CAD 4145, Final Exam

Describe the Monte Carlo simulation tolerance stack-up analysis process.

1. A distribution of many design points is created for each of the input parameters that contribute to the tolerance to be evaluated 2. Each individual set of input parameters is combined using a transfer function which yields a large number of possible outcomes 3. The resulting outcomes are evaluated to provide a measure of the predicted process capability

What is required for drawings based on the GD&T standards?

1. All dimensions that are not reference dimensions must have a tolerance. 2. Basic dimensions should be enclosed in a rectangle and their tolerances are controlled by a feature control frame.

What are the two solid modeling algorithms used to mathematically define whether an arbitrary point is inside or outside of a solid?

1. Boundary Representation 2. Constructive Solid Geometry

What are some methods that can be used to check the results of a finite element solution (besides checking for the convergence of the stress result)?

1. Check stress and displacement results against hand calculations. 2. Check the reaction loads against a static analysis of the loads. 3. Check the displacement solution to insure that all boundary conditions (fixtures) on the problem are correct.

State whether the following are benefits or drawbacks. 1. The amount of waste material generated and the energy required for machining operations. [BLANK] 2. The dimensional accuracy of machining operations as compared to casting, forming, or shaping operations. [BLANK] 3. The time required for a machining operation. [BLANK] 4. The cost to produce a small number of parts with machining operations. [BLANK]

1. Drawback 2. Benefit 3. Drawback 4. Benefit

For which situations is stress convergence required at stress concentrations in order to predict failure?

1. Ductile material under fatigue loading 2. Brittle material 3. Brittle material under fatigue loading

What three things could cause a finite element analysis to be nonlinear?

1. Large displacements or rotations 2. Changing of contact states during the course of a simulation (simulating contact stress in gear teeth would be an example of nonlinear contact, bonded contact is still a linear analysis) 3. Anytime there is a nonlinear relationship between stress and strain (stress beyond yield stress are the mostly likely case where there will be a nonlinear relationship between stress and strain)

What are the three causes of nonlinearity when performing a finite element analysis?

1. Large displacements or rotations. 2. Changing of contact states during the course of a simulation (simulating contact stress in gear teeth would be an example of nonlinear contact, bonded contact is still a linear analysis). 3. Anytime there is a nonlinear relationship between stress and strain (stress beyond yield stress are the mostly likely case where there will be a nonlinear relationship between stress and strain).

What geometric controls require at least one datum reference to be specified?

1. Position 2. Perpendicularity 3. Angularity

What are two facts about the Von-Mises stress measure?

1. The Von-Mises stress is independent of global coordinate system and is always positive. 2. The Von-Mises stress can be compared directly to a materials yield stress to predict failure of ductile materials in static loading situations. The Von-Mises stress is also frequently used to determine if a stress solution has converged.

What are the inherent assumptions associated with statistical tolerance stack-up analysis?

1. The manufacturing process for the components must be controlled and mean centered 2. The process must output normal distributions 3. All variations must be statistically independent 4. The tolerances are assumed to be linearly combined with each contribution having a weighting of one

What are the inherent assumptions associated with worst case stack up analysis?

1. The tolerances are assumed to be linearly combined with each contribution having a weighting of one. 2. There will be no defective assemblies if all of the parts have dimensional variations that are between their lower and upper specification limits

What are some negative consequences of specifying overly tight tolerances for a part?

1. Tight tolerances drive expensive manufacturing processes 2. Tight tolerances drive increased inspection requirements 3. Tight tolerances generate increased scrap

What are all of the following purposes or uses of CAD software or of the models generated by CAD software:

1. To generate realistic renderings or visualizations of a part or assembly. 2. To use finite element software to analyze a design. 3. To define the form, fit, and function of a part or assembly. 4. To communicate design information between design teams

What situations can be handled by a Monte Carlo simulation tolerance stack-up analysis?

1. Tolerances that are statistically correlated 2. Tolerances that are not statistically correlated 3. Cases where some of the input parameters have non-normal distributions 4. Cases where the transfer function used to combine the tolerances is nonlinear.

What are two reasons that tolerances are needed when documenting a part for manufacturing?

1. Tolerancing insures that a part will satisfy its intended form, fit, and function by setting bounds on its shape and size. 2. Tolerancing helps the engineers responsible for manufacturing a part choose the appropriate manufacturing processes to manufacture the part.

How wide of a tolerance range is there between the upper and lower specification limit for a Cp of 1?

3 sigma Cp = (UL - LL)/6sigma

What is the primary reason for using 3N factorial sampling instead of 2N factorial sampling for generating a response surface?

3N factorial sampling allows nonlinear relationships between the variables and the objectives to be characterized.

How many strength values does it take to apply the Tsai-Wu failure criteria to a composite layer?

5

How many elastic constants does it take to completely define an orthotropic material?

9

Summarize the difference between 3-axis and 5-axis milling machines.

A 5-axis milling machine allows for controlling the tilt of the tool relative to the workpiece.

What is the best procedure to use to verify that the peak stress value has converged to the correct value?

