Monday, May 14, 2012

Ürfet Demirkan 503111315 11. Week Unanswered Words


Multiple-Ram Presses (Forging Equipment)

Hollow, flashless forgings that are suitable for use in the manufacture of valve bodies, hydraulic cylinders, seamless tubes, and a variety of pressure vessels can be produced in a hydraulic press with multiple rams. The rams converge on the workpiece in vertical and horizontal planes, alternately or in combination, and fill the die by displacement of metal outward from a central cavity developed by one or more of the punches. Figure 14 illustrates the multiple-ram principle, with central displacement of metal proceeding from the vertical and horizontal planes.


 


Fig. 14


Examples of multiple-ram forgings. Displacement of metal can take place from vertical, horizontal, and combined vertical and horizontal planes. Dimensions given in inches.


Piercing holes in a forging at an angle to the normal direction of forging force can result in considerable material savings, as well as savings in the machining time required to generate such holes.

In addition to having the forging versatility provided by multiple rams, these presses can be used for forward or reverseextrusion. Elimination of flash at the parting line is a major factor in decreasing stress-corrosion cracking in forging alloys susceptible to this type of failure, and the multidirectional hot working that is characteristic of processing in these presses ecreases the adverse directional effects on mechanical properties.

(ASM Handbook, Volume 1 Properties and Selection Irons, Steels, and High-Performance Alloys, P 43)


Contour Forging (Forging Processes)

Open-die contour or form forging requiring the use of dedicated dies has been successfully accomplished for carbon, alloy, and stainless steels as well as for superalloys. Contour forging can be advantageous under such circumstances as the following:

· Enhancement of grain flow at specific locations, when demanded by product application
· Reduction of the quantity of starting material; this is especially critical when using expensive materials
such as stainless steels and superalloys
· Reduction of machining costs; this is critical when machinability or excessive material removal are
factors

Open-die contour forging may be a requirement, as in the case of grain flow, or it may be an option, as in the case of material and machining cost savings. The material and machining cost savings typically outweighs the forging tooling costs.



(ASM Handbook, Volume 1 Properties and Selection Irons, Steels, and High-Performance Alloys, P 132)






Turbine Wheel Forging  (Forging Processes)




Turbine wheels, which are commonly 2.54 m (100 in.) in diameter, are forged by first upsetting a block of steel and then contour forging to provide the thick hub and thin rim sections This is done using a shaped (contoured) bottom die, which supports the entire workpiece, and a shaped partial top (contoured swing) die. Successive strokes are taken with the top die as it is indexed around the vertical centerline of the press. The partial top die minimizes the force required to deform the metal, yet produces the desired forge envelope.

(ASM Handbook, Volume 1 Properties and Selection Irons, Steels, and High-Performance Alloys, P 132)

Hot Swaging (Forging Processes)
Hot swaging is used for metals that are not ductile enough to be swaged at room temperature or for greater reduction per pass than is possible by cold swaging. The tensile strength of most metals decreases with increasing temperature; the amount of decrease varies widely with-different metals and alloys. The tensile strength of carbon steels at 540 °C (1000 °F) is approximately one-half the room-temperature tensile strength; at 760 °C (1400 °F), about one-fourth the room temperature strength; and at 980 °C (1800 °F), about one-tenth the room-temperature strength. In practice, reductions greater than those indicated in Table 1 are sometimes possible by cold swaging without intentionally heating the work metal, because sufficient heat is generated during swaging to cause a substantial decrease in strength and increase in the ductility of the work metal.

The decrease in strength at elevated temperature does not make possible unlimited reductions at high temperatures. Because of the design and capabilities of swaging machines, the work metal must be strong enough to permit feeding of the workpiece into the machine. When the work metal has lost so much of its strength that it bends rather than feeds in a straight line, chopper dies must be used. This type of die limits the reduction in area to 25% regardless of work metal ductility. The temperature to which a work metal is heated for swaging depends on the material being swaged and on the desired reduction per pass.

(ASM Handbook, Volume 1 Properties and Selection Irons, Steels, and High-Performance Alloys, P 304)


Sunday, May 13, 2012

Melkan Çelik-503041311-10th week insufficient words


Mean Time Between Failure(Quality management term)
There is no previous definition.

