CNC Machining: In-Process Measurement

Types of Measuring Devices

In-process measuring devices can be categorized in two ways. Some are used to measure the tool that is doing the cutting and others are used to measure the part that is being cut. All of these measuring devices can be used prior to cutting, during the cutting process and once the part is completed. Throughout the manufacturing process, these devices provide important information about set up positioning, tool identification wear or breakage, dimension or tolerance verification and even surface texture analysis.

• Measuring devices used to measure/check the tool before, during or after the cut: 
  
  • Contact tool setters
  • Non-contact tool setters (laser measuring systems)
• Measuring devices used to measure/check the workpiece before, during or after the cut: 
  
  • Workpiece touch probes
  • Scanning probes
  • Roughness gauges
  • Bore gauges

Contact Tool Setters

Tool Setting Probes are typically mounted on the table providing an economical, contact-based tool setting solution inside the machine. They provide simple tool geometry by measuring the tool’s length and/or radius offset, wear and/or breakage. A CNC program cycle performs all necessary movements to and touching off of the tool. Contact tool setters can be hard wired or wireless and are tied to an interface module which is connected directly to the machine’s control. If the wear tolerance has been exceeded, the software program will alarm the machine. Multiple tools can be measured within the same CNC program and on the same machine tool offering:

• Tool wear
• Tool length and radius measurement
• Tool breakage detection
• Thermal compensation

Non-Contact Tool Setters (Laser Measuring Systems)

Laser Measuring Systems are typically mounted on the table providing a non-contact tool setting and tool monitoring solution inside the machine. Based on the application requirements, these systems can also be mounted using a bracket or mobile unit if needed. Laser Measuring Systems provide data which can be used to analyze tools of various shapes and sizes. As a tool enters the laser beam, these systems continuously measure the shading of the beam to gather data. This type of system can compensate for spindle drift and runout errors that may occur during the manufacturing process. Laser Measuring Systems are hard wired and are tied to an interface module which is connected directly to the machine’s control. Multiple tools can be measured within the same CNC program and on the same machine tool offering:

• Tool identification
• Tool wear
• Tool length and radius measurement
• Tool breakage detection
• Single cutting-edge monitoring
• Thermal compensation
• Preventative maintenance information
  (spindle health, tool life, etc.)

Workpiece Touch Probes

Touch Probes set workpiece origin and measure features on the machined part to verify if component dimensions are within tolerance. Touch Probes inspect the workpiece by touching the part in various predetermined locations based on the CNC program cycle. Probes are mounted in the machine’s spindle and once the part is touched, the probe is triggered and a value is recorded based on the location of the part.

A variety of accessories are available for Touch Probes to expand their capabilities based on a user’s specific application. For example, a crank stylus can be used to record values based on a push-pull method. Also, holes or pockets within a workpiece can be measured by adding an extension onto the Probe therefore allowing the device to reach into deep cavities.

Touch Probes are connected to the machine tools control wirelessly, communicating via infrared or radio. The CNC program can be modified to measure various workpieces within the same machine tool providing:

• Part set-up
• Workpiece measurement
• Thermal compensation
• Tool wear compensation

Scanning Probes

Scanning Probes are similar standard Touch Probes because they verify shape dimensions, but they use a different process. Instead of recording values based on various touches to the part, Scanning Probes actually scan the part, recording a constant stream of data to create a comparative measurement between a master part and the workpiece. This system then provides pass or fail feedback directly onto the machine’s control. Mounted directly into the machine’s spindle, Scanning Probes communicate wirelessly via radio with the machine tool’s control. The CNC program can be modified to scan various workpieces within the same machine tool providing:

