1. GRINDING AND OTHER ABRASIVE PROCESSES Chapter 25
Manufacturing Processes, 1311
Dr Simin Nasseri
Southern Polytechnic State University

2. Material Removal Processes
A family of shaping operations, the common feature of which is removal of material from a starting workpart so the remaining part has the desired geometry.
Material Removal
Machining – material removal by a sharp cutting tool, e.g., turning, milling, drilling.
Abrasive processes – material removal by hard, abrasive particles, e.g., grinding.
Nontraditional processes - various energy forms other than sharp cutting tool to remove material, e.g. electrochemical and thermal energy processes.

3. Machining Processes Planing Traditional Chip Removal
Nontraditional Machining
Ultrasonic
Electrical Discharge
Electro-arc
Optical Lasers
Electrochemical
Chem-milling
Abrasive Jet Cutting
Electron Beam Machining
Plasma Arc Machining
Turning
Milling
Drilling
Boring
Reaming
Shaping
Sawing
Broaching
Planing
Grinding
Honing
Lapping

4. Abrasive Machining
Material removal by action of hard, abrasive particles usually in the form of a bonded wheel
Generally used as finishing operations after part geometry has been established by conventional machining
Grinding is most important abrasive process
Other abrasive processes: honing, lapping, superfinishing, polishing, and buffing

5. Why Abrasive Processes are Important
Can be used on all types of materials
Some can produce extremely fine surface finishes, to m (1 -in)
Some can hold dimensions to extremely close tolerances

6. Grinding
Material removal process in which abrasive particles are contained in a wheel that operates at very high surface speeds.

7. Figure 25.1 Typical structure of a grinding wheel.
Wheel Structure
The grinding wheel:
is usually disk‑shaped and precisely balanced for high rotational speeds.
Consists of abrasive particles and bonding material.
Abrasive particles accomplish cutting.
Bonding material holds particles in place and establishes shape and structure of wheel.
Figure Typical structure of a grinding wheel.

8. Abrasive Material Properties
High hardness
Wear resistance
Toughness
Friability - capacity to fracture when cutting edge dulls, so a new sharp edge is exposed

9. Traditional Abrasive Materials
Aluminum oxide (Al2O3) ‑ most common abrasive
Used to grind steel and other ferrous high‑strength alloys
Silicon carbide (SiC) ‑ harder than Al2O3 but not as tough
Used on aluminum, brass, stainless steel, some cast irons and certain ceramics

10. Hardness of Abrasive Materials
Abrasive material Knoop hardness
Aluminum oxide
Silicon carbide
Cubic boron nitride
Diamond (synthetic)

11. Surface Finish Two main categories of grinding:
Most grinding is performed to achieve good surface finish
Best surface finish is achieved by:
Small grain sizes
Higher wheel speeds
Denser wheel structure = more grits per wheel area
Two main categories of grinding:
Surface grinding
Cylindrical grinding

12. Four Types of Surface Grinding
Figure 25.7 (a) Horizontal spindle with reciprocating worktable, (b) horizontal spindle with rotating worktable, (c) vertical spindle with reciprocating worktable, (d) vertical spindle with rotating worktable.

13. Surface Grinder
Figure Surface grinder with horizontal spindle and reciprocating worktable (most common grinder type).

14. Cylindrical Grinding
Figure Two types of cylindrical grinding: (a) external, and (b) internal.

15. Other Abrasive Processes
Honing
Lapping
Superfinishing

16. Honing
Abrasive process performed by a set of bonded abrasive sticks using a combination of rotational and oscillatory motions.
Creates a characteristic cross‑hatched surface that retains lubrication.
Grit sizes range between 30 and 600.
Surface finishes of 0.12 m (5 -in) or better.
Figure The honing process: (a) the honing tool used for internal bore surface.

17. Honing
Common application is to finish the bores of internal combustion engines.

18. Figure 25.17 The lapping process in lens‑making.
Uses fluid suspension of very small abrasive particles between workpiece and lap (tool).
Lapping compound - fluid with abrasives, general appearance of a chalky paste.
Applications: optical lenses, metallic bearing surfaces, gages.
Figure The lapping process in lens‑making.

19. Superfinishing
Similar to honing - uses bonded abrasive stick pressed against surface and reciprocating motion
Differences with honing:
* Shorter strokes
* Higher frequencies
* Lower pressures between tool and surface
* Smaller grit sizes
Figure Superfinishing on an external cylindrical surface.