How to Check Machining Accuracy on the Machine?

Touch probes provide more support in achieving on-time, high quality and cost-efficient production than just part set-up, meaning that verification of the geometric accuracy of machined parts directly on the machine is equally valuable.

Through this direct accuracy check, programming errors and tooling defects, as well as adverse consequences of the machining process, can be quickly detected.

However, such inspection methods are often not used because of the complexity of the programming or lack of trust in the accuracy of the machine.

While the basic accuracy of the machine is an important prerequisite for the machining of precision parts.

Therefore, the machine should be checked (reviewed) periodically by the geometrical parameters such as a laser interferometer.,

For such measures, Renishaw recommends a laser interferometer system, the ML10 GoldStandard.

In addition, QC10 circular gauges should be used periodically for inspection.

Thus, the subsequent measurement on the machine also creates conditions for process control.

The measurement on the coordinate measuring machine only indicates whether the workpiece has been machined in accordance with the requirements.

It is not possible to distinguish between the effects produced by the machine, the tool and the process.

If machining deviations are measured for a part, it is difficult to determine the actual cause of the deviation.

Therefore, appropriate or necessary corrective measures cannot be reliably derived from the results of such measurements.

Measuring tasks on machine tools

There are basically four typical user requirements for measuring tasks in machine tools:

(1) It is simply the setting or tooling of a workpiece.

(2) It performs a number of incidental measurement tasks based on drawings, where the measurement cycle is integrated into the program flow, controls the process based on the measurement results, and simply outputs the measurement results.

(3) All measurement tasks are directly and completely integrated with the machining program, and the machining is controlled according to the measurement results, the program is prepared according to CAD data, the collision inspection is carried out through graphical simulation, and the measurement results are output in the form of tables.

(4) After processing, the geometric accuracy of the workpiece is inspected, programmed according to CAD data, collision checked through graphical simulation, the measured values are statistically, analytically and processed, and the results are expressed and analyzed in the form of tables and graphs.

Thus, Renishaw’s measurement technologists offer several packages designed to meet different requirements.

If the user only wants to set the workpiece and measure the tool, then the widely popular cycle measurement package for control should be used.

With this package, part set-up and tool measurement can be easily and conveniently programmed.

Control accuracy instead of just checking the accuracy

At Renishaw, the software family productivity can be independent of the machine control system employed.

And with the support of graphical interaction, it is very simple to program all the measurement programs of the milling machine.

The ActiveEditor and ActiveEditorPro are used to incorporate all workpiece and tool measurement programs into the machining program with the input of additional CAD data when programming the program.

Thus, these programs can be adjusted to the process by direct feedback of the measurement results.

This not only makes it possible to correct the machine’s coordinate system and tool data, but also to implement logical decisions based on these data to a certain extent automatically, without the need to recognize the instructions required for control.

In this way, the simple and hierarchical structure of the rules also allows the user to use special NC commands without the need for detailed knowledge of the program structure.

For this purpose, the operator interface provides suitable predetermined values and checks that all absolutely necessary inputs have been implemented.

It is only through the operation of the post-processor that the program and the instructions for the selected control are generated.

As a result, individual parameters can be precisely adjusted as if they were reversed when there is a sudden change in the machine’s machining schedule.

With the CAD input ActiveEditorPro, not only does it simplify programming further, but it also allows for a complete representation of the measured motion and a measurement simulation including collision check.

This simulation also considers the clamping tool.

Measuring and recording accuracy

After machining, in order to inspect the sample directly on the machine, When inspecting complex or large parts, Renishaw has developed Renishaw OMV software in collaboration with the CAD/CAM experts at Delcam UK.

By clicking on the features and surfaces of the entered CAD part model, the OMV software generates the required measurement program.

For example, ActiveEditor provides predetermined values suitable for actual use, and conducts credibility testing during input.

After data entry, the program displays a graphical simulation of the measuring procedure, which undoubtedly increases the user’s confidence in the correctness of the measuring process.

It utilizes a highly accurate resistive strain-gauge based spindle-trigger probe in all measurement directions.

With the new compact OMP400, for example, or with the proven MP700 touch-trigger probe, points on the surface are measured, and the measuring instrument then transmits the data to the PC.

The analysis and processing of the data are done by means of a special measurement calculation method, which is similar to that of a CMM and can therefore also be used to measure complex free-form surfaces.

For this reason, the touch-trigger probes MP700 and OMP400 not only need to be calibrated in all vector directions, but can also measure in all vector directions right away.

This also improves cycle times very significantly, as each part must have a small number of measuring points.

Based on the CAD model, Renishaw’s OMV software not only indicates the measured deviation, but also indicates the value of this deviation in colored dots.

These points produce a colored graph that enables a quick judgment of the accuracy of the part, which provides numerous possibilities for statistical analysis and a graphical representation of the measurement results.

A set of measurement points can be adapted to the CAD model (optimal fit function) to avoid errors during part set-up and datum selection.

As a result, errors can be identified and corrected before the part is removed from the machine.

The possibility to check the dimensional accuracy of workpieces in various machining states not only saves time but also increases the reliability of the machining.

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