Technical

Assess Your Grinding Process for Better Bottom-Line Results

15 May 2025

Taqwa Gilani, Sr. Application Engineer, Norton | Saint-Gobain

The goal of every manufacturer is to increase profit and reduce costs. Experience shows that increasing throughput while adhering to safety and quality standards is a powerful way to improve profitability. In grinding applications, calculating the grinding time is a necessary step for achieving these goals.

Understanding the factors that make up grinding time is fundamental for reducing the cycle time of your overall process. Grinding time is dependent on how fast the volume of material is removed. The material removal rate (MRR), which is often referred to as Q’ (Q-prime) in grinding, is a measure of how much material is being removed from a workpiece per unit of time. It’s a crucial parameter in evaluating the efficiency of the grinding process and is often used to compare different grinding methods or conditions.

Significance of Material Removal Rate

The MRR in grinding consists of two key components: the volume of material removed and the speed at which it is removed. MRR is a commonly used metric to reflect productivity within a given grinding system and contact geometry, and the use of MRR’ (Q’) enables comparisons across systems of varying contact geometries. The objective is to achieve the highest possible MRR, essentially removing material as quickly as possible while ensuring that the part remains within specifications and free of thermal damage. This can only be accomplished by increasing the depth of cut or the infeed rate.

While grinding, it’s important to understand that the speed at which the wheel rotates does not affect the cycle time as it does not control the speed at which the material is removed. Only changes in MRR can impact the grinding process significantly.

Aspects of the Grinding Process Impacted by MRR:

MRR directly impacts the life of a grinding wheel
- A higher MRR means the grinding wheel is removing material at a faster rate, leading the grinding wheel to do more work, which increases the workload on the wheel and results in greater wear.
- Each abrasive grain is subjected to higher forces and friction as the MRR increases, causing the grains to wear out quicker, resulting in dimensional inaccuracies.
- In certain situations, increasing the MRR applies adequate forces to the abrasive grain, allowing them to microfracture and grind more freely.
MRR significantly impacts the part quality
- Increased MRR can result in more heat being generated during the grinding process. This can lead to thermal damage as well as dimensional inaccuracies.
MRR impacts the cooling and lubrication requirement
- With a higher MRR, the demands on the cooling and lubrication systems are greater. As the temperature in the grind zone increases due to the increased forces, inadequate cooling can cause thermal damage and even accelerate wheel wear.
MRR is a main factor influencing cycle time
- Increasing or decreasing the feed rate will directly impact the material removal rate. Increasing the MRR will decrease the cycle time and vice versa.

Overall, MRR has a major influence on selecting the grinder size, choosing the grinding wheel, designing the coolant system, and ensuring the rigidity of the entire system.

Calculating Material Removal Rate in Different Types of Grinding

1. Cylindrical (Outer or Inner Diameter) Grinding

The range for MRR in cylindrical grinding is significantly wide, depending on the material of the workpiece, workpiece diameter, grinding wheel characteristics, coolant conditions, spindle horsepower, machine condition and many other factors. The formulas below will help you calculate and compare MRRs.

2. Surface Grinding and Creepfeed Grinding

Just like in OD grinding, the range for MRR in surface and creepfeed grinding is significantly wide. It depends on the material of the work piece, workpiece geometry, workpiece fixturing, grinding wheel characteristics, coolant conditions, spindle horsepower, machine conditions, and various other factors. The MRR values in surface grinding are usually higher compared to cylindrical grinding due to larger contact areas. Creepfeed grinding is designed for high MRR, using a substantially higher depth of cut and a slow feed rate compared to surface grinding.

Getting the Results You Need

Understanding and calculating your MRR will help you make better decisions for your machine shop. By comparing the MRR of various tools, abrasives, and methodologies, you will be able to define what works best, helping you optimize both your processes and your profitability. When you standardize and train properly on the best practices you identify, you will also be creating a safer, more productive work environment for your people.