MagForming - Development of New Magnesium Forming Technologies for the Aeronautics Industry

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Figure 1. The official MagForming logo.

Introduction MagForming was a 38 month research and development program funded by the European Union under Framework Six Priority 4 Aeronautics and Aerospace. The project began in August 2006 and will conclude September 2009.

The purpose of MagForming was to advance the state of the art in the technology of plastic processing of wrought magnesium alloys for aeronautical applications. The program was focused on six key fabrication methods: forging, super plastic forming (SPF), pad forming, roll bending, deep drawing, and creep forming. The measure for attaining the objectives has been the fabrication of nine aerospace prototypes demonstrating each forming process.

The program is a collaboration of 12 organizations, listed below. These include aerospace OEMs, tier one suppliers, material suppliers and academic institutes. The program was established, and is being coordinated, by Palbam-AMTS who are a tier one supplier to the aerospace industry of both aluminum and magnesium components.

MagForming collaborative partners: • Palbam-AMTS, Israel; • EADS Deutschland, Germany; • Magnesium Elektron Ltd. UK/ Magnesium

Elektron North America; • Airbus Deutschland GmbH, Germany; • Israel Aerospace Industries (IAI), Israel; • SMW Engineering, Russia; • Chemetall, Germany; • Ultratech, Poland; • Alubin, Israel; • Liebherr Aerospace, Toulouse, France; • Charles Univ. Prague, Czech Republic; • Institute of Metal Forming and Metal-

Forming Machines, Leibniz University Hannover, Germany;

MagForming was divided into ten work packages (WP), each dealing with a different forming process or aspect of the project, see

below. This paper sets out to give an overview of each of the forming related WP, describing the prototype and its fabrication methodology. It should be noted that a full description of the work carried out for each of the WP is beyond the scope of this paper. For further details the reader should contact the authors. Work Packages: • WP1 Program Management • WP2 Specifications and Requirements • WP3 Forging • WP4 Super Plastic Forming • WP5 Pad Forming/ Roll Bending • WP6 Deep Drawing • WP7 Creep Forming Integral Structures • WP8 Testing and Validation • WP9 Dissemination and Exploitation • WP10 Assessment and Review

Each WP is described in more detail below. WP1-Program Management, WP8-Testing and Validation, WP9 Dissemination and Exploitation, and WP10 Assessment and Review will not be covered in this paper as they are either not entirely relevant or have not been started as part of the program of work. Review of Forming Process Development WP2 Materials Specifications and Requirements The design process of magnesium prototype components selected by MagForming is shown in Figure 2. This started with material characterization at the academic institutes, enabling alloy systems to be paired with suitable forming processes. The individual components were then matched with a given forming process suited to the geometry being produced. Finite element analysis, employing data collected from the materials characterization, was applied to fine tune the forming process for the parts and aided the design of tooling. Parts were then formed, generally in two alloys, using AZ31B as a control. The finished parts were then analyzed to establish their suitability for the end

application, i.e. tolerances, mechanical properties, surface finish, etc.

Figure 2. Magnesium prototype component design process chain. The alloy systems for the prototypes were selected based on data published by MagForming’s sister program Aeromag, whose primary goal was to demonstrate that magnesium is a suitable engineering material for the aeronautical industry. From this data, and in combination with other work published in the literature, magnesium alloy systems were selected for each forming process. WE43, AZ80 and AZ31B were selected for WP3-Forging due to their high strength; AZ31B was used as a control. ZK10 and AZ31B were applied to WP4-SPF. ZK10 has been shown to demonstrate greater SPF performance over AZ31B whilst maintaining equivalent mechanical properties (Alderman et. al.2006). ZK10 has also been applied to creep forming as this process shares similarities with SPF; both are based on a creep related flow process. Results from Aeromag and the literature (Bohlen (2007);Senn (2008); Wendt (2009)) indicated texture modification and improved formability of ZEK100 relative to AZ31B and as such this alloy was selected for deep drawing applications and rubber pad forming. All of the forging stock and sheet alloys were supplied by Magnesium Elektron. A number of extruded sections were supplied by Alubin for the creep formed demonstrator fuselage panel.

WP3 Forging Development of forging was carried out via the fabrication of three different prototypes, demonstrating large, medium and small forging applications. Part of the evaluation program for forging magnesium involved the assessment of modern die lubricants for the process. This work was carried out at IFUM who employed ring testing to measure the effectiveness of two modern lubrication systems. A schematic of the test set up is shown in figure 3.

