Halil Kayhan - 7th week, definitions

1.Air Carbon Arc Cutting (previous)
In the air carbon-arc cutting (AAC), the arc is normally obtained between a copper- coated graphite or carbon electrode and the workpiece with the molten metal being forced out by means of compressed air at apressure of 550 to 690 kPa. It may be possible to use a very low pressure of order of 280 kPa in some manuan torches for field application but is not generally recommended. The air consumption is in the range of 85 to 1400 L/min depending on the thickness of the metal being cut. The copper coating is used to reduce the oxidation of the electrodes and to help cool the electrode.

(Rao P. N., Manufacturing Tehcnology Vol. I, 2009, p. 394-395)

Air Carbon Arc Cutting (new) (Welding)

The air carbon arc cutting process was developed in the early 1940s and was originally named air arc cutting (ACC). Air carbon arc cutting wan an improvement of the carbon arc process,which was used in the vertical and overhead positions and removed metal by melting a large enough spot that gravity would cause it to drip off the base plate, Figure8.11. This process was slow and could not be accurately controlled. It was found that the molten metal could be blown away using a stream air. This greatly improved the speed, quality, and control of the process.
In the late 1940s the first air carbon arc cutting torch was developed. Before this development, the  process required two welders, one to control the carbon arc and the other to guide the air stream. The new torch housed the carbon electrode holder and the air stream in the same unit.The basic design is still in use today. Figure 8.12.

(Jeffus L., Bower L., Welding Skills, Processes and Practices for Entry-Level Welders, p. 257)

The new one is better.

2. Melt Infiltration:(Previous)
The melt infiltration method involves holding a porous body of the reinforcing phase in a mold and infiltrating it with the molten metallic material, which flows through the interstices to fill the pores, thus producing a composite material. This method can be divided into two categories:

-pressure-assisted infiltration
-pressure-less infiltrration

For pressure-assisted infiltration, either an inert gas or a mechanical device is used as the pressurizing medium. The composite produced using this method generally features a near pore-free matrix. There are also some drawbacks associated with this method:

-Reinforcement preform damage or breakage during infiltration
-Microstructural heterogenecity

In view of these disadvantages, other types of forces such as ultrasonic vibration, electromagnetic force and centrifugal force are used to more effectively force the molen metal into nonwetting reinforcement preforms.

In pressure-less infiltration, the liquid metal infiltrates a porous reinforcement preform without an external pressure or vacuum. This process is also known as spontaneous infiltration. In comparison with the pressure-assisted infiltration method, the composites formed exhibit a higher level of porosity.
(Manoj Gupta, Nai Mui Ling Sharon, Magnesium, Magnesium Alloys and Magnesium Composites, pg:20-21 )

Melt Infiltration:(New)(Manufacturing type)

Handling ceramics at their melting temperatures poses various difficulties and disadvantages. Nevertheless, some systems have been studied to analyze the potential advantages of composite processing via the melt infiltration process. In this process, porous fibers or powder preforms are brought into contact with a molten matrix phase. If the matrix phase wets the preform, surface tension can be sufficient as a driving force to fill the voids. Particulate additions can be used in a fiber preform to increase this driving force. Pressure can be used to improve the infiltration process, such as glass transfer molding, where a porous preform is filled by molten glass in a die cavity.

In one study, B4C+C preforms were infiltrated with molten Si to obtain B4C+SiC composites. Hilling et al. studied the production of Si/SiC CaF2/SiC, SrSiO3/SiC, and SrAl2Si2O8/SiC composites by the melt infiltration process. Their studies indicated that the fibers have to sustain temperatures in excess of 1400 C in these systems and they must resist degradation during processing. The infiltration time and behaviour depend on factors such as the pore size of the preform, the viscocity of the melt, and the wetting characterictics of the preform by the melt. For example, it was observed that CaF2 readily infiltrated into both SiC powder and whisker preforms, but not into SiC (Nicalon) fiber preforms.[1]

The process is illustrated at Fig. 7.3. :

[2]

( Murat Bengisu, Engineering Ceramics, page 202)[1]

(Krishan Kumar Chawla, Composite Materials: Science and Engineering, page 217 )[2]

The new one is better.