MTBF stands for mean operating time between failures (wrongly mentioned as mean time between failures throughout the literature) and is used as a reliability measure for repairable systems. In British Standard (BS 3527) MTBF is defined as follows:
For a stated period in the life of a functional unit, the mean value of the lengths of time between consecutive failures under stated condition.
MTBF is extremely difficult to predict since it depends on several factors such as operating conditions, maintenance and repair effectiveness etc. In fact, it is very rarely predicted with an acceptable accuracy.
Charesteristics of MTBF:
1.      The value of MTBF is equal to mean time to failure (MTTF) if after each repair the system is recovered to as good as new.
2.      MTBF=1/λ for exponential distribution, where λ is the scale parameter (also the hazard function).
Applications of MTBF:
1.      For a repairable system, MTBF is the average time in service between failures. Note that, this does not include the time spent at repair facility by the system.
2.      MTBF is used to predict steady-state availibility measures like inherent and operational availability.
(Dinesh Kumar,U. Dinesh Kumar,  Reliability And Six Sigma, pages 95-98)

Saturday, May 12, 2012

503111312 - Selçuk Keser - 10th WEEK'S UNANSWERED WORD


GAS WARMERS


(OLD DEFINITION)

On occasion, the gas in cylinders is withdrawn so fast that the regulator could ice up because of the change in temperature.İf this occurs, an electrically heated gas warmer is available to be installed in-line, and this warmer would heat the gas out of the cylinder before it reached the regulator.The rule of thumb is to consider a warmer if the use of gas exceeds 35 acfm.The actual figure should be based on experience with the specific type of gas being used.Ask the supplier what his or her experience has been.Carbon dioxide is a particular problem.
Facility piping systems handbook 2nd edition Michael Frnkel p.14.79)



(NEW DEFINITION)


Ruttan's Air Warmer is a double box-stove, which heats by radiation, and also by air which is brought from without, warmed by passing between the inner and outer plates, and delivered into the apartment. The inventor, however, was so intent upon a "system of ventilation" which implied the adaptation of the house to it, that he failed to make his stoves readily available for ordinary use.

(The Popular Science Monthly - Publisher: Bonnier Corporation - "Nov1897-Apr1880", P148)


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Thursday, May 10, 2012

Metin Atmaca 030080007 11th week part 2


3. Acceptance quality level (AQL) (Management):

Previous Definition:

The acceptance quality level (AQL) commonly is defined as the level at which there is a 95% acceptance probability for the lot. This percentage indicates to the manufacturer that 5% of the parts in the lot may be rejected by the consumer (producer's risk). Likewise, the consumer knows that 95% of the parts are acceptable (consumer's risk).

(Kalpakjian S., Schmid S.R., Manufacturing engineering and technology, Ed. 5th, p. 1131)

New Definition (Better):

When an acceptance-sampling plan is designed, management specifies a quality standard commonly referred to as the acceptable quality level (AQL). The AQL reflects the consumer’s willingness to accept lots with a small proportion of defective items. The AQL is the fraction of defective items in a lot that is deemed acceptable. For example, the AQL might be two defective items in a lot of 500, or 0.004. The AQL may be determined by management to be the level that is generally acceptable in the marketplace and will not result in a loss of customers. Or, it may be dictated by an individual customer as the quality level it will accept. In other words, the AQL is negotiated.

The probability of rejecting a production lot that has an acceptable quality level is referred to as the producer’s risk, commonly designated by the Greek symbol α. In statistical jargon, α is the probability of committing a type I error.
There will be instances in which the sample will not accurately reflect the quality of a lot and a lot that does not meet the AQL will pass on to the customer. Although the customer expects to receive some of these lots, there is a limit to the number of defective items the customer will accept. This upper limit is known as the lot tolerance percent defective, or LTPD (LTPD is also generally negotiated between the producer and consumer). The probability of accepting a lot in which the fraction of defective items exceeds the LTPD is referred to as the consumer’s risk, designated by the Greek symbol β. In statistical jargon, β is the probability of committing a type II error.

(Taylor, B.W., Russel, R.S, Operations Management, p.149)



4. Design-for-Manufacturability programs (Manufacturing Program):

There is No Previous Definition.

