Geometry assurance

Question 1

Variation analysis (with Monte Carlo simulation), how this methods work and what they are used for.

Answer 1

Variation analysis (with Monte Carlo simulation):
A statistical method, with random data, using thousands of iterations, where tolerances on parts (inputs) are randomly generated within defined distributions, tolerances, and CPs.
All kinematic relations and sensitivities are captured in a 3D assembly model.
The result for the critical measures are calculated and stored.
The method is used to calculate a statistical prediction of the variation in critical measures.
-> Cp, Normally distributed graph

Question 2

Contribution analysis, how this methods work and what they are used for.

Answer 2

All input parameters are varied (one at a time) within their tolerances on 3 levels. All kinematic relations and sensitivities are captured in a 3D assembly model. System is assembled. Max output is registered for all measures, contribution is calculated in percent as: % contribution_i = 100* (Delta(output_i)^2)/(sum_i_n(delta(output)^2))
It is used to calculate a ranked list of how all input tolerances contributes to the variation in the critical measures.
-> List of components with %

Question 3

Stability analysis, how this methods work and what they are used for.

Answer 3

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, one at a time. All kinematic relations and sensitivities are captured in a 3D assembly model. System is assembled. The output is calculated and their contribution is summarized with RSS (root-sum-square). Can be used for locator positioning

Question 4

Describe how a 3-2-1 locating scheme works

Answer 4

6 DOF locked with 6 points
Primary points, 3 A points: Defines a plane (triangle that you want to maximize), locks 2 rotations and 1 translation: RX, RY, TZ
Secondary points, 2 B points: Forms a line, locks 1 rotation and 1 translation: RZ, TY
Tetriary point: 1 C point: A point, locks 1 translation: TX

Question 5

What characterizes a geometrically robust design?

Answer 5

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

Question 6

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 6

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