Lecture 10 - Grinding and other Abrasives Flashcards
What are the types of Abrasive Machining?
- Grinding (most important)
- Honing
- Lapping
- Superfinishing
- Polishing
- Buffing
Describe the Abrasive machining process
Material removal by action of hard, abrasive particles usually in the form of a bonded wheel. Generally a finishing operations after part geometry has been established.
Why are Abrasive Processes important?
Can be used on all types of materials (Hard or soft)
Can produce extremely fine surface finishes
Can hold extremely close dimension tolerances
What are the Parameters of Grinding Wheels?
1) Abrasive material
2) Grain size
3) Bonding Material
4) Wheel structure
5) Wheel grade
What are the types of Abrasive Materials? What are the material uses?
Aluminum oxide - most common/ cheap. Ferrous High strength steel
Silicon Carbide - Cannot be used for steels due to chemical make up. Used on Aluminum, brass, Stainless
Cubic Boron Nitride - Suitable for hardened tool steels and alloys.
Diamond - Not suitable for steels. Mostly used for ceramics and glasses
Listed above from Softest to hardest
What Grain size should be used for certain materials?
Small grit produces better surface finish and used for harder materials.
Large grit used for larger material removal and used for softer materials
What are the requirements for bonding material?
Must withstand centrifugal forces and high temperatures
Must resist shattering during shock loading
Must hold abrasive grains rigidly in places, yet allow worn grains to be dislodged to expose new grains
What does the Wheel structure refer too?
The relative spacing between pores, bonding materials, and grains
Can be measured in a range of “open” and “dense”, Open has large pores and small grains
Dense has small pores and large grains
What are the Wheel grade ranges and what do they indicate?
Ranges from soft to hard. It is an indication of bond strength of retaining grits. Soft is used for low material removal rates, Hard for high material removal rates
What effects do temperature have and how do you reduce it?
Grinding is characterized by high temperatures and high friction, most of the energy staying in the ground surface. Can cause surface burns, softening of material and stresses in the material.
Reduce the grinding temperature by:
decrease depth of cut
reduce wheel speed
dress the wheel if dull or loaded
reduce number of active grits
use grinding fluid
Creep Grinding vs Conventional Grinding
Creep grinding goes to a depth of 1000 to 10000 times deeper, but reduces feed rate by about the same amount. Material removal and productivity rates are increased.
Dressing vs Truing
Dressing - Abrasive stick held against the wheel to Break off dull grits to expose sharp grains. Removes chips clogged in the wheel. DOES NOT guarantee the shape of the wheel
Truing - Diamond pointed tool fed slowly and precisely across wheel to restore wheel like dressing, but insures straightness across outside perimeter.
What is Blanchard grinding and what are its uses?
Efficiently remove material on large surface areas. Also know as Rotary Surface grinding.
Used for large castings and forgings, large sections of plate stock, large stampings, molds and dies.
Describe honing
Abrasive process performed by a set of bonded abrasive sticks using a combination of rational and oscillatory motion. Created cross-hatched surface that is good for lubrication.
What makes lapping different from other abrasive processes?
Lapping uses fluid suspension of very small abrasive particles between the work piece and lap (tool). Lapping compound appears as a chalky paste (2-4 microinch). Used for lenses metallic bearing surfaces, and gauges.
