Metin Atmaca 030080007 4th week definitions

1. Friction Welding (Manufacturing Process):

Previous Definition:

In principle, friction welding is a press welding method. Intensive friction leads to local heating between two components so that the parts finally weld together without reaching the liquid phase. Therefore, friction welding can be done in air. By intensive rubbing and additional pressure, the surfaces are heated up to temperatures where the usually hot forming takes place,i.e., kinetic energy is converted into heat to bring about controlled degrees of fusion. Although cylindrical workpieces are like shafts or flanges are particularly suitable for this method, friction welding has recently attained a special attention for the production of "blisks"(bladed disks) in jet engine compressors. Friction welding offers cost advantages, particularly for larger blisks sizes.

(C.Leyens, M. Peters, Titanium and titanium alloys: fundamentals and applications, First Edition, p.252)

New Definition (Better):

In friction welding the thermal energy needed to create a weld successfully is produced by mechanical rubbing friction between the two parts to be joined. This is achieved by rotating one half of the joint while the other half is held stationary, except for being pushed axially against the rotating part (Fig. 5.16a2). When the joint area has been heated to a plasticized state, rotation is stopped, and to complete the weld the two parts are even more firmly axially pressed together—typically with a force of 10 MN (Fig. 5.16a4).

Note: This is a similar welding process to flash butt welding except that frictional heat is used instead of an electric arc.

Although this process is limited to joints of which at least one of the two parts must be rotatable in either a chuck or other gripping fixture, it does have the great advantage that dissimilar metals can be readily joined.

For small 1–2 mm diameter components, rotational speeds up to 80000rev/min are necessary, but for much larger parts speeds may be as low as 50 rev/min.

Weld quality is both good and consistent across the whole joint area.

By automating component handling and the welding cycle (which can even incorporate automatic machine removal of excess metal around the outside of the joint), productivity is now sufficiently high to make friction welding a widely used process, particularly in the automotive industry, where it is used in the production of such items as axle casings, transmission shafts and turbocharger internals.

Even thermoplastics can be joined using friction welding and, as energy requirements are small compared with arc and resistance welding, the HAZ is also small.

(Fred Waters, Fundamentals of Manufacturing for Engineers, p. 118)

2. Low-Pressure Die-Casting (Manufacturing Method):

Previous Definition:

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)

New Definition (Better):

This is a slightly more complex die-casting method, but has the advantage that runners are not required, thus offering a greater casting yield for a given volume of metal cast.

The process involves replacing gravity-fed metal into the die with a pneumatic force derived from a lowpressure compressed air source—typically 0.5–1 bar. The air supply is applied to the surface of the molten metal, and this forces it up a ceramic-lined feeder tube into the die cavity (Fig. 2.11). Not having to remove runners or risers reduces fettling costs, as well as minimizing machining requirements. Casting quality is also much more consistent than is achievable with gravity die casting. Die life is normally at least 50000 castings (Palmer et al. 1981).

 Fig. 2.11

Aluminium alloy wheels, multivalve engine cylinder heads and similar complex-shaped parts are typical of the products made by this process.

(Fred Waters, Fundamentals of Manufacturing for Engineers, p. 27)

3. Tube Drawing (Manufacturing Method):

Previous Definition:

Tube Drawing. The possibility of increasing the film thickness in tube drawing has also attracted attention. In tube sinking, a pressure tube or multiple dies can offer benefits. In drawing on a plug, the critical problem is to increase lubricant supply to the plug/inner-tube interface. Pumping of the lubricant through a hollow plug is feasible, but in itself does not help to build up a lubricant film. For this, a double-plug arrangement, with supply of pressurized lubricant to the enclosed space, is needed. Some improvement in plug drawing is achieved simply by using a suitable plug profile, as reported by Rees.

(Handbook Of Workability And Process Design, George Ellwood Dieter, Howard A. Kuhn,page286)

New Definition (Better):

Tube drawing is also similar to thin rod and wire drawing, with the exception that a fixed or fully floating central plug is used to produce the required central hole (Fig. 3.22).

