Abrasive machining processes themselves can be regarded as tribological systems where workpiece material and abrasive tool interact under the influence of cooling lubricant and atmosphere [MARI04]. Abrasive tools are subjected to high temperatures and high pressures in the active cutting zone. Consequently, tool wear occurs. Tool wear happens because of mechanical effects (vibrations and grinding forces), chemical effects (reactions with cooling lubricant and workpiece material), and thermal effects (grinding pressure and friction) [BOLD02, KLOC09, p. 15].
Like in all tribological systems, the wear mechanisms do not appear in single but occur as superposition or sequence [HABI80]. The tribological definition of wear is that particles are removed from the surface of one friction partner under the conditions of the surrounding environment, such as lubricant and atmosphere, and friction parameters, such as pressure, friction speed, temperatures.
|
Grit surface layer wear |
Grit splintering |
Grit-bond-interface wear |
Bond wear |
|
|
[KLOC09] |
Compressive softening, chemical wear, abrasion |
Micro-breakage, grit breakage |
Bonding breakage, chemical and thermal wear of bonding |
|
|
[KONI81] |
Abrasion, micro-cracks, corrosion, diffusion |
Micro-fracture, grain fracture |
Bond fracture, chemical bond wear |
|
|
[MALK08, MALK68] |
Attritious wear |
Grain fracture |
Bond fracture |
|
|
[JACK11] |
Abrasive wear (surface flats) |
Fracture of abrasive grains |
Fracture at interface grit/bond |
Fracture of bond bridges |
|
[BORK92] |
Attrition, surface microchipping |
Grain chipping and cracking |
Grit pull-out |
Bonding bridge failure |
|
[ROWE09] |
Rubbing |
Grain micro — and macro fracture |
Grain pull-out |
Bond fracture |
|
Compressive softening |
Splintering of crystal clusters, partial grit break-out |
Total grit break-out |
|
Table 6.2 Taxonomy and types of wear mechanisms in the literature |
Different researchers use various terms for tool wear (Table 6.2), but the main categories are wear of the grit surface, wear of the grit by splintering, wear of the grit-bond-interface, and wear of the bond. The wear mechanisms of grinding tools leading to profile and sharpness loss as explained in Sect. 6.3 are complex.
Peklenik [PEKL57] highlights the alternating temperature load on the grits, because every grit contact heats up the workpiece surface on a small contact area and the grits are cooled down by the cooling lubricant (Fig. 6.15).
The wheel hardness is an important impact factor on the wear phenomena [STET74]. Softer wheels show higher wear rate, but can also be longer in a sharp
Fig. 6.15 Load at a single grit, left: Cooling effect by the cooling lubricant, right: Peak temperatures during grit engagements of intervals, t0 [PEKL57, p. 88]
|
Spec. material removal rate Q’w Fig. 6.16 Influence of material removal rate on wear phenomena [KLOC09, p. 254, BIER76], with kind permission from Springer Science + Business Media |
cutting state [STET74]. In addition, the process parameters affect also the wear phenomena. For example, higher specific material removal rates result in higher single grit loads, which change the wear mechanism from abrasion to particle break-out and total grit break-out (Fig. 6.16). The different wear phenomena then result in different amounts of wheel profile loss [STET74].
The grit type affects how the grits get dull. For example, green silicon carbide and white aluminum oxide are friable and offer new cutting edges easily [PAUC08, p. 346]. Regular aluminum oxide acts comparatively tough and gets blunt [PAUC08, p. 346].
One way to analyze the wear phenomena is to collect the grinding debris from the grinding zone, wash the debris in benzene and separate the metallic chips magnetically [STET74]. The chips can be weighted and compared to the sieved and weighted wheel wear particles.