ISE 2500 Midterm 2
What is the difference between a roving and a yarn?
A roving consists of untwisted filaments, while a yarn consists of twisted fibers.
How is a prepreg different from a molding compound?
Prepregs have continuous fibers rather than chopped fibers as in molding compounds.
What is an autoclave?
An autoclave is an enclosed chamber which can supply heat and/or pressure at controlled levels.
What does the term anisotropic mean?
Anisotropic means that the properties of a material vary depending on the direction in which they are measured.
What is one of the important applications of titanium nitride, as mentioned in the text?
As a thin coating on cutting tools to prolong tool life.
What are the advantages of a three-plate mold over a two-plate mold in injection molding?
As the mold opens, the three-plate mold automatically separates the molded part(s) from the runner system.
Why are laminated FRP products made by the spray-up method not as strong as similar products made by hand lay-up?
Because in hand lay-up, orientation of the fibers is controlled; whereas in spray-up, the fibers in each layer are randomly oriented.
How does a boring operation differ from a turning operation?
Boring produces an internal cylindrical shape from an existing hole, while turning produces an external cylindrical shape.
Cemented carbides are what class of composites?
A cemented carbide is a cermet; although the cemented carbide industry does not generally think of cemented carbides as cermets, they fit within the definition.
What is the difference between a live center and a dead center, when these terms are used in the context of workholding in a lathe?
A center holds the work during rotation at the tailstock end of the lathe. A live center is mounted in bearings and rotates with the work, while a dead center does not rotate - the work rotates about it.
What is a ceramic?
A ceramic is an inorganic compound, consisting of a metal (or semi-metal) and one or more non-metals.
What is a cermet?
A cermet is a composite material consisting of a ceramic and a metal. In the text, it is defined as a composite consisting of ceramic grains imbedded in a metallic matrix.
What is a copolymer?
A copolymer is a polymer made up of two different types of mers, such as ethylene and propylene.
What are some of the ingredients usually added to the metallic powders during blending and/or mixing?
The additives include (1) lubricants, (2) binders, and (3) deflocculants.
For what is the bend allowance intended to compensate?
The bend allowance is intended to compensate for stretching of the sheet metal that occurs in a bending operation when the bend radius is small relative to the stock thickness. In principle the bend allowance equals the length of the bent metal along its neutral axis.
What are the three basic categories of polymers?
The categories are (1) thermoplastics, (2) thermosetting polymers, and (3) elastomers.
In blanking of a circular sheet-metal part, is the clearance applied to the punch diameter or the die diameter?
The die diameter equals the blank diameter, and the punch diameter is smaller by twice the clearance.
What are some of the factors that influence a polymer's tendency to crystallize?
The factors that influence a polymer's tendency to crystallize are the following: (1) only linear polymers can form crystals; (2) copolymers do not form crystals; (3) stereoregularity - isotactic polymers always form crystals, atactic polymers never form crystals, and syndiotactic polymers sometimes form crystals; (4) slow cooling from the molten states promotes crystal formation; (5) plasticizers inhibit crystal formation; and (6) stretching the polymer tends to promote crystallization.
What are the common forms of the reinforcing phase in composite materials?
The forms are: (1) fibers, (2) particles and flakes, and (3) an infiltrated phase in skeletal structures.
In the screening of powders for sizing, what is meant by the term mesh count?
The mesh count of the screen is the number of openings per linear inch.
In conventional sheet metalworking operations, (a) what is the name of the tooling and (b) what is the name of the machine tool used in the operations?
(a) The tooling is called a punch-and-die. (b) The machine tool is called a stamping press.
What is meant by the designation 12 x 36 inch lathe?
A 12 x 36 lathe has a 12 inch swing (maximum work diameter that can be accommodated) and a 36 inch distance between centers (indicating the maximum work length that can be held between centers)
What is a blind hole?
A blind hole does not exit the work; by comparison, a through hole exits the opposite side of the workpart.
What is a composite material?
A composite material is a material system consisting of two or more distinct phases whose combination results in properties that differ from those of its constituents.
What is the difference between a cutoff operation and a parting operation?
A cutoff operation separates parts from a strip by shearing one edge of each part in sequence. A parting operation cuts a slug between adjacent parts in the strip. See Figure 20.8.
