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Content archived on 2024-05-29


Final Report Summary - TAF (Turn and finish - development of a combined hard turning and superfinishing technology)

The main objective of the TAF project was to develop a combined process of high-precision hard turning and superfinishing in an integrated machining centre to permit a flexible production of high-precision parts made of hardened steel. The combined hard turning and superfinishing process (TAF) will substitute the current process chain of grinding and superfinishing, leading to a drastic reduction of non-productive times and thus to a significant increase of the productivity of the end users of the technology.

The achievement of the objectives would require the development of an innovative technology, which will encompass the following:
- development and integration of a compact superfinishing device into a high-precision lathe;
- combination of the kinematics of a high-precision lathe equipped high-frequency direct motor drives with the kinematics of the compact superfinishing device;
- machining technology development and optimisation;
- optimisation of superfinishing tools.

Besides contributing to an improvement of the bonds between Member States and candidate countries and to a considerable increase the competitiveness of the participating small and medium-sized enterprises (SMEs) the project will encompass scientific, technical and societal objectives, which can be summarised as follows:
- a better scientific and technical knowledge of superfinishing;
- an expansion of the use of superfinishing to other engineering applications and, consequently, enhancement of the life time and reliability of components, machines and other mechanical systems;
- a significant reduction of the use of emulsions in the machining process by using only one machine instead of many;
- The risk of inhaling hazardous oil mist produced in grinding operations increases if the worker spends long time trying to align the parts after re-clamping; by producing parts by means of turning and superfinishing on only one machine, this risk will be considerably reduced and thus there will be an improvement of the health condition of European workers.

The two end-users in the project consortium (Cerobear and HWG) are both producing high-precision bearing components and complete bearings. Since both are using different strategies and process chains the TAF process has to be compared differently to both process chains for the technical and economic evaluation. Cerobear is only using the hard turning technology for their production and HWG is already using a process chain consistent of hard turning and honing but on two different machines. The evaluation was calculated for producing 50 raceways.

Technical and economic evaluation - Cerobear
For the evaluation the following values were provided by Cerobear for turning one raceway:
- process time: 300 s;
- achievable roughness: Ra 0.05 micrometre < 0.07 micrometre
- necessary tool change: after 10 raceways;
- time for tool change: 5 - 10 min (300 - 600 s).

It can be stated that by means of the TAF system a reduction of production time by approx. 83 % and a reduction of tool costs of approx. 79 % is possible. Additionally it has to be asserted that with the TAF system better surface qualities are achieved reliably compared to the actual process chain used by Cerobear.

For the evaluation the following values were provided by HWG for turning and honing one raceway:
- process time: 40 s;
- achievable roughness: Ra < 0.05 micrometre;
- time for machine change: 250 s (5 s per part);
- time for honing machine set-up: 240 min.

It can be stated by means of the TAF system a reduction of production time by approx. 76 % is possible. The tool costs for both processes are comparable.

The final conclusions regarding the results of the project were:
- combined machining of hard turning and honing of bearing rings (inner and outer machining) by means of the TAF system is possible;
- the defined restrictions concerning dimension and form of the machined workpieces could be attained;
- the aim concerning the surface roughness defined during the kick-off meeting of Ra = 0.02 micrometre can be reached with the TAF system;
- the surface roughness after turning has an effect on the outcome of the subsequent honing process;
- best results by means of the TAF process could be achieved with roughness values of Ra = 0.1 micrometre after hard turning;
- surface roughness values (Ra > 0.1 micrometre) achieved with hard turning can be compensated by longer honing time to attain desired final roughness values;
- manufacturing times for the raceway of a bearing ring can be cut up to 83 %;
- tool costs can be cut up to 79 %.

For a commercial and industrial use of the TAF system the following suggestions were made:
- smaller overall size of the honing device to fit into a Hembrug 50 CNC;
- capability for different workpiece sizes (bigger and smaller diameter);
- a simple solution for setting or adjusting the honing frequency and amplitude in the lathe control and NC programmes;
- an absolute way-measurement system for the honing device;
- internal coolant (emulsion) supply for the honing operation capable for inner and outer honing operations.

As final result of this project it can be asserted that the project aims have been reached completely.