Cutting tool shops do the impossible with spark erosion.
By Charles Bates
The ANCA-Vollmer 5-axis CNC QWD 755 horizontal-wire spark-erosion system features a rotating workhead (A and E axes) for continuous-path profiling of complex cutting tool shapes.
With its probe, the QWD 755 locates the tip of a tool blank, identifies center, and starts cutting.
Parameters already defined for materials and operations within the QWD 755's generator menu let users modify and fine-tune the erosion process.
Partnering a CNC tool-and-cutter grinder with a wire-erosion machine lets shops process tools of both polycrystalline diamond (PCD) and carbide.-Typically, shops with these machines first grind a tool's profile and then burn edges and reliefs using the wire-erosion machine, which saves time. The machine also tackles special tool features that are otherwise impossible to produce. Without wire erosion, tooling shops such as Superion Inc. of Xenia, Ohio, most likely grind PCD tools manually in cycles that take up to 8 hr/tool. On a wire-erosion machine, the same tool is done in minutes and with better consistency.
Superion's machine is the Australian Numeric Control Automation (ANCA)-Vollmer 5-axis CNC QWD 755 horizontal-wire sparkerosion system. It features a patented rotating workhead — E and A axes — for continuouspath profiling of complex shapes such as with step and profile tools. The machine's electrode/-wire swivels around the center of the head and cuts angles in hard materials in single setups and in relatively short cycle times.
"This makes it possible to achieve axial and radial clearance angles at any point in the tool profile. The machine produces stepped tools, circular milling tools, radius-profile milling cutters up to 320 mm in diameter, drills and cylindrical tools up to 500 mm in length, and other cutting tool designs," says Al Choiniere, president of Superion.
The QWD 755 includes a probe and special generator. With the probe, the machine locates the tip of a tool blank, identifies center, and starts cutting. The generator has two settings — one for carbide and the other for PCD — that contribute to the machine's versatility and consistency.
"We believe that the Vollmer generator is the key to the machine's erosion quality," says Choiniere. "Erosion output is controlled according to how much material is to be removed and can result in surface finishes of less than 0.2-µ Ra. Many parameters are already defined for materials and operations, and modifying these parameters in the generator menu lets us finetune the erosion process," he adds.Users select from four erosion stages within each generator setting: coarse roughing, roughing, finishing, and fine finishing — each with its own erosion rates. Feedrates are also programmable in each stage to tweak shaping programs for ultrahard materials and complex geometries.
The machine's software adds to the QWD 755's ability to burn extremely complex geometries on tools such as those with internal cutting edges. "Our operator, Steve Noren, answers prompts about the tool to be shaped, and the software develops the program for it. Open architecture lets us implement a range of solutions such as dividing a tool profile into profile elements."
During erosion, the software displays the gap value and erosion speed to help optimize the process. Operatorseasily optimize erosion parameters-through the generator program and generate tool configurations at a CAD workstation. They can also access cutting programs through the control panel by following simple, menu-driven prompts that minimize errors. While one tool is running, another may be programmed.
Superion teams up its wire-erosion machine with an ANCA TX7 production CNC tool-and-cutter grinder. "The direct-drive, 3,000-rpm workhead (A axis), lets us grind stepped or tapered blanks to a final tool. We produce tools complete in a single setup, minimizing production time for many tools that might have required two operations to complete," says Choiniere. The TX7's wheel-mounting system contributes to production quality with a complete and concentric flange contact. The result is a rigid assembly that practically eliminates runout and deflection while also improving wheel life, surface finish, and part tolerance.
A complete changeover of wheel pack, coolant system, and workholding collet takes less than 3 min. Mounted on a manifold, coolant piping changes with the wheel packs so that coolant flow is always tuned to the wheel in use for optimum coolant application.
"Wheel packs and coolant manifolds are prepared off-machine and can be quickly exchanged to grind a new tool; so short runs are not an inconvenience," adds Choiniere. In addition to fast changeovers, the TX7's wheel changer lets Superion apply two wheel packs to one application for more operations in a single setup.
Mounted to the back of the chuck on the grinder's high-speed workhead, the dresser roll is easily accessible and reaches the wheels during the grinding process with minimal axis strokes. According to Choiniere, inprocess wheel dressing is critical for producing high-quality tools with difficult geometries. "The easy availability of dressing further ensures tool accuracy, especially in profile tools," he says.
Along with its QWD 755 and TX7, Superion uses ANCA's CIMulator3D software, which provides an off-line tool-development environment. This makes for efficient designing of new tooling and allows Superion to develop required manufacturing processes without losing production time. In addition, the software reduces setup time for new tools so that Superion can quickly get production started.
Typically used as an off-line workstation, CIMulator3D also simulates tool production programs prior to actual grinding. "With this capability, we can dress the wheels to generate the form required and optimize the process properly and consistently,"comments Choiniere. The shop produces several hundred different tool designs a month, and it stores all design and manufacturing programs in CAD files.
"We have a good understanding of how to cut certain metals," points out Choiniere. "With special cutting tools, you have to look at the whole picture, including the way the customer's metalcutting machines are built and operate. Combining that knowledge with the tool-programming capability in the ANCA software lets us develop specialty tools in hard materials fairly quickly and accurately. When the tool program is finally downloaded, it is virtually proved out, which reduces delivery time."
He goes on to say that standard tools don't always work on all materials. Although nearly anyone can design a tool, he says, the trick is to understand and successfully tune the process used to make it. This requires a lot of creativity on the part of the toolmaker. "The CIMulator3D software lets us put our toolmaking knowledge to work and provides the freedom to alter canned programs to accommodate our methods. It provides a solid foundation on which we can do our thing and be more creative in designing a tool for a specific application."