In the context of fiber reinforcement, what is a mat?
A mat is a felt consisting of randomly oriented fibers held loosely together in a binder.
What is a plasticizer?
A plasticizer is a chemical added to the polymer to make it softer and more flexible. It is often added to improve the polymer's flow characteristics for shaping.
What is a polymer?
A polymer is a compound comprised of long-chain molecules that consist of repeating units, called mers, connected end to end.
What is a terpolymer?
A terpolymer is a polymer with three different mer types. An example is ABS (acrylonitrile-butadiene-styrene) plastic.
What is the difference between threading and tapping?
A threading operation is performed on a turning machine and produces an external thread, while tapping is normally performed on a drilling machine and produces an internal thread.
What is a whisker?
A whisker is a thin, hairlike crystal of very high strength.
What are the advantages of infiltration in PM?
Advantages of infiltration are (1) the resulting structure is nonporous structure and (2) toughness and strength are improved.
Why are ceramic cutting tools generally designed with negative rake angles?
Ceramics possess low shear and tensile strength but good compressive strength. During cutting, this combination of properties is best exploited by giving the tool a negative rake angle to load the tool in compression
What is clay, used in making ceramic products?
Clay most commonly consists of hydrous aluminum silicate; for example, kaolinite (Al2(Si2O5)(OH)4) is a common clay.
What is cross-linking in a polymer, and what is its significance?
Cross-linking is the formation of connections between the long-chain molecules in a polymer. It causes the polymer structure to be permanently altered. If the amount of cross-linking is low, the polymer is transformed into an elastomer; if cross-linking is significant, the polymer is transformed into a thermoset.
How are a polymer's properties affected when it takes on a crystalline structure?
Density, stiffness, and melting temperature increase.
What does the term devitrification mean?
Devitrification is the transformation from the glassy state into a polycrystalline state.
What are some of the disadvantages of PM methods?
Disadvantages include (1) high tooling costs, (2) metal powders are expensive, (3) difficulties in storing and handling metallic powders, (4) certain limitations on part geometry imposed by the uniaxial press methods, and (5) variations in density in a PM component can be troublesome.
What are some of the possible defects in drawn sheet-metal parts?
Drawing defects include (1) wrinkling, (2) tearing, (3) earing, and (4) surface scratches, as described in Section 20.3.4.
Define drawing in the context of sheet metalworking
Drawing is a sheet metalworking operation used to produce cup-shaped or box-shaped, or other complex-curved, hollow parts. Drawing is accomplished by placing a piece of sheet metal over a die cavity and then using a punch to push the metal into the cavity.
What is the most common fiber material in fiber-reinforced plastics?
E-glass.
Elastomers and thermosetting polymers are both cross-linked. Why are their properties so different?
Elastomers are lightly cross-linked, whereas thermosets are highly cross-linked. Light cross-linking allows extensibility; a highly cross-linked structure makes the polymer rigid.
Give some examples of commercial products which are laminar composite structures.
Examples given in Table 9.2 are automotive tires, honeycomb sandwich structures, fiber reinforced polymer structures such as boat hulls, plywood, printed circuit boards, snow skis made from fiber reinforced polymers, and windshield glass.
Name some of the important applications of FRPs.
FRPs are used in modern aircraft as skin parts, automobile body panels, printed circuit boards, tennis rackets, boat hulls, and a variety of other items.
What is filament winding?
Filament winding is a process in which resin-impregnated continuous fibers are wrapped around a rotating mandrel with the internal shape of the FRP product; the resin is cured and the mandrel is removed.
Why are fillers added to a polymer?
Fillers are added to increase strength or simply to reduce the cost of the polymer.
Define glass.
Glass is an inorganic, nonmetallic material that cools to a rigid solid without crystallization
What is the feature that distinguishes glass from the traditional and new ceramics?
Glass is noncrystalline (amorphous), while most other ceramics assume a crystalline structure.
What is glazing, as applied to ceramics?
Glazing involves the application of a surface coating of oxides such as alumina and silica, usually to a porous ceramic product such as earthenware, to make the product more impervious to moisture and more attractive.
What is graphite?
Graphite is carbon in the form of hexagonal crystalline layers, in which covalent bonding exists between atoms in the layers, and the (parallel) layers are bonded by van der Waals forces, thus leading to highly anisotropic properties.
