Geometry assurance again

Question 1

Describe how a 3-2-1 locating scheme works

Answer 1

• Six DOF are locked by six points
• Primary points A1, A2 and A3 defines a plane and locks the geometry in space in two
  rotations and one translation: TZ, RX, RY
• Secondary points, B1 and B2, defines a line and locks the geometry in space in one rotation and one translation: TY, RZ
• Tetriary point C1 locks the geometry in space in one translation: TX

Question 2

Define a 3-2-1 locating scheme for the box in the figure (Se bild!)
- Use the points in the figure (P111-P333, located on the three visible surfaces)
- Try to make it as robust as possible
- Motivate your selection of points

Answer 2

A number of different solutions with almost the same robustness exist. This is one solution.
- Primare points A1, A2 and A3:
——-Points P131, P133 and P112
——This maximizes the area of the triangle defined by the points
- Secondary points B1 and B2
——Points P231 and P233
——This maximizes the length of the line defined by the two points
- Tetriary point C1
——Point P221
——This is the optimal one

Question 3

Variation analysis (with Monte Carlo simulation), Contribution analysis and Stability analysis are three different types of analyses used in CAT (Computer Aided Tolerancing) software. Describe Variation analysis and what it is used for

Answer 3

Variation analysis (with MC):
- Calculates a statistical prediction of the variation in critical measures
- Statistical method - random data
- Tolerances on parts (inputs) are randomly generated within defined distributions, tolerances and Cp
- Distributions for critical measures (outputs) are generated from thousands of iterations
- All kinematical relations and sensitivities are captured in a 3D assembly model

Question 4

In order to perform a 3D variation analysis a 3D assembly model is needed. Describe the necessary components and inputs for a 3D assembly model

Answer 4

A 3D assembly model consist of:
- Parts
- Subassemblies
- Positioning systems
- Input tolerances with range and type of distribution
- Critical measures

Question 5

How does contribution analysis work and for what is it used?

Answer 5

It is used to calculate a ranked list of how all input tolerances contributes to the variation in the critical measures.

Question 6

What characterizes a geometrically robust design?

Answer 6

A geometrically robust design is a design that allows manufacturing and assembly variation without jeopardizing function or aesthetics.

Question 7

What are the factors that contribute to variation in critical dimensions of a product?

Answer 7

Se bild!
- Component variation such as: machine precision, process variation, manufacturing process
- Design concept such as: robustness
- Assembly variation such as: assembly precision, process variation, assembly process

Question 8

Variation analysis (with Monte Carlo simulation), Contribution analysis and Stability analysis are three different types of analyses used in CAT (Computer Aided Tolerancing) software. Describe contribution analysis and what it is used for

Answer 8

Contribution analysis
- Calculates a ranked list of how all input tolerances contributes to the variation in the critical measures
- All input parameters are varied (one at the time) within their tolerances on 3 levels
- Max output is registered
- Contribution is calculated in percent as: (se bild!)

Question 9

Variation analysis (with Monte Carlo simulation), Contribution analysis and Stability analysis are three different types of analyses used in CAT (Computer Aided Tolerancing) software. Describe Stability analysis and what it is used for

Answer 9

Stability analysis
- Can be used to analyze the influence of each part locating scheme on
——variation amplification, color-coding
——Position stability of parts
——Critical product dimensions (Measures)
- It is done by disturbing each locating point with a unit disturbance
- And summarizing their contribution with RSS
- Is often used to evaluate different positioning systems