The right technology to monitor machining processes

More accurate, more stable, faster and more efficient: users want to see their processes improving all the time – so there is growing demand for reliable data as the basis for assessing the processes. Tool design and development, machining strategy and choice of parameters are the aspects where this potential for improvement can generally be found.

Cutting force is one suitable measurand that can be used to assess these influencing factors and optimize processes. It provides information about whether a process is running stably. Appropriate and specially designed sensor technology can be used to measure cutting forces. Two different technologies are used in sensory tool holders, and both of them can be expected to deliver accurate results: piezoelectric technology has been established for several decades as a measurement method for use in machining processes, whereas sensor technology based on strain gauges has only begun to gain ground here in the last few years. Both systems supply data about the forces and moments acting on the tools, but their operating principles are fundamentally different.

Download the full article on comparison of piezoelectric sensors and strain gauges here.

Comparative testing of piezo sensors and strain gauges

Kistler RCD (Piezo technology)

  • Measurands:
    • X, Y - Force
    • Z - Force
    • Torque Mz
  • Sampling rate: 22’000 Hz
  • Measurement anges: depending on the electronic settings, changeable by parameterization

 

 

Strain gauge technology

  • Measurands:
    • X, Y - Bending moments
    • Z - Force
    • Torque Mz
  • Sampling rate: Typically 1500 - 2500 Hz
  • Measurement ranges: depending on the surface moment of inertia of the tool holder (not changeable)

Force measurement Fx,Fy with Kistler

Bending moment with strain gauge

Measurement results tool ø 10 / z = 4 – vc 175 – fz 0.06 – ap 10 – ae 3

XY - Force / Piezo

Bending moment / Strain gauge

Torque Mz / Piezo

Torque Mz / Strain gauge

Piezo technology

  • Bigger and small tool diameters (< 3 mm) can be measured with the same device
  • Clear signals in Fx/Fy, Fz and Mz
  • Cutting edge engagement can be visualized clearly with details
  • All cutting force applications (w. rotating tool) can be measured
  • Force measurement independent from tool length

Strain gauge technology

  • Only bigger tool diameters (> 10 mm) can be measured
  • Clear signal only in bending moment Mx,y with bigger tools
  • Cutting edge engagement not visible at all for small tools and barely useful for big tools
  • Since Fz and Mz signals are dominated by very high noise. Only mean value analysis would be possible. Dynamic changes cannot be monitored
  • Real benefit in drilling is questionable
  • Tool length has influence on result
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