How does the viscosity of a polymer melt differ from most fluids that are Newtonian.
How does the viscosity of a polymer melt differ from most fluids that are Newtonian.
What are some of the principal applications of cemented carbides, such as WC-Co?
Important applications of WC-Co include cutting tool inserts, drawing dies, rock drilling bits, dies for powder metallurgy, and other applications where hardness is a critical factor.
How do the properties of polymers compare with those of metals?
In general, polymers have lower strength, hardness, stiffness, density, and temperature resistance compared to metals. In addition, polymers have low electrical and thermal conductivity.
Distinguish between redrawing and reverse drawing.
In redrawing, the shape change is significant enough (e.g., drawing ratio greater than 2.0) that it must be carried out in two drawing steps, probably with an annealing operation between the steps. In reverse drawing, two draws are accomplished on the part, one in one direction, the second in the opposite direction.
Describe the difference between up milling and down milling?
In up milling, the cutter speed direction is opposite the feed direction; in down milling, the direction of cutter rotation is the same as the feed direction.
What is the basic difference between low-density and high-density polyethylene?
LDPE has a branched structure and is amorphous. HDPE is linear and highly crystalline. These differences account for HDPE having higher density, stiffness, and melting point.
What are some of the simple measures used to assess the feasibility of a proposed cup-drawing operation?
Measures of drawing feasibility include (1) drawing ratio DR = D/Dp; (2) reduction r = (D - Dp)/D; and (3) thickness-to-diameter ratio, t/D; where t = stock thickness, D = blank diameter, and Dp = punch diameter.
What is the difference between powder injection molding and metal injection molding?
Metal injection molding is a subset of powder injection molding, in which the powders are metallic. The more general term includes powders of ceramic.
Name the three basic categories of composite materials.
Metal matrix composites (MMCs), ceramic matrix composites (CMCs), and polymer matrix composites (PMCs).
Name the various ways in which a workpart can be held in a lathe.
Methods of holding the work in a lathe include: (1) between centers, (2) chuck, (3) collet, and (4) face plate.
What is the technical difference between mixing and blending in powder metallurgy?
Mixing refers to the combining of metal powders of different chemistries, while blending means combining particles of the same chemistry but different sizes.
Density, stiffness, and melting temperature increase.
No.
How would one measure the angle of repose for a given amount of metallic powder?
One measure would be to let the powders flow through a small funnel and measure the angle taken by the resulting pile of powders relative to the horizontal.
In addition to fillers and plasticizers, what are some other additives used with polymers?
Other additives include (1) lubricants - to reduce friction and improve flow; (2) flame retardents; (3) colorants; (4) cross-linking agents, (5) antioxidants, and (6) ultraviolet light absorbers.
What are the principal alloying ingredients in high-speed steel?
Principal alloying ingredients in HSS are (1) either tungsten or a combination of tungsten and molybdenum, (2) chromium, (3) vanadium, and (4) carbon. Some grades of HSS also contain cobalt.
What are the principal polymers used in fiber-reinforced polymers?
Principal polymer matrices in FRPs are unsaturated polyesters and epoxies.
Identify some of the important properties of fiber-reinforced plastic composite materials.
Properties include high strength-to-weight ratio, high modulus-to-weight ratio, low density, good fatigue strength, good corrosion resistance, and low thermal expansion for many FRPs.
What does the term refractory mean?
Refractories are heat resistant ceramic materials. The term is sometimes also applied to metals that are heat resistant.
What is sheet molding compound (SMC)?
SMC consists of TS polymer resin, fillers, and chopped glass fibers, all rolled into a sheet of typical thickness = 6.5 mm (0.250 in).
What are the elements in the ceramic material Sialon?
Sialon consists of the elements silicon, aluminum, oxygen, and nitrogen.
What is the primary mineral in glass products?
Silica, or silicon dioxide (SiO2).
What are some of the general considerations that product designers must keep in mind when designing components out of plastics?
