Elif TEMİZ - 030070195 - 1st week Answers

1-Artificial Neural Networks (Previous)

Although computers are much faster than the human brain at sequintal tasks, humans are much better at pattern-based tasks that can be performed with parallel processing, such as recognizing features ( in faces and voices, even under noisy conditions ), assesing situations quickly, and adjusting to new and dynamic conditions. These advantages also are due partly to the ability humans to use several senses ( sight, hearing, taste and touch ) simultaneously and in real time. The branch of AI called artificial neural networks attempts to gain some of these capabilites through computer imitation of way data is processed by human brains.

(Kalpakjian S., Schmid S.R.,Manufacturing Engineering and Technology, 5th Edition, pg.1233)

Artificial Neural Network (New)  (Information Technology)  (Better)

Artificial Neural Network is a system loosely modeled on the human brain. The field goes by many names, such as connectionism, parallel distributed processing, neuro-computing, natural intelligent systems, machine learning algorithms, and artificial neural networks. It is an attempt to simulate within specialized hardware or sophisticated software, the multiple layers of simple processing elements called neurons. Each neuron is linked to certain of its neighbors with varying coefficients of connectivity that represent the strengths of these connections. Learning is accomplished by adjusting these strengths to cause the overall network to output appropriate results.

(Daniel Klerfors, Artificial Neural Networks,pg.2-3)

2-Shielded Metal Arc Welding  (Previous)

Shielded Metal Arc Welding process is a process in which the heat for joining is obtained from an electric arc between a covered metal electrode and the workpiece. The groove is filled by the melting of the electrode core. The molten weld pool is protected from the atmosphere by the gases formed from decomposition of the electrode covering. The molten weld metal is cleaned by the scavenging action of the molten flux. Some of the more common names for SMAW are "stick" welding and "arc" welding.

(Shielded Metal Arc Welding, P E William L Ballis, pg. 23-24)

Shielded Metal Arc Welding (SMAW)  (New) (Manufacturing Method) (Better)

SMAW is an arc welding (AW) process that uses a consumable electrode consisting of a filler metal rod coated with chemicals that provide flux and shielding.. The welding stick ( SMAW is sometimes called stick welding) is typically 225-450 mm (9-18 in) long and 2.5-9.5 mm (3/32- 3/8 in) in diameter. The filler metal used in the rod must be compatible with the metal to be welded, the composition usually being very close to that of the base metal. The coating consists of powdered cellulose (i.e., cotton and wood powders) mixed with oxides, carbonates, and other ingredients, held together by a silicate binder. Metal powders are also sometimes included in the coating to increase the amount of filler metal and to add alloying elements. The heat of the welding process melts the coating to provide a protective atmosphere and slag for the welding operation. It also helps to stabilize the arc and regulate the rate at which the electrode melts.

During operation the bare metal end of the welding stick (opposite the welding tip) is clamped in an electrode holder that is connected to the power source. The holder has an insulated handle so that it can be held and manipulated by a human welder. Currents typically used in SMAW range between 30 and 300 A at voltages from 15 to 45 V. Selection of the proper power parameters depends on the metals being welded, electrode type and length, and depth of the weld penetration required. Power supply, connecting cables, and electrode holder can be bought for a few thousand dollars.

Shielded metal arc welding is usually performed manually. Common applications include construction, pipelines, machinery structures, shipbuilding, fabrication job shops and repair work. It is preferred over oxyfuel welding for thicker section—above 5 mm (3/16 in)—because higly versatile and probably the most widely used of the AW processes. Base metals include steels, stainless steels, cast irons, and certain nonferrous alloys. It is not used or seldom used for aluminum and its alloys, copper alloys, and titanium.

A disadvantage of shielded metal arc welding as  production operation is the use of the consumable electrode stick. As the sticks are used up, they must periodically be changed. This reduces the arc time with this welding process. Another limitation is the current level that can be used. Because the electrode length varies during levels must be maintained within a safe range or the coating will overheat and melt prematurely when starting a new welding stick. Some of the other AW processes overcome the limitations of welding stick length in SMAW by using a continuously fed wire electrode.

