Question & Answer

Name some of the important semiconductor materials.

What is an integrated circuit?

A prototype of a part is to be fabricated using stereolithography. The part is shaped like a right

triangle whose base = 36 mm, height = 48 mm, and thickness = 25 mm. In application, the part

will stand on its base, which is 36 mm by 25 mm. In the stereolithography process, the layer

thickness = 0.20 mm. The diameter of the laser beam (“spot size”) = 0.15 mm, and the beam is

moved across the surface of the photopolymer at a velocity of 400 mm/s. Compute the minimum

possible time required to build the part, if 8 sec are lost each layer to lower the height of the

platform that holds the part. Neglect the time for postcuring.

Stereolithography is to be used to build the part in Figure 33.1 in the text. Dimensions of the part

are: height = 125 mm, outside diameter = 75 mm, inside diameter = 65 mm, handle diameter = 12

mm, handle distance from cup = 70 mm measured from center (axis) of cup to center of handle.

The handle bars connecting the cup and handle at the top and bottom of the part have a

rectangular cross section and are 10 mm thick and 12 mm wide. The thickness at the base of the

cup is 10 mm. The laser beam diameter = 0.25 mm, and the beam can be moved across the

surface of the photopolymer at = 500 mm/s. Layer thickness = 0.20 mm. Compute an estimate of

the time required to build the part, if 10 s are lost each layer to lower the height of the platform

that holds the part. Neglect post-curing time.

The cone-shaped part in Problem 33.5 is to be built using laminated-object manufacturing. Layer

thickness = 0.20 mm. The laser beam can cut the sheet stock at a velocity of 500 mm/s. Compute

an estimate for the time required to build the part, if 10 s are lost each layer to lower the height of

the platform that holds the part and advance the sheet stock in preparation for the next layer.

Ignore cutting of the cross-hatched areas outside of the part since the cone should readily drop out

of the stack owing to its geometry.

A cone-shaped part is to be fabricated using stereolithography. The radius of the cone at its base

= 35 mm and its height = 40 mm. The layer thickness = 0.20 mm. The diameter of the laser beam

= 0.22 mm, and the beam is moved across the surface of the photopolymer at a velocity of 500

mm/s. Compute an estimate for the time required to build the part, if 10 s are lost each layer to

lower the height of the platform that holds the part. Neglect post-curing time.

Solve Problem 33.3, except using the following additional information. It is known that the

diameter of the filament fed into the extruder workhead is 1.25 mm, and the filament is fed into

the workhead from its spool at a rate of 30.6 mm of length per second while the workhead is

depositing material. Between layers, the feed rate from the spool is zero.

The part in Problem 33.1 is to be fabricated using fused deposition modeling instead of

stereolithography. Layer thickness is to be 0.20 mm and the width of the extrudate deposited on

the surface of the part = 1.25 mm. The extruder workhead moves in the x-y plane at a speed of

150 mm/s. A delay of 10 s is experienced between each layer to reposition the workhead.

Compute an estimate for the time required to build the part.

Solve Problem 33.1 except that the layer thickness = 0.40 mm.

A prototype of a tube with a square cross section is to be fabricated using stereolithography. The

outside dimension of the square = 100 mm and the inside dimension = 90 mm (wall thickness = 5

mm except at corners). The height of the tube (z-direction) = 80 mm. Layer thickness = 0.10 mm.

The diameter of the laser beam (“spot size”) = 0.25 mm, and the beam is moved across the

surface of the photopolymer at a velocity of 500 mm/s. Compute an estimate for the time required

to build the part, if 10 s are lost each layer to lower the height of the platform that holds the part.

Neglect the time for postcuring.

There are 11 correct answers in the following multiple choice questions (some questions have multiple

answers that are correct). To attain a perfect score on the quiz, all correct answers must be given. Each

correct answer is worth 1 point. Each omitted answer or wrong answer reduces the score by 1 point, andeach additional answer beyond the correct number of answers reduces the score by 1 point. Percentage

on the quiz is based on the total number of correct answers.

33.1 Machining is never used for rapid prototyping because it takes too long: (a) true or (b) false?

33.2 Which of the following rapid prototyping processes starts with a photosensitive liquid polymer to

fabricate a component (two correct answers): (a) ballistic particle manufacturing, (b) fuseddeposition

modeling, (c) selective laser sintering, (d) solid ground curing, and (e) stereolithography?

