Diamond-Plus, Walter’s tool erosion software, enables an optimal erosion process independent of disturbances, such as differences in material, electrode shape or tool profile, according to the company. Image courtesy United Grinding North America.
Companies that make cylindrical cutting tools from PCD and other materials face two key challenges: meeting the surging demand for PCD tools while retaining the ability to produce HSS, carbide, ceramic and cermet tools.
Being superhard, PCD cutting tools provide long tool life when machining abrasive, gummy materials, such as composites and aluminum alloys. The use of PCD tools is expanding as aerospace manufacturers seek to improve fuel economy by increasing the proportion of lightweight composite and aluminum parts in new aircraft.
Also in pursuit of lighter, more fuel-efficient vehicles, the automotive industry is machining more composite and aluminum workpieces. The extended tool life and clean cutting action provided by PCD tools for these materials outweigh their higher costs.
Toolmakers are producing PCD tools with complex cutting edge geometries to efficiently cut these advanced workpiece materials. However, creating those geometries in PCD is the real challenge.
Grinding PCD with diamond wheels presents the conundrum of grinding diamond with diamond, and it requires careful management of cutting parameters and close attention to wheel wear. An alternative to grinding is the noncontact EDM process. Wire and sinker EDMs can erode PCD, but there are restrictions on the tool features either can produce.
A wire EDM can produce the OD geometry of a PCD tool, for example, but forming some geometric details may not be possible because of the continuous nature of the wire. Similarly, the ability of a sinker EDM to follow a helical contour is limited. Both types of EDMs tend to be dedicated equipment without any grinding capabilities.
To grind the full array of tool materials, Walter developed the Helitronic Diamond Evolution grinding and erosion machine. This two-in-one machine grinds features of rotationally symmetrical carbide, HSS, cermet and ceramic tools while being able to erode PCD and PCBN tools with a rotary-disc EDM electrode.
The electrode rotates on one end of the machine’s two-sided cartridge spindle and produces tool features in the same manner as a grinding wheel. The compact machine has a 2,100mm × 3,100mm (6.9 '×10.2 ') footprint.
Engineered for shops processing small to medium tools, the machine facilitates production or resharpening of tools from 1mm (0.04 ") to 165mm (6.5 ") in diameter, up to 185mm (7.3 ") long and weighing up to 30 kg (66.1 lbs.).
If grinding conventional tool materials becomes a priority, shops can replace the rotary electrode with a second grinding wheel set. When erosion work returns, the rotary electrode can be quickly refitted.
The same fluid is applied for both processes. Walter research determined that dielectric, which is necessary for EDMing, performs quite well as grinding coolant.
The dual-process nature of the machine also simplifies programming. Because the rotary EDM electrode disc produces tool features in the same manner as a grinding wheel, the software to control the electrode’s motion is similar to that used for grinding. Some operator training is necessary, however, because setting up the erosion process requires entry of information different than that typical of grinding.
Diamond-Plus, the most recent generation of tool erosion software from Walter, employs a new variable-acceleration factor that continually optimizes the erosion process to compensate for differences in material, electrode shape, stock removal and tool profile.
In the past, it was always necessary to finish-grind PCD tools, but now, many applications require only finish eroding. And Walter’s Superfine finish erosion technology limits cutting edge chipping to 5µm.
Automation can enhance the productivity of the erosion process, and robot loaders and extensions for cylindrical and HSK tools are available as options. Untended or semitended operation is an important factor when employing the erosion process, which usually is more time-consuming than conventional grinding. In addition, automation permits loading a series of tools and utilizing on-machine probing to monitor the operation, freeing operators to tend multiple machines.
As OEMs incorporate more weight-reducing composites and exotic materials, the demand for PCD tools to machine them will continue to grow, placing more pressure on cutting tool manufacturers to deliver.
Related Glossary Terms
- abrasive
abrasive
Substance used for grinding, honing, lapping, superfinishing and polishing. Examples include garnet, emery, corundum, silicon carbide, cubic boron nitride and diamond in various grit sizes.
