“It’s not uncommon for people to think of pallet changers on vertical machining centers for high volume production jobs. Changing parts and cleaning chips on the ‘off pallet’ while the machine cuts and doubling your production is easy,” says Steve Brown, vice president of SMW Systems, the Santa Fe Springs, California-based machine tool accessory supplier. “Perhaps because most builder-supplied APCs (automatic pallet changers) don’t easily allow the introduction of ‘extra’ pallets, the idea of using a pallet changer for short runs is not what people think of. Why is it that APCs for horizontal machining centers make it easy to have many extra pallets, but APCs for VMCs don’t?”
The following story is personally interesting in that the company bought a pallet changer for a particular high production job and later discovered the setup changing benefits for small batch Just-In-Time production.
Archimedes Products, Inc. purchased its first pallet changer to improve its productivity on a long run production job it was machining for one of its customers. The machining cycle time was 15 minutes, and it was taking another 14 minutes to pull out the completed parts, brush off the chips and load new blanks. When Archimedes learned of the vertical machining center pallet changer, the investment was an easy decision. With the pallet changer the company nearly doubled production by doing all the workpiece unloading, chip cleaning and reloading off-line (outside of the machine) while the spindle was cutting on the other pallet. Switching the pallets, the only portion of the load-unload cycle done while the machine was idle took less then a minute compared to the former 14 minutes. The pallet changer paid for itself in a few weeks, and the rest was profit.
What Archimedes didn’t realize when it bought the pallet changer for the high production job were the benefits of using the system to cut setup times from hours to just a few minutes. Maybe some salespeople mentioned the concept, but it didn’t click until Archimedes actually had it in its facility. “We no longer run that particular volume production job, though we’re prepared to out-bid any competitor next time we see a similar contract available. But we do run a lot of small batch jobs very efficiently,” states the shop manager. Since its original investment, Archimedes has bought a total of 14 pallets and equipped three vertical machining centers in an identical manner.
Archimedes has two pallets with indexers permanently mounted, six pallets with a variety of 4-inch and 6-inch vises permanently mounted, two with angle plates, four with fixtures and two with a threaded grid pattern. With all these permanent yet flexible setups aligned and dialed in, Archimedes can set up any VMC table for the next job in just minutes. And the company knows right where the zero datums are so it can proceed with first article machining with confidence. On a regular basis Archimedes even goes so far as running the first and second operations on parts sequentially and simultaneously on two different pallets. This way it gets the volume production benefits of changing workpieces while the machine is cutting; plus reduces the lead time to get parts finished through two operations from hours to minutes or days to hours, depending on the part and production batch size, and of course the table setup time savings.
For small batch vertical machining, the pallet changer has proven to be at least as valuable as it was for the volume production job Archimedes originally bought it for. Whether the company is doing high volume production or small batch JIT machining, the vertical machining centers will be taking advantage of the benefits of pallet changers.