Grinding (abrasive cutting)

Grinding is a machining, wegbestimmtes manufacturing processes for machining surfaces or separating of material parts with abrasives and bonded abrasive grain. This can be done manually or on grinding. According to DIN 8580, it belongs to the main group separation. Moreover, it belongs to the group of of machining with geometrically undefined cutting edges.

Features

The advantages of grinding over other types of machining are the good workability of hard materials, the high dimensional and shape accuracy (tolerance class ISO 5-6 ) and the low waviness and roughness (Rz = 0.5 to 10 microns ) ground surfaces.

Grinding process

Abrasive

Most grinding wheels include abrasive grains of corundum (white, pink ) or silicon carbide (green, black). The grain toughness decreases with increasing hardness of the abrasive grain. A sufficient toughness prevents the premature grain fracture at large grain load ( pre-grinding ). Another suitable material for abrasive grains is boron nitride ( BN), in particular cubic boron nitride (CBN) having a diamond structure.

Abrasive grains should have a high hardness and a sufficient grain toughness and heat resistance.

Binding

The binding has the task of the individual grains hold until they have become dull. Type and amount of binder used affect the hardness and abrasive properties of the abrasive body.

Usual types of bonds

  • Ceramic
  • Resin
  • Metallic
  • Galvanic
  • Rubber bonds

Abrasive characteristics

The structure (the structure ) describes the ratio of abrasive grains (grain size ), binding and pore space ( chip space ) in the grinding body. The pores act as chip and coolant chambers and promote cooling and the removal of chips during grinding. If the pores are too small to put them to increasingly so that additional friction occurs and thus the pressure and temperature rise during grinding. Here, the clamping process or the removal rate or the chip performance can be reduced and the risk increases that the grinding wheel is damaged. In a grinding fire mainly the binding is affected.

Abrasive grain size

The grain size number corresponds to the number of meshes of a sieve from a standard screen mesh to an inch in length, through which the designated grain just falls through, while it remains on the next narrower sieve. The very fine grains are separated in the slurry method. The grain size of diamond and boron nitride is specified according to the sieve mesh size in microns: Diamond Grain D150 has a particle size of 125-150 microns.

The outbreak of abrasive grains is referred to as self-sharpening.

Hardness of a grinding wheel

With hardness of a grinding wheel is understood to mean not the hardness of the abrasive grains, but the resistance of the bond against the breaking of the abrasive grains.

Areas of application

  • For shaping, drafting of the cut in precious stones, and of incised ornaments in glass ( glass grinding )
  • As tool grinding for sharpening cutting tools, such as swords, knives, scissors, scythes, axes, drills, saws, lathe tools, milling cutters, by hand or machine
  • Separate pieces of material with special cutting discs
  • As vibratory finishing to smooth surfaces and for rounding edges
  • For fine machining of hardened surfaces, such as sealing surfaces, functional surfaces, measuring equipment ( straightedge ), storage areas by cylindrical grinding, surface grinding, creep feed grinding, profile grinding and jig grinding.
  • Manufacturing hydraulic areas of water turbine parts using templates to define the final contour ( Kaplan, Francis and Peltonturbinenrädern, and their vanes )
  • Preparation of thin sections for microscopic examination

With the latest fine grinding methods such as flat honing can be almost as smooth and dimensionally accurate workpieces produced as lapping. When grinding while higher removal rates can be achieved, thus the grinding is cheaper.

Safety rules

  • A sound test is carried out before each mounting a ceramic disc.
  • The grinding wheels must be slid onto the spindle without violence.
  • The minimum diameter of the wheel flanges is for straight grinding wheels ⅓ times diameter, with conical washers ½ times diameter.
  • Only the same size, same shape and turned behind mounting devices are used with soft, elastic pads to ensure the plan run.
  • Grinding wheels with a diameter > 80 mm have a trial run of at least 5 minutes at idle exist under the maximum permissible speed in safe danger area after chucking.
  • The workpiece support or the guard should only be readjusted with a stationary sander.
  • When grinding goggles must be worn.

Images of different grinding

Loops of an inner diameter ( internal grinding )

Bench grinder, such as the grinding of drills

Grinding machine

Centerless

Grinding wheel

Surface Grinding Machine

Cylindrical Grinding Machine

Metallic bonding Natural rubber Knife Hatchet Microscope
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