New Definition:

General-purpose DFM programs include modules for assembly, stamping, and other processes as well as machining. Because desirable machining practices vary depending on the volume of production and the machine tools available, it is difficult to write a widely applicable general-purpose design-for-machining module. Some large companies have proprietary in-house codes used to apply design-for-machining rules in a manner tailored to their business operations.

A DFM program typically has an input module and an analysis module. Data input is not as automated as in CAPP programs; rather than reading required geometric information from a CAD file, part features and dimensions must generally be input manually according to some format and classification scheme. This is partly because DFM programs are intended to be applied at an earlier stage of the design process (when no complete CAD model of the part may be available), and partly because additional subjective information, such as the perceived relative machinability of various materials or the relative penalty associated with given undesirable features, is often required.

Once data are input, the analysis module is used to compute a relative machinability score for the design as entered. The algorithm used to compute the score varies from program to program, but in general the score depends on the complexity of the design and the penalties associated with difficult-to-machine materials or features. In DFM workshops, some rough estimate of the machining cost can also be computed (e.g., using a spreadsheet) for the given design. The output of the program is a detailed breakdown of components of the score due to individual features, which often clearly identifies the feature(s) most responsible for complexity or excessive cost.

Unlike CAPP programs, DFM programs are used for comparison rather than formal optimization. Usually several design alternatives are compared to a benchmark design, and based on the DFM score the best design is chosen and refined. For complex parts, the process may be repeated at various stages of the design (e.g., at an early stage and before fabrication of the first prototype). Design for manufacturability programs can be used for parts manufactured on either CNC or dedicated production equipment. They are well suited for designing complex parts for mass production and are currently more widely used than CAPP programs in these applications.

(ASM Handbook Vol. 20 Materials Selection and Design, p. 1797)

Wednesday, May 9, 2012

Mehmet Can ÇAPAR 030070131 11th week definitions (Bonus Week) Part 2



3-Sctratch Hardness Test (Group:hardness test)

There is no older definition

(new definiton)
     One of the oldest hardness testing methods is the hardness scale according to Mohs, which is based on a series of minerals using the principle: “Who scratches whom?” The scale according to Mohs provided comparison values (see table 1). Thus, the Mohs hardness 5 (apatite) is, for example, harder than the Mohs Hardness 4 (fluorite)
     The advantages of scratch hardness testing is:
-It is an easy-to-handle method.
     Disadvantages include:
-It is appliciable to metallic materials to a limited degree only.
-The differentiation of the hardness values is inadequate for metals.

(Konrad Herrman, Hardness Testing: Principles and Applications, pg:95)




4-Elastoviscoplasticity (material behaviour)
(old definiton)
The elasto viskoplastic rheological model consisits of a slider and a dashpot in parallel and this combination is in series whit a Hookean spring. Fort he uniaxial model the behaviour is purely elastic until the stress exceeds the yield stress . Onece in the plastic region the viscous component becomes active and for raidly applied loads the stress can exceed the pşastic limit. If unloading takes place form the yielded state the strain path followed is different form that of loading and permanent deformation takes place. Elastoviskoplastic behaviour is also loading path dependent since it has been demonstrated by experiments that if two loading paths reach the same point on the yield surface by different routes .

(The Finite element method in heat transfer analysis ; Roland Wynne Lewis ; pg.198 , 1996)

(new definiton) (better)
The deformation of solid materials is usually purelly elastic when the stresses are below a certain critical level, called the yield stres. When the stresses are above this threshold, a combination of elastic and plastic deformation ocur, where the latter type of deformation is recognized by being permanent.

(Hans Petter Langtangen, Computational Partial Differential Equations: Numerical Methods and Diffpack, pg: 522)

Berk Korucu - 030080104 - 11th Week

1) Microhardness Test (Hardness Test)


There is no previous definition.



Current practice in the United States divides hardness testing into two categories: macrohardness and microhardness. Macrohardness refers to testing with applied loads on the indenter of more than 1 kg and covers, for example, the testing of tools, dies, and sheet material in the heavier gages. In microhardness testing, applied loads are 1 kg and below, and material being tested is very thin (down to 0.0125 mm, or 0.0005 in.). Applications include extremely small parts, thin superficially hardened parts, plated surfaces, and individual constituents of materials.