The lubrication systems tested were supplied by Chemetall in the form of a pretreatment, Gardobond X4729, and a high temperature lubricant, Gardolube 6300. The lubricant was tested with and without the pretreatment. IFUM found that the lubrication systems showed a good performance during the magnesium forging process. Examination of the temperature dependence up to 440°C (824°F) showed a slight increase in the friction between tool and specimen at higher temperatures. Analysis of forged specimens showed that the lubricant film was still present after the forging tests. Furthermore the Gardobond X4729 pretreatment resulted in a reduced friction in comparison to a standard lubrication alone and facilitated easy removal of the coating after forging. � The large forging prototype was an Airbus A340 window frame, fabricated from AZ31B and AZ80, see Figure 3. The tooling for the

Figure 3. Schematic of the high temperature lubrication testing via the forging of rings carried out at IFUM.

window frame was machined by Ultratech in Poland. These were shipped to SMW Engineering in Russia, who are specialists in the forging of magnesium alloys. Demonstrator parts had not yet been fabricated at the time of writing this paper.

The medium size forging prototype part was the pre-form for a compressor impeller from an air-conditioning system assembled by Liebherr Aerospace Toulouse, see Figure 4.

The medium scale forging prototype was formed by the Institute of Metal Forming and Metal-Forming Machines (IFUM) at Leibnitz University Hannover. This prototype was net shape forged. Modeling was used to calculate the size of the blank required to fill the die at 100% closure of the tool pieces. The AZ80 part was formed at 280-350°C (536°F-662°F) with a ram speed of 10mms-1 in one forging step. The WE43 part was formed at a slightly higher forging temperature range, 300-400°C (572°F- 752°F), to allow for its higher elevated temperature strength. The ram speed was 10ms-1 and the pre-form was forged in one step. These pre-forms were machined into the final impeller part and at the time of writing this paper were being tested by Liebherr.

The small scale forging prototype was a door stop for the Airbus A380. This part was net shape forged at IFUM using similar principles to the compressor wheel. This part was more challenging due to its complex shape. The part was formed in AZ80 and WE43 using temperature ranges of 300-320°C and 300-350°C respectfully. The ram speed was 5mms-1 and the part was forged using a two step process.

Figure 6. WP3 Small scale forged part, Airbus A380 door stop fabricated in both WE43 and AZ80.

Figure 3. WP3 Large forging prototype. Engineering drawing of an Airbus A340 window frame. This part will be forged from plate feed stock in both AZ31B and AZ80.

Figure 4. The as forged blank of a compressor wheel. This part has been forged in both WE43 and AZ80 for a compressor impeller used in an air-conditioning system assembled by Liebherr Aerospace, Toulouse.

Figure 5. CAD model of the finished compressor impeller.

WP4 Super Plastic Forming SPF employs gas pressure to blow superplastic alloy sheet onto a forming die at elevated temperature. A detailed report of magnesium SPF was provided by Alderman (2006). The demonstrator prototype for SPF was a service door stiffener panel from a Gulfstream G-200. This panel was 760mmx1300mm (29.9 inch x 51.2 inch) and was formed in both AZ31B-H24, as a control, and ZK10, see Figure 7. The forming was carried out by Palbam-AMTS. It was found that both the AZ31B and ZK10 sheet formed comparably to the current specification material AA5083. However ZK10 formed slightly more readily that AZ31B.

Figure 7. WP4 Superplastically formed Gulfstream G-200 service door inner panel. The panel was formed in both AZ31B-H24 and ZK10. WP5 Pad Forming/ Roll Bending Rubber pad forming involves pressing a sheet metal blank into a rubber pad using a male die. The process is conventionally operated at room temperature on a range of sheet metals including aluminum and steel. Two sets of pad forming trials were carried out, one by Airbus and the other by IAI. The pad forming trials carried out at Airbus Deutschland GmbH used a standard reference part employed to test materials for the process.

The forming parameters were adopted from an aluminum part, making this a relatively severe test for magnesium sheet. Forming was carried out at room temperature on an ASEA Press using 700 bar pressure. The part was initially formed with 2mm gage AZ31B-O and ZEK100. The AZ31-O sample cracked on the bend radii at the edge flanges and in the circular depression, see Figure 8. The 2mm gage ZEK100 did not fail as severely as the AZ31B-O part, showing only two small cracks in the edge flanges.

