| A | B |
|---|
| Abrasive machining | involves material removal by the action of hard, abrasive particles that are usually in the form of a bonded wheeL Grinding is the most important of the abrasive processes. |
| Abrasive processes are important commercially and technologically for the following reasons: | > They can be used on all types of materials ranging from soft metals to hardened steels and hard nonmetallic materials such as ceramics and silicon. > Some of these processes can produce extremely fine surface finishes, to 0.025 I'm (1 I'-in). :;.- For certain abrasive processes, dimensions can be held to extremely close tolerances. |
| Grinding | is a material removal process accomplished by abrasive particles that are contained in a bonded grinding wheel rotating at very high surface speeds. |
| Grinding can be likened to the _______ process | milling |
| Peripheral grinding is much more common than face grinding (know) | Peripheral grinding is much more common than face grinding |
| Despite these similarities, there are significant differences between grinding and milling: | (1) the abrasive grains in the wheel are much smaller and more numerous than the teeth on a milling cutter; (2) cutting speeds in grinding are much higher than in milling; (3) the abrasive grits in a grinding wheel are randomly oriented and possess on average a very high negative rake angle; and (4)a grinding wheel is self-sharpening-as the wheel wears, the abrasive particles become dull and either fracture to create fresh cutting edges or are pulled out of the surface of the wheel to expose new grains |
| A grinding wheel consists of | abrasive particles and bonding material. |
| the five basic parameters of the grinding wheel: | (1) abrasive material, (2) grain size, (3) bonding material, (4) wheel grade, and (5) wheel structure. To achicve the desired performance in a given application, each of the parameters must be carefully selected |
| Friability | refers to the capacity of the abrasive material to fracture when the cutting edge of the grain becomes dull, thereby exposing a new sharp edge. |
| The grain size of the abrasive particle is important in determining: | surface finish and material removal rate. Small grit sizes produce better finishes, while larger grain sizes permit larger material removal rates. |
| Aluminum oxide (abrasive in grinding) | Most common abrasive material (Section 7.3.1), used to grind steel and other ferrous, high-strength aloys |
| Silicon carbide (abrasive in grinding) | Harder than AI20), but not as tough (Section 7.2.2). Applications include ductile metals such as aluminum, brass, and stainless steel, as well as brittle materials such as some cast irons and certain ceramics. Cantlot be used effectively for grinding steel because of the strong chemical affinity between the carbon in SiC and the iron in steel |
| Cubic boron nitride (abrasive in grinding) | When used as an abrasive, cBN (Section 7.3.3) is produced under the trade name Borazon by the General Electric Company. cEN grinding wheels arc used for hard materials such as hardened tool steels and aerospace alloys |
| Diamond (abrasive in grinding) | Diamond abrasives occur naturally and are also made synthetically (Section 7.5.1). Diamond wheels are generally used in grinding applications on hard, abrasive materials such as ceramics, cemented carbides, and glass |
| Vitrified bond | Consists chiefly of baked clay and ceramic materials. Most grinding wheels in cornman use are vitrified bonded wheels. ·They are strong and rigid, resistant to elevated temperatures, and relatively unaffected by water and oil that might be used in grinding fluids. |
| Silicate bond | Consists of sodium silicate (Na2S03). Applications are generally limited to situations in which heat generation must be minimized, such as grinding cutting tools |
| Rubber bond | Most flexible of the bonding materials and used as a bonding material in cutoff wheels. |
| Resinoid bond | Consists of various thermosetting resin m.aterials, such as phenol-formaldehyde. It has very high strength and is used for rough grinding and cutoff operations |
| Shellac bond | Relatively strong but not rigid; often used in applications requiring a good finish |
| Metallic bond | Metal, usually bronze, is the commOn bond material for diamond and cBN grinding wheels. Particulate processing (Chapters 16 and 17) is used to bond the metal matrix and abrasive grains to the outside periphery of the wheel, thus conserving the costly abrasive materials |
