Grinding (manufacturing process)
Grinding is a cutting manufacturing process for fine and finishing workpieces that has been known since ancient times. It can be used manually or on grinding machines . As with all machining processes, excess material is separated off in the form of chips . The edges of the microscopically small, hard, mineral crystals in the grinding tool act as cutting edges. In ancient times, grinding tools consisted of suitable types of stone, such as mill sandstone . Today, grinding tools are usually manufactured industrially by adding a binding agent to mineral bulk material such as corundumGrinding wheels , stones or belts is joined.
Grinding counts together with honing for chipping with bound grain, while with lapping and sliding chipping the grain is loose. Since the number of grains in engagement is just as little known as their geometry or position in relation to the workpiece, grinding, as well as honing and lapping, counts for machining with a geometrically undefined cutting edge . However, it is known that most grains have a negative rake angle . The chips produced as a by-product or waste product during grinding are known as grinding dust .
Grinding is also suitable for hard materials such as hardened steel or ceramics, which up until the end of the 20th century could not be machined using a geometrically defined cutting edge such as turning , milling or drilling . For this reason, the desired shape of the workpieces was and is usually first roughly worked out in the soft state by this method in order to achieve the final shape and surface quality after hardening by grinding. Since hard machining on the one hand and increasingly efficient grinding processes on the other, this boundary has become increasingly blurred.
Grinding and grinding machines have been known since ancient times. In ancient Greece, grindstones that were cooled with oil or water are also known. In the Middle Ages in the area around Solingen there were numerous hammer mills on tributaries of the Wupper, which were driven by water mills to forge blades. The grinding mills for finishing were located directly on the Wupper, as they required more energy that was not available on the secondary runs. Therefore, the forged blades were transported there.
Grinding is more precise than cutting processes with a geometrically defined cutting edge. Achievable dimensional and shape accuracies during grinding are in tolerance classes IT6 to IT8 for surface grinding, IT4 to IT5 for profile grinding and IT4 to IT6 for centerless grinding. The surface quality that can be achieved is R z 1 to 6.3 µm for surface grinding, 2.25 to 4 µm for profile grinding and centerless grinding.
Categorization and definition according to DIN 8589
In DIN 8580, the manufacturing processes are divided into main groups. The main group of cutting is defined in more detail in DIN 8589. It is divided into cutting , cutting with a geometrically defined cutting edge , cutting with a geometrically undefined cutting edge , removal , dismantling , cleaning and evacuation. In addition to honing and lapping , three grinding processes are assigned to machining with geometrically undefined cutting edges :
- Grinding with rotating tools is cutting with multi-edged tools, the geometrically indeterminate cutting edges of which are formed by a large number of bound grains of natural or synthetic abrasives and which cut the material at high speed, usually with non-constant contact between the workpiece and the abrasive grain.
- Belt grinding is cutting with a multi-edged tool made of abrasive grains on a backing (grinding belt), which revolves over at least two rotating rollers and is pressed against the workpiece to be ground in the contact area by one of these rollers, another additional support element or even without a support element, and its geometrical shape Cutting off the material with indefinite cutting edges at high speed with non-constant contact between the workpiece and the abrasive grain.
- Stroke grinding is machining with a non-rotating tool, the geometrically indeterminate cutting edge of which is formed by a large number of bonded abrasive grains and which sever the material from the workpiece by means of a reciprocating, essentially straight cutting movement (stroke).
All grinding processes are counted as cutting with bonded grain. The working principle is called "track-bound", since the individual grains move on a path given by the tool . In contrast to this, honing is one of the "force-bound" processes, since the path of the tools is generated by the contact pressure on the workpiece.
|Feed direction||Longitudinal grinding , cross grinding|
|Effective area of the grinding wheel||Circumferential grinding , face grinding|
|Area to be generated||
Position : external grinding , internal grinding
Type : profile grinding , form grinding , surface grinding , cylindrical grinding , generating grinding
|Cutting speed||Conventional grinding, high speed grinding|
|delivery||Pendulum grinding , deep grinding|
|roughness||Roughing (coarse), finishing , fine grinding|
|Clamping the workpiece||Vice , between points , centerless|
When grinding, a lot of heat is released due to the high friction. It can basically lead to thermal expansion of the workpiece or to temperature damage. That is why cooling lubricants are almost always used for grinding . The cutting speed during grinding is around 25 to 45 m / s in exceptional cases up to 120 m / s. On average, it is around 20 times higher than when turning, which also results in very low cutting forces .
Areas of application
There are three main areas of application: tool grinding for sharpening cutting tools or blades such as knives and scissors, fine machining of workpieces in order to work out the desired shape and surface and rough machining by cleaning, cleaning and abrasive cutting. The last group has the largest share in terms of the consumption of grinding wheels in terms of value.
For the fine machining of machine parts, it is used, for example, for ball bearing running surfaces, bearing rings, bearing seats, milling cutters, threads, turbine blades, cylinder heads, camshafts, valve tappets, sealing surfaces on housings and gear shafts.
In the field of decorative sanding technology, there are different methods and the resulting surface finishes.
- The longitudinal grinding or transverse grinding is a common grinding that draws straight lines on a metal surface.
- The cross-cut is a design cut in which oblique lines are sanded on top of each other on the material.
- In the case of hairline sanding , a continuous line runs across the entire component.
- Rotary sanding results in circularly torn lines, for example the beading technique results in a pearl cut finish .
- The metal decorating grinding technique produces decorative cuts, for example in the form of logos.
- Chip formation during grinding
- List of machining processes
- High speed machining
- Energy conversion and heat during machining
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