 (Mikell P. Groover, Fundamentals of Modern Manufacturing: Materials, Processes, and Systems, 3rd Edition, pg.709-710)





3-Gas Metal Arc Welding(Previous)

Gas Metal Arc Welding is an arc welding process that uses an arc between a consumable electrode and the welding pool with a shielding from externally supplied gas without any application of pressure. In Europe GMAW is also called metal inert gas (MIG) and metal active gas (MAG). GMAW is used for welding the aluminium under Ar gas for shielding the metal. 
(Modeling, Sensing and Control of Gas Metal Arc Welding, Desineni S. Naidu,Selahattin Ozcelik,Kevin L. Moore, pg.2)



Gas Metal Arc Welding (GMAW) (New) (Manufacturing Method) (Better)

GMAW is an AW process in which the electrode is a consumable bare metal wire, and shielding is accomplished by flooding the arc with a gas. The bare wire is fed continuously and automatically from a spool through the welding gun, as illustrated in figure 30.4. Wire diameters ranging from 0.8 to 6.5 mm ( 1/32- ¼ in) are used in GMAW , the size depending on the thickness of the parts being joined and the desired deposition rate. Gases used for shielding include inert gases such as argon and helium, and active gases such as carbon dioxide. Selection of gases ( and mixture of gases) depends on the metal being welded, as well as other factors. Inert gases are used for welding aluminium alloys and stainless steels, while CO₂ is commonly used for welding low and medium carbon steels.The combination of bare electrode wire and shielding gases eliminates the slag covering on the weld bead and thus precludes the need for manual grinding and cleaning of the slag. The GMAW process is therefore ideal for making multiple welding passes on the same joint.

The various metals on which GMAW is used and the variations of the process itself have given rise to a variety of names for gas metal arc welding. When the process was first introduced in the late 1940s, it was applied to the welding of aluminium using inert gas (argon) for arc shielding. The name applied to this process was MIG welding (for metal inert gas welding). When the same welding process was applied to steel, it was found that inert gases were expensive and CO₂ was used as a suitable. Hence the term CO₂ welding was applied. Refinements in GMAW for steel welding have led to the use of gas mixtures, including CO₂
and argon, and even oxygen and argon.

(Mikell P. Groover, Fundamentals of Modern Manufacturing: Materials, Processes, and Systems, 3rd Edition, pg.710-711)


4- Green Sand Molding (Previous) (Better)

Green-Sand molding utilizes a mold made of compressed or compacted moist sand. The sand is called "green" because of the moisture present. The mold is not baked or dryed. The mold materials consist of silica sand mixed with a suitable bonding agent(moist clay). To produce the mold, a metal or wood frame is placed over the pattern to produce a cavity representing one half of the casting. Compaction or ramming of the sand is achieved by either jolting or squezzing the mold. The opposite half of the mold is made by same manner. The two flacks are positioned to form the complete mold.
(Rapid Tooling Guideline for Sand Casting, Wanlong Wang,Henry W. Stoll,James G. Conley, p.g. 4-5)

Green Sand Molding (New) ( Manufacturing Process)

In green sand molding, a mold is produced with an aggregate consisting of refractory material and a binder. The basic ingredients are silica sand, the aggregate, and a refractory clay as the binder. Two types of green sand are commonly used: natural, bonded molding sand and so-called synthetic sand.

Natural bonded sand is a mixture of sand and clay, ingredients found in Nature, mined and sold to foundries by foundry suppliers. They are graded according to their best application. It is common to find several grades in one mine or digging. A much-used natural bonded molding is called Albany sand—from Albany, New York. It is strip mined in seven grades from No.00 for very small iron, brass, and aluminium castings, to a No.3 for heavy castings.

(C.W. Ammen, Metalcasting, pg.32)

5-Investment Casting (19.04.2011-15.00) ( Previous) (the Best )

Investment casting is actually a very old process-used in ancient China and Egypt are more recently performed by dentists and jewelers for a number of years. It was not the end of World War 11, however, that it attained a significant degree of industrial importance. Products such as rocket components and jet engine turbine blades required the fabrication of high-precision complex shapes from high-melting-point metals that are easily machined. Investment casting offers almost unlimited freedom in both the complexity of shapes and the types of materials that can be cast, and millions of investment castings are now produced each year.