• Contour scan
• Shape profile
• Detection of part discontinuity

Roughness Gauges

Using a similar process to Scanning Probes, the Roughness Gauge inspects the surface finish of a workpiece inside the machine tool and provides feedback directly to the machine’s control. This type of measurement device uses a pulling movement to measure the amount of deflection as it relates to the distance traveled to evaluate the surface texture of the part. Data generated can provide valuable information related to the cutting parameters which can provide insight to improve the manufacturing process. Roughness Gauges are mounted directly into the machine’s spindle and can communicate with the machine tool’s control wirelessly. The CNC program can be modified to measure various workpieces within the same machine tool providing:

• Roughness measurement

Bore Gauges

Bore Gauges are used to measure bore diameters during mass production of identical workpieces. This device uses floating sensors to record measurement data once positioned within a bore. Measuring heads are usually custom designed based on the application and bore size. Bore Gauges can be mounted directly into the machine’s spindle but this isn’t a requirement. The device generates measurement data independent of the machine tool’s positioning therefore it can also be mounted outside of the machine tool, on a robot arm for example. This system communicates directly with the machine tool’s control wirelessly. An individual measuring head is needed to measure each diameter size, but a multi-step measuring head can be used for an application where a single part includes multiple diameter sizes.

• Diameter measurement
• Position measurement
• Roundness measurement
• Cylindricity measurement
• Concentricity measurement

Where are these measurement devices most effective? 

Automotive
As automotive manufacturers race for optimized productivity, efficient lights out operation under the highest production standards is a key metric. One thing is clear: time is money! Integrating in-process metrology technology enables automated measuring and inspection, allowing for unattended 24/7 machining therefore reducing cycle times and overall cost.

Medical
Many medical products involve complex geometries and extremely tight tolerances. Therefore, these parts can have long and costly cycle times. Compromises between safety and machining time don’t have to be made when incorporating a measuring device into the process. Verifications of workpiece dimensions occur automatically, saving time and reducing scrap without sacrificing quality.

Wind Power & Energy
In the Wind Power and Energy sector, many workpieces are extremely large in scale. Any machining errors that are detected outside of the machine tool can likely only be corrected at a considerable extra cost. Detecting possible machining errors in the original setting, therefore enabling immediate rework, proves to be invaluable in this industry.

Aerospace
In the aerospace industry parts are often made from extremely hard or heavy materials such as titanium or Inconel. Using these types of materials often result an increase in tool wear and/or breakage. Utilizing a measuring device to monitor the health of your tool can help you get the most life from the tool.

Mold & Die
In the Mold and Die industry any deviations are ultimately reproduced at the same scale in the end product. Measurement devices can be used to detect deviations at the original setting stage to avoid costly rejects. In addition, these devices can be help minimize the post-process manual adjustments, such as polishing, which often are a timely and costly piece of the manufacturing process in this industry.

The price point of different measuring devices:

The exact price of an in-process measuring system depends on a number of factors. The machine model and control type should be considered, as not all machine tools have the ability to utilize all measuring device types. Other considerations should be made based on what type of system is required: contact or non-contact. Similarly, the cost for a system could be affected by whether it utilizes radio or infrared communication with the machine’s control. Also, consider your application. As noted, there are a variety of measuring devices, each with individual features and benefits. Considering what is most important in your manufacturing process whether that be cycle time, tolerance allotment, automation or overall cost, will be important factors to consider when deciding what system is best for you.

Price points vary widely after considering all of the factors listed above. For example, a standard contact-based tool setter can have a starting price around $2,500, excluding any installation costs. Whereas a non-contact laser measuring system is more likely to start around $10,000, excluding installation. The price increase is largely based on the additional capabilities a non-contact laser measuring system can offer.

Similarly, Touch Probes might have a starting price around $7,000 excluding installation. When upgrading to a Scanning Probe with additional technology, the price will likely increase. As for Roughness or Bore Gauges, these devices are custom designed and rely heavily on each individual application and needs. Therefore, the price can vary greatly.

It’s important to remember that in-process measurement devices can not only help the implementation of a continuous process chain through automation, reducing the need for manual intervention throughout the process, they also help ensure you produce the right part the first time.

If you're interested in pricing for your specific application, please request a quote.