Some of the general considerations are the following: (1) Plastics are not as strong or stiff as metals and should not be used in applications where high stresses will be encountered. (2) Impact resistance of plastics is general good, better than many ceramics. (3) Service temperatures of plastics are limited relative to engineering metals and ceramics. (4) Thermal expansion is greater for plastics than metals; so dimensional changes due to temperature variations are much more significant than for metals. (5) Many types of plastics degrade from sunlight and certain other forms of radiation.Also, some plastics degrade in oxygen and ozone atmospheres. Finally, plastics are soluble in many common solvents.
What are some of the reasons why a controlled atmosphere furnace is desirable in sintering?
Some of the purposes of a controlled atmosphere furnace are (1) to protect against oxidation, (2) to provide a reducing atmosphere to remove existing oxides, (3) to provide a carburizing atmosphere, and (4) to remove lubricants and binders from pressing.
What is springback in sheet-metal bending?
Springback is the elastic recovery of the sheet metal after bending; it is usually measured as the difference between the final included angle of the bent part and the angle of the tooling used to make the bend, divided by the angle of the tooling.
What is stretch forming?
Stretch forming of sheet metal consists of simultaneously stretching and bending the sheet-metal workpart to achieve shape change.
What are the two basic types of clamping units?
The clamping units are: (1) mechanical toggle clamp and (2) hydraulic. In addition, there are hydromechanical units which combine hydraulic and mechanical actuations.
An injection-molding machine is divided into two principal components. Name them.
The components of an injection-molding machine are (1) the injection unit and (2) the clamping unit.
Discuss some of the defects that can occur in plastic injection molding.
The defects include (1) short shots, in which the polymer melt solidifies before filling the cavity; (2) flashing, in which the polymer melt is squeezed into the parting surfaces between the mold halves and around ejection pins; (3) sink marks, in which the surface is drawn into the molding by contraction of internal material; and (4) weld lines where the melt has flowed around a core or other convex detail in the mold cavity and met from opposite directions, thus resulting in mechanical properties that are inferior to those in the rest of the part.
What does the degree of polymerization indicate?
The degree of polymerization indicates the average number of mers or repeating units in the polymer molecule.
What is the function of gates in injection molds?
The function of gates in an injection mold is to constrict the flow of molten plastic into the cavity, which increases the shear rate and reduces the viscosity of the polymer melt.
What are some of the functions of the ingredients that are added to glass in addition to silica? Name at least three.
The functions of the additional ingredients include: (1) acting as flux (promoting fusion) during heating; (2) increasing fluidity in the molten glass during processing; (3) retarding devitrification, which is the tendency to crystallize from the glassy state; (4) reducing thermal expansion in the final product; (5) increasing the chemical resistance against attack by acids, basic substances, or water; (6) adding color to the glass; and (7) altering the index of refraction for optical applications (e.g., lenses).
What is meant by the term green compact?
The green compact is the pressed but not yet sintered PM part.
Identify the mechanisms by which cutting tools wear during machining.
The important tool wear mechanisms are (1) abrasion, (2) adhesion, (3) diffusion, and (4) plastic deformation of the cutting edge.
What is the physical interpretation of the parameter C in the Taylor tool life equation?
The parameter C is the cutting speed corresponding to a one-minute tool life. C is the speed-axis intercept on the log-log plot of the tool life data.
What are the principal methods used to produce metallic powders?
The powder production methods are (1) atomization - the conversion of molten metal into droplets which solidify into powders; (2) chemical reduction - reducing metallic oxides by use of reducing agents which combine with the oxygen to free the metals in the form of powders; and (3) electrolysis - use of an electrolytic cell to deposit particles of the metal onto the cathode in the cell.
Identify the principal components of a stamping die that performs blanking.
The principal components are the punch and die, which perform the cutting operation. They are attached respectively to the punch holder (a.k.a. upper shoe) and die holder (a.k.a. lower shoe). Alignment of the punch and die during the stamping operation is achieved by means of guide pins and bushings in the punch holder and die holder.
Why is PM technology so well suited to the production of gears and bearings?
The reasons are (1) the geometries of these parts lend themselves to conventional PM pressing, which consists of pressing in one direction, and (2) the porosity allows impregnation of the PM parts with lubricants.
What is the rule of mixtures?
The rule of mixtures applies to certain properties of composite materials; it states that the property value is a weighted average of the property values of the components, the weighting being by proportions of the components in the composite.
Name the seven elements of tool geometry for a single point cutting tool.
