Burcu Atay, 140060029, 4th week

Slip Casting

Forming a hollow ceramic part by introducing a pourable slurry into a mold. The water in the slurry is extracted into the porous mold, leaving behind a drier surface. Excess slurry can then be decanted.

(Askeland, D.R.,The Science and Engineering of Materials,3rd Edition,PWS Publisihing Company, pg.464)

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Green compacts for tungsten, molybdenum, and other powders are sometimes made by slip casting. The powder, converted to slurry mixture, is first poured into a plaster of Paris mold. Because the mold is porous, the liquid gradually drains off into the plaster leaving a solid layer of material deposited on the surface of the mold. For hallow objects, after sufficient time has been allowed for a desired thickness to accumulate, the remaining slurry is poured out. Upon drying the green components are sintered in the usual manner. This procedure is simple and permits considerable variation in size and shape.

Increasing emphasis is being directed to this process because parts can be made that are too large or too complex to pres. An expensive pres is not required, and improved physical properties are additional advantages. The principal disadvantage is time lag in producing parts.

(Amstead, B.H., Ostwald P.F., Begeman, M.L., Manufacturing Processes, 8th Edition, John Wiley & SOns, Inc, pg.202)

Hot Pressing

Hot pressing is similar to dry pressing, except that the process is carried out at elevated temperatures, so that sintering of the product is accomplised simultaneously with pressing. This eliminates the need for seperate firing step in the sequence. Higher densities and finer grain size are obtained, but die life is reduced by the hot abrasive particles against the die surfaces.

(Groover, M.P., Fundamentals of modern manufacturing: materials, processes, and systems,4th Edition, pg. 377)

Hemming

Hemming involves bending the edge of the sheet over on itself, in more than one bending step. This is often done to eliminate the sharp edge on the piece, to increase stiffness, and to improve appearance. Seaming is a related operation in which two sheet-metal edges are assemble.

(Groover, M.P., Fundamentals of modern manufacturing: materials, processes, and systems,4th Edition, pg. 454)

Ultrasonic Cleaning

Ultrasonic cleaning combines chemical cleaning and mechanical agitation of the cleaning fluid to provide a highly effective method for removing surface contaminants.The cleaning fluid is generally an aqueous solution containing alkaline detergents. The mechanical agitation is produced by high-frequency vibrations of sufficient amplitude to cause cavitation-formation of low- pressure vapor bubbles or cavities. As the vibration wace passes a given point in the liquid, the low-pressure region is followed by a high-pressure front that implodes the cavity, thereby producing a shock wave capable of penetrating contaminant particles adhering to the work surface. This rapid cycle of cavitation and implosion occurs throughout the liquid medium, thus making ultrasonic cleaning effective even on complex and intricate internal shapes. The cleaning process is performed at frequencies between 20 and 45 kHz. And the cleaning solution is usually at an elevated temperature, typically 65°C to 85°C(150°F-190°F)

(Groover, M.P., Fundamentals of modern manufacturing: materials, processes, and systems,4th Edition, pg. 670-671)