Available online at ScienceDirect. Procedia CIRP 42 (2016 )

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Laminated Electrode Wang Chunliang, Chen Jipeng, Gu Lin, Zhao Wansheng* State Key Laboratory of Mechanical System and Vibration, School of Mechanical Engineering, Shanghai Jiao Tong University,

1 Available online at ScienceDirect Procedia CIRP 42 (2016 ) th CIRP Conference on Electro Physical and Chemical Machining (ISEM XVIII) Blasting Erosion Arc Machining of Turbine Blisk Flow Channel with Laminated Electrode Wang Chunliang, Chen Jipeng, Gu Lin, Zhao Wansheng* State Key Laboratory of Mechanical System and Vibration, School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai , China * Corresponding author. Tel.: ; fax: address: zws@sjtu.edu.cn Abstract This paper presents a new process for machining the flow channels of wide gap shrouded blisk. It utilizes the blasting erosion arc machining (BEAM) process with laminated electrode which contains a number of curved flushing holes. The laminated electrode is an integration of several layers (slices) of electrode plates. As a strong inner flushing in the gap is the prerequisite for the hydrodynamic arc breaking mechanism for BEAM, curved flow slots are machined on each electrode plate surface to enable the working fluid to flow through and perform a strong inner flushing. Machining experiment with laminated electrode was carried out to demonstrate the feasibility of this novel machining technology. By optimizing the contour profile of the laminated electrode, the geometry of the inner slots as well as the feeding path, a stable and continuous electro-arcing process of BEAM was achieved and a blisk channel was machined efficiently The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license 2016 The Authors. Published by Elsevier B.V. ( Peer-review under responsibility of the organizing committee of 18th CIRP Conference on Electro Physical and Chemical Machining (ISEM Peer-review XVIII). under responsibility of the organizing committee of 18th CIRP Conference on Electro Physical and Chemical Machining (ISEM XVIII) Keywords: blasting erosion arc machining (BEAM), turbine blisk, laminated electrode, inner flow slots, fluid flushing 1. Introduction Turbine blisks in aerospace industries are usually made from super alloys which have excellent mechanical properties [1], but these alloys are also belong to difficult-tocut materials and hard to be machined by traditional cutting processes [2]. It induces workpiece vibration and severe tool wear [ 3 ] during machining. Milling process for Ni-based alloys has economical drawbacks such as long machining time and high tool cost. Non-traditional machining processes such as EDM, ECDM [4][5] show a great advantage in processing of the difficult-to-cut materials. The averaged MRR of EDM for Ti6Al4V is 220 mm 3 /min [4]. Normal EDM doesn t have high efficiency. By applying pipe electrode, high speed EDM milling and arc machining [6][7] can achieve a high material remove rate (MRR) of 21,494 mm 3 /min with 700 A peak current, when processing titanium alloy Ti6Al4V. High speed electro-erosion milling of super alloy has also shown high efficiency and potential in blisk machining [8][9]. Blasting Erosion Arc Machining (BEAM) [10] is a new technique of non-traditional machining. Different from Electric Discharge Machining (EDM), it erodes material by electric arc instead of electric spark. It can reach a high MRR, up to 14,000 mm 3 /min when machining nickel-based alloy with a 500 A peak current [11 ]. Therefore, high efficiency is the great advantage of BEAM. Since BEAM is an economic way to perform bulk material especially the difficult-to-cut alloys removal, its potential on machining wide gap blisk should be investigated. The key mechanism of BEAM is how to control the electric arc during machining. The inner flushing between electrode and workpiece induces intensive hydrodynamic force on the arcing plasma column to distort, elongate, or even break the arc column. During the arc breaking process, the blasting force will blow off the molten material and form a deep crater. Hydrodynamic arc breaking mechanism is the principle of BEAM and a strong inner flushing is a prerequisite for BEAM process [10]. Besides, the flushing The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license ( Peer-review under responsibility of the organizing committee of 18th CIRP Conference on Electro Physical and Chemical Machining (ISEM XVIII) doi: /j.procir

318 Wang Chunliang et al. / Procedia CIRP 42 ( 2016 ) 317 321 fluid can carry large amount of heat and debris away from the gap.