The forming process was repeated using 1.4 mm gage ZEK100 and the reference part was produced defect free, see Figure 9. The thinner gage material increased the radius:thickness (r:t) ratio, reducing the tensile and compressive stresses on the outer and inner surfaces of the bend respectively. Airbus have stated that

Figure 8. WP5 Rubber pad formed reference part from Airbus Deutschland GmbH. This part is used to evaluate the forming ability of various materials. The part depicted was formed using 2mm gage AZ31B-O temper material. It can be seen that the part fractured in a number of places.

“…ZE10 [ZEK100] material is assessed to be suitable for the use in the pad-forming process on similar parts…”

Figure 9. Rubber pad formed reference part from Airbus Deutschland GmbH. This part was formed using 1.4mm ZEK100 and demonstrated the improved formability over AZ31B-O, producing a sound part whilst being formed at room temperature. Further pad forming trials were carried out by IAI who employed a trailing edge wing rib as a demonstrator prototype to evaluate the process. The part was formed in both AZ31B-O and ZEK100. The forming was carried out at elevated temperatures and utilized a lubricant on the sheet. Chemetall supplied Gardolube L6301 S for the lubricant to reduce friction between the sheet and the male tooling.

Figure 10. WP5 Rubber pad formed wing trailing edge rib. These parts were formed in both AZ31 and ZEK100. IAI found that magnesium required a larger bend radius compared to aluminum when formed at room temperature. To obtain the same part geometry the blank had to be pre-

heated to 300°C (572°F). Additionally the tooling needed to be modified to accommodate a greater degree of spring back. However, these issues were resolved and sound parts were fabricated as shown in Figure 10. Roll bending of sheet utilizes a rubber friction belt to shear the sheet around a former roll. This resulted in a constant arc being produced. Palbam-AMTS have demonstrated the method using ZEK100 at room temperature, forming two diameters of cylinder, 150mm (5.9 inch) and 200mm (7.9 inch), see Figure 11. No prototype application currently exists for the process.

Figure 11. WP5 Roll bending. The cylinders shown were roll bent using ZEK100 at room temperature. No prototype currently exists for demonstrating the forming method. The cylinders have diameters of 150mm (5.9 inch) and 200mm (7.9 inch). WP6 Deep Drawing Deep drawing is the process whereby sheet metal is formed using matched dies. The male die is used to plastically draw the material into a female die. It is generally more difficult to deep draw magnesium sheet due to its lower formability, resulting from fewer active slip planes and the strong basal texture that exists in the sheet. This leads to localized work hardened and premature thinning of the material, which eventually necks and fails, resulting in a tear. However through appropriate alloy selection, and careful control of the forming process, complex parts can be fabricated.

Two prototype parts have been used to assess AZ31B-H24 and ZEK100 sheet, and their ability to be deep drawn. The first was an antenna support for the Eurocopter and the second was a compressor scroll from an air-conditioning system produced by Liebherr Aerospace Toulouse, see Figure 12.

Figure 12. WP6 Deep drawn prototype parts. a) Eurocopter antenna support. b) Compressor scroll. Numerical simulation was used to model both parts. This was carried out at IFUM, Leibniz University Hannover using the sheet forming modeling package Autoform.

The Autoform simulation indicated that the antenna support geometry required slight modification to achieve a sound part. The radius at the peak of the cover was increased.

The modeling also indicated that attempting to deep drawing the part using a single set of dies would lead to significant thinning of the part, see Figure 13. As such a two stage forming process was developed, see Figure 14. This produced a pre-form with a more even thickness distribution, which was then finished using a second set of dies. Figure 15 shows the finished antenna cover.

Figure 13. Modeling results of the Eurocopter antenna support. The simulation showed the variation in gage as the part is being formed.

Figure 14. A two stage forming process was adopted to reduce the amount of thinning that occurred during the deep drawing process of the Eurocopter antenna support. The part in the foreground shows the first stage of the process. The pre-form was then formed into the final part on a second set of dies.

Figure 15. Eurocopter antenna support deep drawn by Palbam-AMTS in both AZ31B and ZEK100.

