Fatih GÜNDÜZ 030060144 6th week Answers

Shaped tube electrolytic machining (STEM): (Previous)

A second process, known as the shaped-tube electrolytic machining (STEM) process, was also created in response to unique challenges presented in the jet engine industry. Like the electrostream process, STEM is also capable of gang drilling small holes in difficult-to-machine materials However, the STEM process is generally not capable of drilling holes smaller than about 0.02 in. STEM is capable of making shaped holes with aspect ratios as high as 300:l. Holes up to 24 in. m depth have been drilled. Like the electrostream process, it uses an acidic electrolyte to minimize clogging due to sludge buildup. The major differences between the STEM process and the electrostream process are the reduced voltage levels (5 to 10 V dc) and the special electrodes, which are long, straight, metallic tubes coated with an insulator. The insulator helps to eliminate taper by constraining the electrolytic action between the bottom of the tool and the workpiece. Titanium is often used for its ability to resist acids. The electrolyte is pressure-fed through the tube and returns through the gap (0.001 to 0.002 m.) between the insulated tube wall and the hole wall. Electrolyte concentrations may include up to 10% sulfuric acid. Lower concentrations may be used to increase tool life.

(MATERIALS AND PROCESSES IN MANUFACTURING 10th edition, J. Temple Black, Ernest Paul DeGarmo, Ronald A. Kohser, p.507)

Shaped tube electrolytic machining (STEM): (New)(Better)(Machining)

Shaped tube electrolytic machining (STEM) is a specialized ECM technique for drilling small, deep holes by using acid electrolytes (Fig.48). Acid is used so that the disaaloved metal will go into the solution rather than form a sludge, as is the case with the salt-type electrolytes of ECM. The electrode is a carefully straightened acid resistant metal tube. The tube is coated with a film of enamel-type insulation. The acid is pressure-fed through the tube and returns via a narrow gap between the tube insulation and the hole wall. The electrode is fed into the workspiece at a rate exactly equal to the rate at which the workpiece EDM is suitable for cutting materials regardless of their hardness or toughness. Round or irregular-shape holes 0.002 in. diameter can be produced with L/D ratio 20:1. Narrow slots as small as 0.002-0.010 in. wide are cut by EDM.
(Handbook of materials selection, Myer Kutz, p.917)

Electrochemical Corrosion: (Previous)

Electrochemical Corrosion is understood to include all corrosion processes that can be influenced electrically. Corrosion in general is the chemical reaction between the metal and the surrounding environment. Electrochemical corrosion occurs in corrosive environments depending on the galvanic series. There are several types of electrochemical corrosion such as uniform corrosion, galvanic corrosion, hydrogen induced cracking etc. these can be present either one at a time or both in one case.

(Baeckmann, W, Handbook of cathodic corrosion protection, p.29) 

Electrochemical Corrosion (New)(Better)(Corrosion Type)
Electrochemical corrosion in metals in a natural enviroment, whether atmosphere, in water, or underground, is coused by a flow of electricity from one metal to another, or from one part of a metal surface to another part of the same surface where conditions permit the flow of electricity.
For the flow of energy to take place, either a moist conductor or an electrolyte must be present. An electrolyte is an electricity-conducting solution containing ions, which are atomic particles or radicals bearing an electrical charge. Charged ions are present in solutions of acids, alcalis, and salt. The presence of an electrolyte is necessary for corrosion to occur. Water, especially salt water, is an excelent electrolyte. 
( Surface engineering for corrosion and wear resistance, Joseph R. Davis, p.12)

 

 

Addition Polymerization: (Previous) 
Addition polymerization is the polymerization of the monomers by a chain mechanism involving active sites on the growing chain. Addition polymerization is frequently accomplished with unsaturated monomers, it is also called vinl polymerization when the unsaturated monomer contains the group -CH2=CH2-
(Charles A. Harper, Edward M. Petrie, Plastics materials and processes: a concise encyclopedia page 13)


Addition Polymerization: (New)(Better)(Synthetic Materials)
Polyethylene is the simplest polymer. It forms by making carcon-carbon bond between adjacent molecules of gaseous ethylene (C2H4). Polymerization is initiated by oxygen at high temperature and pressure, by spported metal catalysts, or by titanium-based catalysts in solution. Recall that such as a species is a free radical. The free radikal can add to the double bond of another ethylene molecule to form a new carbon carbon bond and generate an unpaired electron on the end of the  growing chain. Because of the polymer forms by adding ethylene molecules to the growing chain, the process is termed addition polymerization.
(Braving the elements, Harry B. Gray,John Douglas Simon,William C. Trogler, p.226)