(H. Chandler, Hardness Testing  2nd Edition, p.3)


2) Special Indentation Test (Hardness Test)


There is no previous definition.



Special Indentation Tests: Modifications of this type test have been developed, and a few have had some commercial acceptance. Perhaps the best example is the Monotron test. This instrument used a 0.75 mm (0.03 in.) hemispherical diamond indenter. The Monotron principle was the reverse of the more conventional indentation testers such as the Brinell and Rockwell. Instead of using a prescribed force and measuring the depth or area, the Monotron indenter was forced into the material being tested to a given depth, and the hardness was determined by the force required to achieve this depth of penetration. This instrument was developed primarily for evaluating the true hardness of nitrided cases, which were, at one time, difficult to evaluate
accurately. The Monotron has not been manufactured for many years, and it is doubtful whether any are still in use.


(H. Chandler, Hardness Testing  2nd Edition, p.10)


3) Machining Costs (Accounting)


There is no previous definition.



The total cost of a machining operation includes contributions from some or all of the following components:

· Raw material costs: The cost of unmachined stock, which may be in the form of a standard bar or slab, casting, or forged blank · Labor costs: The wages for the machine operator, usually measured in units of standard hours · Setup costs: The cost of special fixtures or tool setups and the wages paid to setup personnel · Tooling costs: The cost of perishable tooling, including inventory, and any special tooling required for the operation · Equipment costs: The cost of the machine tools, including required capital expenditures, facilities costs, and machine depreciation · Scrap and rework costs: The cost of repairing or disposing of finished or partially finished parts of unacceptable quality · Programming costs: The cost of writing numerical control (NC) programs to generate the required toolpaths · Engineering costs: salaries paid to engineers for process design, validation, and other overhead functions.


(P. Andersen et al. , ASM Handbook vol 20 Materials Selection And Design, p.1771)


4) Early Cost Estimating (Accounting)


There is no previous definition.



The problem of estimating part and tooling costs before the part has been fully detailed is
discussed using machining as an example because this is one of the most common shape-forming processes. Several conventional cost estimating methods for machining are available both in handbook form, such as the Machining Data Handbook (Ref 18) and the AM Cost Estimator (Ref 19) and in software form. However, all of these methods are meant to be applied after the part has been detailed and its production has been planned, and they are not tailored for use by a designer. During the early stages of design, the designer will not wish to specify, for example, all the work-holding devices and tools that might be needed--a detailed design will not yet be available. Indeed, a final decision even on the work material might not have been made.


For early cost estimating an important assumption has to be made. The designer should be able to expect that, when the design is finalized, care will have been taken to avoid unnecessary manufacturing expense at the detail-design stage and that manufacturing will take place under efficient conditions.


To illustrate how such an assumption can help in providing reasonable estimates, consider the effect of the metal-removal rate on grinding costs, as shown in Fig. 6. These cost curves indicate that as the removal rate is increased the cost of grinding-wheel wear increases in proportion. At the same time, the cost of grinding decreases because the grinding cycle
is shortened; in fact, the grinding costs are inversely proportional to the removal rate.


(P. Andersen et al. , ASM Handbook vol 20 Materials Selection And Design, p.1558)

Tuesday, May 8, 2012

Proje Notları

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Serdar Yüksel 030070129 11th week words

1. Delayed Fracture (Hydrogen Embrittlement) (new)   (material properties)


          THERE IS NO OLDER DEFINITION


Internal Hydrogen Embrittlement (IHE)Internal hydrogen embrittlement (IHE) is caused by
hydrogen, contained (pre-existing) in the material, that acts
in combination with extant stress, residual and applied.
When a steel part fractures while sitting in air on a shelf,
with no externally applied stress, this process of timedelayed
fracture is caused by residual stress in a process
that is classically termed internal hydrogen embrittlement
(IHE). This behavior is usually associated with steels of
relatively high strength levels, such as those used in bolts or
landing gears. It is caused by the presence of residual hydrogen
and residual stresses from processing. These "causes"
initiate microcracking that proceeds eventually to rupture.
Applied tensile stresses in combination with residual stresses
from processing can also produce time-delayed fracture or
IHE, as in electrochemically plated tensile bolts. Commercially,
IHE is treated differently than environmental hydrogen
embrittlement (EHE), which includes any gaseous or
aqueous environment that promotes hydrogen charging of
the material. In both processes, the cracking is associated
with diffusion and localization of hydrogen near defects and
microcracks.

