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43 Cards in this Set
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pure metals
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have clearly defined melting or freezing point; solidification takes place at constant temperature
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Alloy
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solidifies over a range of temperatures. Begins when the temperature of the molten metal drops below the LIQUIDUS and is complete when the temperature reaches the SOLIDUS
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Liquidus
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at this temperature the molten metal alloy begins to solidify
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Solidus
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At this temperature the alloy is completely solidified
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solid solution (def and two types)
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A solution in which two or more elements are soluble in a solid state, forming a single homogenous material in which the alloying elements are uniformly distributed throughout the solid. (substitutional, interstitial)
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substitutional solid solution
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If the size of the solute atom is similar to that of the solvent atom, the solute can replace solvent atoms and form a substitutional solid solution
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interstitial solid solution
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If the size of the solute atom is much smaller than that of the solvent atom, the solute atom occupies an interstitial position and forms a interstitial solid solution
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Intermetallic compounds
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complex structures in which solute atoms are present among solvent atoms in certain specific proportions
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Two-phase alloy
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An alloy that consists of two or more solid phases
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Lever rule
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construct a lever between the solidus and liquidus lines (tie line), which is balanced at the nominal weight composition C_0 of the alloy
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Eutectoid reaction
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at a certain temperature a single solid phase (austenite) is transformed into two other solid phases
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Three basic fluid principles (name and equation)
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Bernouilli's: h+P/rho*g+v^2/2g=constant mass continuity: Q=A1V1=A2V2
Reynold's number: Re=vDrho/zeta where zeta=viscosity |
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Chvorinov's rule for solidification time
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solidification time=C(volume/surface area)^n
where C is a mold material, metal property, and temperature dependent constant, and n typically is between 1.5 and 2 (usually 2) |
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two types of molding process
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expendable mold, permanent mold
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expendable mold (different types, examples of parts using this method)
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sand casting, shell-mold casting, vaccuum casting. Engine blocks and cylinder heads are parts using sand casting
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Permanent mold casting (def, different types, examples of parts using this method)
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molds that are used repeatedly and are designed so that the casting can easily be removed and the mold reused. Molds are made of metals that retain their strength at high temperatures. These have higher rates of cooling. Types: die casting, pressure casting
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List of bulk deformation processes
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forging, rolling, extrusion, drawing, swaging
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forging
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COMPRESSIVE FORCES. Discrete parts are made with a set of dies; finishing processes usually necessary; performed at elevated temperatures
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rolling
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COMPRESSIVE FORCE. reduces the thickness via compressive forces applied through a set of rolls. Good surface finish.
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Extrusion
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COMPRESSIVE FORCE. Production of long lengths of solid or hollow products cut to length with constant cross sections, usually performed at elevated temperatures.
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Drawing
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TENSILE FORCE. Production of long rod, wire, and tubing, with round or various cross sections (smaller than extrusions); good surface finish.
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Swaging
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COMPRESSIVE FORCE. When a rod or tube is reduced in diameter by the reciprocating radial movement of two or four dies (radial forging). Generally carried out at room temperature.
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factors that contribute to dimensional inaccuracies (defects) in forging
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Most are caused by material flow patterns into cavity. Excess material in web, die radii, mismatching of the dies
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Roll of friction in forging
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frictional forces at the die-workpiece interface oppose the outward flow of the material, causing barreling.
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Effect of temperature on forging
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material flows easier into die cavities,
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Effect of friction in rolling
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Without friction the rolls cannot pull the strip into the roll gap
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Defects present in rolled materials
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structural defects result from inclusions and impurities in the material or on the surface. Structural defects distort or affect the integrity of the rolled product. Called wavy edges and alligatoring
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Defects in rolling
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surface defects may result from inclusions and impurities in the material or on the surface. Structural defects are those that distort or affect the integrity of the rolled product. Called wavy edges and alligatoring
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total energy per unit volume (specific energy) u_t
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u_t=F_c/wt_o
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specific energy for friction u_f
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u_f=[(f_csinalpha+F_tcosalpha)r]/wt_0
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specific energy for shearing u_s
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u_s=F_sV_s/wt_0V
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total specific energy u_t
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u_t=u_f+u_s
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cutting power
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Power=F_cV
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Machining temperature cause and effect
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Machining increases temperature...adversely affects strength, hardness, wear resistance of the cutting tool; causes dimensional changes in the part being machined, making control of dimensional accuracy difficult; induces thermal damage to machined surface, affecting its properties and service life.
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variables that effect tool wear
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high forces, elevated temperatures, and sliding
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Wear mechanisms
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Flank wear, crater wear
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Flank wear
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this is attributed to sliding of the tool along the machined surface, causing adhesive and/or abrasive wear; temperature rise.
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Tool wear relationship (Taylor tool life equation)
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VT^n=C where V is the cutting speed, T is the time (minutes) it takes to develop a flank wear land, n is the exponent that depends on cutting conditions, and C is a constant.
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Required properties for tool materials
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Hardness (particularly at elevated temperatures), toughness, wear resistance, chemical stability.
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Required properties for tool coatings
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High hardness at elevated temperatures, chemical stability, lower thermal conductivity, good bonding to substrate to prevent flaking, little or no porosity.
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Functions of metal cutting fluids (lubricants)
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cool cutting zone thus reducing distortion and hence improving tool life, reduce friction and wear, improving tool life and finish, reduce forces and energy consumption, wash away chips, protect newly machined surface from environmental attack.
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Chatter and how to reduce it
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"self excited vibration"... is caused by the interaction of the chip-removal process with the structure of the machine tool; these vibrations usually have high amplitude. Reduce by 1. increasing the dynamic stiffness of the system or 2. by damping
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Forced vibration and how to reduce it
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Generally caused by some periodic force present in the machine tool (an imbalance between machine-tool components for example). To reduce: increase the stiffness or damping of the system. Also changing the cutting speed can help.
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