3. Carbonitriding (previous)
Carbonitriding is one of the case hardening process in which carbon and nitrogen are diffused into
the surface of the component simultaneously at a predetermined temperature followed by
quenching.
The process is carried out in a controlled atmosphere so that both carbon and nitrogen are absorbed
simultaneously by teh heated component. The concentration of hardening elements is more at
the outer surface of the steel and decreases progressively towards the core. The carbonitrided
components may be subsequently heat treated so as to form a hard wear-resistant case of the
type normally obtained by treatment in a cyanide salt bath.
The process is used in the production of shallow cases on carbon and alloy steels. The treatment is
usually done at 850-900 centigrade degree using a carburizing gas with low additions of ammonia.
Ammonia dissociates into hydrogen and nitrogen, the latter reacting with the surface of the steel
to form nitrides. In addition, however, a small amount of nitrogen goes into solution increasing the
hardenability to some extent. The subsequent quenching ensures the final full skin hardness.
Carbonitriding results in a higher hardenability of the surface layer as compared to carburizing
and allows steel with lower content of alloying elements to be used.
The primary object of carbonitriding is to impart a hard case to the steel in order to provide
resistance to metallic and abrassive wear. The process competes with liquid cyaniding, carburizing
and to a lesser extent with nitriding.
( K. H. Prabhudev, Handbook of Heat Treatment of steels, p.386)

Carbonitriding (new) (Surface Hardening)
This process is specially used for improving wear resistance of mild, plain carbon or very low alloy steels. Carbonitriding is carried out at lower temperatures (in the range 800-870 C) in a gas mixture consisting of a carburizing gas and ammonia. A typical gas mixture contains about 15% NH3, 5% CH4, and 80% neutral carrier gas. Carbon and nitrogen are diffused at the same time into the surface of the steel in the austenitic-ferritic condition and gives case thickness of the order of 0.05-0.75 mm. Nitrogen is more effective in increasing hardenability of the case as compared to carbon. Bitrogen content of the steel depends on ammonia content and temperature.

After carbonitriding, quenching is done in oil to avoid cracking. This is followed by tempering at 150-180 C.
Heat treatment produces a case having a hardness of 850 VHN.

In this process, surface hardenability, wear resistance and corrosion resistance are better than in the carbuzing process. But the time required for heat treatment is longer than that for carburizing.

(Rajan T. V., Sharma C.P., Sharma A., Heat Treatment Principles and Techniques, p.137-138)

The new one is better.

4. Superfinishing (previous)

Superfinishing is widely used as a subsequent operation after grinding to reduce surface roughness and increase bearing load capacity. During superfinishing of cylindrical surfaces, an axially oscillating abrasive stone is pressed against a rotating workpiece. The ratio of axial oscillation frequency to workpiece rotational frequency should be selected so as to avoid integer values, which result in low stock removal, and half values, which can lead to lobe formation. Finer grit stones provide smoother surface finishes but less stock removal; therefore, the grit size selected should be only fine enough to generate the required surface roughness.
(i) Correcting inequalities of geometry
(ii) Removing surface fragmention.
(iii) Reducing surface stresses and burns and thus restoring surface integrity

(Rajput R. K., A Textbook of Manufacturing Technology: Manufacturing Processes, p. 552)

Superfinishing (new) (Finishing)

The superfinishing method, alsı called superhoning or shortstroke honing, is a precision finishing process in which a workpiece rotates and an abrasive wheel, which is pressed against the workpiece, simultaneously performs a rapid longitudinal vibration of only few milimetres(Figure 17.1).

