White Paper: Understanding Forces in Creepfeed Grinding for Reducing Costs and Improving Consistency

One of the major benefits to creepfeed grinding is the combination of quick material removal with the ability to generate a precision ground surface on difficult-to-grind materials. Typically, creepfeed grinding results in a lower undeformed chip thickness relative to surface grinding, thereby improving surface finish on the workpiece and reducing wheel wear.  However, this advantage comes with a few drawbacks. Creepfeed grinding applications tend to draw more power and have higher forces. Hence, it requires higher power spindles and more robustly engineered machines and fixtures than traditional surface grinding applications. 

When developing new creepfeed grinding applications, factoring in the grinding forces can be beneficial to ensuring adequate fixture design, clamping pressures, and part support. They also influence wheel specifications and process conditions. This article will highlight some of the basic forces that can be calculated in creepfeed grinding, and will conclude with an example application.

Forces in Creepfeed Grinding

Consider a simple 2D creepfeed grind as shown in Figure 1. In this application, there are two primary forces which act on the wheel – tangential force and normal force. The normal force (fn) is the force applied perpendicular to the contact area between the wheel and workpiece, and tangential force (ft) is the force applied parallel to the contact area between the wheel and the workpiece. The magnitude and direction of the grinding forces drives the design requirements for fixturing, workpiece clamping, and system rigidity. The direction of these forces is a particularly important consideration for processes where the point of tangency between the wheel and workpiece might change during the grinding process, resulting in a change in direction of the grinding forces, for example in 5-axis grinding operations.

The tangential force is the force required to maintain the wheel speed while it is engaged with the workpiece under the given frictional and cutting forces. It is the sum of the abrasive cutting forces (i.e. forces required to remove material) and frictional forces between the grains, swarf and wheel bond material. Tangential force is influenced by coolant lubricity, grinding wheel sharpness, abrasive grain density, workpiece material properties and wheel profile.

It is possible to calculate the tangential forces (F_t ) acting on the wheel in creepfeed grinding in two ways. The first is directly from the grinding spindle power and wheel speed as shown:

A second method to measure the tangential force is to use a dynamometer and measure the vertical and horizontal forces during the grind. Then, knowing the normal force vector angle (θ - see Figure 1), the normal and tangential forces can be calculated from the following equations: