Mehmet Can ÇAPAR 030070131 9th week definitions

1-Mechanical Thermoforming (plastic process method)

(old answer)
The mechanical thermoforming uses matching positive and negative molds that are
brought together against the heated plastic sheet, forcing it to assume their shape.
In pure mechanical forming, air pressure is not used at all. The process is illustrated
in Figure13.39, Its advantages are better dimensional control and the opportunity for
surface detailing on both sides of the part. The disadvantages is that two mold halves
are required; therefore, the molds for the other two methods are less costly.


(Fundamentals of Modern Manufacturing: Materials, Process, and Systems, M.P. Groover, p.305)



(new answer) (better)

     Mechanical forming of plastics spans the continuum from very simple to very complex
and expensive. some of the simpliest forming processes are mechanical. Using a strip heater
to heat a select area of a sheet and simply bending the sheet to a a new shape is one example
of mechanical forming. This process is used for low volume items such a drink menu holders
in restaurants, picture holders, and various retail displays.
    On the other end of the complexity, and cost, continuum is matched mold forming. In this
process two moldsare created with space between them for the heated sheet. Themold closees
onto the sheet, Forming it to the mold geometry where it is cooled. This process can be produce
the  greatest forming force and can add details to the part surface such as lettering, embossing,
textures, etc. This process is very similar to the metal stamping process used to produce body parts
for automobiles. In mold trimming is also frequently done in this process as the forces required for 
trimming even heavy gage materials are used to form the sheet. This process is the most costly of the thermoforming process and therefore has limited application.

(Peter KleinFundamentals of Plastics Thermoforming, pg:27,28)

2-Surface Processing Operations (surface treatments)


(There is no old answer)

    
(new answer)
The major categories pf surface processing operations are (1)cleaning, (2) surface treatmens,
and (3) coating and thin film deposition. Cleaning refers to industrial cleaning process that
remove soils and contaminants that result from previous processing or the factory environment.
They include both chemical and mechanical cleaning methods. Surface treatment are mechanical
and physical operations that after the part surface in some way, such as improving its finish
or impregnating it with atoms of a foreign material to change its chemistry and physical properties.
   Coating and thin film deposition include various processes that apply a layer of material to
a surface.Products made of metal are almost always coated by electroplating(e.g. chrome plating),
painting, or other process. Principal reasons for coatinga metal are to (1) provide corrosion
protiection, (2) enhance product appearance (e.g. providing a specified color or texture),
(3) increase wear resistance and/or reduce friction of the surface, (4) increase electrical
conductivity, (5) increase electrical resistance, (6) prepare a metallic surface for subsequent
processing, and (7) rebuild surfaces worn or eroded during service. Nonmetallic materials are also
sometimes coated. Examples include (1) plastic parts coated to give thnem a metallic appearance;
(2) antireflection coatings on optical glass lenses; and (3) certaşn coating and deposition process
used in the fabricationof semii-conductor chipsand printed circuit boards. In all cases, good
adhesion must be achieved between coating and substrate, and for this to occur the substrate
surface must be very clean.

(Mikell P. GrooverFundamentals of Modern Manufacturing: Materials, Processes, and Systems, pg:668)

3-Double cantilever beam tests (DCB) (test method)

(old answer)

This popular test (ASTM 3433) is used to obtain the mode I fracture energy of the adhesive bonds, which is a measure of the fracture toughness of the adhesive in the presence of flaws. Similar to a wedge test, a crack is initiated first by inserting a wedge. The specimen is then loaded by pulling apart the two beams at a certain rate, this increasing load resulting in increased deflection of two beams. At a certain critical load, the crack begins to propagate resulting in a slight drop in the load (due to the increased compliance). At this point, the beams are stopped from moving apart, thus keeping the deflection constant. The drop in load (due to increasing crack length) and the crack length are carefully followed. Following the equilibration of the crack, the specimen is consecutively unloaded and then loaded. Ideally, the compliance of the fixture should remain the same during these two cycles if there is no further propagation of the crack. This overall procedure is repeated several times leading to total cleavage of the specimen. The data finally collected at various times consists of load, deflection, crack length and the compliance.

