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Modelling methodology in CATIA V5- Part 7Posted by Alex Fernandes on 22-Jan-2018 11:00:00Find me on:

Additional Rules

This is the seventh article of a series concerning how to implement and use modelling methodology inCATIA V5.

In this article, we will discuss additional rules to be considered when de ning part les. This article closesthe main set of modelling methodology for prismatic geometry driven parts, with single body.

Additional rules

The following rules are inserted in this article, as a complimentary group of rules, which are to beconsidered additionally to the others presented in previous articles.

Part number must be defined

Every modelled part le de nes the geometry of a real part; that is either bought or manufactured. For thisreason, all parts need to be correctly identi ed with a part number de ned according to companystandards. This will help when les are saved, as CATIA will automatically apply the part number to the lename. It also help with instantiation at assembly level because CATIA de nes the instance numberaccording to the part number of the le instantiated in the assembly.

Do not insert geometrical sets inside bodies

A body and ordered geometrical sets are linear containers; you can de ne an in work object and the orderof the elements will a ect the nal geometry.

A geometrical set is a non-linear container; there is no in work object and the order of the elements storedin them is irrelevant for the nal geometry.

CATIA allows a geometrical set to be inserted inside a body but it is bad practice as their behaviour in anupdate cycle is di erent and this can cause issues in the model.

Use the publication tool

A publication is an internal pointer in a part le. Publication is useful to de ne all elements in a part thathave external relations.

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Publications are particularly interesting when working in concurrent environment or when developing anew product because links between les will be done using the published entities and their respectivename instead of the elements de ned in the speci cation tree. This makes replacing a component atassembly level much easier and avoiding all the problems with broken links.

Publish the positioning entities

Publishing the positioning entities helps to guarantee that the assembly level constraints are alwayslinking the correct elements between les. For this reason, all positioning elements of a part should bepublished.

Check for micro-bodies

In some situations, usually deriving from Boolean operations and multi-body methodology, we may have aloose volume of solid geometry hovering in space next to our modelled part; these are called micro-bodies or lumps and need to be removed from the model always.

Easiest way is to apply the remove lump tool to eliminate the lump.

Break all links to external files

A nished model represents a part that is ready for production.

Beside the modelled geometry, that part le has a part number, material, mass and dynamic propertiesand a cost associated to it. All of these elements are considered for multiple aspects of a project andcannot be subject to unintentional change. For this reason, all external links that can a ect a part and itsgeometry must be isolated once a part is nished and the geometry modelled in it correctly.

Delete empty containers

You can create as many bodies and geometrical sets as required in a model but remember to delete themif you are not using them when the model is complete. Empty containers make the model harder toanalyse and edit at a later stage.

Hide all non-solid geometry entities

To clarify representation of parts, all geometrical entities should be in hidden space apart from the solidgeometry representing the model, stored in the PartBody.

De ne your PartBody as your in work object before save

This will guarantee that the model’s in work object is the last geometrical feature in the body and thereforall geometrical features in the body are represented in the model.

Update before save

The update is just to guarantee that there are no unresolved elements in the model’s tree that may preventits complete update cycle, prevent its reopening or cause issues at assembly level. This is particularlyimportant when there is linked geometry between multiple les at assembly level.

Create Master Part (define standardized file for part families)

A master part is a part that is used to de ne other parts that are similar or share similar geometry. Themaster part is never used to represent a part for production. Master parts can have linked geometry anddeactivated elements if necessary.

A master part is de ned with the knowledge that it will be used to de ne a part family. The time used toguarantee proper design intent would be greatly compensated with the new parts created for the partfamily, as they are needed.

Edit similar parts

The idea behind is to never re-invent the wheel; if you need to model a part, which is similar to previouslycreated part, then you should use the previously created part and start from there. This is why parts shouldbe modelled with design intent and using all the rules mentioned before. As mentioned above, if you needto create a family of parts, all sharing similar geometry, then you should create a Master Part and use it asdiscussed above.

Use symmetry

The use of symmetry will reduce design time and avoids unnecessary modelling. When a part is onlypartially symmetric, create only the symmetry for the required geometry and complete the remainingmodelling operations as normal.

Declare user-defined parameters

User-de ned parameters are extremely useful to convey design intent into a model, in particular, if youfeel you will need to edit it at a later stage. They need to be associated to the model through formulas.

With declared user-de ned parameters, you can control the model’s geometry outside the geometricalfeatures and control multiple elements with a single parameter.

Create relations

Relations are created to convey design intent in a model as required by the designer. Relations come oftenin the form of formulas, equivalence conditions or design tables. Relations often come together with user-de ned parameters, presented above.

Do not use filters and layers in 3D design

CATIA V5 does not require layers or lters because it has geometrical sets and bodies to store wireframeand surface elements or solid geometry respectively. CATIA V5 has layers for legacy purposes only.

Multibody parts are not assemblies

Apart from a short number of exceptions (such as o

w analysis over an assembly) a part should never represent an assembly. A multibody part should not beused as such. An assembly de ned in this manner should be transformed to a product le with each bodyde ned in individual part les.

 

In this article, we discussed additional rules for part le de nition in CATIA V5.

In the next article, we are going to discuss surface based part design.

 

Figure 3 - PartBody structure, with functional groups

 

Related articles:  

Modelling Methodology in CATIA V5 - Part 1 >>

Modelling Methodology in CATIA V5 - Part 2 >>

Modelling Methodology in CATIA V5 - Part 3 >>

Modelling Methodology in CATIA V5 - Part 4 >>

 

 Learn more about CATIA V5 >>

  Want to know more? Request a call back >>Want to know more? Request a call back >>

 

Topics: Dassault Systemes, Training, CATIA

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