Presentation on theme: "GRINDING AND OTHER ABRASIVE PROCESSES Chapter 25"— Presentation transcript:
1 GRINDING AND OTHER ABRASIVE PROCESSES Chapter 25 Manufacturing Processes, 1311Dr Simin NasseriSouthern 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 RemovalMachining – 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.
4 Abrasive MachiningMaterial removal by action of hard, abrasive particles usually in the form of a bonded wheelGenerally used as finishing operations after part geometry has been established by conventional machiningGrinding is most important abrasive processOther abrasive processes: honing, lapping, superfinishing, polishing, and buffing
5 Why Abrasive Processes are Important Can be used on all types of materialsSome can produce extremely fine surface finishes, to m (1 -in)Some can hold dimensions to extremely close tolerances
6 GrindingMaterial 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 StructureThe 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 hardnessWear resistanceToughnessFriability - capacity to fracture when cutting edge dulls, so a new sharp edge is exposed
9 Traditional Abrasive Materials Aluminum oxide (Al2O3) ‑ most common abrasiveUsed to grind steel and other ferrous high‑strength alloysSilicon carbide (SiC) ‑ harder than Al2O3 but not as toughUsed on aluminum, brass, stainless steel, some cast irons and certain ceramics
10 Hardness of Abrasive Materials Abrasive material Knoop hardnessAluminum oxideSilicon carbideCubic boron nitrideDiamond (synthetic)
11 Surface Finish Two main categories of grinding: Most grinding is performed to achieve good surface finishBest surface finish is achieved by:Small grain sizesHigher wheel speedsDenser wheel structure = more grits per wheel areaTwo main categories of grinding:Surface grindingCylindrical 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 GrinderFigure Surface grinder with horizontal spindle and reciprocating worktable (most common grinder type).
14 Cylindrical GrindingFigure Two types of cylindrical grinding: (a) external, and (b) internal.
15 Other Abrasive Processes HoningLappingSuperfinishing
16 HoningAbrasive 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 HoningCommon 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 SuperfinishingSimilar to honing - uses bonded abrasive stick pressed against surface and reciprocating motionDifferences with honing:* Shorter strokes* Higher frequencies* Lower pressures between tool and surface* Smaller grit sizesFigure Superfinishing on an external cylindrical surface.