Robots match "black art" of surface finishing

Six-axis robots are now capable of matching the performance of highly skilled manual grinding and polishing operations to produce precision components with tolerances down to 0.04mm and less.

Six-axis robots are now capable of matching the performance of highly skilled manual grinding and polishing operations to produce precision components with tolerances down to 0.04mm and less with a surface finish of better than Ra 1.4mm.

High precision surface finishing has been a sector of manufacturing where a certain amount of 'black art' has remained part of the accepted scene.

Highly skilled grinders and polishers long service men would carefully, using all their experience, make the final metal removal passes on the aerofoil, turbine blade or medical implant to produce a finished component to the closest tolerance and highest quality surface finish.

Staubli's RX range of six-axis robots are now making inroads into the manufacturing lines for these high precision components and challenging the assumption that manual finishing is still necessary.

RX robots are currently operating successfully in the production of a wide range of aerofoils, turbine blades and machined parts for aerospace and other precision engineering sectors.

Reject rates have been dramatically reduced and of course the robot can operate consistently and reliably on a 24/7 basis.

One of the main drivers behind this breakthrough is the availability of CAD drawings, which can be used as a master reference file for each actual component, indicating exactly where the final metal removal is required.

The actual component to be machined is compared to the 'perfect' model held in the CAD file and the robot movements derived from the difference.

This method is faster and more accurate than having to programme separately the robot's trajectory for each component.

Staubli's V_CAT computer aided trajectory software allows rapid programming, process simulation and robot trajectory generation.

Using CAD models the entire process can be programmed offline.

An additional benefit is that feasibility, accessibility and collisions can be validated and precise adjustments made to match specific component features.

Medical implants typically for hip or knee joints are manufactured either by investment casting, forging or CNC machining, these are subsequently deburred, precision ground and polished.

Delicate grinding of specific areas is necessary to ensure the precise angle for each joint, the use of a robot arm can provide improved access to difficult to reach areas.

Precise stock removal minimises the extent of the mirror finish polishing operation, which completes the processing sequence.

Turbine blades for use in power generation or aerospace require fine grinding or fine belt polishing following the initial forging and CNC machining operations.

The tool tips used in machining produce a series of ridges and waves on the critical surfaces of each blade.

Robot controlled stock removal eliminates these surface imperfections to achieve a very smooth surface finish up to Ra 1.6/2.0mm levels or better.

The blending of aerofoil sections with the platform of the blade, frequently involving a tight radius and negative angles is a particularly difficult task.

Small tools are required which need to be changed frequently and speed of processing is critical to avoid heating the component to a degree that may jeopardise the tight tolerances.

Manual operation for these applications is a very slow process and results in a high level of rejections.

Robot stock removal, following faithfully a complex trajectory, eliminates these problems producing consistently high quality components to tight tolerances with significantly lower rejection rates.

The repair of turbine blades is an important market where robot precision is benefiting manufacturers.

Staubli provide offline programming using detailed 3D modelling software for planning the robot movement paths, access to the relevant CAD file provides the data for comparison with scans of the actual blade to be repaired.

The shape of the blade is closely controlled giving a longer service life and improved air/gas flow performance.

Robot based manufacturing produces consistent components with high precision, recognising the critical areas, for example, adjusting the applied pressure and taking extra care on thin sections to avoid distortion.

Replacement turbine components are often milled directly from bar stock since there is rarely sufficient time to obtain forgings.

Six-axis robots have the adaptability and functionality to be readily programmed to deal with this change in manufacturing route, producing components identical to the original.

Staubli RX robots are compact, capable of high speed and robust with a rigid mechanical structure.

They can be floor, wall or ceiling mounted and provide a wide spherical work envelope.

Repeatability, measured to ISO9283 standards, is +/-0.02mm.

Precise trajectory control enables the robot to accurately grind, polish or buff components with the most complex geometry.

The recruitment and training of precision grinders and polishers is proving increasingly difficult, manufacturers of high precision components are seeking to reduce or eliminate completely the need for this highly skilled manual processing.

The inherent accuracy and precision of the Staubli RX six-axis robot is proving ideal for the automation of these demanding tasks.

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