- alloys
alloys
Substances having metallic properties and being composed of two or more chemical elements of which at least one is a metal.
- aluminum alloys
aluminum alloys
Aluminum containing specified quantities of alloying elements added to obtain the necessary mechanical and physical properties. Aluminum alloys are divided into two categories: wrought compositions and casting compositions. Some compositions may contain up to 10 alloying elements, but only one or two are the main alloying elements, such as copper, manganese, silicon, magnesium, zinc or tin.
- composites
composites
Materials composed of different elements, with one element normally embedded in another, held together by a compatible binder.
- coolant
coolant
Fluid that reduces temperature buildup at the tool/workpiece interface during machining. Normally takes the form of a liquid such as soluble or chemical mixtures (semisynthetic, synthetic) but can be pressurized air or other gas. Because of water’s ability to absorb great quantities of heat, it is widely used as a coolant and vehicle for various cutting compounds, with the water-to-compound ratio varying with the machining task. See cutting fluid; semisynthetic cutting fluid; soluble-oil cutting fluid; synthetic cutting fluid.
- electrical-discharge machining ( EDM)
electrical-discharge machining ( EDM)
Process that vaporizes conductive materials by controlled application of pulsed electrical current that flows between a workpiece and electrode (tool) in a dielectric fluid. Permits machining shapes to tight accuracies without the internal stresses conventional machining often generates. Useful in diemaking.
- grinding
grinding
Machining operation in which material is removed from the workpiece by a powered abrasive wheel, stone, belt, paste, sheet, compound, slurry, etc. Takes various forms: surface grinding (creates flat and/or squared surfaces); cylindrical grinding (for external cylindrical and tapered shapes, fillets, undercuts, etc.); centerless grinding; chamfering; thread and form grinding; tool and cutter grinding; offhand grinding; lapping and polishing (grinding with extremely fine grits to create ultrasmooth surfaces); honing; and disc grinding.
- grinding wheel
grinding wheel
Wheel formed from abrasive material mixed in a suitable matrix. Takes a variety of shapes but falls into two basic categories: one that cuts on its periphery, as in reciprocating grinding, and one that cuts on its side or face, as in tool and cutter grinding.
- high-speed steels ( HSS)
high-speed steels ( HSS)
Available in two major types: tungsten high-speed steels (designated by letter T having tungsten as the principal alloying element) and molybdenum high-speed steels (designated by letter M having molybdenum as the principal alloying element). The type T high-speed steels containing cobalt have higher wear resistance and greater red (hot) hardness, withstanding cutting temperature up to 1,100º F (590º C). The type T steels are used to fabricate metalcutting tools (milling cutters, drills, reamers and taps), woodworking tools, various types of punches and dies, ball and roller bearings. The type M steels are used for cutting tools and various types of dies.
- outer diameter ( OD)
outer diameter ( OD)
Dimension that defines the exterior diameter of a cylindrical or round part. See ID, inner diameter.
- polycrystalline cubic boron nitride ( PCBN)
polycrystalline cubic boron nitride ( PCBN)
Cutting tool material consisting of polycrystalline cubic boron nitride with a metallic or ceramic binder. PCBN is available either as a tip brazed to a carbide insert carrier or as a solid insert. Primarily used for cutting hardened ferrous alloys.
- polycrystalline diamond ( PCD)
polycrystalline diamond ( PCD)
Cutting tool material consisting of natural or synthetic diamond crystals bonded together under high pressure at elevated temperatures. PCD is available as a tip brazed to a carbide insert carrier. Used for machining nonferrous alloys and nonmetallic materials at high cutting speeds.
- wire EDM
wire EDM
Process similar to ram electrical-discharge machining except a small-diameter copper or brass wire is used as a traveling electrode. Usually used in conjunction with a CNC and only works when a part is to be cut completely through. A common analogy is wire electrical-discharge machining is like an ultraprecise, electrical, contour-sawing operation.
