NX - Rotor Balancing Wizard 

Why

For many kinds of rotors, a key performance criterion and a major concern of design engineers is that the rotor is properly balanced. This is crucial for the smooth and safe operation of various machines and systems. Here are some key points to expand on the importance of rotor balancing:
Minimizing Vibrations – Unbalanced rotating components can generate excessive vibrations. These vibrations not only affect the quality of the machine's output but can also lead to costly downtime. Vibrations can also be transmitted to surrounding structures and cause discomfort to operators.
Improving Quality – In precision machinery, such as machine tools or manufacturing equipment, unbalance can result in products with lower quality and insufficient surface roughness.
Preventing Catastrophic Failure – Severe unbalance in rotating components can lead to catastrophic failures. For example, in turbines or aircraft engines, unbalance can cause blades to crack or break, leading to potentially disastrous consequences. In critical systems, such as power plants or transportation, these failures can have far-reaching impacts.
Extending Component Life – Balancing rotors can significantly extend the lifespan of the components and the entire system. Unbalance places undue stress on bearings, shafts, and other parts, causing premature wear and failure. Properly balanced components experience less stress and wear, leading to longer service life.
Enhancing Safety – Unbalance not only threatens the machinery but also poses risks to personnel working with or near the equipment. Flying debris, increased noise levels, and the potential for catastrophic failures can jeopardize worker safety.
Reducing Noise – Unbalance can result in increased noise levels, which can be both disruptive and harmful to workers' hearing. Balancing the rotor helps reduce noise pollution.

Technical Background

In general, we must distinguish between rigid and flexible rotors. In this article we are focusing on balancing of rigid rotors. However, Siemens offers with Simcenter 3D Rotor Dynamics excellent capabilities to analyze (e.g., critical speed) and improve flexible rotors with the inclusion of the bearings and surrounding components.
We must deal with 2 types of unbalances:

• Static unbalance – Occurs when the axis of rotation does not pass through the center of gravity of the rotating body. The eccentricity of the center of mass from the axis of rotation results in unwanted centrifugal loading (force) of the rotor.
• Dynamic unbalance – Occurs when the axis of rotation is not parallel to one of the rotor's stable principal inertial axes and causes a moment load (tumbling motion).

NX Rotor Balancing Wizard – Rotor Balancing made easy in NX

Mass needs to be removed or added (counterweight) at suitable locations of the rotor to get rid of the unwanted static and dynamic unbalance.

For the balancing process we let the rotor rotate between two imaginary bearings with a constant rotational speed.

Unbalances will cause radial forces in the bearings. The mass distribution of the rotor must now be changed until the bearing forces are ideally reduced to zero. This optimization task is performed with the Design Space Explorer (DSE) in NX which is leveraging the powerful optimization capabilities of HEEDS.

The Design Objective is to minimize the Bearing Force and hence a tool is needed which calculates the Bearing Force. A new NX command, called Calculate Bearing Force, was first developed for this purpose with NX Open. The calculated bearing force is written to an Expression so that it can be used later easily as a Design Objective within the DSE. This calculation can be added with a desired feature name to the model history in the Part Navigator manually or automatically with the newly developed Rotor Balancing Wizard with step-by-step guidance for defining the complete optimization study.

Toolbar - Rotor Balancing Wizard
Starts the Design Space Explorer, which provides tools to create and run optimization studies.	Launch the Rotor Balancing Wizard, which guides you to create a study for optimizing the mass distribution.	Adds a custom feature to the model history for calculating the Bearing Force and will update with any design modifications.

The Rotor Balancing Wizard requires the following user input:

• Rotational axis and speed
• Distance between (imaginary) bearings. A larger distance leads to a higher weighting of the static unbalance during optimization, while a smaller distance provides for more weighting of the dynamic unbalance.
• Design Variables (Expressions) that affect mass distribution (dimensions and location of counterweights, dimensions and location of holes, ...)
• Number of Iterations (in most cases: More iterations à less remaining unbalance)

Example – Balancing of a crankshaft

Download

The Rotor Balancing Wizard can be downloaded at NX / Simcenter 3D API: Rotor Balancing Wizard

Additional references

• Webinar: Rotor dynamics analysis: Proven strategies to overcome engineering challenges faster and smarter
• White Paper: Explore the capabilities of rotor dynamics with the power of digital twin simulation