Tube is generally produced from a hot-extruded annular-shaped billet. This is then drawn down to the required size and shape (not all tubes are circular) in a number of stages, with interstage annealing when required. Much of the tubing produced is made from copper and its alloys, with external diameters from 400 mm down to 0.5 mm being common.

Small-diameter tubing, like wire, also presents a mechanical handling problem. Although this difficulty is again solved by the use of drum storage, extra care must be taken to ensure that the finished product is not too tightly coiled to avoid the central hole being deformed.

Larger diameters are produced in relatively long lengths and then cut into more manageable lengths of approximately 10 m.

The cold drawing process is particularly attractive to tubing producers as it offers exceptional surface finish as well as consistent accuracy of wall thickness, bore and outside diameter. It is also possible to achieve the required degree of surface hardness and material toughness by suitably adjusting the number of draws used, the degree of reduction made on the final draw and the final heat treatment.

(Fred Waters, Fundamentals of Manufacturing for Engineers, p. 63)

4. Manufacturing Enterprise (Business Process):

There is no previous definition.

New Definition:

An Enterprise Model can define an enterprise in terms of its functions, resources, processes, products, data requirements and constraints. In the manufacturing enterprise, this model defines a unique set of business processes that are performed to design, plan, produce and market the enterprise’s products.

The Manufacturing Enterprise Model is a general description. There may be many unique variations to the model. Some enterprises may not require all functions, while others may require more functions than those described in the generic model. Figure 1 depicts how a Manufacturing Enterprise Model can be presented in a way that is independent of the type of product being manufactured:

(Object Management Group’s Manufacturing Special Interest Group, Manufacturing Enterprise Systems, p. 9)

5. Roll Crushing (Material Recovery):

Previous Definition:

This process is used in material recovery operations to grind brittle materials such as glass and flatten malleable materials such as metal cans and plastic bottles. This allows for subsequent separation by screening. Roll crushers were first employed for the reclamation of materials from incinerator residue and more recently are being used to process source separated recyclables, mainly glass containers and aluminum and steel cans. Once crushed this mixture can be sorted using screens and magnets, the material remaining being aluminum cans.

(McDougall F.R., White P.R., Integrated Solid Waste Management: A Life Cycle Inventory, p.232) 

New Definition (Better):

Roll crushers are used in resource recovery operations for the purpose of crushing brittle materials (such as glass) while merely flattening ductile materials (such as metal cans), hence allowing for subsequent separation by screening. Roll crushers were first employed in materials recovery facilities for the reclamation of metals from incinerator residue and have found use in processing partially source-separated refuse composed of glass containers and aluminum and steel cans.

A variation of the roll crusher is the roll crusher/perforator. Curbside recycling programs typically collect PETE (soda bottles) and HDPE (milk containers) from residents. Even though instructed not to, some residents screw the lids back onto the empty containers. When these containers are baled, they then do not compress and can cause problems with the finished bales. To solve this problem, some processors have placed roll crushers/perforators in front of the baler. Puncturing the container prior to baling eliminates the problem.

Roll crushers work by capturing and forcing the feed through two rollers operating in opposite directions—exactly like the wringers on older washing machines. The first objective of roll crushing is to capture the pieces that are to be crushed. This capture depends on the size and characteristics of the particles and the size, gap, and characteristics of the rollers. To illustrate the importance of this capture, imagine attempting to force a basketball through a clothes wringer. A small rubber ball, on the other hand, could be captured readily and flattened.

The variables involved in the analysis of roll crushing are shown in Figure 5-21.

The diameters of the two rolls are D, while the diameter of the particle to be crushed is d. The normal force between the particle and the rollers is N, and the tangential force is T. If the resultant force R is pointed downward, the particle will be captured and crushed. If it points upward, the particle will ride on the rollers.

(Worrell W. A., Vesilind, P.A., Solid Waste Engineering, p. 192)