The seven elements of single-point tool geometry are (1) back rake angle, (2) side rake angle, (3) end relief angle, (4) side relief angle, (5) end cutting edge angle, (6) side cutting edge angle, and (7) nose radius.
What are the three basic steps in the conventional powder metallurgy shaping process?
The steps are (1) blending and/or mixing, (2) pressing, and (3) sintering.
Identify the three basic types of sheet metalworking operations.
The three basic types of sheet metalworking operations are (1) cutting, (2) bending, and (3) drawing.
What are the three steps in the sintering cycle in PM?
The three steps in the cycle are (1) preheat, in which lubricants and binders are burned off, (2) sintering, and (3) cool down.
Cross-linking (curing) of thermosetting plastics is accomplished by one of three ways. Name the three ways.
The three ways are (1) temperature-activated systems, in which elevated temperatures accomplish curing; (2) catalyst-activated systems, in which small amounts of a catalyst cause cross-linking; and (3) mixing-activated systems, in which two reactive components are mixed and curing occurs by their chemical reaction.
What are the two forms of sandwich structure among laminar composite structures? Briefly describe each.
The two forms are (1) foamed-core sandwich, in which the core is polymer foam between two solid skins; and (2) honeycomb, in which the core is a honeycomb structure sandwiched between two solid skins.
How do the properties of thermosetting polymers differ from those of thermoplastics?
Thermosets are more rigid, brittle, capable of higher service temperatures, and cannot be remelted.
What are the three general factors that determine the properties of a composite material?
Three factors are given in the text: (1) the component materials; (2) the geometric shapes of the constituents - the reinforcing phase in particular - and the resulting structure of the material; and (3) the interaction of the phases.
What is the difference between the traditional ceramics and the new ceramics?
Traditional ceramics are based primarily on clay products (e.g., pottery, bricks) while new ceramics are more recently developed ceramics which are generally simpler in chemical composition (e.g., oxides, carbides).
How are traditional composites distinguished from synthetic composites?
Traditional composites have been used for decades or centuries; some of them are obtained from sources in nature, such as wood. Synthetic composites are manufactured.
What are the two basic categories of structural frames used in stamping presses?
Two basic categories of press frame are (1) gap frame, also called C-frame because its profile is the shape of the letter "C", and (2) straight-sided frame, which has full sides for greater strength and stiffness of the frame.
What are the general mechanical properties of ceramic materials?
Typical mechanical properties include high hardness, brittleness, and no ductility.
What are the general physical properties of ceramic materials?
Typical physical properties include electrical and thermal insulating, medium density (mostly below the density of metals), high melting temperatures, and thermal expansion usually less than metals.
Identify some of the characteristic properties of composite materials.
Typical properties include (1) high strength-to-weight and stiffness-to-weight ratios; (2) good fatigue properties and toughness; (3) anisotropic properties in many cases; and (4) other properties and features that are difficult or impossible to obtain with metals, ceramics, or polymers alone.
How are FRPs cut?
Uncured FRPs are cut by methods that include knives, scissors, power shears, steel-rule blanking dies, laser beam cutting, and water jet cutting. Cured FRPs are cut by cemented carbides and HSS cutting tools, diamond cutting tools, and water jet cutting.
What does viscoelasticity mean, when applied to a polymer melt?
Viscoelasticity is a combination of viscous and elastic properties which cause the melt to exhibit memory - the tendency to return to its previous shape, as exhibited by die swell in extrusion.
Viscosity is an important property of a polymer melt in plastics shaping processes. Upon what parameters does viscosity depend?
Viscosity of a polymer melt depends on (1) temperature and (2) shear rate. Also, (3) the molecular weight of the polymer affects viscosity.
What are some of the weaknesses of ceramics that might be corrected in fiber-reinforced ceramic matrix composites?
Weaknesses of ceramics include low tensile strength, poor toughness, and susceptibility to thermal cracking.
What are the two principal locations on a cutting tool where tool wear occurs?
Wear occurs on the top face of the cutting tool as crater wear and on the side or flank of the tool, called flank wear. Portions of flank wear are often identified separately as notch wear, corresponding to the surface of the work; and nose radius wear, corresponding to the tool point
What is meant by the term interface in the context of composite materials?
What is meant by the term interface in the context of composite materials?
