Manufacturing Technology II LO 4 Abrasive Process and

Manufacturing Technology II LO # 4 Abrasive Process and Broaching Abrasive Processes Surface Measurement Broaching works Manufacturing Technology 1

Abrasive Processes q Abrasive machining involves material removal by the action of hard abrasive particles that are usually in the form of a bonded wheel. q Grinding is the most important abrasive process. In terms of number of machine tools in use, grinding is the most common of all metalworking operations. q Other traditional abrasive processes include honing, lapping, superfinishing, polishing, and buffing. The abrasive machining processes are generally used as finishing operations, Manufacturing Technology 2

Abrasive Processes Abrasive processes are important commercially and technologically for the following reasons: q 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. q Some of these processes can produce extremely fine surface finishes, to 0. 025 mm (1 m. in = 1 milli inch). q For certain abrasive processes, dimensions can be held to extremely close tolerances. Manufacturing Technology 3

Grinding Wheels q A grinding wheel consists of abrasive particles and bonding material. The bonding material holds the particles in place and establishes the shape and structure of the wheel. These two ingredients and the way they are fabricated determine the five basic parameters of a grinding wheel: (1) abrasive material, (2) grain size, (3) bonding material, (4) wheel grade, (5) wheel structure. To achieve the desired performance in a given application, each of the parameters must be carefully selected. Manufacturing Technology 4

Grinding Wheels (1) Abrasive material General properties of an abrasive material used in grinding wheels include high hardness, wear resistance, toughness, and friability. Hardness, wear resistance, and toughness are desirable properties of any cutting-tool material. 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 abrasive materials of greatest commercial importance are aluminum oxide, silicon carbide, cubic boron nitride, and diamond. Manufacturing Technology 5

Grinding Wheels (1) Abrasive material Manufacturing Technology 6

Grinding Wheels (2) Grain Size The grain size of the abrasive particle is important in determining surface finish and material removal rate. Small grit sizes produce better finishes, whereas larger grain sizes permit larger material removal rates. Thus, a choice must be made between these two objectives when selecting abrasive grain size. The selection of grit size also depends to some extent on the hardness of the work material. Harder work materials require smaller grain sizes to cut effectively, whereas softer materials require larger grit sizes. Grain sizes used in grinding wheels typically range between 8 and 250. Grit size 8 is very coarse and size 250 is very fine. Even finer grit sizes are used for lapping and superfinishing. Manufacturing Technology 7

Grinding Wheels (3) Bonding Materials The bonding material holds the abrasive grains and establishes the shape and structural integrity of the grinding wheel. Desirable properties of the bond material include strength, toughness, hardness, and temperature resistance. The bonding material must be • able to withstand the centrifugal forces and high temperatures experienced by the grinding wheel, • resist shattering in shock loading of the wheel, and • hold the abrasive grains rigidly in place to accomplish the cutting action • while allowing those grains that are worn to be dislodged so that new grains can be exposed. Manufacturing Technology 8

Grinding Wheels (3) Bonding Materials Manufacturing Technology 9

Grinding Wheels (4) Wheel Structure Wheel structure refers to the relative spacing of the abrasive grains in the wheel. In addition to the abrasive grains and bond material, grinding wheels contain air gaps or pores. The volumetric proportions of grains, bond material, and pores can be expressed as; Pg +Pb + Pp = 1. 0 Where, Pg : proportion of abrasive grains in the total wheel volume, Pb : proportion of bond material, and Pp : proportion of pores (air gaps). Manufacturing Technology 10

Grinding Wheels (4) Wheel Structure Wheel structure is measured on a scale that ranges between ‘‘open’’ and ‘‘dense. ’’ An open structure is one in which Pp is relatively large, and Pg is relatively small. That is, there are more pores and fewer grains per unit volume in a wheel of open structure. It is recommended in situations in which clearance for chips must be provided. A dense structure is one in which Pp is relatively small, and Pg is larger. Dense structures are used to obtain better surface finish and dimensional control. Manufacturing Technology 11

Grinding Wheels (5) Wheel Grade Wheel grade indicates the grinding wheel’s bond strength in retaining the abrasive grits during cutting. This is largely dependent on the amount of bonding material present in the wheel structure Pb. Manufacturing Technology 12

Grinding Wheels Marking/Identification system – ANSI B 74. 13 – 1977 [3] Manufacturing Technology 13

Grinding Wheels Marking/Identification system – ANSI B 74. 13 – 1977 [3] Manufacturing Technology 14

Grinding Wheels Marking/Identification system – ANSI B 74. 13 – 1977 [3] Manufacturing Technology 15