A general rule of thumb is to reduce the mesh size at the location of the peak stress by half until the stress does not change by more than 10%

Why does too low of a feed per tooth reduce tool life?

A proper chip is not formed resulting in abrasion rather than cutting.

If a peak stress is occurring at a sharp corner in a model for a fatigue loading scenario, what approach should be taken to determine the stress at that location?

Add a fillet or round to represent the true geometry at that location and refine the mesh until the stress converges.

What is possible with a nonlinear buckling analysis but are not possible with a linear buckling analysis?

Both linear and nonlinear buckling analyses can be used to determine the buckling critical load. Only a nonlinear buckling analysis can account for the impact of an offset load or provide stress and displacement values at loads below the buckling load.

How should correlated tolerances be handled when performing a statistical tolerance stack up analysis?

Combine the correlated tolerances using the worst case tolerance stack-up equation and then combine with the rest of the tolerances using the statistical tolerance stack-up equation.

T/F: When dimensioning a drawing in either mm or in, mm can have more than 1 decimal place and inches cannot.

False, units in mm should only use one decimal place and in inches you can use more than one.

T/F: The displacement scaling of the mode shapes obtained from a modal analysis can be used to predict structural failure.

False: The displacement scaling for modal and linear buckling analyses is arbitrary.

MODULE 3 BELOW:

GD&T

When performing a modal superposition analysis, what is the correct approach to ensure that enough modes have been used in obtaining the solution?

Increase the number of modes until adding additional modes does not change the modal superposition solution. Alternatively, include all of the modes up to twice the highest excitation frequency.

All solid modeling applications need to be able to answer the question: Is an arbitrary 3D point (with coordinates x,y,z) [blank] or [blank] of a part or assembly?

Inside or outside.

What is true about the micromechanics approach to determining the elastic constants for a continuous fiber composite?

Micromechanics allows the elastic properties of the composite lamina to be estimated based on the properties of the fiber and matrix materials.

The natural frequencies for a structure can be most easily obtained using what type of finite element analysis?

Modal analysis

What equation should you use for statistical stack-up analysis?

Sqrt of the summed squared Ti values)

T/F: Nonlinear finite element solve times are generally longer than linear finite element solve times for meshes of similar size.

TRUE: The superposition principle does not apply to nonlinear finite element analyses. The superposition principle says that adding the results of two simulations with two different loading conditions yields the same results as applying all of the loads to a single simulation run. The superposition principle applies to linear finite element analysis. Nonlinear finite element solve times are often drastically longer than linear finite element solve times for similar meshes. This is because nonlinear finite element solves are iterative in nature and may take many iterations before a solution is reached. Mesh element quality is more import for nonlinear finite element analysis for two reasons. One is that the elements will oftentimes be deformed by large deformation so a better quality initial mesh will maintain higher quality as it is deformed. Second, nonlinear finite element solutions are slower to converge to a correct solution when the element quality is poor.

For a feature size, what is the correct interpretation of the tolerance on the dimension that specifies the size of that feature?

The feature of size must meet the specified dimension tolerance at all locations and, additionally, no element of a feature of size shall extend beyond the maximum material condition boundary envelope

What is the primary reason that heat generally reduces the life of cutters used in machining operations?

The hardness of the tool decreases with increasing temperature.

What is the correct interpretation of the maximum material condition modifier in a position control?

The maximum material condition modifier indicates that the position tolerance is specified at the feature's maximum material condition and that the tolerance increases as the feature gets closer to the least material condition.

What is the definition of a pareto front for a design space?

The set of all efficient designs.

What is true when predicting failure of a composite laminate structure?

The stress state of each layer needs to be considered individually since the stress state can vary from layer to layer.

T/F: ASME (formally ANSI) and ISO are the primary standards organizations that provide standards for dimensioning and tolerancing

True

T/F: Only the ASME drafting standard allows inch drawings

True

T/F: A harmonic response completely defines the input-output relationship for a linear dynamic system

True: A harmonic response completely defines the input-output relationship for a linear dynamic system. Including too few modes may lead to inaccurate results if not enough modes are included to capture the dynamics of the system. A harmonic analysis assumes a linear relationship between force and displacement.

T/F: A transversely isotropic material is also orthotropic.

True: A transversely isotropic material is a special case of orthotropic materials where there is one plane that is isotropic. Continuous fiber composite materials are transversely isotropic. Transversely isotropic materials require 5 elastic constants to be completely defined.

T/F: When defining an orthotropic or a transversely isotropic material, the orientation of the material properties relative to the coordinate system needs to be considered.

True: Since orthotropic or transversely isotropic materials have material properties that depend on orientation, the orientation of the material property definitions relative to the parts coordinate system must be specified.

T/F: The failure strength values for a composite laminate cannot be predicted well from the failure strength of the fiber and matrix materials so testing is generally required to obtain accurate strength values for a composite laminate?

True: The strength of a composite layer is highly dependent on processing conditions and the adhesion between the matrix and the fibers so testing is required to obtain accurate strength values.

T/F: Climb (down) milling should only be used on machines with zero backlash.

