A further complication revealed itself late in the project. Constantly changing and reconfiguring the worktables with different workholding fixtures also meant the system was prone to operator error. To address this, a radio frequency identification system (RFID) read/write station was incorporated into each pallet receiver location.
By reading the tooled fixture pallet tag, it was now possible to compare the “workholding fixture” installed in a given pallet location to the part program pulled down to the CNC. This ensured that the program, part, and tool matched. Additionally, the same system was used to scan the tools in the tool changer and could be used to verify the correct tools were available to machine the selected part before the actual machining cycle began.
Switching from aluminum parts to CFRP (carbon-fiber-reinforced polymer) composite parts required a chip and water filtration system to convey both chips and sludge-like material. The waste material needed to be separated from the coolant. First, the chips from composite sludge, then the coolant-suspended CFRP fines had to be filtered from the coolant. Material separation and disposal was not just an operational issue; it was also a facility and hazardous waste disposal issue.
The machine was equipped with a flush-and-wash feature that allowed the entire work zone to be washed down and cleaned before the next material was machined. For chip collection and removal, a conventional chip conveyor was used to transport chips out of the machining area. The chips were separated and put into a dumpster. The cutting fluid carrying liquid and suspended composite particles was pumped to a cyclonic separator, where the sludge was separated and fleece paper filtered for separate disposal.
For long-part machining, “hole pattern” to “hole pattern” accuracy was critical, and thermal growth of the part relative to the machine was factored into the design. Knowing the temperature of the part (so that appropriate length compensation could be applied) was critical when parts needed to snap together at assembly. To this end, each work zone was equipped with a material sample station. A sample piece of the material was mounted, its temperature measured, and the information fed to the CNC for corresponding machining thermal positioning adjustment.
To interface with the shop floor managing network, a front-end PC equipped with a bar code reader allowed the operator to scan work order information and, together with pallet loading instructions, send the right part program for the part(s) to be manufactured as needed to meet daily production requirements.
The operator loaded workholding tooled pallets, as directed, to a specific pallet receiver location, while the system verified that the correct tools were available in each tool changer. The operator could then arm (enable) the work zone in which machining was to next take place and wait until the part(s) in the other zone had been manufactured. The process repeated throughout the day with nearly 100 percent spindle and operator utilization in a “one-off” demand-driven environment.
To ensure the tools of correct size and length were being used, each ATC was equipped with its own tool-length setter. Each tool could be measured, with offsets adjusted prior to machining. A spindle probe, one for each work zone, allowed fixtures and parts to be probed for location with corresponding work coordinate adjustments. A special marking tool allowed information to be written on a part in easily readable script.
This mystery had been solved, though the trail-and-error stages were many, and we needed to avoid the Rube Goldberg look to the machine, where every contraption imaginable would be onboard. As engineers, we certainly had that ability, but the machine’s limitations needed to be set, and there was, of course, a budget constraint.
While not every manufacturer has these same complex problems, having such a flexible, large machine to make both long and short parts in one-off or short runs makes sense for various manufacturers. As a result, any manufacturer who needs flexibility and reconfigurable worktables can quickly adapt his machine tool to meet a wide variety of such machining needs.
One might say, to quote Sherlock, “Exceedingly so!”
This entry was submitted by Rich Bertsche and edited by Rob Spiegel.
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