Grinding Wheels Marking/Identification system – ANSI B 74. 13 – 1977 [3] Manufacturing Technology 16

Grinding Wheels Analysis of the Grinding Process Manufacturing Technology 17

Grinding Wheels Analysis of the Grinding Process V : Surface speed of wheel, mm/min N : Spindle speed, rpm MMR : Material Removal Rate, mm 3/min D : Wheel diameter, mm d : Depth of Cutting (= Infeed), is the penetration of the wheel below the original work surface, mm w : With of the grinding path (=Crossfeed). mm Lc : The length of the chip, mm Vw : Work speed, mm/min. Manufacturing Technology 18

Grinding Wheels Analysis of the Grinding Process Example : Calculate the RPM for a Ø 250 mm grinding wheel to run at 1520 m/min. RPM = 1520 / ( π x 0. 25 ) = 1935 rev/min Manufacturing Technology 19

Application guideline for Grinding ductile metals And Manufacturing Technology Grinder dressing https: //www. youtube. com/watch? v=Bky. Lua 8 t 10 M 20

Grinding Operation and Grinding Machine 1. Surface Grinding 2. Cylindrical Grinding 3. Centerless Grinding 4. Creep feed grinding 5. Other Grinding Operation Manufacturing Technology 21

Grinding Operation and Grinding Machine 1. Surface Grinding Surface grinding is normally used to grind plain flat surfaces. It is performed using either the periphery of the grinding wheel or the flat face of the wheel. Manufacturing Technology 22

Grinding Operation and Grinding Machine 1. Surface Grinding Manufacturing Technology surface grinding machine https: //www. youtube. com/watch? v=gc. Wj 4 Octe. Tk 23

Grinding Operation and Grinding Machine 2. Cylindrical Grinding CYLINDRICAL GRINDER MACHINE https: //www. youtube. com/watch? v=N 0 C 6 rnbtq. Qk https: //www. youtube. com/watch? v=GIZub. Rz 706 U A cylindrical grinding is used for rotational parts. These grinding operations divide into two basic types (a) external cylindrical grinding and (b) internal cylindrical grinding. Crankshaft Grinding https: //www. youtube. com/watch? v=-7 Al 0_ih. Wgs Manufacturing Technology 24

Grinding Operation and Grinding Machine 3. Centerless Grinding Centerless grinding is an alternative process for grinding external and internal cylindrical surfaces. As its name suggests, the workpiece is not held between centers. External Centreless Grinding CENTERLESS GRINDING MACHINE https: //www. youtube. com/watch? v=y 3 Sx. F 3 Hsq. Ro Manufacturing Technology 25

Grinding Operation and Grinding Machine 3. Centerless Grinding Internal Centreless Grinding Manufacturing Technology 26

Grinding Operation and Grinding Machine 4. Creep Feeding Grinding Creep feed grinding is performed at very high depths of cut and very low feed rates; hence, the name creep feed. The comparison with conventional surface grinding is illustrated below. Manufacturing Technology 27

Grinding Operation and Grinding Machine 5. Other Grinding Operations Disk Grinder Abrasive Belt Grinder Pipe Belt Grinder https: //www. youtube. com/watch? v=Jh. ARKPk. Ca. Bg Manufacturing Technology 28

Related Abrasive Processes Lapping https: //www. youtube. com/watch? v=X 0 -_Owj. QBg. I https: //www. youtube. com/watch? v=JTz-lku 2 k. Ms https: //www. youtube. com/watch? v=Z 6 tog. IVq. C 4 M Lapping is an abrasive process used to produce surface finishes of extreme accuracy and smoothness. It is used in the production of optical lenses, metallic bearing surfaces, gages, and other parts requiring very good finishes. https: //www. youtube. com/watch? v=Z 6 tog. IVq. C 4 M Manufacturing Technology 29

Related Abrasive Processes Honing Process https: //www. youtube. com/watch? v=Az-El 3 QHSl. E https: //www. youtube. com/watch? v=mye. KVBH 5 ALc Honing is an abrasive process performed by a set of bonded abrasive sticks. A common application is to finish the bores of internal combustion engines. Other applications include bearings, hydraulic cylinders, and gun barrels. https: //www. youtube. com/watch? v=dz. MTysjhj. GQ https: //www. youtube. com/watch? v=xy_g 1 r. G 7 m. KQ Manufacturing Technology 30

