Lec 10 Flashcards
Abrasive machining adv
High dimensional accuracy
What is abrasive machining
Abrasion used to remove small amounts of material by cutting processes that introduce tiny chips
Each abrasive grain removes only small amount of material
A method used to produce parts with high
dimensional accuracy
Each particle acts as a cutting tool
Types of bond (grinding wheel)
Clay and Feldspar crystalline material
vitrification used to produce a glassy amorphous structure strong and stiff resistant to oil acid and water
Bond too strong (grinding wheel)
Dull grains cannot be dislodged to
allow other sharp grains to perform grinding
Bond too weak (grinding wheel)
Grains become dislodged easily,
hence maintaining dimensional accuracy
becomes difficult
What is attritious wear (grinding wheel)
Wear of grains (flank wear of cutting tool) caused by friction between grain and workpiece involving chemical and physical reactions
Why are abrasive grains brittle (grinding wheel)
if grains dull grinding inefficient therefore should fracture moderately to expose new sharp grains
continuously being sharpened
Why is porosity important (grinding wheel)
Essential in bonded wheels provides cooling and clearance for minute chips produced
What is grinding?
chip removal process - The grinding tool is made up of irregular shaped grains spaced randomly along the
periphery of the cutting wheel
Range of machines available for different workpiece geometries - CNC automation load - unload clamp repeat cycle path will sharpen wheel between processes
Ultrasonic machining (drawing)
removal by micochipping or erosion with fine abrasive grains
Ultrasonic machining process
high freq
Tip of tool vibrates
amplitude 0.05
vibration drives grain at workpiece high velocity
high stress between grain and workpiece - small area short contact time
Tool vibration speed 20kHz or 3000000kHz ultrasonic machining
20kHz
Ultrasonic machining best suited for
Brittle materials as high enough stresses causes microchipping - glass ceramics silicon hardened steels precious tones
What is a Finishing operations how do they affect a design
These are used to improve the surface finish of a
workpiece
Can contribute significantly to production time
and product cost
Finishing operations What is Sanding
Uses coated abrasives sand paper emery cloths
Construction of sandpaper (diagram)
The grains are electro-statically deposited on backing
material
Coating is made of resin
What types of surface can sanding be used on?
Any! Widely used in finishing flat or curved metallic non metallic
What is honing (diagram)
stock removal process abrasive stones remove smallamounts of metal
What is honing used for
Size and finish bored holes (engine cylinders)
remove errors left by boring
tool marks left by grinding
What is lapping? (diagram)
fine abrasive particles embedded in relatively soft material called lap (leather/cloth/cast iron/copper)
Shapes and materials used for lapping
Flat cylindrical metal and non metal
What is polishing
Produces a smooth, lustrous surface finish - takes time costs alot of money
What is an abrasive
Is a small, non-metallic hard particle with sharp
edges and irregular in shape
For higher material removal rates what is done
Abrasives are bonded together to form a grinding
wheel
What is Vitrification
Used to produce a glassy, amorphous
structure
The selection of a grinding process depends
on x4
Part shape Part size Ease of fixing Production rate
Limitations of Ultrasonic machining
Each job requires special tooling
Purpose of grooves in lapping plate
serve to hold slurries, removing cutting chips and evenly supply slurry to workpiece
uniformly distribute pressure across workpiece - improves flatness accuracy
How is polishing done
It is done with disks or belts of fabric or leather coated
with fine powders of aluminium oxide or diamond
What is electro-polishing
polishing using electrolysis
What is electro-polishing
polishing using electrolysis
How is electro-polishing done (diagram)
A DC electric circuit is constructed using the workpiece
as the anode, usually submersed in electrolyte
As current is applied, material is oxidised and then
dissolved by the electrolyte, stripping it from the
surface
Order of surface finish highest to lowest; Finish turn, Hone, Rough turn, Grind Semi-finish turn, As cast
or cut
Process/surface finish micrometres/machining cost (%)
As cast or cut/500/0, Rough turn/500-10/20, Semi-finish turn/5-4/70, Finish turn/2/100, Grind/0.8/250, Hone/0.4/400
