphery. The holes match the diameter of the parts to be loaded; the diameter of the parts also determines the number of blanks that can be accommodated. The holes (and the lathe collet) may also be shaped to accept extruded materials such as hex bar. The round plate, or dial, mounts directly on an indexing shaft and is secured with a large handscrew. The user can either order dials drilled with the required hole sizes and quantities for specific parts from the builder or machine them.
Over time, users will probably accumulate a library of dial plates with patterns of holes of various diameters. Because the dial plates are relatively easy to make, some users may wish to dedicate plates for jobs that regularly repeat. When a dial plate’s holes are worn, it can be recycled simply by redrilling the holes to the next larger size for use on other jobs.
A backer plate mounted behind the dial on the indexing shaft serves as a dead stop for the loaded blanks. It can be moved toward or away from the dial plate to adjust for part length. (The system accepts part blanks up to 4 inches long.)
The second major component of the dial loader is a two-axis slide with a gripper that removes the blanks from the dial one at a time and loads them in the lathe collet for machining. As with the holes in the dial, the gripper can be machined to correspond to the cross section of the part being machined.
To set up the dial loader, the operator installs a dial with the appropriate hole pattern on the unit’s dial-indexing shaft. The operator then loosens the dead-length plate mounted behind the dial plate on the indexing shaft, adjusts it for the length of the part to be run, and retightens it. On a thumbwheel switch, located on the lathe’s spindle cover, the operator indicates the number of holes in the dial. The unit’s controller uses that information to determine the number of degrees that the dial must index to present each blank in turn to the load-unload arm.
Next, the operator adjusts the two-axis slide for the length of the part and the location of the drilled holes. Depending on the length and cross sectional shape of the part, the jaws may also need to be adjusted for position or replaced.
The operator places the blanks in the dial by hand, which minimizes the chances of wrong-ending one or more blanks. When we visited Star S, the dial loader was being used to load ½-inch-diameter blanks into the lathe and could accommodate approximately 2 dozen blanks at a time. According to OmniTurn, the dial loader can accommodate as many as 300 (small-diameter) parts, which, at 45 seconds per part, would permit the lathe to run unattended for nearly 4 hours.
How It Works
In operation, the two-axis slide travels to the dial plate, removes a blank from a hole in the dial plate, carries it to and loads it in the collet, and then parks in front of the dial plate while the blank is being turned. After the blank has been machined, the arm returns to the collet, extracts the part and carries it out of the machining area. The arm can be programmed to simply release the machined part, or if the part must be protected from nicks or scratches, it can return it to the hole in the dial plate from which it came. In either case, the dial plate indexes to present the next blank to the arm, and the cycle repeats.
For Star S’s Roger Schrager, the biggest advantage of the dial loader is that it enables the lathe to run for long periods unattended, which frees the operator for other tasks. As the photo at left shows, the lathe is located directly across from one of the shop’s older screw machines, and the operator tends both machines. The Schragers are confident that when the time comes to buy another dial loader-equipped lathe, an operator would be able to handle three machines.
Because the operator tends both machines, the shop can divide the operator’s hourly rate between the two machines to reduce labor costs charged to jobs. Roger Schrager estimates that he is saving at least 10 percent on labor costs for jobs that go across either of the two machines, a savings that he is happy to pass along in lower, more competitive quotes.
70 Cents Per Hour
Compared to other automatic load-unload alternatives, the dial loader is relatively inexpensive. “Instead of buying a custom automation system or a robot, we’ve bought a standard, off-the-shelf part-loading system,” Mr. Schrager adds. “We could have leased the dial loader for 5 years for about 70 cents an hour, based on 40 hours of usage per week. Where would we find someone to stand in front of a lathe for that kind of money?”
The dial loader also helps Star S deal with the shortage of skilled workers. Less-skilled (lower-hourly-rate) employees can be used to load and unload the dial loader for medium and long runs, freeing more skilled workers for tasks that make better use of their skills.
The dial loader has also increased the shop’s flexibility. “The setup time for the dial loader is 10 to 20 minutes,” Robin Schrager explains. “That improves our ability to take on short run jobs. The hardest part of a short run job is the setup, and because the setup time for the dial loader is so fast we can be confident that we can do the job fast enough to be profitable. We can also accommodate emergency orders more readily, knowing that we won’t be incurring a lengthy down time penalty by interrupting a job.”
As proof of the latter point, while we were observing the operation of the loader during our visit to Star S, Roger Schrager walked up to the machine and placed 12 blanks and a blueprint in the hands of operator Mike Smith with an order to run the parts ASAP. Mr. Smith interrupted the job he was working on and prepared to run the new part. It was shorter and a bit smaller in diameter than the interrupted job, so he was able to use the existing dial plate setup with an adjustment to the dead stop plate to accommodate the shorter length of the new part.
Next, Mr. Smith added a drill to the lathe’s gang tooling plate and changed some offsets for the turning and threading tools used for the previous job. He made a trial cut, checked the thread with a thread gage, made another minor adjustment, recut and checked the thread again and announced the part ready to run. He then loaded 10 parts into 10 consecutive holes in the dial plate and began running the job. Time from start to finish was about 25 minutes—and would have probably been a little faster if it were not for the presence of a stranger looking over his shoulder. Cycle time for the parts was short, and the 10-part run was completed in just a few more minutes.
“We bought the OmniTurns to keep up with changing times,” Roger Schrager explains. “Customers have been placing smaller and smaller orders, but at the same time they’ve demanded greater precision, finer finishes and greater consistency from part to part. Our Brown & Sharpes were and still are great for slugging out parts, but they can’t hold tenths or produce a 32 micro finish. Setup times for these machines can be lengthy too. If the initial setup does not work, you have to change your cams, which is a 2- or 3-day job. After the second try, you may have to change them again. Before you know it, 2 weeks have gone by and the job still isn’t running.
“By contrast, the new CNCs are easier to set up and run,” he continues. “If there are problems with the initial setup you can make the needed adjustments quickly and easily and have the job up and running. The dial loader is a perfect complement to the lathe because it is so easy to change over for the next job. Many of our jobs are short runs, so we need a loader that is as fast and as easy to change over as the lathe it serves. We didn’t want something that takes a day and a half to set up. The simpler it is, the easier it is, the faster the job goes. That pretty much sums up the dial loader.”
The new dial loader-equipped lathe also gives Star S the extra CNC turning capacity it needs to begin limited production of a product the company has been thinking about manufacturing for a while now—a paintball gun. The gun requires a number of turned parts that will be on the shop’s CNC lathes, and the Schragers expect that six or seven of the parts will be made on the dial loader-equipped machine.
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