Hartwell Corp., based in Placentia, CA, developed a quick-access latching system for flight deck cabin doors that exceeded post-9/11 security and pressurization guidelines. The design’s success made it essential that the company quickly implement improvements to its existing machining processes to meet customer cost requirements. Hartwell engineers worked with a consultant to develop a new process utilizing multifunction machines that help achieve manufacturing cost targets by reducing cycle time from 25 to 5 min. A critical aspect of this improvement was developing new CNC programming methods to take full advantage of the multifunction machines. ESPRIT CNC software helped Hartwell quickly generate programs for 300 parts and optimize them to achieve an even greater cycle time reduction than targeted.
Hartwell previously did basic machining on three- and four-axis machining centers and lathes. It used commercial software to program the machining centers and programmed the lathes by hand. The existing machines were at or near capacity and lacked the rigidity to support process quality and volume requirements.
Hartwell made the decision to upgrade its machining capabilities by replacing most of its existing machines with the latest products such as Mori Seiki NL and NT series machines. The NL series machines have two live spindles, live tooling, and a Y-axis for off-center milling. The NT series machines consist of a multi-axis, two-spindle machining center with full five-axis milling, as well as a lower turret. Both multifunction machines provide the capability to perform what previously took three or four operations in a single operation, reducing setup and cycle time and improving quality.
Hartwell also purchased Mori Seiki NV5000 vertical machining centers with 30-tool automatic tool changers and 12,000 rpm, 30-hp spindles. The machines were equipped with a 1000 psi, 8-gal/min high-pressure coolant system and Renishaw spindle and tool setting probes to improve process flow. The company also purchased a linear pallet pool line that connects four NH5000 horizontal machining centers.
Multitasking machines can substantially increase productivity, but they also substantially increase the complexity of the task of programming. The operations are the same, but performing several of them simultaneously is much harder to choreograph. Since this was Hartwell’s first foray into multifunction machines and the machines are notoriously difficult to program, it sought assistance from Ellison Technologies, a Mori Seiki dealer that also provides application engineering services.
There were about 300 components that needed to be programmed for the contract. Hartwell and Ellison agreed that Ellison would program 150 of these parts and Ellison would train Hartwell engineers to deliver the other 150 parts. Ellison recommended that Hartwell upgrade to ESPRIT software because of its capabilities for programming multifunction machines.
Hartwell and Ellison engineers worked together to utilize ESPRIT’s advanced capabilities for optimizing programs for multifunction machines. The company utilized a machine definitions library provided by DP Technology that includes a template that accurately reflects every component in the machine, including the spindle, chuck, and tooling. The machine definitions library eliminates the need to manually define the machine geometry and also makes it possible to identify potential crashes when the program is simulated to avoid crashes on the shop floor. Hartwell engineers imported solid-model geometry from the CAD software used to design the parts. They interactively defined the features for most parts and are planning to make use of ESPRIT’s automatic feature recognition to catalog the features in the solid model.
The next step was applying machining operations to each feature. Hartwell began by developing a library of the company’s most common machining operations, including rough and finish profiling, facing, and cutoff operations on a lathe. The use of standardized operations optimizes productivity while reducing machining time.
ESPRIT provides a range of options for taking advantage of the special capabilities of multifunction machines. For example, there are eight different options for clearance planes used for entering or exiting the cut. The tool rapidly advances to the clearance plane to avoid wasting time cutting air. The tool can also enter in the Z-axis by automatically recognizing the X-axis position of the cut and feeding in from a perpendicular direction to again avoid wasted time cutting air. ESPRIT saves additional time by automatically recognizing where holes start and stop even if they are at an angle or counter-bored. The tool is automatically rapid-traversed to the beginning of the cut without cutting air.
After Hartwell engineers have created the operations, ESPRIT makes it possible to assign them to different turrets, change their sequence, and synchronize operations in different turrets. Engineers then view a simulation that shows the machine, turrets, spindles, tools, and workpiece in real-time operation.
The graphical depiction of the machining operation gives engineers the opportunity to think of ways to improve the CNC program and allows them to go back and change the order of a few operations or change the sync points and run the simulation again. The comparison function in ESPRIT highlights any variation between the part machined by the program and the design intent, such as excess or over-removed material.
By a process of continuous improvement, Hartwell engineers have been able to reduce cycle times for some common components by as much as 80% from the previous single-function machines by utilizing multifunction machines.
Hartwell engineers also perform interference checking to fine-tune the program during the simulation. Multitasking machines have more turrets and spindles that are all moving at once so avoiding crashes can be very challenging. The ability to visualize the machine, spindle, tooling, fixture, and workpiece makes it possible to do all of the prove-out and debugging at the CAM station and then post directly to the machine tool without any editing.
The software Hartwell used in the past was designed around the requirements of single-function machines, so it would have been very difficult to write working programs for multifunction machines and much more difficult to achieve their full potential. ESPRIT, through its developer’s partnerships with the leading multifunction tool builders, provides a wide range of tools that have helped Hartwell achieve the full productive potential from its multifunction machines.
Jon Finn, Manufacturing Engineering Manager, Hartwell Corp., wrote this article for Aerospace Engineering & Manufacturing.