 


Poly-Ond: a new technology for plating metal (Previous)
Poly-Ond, a proprietary formulation developed in 1976, is a liquid bath process which chemically deposits nickel phosphorus, impregnated with polymers, on the surface of metal parts. This process permits the use of less expensive metals when anticorrosive materials are called for. 
(Modern Manufacturing Processes, Brown, p.44)

Poly-Ond: (New)(Better)(Plating Metal)
Poly-Ond plating is basically an electroless nickel plating impregnated with a flouropolymer. This yields a öoderately hard, corrosion-resistant layer with a low coeficcient of friction. The low coeficient of friction makes it attractive to use in injection molds and on extruder screws. Luker from Killion Extruders reported [35] on tests with Poly-Ond plated extruder screws. He reported output increases from 5 to 36% for a number of different polymers.
(Polymer extrusion, Chris Rauwendaal, p.659) 


Metallizing: (Previous)
Plastics are nonconductors of electricity, which allows them to be used in many unique applications, such as electronic devices, protective housings, and advanced military systems (stealth vehicles). There are many applications that demand plastic materials to be electrically conductive or highly reflective. Compact discs, automotive lightning systems, and chrome-like decorative surfaces for auto and truck grills have unique demands for plastic materials, and all of these applications require a metal layer to be somehow applied to the surface of the plastic. The use of metallizing is categorized as follows:

• Functional: Used to reflect or conduct energy, such as light or electricity, in electromagnetic interference (EMI) reduction and radio frequency interference (RFI) reduction
• Decorative: Used to create an appearance, such as auto/truck grills
• Both: Provides both a functional and decorative service

Although there are many ways to achieve functional and decorative metallization of plastics and plastic products, the main mathods include hot stamping, printing and coating, vacuum metallizing, electroless plating, and electrolytic plating.
(Edward A. Muccio, Decoration and Assembly of Plastic Parts, p. 161)

Metallizing: (New)(Better)(Coating)

Metallizing is the deposition of an adherent coating of finely divided particles of metal, intermetalics, or metalic oxides upon a base metal. The corrosion protection of aliminum and zinc coating applied to low-carbon steel is considered in this paper. Panels coated with these metals were exposed to urban, industrial and marine enviroments over a nine-year period. Studied were thicknesses of coating, effect of methods of steel preparation, and effect of seal coats. Addequate corrosion protection was afforted in nearly all cases, aliminum providing slightly better protection than zinc.
Metalizing, shown in Fig. 1, is the process of depositting finely divided particles of metal, itermetallics or metallic oxides in a heated, semi-molten condition in order to form an adherent coating. Metal in the form of wire or powder is fed to a 'gun' heated by an oxy-fuel gas or plasma arc, and delivered to the work by high velocity air.
(Finishes for metals: paintability of galvanized steel, corrosion resistance, Building Research Institute, p.35) 

Evrim Berk 030060161 6th Week - Part #2

3-) Film Deposition

Previous One

Thin-film deposition is about phase transition from the vapor phase to solid phase. Atoms condense on a substrate. These adsorbed atoms are subject to desorption and surface diffusion. Some adsorbed atoms bond to each other, reducing the desorption probability. More atoms aggregate and some of the bigger clusters avoid desorption. (Franssila, S., Introduction to Microfabrication, p. 78)

New One

Films are typically the most desirable medium for use in semiconducting devices. The hybrid perovskites are often soluble in common polar solvents and both components generally volatilize at relatively low tepmperatures. In addition, the range of interactions both within and between the organic and inorganic components structure typically strongly favors the formation of the hybrid perovskite crystals or thin films using a number of simple processes, including vacuum thermal evaporation, solution-based techniques such as spin-coating and stamping, and even melt processing. Each of these options provide advantages for selected applications, thereby enabling convenient deposition on a range of substrates, including those envisioned for flexible plastic displays and low-cost electronic devices.

