Surface grinding is a widely used process of machining in which a spinning wheel covered in rough particles cuts chips of metallic or non metallic substance making them flat or smooth.
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Process
Spark out is a term used when precision values are sought and literally means "until the sparks are out (no more)". It involves passing the workpiece under the wheel, without resetting the depth of cut, more than once and generally multiple times. This ensures that any inconsistencies in the machine or workpiece are eliminated.
As with any grinding operation, the condition of the wheel is extremely important. Diamond dressers are used to maintain the condition of the wheel, these may be table mounted or as the first image shows, mounted in the wheel head where they can be readily applied.
Lubrication
Lubricants are sometimes used to cool the workpiece and wheel, lubricate the interface, and remove swarf. It must be applied directly to the cutting area to ensure that the fluid is not carried away by the grinding wheel. Common lubricants include water-soluble chemical fluids, water soluble oils, synthetic oils, and petroleum-based oils. The type of lubrication used depends on the workpiece material and is outlined in the table below.[1]
| Workpiece material | Lubricant |
|---|---|
| Aluminium | Light duty oil |
| Brass | Light duty oil |
| Cast iron | Heavy duty emulsifiable oil, light duty chemical and synthetic oil |
| Mild steel | Heavy duty water-soluble oil |
| Stainless steel | Heavy duty emulsifiable oil, heavy duty chemical and synthetic oil |
| Plastics | Water-soluble oil, dry, heavy duty emulsifiable oil, light duty chemical and synthetic oil |
Equipment
A surface grinder is a machine tool used to provide precision ground surfaces, either to a critical size or for the surface finish.
The typical precision of a surface grinder depends on the type and usage, however +/- 0.002 mm (+/- 0.0001") should be achievable on most surface grinders.
The machine consists of a table that traverses both longitudinally and across the face of the wheel. The longitudinal feed is usually powered by hydraulics, as may the cross feed, however any mixture of hand, electrical or hydraulic may be used depending on the ultimate usage of the machine (ie: production, workshop, cost). The grinding wheel rotates in the spindle head and is also adjustable for height, by any of the methods described previously. Modern surface grinders are semi-automated, depth of cut and spark-out may be preset as to the number of passes and once setup the machining process requires very little operator intervention.
Depending on the workpiece material, the work is generally held by the use of a magnetic chuck. This may be either an electromagnetic chuck, or a manually operated, permanent magnet type chuck; both types are shown in the first image.
Aluminum oxide, silicon carbide, diamond, and cubic boron nitride (CBN) are four commonly used abrasive materials for the surface of the grinding wheels. Of these materials, aluminum oxide is the most common. Because of cost, diamond and CBN grinding wheels are generally made with a core of less expensive material surrounded by a layer of diamond or CBN. Diamond and CBN wheels are very hard and are capable of economically grinding materials, such as ceramics and carbides, that cannot be ground by aluminum oxide or silicon carbide wheels.
The machine has provision for the application of coolant as well as the extraction of metal dust (metal and grinding particles).
Effects on work material properties
The high temperatures encountered at the ground surface create residual stresses and a thin martensitic layer may form on the part surface; this decreases the fatigue strength. In ferromagnetic materials, if the temperature of the surface is raised beyond the Curie temperature then it may lose some magnetic properties. Finally, the surface may be more susceptible to corrosion.[2]
See also
- Angle grinder
- Bench grinder
- Cylindrical grinder
- Flick grinder
- Tool and Cutter grinder
- Jig grinder
- Centerless grinder
References
- ^ a b Todd, Allen & Alting 1994, p. 141.
- ^ Todd, Allen & Alting 1994, p. 139.
Bibliography
- Todd, Robert H.; Allen, Dell K.; Alting, Leo (1994), Manufacturing Processes Reference Guide, Industrial Press Inc., ISBN 0-8311-3049-0, http://books.google.com/books?id=6x1smAf_PAcC.
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