Bundled electrode [12], multi-hole solid electrode [11], and laminated electrode [1] have various structures with specific functions for certain cavities machining.

2 318 Wang Chunliang et al. / Procedia CIRP 42 ( 2016 ) fluid can carry large amount of heat and debris away from the gap. To perform a high velocity inner flushing, there are multi-holes inside all BEAM electrodes. Bundled electrode [12], multi-hole solid electrode [11], and laminated electrode [1] have various structures with specific functions for certain cavities machining. A Bundled electrode composes of many hollow tubular cell electrodes and its surface fits to the surface of a traditional solid electrode. A bundled electrode usually feeds in one direction, especially the Z axis. A multi-hole milling electrode is a solid cylinder electrode with some inner holes. During BEAM process, the electrode rotates and feeds in a milling type, accompanying with a strong inner flushing. By feeding in a milling-like mode, it s possible to machine most open and semi-open cavities. However, for some special features with complex concaves or curved flow channels, such as the shrouded blisk, how to design a suitable electrode is still a big challenge for the BEAM process. Neither bundled electrode nor solid tubular multi-hole electrode is suitable for machining such features. The blisk channels can only be BEAM machined by using a solid multi-hole electrode and performing a 4-axis or 5-axis NC machining. Generally, the channels are not straight and even the cross sections are different for an optimized flow field. As can be seen in figure 1., the shrouded turbine blisk has curved flow channels. Figure 1. is the model of one simplified shrouded channel which also generates the model of electrode introduced in the second part. How to fabricate multiple flushing channels inside a solid electrode is a big challenge. In order to solve this problem, laminated electrode was proposed. A laminated electrode is composed by several layers of electrode which has flow slots on the surface of each electrode. After stacking and fixing the laminated electrodes together, the outside profile of the electrode is machined to fit the geometry of solid electrode accurately. The inner slots will provide strong inner fluid flushing during machining. Hence it is capable to perform die-sinking BEAM and machine complex 3D cavities. This paper fist studied the principle of laminated electrode design, and then investigated feasibility of BEAM with this electrode via demonstration experiment. 2. Laminated Electrode For one specific cavity machining, the contour shape of the laminated electrode is almost same as the solid diesinking electrode. Because an intensive flushing is a prerequisite of BEAM process, the key feature of laminated electrode is that it has flow slots going through from the working fluid entrance to the top end of the electrode. So the difference between these two electrodes is the flow slots inside the laminated electrode can be curved or even have a varied cross-section while it is impossible to prepare such channels in the solid electrode Design of Laminated Electrode The design of laminated electrode includes two stages: retrieve the outline profile geometry and design the inner fluid chamber and slots on each layer. According to the turbine blisk model, the flow slots can be separated by subtracting the blisk from a bounding 3D body. Then the cavity part of the workpiece could be acquired by trimming using specific planners. And it s also the part to be removed during machining. The solid diesinking electrode was generated by considering the machining allowance. Then the outline geometry of the designed electrode was acquired, as shown in figure 2. Figure 2. The outline geometry of the designed laminated electrode The second step was to design the working fluid chamber inside the laminated electrode. By considering the rigidity of each layer, the whole electrode was divided into several 8 mm thick layer electrodes. On the surface of each layer, flow slots were designed to guide the flow inlet from the chamber to the outlet at the end. The main purpose of the chamber inside the electrode is to decrease the hydraulic resistance and increase the flow velocity as much as possible. The width and depth of the slots are about 2-3 mm to keep the fluid flushing in a high speed. Another problem is to keep the strength of the layer electrode. When designing the structure of the whole electrode and each layer, the mechanical property and machinability of the electrode should also be considered. The final designed laminated electrode with inner flow slots is shown in figure 3. There are through-holes on each layer of the laminated electrode, therefore 2 bolts can be used to fasten and stack them together. Figure 1. A turbine blisk; A shrouded blisk channel

Wang Chunliang et al. / Procedia CIRP 42 ( 2016 ) 317 321 319 EDM process (Makino U32j). A machined laminated electrode and its sliced layers are shown in figure 4.

