Exploring Advanced Manufacturing Technologies. Steve Krar
plunge, and other conventional grinding operations for producing relatively simple geometries.
Fig. 2-2-8 The CNC controller and servodrive system guides the wheel and table to follow simple or complex forms to within two microns of accuracy. (Junker Machinery Inc.)
In applications where there is complexity, single-point grinding will do a better job because the narrow grinding wheel allows access to features that a conventional wheel cannot get to without significant wheel dressing. Varying widths of flat and tapered surfaces, crowned surfaces, slots, and undercuts can all be produced by the single-point process.
The use of superabrasives also enhances the flexibility of the single-point process for use in a variety of materials.
In one application, an electric motor rotor composed of three distinct materials was ground in one setup.
▪The rotor had a soft steel shaft with an aluminum armature pressed on the shaft.
▪Tungsten carbide was used on the shaft as contacts for the bearings.
▪All three materials were ground using two wheels, a diamond wheel for the tungsten carbide and a CBN (cubic boron nitride) wheel for the soft steel shaft and aluminum.
▪Concentricity was maintained because the workpiece was ground complete in one chucking.
ADVANTAGES OF SINGLE-POINT GRINDING
The single-point grinding process using CBN grinding wheels can benefit many grinding shops, especially those that can only afford one cylindrical grinder.
▪The single-point process can be up to six times faster than conventional OD grinding.
▪Due to low grinding forces, workpiece drivers are not required since in most cases the frictional pressure for the centers is enough to rotate the part.
▪Complete grinding of almost all possible contours in one setup is possible.
•The work done on this type of machine normally requires two or three specialized grinders to produce the same lot quantities.
▪It is ideal for low-volume shops that cannot afford to buy specialized grinders to perform specific operations.
▪Indirect cost savings result from fewer operators required, lower maintenance, and less consumables.
▪Better workpiece accuracy is maintained because all operations are done in one setup.
▪Contours are easily ground by CNC programming of the axes and form requirements.
▪The workhandling time normally done on conventional grinders is reduced.
▪Long CBN wheel life between dressing cycles result in consistently producing high-quality parts.
▪There is little or no thermal damage to the parts being ground because less heat is generated during single-point grinding with CBN wheels.
▪The process is competitive with straight plunge and other conventional grinding operations for producing relatively simple geometries.
SINGLE-POINT VS CONVENTIONAL GRINDING
The following is a comparison of some of the major points between single-point and conventional grinding.
Single-Point Grinding
▪High stock removal with little or no thermal damage to the part
▪Minor production related forces and largely driver-free operation
▪Consistent part accuracy for long production runs
▪Long CBN grinding wheel life with few dressing cycles
▪Higher initial CBN grinding wheel cost but lower cost per part produced
▪Complete grinding of a part in one setup (chucking) replacing the need for multiple machines
▪Economical for small and large production runs
Conventional Grinding
▪Long cycle times – multiple setups (chucking) required
▪Danger of workpiece thermal damage because of heat buildup
▪High machine and grinding wheel wear
▪Frequent grinding wheel dressing cycles required
▪Inconsistent quality parts due to wheel wear
▪Complex formed wheels minimize the range of part contours that can be ground
SUMMARY
The grinding process has been under fire for some time now. Many shops are looking at alternative methods to reduce or eliminate grinding from their process. Hard turning is one example.
▪Single-point grinding may be a way to use the accuracy and surface finish benefits of the grinding process in a way that has a lower impact on the material flow in the shop.
▪In virtually all metalworking operations including milling and turning, many businesses are looking to perform more operations in a single workpiece handling.
▪For medium volume production grinding of complex workpieces, the single-point grinding process may be a way to accomplish this for shops that rely on grinding for a living.
For more information on SINGLE-POINT OD GRINDING see the Website: www.junker-machinery.com
(Dirk Smits, President – Bethel Technologies, Inc.)
Grinding is a metal-removal process that uses an abrasive cutting tool to finish a part to an accurate size and produce a high surface finish. The most common abrasive tool used is a grinding wheel that consists of many thousands of abrasive grain bonded together. In a grinding process, a revolving grinding wheel is brought into contact with the surface of the part to be ground. As each abrasive grain on the periphery of the wheel contacts the part surface, it acts as a cutting tool and removes a minute (very small) chip of metal, Fig. 2-3-1.
Cylindrical grinding may be defined as grinding the periphery of a rigidly supported, revolving part. Cylindrical grinders fall into three general classes: plain cylindrical, universal cylindrical, and special cylindrical grinders. The centerless grinder, one of the special grinders, makes it possible to grind cylindrical parts without supporting the part between centers or holding it in some from of fixture, Fig. 2-3-2. Centerless grinders are precision machine tools capable of mass-producing countless numbers of parts held to close tolerances of size, shape, and surface finish. The modern grinding machine is capable of finishing soft or hardened parts to tolerances of .0002 in. (0.005 mm) or less on high-production machines, while producing very fine surface finishes.
The goal of every manufacturing operation is to produce quality products as quickly and accurately as possible. To accomplish this goal, it is important that every component in the manufacturing process be in top condition so that inaccurate parts are not produced. Inaccuracies in manufacturing result in parts that may have to be repaired, replaced, or scrapped, which affects the productivity and profitability of any operation.
Virtual Reality and certain software programs can be used to simulate a manufacturing operation on a computer before starting to actually manufacture a product. This allows any potential manufacturing errors or operational sequences to be corrected before spending time, material, and labor on a process that may not produce satisfactory results.