By forming the antenna cover in both ZEK100 and AZ31B-H24 it was possible to compare the two alloy systems. AZ31B-H24 wrinkled and cracked if formed below a temperature of 220°C. However, it was possible to deep draw the same part in ZEK100 at 190°C. The compressor scroll was a two part component. 3D CAD was used to determine the optimum split-line such that no overhang of the geometry occurred. Numerical simulation of the scroll indicated that deep drawing the upper part would result in excessive thinning of the sheet, see Figure 16.

To overcome the thinning of the upper section of this part an innovative combination of technologies using both deep drawing and SPF

has been developed by Palbam-AMTS. This will involve a two stage deep drawing process to yield a pre-form with near uniform gage. The final detail of the part will then be “blown” in using a SPF like process. The tooling construction and fabrication of the part will be carried out at Palbam-AMTS. WP7 Creep Forming Creep forming enables large panels to be deformed into double curvatures by pressing them on to a jig with weights and heat treating them in a furnace to induce creep. An advantage of the process is there is no spring back in the part following forming, allowing very precise tolerances to be achieved. Figure 17 shows the set up of a jig with a formed panel in place.

Figure 17. WP7 Creep formed demonstrator fuselage panel fabricated by EADS Deutschland. Fabrication of this part was achieved by laser welding stringers to the flat sheet and creep forming to obtain the final shape. This production method greatly reduced the number of steps needed to fabricate the panel compared to the standard AA2024 component by utilizing laser beam welding and creep forming. The prototype part used in WP7 was a demonstrator fuselage panel from Airbus, fabricated by EADS Deutschland GmbH. The panel was stiffened by a series of stringers welded to the sheet using two Nd-Yag lasers with a power output of 2.3 kW and 3.5 kW. EADS have developed laser beam welding of

Figure 16. Numerical simulation of the thinning of the compressor scroll walls formed using single step deep drawing. a) the lower section of the part with acceptable levels of thinning. b) the upper section of the part indicating excessive thinning in the scroll walls.

magnesium alloys as part of the Aeromag and MagForming programs. Figure 18 shows a cross section through one of the welds, indicating good penetration of the bead.

A large driver for the fabrication of the Airbus fuselage panel via laser beam welding (LBW) and creep forming was cost saving. The original fabrication method in AA2024-T3, using stretch forming and riveting, involved 22 steps. The 2nd generation of the panel was fabricated from AA6013-T6 using stretch forming and LBW. This required 16 steps to complete. The potential production route using magnesium sheet alloys only required nine steps to complete the panel. Creep formed fuselage panels were prepared from ZK10 sheet with ZK30 extruded stringers. The stringers were extruded by Alubin. Conclusions The MagForming project has developed and show-cased a number of commercially viable forming solutions for conventional and new magnesium alloy systems. The goal of the program has been to facilitate the tools needed to realize magnesium as an attractive engineering material for future generations of

aircraft. The driver for this, as always, is light weighting to improve both performance and fuel efficiency. The aerospace industry recognizes this to be key in future aircraft design, which will need to be quieter, have greater range, and be more fuel efficient (Gehmand, 2009). If magnesium can be formed to meet the requirements of modern engineering solutions it will play a key role in aircraft of the future. References Alderman M.L., Barnes A.J., Bhayani R., and Cottam R. (2006) Superplastic Forming of Magnesium Based Alloys, Proc. 14th International Magnesium Association Magnesium Automotive and User Seminar 2006

Bohlen J., Nurnberg M.R., Senn J.W., Letzig D. and Agnew S.R. (2007) The Texture and Anisotropy of Magnesium-Zinc-Rare Earth Alloy Sheets, Acta Materialia, Vol.55, pp, 2101-2112. Gehmand D. (2009) Traveling light, travelling easy, Aerospace Engineering & Manufacturing, SAE International, Jan/Feb 09, pp22 Senn J.W. (2008) Texture Randomization of magnesium alloys containing Rare Earth Elements, Magnesium Technology 2008, edited Pekguleryuz M.O., Neelameggham N.R., Beals, R.S., Nyberg, TMS, Warrendale, pp153-158. Wendt j., Kainer K.U., Arruebarrena G., Hantzsche K., Bohlen J., and Letzig D. (2009) On the Microstructure and Texture Development of Magnesium Alloy ZEK100 During Rolling, Magnesium Technology 2009, edited Nyberg E., Agnew S.R., Neelameggham N.R., and Pekguleryuz, TMS, Warrendale, pp289-293.

Figure 18. Laser beam weld of a stringer to AZ31B flat sheet showing good penetration of the weld.