Replace components in a machined assembly

Overview

Some time before, I promised to look at the special techniques which help to replace components in assemblies with machining features applied to them. In this article I’ll describe them in detail.

In complex products, machining after assembly is a typical scenario. On the other hand, it is often required to replace components in a CAD assembly. It is done in at least two major cases:

  • A design change is required, which involves replacing components with their updated versions
  • A new design is being created based on the old one, which requires replacing a number of components with different ones.

Therefore, it is often needed to replace components which have modeling features applied to them at the assembly level. In NX it is not very difficult, but some restrictions must be taken into account and certain approach to the feature tree must be implemented.

In this article I look at assemblies where machining is modeled with the use of Assembly Cut or Promote Body feature.

Replacement of Components

In case of the machined component being replaced, we need to be aware of one important thing: if ‘Replace Component’ tool is used, then old component will simply be swapped for a new one, and all modeling features applied to the old component at the assembly level will be deleted or at least lose their target bodies. This is the issue that needs to be addressed.

A good technique to avoid this is the following: do not actually replace components. Do this instead:

  • Add new component
  • Remap features from the old component to the new component
  • Delete the old component

This way you lose no features, and have an opportunity to remap them in a controlled manner.

Feature Tree

Typical approach to the feature tree is to apply features one by one: starting with major ones, like a big subtraction; and finishing with smaller ones, like fillets and chamfers. This approach works well at the part level, but when we look at the assembly level, certain adjustments have to be made.

If we have features that model machining after assembly, we cannot use ‘Replace Feature’ tool and remap those features from old bodies to the new ones. We will have to do this manually. This means the following: the feature tree at the assembly level must be as short as possible.

A very good way to achieve this is to use a negative tool body. Imagine that you need to make a big subtraction and apply few chamfers and fillets to it. Make it this way:

  • Create a body that represents the volume that you need to subtract – but do not subtract it yet
  • Apply all needed chamfers and fillets to this body
  • Finally use this body as a tool in the Assembly Cut operation or subtract it from the promoted bodies of components.

This technique enables you to avoid remapping many individual operations. Instead of this, you only need to remap few major ones.

Also, consider using hole features to the maximum extent. Hole-modeling tools in NX are well-developed and offer a lot of options. When set up properly, they allow to create holes with chamfer and various reliefs already applied. And have a close look at the Hole Series option – it allows to create multiple aligned holes in few bodies at once. Proper use of hole features can significantly reduce the effort required to remap assembly-level features to the new components.

Another good way to get operations together is User Defined Feature. With this tool you can combine different modeling operations under the single top-level feature and this can also can help to remap them quickly to the new components. User Defined Features are better used to model standard features, which are used in many different models.

Conclusion

You might not know in advance whether you would need to do the actual replacement. But, the use of the described techniques does not take much time and it has a potential to significantly reduce subsequent effort.

Replacing components that are machined after assembly requires some planning. But if you did everything right, that is no more difficult than replacing features at the part level.

Do you need to replace components in machined assemblies? How do you do that?

2 Comments:

  1. Hello Chris! Thanks for taking time to read the article!
    Obviously, WAVE is one of the possible methods, but my article deals specifically with the situations when WAVE is not used.
    I had another article on a subject of machining after assembly, where I weighed all options: http://cadroad.com/replace-machined/
    In my opinion, using WAVE to model machining after assembly should be reserved for special cases only, because it can be quite problematic in specific areas, like weight management.

  2. As an alternative to this method, you could consider using WAVE-Linking. Bring your component into your machining assy. Extract a WAVE-Linked copy of the solid body. Set your component’s Reference Set to Empty. Add your machining features to the WAVE-Linked body.

    If you update the component solid, the WAVE linked copy will update to reflect the new configuration. Depending on new topology, some of the machining features may need to be edited, reattached or recreated.

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