(Gomez-Romero P. Sanchez C., Functional Hybrid Materials, p. 362)

4-) Photochemical Machining

Previous One

The specific steps that are involved when photochemical machining (PCM) is performed with the use of photoresists. These are as follows: 1. Clean the workpiece. 2. Coat the workpiece with a photoresist, usually by hot-roller lamination of dry-film photoresists, on both sides, although liquid photoresists may also be applied by dipping, flowing. rolling, or electrophoresis (i.e., migration of charged molecules in the presence of an electric field). For liquid photoresists, the coating is heated in an oven to remove solvents. 3. Prepare the artwork. A drawing of the workpiece is made on a computer-aided design (CAD) system. 4. Develop the phototool. The CAD file is used to derive a photographic negative workpiece. Several methods may be used. Typically, the CAD drawing is downloaded to a laser-imaging system that exposes the desired Image directly onto photograph (e.g., silver halide) film. In the past, oversized artwork was used to Increase the curacy of the phototool through photographic reduction of the artwork. 5. Expose the photoresist. Bring the phototool in contact with the workpiece, a vacuum frame to ensure good contact, and expose the workpiece to Intense violet (UV) light 6. Develop the photoresist. Exposure of the photoresist to intense UV light alters the chemistry of the photoresist, making it more resistant to dissolution in certain solvents. By placing the exposed maskant in the proper solvent, the unexposed areas of the resist are removed, exposing the underlying material for etching. All residue is rinsed away 7. Spray the workpiece with (or immerse it in) the reagent 8. Remove the remaining maskant. PCM has been widely used for the production of small, complex parts, such as printed circuit boards, and very thin parts that are too small or too thin to be blanked or milled by ordinary sheet metal forming or machining operations, respectively Refinements to the PCM process are used in the microeletronics fabrication.

(MATERIALS AND PROCESSES IN MANUFACTURING 10th edition, J. Temple Black, Ernest Paul DeGarmo, Ronald A. Kohser, p.489)

New One

Photochemical machining, as also known chemical blanking, involves producing parts by chemical action. It is accomplished by placing an exact image of the part to be produced on a sheet of metal and immersing them both in a chemical. The chemical action dissolves all of the metal except the desired part. Most photochemically machined parts are thin and flat.

Photochemical machining has a number of applications where in it provides unique advantages. Some of these include: working on extremely thin materials when handling difficulties and die accuracies preclude the use of normal mechanical methods; working on hardened or brittle materials when mechanical action would cause breakage or stress concentration points. Production of extremely complex parts for which die costs would be prohibitive. And producing short-run parts for which the relatively low setup costs and short time from print to production offer advantages. This is especially important in research and development projects and in model shops.

(Goetsch L.D., Technical Drawing, p. 774)

5-) Proximity Sensors

Previous One

Proximity sensing using optical or acoustic techniques is useful when a robot tool is brought into contact with a workpiece. Since the robot is designed to be very stiff and the workpiece is usually quite rigid, the contact force between them builds very rapidly when the robot contacts the workpiece with finite velocity. Even if force sensing is used, the contact force may build to damaging levels before the system can respond. Proximity sensors are short-range, noncontact sensors which allow fine control of tool velocity shortly before contact to avoid severe impacts. Optical systems based on triangulation or simply the intensity of light reflected off the workpiece have been tested. Ultrasonic rangefinders using a sonar-type principle offer an alternative technology.

(Standard Handbook of Machine Design, Robots and Smart Machines, Kenneth J. Waldron, Ph.D.,p47.20)

New One

Proximity Sensing is the technique of detecting the presence or absence of an object with an electronic noncontact sensor.

Mechanical limit swtiches were the first devices to detect objects in industrial applications. A mechanical arm touching the target object moves a plunger or rotates a shaft which causes an electrical contact to close or open. Subsequent signals will produce other control functions through the connecting system. The stich may be activating a simple control relay or a sophisticated programmable logic control device, or a direct interface to a computer network. This simple activity, once done successfully, will enable variaties of manufacturing operations to direct a combination of production plans according to the computer-integrated-manufacturing strategy.

Inductive proximity sensors are used in place of limit switches for noncontact sensing of metallic objects. Capacitive proximity switches are used on the same basis as inductive proximity sensors; however capacitive sensors can also detect non-metallic objects. Both inductive and capacitive sensors are limit switches with ranges up to 100 mm.

The distinct advantage of photoelectric sensors over inductive or capacitive sensors is their increased range. However dirt, oil mist, and other environmental factors will hinder operation of photoelectric sensors during the vital operation of reporting the status of a manufacturing process. This may lead to significant waste and buildup of false data.

(Soloman S., Sensors Handbook, p1.21)