The Superfinishing method:
15 years ago, stone grinding was state of the art technology for precise surface finishing. Today, the polishing belt grinding procedure, also called â€žSuperfinishingâ€œ or â€žMicrofinishingâ€œ, sets a new standard.
Superfinishing complements stone grinding and hard turning, optimizes surfaces and reduces finishing time. The result: prefinished surfaces can be finished at a much lower cost.
This method makes it possible to reach high and reproducible surface finish quality on rotationally symmetrical workpieces with practically every kind of material. The surface structure is improved in the micron range - up to 0,004 µm Ra!
The main advantage of this method is consistent finish over the entire surface. Superfinish improves the bearing ratio (Tp) resulting in greatly improved wear resistance. Stock removal is typically in the order of a few microns. The achievable surface finish quality is comparable to levels reached only by honing or lapping.
Superfinishing removes the amorphous structure of the material, or "soft skin". This layer is usually, 0.002 to 0.008 mm thick and is created by high temperatures generated by the grinding wheel.
Superfinishing enables the user to achieve virtually any-surface texture parameter, because only the roughness peaks are removed. The geometry of the workpiece remains unchanged.
This surface finishing process uses Superfinishing tape rolls available in 15 or 50 m lengths and in aluminium oxide grain sizes from 0.1 to 100 µm.
As the work piece is rotating, Superfinishing tape is creep-fed by a speed-controlled motor. The film feed rate is infinitely adjustable. The tape is backed by a pressure controlled oscillating rubber contact roll. Continuous tape feed guarantees a consistent finish over the entire surface.
The combination of work piece rotation and high frequency tape oscillation causes a random sinusoidal scratch pattern on the work piece surface. This is a wet operation using a coolant or emulsion flood. All machines are configured to mount on to a standard lathe tool post holder. The benefits of Superfinishing can also be achieved on a standard tool room lathe.
Surface of workpiece
Microscopic view depicts typical peaks and valleys.
Bonded mediums create a finer finish but generate fishtails, chatter marks and traverse marks.
A single layer, constantly indexing, abrasive oscillates and rapidly removes peaks, chatter marks, fishtails and traverse marks.
Superfinishing vs. stone grinding
In grinding with bonded wheels or honing stones, small pieces of the stone break loose and are forced between the work piece and the stone causing chatter marks and "tearing" as they pass through. Because tape superfinishers use a compliant rubber roll to back the tape, this condition is avoided.
The Superfinishing process is a very clean process, because coolant or grinding emulsion is used instead of honing oils like stone grinding. Recycling and waste disposal are simplified.
Superfinishing vs. roller burnishing
Unless compaction of the surface is required for other process reasons, superfinishing has a distinct advantage in improving surface finish. Roller burnishing can oly be used in few, clearly defined cases and with special work pieces. For example, if the peak-to-valley-height is too great, the peaks can bend over and create a fish scale pattern. In addition, roller burnishing machines are very heavy, because they have to exert extremely high forces to the work piece causing deformation.
Loeser has accumulated a great deal of superfinishing process experience through years of research and development on a large variety of materials such as: hard chrome and tungsten carbide coatings, high density metals, aluminum, copper, rubber, ceramic, plasma coated materials and many others.
Printing rollers, rubber rollers, rollers for foil rolling, feed rolls, rocker shafts, piston rods, rollers for copying machines, pneumatic pistons, pistons for pneumatic springs, valve slides, control levers, valves, printer axles, diesel engine rocker shafts etc.
Profit from our experience
To achieve the desired results, the operation parameters have to be adjusted optimally to the work piece. In praxis, the most common questions are:
> How fast must the workpiece rotate?
> Which grinding pressure should be used?
> Which oscillation frequency?
> Which tape feed is best?
> Which grinding emulsion should we use?
> Which grain size is optimal?
Extensive experience is required to answer these questions. Loeser has more than ten years of process development experience. Our technical staff is capable of determinating the optimal parameters for Superfinishing applications in a just few minutes.
Superfinishing is a state of the art method for surface finishing in the micron range. A consistent, reproducible surface quality up to 0.004 µm can be achieved. It is possible to finish a great variety of materials and work pieces. This is a very efficient method of producing superior quality surface finishes.
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