Automated Polishing for the European Tooling Industry
The poliMATIC research project has received funding from the European Community´s 7th Framework Programme (FP7/2007-2013) in the call
Establishing a metrology frame-work Metrology for objective characterization of polished surfaces
A method for grouping measurement systems for control functional surfaces of laser- and robot polishing is established, so called "Stedman diagrams". The diagram express in an easily interpreted way the instruments´ ranges and resolutions in the lateral and vertical axis.

The Steadman diagrams will be used to enable selections of the optimal equipment needed to characterise the surfaces in this project.

Implementation of optical metrology in the laser- and robot processes

• Laser polishing need complete mapping of laser waves on the whole polished surface to detect wavelengths between 300-2000 µm with a lateral resolution of 100 µm and vertical resolution approx: 0,2 µm.
• Robot polishing need to firstly identify the roughest area over the polished surface and then measure it in order to aid the polishing process needed for a following polishing step. For example to set the polishing variables: grain size, paste type, polishing time and force.
• Robot polishing roughness to measure for the initial process steps is in the range of Ra = 1 - 100µm. Nanometer range Ra measurements are only required at finishing steps.

Investigation of different measuring systems suitable for laser-, robot- or manual polished surfaces

The interferometric point sensor
The point-scanning interferometric sensor allows vertical measurements in the nm range as can be seen in the Stedman diagram.

The line sensor will permit a large reduction of the measurement time, especially for the more rougher surfaces in the initial polishing steps

Interferometric sensor (left) and nano-scratches on glass (right) with a "zoomed" 3.2 nm deep scratch.

The interferometric line sensor
Each of the 180 white light source pinholes used in this sensor are imaged through a common chromatic objective, into a continuum of monochromatic images along the optical axis, thus providing a series of »color coded« optical axes.

When an object is placed in these colored fields, a unique wavelength is perfectly focused at its surface for each point, and then efficiently reflected into the objective. These monochromatic light beams go through a series of filtering pinholes into an array of spectrographs.

The analysis of the wavelengths that have passed through the filtering pinholes allow for each point to accurately determine its position in the measuring field.

This line sensor then provides instant profile measurements, each profile being made of 180 points simultaneously acquired. A complete measuring of a products´surface at the highest resolution will provide large amount of data in a large amount of time but most of the information won´t be used.

The interferometric point- and a line sensors were introduced by Altimet.

Scattering instrument
A scattering instrument has been developed to measure statistical surface structures over a larger area. The philosophy of the scattering instrument is to be as simple as possible to make it robust and useful in harsh industrial conditions. The functionality of the new instrument has been shown and it is now ready to be produced and tested on-line in industrial conditions.

The instrument is especially useful for quality statistical measurements over large areas. It is estimated to be both fast and robust. Presently some additional real-time programming is required to make it available for on-line measurements.

The shape and intensity scattered laser light (top right) will be interpreted by the instrument as a secondary indication of the roughness for comparative purposes e.g. for supporting the manual polisher or the laser/robot polishing with robust feedback of the status of the surfaces being polished.

For example laser and robot polished surfaces, measured with the scattering interferometer using different magnifications are presented in the pictures below.

The polarization interferometer
A new polarization interferometer is being developed and tested in lab. Also a white light interferometer was constructed as part of this work.

The polarization interferometer is estimated to be ready for on-line tests by the end of 2011. A photo of the laboratory set-up is shown together with the first light topographic image in the figure below. The topographic data have been phase unwrapped to increase the range to more than three wavelengths (0-2 micrometers with a resolution of better than 1 nanometer).

Develop a novel characterization system
A recently developed system presented by Uddeholm Tooling at the 2´nd Polishing workshop in Aachen 2010 for description of different defects on polished surfaces has been adopted for test in the poliMATIC-project.

An uniform and general classification of surface defects of polished surfaces are of great importance to enable easy communication.

Establishing a metrology framework for in-machine control of laser- and robot polishing

Development of an interferometric point scanning device and integration in laser and robot applications
Design solutions for the integration of the interferometric point scanning probe to control the laser polishing as well as for the polishing robot has been developed. The hardware and software are now tested for installation in poliMATIC demonstrators.

The optical point scanning instrument here in a simulated integration in the laser polishing device at Fraunhofer ILT (left) and mounted in the polishing robot at IPT (right).

Development of the laser scatter device for in-process control
A scattering instrument has been developed and integrated on the robot arm at the Fraunhofer IPT Institute. The figure below shows the installation with the measurements being done with the robot arm.

In-line measurements of the robot polished surfaces in progress. The scattering sensor is here replacing the polishing head during a break in the polishing sequence for test of feed-back measurements and the initial installation.

Development a novel general characterisation system for polished surface structures −aiming at in-line feed back of topography data
Off-line investigations have been made with robot and laser polished surfaces. The figure below shows a laser robot part of 100x100 mm which has been polished in four different ways. The surface is shown here to the left as coloured areas indicating the significant differences of scattered laser light appearance at different parts of the surface.

Scattering measurements of a robot polished part. Left panel shows the measurements as evaluated from the laser scattering instrument; right panel shows an image of the part.

A number of spot measurements on the surface of parts polished with Laser and Robot techniques has been evaluated.

Scatter intensity maps were developed in order to illustrate clear differences in the scatter meter response to surface structure −see the figure below.

The scatter intensity in scatter angle and spatial frequency for three differently polished samples.

last update 2013-03-14 © poliMATIC 2010