Environmental Hydrogen Embrittlement (EHE)
and Stress Corrosion Cracking (SCC)
When cracking occurs in an aqueous solution, a distinction
is made between two forms Environmentally Assisted
Cracking (EAC): stress corrosion cracking (SCC), and Environmental
Hydrogen Embrittlement (EHE). An impressed
cathodic current may often provide protection against SCC,
but steel that is "protected" against corrosion by this means
may be subject to EHE by cathodic hydrogen absorption/
adsorption. For an impressed anodic current, the converse
is true. Although this is a simplistic view of SCC, it is
sometimes useful. Nevertheless, it would be remiss to fail to
note that under anodic polarization, hydrogen production
might still result at a crack tip where its presence can be
most harmful. Bulk anodic polarization does not ensure
that the crack tip is polarized.
Differences and similarities between SCC and EHE are
further described by Latanision [19], who also discusses
hydrogen-induced phase transformations in the solid, the
observation of hydrogen evolution from the tip of a propagating
crack, fractography, crystal structure, and the influence
of solid-state impurities.
Thompson, Bernstein and Pressouyre [20,52] discuss the
significance of a number of metallurgical variables (including
chemical composition), microstructural components (precipitates,
grain size and shape, crystallographic texture), heat
treatment and its effects on these variables, and processing,
especially thermomechanical treatments for enhancement/
optimization of properties.
Treseder [21] indicates ranges of electrode potentials for
SCC in various environments and indicates that EHE may
be a factor in complex environments of sulfides, cyanides,
carbonates, and ammonia, and he notes that the term SCC
is attributed to various literature references where EHE is
the appropriate environmental influence.

(Hydrogen Damage, C. G. Interrante, L. Raymond, 2005, page: 325)




2. River Patterns (Cracking) (new)        (cracking mechanism)
 
           THERE IS NO OLDER DEFINITION

As a cleavage crack propagates through a crystal, it is most often
broken into a set of parallel cracks by interaction with imperfections
and microstructural features. Thus, gross crack propagation may be the
net result of the simultaneous propagation of individual crack segments
on sets of parallel planes. As the individual segments approach
one another (and possibly overlap), the segments join by fracture of
the connecting ligament, producing steps in the fracture surface. These
steps are generally observed to converge in the direction of local crack
propagation, either cancelling or reinforcing each other to produce the
familiar fiver patterns on individual facets.
Comprehensive investigations of the nature of steps observed in
cleavage fractures have been carried out by Berry [25] and Low [26].
These investigations established that the steps within a single cleavage
facet may be attributed to one or more of the following factors: intersection
of screw dislocations with the cleavage plane, secondary
cleavage, shear, secondary fracture on a twin-matrix interface or, in
the case where considerable overlap of two crack segments occurs,
deformation and necking-down of the interconnecting ligament. Since
a number of processes may be involved in the formation of cleavage
steps, facets exhibiting' wide variations in the appearance of steps and
river patterns are observed. Examples illustrating the extremes in appearance
of steps and river patterns are given in Fig. 7. 4 Steps formed
by secondary cleavage, shear, or twin-interface separation may be expected
to appear as distinctly resolvable subfacets (Fig. 7a), while
those associated with the formation of flaps or extensive local deformation
would appear as heavy lines with less resolvable detail (Fig. 7b).
Since steps and river patterns result from the division of a crack
into parallel segments, they may be expected to originate at regions of
mismatch (grain boundaries or subboundaries). Figure 8 illustrates a
case where new river patterns initiated at the point where the crack
crossed a boundary. In cases where the crack crosses a low-angle
boundary, an increase in step density occurs. Propagation of a cleavage
crack across a high-angle grain boundary usually requires the initiation
of a new crack in the second grain, resulting in the formation of new
sets of rivers or steps.