Traceable in-process dimensional measurement: The Project

Background

The accuracy of measurements on machine tools is affected by the unfavourable dynamically changing ambient conditions, vibration, noise, sound and light, that prevail in or close to the production floor as well as the high probing forces of measurement devices. Other factors include:

Existing machine tool calibration techniques are not sufficient to characterise and mitigate against the limitations of shop floor conditions.
Machine force and loads generate heat during machining operation and this hinders the application of machine tools as traceable and reliable measuring devices. Laser-based calibration techniques do not account for the measurement errors of the probing system, machining forces and heat loads.
Paucity of suitable procedures to assess the uncertainty of dimensional measurements on machine tools makes it impossible to rely on in-process measurement results, thus leads to long production downtimes and to high manufacturing costs.

This JRP will go beyond the state of the art by enhancing the accurate and traceable measurement of in-process dimensional measurements. It will:

Deliver standards and procedures for ensuring the improvement of measurement accuracy and the reliability of in-process measurement through the provision of robust and thermal invariant multi-purpose material standards.
Overcome the challenges caused by thermo-mechanical machine errors that are mostly induced by the effect of temperature variations within the machine through the provision of highly accurate, thermo-invariant multi-purpose material standards.
Provide a technique that surpasses the conventional research approach, which investigates machine tool errors under stationary and constant environmental conditions by robust procedures for mapping and correcting kinematic and thermo-mechanical errors at varying operational and environmental conditions.
Provide a novel, innovative mobile chamber for the simulation of varying shop floor environmental conditions.
Determine the uncertainties associated with “specific assigned measurement tasks”. This will cover the task-specific measurement uncertainties of size, form, and position measurements for different geometrical shapes such as sphere, cone, cylinder and plane.
Provide procedures that will enable the assessment of fitness-for-purpose and will empower the end-user to confirm reliably whether or not a machine tool is capable of manufacturing and inspecting machined work-pieces correctly without further laboratory measurements.

Need for the project

Traceable in-process dimensional measurements by machine tools offer high product quality, lower manufacturing costs, high productivity and prompt and real-life assessment of product quality. Measurement errors of machine tools are from different sources and are influenced by complex environmental factors on the shop floor. In order to adequately and accurately realise reliable and highly accurate measurement results on machine tools, this needs to address the following:

To address the known issues associated with measurement errors when measuring with machine tools on the shop floor including static, kinematic, thermo-mechanical, and dynamic machine errors and errors of the probing system.
To establish traceable in-process measurements on machine tools. The foundation of a traceability measurement is through the national standards provided by national metrology institutes (NMIs) to the industrial end-users. This requires the provision of a new generation of robust material standards, procedures and guidelines for the assessment of machine tool measurement performance directly on the shop floor.
To ensure the efficacy of machine tool acceptance, re-verification and decision making testsl: acceptance of a machine tool measurement performance requires series of tests. Fitness-for-purpose verification of a machine tool is required in order to determine whether it is meeting the specifications that ensures the go or no-go decision is made based on the obtained measurement accuracy.
To meet the need for high product quality at an economically advantageous cost.

Scientific and technical objectives

The scientific and technical objectives of this JRP comprise:

Establishing the scientific and technical background for developing standards and procedures for assessing and assuring the traceability of in-process measurements.

Developing methods for implementing high accuracy dimensional measurements on machine tools by developing high precision and robust material standards that can be used on the industrial machine tools that are used in the manufacturing industries and beyond.

Development of a portable shop floor chamber that is suitable for simulating environmental conditions on the manufacturing floor in order to prevent the adverse influence on the quality of the manufactured parts.

Provision of procedures and a good practice guide to ensure reliable measurement on machine tools.

Ensuring a smooth uptake of the project results through industrial demonstrations and the end-user involvement in implementation . This will focus on the potential economic and technological impacts in the manufacturing and machine tools industry and beyond.

The methods to be developed target a measuring accuracy of a few µm within a metre cube.

Expected results and potential impact

The ability to measure fabricated parts accurately ‘in-process’ will significantly improve and facilitate automation in Europe.
Enhancing ‘in-process metrology´ will provide market benefit and it will ensure that European companies remain competitive globally.
With the aid of the new environmentally controllable portable test chamber (large enough to house a medium size machine), industry will be able to verify the metrological performance of machine tools on site.
The test chamber facilitates and accelerates the verification of machine performance.
Reducing unnecessary scrap and reworking by improving the quality of manufactured parts, so that end-users can make better decisions about part conformance.
Improved in-process metrology means cost reduction.
Knowledge transfer and dissemination via stakeholder group, paper publications, conferences, workshops, best practice guides and the project web-site.
Training and dissemination of JRP knowledge via standardisation bodies, workshops, visits and exchange of staff.
Exploitation of the JRP’s results: new procedures on the quality assessment of in-process parts, machine performance evaluations, simulation of machine working environments.

Obtained results

The following main results have been achieved so far:

A summary of existing artefacts available on the market as well as other artefacts developed by industry and academic laboratories to areas of dimensional in-process metrology is achieved. The key JRP-Partners concerned discussed outline design concepts for the artefacts that are to be developed.
The investigation into the methods of in-process measurement verification that are available in different areas of in-process measurements has been started. The method of in-process measurement verification based on calibrated material standards applied in calibrated model of CNC machining tool is under development.
Design drawings and construction specifications for all proposed standards: 3D-MS, TSEM-MS, TSMU MS, WR-MS, FF-MS, and R-MS have been prepared. In addition, the required design data on the technical attributes, function, construction material, manufacturing techniques, uncertainties for all designed standards have been agreed. After discussions held, the JRP-Partners decided which standards will be manufactured.
A document has been produced which describes the evaluations of the optical properties of the different materials which are suitable for the manufacture of measurement standards, but notably appropriate for types TSEM-MS, TSMU-MS and 3D-MS. After much research, a report on the mathematical modelling of standards at different temperatures using FEA to detect potential problems has been written up.
The JRP-Partners worked on specifying the measurement and calibration tasks including the procedures and methods to be used for the calibration of the manufactured standard FF-MS.
A first specification of technical requirements and geometrical attributes for a mobile climate simulation chamber has been made. This specification is a result of intensive discussions with a machine tool builder who has performed first tests in the field of climate simulation. These requirements and information will be used as a basis for the design of the mobile climate simulation chamber.
The development of a mobile climate simulation chamber has the aim to simulate shop floor conditions to which a machine tool is exposed in daily use. Based on analysing the variety of influencing factors to be simulated, different concepts for the design of the mobile simulation chamber have been developed. By working on these designs it got evident that plenty of parameters related to the shell of the simulation chamber and of the air conditioning system have a strong influence on the finale performance and the usability of the chamber. Due to this, more time has been needed for the development of a final concept which is currently in the final specification.
The stakeholder committee has been formed consisting of members from industry and academia. A first meeting took place in May 2014 in Prague.