The model of laminated design with inner flow chamber and slots; The side view of the laminated electrode; (c) Overview of the second layer of laminated electrode The reason why the laminating method

As shown in figure 5, although the inlet flow hole can be machined directly, the inner chamber has larger size in depth, normal tool for milling cannot reach the corner.

These could not be machined either from the left or the right end of one solid electrode. 2.

its high melting point and good thermal conductivity. The G code in CNC system is generated in UG NX software.

After all the layers were machined, they were stacked together to machine the outline geometry of the whole laminated electrode.

3 Wang Chunliang et al. / Procedia CIRP 42 ( 2016 ) EDM process (Makino U32j). A machined laminated electrode and its sliced layers are shown in figure 4. Inlet Hole Inner Chamber Slope Figure 4. The whole electrode with 4 layers stacking together; Each layer of electrode after machining Bolt Holes 3. BEAM Experiment (c) Figure 3. The model of laminated design with inner flow chamber and slots; The side view of the laminated electrode; (c) Overview of the second layer of laminated electrode The reason why the laminating method is necessary is that the inner fluid cavity of the electrode cannot be machined on a solid electrode. As shown in figure 5, although the inlet flow hole can be machined directly, the inner chamber has larger size in depth, normal tool for milling cannot reach the corner. Besides, the right side of the electrode has slopes and the outlet flow slots is curved to fit the outline profile. These could not be machined either from the left or the right end of one solid electrode Machining of Laminated Electrode Curved Slots In order to sustain high temperature generated by the electric arc during the BEAM process, the laminated electrode was made from graphite because of its high melting point and good thermal conductivity. The G code in CNC system is generated in UG NX software. For the inner chamber and slots of each layer, a 3- axis machine center (Makino E33) was chosen to conduct slot milling and hole drilling on layer electrodes. After all the layers were machined, they were stacked together to machine the outline geometry of the whole laminated electrode. The outline profile was machined using Wire After a laminated electrode has been machined, its feasibility in Blasting Erosion Arc Machining was verified by machining a shrouded blisk channel Experiment Set-up The machining system included a five-axis machine, dielectric fluid inner flushing system, laminated electrode, a high-current pulse power supply, and one workpiece as shown in figure 5. The graphite laminated electrode as designed in the second part was clamped on the Z-Axis of the machine. The 304 stainless steel workpiece was fixed on the machining platform. The inner flushing system was connected with a pump and the electrode to provide high velocity flushing into the discharge gap. Laminated Electrode Flush Inlet Positive Pole Workpiece Negative Pole Figure 5. Experiment set-up

320 Wang Chunliang et al. / Procedia CIRP 42 ( 2016 ) 317 321 3.2. Experimental Parameters The experimental conditions are listed in Table 1.

The machining feed rate f was 2.0 mm/min, mainly in X and Y direction. Table 1.

Laminated electrode after BEAM experiment As the Voltage-Current wave shown in figure 8, the gap condition was very stable during machining.

