Mechanical Design

Using Solid Procedure for Mechanical Design

For mechanical part design, the more productive procedure is the Solid procedure, in CAD/CAM system, a solid models a piece of 3D space limited by a closed skin which represents the material volume of the real solid, when in the Surfacic procedure there is no material notion: a surface have no thickness.

In the Solid procedure, the designer works with the shapes, dimensions and locations of basic components from the mechanical functions. These mechanical functions are able to create, to modify, to dress-up and to operate solids.

There are three mechanical function categories:

1. Creating a solid from components other than solids from the following functions:

   Pad, Shaft, Rib, Loft, Close Surface and Thick Surface in an empty part body.

2. Combining two solids to generate another one from the following functions:

   Pad, Shaft, Rib, Loft, Add, Union Trim and Assemble to add material.
   Pocket, Groove, Slot, Remove Loft, Hole, Remove, Intersect, Remove Lump and Assemble to remove material.

   These two mechanical function categories create Form features.

3. Operating the solid from the following functions:

   Fillet, Chamfer, Draft, Thickness, Shell, Sewing and Split.

   This mechanical function category creates Contextual features.

You can retrieve in details these concepts in the article entitled "Contents of the Specification Container - Part 2" [2]

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Integrating the Procedural Model: the Build Method

The CAA V5 architecture offers a common procedural infrastructure for all applications. This infrastructure picks up and manage the input/output dependencies between the objects which are evaluated and computed one after the others in a compatible order according to their dependencies. The procedural infrastructure allows applicative objects to be built from the virtual method: Build. All application and particularly the Part Design workbench which wish to have the procedural update must implement a Build method for each of its classes and responsible for the method contents.

The technical article entitled "Integrating a New Geometrical Feature in the Update Mechanism" [3] explains the implementation of the Build method for a new geometrical feature in general an gives some explanations for a shape feature in particular. The "Implementing a Mechanical Design Feature Building" [4] use case is an illustration.

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Creating a Shape-Based Solid: the BuildShape Method

The usually solid creation is to extrude a planar profile along a direction or a revolution axis, a surface or plane may be used to limit the extrusion. To integrate the procedural infrastructure the Build method is programmed for each solid type, and in creation case this method calls the BuildShape method dedicated to create a solid.

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Combining Two Solids

By example, a Hole function is seen by user as one operation on the solid. Nevertheless there are two steps: the solid form creation to be combined (a cylinder for a simple hole) then the Boolean operation between this solid and the current solid (cylinder subtraction for the drilling operation).

The BuildShape method builds the solid form to be combined, named tool solid.

The Build method chained the BuildShape method which returns the tool solid then subtracts it from the current solid.

This architecture reuse the solid creation and the Boolean operation code to guarantee a stable behavior of the system.

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Dressing Up a Solid

A dress-up function operates directly a solid and there is no preliminary step with a tool solid. The usually dress-up functions are Fillet, Chamfer, Draft Angle, Thickness, etc., and consist in operating a solid locally. This operation prohibits a Boolean operation structure because it may adds and removes material to a solid at the same time: a draft operation on a face with a plane as neutral element normal to it, adds/removes material below/ above the plane. The know how of these functions is contained in the Build method.

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Integrating the Generic Naming: the CreateprocReport Method

Mechanical functions create, delete, cut, combine solids which are represented with orientated closed skins themselves made of adjacent faces. To replay an operation where its input is a BRep element (face, edge, vertex) or to define the available mechanical function according to the selected face of the solid, we have to give the relation between the mechanical functions and the topological faces created or cut from it: this is the Generic Naming objective. The solid skin is continually regenerated according to the solid modifications and updates, so the relation must be regenerated to.

A mechanical function must indicates to the Generic Naming the symbolic name of the generated faces from it. The symbolic name or label is linked with the topological faces and followed by the topological operations, to know which face is generated by which mechanical function. The CreateprocReport method allows the mechanical functions and the Generic Naming to communicate.

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References

In Short

This article has explained whar are the solid features and how to integrate them in the procedural model.

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History

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