Grinding/Abrasive Process Flashcards
What properties are important in abrasive materials?
High hardness
Wear resistance
Toughness
Friability (the ability to fracture off when dull)
What are the four typical abrasive materials, and what are they used for?
Aluminum Oxide (Al2O3) : used for for steel and ferrous alloys
Silicon Carbide (SiC) : used for aluminum, brass, stainless steel, cast iron, and some ceramics
Cubic Boron Nitride (cBN) : hardened steels and aerospace alloys
Diamond: ceramics, cemented carbides, glass
What is the purpose of different grit sizes? What does grit number indicate?
Small grit is used for finer finish and harder work
Larger grit is used for higher material removal rate, and softer work
Grit number is mesh size, so smaller number, larger grit
What are the necessary properties of a bonding material?
Must withstand centrifugal force, high temp, shock loading, and must hold grains rigidly but allow worn grains to fall off.
What is the volumetric proportion ratio in a grinding wheel?
Pg + Pb + Pp = 1
What is an open structure? What is a dense structure?
Open structure has large Pp and small Pg - used for when clearance for chips is needed
Dense structure has small Pp and large Pg - used for good surface finish and dimensional control.
What is the wheel grade?
Ability to retain grits while cutting, depends on Pb
Soft wheels lose grains easily - used for low material removal and hard work
Hard wheels retain grains - used for high material removal and soft work
What is the meaning of the grinding wheel specification A-##-H-#-V?
Abrasive - grit size - grade - structure - bonding agent
What are the main types of grinding wheels?
Straight
Recessed two sides
Metal frame with abrasive on the outside
Abrasive cut off
What are the three types of grain action?
Cutting : forms a chip
Plowing : Surface deformation, but no material removed
Rubbing : consumes energy, but no material removed
What are the effects of temperature in grinding?
Grinding produces friction and therefore high temp
Can create surface burns and cracks
Softening of work surface if heat treated
Residual stresses in the work surface
How can grinding temperatures be reduce?
Decrease depth of cut
Decrease wheel speed
Reduce number of active grits
Use a grinding fluid
What causes wheel wear?
Grain fracture - when a portion of the grain breaks off
Attritious wear - dulling of grains resulting in flat spots and rounded edges
Bond fracture - when grains pull out of bonding material
What is the grinding ratio?
GR = Vw/Vg
Vw is volume of work removed
Vg is volume of wheel worn off
What is ‘dressing’ a wheel?
When something is held against a rotating grinding wheel to remove chips and break off dull grits
