Tech Talk
What is "Rotary Disk Truing of CBN Grinding Wheels"?
The ability of a CBN wheel to grind is strongly dependent on the mechanical interaction between the CBN and diamond grits during truing process. A mathematical model has been developed to predict the number of collisions that a CBN grit is subjected to in a truing process when various designs of truing disck are used. Geometric and kinematic characteristics of wheel-truer engagement, and interaction between colliding grits, are used in the model. Various characteristics of truer, whell and truing process are also taken into account. The overall efficiency of a grinding operation depends largely on the preparation process of the grinding whell. Wheel preparation can be divided into two processes. First, truing, which creates a desired geometrical form of the wheel by removal of bond material and whole abrasive grains or parts of them. Truing results in exposure of new abrasive grains and creation of new cutting edges of grains fractured during collisions with abrasive grains of the truing device. Second, dressing, which opens wheel surface by exposing grits from surrounding bond, resulting in better chip formation and coolant flow into the grinding zone. These two processes are used for initial preparation of the wheels before the grinding process, as well as for periodical restoration of the wheel surface and shape, sometimes called conditioning. An extensive research in the subject of wheel truing and dressing has been documented in a number of scientific publications. These papers descrive various truing and dressing techniques, tools and process parameters used mainly for a specific application. From truing techniques used for CBN wheels, rotary tools are the most suitable, because they assure high consistency of truing forces and wheel surface gneration throughout truer life due to distribution of wear over many diamonds, resulting in less interruption to production process. The most often used designs of rotary truers are disc, cup and plunge roll. Efficiency of truing is influenced by kinematic parameters of the process: truing lead, truing infeed and truing speed ration. Truing overlap ratio (defined as a ration of the active width of truing tool to the truing lead) is used by some researchers as another truing parameter. However, the ratio does not include truer characteristics influencing its cutting ability like number and size of grits in contact with the wheel, making this parameter not so flexible for comparing performances of different truing tools. Truing tools for CBN wheels feature diamond grits as cutting abrasive and cutting sharpness of a CBN wheel can be traced to the interaction between CBN and diamond grits during truing process. Consequently, there is a practical need for a direct comparison of results of different truing processes and tools in order to optimize the process of choosing an appropriate tool and parameters for a particular operation. Recently, numerical models were used in computer simulation of the grinding wheel surface gererated after truing with a disc having a single row of diamonds. Results show good correlation of some wheel surface roughness paramaters to results of preliminary experiments, for gentle truing parameters.
