Mehmet Özer, 030070050, 4th Week (17.03.2012)

1.Holography (Visual technology)

Previous answer

The term "holography" is a compound of the Greek words "holos=complete" and "graphein=to write". It denotes a procedure for three dimensional recording and displaying of images and information without the use of lenses. Therefore holography opens up completely new possibilities in science, engineering, graphics and arts. Fields of application are interferometric measurements techniques, image processing, holographic optical elements and memories as well as part holograms. Holography uses the properties interference and diffraction of light which make it possible to reconstruct the object wave completely. To be able to see these effects coherent laser light has to be used. "Coherence" means that the light wave is constant and contiguous.

(G. Ackermann,J. Eichler, Holography: a practical approach, p.4-5)

New answer (better)

Holography is a type of ‘lensless’ photography invented by Denis Gabor in the UK in 1948. It is a process based upon the phenomenon of light interference, allowing both the amplitude and the phase of the propagating waves to be recorded (hence the name holography: ‘recording of the whole’). By this means, true three-dimensional images can be shown; it is possible for an observer literally to walk around the image, seeing it as it would be in reality.

Holography remained an interesting, but impractical invention until powerful sources of monochromatic, coherent (meaning that the waves are all in step) radiation were developed. Einstein had postulated the possibility of stimulated emission of radiation in 1917, but it was not until the 1950s that this idea was embodied in a practical device. Fabrikant in the USSR filed for a patent in 1951, but failed in his efforts to use caesium for optical amplification.

Holography and the laser exhibit very well the dual nature of light:holography can only be understood by considering light as waves, but lasersare best conceived in terms of light as tiny energy packets—photons. Becauseholography is a means of recording wave phenomena, not only images madeby light may be so captured, but waves from other parts of the electromagneticspectrum—particularly microwaves; as well as those generated mechanically (byvibration) —particularly water and sound waves.

(McNeil, I.,An Encyclopaedia of the  History of Technology, pp.737-738)

2.Hemming(Forming)

Previous answer

Hemming involves bending the edge of the sheet over on itself, in more than one bending step. This is often done to eliminate the sharp edge on the piece, to increase stiffness, and to improve appearance. Seaming is a related operation in which two sheet-metal edges are assemble.

(Groover, M.P., Fundamentals of modern manufacturing: materials, processes, and systems,4th Edition, pg. 454)

New answer (better)

Hemming is the bending of a sheet edge back 180 degrees on itself to provide a rounded edge or reinforcement. The bend can be produced by roll forming, or by two bending operations, or in one operation with a cam-operated or compound die. Seaming is the joining of two opposite edges of a workpiece with interlocking hems or other interlocking bends. It is frequently used in the manufacture of containers such as pails, drums, and cans. Special machines are often used for the operation, particularly in high production applications. Fig. 2D10 illustrates both hems and seams.

(Bralla, J. G., Handbook Manufacturing Processes, How Products, Components and Materials Are Madepp.56-57)

3.Process Monitoring (Analyzing)

Previous answer

Computer process monitoring system involves a computer which is directly connected ith the manufacturing process for the purpose of collecting the data on the process and the equipment.

The hardware components of the computer process monitoring system used to input the data from the process are sensors and transducers, analog-to-digital converters, limit switches and photo detectors, pulse generators etc.

A data acquisition system is a computer system used to collect the data from a process or piece of equipment. These perform an analysis of data or transmit the data to another computer for processing and analysis. A microprocessor is used as the controller/processor in a DAS. Other controllers use minicomputers or single board computers. The function of the controller/processor is to synchronize the data sampling and storage and tabulate data for presentation and statistical and other analysis.

( CAD/CAM/CIM, P. Radhakrishnan S. Subramanian V. Raju,p652)

New answer (better)

Computer process monitoring is one of the ways in which the computer can be interfaced with a process. Computer process monitoring involves the use of the computer to observe the process and associated equipment and to collect and record data from the operation The computer is not used to directly control the process. Control remains in the hands of humans who use the data to guide them in managing and operating the process The data collected by the computer in computer process monitoring can generally be classified into three categories:

1. Process data. These are measured values of input parameters and output variable, that indicate process performance, When the values are found to indicate a problem, the human operator takes corrective action.

