Taha Selman Cakir
030070023
5th week

Thermoforming:

Thermoforming is a process for forming thermoplastic sheets or films over a mold by means of the application of heat and pressure. In this process, a sheet is clamped and heated to the sag point (above the glass-transition temperature of the polymer), usually by radiant heating, and forced against the mold surfaces through the application of a vacuum or air pressure. The sheets used in thermoforming usually are made by sheet extrusion and are available filled with various materials for making parts with specific applications.

The mold is generally at room temperature, thus the shape produced becomes set upon contact with the mold. Because of the low strength of the materials formed, the pressure differential caused by a vacuum usually is sufficient for forming. However, thicker and more complex parts require air pressure, which may range from about 100 to 2000 kPa (15 to 300 psi), depending on the type of material and thickness of the sheet. Mechanical means, such as the use of plugs, also may be employed to help form the parts.

(Kalpakjian S., Schmid S.R., Manufacturing engineering and technology, Ed. 5th, p. 555,556)

Gun drilling:

Developed originally for drilling gun barrels, gun drilling is used for drilling deep holes and requires a special drill. The depth-to-diameter ratios of holes produced can be 300:1 or even higher. The thrust force (the radial force that tends to push the drill sideways) is balanced by bearing pads on the drill that slide along the inside surface of the hole. Consequently, a gun drill is self-centering-an important feature when drilling straight, deep holes.

(Kalpakjian S., Schmid S.R., Manufacturing engineering and technology, Ed. 5th, p. 707,708)

Porosity:

Porosity in a casting may be caused by shrinkage, or gases, or both. Porous regions can develop in castings because of shrinkage of the solidified metal. Thin sections in a casting solidify sooner than thicker regions; as a result, molten metal flow into the thicker regions that have not yet solidified. Porous regions may develop at their centers because of contraction as the surfaces of the thicker region begin to solidify first. Microporosity also can develop when the liquid metal solidifies and shrinks between dendrite branches.

Most welded joints contain some porosity, which is generally in the shape of spheres or of elongated pockets. Porosity in welds is caused by:
-Gases released during melting of the weld area but trapped during solidification.
-Chemical reactions during welding
-Contaminants.

(Kalpakjian S., Schmid S.R., Manufacturing engineering and technology, Ed. 5th, p. 277,962)

Hacksaw blades:

Hacksaws have straight blades and reciprocating motions. Developed in the 1650s, they generally are used to cut off bars, rods, and structural shapes. They may be manual or power operated. Because cutting takes place during only one of the two reciprocating strokes, hacksaws are not as efficient as band saws. Power hacksaw blades are usually 1.2 to 2.5 mm (0.05 to 0.10 in.) thick and up to 610 mm (24 in.) long. The rate of strokes ranges from 30 per minute for high-strength alloys to 180 per minute for carbon steels. The hacksaw frame in power hacksaw is hacksaw is weighted by various mechanisms, applying as much as 1.3 kN (300 lb) of force to the workpiece to improve the cutting rate. Hand hacksaw blades are thinner and shorter than power hacksaw blades, which have as many as 1.2 teeth per mm (32 per in.) for sawing sheet metal and thin tubing.

(Kalpakjian S., Schmid S.R., Manufacturing engineering and technology, Ed. 5th, p. 747)