Case Studies

Measurement of Cutting Force

Cutting force is the most sensitive indicators of machining performance. Both the static and dynamic components of the cutting force contain information about the sate of chip formation and the cutting tool. To measure cutting force, force sensors can be mounted on a tool holder to monitor the cutting force in 1 or 2 orthogonal directions. Kistler gives a force measurement method. The following figure shows this system.

Kistler uses Quartz dynamometer as the force transducer. Quartz is ideal for the construction of 3-component force sensors. Two pairs of shear-sensitive quartz elements for Fx and Fy together with one pair for compression for Fz result in a very compact 3-component sensor. Quartz is a piezoelectric material that yields an electrical charge when mechanically loaded.

The mechanical stress induced in the quartz measuring element by the force to be measured, which can be either tensile or compressive, produces the output signal with only minimal mechanical deflection. A very important factor when measuring very slow, quasi-static forces. The high rigidity is also important when measuring dynamic forces as it provides for a high natural frequency thus allowing the measurement of very fast force pulses.

The figure shows Kistler's dynamometers which is adaptable to machine tool for measuring cutting forces on turret lathes.  Simple mounting on the turret in place of tool holders, e.g. tool mounting system. Max. shank cross section of external tools: 20 x 20mm. Max boring bar for internal milling: 20 mm.

The dynamometer consists of 3 parts. It can only be used for cutting force measurements if the three parts and the connecting cable are mounted. Part 1 Revolver adapter developed for the revolver tool clamping system, with integrated cooling agent connection. Part 2 Dynamometer with mounted quartz sensors. Part 3 Tool holders for tools turning the outside diameter or tool holders for boring bars.

The dynamometer consists of four three-component force sensors fitted under high preload between a base plate and a top plate. Each sensor contains three pairs of quartz plates, one sensitive to pressure in the z direction and the other two responding to shear in the x and y direction respectively. The force components are measured practically without displacement. The four sensors are mounted ground isolated. Therefore ground loop problems are largely eliminated. The dynamometer is rustproof and protected against penetration of splashwater and cooling agents. Together with the connecting cable. Using this system, cutting force measurements on turning machines with tool turret can be carried out.