# Why combining GD&T with physical variations is critical to robustness?

Product engineers interested in robust tolerance analysis will want a tolerance analysis software which combines: dimensional, geometric and physical variation analysis. Enventive Concept does it all.

Doing functional analysis is a critical steps to the product design. Part of these functional analysis, the FMEA allow engineering teams to specifiy the functional limits and associated severity. So the outcome will be an objective ppm on each function. Each function can be a combination of functional criterias and these criterias can be of different types.

## Achieving functional conditions using “rigid” and “non rigid bodies” analysis software

In the industry, at the side of the CAD solvers, there are two different type of software used:

1/ NON RIGID BODIES: The part material plays a critical role as it can deformate under load, needs to resistant to the environment during the complete products lifecycle… In this case, FEA software will used to ensure the loaded parts remain within the elastic domain to secure the function. And this for the for a defined number of cycles. In this case the assumption the solver assumes non rigid bodies. The calculation resources and time are significant but needed in all industrial critical applications

2/ RIGID BODIES: The parts are put together into assemblies. With a different material for different functions, mastering variations is critical. Above and beyond thermal expansion differences at customer site, wear, noises,… The parts must fit well together. The more parts th more function variables…. On static assemblies we typically need to analyse gaps between components relying on a combination of Dimensional and Geometrical tolerances. However Physical tolerances are not to be neglected. Kinematics systems will see the need for ensuring that forces remains within specific limits. Thermal expansion, frictions, wear… are also to mastered.

Enventually adressing all the needs of the FMEA requires: a CAD software, an FEA software and a tolerances analysis software such as Enventive Concept which combines, dimensional, geomatrical and physical variation analysis.

## The 3 types of tolerances

### DIMENSIONAL TOLERANCING

A ** Dimension tolerance** locates, for example, a feature relative to another. It can also specify the size of a feature, like the diameter of a hole or the radius of a fillet.

### GEOMETRIC TOLERANCING

A ** Geometric tolerance** defines the geometry of a part. Five categories of geometric tolerance exists: Form, Profile, Orientation, Location and Runout.

### PHYSICAL TOLERANCING

In addition, Enventive Concept allows the definition of a ** Physical torelance**. It could be the tolerance associated to a physical parameter like a coefficient of friction or a reference temperature used to calculate thermal dilatation.

Those three types of tolerances can be easily combined in Eventive Concept using either the RSS calculation method or Monte Carlo.

Some CAD and CAE (*Computer Aided Engineering*) software integrate **Dimension tolerance** in a CAD environment. Other computer aided tolerancing software also include **Geometric tolerance**. But only Enventive Concept combines the three types by including the **Physical tolerance**.

For example, the following image shows the setup of a motorcycle brake piston analysis. The aim of this study is to determine the variation of the force apply on the handle during braking. To achieve this study different physical parameters (coefficient of friction, spring initial length and stiffness, etc) and their associated tolerance intervals have been included.

## The importance of muti-criteria analysis

Each functional condition is often the result of a combination of multiple functional criterias. Think of a rotor in a stator. In that case all 4 gaps at the 4 corners must be optimized so that the function “rotor rotating” is guaranted.

IN THIS SECTION WE NEED TO ADD AN ILLUSATRATION OR A LINK TO AN ARTICLE…

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## Further reading

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