Precision Abrasive Finishing
What is the best process for producing flat surfaces with the highest precision? Given the wide range of applications for an enormous variety of workpieces, this question poses great challenges for manufacturers.
Supfina has the answer — and three superior methods for getting the job done: double-disk grinding, flat finishing, and fine grinding.
Considered one of the “classic” grinding processes, double-disk grinding is performed when both sides of a workpiece must be ground so that both surfaces are exactly plane and parallel. The workpiece is not fixed for this process. Instead, it is loosely placed in the “nest” of the workpiece carrier. Then both sides of the workpiece are simultaneously machined between two grinding wheels. The upper grinding wheel is adjusted with the “tilt” navigation setting, which allows the upper wheel to maintain the desired angle with the lower wheel. Thus, the gap between the grinding wheels is greater on the infeed side than on the outfeed, resulting in the required amount of stock removal.
Through regular dressing, the grinding wheels maintain their form and sharpness.
Flat finishing is primarily the process of using a cup wheel to machine a workpiece’s face. The workpiece is clamped in a chuck and rotated. The rotating cup wheel is then precisely advanced to the workpiece’s surface.
Precision slides allow the finishing unit to be adjusted in multiple directions — thus giving the workpiece a characteristic “cross-hatch” pattern, in addition to concave or convex adjustments. With these capabilities a flat, concave, convex, or spherical surface can be produced. One key difference between double-disk grinding and flat finishing is that, for the latter process, the tool is self-dressed during the machining of components and regular wheel dressing is not necessary.
Fine grinding is also used when workpieces require both surfaces to have plane parallelism, but with more precision than can be achieved with double-disk grinding. Workpieces are placed in carriers that have teeth on the outside diameter. An inner pin ring rotates the carriers as they shift on a stationary outer pin ring in an orbiting manner. Machining takes place between two rotating grinding wheels. The optimal machining force is applied by the upper wheel, which is mounted on an oscillating pendulum. Fine grinding’s central feature is that a fixed number of parts can be processed simultaneously, or in batches.
Each of these machining technologies has its particular strengths. For maximum stock removal as well as output of finished workpieces, double-disk grinding is preferred. For example, within large-scale production, single cams can be ground with a cycle time of fewer than 0.5 seconds with a continuous-feed loading system.
However, for maximum precision and size accuracy, fine grinding is preferred. Hydraulic components, for example, can be finished with an accuracy of ± 0.001 mm.
Flat finishing distinguishes itself in that workpieces are clamped, therefore making the clamped surface a geometric reference point for perpendicularity and flatness. Thus, in the case of transmission components, the perpendicularity of flat surfaces and bores can be ensured.