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Laser Beam Cutting: A laser weld and laser cut both bring the maetrial to a molten state. In the welding process the matreial is allowed to flow together and cool to form the weld metal. In the cutting process a jet of gas is directed into the molten material to expel it through the bottom of the cut. Although the alser is used primarily to cut very thin materials, it can be used to cut up to 1 inch of carbon steel. The cutting gas assist can be either a nonreactive gas or an exothermic. Nonreactive gases do not add any heat to the cutting process; they simply remove the molten material by blowing it out of the kerf. Exothermic gases react with the material being cut, like an oxyfuel cutting torch. The additional heat produced as the exothermic cutting gas reacts with the metal being cut helps blow the molten material outmof the kerf. Some of the advantages of laser cutting include: *narrow heat-affected zone- little or no heating of the surrounding material is observed. ıt's possible to make very close parallel cuts without damaging the strip that's cut out. *no electrical conductivity required- the part being cut does not have to be electrically conductive, so materials like glass, quartz, and plastic can be cut. There is also no chance that a stray electrical charge might damage delicate computer chips while they are being cut using a laser. *noncontact- nothing comes in contact withb the part being cut except the laser beam. Small parts that may have finished surfaces or small surface details can be cut without the danger of disrupting or damaging the surface. It's also not necessary to hold the parts securely as it is when a cutting tool is used. *narrow kerf- the width of the kerf is very small, which allows the nesting of the parts in close proximity to each other, which will reduce waste of expensive materials. *automation and robotics- the laser bema can easily be directed through an articulated guide to the working end of an automated machine or robot. *top edge- the top edge will be smooth and square without being rounded. (L. F. Jeffus, Welding: principles and applications, p.190) Ultrasonic Machining: Ultrasonic machining (USM) actually involves two different processes: ultrasonic impact grinding and rotary ultrasonic machining. Ultrasonic impact grinding (USIG) involves rapid oscilation of a shaped tool immersed in a slurry of abrasive that is also in contact with the workpiece. This oscilation drives abrassive particles against the workpiece and cuts in it a cavity that has the same shape as the tool. The oscillating frequency of the tool is from 19,000 to 25,000 Hz, and its amplitude is only 0.013 to 0.063 mm. The gap between the tool and the workpiece is small and the abrassive slurry is pumped through this gap. The tool is normally of low-carbon or stainless steel and is fastened to an ultrasonic generator through a horn of Monel metal. The abrassive particles may be aluminum oxide, silicon carbide, or boron carbide. Rotary ultrasonic machining is similar to conventional drilling or milling of glass or other nonmetallics except that the rotating diamond-coated tool is also vibrated at an ultrasonic frequency (20 kHz). There is no abrassive slurry as in ultrasonic impact grinding, but there is a coolant(usually water) that flushes away the removed material. The ultrasonic vibration reduces the pressure on the cutting tool an the friction at the point of cutting. It provides better coolant flow andbetter flushing of removed material. These factors result in faster cutting action. (J.G. Bralla, Design for manufacturability handbook, p.142) Cutting Fluids: Cutting fluids are compounds applied to tool points to facilitate metal-cutting operations. There are two general classes: straight-oil cutting fluids and emulsion cutting fluids or the so-called water-soluble oils. The straight oils are usually viscous,dark colored, chemically trated mineral oils, containing sulphur or chlorine or both, and proportions of animal or vegetable oils. Water- soluble or emulsifying oils also conssit of a mixture of mineral oil and animal or vegetable oil chemically treated with sulphur or chlorine. These chemically treated animal or vegetable oils are commonly sulphonated or chlorinated oils according to the process of chemical treatment which they have gone. Soluble oils also contain an emulsifying agent, that is a substance which has the property of causing the oil to form a mily solution or emulsion when stirred into water. Many compounds such as certain soaps and alkaline compounds are used as amulsifying agents. For use, soluble oils are mixed with water in varying percentages from 5 to 95 percent, according to recommendations to the manufacturer. (G.L. Martin, Popular Mechanics, p. 146) Sandwich structure: One of the main problems and limitations of the skin material in stressed skin is its lack of rigidity. Skins often have to be made thicker than they might otherwise need to be because of a tendency to crumple under some types of load. A strip of paper illustrates this problem very well; one can pull it but not push it. A way of providing thin sheets with rigidity is to make a sandwich with one very thin sheet, a layer of very light but fairly rigid core material, and another very thin sheet, all bonded together with an appropriate adhesive. As with conventional semi monocoque structures, wooden construction led the way with sandwich structures. The famous and elegant de Havilland Mosquito of 1940 was built with plywood skins either side of a balsa-wood core. In today's major structures, a metal core of honeycomb-like cells is reconginsed as the most suitable core for metal-faced sandwich. (John Cutler,Jeremy Liber, Understanding aircraft structures , p. 14)