4 320 Wang Chunliang et al. / Procedia CIRP 42 ( 2016 ) Experimental Parameters The experimental conditions are listed in Table 1. It has been demonstrated that negative polarity BEAM can achieve a larger MRR than that of positive BEAM. In this paper the pulse power conditions were selected according to previous research. The machining feed rate f was 2.0 mm/min, mainly in X and Y direction. Table 1. Machining Parameters Parameters Value Electrode polarity Negative Peak current I p (A) 200 Pulse duration t on (μs) 5000 Pulse interval t off (μs) 1000 Flushing inlet pressure (MPa) 1.6 Figure 7. Laminated electrode after BEAM experiment As the Voltage-Current wave shown in figure 8, the gap condition was very stable during machining. And the discharge wave indicated there were no short circuit during this process Machining Feed Path Besides the main feeding movement, the laminated electrode also performed a rectangular orbiting movement after feeding every 5 mm in Y direction. The additional motion could generate a 1 mm gap around the electrode, which made it easier for the fluid flushing out through the gap Results and Analysis The BEAMed blisk channel is shown in figure 6 and the electrode after the BEAM experiment is shown in figure 7. The width and height were marked, and the shape is accordant with the theoretical model designed before experiment, as can be seen in figure 1.. The surface roughness was a little coarse because of this specific BEAM die-sinking mode with laminated electrode mm mm Figure 6. BEAMed blisk channel in machined workpiece Figure 8. Discharge V-A wave by oscilloscope MRR was calculated based on the volume of removed workpiece material per minute. The MRR in this experiment was over 2,560 mm 3 /min, which suggests the applicability of this technology. Laminated electrode can be used with BEAM process to machine blisks efficiently and economically. The tool wear ratio (TWR) is the volumetric ratio between volume loss of the tool electrode material and that of the workpiece. The TWR was about 4.5% in this experiment. The electrode wear was mainly concentrated at the front side of the laminated electrode, the interface and the corners of each layer. At these areas, the electric arc discharge happened the most frequently and severely. Conclusion and Discussion A new BEAM process was proposed to machine shrouded blisk channel by applying laminated electrode. The design of laminated electrode and the BEAM experiment was introduced in detail. Verification experiment was conducted to demonstrate its capability. Compared with traditional milling process and sinking EDM, it is an economic and efficient way for bulk removing in blisk machining. Further research will focus on how to improve the MRR and reduce the TWR of laminated electrode die-sinking BEAM by optimizing the structure of the electrode shape and the inside flow slots. Besides, machining conditions should also be optimized by analysis and experiments.

5 Wang Chunliang et al. / Procedia CIRP 42 ( 2016 ) Acknowledgements Authors acknowledge the National Natural Science Foundation of China (Grant No.: and ), and the State Key Laboratory of Mechanical System and Vibration for their financial supports. References [1] Yilmaz O, Noble D, Gindy N N Z, et al. A study of turbomachinery components machining and repairing methodologies[j]. Aircraft Engineering and Aerospace Technology, 2005, 77(6): [2] Klocke F, Klink A, Veselovac D, et al. Turbomachinery component manufacture by application of electrochemical, electro-physical and photonic processes[j]. CIRP Annals-Manufacturing Technology, 2014, 63(2): [3] Denkena B, Boess V, Nespor D, et al. Engine blade regeneration: a literature review on common technologies in terms of machining[j]. The International Journal of Advanced Manufacturing Technology, 2015: 1-8. [4] Klocke F, Zeis M, Klink A, et al. Technological and economical comparison of roughing strategies via milling, sinking-edm, wire- EDM and ECM for titanium-and nickel-based blisks[j]. CIRP Journal of Manufacturing Science and Technology, 2013, 6(3): [5] Xu Z Y, Xu Q, Zhu D, et al. A high efficiency electrochemical machining method of blisk channels[j]. CIRP Annals-Manufacturing Technology, 2013, 62(1): [6] Wang F., Liu Y., Zhang Y., Tang Z., Ji R., Zheng C. Compound machining of titanium alloy by super high speed EDM milling and arc machining [J]. Journal of Materials Processing Technology.2014, 214: [7] Wang F., Liu Y., Tang Z., Ji R., Zhang Y., Shen Y. Ultra-high-speed combined machining of electrical discharge machining and arc machining [J]. Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture.2014, 228(5): [8] Yuan R., Wei B., Luo Y., et al. High-Speed Electroerosion Milling of Superalloys [C]. ISEM-16, Shanghai. 2010: [9] Wei B., Trimmer A.L., Luo Y., et al. Advancement in High Speed Electro-Erosion Processes for Machining Tough Metals [C]. ISEM-16, Shanghai.2010: [10] Zhao W, Gu L, Xu H, et al. A novel high efficiency electrical erosion process blasting erosion arc machining[j]. Procedia CIRP, 2013, 6: [11] Xu H, Gu L, Chen J, et al. Machining characteristics of nickel-based alloy with positive polarity blasting erosion arc machining[j]. The International Journal of Advanced Manufacturing Technology, 2015: [12] Gu L, Li L, Zhao W, Rajurkar KP. Electrical discharge machining of Ti6Al4V with a bundled electrode[j]. International Journal of Machine Tools and Manufacture.2012, 53(1):

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