Grinding burn or thermal damage is a common cause of machine or engine component failure. When grinding heat is not quickly detected and removed by a suitable cooling solution, it can have a big impact on the service life of the product. In order to detect grinding burn in an early stage, it is important to know what causes grinding burn. In this blog I share the five most common causes of grinding burn. 

 

1)    Worn out dressing tool.

The most common root cause for a worn out dressing tool lies in the fact that there is a lack of cooling. Diamonds graphitise at about ±700 degrees Celsius. This temperature is easy to reach without proper cooling.

How do we see when a diamond is in a bad shape? They often colour black and aren’t transparent anymore.

What to do? Aim with the right amount of coolant and coolant speed in the working area between grinding wheel and diamond.

 

 

2)    Dull grinding wheel

A dull grit in a worn, 46-mesh, vitrified-bond, Al2O3 grinding wheel. Wheel dulling causes increased heat generation and grinding burn, increased normal forces and chatter and a finer surface finish.

Dull grits in a worn, 46-mesh, vitrified-bond, Al2O3 grinding wheel. This wheel was excessively dull, and the wear flats were visible to the naked eye. This wheel was “too hard”, meaning it had too much bond material and dull grits did not break out of the bond.

Dull grinding wheel
Courtesy of Jeffrey A. Badger, Ph.D. “The Book of Grinding by The Grinding Doc”

 

3)    The coolant does not reach the working area

Why doesn’t my coolant reach the working area? the coolant speed is too low. With INNOZL it has to be 30% to 50% of the wheel speed. For high speed grinding with EP wheels or Vit. CBN you have to match up to 80% of the wheel speed.

What does coolant need to do? It has to cool, lubricate and clean the grinding wheel.

For ID grinding you sometimes have to deal with aquaplaning: avoid this by using INNOZL SF or SFGR nozzle technology. This gives better roundness.

The coolant does not reach the working area

 

4)    Clogged grinding wheel

When a grinding wheel clogs, this is mainly caused by a lack of coolant and coolant speed. Coolant not only has to cool but also has to clean and lubricate.

How to avoid clogging? Check for the right attack angle and coolant speed.

Always avoid the following principle: Spray and Pray

 

5)    Unbalanced grinding wheel causing re-hardening burn

Balancing grinding wheels is primarily underestimated and always causes grinding burn.

How to avoid this issue? Always balance your grinding wheels, at least static. Repeat this after you have used 25% of it. When grinding Chrome plating there is a 100% chance of creating grinding burn with unbalanced wheels. The only way to check a grinding burn below a chrome plating is to use Barkhausen Noise Analysis

 

Detecting grinding burn in an early stage is crucial to prevent impact on your production process. Want to know more about how to prevent, detect and solve grinding burn?

 

Helping customers out setting Barkhausen acceptance criteria is one of the competences we provide. BNA (Barkhausen Noise Analysis) is based on a disruptive magnetisation/demagnetisation of a ferromagnetic material when applying an external magnetic field. To work with this method reference samples need to be made. The reference samples (master samples) and work piece must be comparable at all times, so these important rules have to be taken into account.

1. Same material (e.g. 100Cr6)

2. Same heat treatment

3. Same mechanical operation (e.g. grinding, milling)

Referencing to Barkhausen Analysis can be done by using e.g. nital etch, micro Vickers method. As process owner you are the one who sets the limits. We will help you with the interpretation and process settings.

Curious how this Barkhausen ViewScan plot below can help you?
Download the complete guidelines for creating reference parts for Barkhausen Noise Analysis for Rollscan systems.

The Innogrind brochure explains why to detect thermal damage in an early stage | how to solve grinding burn | why to train your people on grinding burn prevention

Innogrind has again provided a Barkhausen training at KLM Royal Dutch Airlines recently. A case study that was done together with Innogrind in the past revealed that Barkhausen Noise Analysis is the only NDT method to discover grinding burn under a chrome layer. The question has been asked to upgrade quality engineers skills in this NDT technique.

To prevent grinding burn or thermal damage, production processes need the right coolant flow rate to achieve adequate cooling. Among other demands, this requires coolant nozzles with optimum geometry and exceptional durability. The use of 3D printing gives us complete freedom to design custom coolant nozzles. Check out the video how it works!