What Is In-Machine Measurement? An Overview of the Purpose and Examples of How In-Machine Measurement Can Help Solve Issues

What Is In-Machine Measurement?

In-machine measurement refers to measuring a workpiece inside the machine tool. In in-machine measurement, the workpiece is measured during the machining cycle using sensors such as a touch probe.

Performing in-machine measurement makes it possible to detect machining errors before many defective items are produced. By detecting machining errors, steps can be taken to prevent their recurrence, and the number of inspections required when an error is discovered can also be reduced.

In-machine measurement does not need to be performed for every item. For an automatic lathe operating 24 hours a day, in-machine measurement not only prevents machining errors before they occur, it also has the potential to significantly reduce the amount of inspection work required.

What Is Out-Of-Machine Measurement?

Out-of-machine measurement is a method of removing a workpiece from the machine and measuring it with a measuring instrument. Generally, measurements of the accuracy of machined workpieces are performed manually using instruments such as calipers, micrometers, and coordinate measuring machines.

With out-of-machine measurement, measurements are taken after the workpiece has been machined, so if a defective item is produced, the number of inspections may be enormous. Other disadvantages include the potential difference in inspection method and force used by inspectors, as well as human error.

In-machine measurement helps solve these issues in out-of-machine measurement.

Purpose of In-Machine Measurement

One of the reasons why accuracy may not be achieved during machining of a workpiece is thermal displacement of the machine. The expansion and contraction of ball screws and the change in shape of casts, etc. due to heat and temperature changes can cause deviations from the machining position specified on the NC, resulting in loss of accuracy.

Introducing in-machine measurement has the potential to prevent such problems from occurring. It is also useful in understanding the cause of machining errors, reducing the number of inspections upon detection, and identifying the cause of machining errors.

Allows Dealing With Machining Errors Before Defective Items Are Produced

When operating the machine continuously and the accuracy drops or a malfunction occurs, a large number of defective items will be produced. In-machine measurement makes it possible to stop the machine and take action to deal with the problem before such a situation occurs.

Additionally, measuring and correcting the machining zero point position inside the machine using a touch probe enables reliable machining accuracy without misalignment.

Quickly Understanding the Cause of Machining Errors

Regular in-machine measurements enable the identification of when a machining error occurred and allow for a quick determination of its cause. Quickly understanding the cause of a machining error is also useful in working out measures to prevent its recurrence as early as possible. Swiftly taking action to prevent recurrence can prevent similar machining errors from occurring in the future.

Reducing the Number of Inspections Required When an Error Is Discovered

When an error is found in a machined workpiece, it becomes necessary to inspect all the workpieces that have been machined consecutively, resulting in a lot of time and effort spent on inspecting for errors. Even if an error occurred, if it is quickly discovered through in-machine measurements, the number of workpieces that require inspection for errors can also be reduced.

Devices Used for In-Machine Measurement

In this section, we will introduce the types of devices used to measure inside machine tools.

Touch Probe

The touch probe, a contact sensor, is a device that can perform in-machine measurements again when the machining zero point has deviated due to thermal displacement of the machine, misalignment when loading and unloading workpieces, or errors during robot transport. Based on the measurement results, depending on the amount of misalignment, the workpiece can be reloaded, the machining zero point can be reset, or other steps can be taken, providing reliable machining.

Tool Breakage Detector

As the name suggests, a tool breakage detector is a device that detects tool breakage. Measurements with a tool breakage detector can prevent errors due to incomplete machining, such as machining not being performed according to the program.

Tool Length Measuring Device

A tool length measuring device automatically measures tools inside machine tools. Measurements with a tool length measuring device can reduce pre-machining setup time and prevent mistakes during setup.

ATC Runout Detection System

The ATC runout detection system is a system that uses a sensor to detect tool runout caused by fastening errors during automatic tool changer (ATC) operation or by chips getting caught inside, which are difficult to reproduce. The ATC runout detection system can prevent machining to dimensions different from the drawing and other errors.

Examples of How In-Machine Measurement Can Help Solve Problems

Using these devices through in-machine measurement to prevent various problems, some common issues in the cutting process can be solved. Below are five examples where introducing in-machine measurement helped solve a problem.

Example in Robot Transport

In a case where robot transport was used, there was a problem with the cutting tool breaking during drilling, caused by the tilt of the workpiece during transport.

Measuring height in the Z direction using in-machine measurement with a touch probe, and setting an alarm to go off and stopping the machine when a tilt exceeding the tolerance is detected, drill breakage was eliminated along with the outflow of defects. The ATC runout detection system is a system that uses a sensor to detect tool runout caused by fastening errors during automatic tool changer (ATC) operation or by chips getting caught inside, which are difficult to reproduce. The ATC runout detection system can prevent machining to dimensions different from the drawing and other errors.

Example of a Change in Machining Zero Point Caused by Difference in Workpiece Thicknesses Before Machining

This is a case where a change in machining zero point was caused by a variation in workpiece dimensions before machining.

Although the machine moves from the machining zero point according to the program, the issue was that stable production could not be maintained due to varying workpiece dimensions before machining.

In this case, the problem was solved by measuring the height with a touch probe and resetting the machining zero point before machining. Using in-machine measurement with a touch probe, the machining zero point can be changed to match the dimensions of each workpiece.

The measured workpiece thickness is saved in a macro variable and can be used for subsequent machining.

Example of Machining Not Being Performed Even When the Program Is Run

This is a case where the machine itself is working according to the program but machining is not being performed. The reason for this may be a broken tool.

However, because the machine door is closed during machining, it is not possible to check whether the tool is broken. Using in-machine measurement, it is now possible to check whether the tool is broken by placing the cutting tool against the measuring device before machining. With in-machine measurement, the tip can be searched and measured even without inputting the tool offset. Additionally, tools larger than the tool contact surface of the measuring device can be offset and measured.

By measuring tool length and tool breakage through in-machine measurement, the outflow of defective workpieces can be prevented before they occur.

Example of Time-Consuming Setup for Tool Length Measurement

Using a tool presetter to manually measure a tool outside the machine takes about 20 minutes. Moreover, manual measurement can lead to human errors such as incorrect tool numbers.

With the introduction of in-machine measurement, 21 tools can now be measured in just 90 seconds. Implementing automatic measurement of all tools makes it possible to shorten work times and improve setup quality.

Example of a Machined Hole Larger Than Dimensions and Other Unexpected Problems

When a machined hole is larger than the specified dimensions or other unexpected problems occur, the likely cause is tool runout.

Tool runout can be caused by fastening errors between the cutting tool and holder, chips getting caught in the spindle taper, and other factors. The ATC runout detection system is useful for solving this kind of tool runout. With an eddy current sensor attached to the head, an alarm goes off when runout is found in the tool, notifying the user of an abnormality. This prevents the outflow of defects caused by unexpected problems.

In-Machine Measurement Helps Prevent Machining Errors and Enables Faster Setup Effortlessly

Machining errors that lead to lower productivity are considered a management risk.

Switching from out-of-machine measurement, which requires a lot of time, effort, and operators, to in-machine measurement, which makes it possible to measure workpieces and tool lengths inside the machine tool, not only prevents various machining errors, but also shortens the time required for pre-machining setup and improves quality.

Consider introducing in-machine measurement as a strategy to reduce costs and improve productivity.