Related Abrasive Processes Superfinishing Superfinish https: //www. youtube. com/watch? v=v. ETFctgk. Qq. Y https: //www. youtube. com/watch? v=Q 1 QP 79 V 4 IMA https: //www. youtube. com/watch? v=j. Qm. Ok. GSh-30 Superfinishing is an abrasive process similar to honing. Both processes use a bonded abrasive stick moved with a reciprocating motion and pressed against the surface to be finished. Superfinishing differs from honing in the following respects: (1) the strokes are shorter, 5 mm (3/16 in); (2) higher frequencies are used, up to 1500 strokes per minute; (3) lower pressures are applied between the tool and the surface, below 0. 28 MPa (40 lb/in 2); (4) workpiece speeds are lower, 15 m/min (50 ft/min) or less; and (5) grit sizes are generally smaller. https: //www. youtube. com/watch? v =f. Nemcj. Agh 50 Manufacturing Technology 31

Related Abrasive Processes Polishing and Buffing Polishing is used to remove scratches and burrs and to smooth rough surfaces by means of abrasive grains attached to a polishing wheel rotating at high speed— around 2300 m/min (7500 ft/min). Buffing is similar to polishing in appearance, but its function is different. Buffing is used to provide attractive surfaces with high lustre. Polishing Buffing Manufacturing Technology 32

Related Abrasive Processes Comparison and Applications Manufacturing Technology 33

Surface Measurement Surfaces are described as consisting of two parameters: (1)surface texture. (2)surface integrity. Manufacturing Technology 34

Surface texture q Nominal surface ; - It representing the intended surface contour of the part, and is defined by lines, ideal circles, round holes, and other edges and surfaces that are geometrically perfect. q Surface texture; - Surface Texture or Surface Topography is the local deviations of a surface from a perfectly flat plane. The measure of the surface texture is generally determined in terms of its roughness, waviness, lay, and flaws. Manufacturing Technology 35

Surface texture q Roughness; refers to the small, finely spaced deviations from the nominal surface that are determined by the material characteristics and the process that formed the surface. q Waviness ; is defined as the deviations of much larger spacing; they occur because of work deflection, vibration, heat treatment, and similar factors. Roughness is superimposed on waviness. q Lay ; is the predominant direction or pattern of the surface. It is determined by the manufacturing method used to create the surface, usually from the action of cutting tool. q Flaws ; are irregularities that occur occasionally on the surface; these include cracks, scratches, inclusions, and similar defects in the surface. Manufacturing Technology 36

Surface texture Manufacturing Technology 37

Surface Integrity q Surface texture alone does not completely describe a surface. q There may be metallurgical or other changes in the material immediately beneath the surface that can have a significant effect on its mechanical properties. q Surface integrity is the study and control of this subsurface layer and any changes in it because of processing that may influence the performance of the finished part or product. Manufacturing Technology 38

Evaluation of Surface Integrity q Surface texture. Surface roughness, designation of lay, and other measures provide superficial data on surface integrity. This type of testing is relatively simple to perform and is always included in the evaluation of surface integrity. q Visual examination can reveal various surface flaws such as cracks, craters, laps, and seams. This type of assessment is often augmented by fluorescent and photographic techniques. q Microstructural examination. This involves standard metallographic techniques for preparing cross sections and obtaining photomicrographs for examination of microstructure in the surface layers compared with the substrate. Manufacturing Technology 39

Evaluation of Surface Integrity q Microhardness profile. Hardness differences near the surface can be detected using microhardness measurement techniques such as Knoop and Vickers. The part is sectioned, and hardness is plotted against distance below the surface to obtain a hardness profile of the cross section. q Residual stress profile. X-ray diffraction techniques can be employed to measure residual stresses in the surface layers of a part. Manufacturing Technology 40

Measurement of Surface – Profile meter In these electronic devices, a cone-shaped diamond stylus with point radius of about 0. 005 mm(0. 0002 in) and 90 tip angle is traversed across the test surface at a constant slow speed. The operation is depicted in the figure below. As the stylus head is traversed horizontally, it also moves vertically to follow the surface deviations. The vertical movement is converted into an electronic signal that represents the topography of the surface. This can be displayed as either a profile of the actual surface or an average roughness value Manufacturing Technology 41

Surface – Effect of Manufacturing Processes Poor Medium Manufacturing Technology Good Very Good Excellent 42

Broaching (Machine) Broaching is performed using a multiple-teeth cutting tool by moving the tool linearly relative to the work in the direction of the tool axis. Advantages include good surface finish, close tolerances, and a variety of work shapes. Manufacturing Technology 43

Broaching (Machine) q The total material removed in a single pass of the broach is the cumulative result of all the steps in the tool. q The speed motion is accomplished by the linear travel of the tool past the work surface. q The shape of the cut surface is determined by the contour of the cutting edges on the broach, particularly the final cutting edge. Vertical Broaching Horizontal Broaching Manufacturing Technology 44