True: climb milling will cause chatter on machines without zero backlash.

What does the third-angle projection symbol look like?

Two circles first, then sideways triangle.

Which of the following can impact the machinability of a material (in other words, which of the following are machinability criteria)? a. A material's ability to hold a tolerance. b. Power required to remove material. c. Material hardness. d. Achievable surface finish for a material. e. Tendency to burr. f. Ductility.

a. A material's ability to hold a tolerance. b. Power required to remove material. c. Material hardness. d. Achievable surface finish for a material. e. Tendency to burr. f. Ductility.

Which of the following are examples of the application of computer aided manufacturing (CAM) (select all that apply)? a. CNC machining of manufacturing tooling such as injection molding dies or fixtures. b. Robotic control of a manufacturing process such as welding, assembly, or painting. c. 3D Printing. d. CNC Machining.

a. CNC machining of manufacturing tooling such as injection molding dies or fixtures. b. Robotic control of a manufacturing process such as welding, assembly, or painting. c. 3D Printing. d. CNC Machining.

Which of the following are true for coolant when used for machining operations (select all that apply)? a. Coolant cools the cutting zone. b. Coolant helps to clear chips away from the cutting tool. c. Coolant reduces cutting forces and reduces energy consumption. d. Coolant reduces friction and tool wear. e. Coolant is always a liquid.

a. Coolant cools the cutting zone. b. Coolant helps to clear chips away from the cutting tool. c. Coolant reduces cutting forces and reduces energy consumption. d. Coolant reduces friction and tool wear.

Which of the following are DFM responsibilities of design engineers (select all that apply)? a. Design engineers should work with the relevant manufacturing/process engineers if they need to push the limits of the DFM guidelines of the process they are designing their part for. b. Design engineers should design without consideration of a manufacturing process since designing for a particular manufacturing process is too limiting. c. Design engineers must have a good understanding of the processes that will be used to produce their parts and assemblies in order to ensure that their designs will be manufacturable at a reasonable cost.

a. Design engineers should work with the relevant manufacturing/process engineers if they need to push the limits of the DFM guidelines of the process they are designing their part for. c. Design engineers must have a good understanding of the processes that will be used to produce their parts and assemblies in order to ensure that their designs will be manufacturable at a reasonable cost.

Which of the following are true when describing modern design for manufacturability best practices (select all that apply)? a. Design for manufacturability (DFM) and design for assembly (DFA) principles should be considered from the earliest phases of the design process. b. Design for manufacturability (DFM) is only required when designing with difficult to machine materials. c. Design engineers and manufacturing/process engineers should work together from the beginning of the design process to address manufacturing issues early. d. Design for manufacturability (DFM) activities should begin after the design is in production since the manufacturing issues are too difficult to predict in the design phase.

a. Design for manufacturability (DFM) and design for assembly (DFA) principles should be considered from the earliest phases of the design process. c. Design engineers and manufacturing/process engineers should work together from the beginning of the design process to address manufacturing issues early.

Which of the following are true for response surfaces when used to optimize mechanical systems (select all that apply). a. Design points obtained using a response surface should always be validated using the full finite element model b. A response surfaces allows for a design space to be explored quickly because it can be evaluated efficiently compared to the original finite element model. c. Response surfaces can only handle linear relationships between input and output parameters.

a. Design points obtained using a response surface should always be validated using the full finite element model b. A response surfaces allows for a design space to be explored quickly because it can be evaluated efficiently compared to the original finite element model.

Which of the following are DFM responsibilities of manufacturing/process engineers: a. Manufacturing/process engineers will often be asked to ensure that the design provided to the manufacturing organization is satisfactory from a manufacturability standpoint (design review). b. Manufacturing/process engineers should avoid documenting DFM guidelines since they change so rapidly. c. Manufacturing/process engineers should document DFM guidelines for the manufacturing processes they are responsible for.

a. Manufacturing/process engineers will often be asked to ensure that the design provided to the manufacturing organization is satisfactory from a manufacturability standpoint (design review). c. Manufacturing/process engineers should document DFM guidelines for the manufacturing processes they are responsible for.

Which two of the following are assumptions of a gradient based minimization techniques (in other words, techniques based on Newton's method)? a. Only a local minimum or maximum will be found. b. The object function does not need to be smooth (differentiable) as long as it is defined at all locations. c. The global maximum or minimum will always be found. d. The object function is smooth (differentiable).

a. Only a local minimum or maximum will be found. d. The object function is smooth (differentiable).

Which of the following are file formats commonly used to exchange solid models (select all that apply)? a. STEP. b. STL. c. PNG. d. TFF.

a. STEP. b. STL.

Which of the following are true statements about the number of flutes on an end mill (select all that apply)? a. The table feed rate required to achieve a desired feed per tooth is proportional to the number of flutes on an end mill. b. End mills with a large number of flutes are more likely to be center cutting than those with 2 or 3 flutes. c. An increased number of flutes on an end mill requires higher spindle speeds to achieve a desired cutting speed.

a. The table feed rate required to achieve a desired feed per tooth is proportional to the number of flutes on an end mill.