For grinding processes the actuated variables (e.g., cutting speed, feed velocity) and the system variables (e.g., grinding tool properties) have to be distinguished from the grinding parameters. The grinding parameters depend on the actuated and system variables and allow a good correlation to the process forces, process temperatures, surface roughness, and grinding tool wear. The most important grinding parameters, that are described here, are the material removal rate Qw, the material removal rate per unit active grinding wheel width Q′w, the geometrical contact length lg, the kinematic contact length lk, the equivalent chip thickness heq, and the medium single-grain chip thickness hcu.
Theory and Application
The grinding process is a geometrically undefined cutting process due to the undefined number and geometry of cutting edges interacting with the workpiece. The load on the workpiece as well as the load on the grinding wheel is a result of the programmed actuated variables, the cutting tool properties, and the workpiece properties. Due to the complex interrelationships in the grinding process, the parameters have been defined to describe the process behavior. These parameters are described in the following entry (see also standard ISO 3002–5 1989).
Further parameters relevant for grinding processes are the width of the grinding wheel bs, the width of the workpiece bw, and the diameter of the grinding wheel ds as well as for cylindrical grinding the diameter of the workpiece dw.
In general, the material removal rate can be calculated by the actuating cross section Aw, which is the cross section between tool and workpiece orthogonal to the feed direction. A general overview on the process parameters and the calculation of the material removal rate for these processes is given in Fig. 1.
Geometrical and Kinematic Engagement Conditions
(+ down grinding, − up grinding)
while the parameter q is the speed ratio vc/vft.
Kurrein also defined the external material removal rate Qwa, which can be calculated equal to the material removal rate Qw (Kurrein 1927).
Every grain is cutting actively.
Every grain has the same protrusion height.
Elastic and plastic deformations are not considered.
The path overlap is not considered.
Lambda is a factor that describes the shape of the grains.
The number of active grains in the contact area NA depends on the geometric contact area as well as the grain size and the grain concentration in the grinding wheel. This means that the medium chip thickness per grain depends on the grinding wheel properties as well as the actuated values. The medium grain chip thickness can be increased by increasing the feed rate, the working engagement, the grain size, and the grinding wheel radius or by decreasing the cutting speed and the grain concentration in the grinding wheel. Several results show that the values contact length as well as medium grain chip thickness show a good correlation to the process results tool wear and workpiece properties (Brinksmeier 1991; Lierse 1998). An increasing contact length leads to higher temperatures in the contact zone and though to a higher tendency toward grinding burn. A higher medium grain chip thickness leads to a higher mechanical load on the grains and though to a higher tendency toward grain breakout and to higher wear rate. Furthermore, a higher medium grain chip thickness results in a higher workpiece roughness. With this knowledge, the grinding process can be optimized regarding tool wear, workpiece properties, and productivity.
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