Measuring systems for tool monitoring

The integration of highly sensitive piezoelectric force sensors directly into the tool holder of Swiss-type turning machines for micro-machining – close to the tool’s cutting edge, where the acting force is the greatest – allows for precise, high-resolution indirect measurement of cutting forces throughout the machining process, from roughing all the way to finishing. 

Our application-specific solution for micro-machining relies on the “linear unit” of the quick-change system of the Piezo Tool System (PTS linear), which was developed in collaboration with Paul Horn GmbH. The clever positioning of the sensors between the machine interface and the baseplate retains the advantages of quick tool changes. At the same time, the sensors can monitor a variety of different tool holders. 

Real-time measurement of extremely small cutting forces in micro-machining generates critical, high-resolution cutting force data. It makes it possible to capture even the smallest force variations and vibrations, which can indicate deviations in the machining process as the result of tool wear. Cutting force measurement with the PTS enables plant operators to intervene in good time (machine stop) before damage can result from tool wear or tool breakage. 

Our application-specific solution for tool monitoring of highly automated CNC lathes or multi-spindle lathes with rotating tool systems is based on the Piezo Tool System (PTS) tool holders developed by Paul Horn GmbH developed by Paul Horn GmbH with an integrated Kistler piezoelectric force sensor. In rotating systems, a telemetric measuring system (TMS) transmits signals from the rotating machine element.

A wide range of PTS tool-holder systems for a variety of turning applications enables the measurement of cutting forces and detection of the smallest force variations that may indicate deviations in the machining process as a result of tool wear. Real-time cutting force measurement with the PTS makes it possible to intervene (machine stop) in ongoing turning processes on CNC machining centers in good time before damage occurs as a result of tool wear or tool breakage – from the roughing process to the finishing process.

Changing tools during rough machining of workpieces on CNC machines with tool turrets is a rapid process involving high cutting forces. Tool wear is significant and increases the risk of tool breakage. Excessive cutting forces damage the material and can result in thermal deformations, cracks and rough surfaces, which can cause damage to tools and necessitate reworking. Once again, monitoring of cutting forces is the means of choice to check for rapid tool wear and prevent tool breakage. 

Cost-efficient solution from Kistler:

For this purpose, we integrate a piezoelectric force sensor directly under the bolt that secures the turret housing on the slide in order to measure the moment transferred to the bolt by the cutting forces. This system is especially suitable for rough machining processes, where the cutting forces are high enough to be transferred within the machine structure and measured relatively by the sensor. The precision of this kind of measurement is mainly dependent on the stiffness of the structure and the magnitude of the cutting forces. Thanks to the highly sensitive piezo technology, even the smallest changes in the process can be recorded.

Advantages of process monitoring and tool monitoring in CNC machining centers with tool turrets through the integration of piezoelectric force sensors:

• Reduction of tool costs thanks to optimized tool lifetimes 
• Less scrap and higher, more uniform quality of workpieces
• Minimization of machine downtime

One method for monitoring the tool status in single-purpose machines is the integration of piezoelectric strain sensors and force sensors into the machine structure. Cutting forces cause strain in the machine structure. Depending on the positioning and how the forces acting on the machining point are transferred to the machine structure, this strain can be monitored very well in relative terms via highly dynamic measurement using piezoelectric sensors. An increase in cutting forces results in greater strain in the structure of the machine. This, in turn, allows us to draw conclusions about the degree of tool wear or anomalies in the machining process. The system is easy to retrofit on existing systems. 

Advantages of machine monitoring and tool monitoring in single-purpose machines through the integration of strain and force sensors: 

• Extension of tool lifetimes 
• Minimization of machine downtime
• Machine stoppage in the case of process deviations
• Material batch comparison and monitoring
• Separation of potential scrap parts

When it comes to procuring a new machine tool for end customers, the ideal solution for monitoring the machining process and the tools themselves is often a fully integrated monitoring solution that requires no additional installation work and which displays measurement data directly in the machine control. Many machine tool manufacturers already offer corresponding solutions that tend to observe machining processes via active current monitoring of machine spindles. 

These kinds of systems are sufficient for a broad spectrum of applications. However, when it comes to workpieces with extremely small diameters and therefore the smallest force-measuring ranges, these solutions often reach their technological limits. As an expert development and technology partner, this is where we come in: with piezoelectric measurement solutions for machine tools – from early concept development to prototype testing all the way to market launch. 

Advantages of a collaboration to develop monitoring solutions in machine tools:

• Benefit from Kistler’s expertise and core competency in the field of piezoelectric measurement technology
• Draw on an extensive product range of generic sensors, load amplifiers and integration possibilities in machines

Collaborative development of innovative measurement solutions for integration into machine tools

Coverage of customer-specific requirements using Kistler’s entire generic measurement technology portfolio

Legend

1. Broad portfolio of sensors for different measurands

2. Components for signal transmission and machine integration

3. Industrial charge amplifiers and data acquisition systems

4. Data integration into the machine tool

Collaborative development of innovative measurement solutions for integration into machine tools

Coverage of customer-specific requirements using Kistler’s entire generic measurement technology portfolio

Legend:

1. Broad portfolio of sensors for different measurands 

2. Components for signal transmission and machine integration

3. Dedicated processs monitoring systems

4. Digital output signals to interact with the machine