33.3 Of all of the current material addition rapid prototyping technologies, which one is the most widely

used: (a) ballistic particle manufacturing, (b) fused deposition modeling, (c) selective laser

sintering, (d) solid ground curing, and (e) stereolithography?

33.4 Which one of the following RP technologies uses solid sheet stock as the starting material: (a)

ballistic particle manufacturing, (b) fused-deposition modeling, (c) laminated-object manufacturing,

(d) solid ground curing, or (e) stereolithography?

33.5 Which of the following RP technologies uses powders as the starting material (two correct

answers): (a) ballistic particle manufacturing, (b) fused-deposition modeling, (c) selective laser

sintering, (d) solid ground curing, and (e) three-dimensional printing?

33.6 Rapid prototyping technologies are never used to make production parts: (a) true or (b) false?

33.7 Which of the following are problems with the current material addition rapid prototyping

technologies (three best answers): (a) inability of the designer to design the part, (b) inability to

convert a solid part into layers, (c) limited material variety, (d) part accuracy, (e) part shrinkage, and

(f) poor machinability of the starting material?

What is the starting material in fused-deposition modeling?

Describe the RP technology called laminated-object manufacturing.

Describe the RP technology called solid ground curing.

Of all of the current rapid prototyping technologies, which one is the most widely used?

What is the common approach used in all of the material addition technologies to prepare the

control instructions for the RP system?

Besides the starting material, what other feature distinguishes the rapid prototyping technologies?

What are the three types of starting materials in rapid prototyping?

What is rapid prototyping? Provide a definition of the term.

A pin is to be inserted into a collar using an expansion fit. Properties of the pin and collar metal are:

coefficient of thermal expansion is 12.3 x 10^-6 m/m/°C, yield strength is 400 MPa, and modulus of

elasticity is 209 GPa. At room temperature (20°C), the outer and inner diameters of the collar =

95.00 mm and 60.00 mm, respectively, and the pin has a diameter = 60.03 mm. The pin is to be

reduced in size for assembly into the collar by cooling to a sufficiently low temperature that there is

a clearance of 0.06 mm. (a) What is the temperature to which the pin must be cooled for assembly?

(b) What is the radial pressure at room temperature after assembly? (c) What is the safety factor in

the resulting assembly?

A steel collar whose outside diameter = 3.000 in at room temperature is to be shrink fitted onto a

steel shaft by heating it to an elevated temperature while the shaft remains at room temperature. The

shaft diameter = 1.500 in. For ease of assembly when the collar is heated to an elevated temperature

of 1000°F, the clearance between the shaft and the collar is to be 0.007 in. Determine (a) the initial

inside diameter of the collar at room temperature so that this clearance is satisfied, (b) the radial

pressure and (c) maximum effective stress on the resulting interference fit at room temperature

(70°F). For steel, the elastic modulus = 30,000,000 lb/in2 and coefficient of thermal expansion = 6.7

x 10^-6 in/in per °F.

A bearing for the output shaft of a 200 hp motor is to be heated to expand it enough to press on the

shaft. At 70°F the bearing has an inside diameter of 4.000 in and an outside diameter of 7.000 in. The shaft has an outside diameter of 4.004 in. The modulus of elasticity for the shaft and bearing is

30 x 10⁶ lb/in² and the coefficient of thermal expansion is 6.7 x 10^-6 in/in per °F. (a) At what

temperature will the bearing have 0.005 of clearance to fit over the shaft? (b) After it is assembled

and cooled, what is the radial pressure between the bearing and shaft? (c) Determine the maximum

effective stress in the bearing.

A steel collar is to be heated from room temperature (70°F) to 700°F. Its inside diameter = 1.000 in,

and its outside diameter = 1.625 in. If the coefficient of thermal expansion of the steel is = 6.7 x 10^-6

in/in per °F, determine the increase in the inside diameter of the collar.

A steel ring has an inside diameter = 30 mm and an outside diameter = 50 mm at room temperature

(21°C). If the coefficient of thermal expansion of steel = 12.1 x 10-6 mm/mm per °C, determine the

inside diameter of the ring when heated to 500°C.

A shaft made of aluminum is 40.0 mm in diameter at room temperature (21°C). Its coefficient of

thermal expansion = 24.8 x 10^-6 mm/mm per °C. If it must be reduced in size by 0.20 mm in order

to be expansion fitted into a hole, determine the temperature to which the shaft must be cooled.