Investment casting uses the same type of molding aggregate as the ceramic molding process and typically involves the following sequential steps:

1. Produce a master pattern-a modified replica of the desired product made from metal wood, plastic, or some other easily worked material.

2. From the master pattern, produce a master die. This can he made from low-melting point metal, steel, or possibly even wood. If a low-melting-point metal is used, the die may be cast directly from the master pattern. Rubber molds can also be made directly from the master pattern. Steel dies are often machined directly. eliminating need for step 1.

3. Produce wax patterns. Patterns are made by pouring molten wax into the master or injecting it under pressure (injection molding), and allowing it to harden. Release agents, such as silicone sprays, are used to assist in pattern removal. Plastic and frozen mercury are alternate pattern materials. The polystyrene plastic may be preferred for producing thin and complex surfaces, where its higher strength and greater durability are desired. Frozen mercury is seldom used because of its cost. handling problems, and toxicity. If cores are required, they can generally be made from soluble wax or ceramic. The soluble wax cores are dissolved out of the patterns prior to further processing, while the ceramic cores remain and are not removed until after solidification of the metal casting.

4. Assemble the wax patterns onto a common wax sprue. Using heated tools and melted wax, a number of wax patterns can be attached to a central sprue and runner system to create a pattern cluster, or a tree. If the product is sufficiently complex that its pattern could not be withdrawn from a single master die, the pattern may be made in pieces and assembled prior to attachment.

5. Coal the cluster or tree with a thin layer of investment material. This step is usually accomplished

by dipping into a watery slurry of finely ground refractory material. A thin but very smooth layer of investment material is deposited onto the wax pattern, ensuring a smooth surface and good detail in the final product.

6. Form additional investment around the coated cluster. After the initial layer has dried, the cluster can be redipped, but this time the wet ceramic is coated with a layer of sand or coarse refractory, a process called stuccoing. After drying, the process is repeated until the investment coating has the desired thickness (typically 5 to 15 mm or 4 to 5 . g inch with up to eight layers). As an alternative, the single-dipped cluster can be placed upside down in a flask and liquid investment material poured around it. The flask is then vibrated to remove entrapped air and ensure that the investment material now surrounds all surfaces of the cluster.

7. Allow the investment to fully harden.

8. Remove the wax pattern from the mold by melting or dissolving. Molds or trees are generally placed upside down in an oven where the wax can melt and run out, and any residue subsequently vaporizes. This step is the most distinctive feature of the process because it enables a complex pattern to be removed from a single-piece mold. Extremely complex shapes can be readily cast. (Note: In the early years of the process, only small parts were cast, and when the molds were placed in the oven, the molten wax was absorbed into the porous investment. Because the wax "disappeared," the process was called the lost-wax process, and the name is still used.)

9. Heat the mold in preparation for pouring. Heating to 550" to 1100°C (1000" to 2000°F) ensures complete removal of the mold wax, cures the mold to give added strength, and allows the molten metal to retain its heat and flow more readily into all of the thin sections and details. Mold heating also gives better dimensional control because the mold and the metal can shrink together during cooling.

10. Pour the molten metal. While gravity pouring is the simplest, other methods may be used to ensure complete filling of the mold. When complex, thin sections are involved, mold filling may be assisted by positive air pressure, evacuation of the air from the mold, or some form of centrifugal process.

11. Remove the solidified casting from the mold. After solidification, techniques such as mechanical chipping or vibration, high-pressure water jet, or sand blasting are used to break the mold and remove the mold material from the metal casting.