(Crystallization, Morphology, Thermal Stability and Adhesive Properties of Novel High Performance Semicrystalline Polyimides Chapter 7: Wedge and Double Cantilever Beam Tests on a High Temperature Melt Processable Polyimide Adhesive, RATTA, VARUN)

(new answer) (better)

The mode I fracture resistance of adhesive joints is most commonly determined using the double cantilever beam (DCB) test. This test was initially described in the ASTM standard (ASTM 1990) and has been developed more recently in the British standard (BSI 2001) and the international standard (ISO 2009). The original ASTM test standard specified metallic substrates and the critical strain energy release rate in mode I, G.k, was determined for repeated crack initiations using a version of simple, shear corrected beam theory. The later standards additionally accommodate nonmetallic substrates and employ corrected beam theory to determine values of Gk at both crack initiation and during steady-state crack propagation.

The DCB adhesive-joint test specimen, as shown in O Fig. 20.2, comprises two substrates (the double cantilevers) bonded together with a thin layer of adhesive to form the joint. During joint fabrication, an initial crack is formed at one end of the joint. In the ASTM method, this can be achieved by positioning a shim at one end of the joint and having an area over which no adhesive is applied. In the BS and ISO standards, the initial crack is formed by placing a releasing film centrally in the adhesive layer during joint fabrication. This film, typically a fluoropolymer and 12-14 mm in thickness, is then molded into the joint during adhesive cure.The AS.GM test specimen comprises of substrates 300 mm long, 25 mm wide, and 12.7mm high (24 x I x 0.5 in). These are cut out from a larger bonded panel. The BS and ISOstandards are more flexible on the substrate dimensions allowed, but have a requirement thatplastic deformation of the substrates must always be avoided. Typically, those following the BSand ISO test standards manufacture smaller test specimens than specified in the ASTM standard. They may either be fabricated individually, or by cutting from a larger bonded panel.

(Lucas Filipe Martins Silva,Andreas Öchsner,Robert AdamsHandbook of Adhesion Technology, 2. cilt, pg:478)

4-Sandcast Alloy (material type)

(old answer) (better)

The grain sizes of sand cast alloys are typically of 200µm. The fraction of retained intermetallics in T6 samples of the ZA84, ZA85, ZA105 and ZA107 alloys increased with alloying content. The primary intermetallic particles reatined in the T6 samples of the sand cast alloys were found to be equilibrium ƥ phase. Fig.3(a). The peak-aged microstructures had a relatively fine-scale distribution of icosahedral precipitates. The distribution of such porecipitate varied from grain to grain for each alloy. Fig.3(b). Examinations of peak aged microstructures of all four alloys did not detect any particles or precipitates of Mg12Al12 phase.

(K.U. Kainer, Magnesium: Proceedings of the 7th International Conference,p.28)

(new answer)

Relative rankings of the cast alloys are preset\led in Fig. 5.4. Alloy A444"O-F, the lowest strength cast alloy, ranks highest, but 8535.0-F also stands out for its high notch-yield ratio. The poorest performance is for sand cast alloys 240.0-F and 356.0-T6. Among the higher-"sirength casting alloys, the premium-quality castings (that is, sand castings made wt.th special care to provide high metal chill rates in highly stressed regions) rate well. and A356.0-T6 consistently has higher toughness than does 356.0-T6, the positive effect of its higher purity (i.e., lower content of impurities such as iron and silicon).

Looking at the relationship between notch-yield ratio (NYR) and tensile yield strength (TYS) also provides interesting information for castings (Fig. 5.5), most notably the relationship of their performance to that of wrought alloys. Alloys A444.O-F and 8535.0-F fall in the band for wrought alloy data, but the other alloys fall at least slightly below the band. The premium-quality castings show the best performance in this
respect. and the sand cast alloys the poorest; permanent mold castings generally fall in the middle of the range.

( John Gilbert KaufmanFracture Resistance of Aluminum Alloys: Notch Toughness, Tear Resistance, pg:19)