Final Report Summary - MACHERENA (New tools and processes for improving machining of heat resistant alloys used in aerospace applications)
The main goal of the project MACHERENA was the improvement of the machining process of aeronautic heat resistant alloys by means of more efficient tools and processes.
Three materials families have been studied:
- Fe-Ni alloys. These heat resistant alloys, like A-286, are used in many structural components.
- Ni alloys. Two of the most relevant alloys are INCONEL 718 and IN100. Due to their high heat resistance, it is mainly used in aero engine parts.
- gamma-TiAl intermetallic. In its gamma phase is a good candidate for high temperature applications. Due to its high cost and high difficulty in machining very few applications can be found for this material.
This improvement has come by a reduction of the cost of the part by an extension of the tool life and reduction of the machining time by new cutting technologies. This was achieved by the application of new surface treatments on tools (nano-structured coatings), new cutting technologies combined with high pressure cooling systems and re-design of machining tools according to the new surface properties (hardness, friction, material adhesion, sharpness, etc.).
This has led to the following industrial objectives:
- tool life increase;
- reduction of production costs;
- increase of machining productivity (more advanced cutting parameters);
- optimal coolant utilisation;
- improvement of finishing quality.
The project objectives have been addressed by the development of new tool geometries, hard and low-friction nanocomposite coatings produced by PVD methods and new machining processes (high pressure cooling). At a first stage, the machining shops and end users collaborated with the research and development (R&D) centres and the tools and coating producers in defining which machining processes and tools will be used to evaluate the new developments:
- Inconel 718 roughing, finishing and drilling;
- IN100 roughing and finishing;
- A286 roughing, finishing and turning.
Two demonstrators were defined, as they were used at the end of the project to evaluate the performance of the new tools, coatings and machining processes. With the defined characteristics of the tools and their problems, the possibility of addressing new tool designs were evaluated, taking into account that these tools would be coated. A Taguchi testing approach was used to select the best coating geometries.
New nanocomposite coatings were developed, considering the special requirements specified by the end users and machining shops. The lines of the research were mainly three. The system AlTiSiN was optimised to cope with the demands of hardness and friction. An approach was also made to other compositions, where the Ti was substituted by other elements that have shown better friction behaviour (Zr, Cr), or where low-friction phases are added.
The developed nanocomposite coatings were tested in the laboratory facilities. The coatings were applied on both standard and newly developed tools, and the machining parameters that showed the best behaviour of the tool from the efficiency point of view were selected. The tools were also analysed to determine the failure modes, and this analysis acted as inputs for the coatings optimisation. One of the main efforts was done in avoiding the chipping failure modes on tools as this led to unreliable and little predictable machining processes.
At this point, optical microscopes, scanning electron microscopes (SEM), profilometry, roughness measurement devices, wear tests and metallography facilities were used. Furthermore, advanced machining processes, like high pressure cooling machining, was tested in the coated tools to increase even more the efficiency: tool lifetime, machining speed, etc.
The third leg of the testing table will consist on the real production tests performed at the machining shops. The results of these tests gave goof feedback information and helped the optimisation of both coatings and machining parameters. The final results were finally evaluated in the production of real parts (demonstrators).
The main achievements of this project have been:
i) Improved understanding of the nanocomposite coatings fundamentals, mainly focussed on the effect of impurities (e.g. oxygen) in the coating properties and the importance of having one monolayer of interfacial Si3N4.
ii) Development of new nanocomposite coatings that improve machining processes: nc-AlTiSiN, TiAlN, nc-CrAlSiN and AlTiCO.
iii) Machining processes are complex, and during this project the optimisation had to be focussed on many aspects, and the right combination of all of them resulted in the optimum cutting procedures:
- tool design: tool geometry;
- tool substrate: a compromise of a hard carbide able to machine difficult to cut materials but with a good toughness value to avoid cracks and brittle tool failure;
- surface preparation: this improves the tool cutting performance by optimising edge geometry and reducing stress;
- coating: that increases surface hardness, reduces friction or improves thermal performance of the tools.
iv) This has resulted in the development of new high performance tools:
- rough mill for Inconel and A286 alloys;
- rough and finishing mills for IN100;
- drill for Inconel.
v) Tool life of drills for Inconel has been increased over 50 % by using high pressure cooling, with pressures up to 120 bar.
vi) Increase of tool life by changing the wear mechanism from chipping (catastrophic) to continuous wear. This makes tool life much more predictable and decreases the risk of unexpected failure (which can cause severe damage in very expensive components).