(MATERIALS AND PROCESSES IN MANUFACTURING 10th edition, J. Temple Black, Ernest Paul DeGarmo, Ronald A. Kohser, p.304)

Investment casting(Previous)

 In investment casting, the ceramic slurry of a metarial such as colloidal silica ( consisting of nano-sized ceramic particles) coats a wax pattern. After the ceramic hardens(i.e., the colloidal silica dispesion gels), the wax is melted and drained from the ceramic shell, leaving behind a cavity taht is filled with molten metal. The investment casting process, also known as the lost wax process, is best suited for generating most complex shapes. Dentist and jewelers orginally used the precision investment casting process. Currently, this process is used to produce such components as turbine blades, titaniun heads of golf clubs, and parts for kneel and hip prosthesis. In another process known as the lost foam process, polystyrene beads, similar to those used to make coffee cups or packaging materials, are used to produce a foam pattern. ( Essential of materials science and engineering - Donald R. Askeland, Pradeep P. Fulay - page 274 )

Investment Casting (New) (Manufacturing Method)

Precision casting, such as that used to make jewellery and small model parts, was first developed to cast precision dental parts. Other industries recognized the usefulness and climbed right on the wagon, so the process is very popular now.

There are fixed essential steps to precision investment casting:

1.      Make the wax pattern—this is expendable before casting, or “lost.”

2.      Case or invest the pattern in a refractory material that can stand high heat and reproduce every detail in the pattern as the mold forms.

3.      Burn out the pattern, leaving a negative mold inside the investment material.

4.      Cast by filling the mold with metal.

5.      Destroy the mold to recover the casting.

It sounds easy, and in most aspects, it is easy, but there are details to be considered that make for a more, or less, perfect job.

Making the Pattern

This step is the most involved and difficult, because the whole idea is to make a complex pattern that reproduces perfectly in reverse ( negative) in the investment material. There are a number of kinds of waxes, some for carving and some for molding, each with different features. The only way to decide on a wax for a particular job is to experiment to see which does best in your hands. Blended waxes include waxes like beeswax (usually  white), carnuba, ozenite, and synthetic waxes; resins like shellac, rosin, balsam, and other tree saps; and fillers like talc, starch, chalk, pumice, wood flour ( fine sawdust), and others.

You need to make or buy a wax that lets you work it as you wish, whether you’re carving or molding by hand, or combining the procedures. Carving waxes are readily available in tubes, rods, blocks, and sheets as thick or as thin as you need. Hardness is variable, but most carving wax is not easily bent or finger-shaped. Modeling wax is softer and is easily formed by hand.

Melting wax is a simple process, but needs care, because liquid and near liquid waxes may reach a flash point and catch fire explosively. Melting wax should be done in double-boiler arrangement, never in a single pan. This prevents really bad overheating (as long as you keep water in the lower pan). Speaking of water,  whenever you’re heating wax, keep a pan of cool or cold water nearby. A fast douse with the water can reduce burning considerably, should some hot wax splash on you.

Keep melted wax away from open flames (although an open flame can be used to melt wax enough to weld blocks together).Never set a solid pot of wax on a burner. Wax expands as it heats, and the cap, or top, will heat and melt last, creating a pressure build-up that can be dangerous.

Processes and tools used to work the wax depend on the size and shape of the mold needed: if you’re working gold or silver, it’s unlikely massive molds will be made, but for fine brass or other castings, larger molds may be needed. It’s beyond the province of this book to provide lots of model-making information. You will do lots of filling with coarse-toothed files, and eventually will find you need to make many of your own shaping tools, but that process itself becomes a lot of fun, once you decide what you need to do and how best to modify a tool to do a better job.

Carving wax may also be shaped on a lathe, with a soldering iron, or with wood carving tools. Smoothing is done with fine files, or even a nylon stocking or piece of paper towel. Don’t use materials like sandpaper or steel wool ( no matter how fine) that can leave grit or debris stuck in the wax.

Special wax pens are available for various kinds of shaping uses,  which saves the overheating problem common with soldering irons or wood burning tools. If you’ve already got a soldering iron or wood burning tool on hand, then you can mount a dimmer switch ( potentiometer) into a small box, run a cord to plug, and place the potentiometer in the circuit between the plug and an outlet on your box. Mark the dial around the potentiometer so you can judge heating levels.

(C.W. Ammen, Metalcasting, pg.114-115)