Question: Is there a CAD format, which allows to describe mechanical bonds between objects (axes, joints, springs, etc.) and/or motion of objects ?

Answer: 
A gotcha with the k-means alogrithm is that it is not optimal. That means, it is not sure to find the best solution, as the problem is not convex (for the optimisation).

You may be stuck into local minima, and hence the result of your algorithm depends of your initialization (of your centroids). A good practice in order to find a good minimum is to rerun the algorithm several times with several initializations and keep the best result.

As stated by the others, `random_state` makes the results reproducible and can be useful for debugging
Random state in Kmeans function of sklearn mainly helps to 

1. Start with same random data point as centroid if you use Kmeans++ for initializing centroids.
2. Start with same K random data points as centroid if you use random initialization.

This helps when one wants to reproduce results at some later point in time.