2. Equipment data. These data indicate the status of the equipment in the work cell. Functions served by the data include monitoring machine utilization, scheduling tool changes, avoiding machine breakdowns. diagnosing equipment malfunctions, and planning preventive maintenance

3. Product data. Government regulations require certain manufacturing industries to collect and preserve production data on their products, The pharmaceutical and medical supply industries are prime examples. Computer monitoring is the most convenient, means of satisfying these regulations. A firm may also want 10 collect product data for its own use.

Collecting data from factory operations can be accomplished by any of several means Shop data can be entered by workers through manual terminals located throughout the plant or can be collected automatically by means of limit switches, sensor systems, bar code readers, or other devices.

(Groover, M. P., Automation,Production Systems and CIM, pp.96-97)

4.Porosity(Material property)

Previous answer

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)

New answer (better)

Porosity represents an alternative way of considering the packing characteristics of a powder. Porosity is defined as the ratio of the volume of the pores (empty spaces) in the powder to the bulk volume. In principle Porosity + Packing factor  =  1

The issue is complicated by the possible existence of closed pores in some of the particles. If these internal pore volumes are included in the above porosity, then the equation is exact.

Porosity is a unique and inherent characteristic of powder metallurgy technology. It can be exploited to create special products by filling the available pore space with oils, polymers, or metals that have lower melting temperatures than the base powder metal.

(Groover M.P., Fundamentals of Modern Manufacturing: Materials, Processes, and Systems 3rd Edition, pp. 357,357)

(Singh, R., Introduction to Basic Manufacturing Processes and Workshop Technology, pp. 266)

Most ceramic objects are made from powder by pressing and sintering, so most contain some porosity. Porosity is desired in materials used for insulation and filters, but for most applications, porosity is undesirable because it adversely affects the mechanical properties. The elastic modulus decreases with porosity. This is shown in Figure 19.5 for the case of alumina. It can be seen that 10% porosity causes a decrease of the modulus by about 20%. The effects of porosity on strength and on creep rate at elevated temperatures are even more pronounced, as illustrated in Figures 19.6 and 19.7. The solid line in Figure 19.6 is the prediction of the equation

σ = σoexp(−bP)

where P is the volume fraction porosity and the constant, b, is about 7. Fracture toughness also falls precipitously with porosity.

(Hosford, W. F.,Mechanical Behavior of Materials, pp329-330)

5.Integrated Circuits (IC)(Electronics)

Previous answer

An integrated circuit (IC) is a collection of electronic devices such as transistors, diodes, and resistors that have been fabricated and electrically intraconnected onto a small flat chip of semiconductor material. The IC was invented in 1989 and has been the subject of continual development ever since (Historical Note 35.1). Silicon (Si) is the most widely used semiconductor material for ICs, due to its combination of properties and low cost.

(Groover M.P., Fundamentals of Modern Manufacturing: Materials, Processes, and Systems 3rd Edition, page 798)

New answer (better)

Integrated circuits are electronic circuits in micro- miniature size, existing on a single piece of silicon, germanium, gallium arsenide, or inert material (glass or ceramic) containing up to tens of millions of transistors and other devices (diodes, resistors, capacitors). These devices are formed in the semiconductor substrate, or as part of film layers  added to it. Twenty or more layers of circuitry may be involved and the devices are all permanently interconnected. Circuit elements and devices on each chip are extremely small and wiring paths are as narrow as 5 millionths of an inch (0.13 microns), or less. (Process and design improvements are continually being made. The Semiconductor Industry Association has projected circuit dimensions of 0.05 microns, 50 nanometers, or 2 millionths of an inch by 2012.)12 ICs are produced in mass-production quantities with extensive, highly sophisticated, extremely precise and extremely clean manufacturing processes, often involving 600 or more steps before each chip is completed. Chips vary in size but a common surface area is 0.24 sq. in (1.5 sq cm).

Integrated circuits are the brains of computers and-other electronic devices including televisions, radios, stereo equipment, cellular and regular phones, instruments, control devices, military navigation equipment and firearms, aircraft, spacecraft, missiles, medical devices, digital watches, automotive diagnostic devices, traffic control, environmental monitoring, industrial process controls, video games and appliance controls.

(Bralla, J. G., Handbook Manufacturing Processes, How Products, Components and Materials Are Made, p. 551)