The abrasive wheel is similar to the honing stone. Sometimes the wheel or wheels is/are fixed on a tool carrier, which carries out the oscillating motion. The slide on which the tool carrier is based generatesthe feed motion.
The overlapping of the two motion (the rotary motion of the workpiece and the oscillating - and feed motions of the tool) causes the grinding grains to pass over the workpiece surface on always different trajectories that are never the same. This results in particularly high surface qualities.
Due to the short longitudinal motion of the abrasive wheel, which is similar to honing, the method is also called ''shortstroke honing''.
Since the abrasive wheel carries out a vibrational motion (back and forth motion), the technique is also called ''superhoning''.
In lieu of the term ''superfinishing'', the terms ''precision honing'' or ''superfine honing'' are also used. The German equivalent of these terms is derived from honing.
Application Of Superfinishingg
This method is used when, in addition to the best possible surface quality, the structure of the machined workpiece, up to the outermost load-bearing layer, needs to be totally heterogeneous. If the part's microstructure has to fulfil high requirements, then a superfinishing technique is indicated. Requirementts like these occur, for example, in the case of bearing yokes, heavily loaded bearing pins on shafts and heavily loaded anti-friction bearings.

( Heinz Tschätsch, Applied Machining Technology, page 309)
The new one is bettter.


4. Chemical Blanking (previous)
Chemical blanking uses chemical erosion to cut very thin sheet -metal parts- down to 0.025 mm thick and/or for intricate cutting patterns. In both instances, conventional punch-and-die methods do not work because the stamping forces damage the sheet material, or the tooling cost would be prohibitive, or both. Chemical blanking produces parts that are burr free, an advantage over conventional shearing operations. Methods used for applying the maskant in chemical blanking are either the photoresist mothod or the screen resist method. For small and /or intricate cutting patterns and close tolerances, the protoresist method is used; otherwise, the screen resist method is used. The small size of the work in chemical blanking exludes teh cut and peel maskant method.Application of chemical blanking is generally limited to thin materials and/or intricate patterns. Maximum stock thickness is around 0.75 mm. Also, hardened and brittle materials can be processed by chemical blanking where mechanical methods would surely fracture the work. Tolerances as close as +- 0.0025 mm can be held on 0.025 mm thick stock when the photoresist method of masking is used. As stock thickness increases, more generous tolerances must be allowed. Screen resist masking methods are not nearly so accurate as photoresist. Accordingly, whwn close tolerabces on the part are required, the photoresist method should be used to perform the masking step. 

(M. P. Groover, Fundamentals of Modern Manufacturing: Materials, Processes, and Systems, pp.638-640)

Chemical Blanking (new) (Cutting method)

Chemical blanking is used chiefly on thin sheets and foils. Im most applications, photoresist (photosensitive masking) is used to define the location on the workpiece at which the material is to be etched.
       Process Steps for Chemical Blanking
A flow chart showing the principal process steps for chemical blanking by the photoresist method is given in Fig. 14.71 and is described below.
Preparation of workpiece The workpiece is cleaned, degreased and pickled by acid or alkalis. The cleaned metal is dried and photoresist material is applied. It is then dried and cured.
Preparation of Masters Masters, the tools for chemical blanking, consist of the artwork and negatives used to produce the acid resistant image. The artwork for chemical blanking should be made on dimesnsionally stable material such as paper, polyester film or glassbase scribing film. The original artwork usually is made 4 times the actual size of work, but it may range from 2 to 200 times the actual size depending on the equipment , part size and accuracy required. Individual part size can vary from micro dimensions to a maximum of 350x550 mm. This is then reduced photographically and multiple image masters are made.
Masking with photoresists   Photoresists are applied to the workpiece by dipping, whirl coating or spraying. Whirl coating gives an uniform coating. This is then dried at room temperature and baked for about 15 minutes at a temperature of 110 C to remove the residual solvent. Lower temperatures can be used by prolonging the baking time.
Exposure of conventional photoresist to ultraviolet light partly polymerizes the exposed areas of light sensitive resins thus increasing its resistance to organic solvents used as developers. Each side of the workpiece can be exposed individually or the two sides can be exposed at the the same time between a pair of mirror - image masters. A vacuum printing frame with a vacuum of 500 mm of mercury is used for this purpose. Printing frames must be padded correctly or the glass masters will break in the evaluated frame.

This flow chart showing the principal process steps for chemical blanking by the photoresist method.

(Bangalora H.M.T., Production Technology, McGraw-Hill Education, p. 491)

The new one is better.