Three materials families have been studied:
- Fe-Ni alloys. These heat resistant alloys, like A-286, are used in many structural components.
- Ni alloys. Two of the most relevant alloys are INCONEL 718 and IN100. Due to their high heat resistance, it is mainly used in aero engine parts.
- gamma-TiAl intermetallic. In its gamma phase is a good candidate for high temperature applications. Due to its high cost and high difficulty in machining very few applications can be found for this material.
This improvement has come by a reduction of the cost of the part by an extension of the tool life and reduction of the machining time by new cutting technologies. This was achieved by the application of new surface treatments on tools (nano-structured coatings), new cutting technologies combined with high pressure cooling systems and re-design of machining tools according to the new surface properties (hardness, friction, material adhesion, sharpness, etc.).
This has led to the following industrial objectives:
- tool life increase;
- reduction of production costs;
- increase of machining productivity (more advanced cutting parameters);
- optimal coolant utilisation;
- improvement of finishing quality.
The project objectives have been addressed by the development of new tool geometries, hard and low-friction nanocomposite coatings produced by PVD methods and new machining processes (high pressure cooling). At a first stage, the machining shops and end users collaborated with the research and development (R&D) centres and the tools and coating producers in defining which machining processes and tools will be used to evaluate the new developments:
- Inconel 718 roughing, finishing and drilling;
- IN100 roughing and finishing;
- A286 roughing, finishing and turning.
Two demonstrators were defined, as they were used at the end of the project to evaluate the performance of the new tools, coatings and machining processes. With the defined characteristics of the tools and their problems, the possibility of addressing new tool designs were evaluated, taking into account that these tools would be coated. A Taguchi testing approach was used to select the best coating geometries.
New nanocomposite coatings were developed, considering the special requirements specified by the end users and machining shops. The lines of the research were mainly three. The system AlTiSiN was optimised to cope with the demands of hardness and friction. An approach was also made to other compositions, where the Ti was substituted by other elements that have shown better friction behaviour (Zr, Cr), or where low-friction phases are added.
The developed nanocomposite coatings were tested in the laboratory facilities. The coatings were applied on both standard and newly developed tools, and the machining parameters that showed the best behaviour of the tool from the efficiency point of view were selected. The tools were also analysed to determine the failure modes, and this analysis acted as inputs for the coatings optimisation. One of the main efforts was done in avoiding the chipping failure modes on tools as this led to unreliable and little predictable machining processes.
At this point, optical microscopes, scanning electron microscopes (SEM), profilometry, roughness measurement devices, wear tests and metallography facilities were used. Furthermore, advanced machining processes, like high pressure cooling machining, was tested in the coated tools to increase even more the efficiency: tool lifetime, machining speed, etc.
The third leg of the testing table will consist on the real production tests performed at the machining shops. The results of these tests gave goof feedback information and helped the optimisation of both coatings and machining parameters. The final results were finally evaluated in the production of real parts (demonstrators).
The main achievements of this project have been:
i) Improved understanding of the nanocomposite coatings fundamentals, mainly focussed on the effect of impurities (e.g. oxygen) in the coating properties and the importance of having one monolayer of interfacial Si3N4.
ii) Development of new nanocomposite coatings that improve machining processes: nc-AlTiSiN, TiAlN, nc-CrAlSiN and AlTiCO.
iii) Machining processes are complex, and during this project the optimisation had to be focussed on many aspects, and the right combination of all of them resulted in the optimum cutting procedures:
- tool design: tool geometry;
- tool substrate: a compromise of a hard carbide able to machine difficult to cut materials but with a good toughness value to avoid cracks and brittle tool failure;
- surface preparation: this improves the tool cutting performance by optimising edge geometry and reducing stress;
- coating: that increases surface hardness, reduces friction or improves thermal performance of the tools.
iv) This has resulted in the development of new high performance tools:
- rough mill for Inconel and A286 alloys;
- rough and finishing mills for IN100;
- drill for Inconel.
v) Tool life of drills for Inconel has been increased over 50 % by using high pressure cooling, with pressures up to 120 bar.
vi) Increase of tool life by changing the wear mechanism from chipping (catastrophic) to continuous wear. This makes tool life much more predictable and decreases the risk of unexpected failure (which can cause severe damage in very expensive components).
