A Balancing Act

What is rotor balancing?

Rotor balancing is the process of bringing the mass center axis of a rotor in line with the rotor’s shaft axis, within certain industry balance standards. A rotor, balanced or unbalanced, wants to revolve around its mass center axis. The balancing process brings these two axes together. As illustrated below, when the mass that causes the imbalance is removed, the two axes merge.

 

Why do we need to balance?

When bearings are applied to the rotor, they restrict rotation about the mass center axis and force rotation about the shaft axis. Imbalances that remain in the rotor at this point will manifest themselves in vibrations in the motor. This can lead to noise, poor motor performance, and, in extreme cases, wear and disintegration of the rotor itself. On a large scale this can be seen in cars; an imbalance in the wheels can cause your steering wheel to shake and wear your tires. Have you ever gotten on the highway and as your speed increases you start to feel the steering wheel shake more and more? Buckle up, because the same principle applies to a rotor!

How do we and other companies traditionally balance?

At Portescap and at other companies a balancing machine must be used to measure the imbalance of each part. These machines are highly accurate and can range in size and complexity, but all perform the same basic task; the machine spins a part and creates a centrifugal force which allows the imbalance to be registered and relayed back to the user. The user then removes material to correct the imbalance and measures the part again. The process is repeated until the part falls within defined standards, i.e. significant imbalance has been removed. Our current method of material removal is the use of a grinding wheel, but other common industry practices include drilling, milling, and cutting to remove mass.

What's so special now?

Currently, there are machines that will perform the entire balancing process from start to finish autonomously using an operator for loading and unloading only. These machines tend to have a very large footprint, a high tooling cost, and low variability in parts. In many cases it can take hours to change the tooling between setups. The machines work very well for low part variability and high run rates as tool changes are very complex and expensive. For Portescap, these solutions aren’t an option. Our high levels of customization require quick changeovers and a small footprint so that we can meet our growing customer demands quickly and efficiently.

At Portescap, with the help of outside resources, a new machine has been developed which integrates the standard balancing machine with laser machining. To our knowledge, and to the knowledge of industry leaders in balancing, this has never been done before. The automated laser balancing machine reads the output of the internal balancing unit and uses a laser to remove the material from the rotor that is causing imbalance. This laser balancing machine has a comparable cycle time to our manual balancing process, a higher repeatability, and tighter tolerances.

Creating new tooling, processes, and software is part of our everyday lives at Portescap, but this new technology has the capability disrupt the industry and tip the balance in Portescap’ favor.