How to make twisted bar in catia??

I have attached a tutorial for modeling a twisted 25mm square bar. You could possibly use this method to produce the part you want.

You could follow Lawrie's tutorial, using multiple profiles to get the twist in a Multi-Section solid. But that's a lot of work drawing all those profiles.

I think a better, quicker way is to make a Swept Surface that can be closed as a solid later.
- the 7x7 square is the profile
- use Explicit profile option
- With Reference Surface (use a plane)
- the Guide curve will be an 18mm long line normal to the profile
- for the Angle, click the Law button and enter 0° to start, 6*360° to end, and choose the S-type
- the spine will the 18mm long line

To make producing this type of model even more efficient, I have made an Alibre Design template to quickly make twisted sections of square and rectangular bars. Despite being way cheaper than Solid Works or Inventor Alibre Design has many feature that make it great in a production environment. The design parameter file is one of these. Once the file is linked to a part file or many part files editing the parameters enable different versions of part almost instantly.

Here is one for twisted sections twisted

Can you better define "6 times"?
I read that as six revolutions (2160°) in the span of 18mm. The result looks more like a threaded bolt than the example you show.

A screenshot with 1 revolution in 18mm is shown