Typical areas of application for surface grinding are in tool and die making grinding the grinding of punching tools, mould inserts, cutting tools, and guideways on machine beds, various knives or small parts.
Grinding processes are classified according to several aspects
There are various areas of application for grinding and thus different grinding processes are used.
The grinding processes are often classified according to the following criteria:
- Type of surface to be produced (surface grinding, profile grinding, cylindrical grinding, generating grinding)
- Processing position on the workpiece (internal or external grinding)
- Effective area of the grinding wheel (peripheral or side grinding)
- Type of feed movement (longitudinal, transverse, inclined grinding)
In this section you will find the most important grinding processes for grinding wheels, including surface grinding, profile grinding, cylindrical grinding (with external cylindrical grinding, internal cylindrical grinding and centerless grinding) and generating grinding.
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The Surface grinding Surface grinding is widespread in industrial applications and is used for machining flat work piece surfaces. In general usage, “surface grinding” often only refers to the process of horizontal-spindle peripheral surface grinding. This peripheral surface grinding with the grinding wheels’ circumferential surface as the effective surface is done in two variants: conventional surface grinding and creep feed grinding.
Conventional surface grinding is most frequently used. In this grinding method, the grinding wheel moves back and forth over the workpiece at a relatively small, stepwise infeed with high feed speed. The material is ground during both directions of movement.
Creep feed grinding, on the other hand, works with comparably high infeed and very low feed speed. Furthermore, it is differentiated in two variants depending on the direction of the grinding wheels’ movement and the workpiece movement (same or different directions).
In comparison, the contact zone between grinding wheel and workpiece is relatively small in conventional surface grinding and relatively large in creep feed grinding.
In addition to peripheral surface grinding, there is side grinding (vertical-spindle grinding), where the effective surface is the side of the grinding wheel and the workpiece is mounted on a reciprocating table. –––
In addition, there is surface grinding with circular feed movement (on rotary table), side grinding with circular feed movement (on rotary table) and double side face grinding. In double side face grinding, the workpieces are guided between two grinding wheels and thus the two parallel, opposite surfaces of the workpiece are ground simultaneously.
Profile grinding with profiled grinding wheels
Profile grinding uses a profiled grinding wheel. The profile of the grinding wheel corresponds to the negative profile of the profile to be produced on the workpiece. In deep profile grinding, the desired profile is inserted into the workpiece in a few strokes.
Cylindrical grinding is divided into external cylindrical grinding and internal cylindrical grinding and these in turn into the two types of feed motion: traverse feed and plunge-cut (with radial feed). In addition, centerless grinding, a special form of cylindrical grinding, is divided into through-feed grinding and plunge-cut grinding. Below you will find a brief overview of these processes and their variants.
External cylindrical grinding (OD grinding)
In external cylindrical grinding (or outside diameter / OD grinding), a rotationally symmetrical workpiece is clamped either on one side or between centres. Machining takes place on the circumference of the mostly cylindrical or conical workpiece.
Depending on the process variant, the grinding wheel is moved by means of a longitudinal movement along the axis of the workpiece (traverse feed in external cylindrical grinding), a plunge motion radial (plunge-cut feed in external cylindrical grinding) or oblique to the workpiece (angular plunge grinding).
With external cylindrical grinding with traverse feed, the workpieces are generally wider than the grinding wheel width. During grinding, the grinding wheel travels along the machining surface of the workpiece, with the infeed always taking place at the reversal point.
The entire allowance in a rough grinding operation is ground in so-called peel grinding. In contrast to traverse feed in external cylindrical grinding, the contour of the workpiece is ground with only a point-sized contact area between the grinding wheel and the workpiece. The infeed takes place before or outside the workpiece engagement. In peel grinding, grinding is carried with a large infeed and opposing rotational movement of grinding wheel and workpiece. Feed rate and workpiece speed are lower than at traverse feed in external cylindrical grinding.
At plunge-cut feed in external cylindrical grinding, the grinding wheel is moved radially to the workpiece. By using profiled grinding wheels, workpiece contours can also be created with plunge-cut grinding.
One variant of plunge-cut grinding is angular plunge grinding. In this case, plane shoulders and circumferential surfaces can be ground at the same time. The infeed and feed takes place both radially and along the workpiece or grinding wheel axis.
Centerless grinding: through-feed grinding and plunge-cut grinding
In centerless grinding, the cylindrical workpiece is not firmly clamped but guided between the grinding wheel, regulating wheel (feed wheel) and a work rest blade. Centerless grinding enables high output quantities with short cycle times at the same time. Two variants are differentiated: Centerless through-feed grinding and centerless plunge-cut grinding.
Centerless through-feed grinding is a very productive process and is therefore widely used in series or mass production for the finishing of rotationally symmetrical workpieces.
In centerless through-feed grinding, one part after the other is guided through the grinding zone. Due to the tilted regulating wheel and the angular-topped work rest blade, the workpiece is moved through the grinding gap. Workpieces with a uniform diameter can be ground. The throughput speed of the workpiece is determined by the speed and the diameter of the regulating wheel.
The two wheels, grinding wheel and regulating wheel, run at different speeds. The cutting speeds are usually between 30 and 63 m/s. The dimensions of the grinding wheels in centerless grinding are usually in the diameter range 300-600 mm and in the width range 40-500 mm. The control wheels for centerless grinding are usually made of normal corundum in rubber bond, while grinding wheels with various grain qualities in vitrified bond and resin bond are used.
Centerless plunge-cut grinding is used for rotationally symmetrical workpieces with different outside diameters. The workpieces are fed into the grinding zone of the machine with help of a suitable loading device. The grinding wheel has a profile that corresponds to the negative profile of the desired workpiece contour. Thus, different diameters can be ground in one plunge cut.
Internal cylindrical grinding (ID grinding)
Internal cylindrical grinding (inner diameter / ID grinding) is mainly used for grinding cylindrical or tapered bores. The contact area between grinding wheel and workpiece is considerably larger with internal cylindrical grinding than with external cylindrical grinding. This makes the removal of chips and the supply of coolant lubricant more difficult. The grinding wheels should therefore allow cool grinding with simultaneous high cutting performance.
Typical applications for cylindrical grinding in series production include the grinding of axles, drive shafts, pins, bushings, nozzle needles, piston parts such as piston pins, needle rollers, grooves, profile rollers, pipes, roller bearings, rotors, bars, rods, pins, valves, shafts, shaft heels, tool holders, cylinder heads or cylindrical rollers.
Generating grinding is divided into continuous generating (gear) grinding and discontinuous generating grinding.
Continuous generating grinding
In continuous generating (gear) grinding or gear grinding, the profiled grinding wheel and the workpiece perform a rolling movement so that an involute shape is created on the tooth flanks. The grinding wheel and the workpiece are in continuous contact and the workpiece is moved past the grinding wheel.
Discontinuous generating grinding
In discontinuous generating grinding, one or a maximum of two tooth flanks are processed simultaneously. The tooth flanks are processed individually one after another. The profile of the grinding wheel corresponds to the desired finished profile of the workpiece.
Typical applications for generating gear grinding are, for example, the grinding of spur gears, gear racks, gear wheels or cylindrical gears.