Kayra Ermutlu-030060081 (5th Week)

Foundry

A foundry is a factory equipped for making molds, melting and handling metal in molten form, performing the casting process, and cleaning the finished casting.

(Groover M.P., Fundamentals of Modern Manufacturing:Materials, Processes and Systems, pg.207, Kayra Ermutlu)

Roll Forming

Roll forming (also called contour roll forming) is a continuous bending process in which opposing rolls are used to produce long sections of formed shapes from coil or strip stock. Several pairs of rolls are usually required to progressively accomplish the bending of the stock into the desired shape.

Products made by roll forming include channels, gutters, matel siding sections (for homes), pipes and tubing with seams and various structural sections. Although roll forming has the general appearance of a rolling operation (and the tooling certainly looks similar), the difference is that roll forming involves bending rather than compressing the work.

(Groover M.P., fundamentals of Modern Manufacturing: Materials, Processes and Systems, pg. 472, Kayra Ermutlu)

Low-Pressure Die-Casting

Low pressure die casting has been lately developed to enable produciton of castings that are flawless, have very thin sections and register a yield approaching 100% even in metals such as aluminium and magnesium. The mould, which is made in metal (usually cast iron), is filled by upward displacement of molten metal from a sealed melting pot or bath. This dispalcement is effected by applying relatively low pressure of dry air (0.5~1.0 kg*(mm^-2) on the surface of the molten metal in the bath. The pressure causes the metal to rise through a central cast iron tube and move into the die cavity. The dies are provided ample venting to allow the escape of air. The pressure is maintained till the metal is solidified: then it is released enabling the excess liquid metal to drain down the connecting tube back into the bath. Since the system of upward filling requires no runners and risers, there is hardly any wastageof metal. As positive pressure is maintained to force the metal to fill recesses and cavities, casting with excellent surface quality, finish and soundness are produces. Low pressure on the metal completely eliminates turbulence and air aspiration. Cores, if required, can be used in the dies: they may be of sand or shell.

(Jain P.L., Principles of Foundry Technology, pg.170, Kayra Ermutlu)

Ultrasonic Welding

Ultrasonic welding is an industrial technique whereby high frequency ultrasonic acoustic vibrations are locally applied to work piece that are held together under pressure to create a solid state weld. In ultrasonic welding there are no connective bolts, nails, soldering materials or adhesives necessary to bind the materials together. This process is speacially used for plastics and for joining dissimilar metals like thin copper, aluminium, nickel etc. used in fuel cells.

Ultrasonic welding is not due to heating but occurs due to high pressure dispersion of surface oxides and local motion of material. Vibrations are introduces along the joint being welded. Common frequencies used in welding of plastics are from 15 kHz to 70 kHz.

The basic components of ultrasonic welding processes include the following:

1. A pressure to put two parts of material to be assembled under pressure.
2. An anvil where the parts are placed and allowing high frequency vibrations to be directed to interfeces.
3. An ultrasonic generator to produce frequencies of 15 kHz to 70 kHz.
4. A converter that conversts the electrical signal into mechanical vibrations.
5. Sonotrade that applies mechanical vibrations to the parts to be welded.
6. A controller that controls the movement of the press and the delivery of ultrasonic energy.

Benefits of ultrasonic welding:

• Very neat weld seams: As no additional adhesive or parts are needed, ultrasonic welding joints created are extremely neat and visually attractive.
• High level quality: As all welding parts of the operations are automated, each part produced will be of high quality.
• Low cycle times: The actual time it takes a part to be welded is typically less than one second. Thus large batches can be produced in a short span of time.

(Rajagopal K., Textbook of Engineering Physics-Part I, pg.16-17, Kayra Ermutlu)