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Ironing 21:14 15.04.2011

In deep drawing the flange is compressed by the squeezing action of the blank perimeter seeking a smaller circumference as it is drawn toward the die opening. Because of this compression, the sheet metal near the outer edge of the blank becomes thicker as it moves inward. If the thickness of this stock is greater than the clearance between the punch and die, it will be squeezed to the size of the clearance, a process known as ironing. Sometimes ironing is performed as a separate step that follows drawing.Ironing makes the cylindrical cup more uniform in wall thickness. The drawn part is therefore longer and more efficient in terms of material usage. Beverage cans and artillery shells, two very high-production items, include ironing among their processing steps to achieve economy in material usage.

(Mikell P. Groover, Fundamentals of Modern Manufacturing, Materials, Processes and Systems ,page 459)

Rotational Molding 09:13 14.04.2011

Rotational molding uses gravity inside a rotating mold to achieve a hollow form. Also called rotomold'mg, it is an alternative to blow molding for making large, hollow shapes. It is used principally for thermoplastic polymers, but applications for thermosets and elastomers are becoming more common. Rotomolding tends to favor more complex external geometries, larger parts, and lower production quantities than hlow molding. The process consists of the following steps: (1) A predetermined amount of polymer powder is loaded into the cavity of a split mold. (2) The mold is then heated and simultaneously rotated on two perpendicular axes, so that,the powder impinges on all internal surfaces of the mold, gradually forming a fused layer of uniform thickness. (3) While still rotating, the mold is cooled so that the plastic skin solidifies. (4) The mold is opened, and the part is unloaded. Rotational speeds used in the process are relatively slow. It is gravity, not centrifugal force, that causes uniform coating of the mold surfaces.Molds in rotational molding are simple and inexpensive compared to injection molding or blow molding, but the production cycle is much longer, lasting perhaps 10 min or more. To balance these advantages and disadvantages in production, rotational molding is often performed on a multicavity indexing machine, such as the three-station machine shown in Figure 13.34. The machine is designed so that three molds are indexed in sequence through three workstations. Thus, all three molds are working simultane­ously, The first workstation is an unload-load station where the finished part is unloaded from the mold, and the powder for the next part is loaded into the cavity. The second station consists of a heating chamber where hot-air convection heats the mold while it is simultaneously rotated. Temperatures inside the chamber are around 375°C (700°F), depending on the polymer and the item being molded. The third station cools the mold, using forced cold air or water spray, to cool and solidify the plastic molding inside.
A fascinating variety of articles are made by rotational moiding. The list includes hollow toys such as hobby horses and playing balls; boat and canoe hulls, sandboxes, small swimming pools; buoys and other flotation devices; truck body parts, automotive dashboards, fuel tanks; luggage pieces, furniture, garbage cans; fashion mannequins; large industrial barrels, containers, and storage tanks; portable outhouses, and septic tanks. The most popular molding material is polyethylene, especially HDPE. Other plastics include polypropylene, ABS, and high-impact polystyrene.

(Mikell P. Groover, Fundamentals of Modern Manufacturing, Materials, Processes and Systems ,page 292-293)

Three-Plate Mold 00:10 14.04.2011

The two-piate mold is the most common mold in injection molding. An alternative is a three-plate mold, shown in Figure 13.24, for the same part geometry as before. There are advantages to this mold design. First, the flow of molten plastic is through a gate located at the base of the cup-shaped part, rather than at the side. This allows more even distribution of melt into the sides of the cup. In the side gate design in the two-plate mold of Figure 13.23, the plastic must flow around the core and join on the opposite side, possibly creating a weakness at the weld line. Second, the three-plate mold allows more automatic operation of the molding machine. As the mold opens, it divides into three plates with two openings between them. This forces disconnection of runner and parts, which drop by gravity (with possible assistance from blown air or a robotic arm) into different containers beneath the nioid.

(Mikell P. Groover, Fundamentals of Modern Manufacturing, Materials, Processes and Systems ,page 279-280)

Penetrant Testing 00:25 14.04.2011

A typical penetrant testing involves use of a variety of materials for cleaning and developing as well as the penetrant material itself.In general, the fluids involved in the penetrant process are either petroleum-or-water-based and the solvents or cleaners are selected according to the type of penetrant.Penetrant material consists of the indicating dye plus the carrier fluid. The indicating dye may give a colour contrast with respect to the suroundings, as is the case for visible dye penetrant methods, or a brightness contrast for the flourescent penetrants, the dye appears bright yellow green under ultraviolet light.

(Baldev Raj,Practical Non-Destructive Testing,second edition page 11)

Thermoforming 09:09 14.04.2011

Thermoforming is a process in which a flat thermoplastic sheet is heated and deformed into the desired shape. The process is widely used in packaging of consumer products and to fabricate large items such as bathtubs, contoured skylights, and internal door liners for refrigerators.
Thermoforming consists of two main steps: (1) heating and (2) forming. Heating is usually accomplished by radiant electric heaters, located on one or both sides of the starting plastic sheet at a distance of roughly 125 mm (5 in). Duratio n of the heating cycle needed to sufficiently soften the sheet depends on the polymer—its thickness and color. The methods by which the forming step is accomplished can be classified into three basic categories: (1) vacuum thermoforming, (2) pressure thermoforming, and (3) mechanical thermoforming. In our discussion of these methods, we describe the forming of sheet stock; in the packaging industry, most thermoforming operations are performed on thin films.

(Mikell P. Groover, Fundamentals of Modern Manufacturing, Materials, Processes and Systems ,page 293)