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Research Papers

Hot Extrusion of Thin-Wall Multichannel Copper Profiles

[+] Author and Article Information
Frank F. Kraft

Associate Professor
Mem. ASME
e-mail: kraftf@ohio.edu

Jonathan Kochis

e-mail: kochisj@gmail.com
Mechanical Engineering Department,
Ohio University,
Athens, OH 45701

1Corresponding author.

Manuscript received May 1, 2013; final manuscript received September 18, 2013; published online November 5, 2013. Assoc. Editor: Yung Shin.

J. Manuf. Sci. Eng 135(6), 061008 (Nov 05, 2013) (8 pages) Paper No: MANU-13-1209; doi: 10.1115/1.4025496 History: Received May 01, 2013; Revised September 18, 2013

This paper presents the development of a unique, net shape, hot-extrusion process to produce precision, thin-wall, multichannel copper profiles for high efficiency heat-exchangers. This process is a departure from conventional copper extrusion, which is a nonisothermal process used primarily to produce simple semifinished products and hollow profiles requiring cold drawing after hot extrusion. A lab-scale apparatus was developed to simultaneously extrude multiple heated billets through a porthole type hollow die to form the multi-channel profiles. The process is performed at 700–750 °C, essentially at isothermal extrusion conditions. Temperature and tooling strength considerations necessitated the use of superalloys for the apparatus (which included dies, container, ram stems, and support tooling). A 250 kN computer controlled servo-hydraulic MTS® machine was used to provide the extrusion ram force. Two part designs were extruded to demonstrate process feasibility and versatility. A two-channel design with 0.2 mm wall thicknesses and an 11-channel design with wall-thicknesses of 0.3 mm were extruded. The extrusion ratios for these profiles are 67 and 25, respectively. Experimental data and an approach to analytically model the process are presented. Because solid-state welds in the tube walls are necessitated by the use of hollow extrusion dies, the microstructure in these regions is also presented.

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References

Figures

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Fig. 1

Experimental extrusion apparatus. Figure (a) shows an annotated sketch of the components for the extrusion tooling, from the US patent [4]. Figure (b) shows the apparatus after an extrusion trial (the copper tube exits the nitrogen-cooling tube, at the bottom right). Detached dummy blocks are used during extrusion.

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Fig. 2

Photo of the extrusion apparatus just after an extrusion trial of copper tube. The insulation that surrounded the heated container has just been removed.

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Fig. 3

Progression of dual-billet extrusion from container/billets to final profile. The metal forming the internal walls flows together in the weld chambers of the mandrel.

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Fig. 4

(a) Photos of the 11-channel copper tube with two billets that are similar to the ones used during the extrusion process. (b) Extrusion die, showing the billet entrance and the exit (inset).

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Fig. 5

Tooling material strength as a function as a function of temperature. The data are from Uddeholm, ATI Allvac, and High Temp Metals [6-8].

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Fig. 6

Ram pressure is graphed as a function of ram displacement. The temperature at the entrance of the die was 727 °C and the ram velocity was constant at 9 mm/min (0.006 in/s). The extruded profile was the 16 mm × 1.9 mm × 11 channel design.

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Fig. 7

These graphs show ram velocity and temperature data for a constant force extrusion trial. The billet temperature at the entrance of the die was ∼720 °C and the force was constant at 200 kN (45,000 lbs). The extrusion profile was the 16 mm × 1.9 mm × 11 channel design.

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Fig. 8

Ram force and velocity is shown as a function of time and ram displacement. The temperature at the entrance of the die was 727 °C and the ram velocity was constant at 9 mm/min (0.006 in/s). The profile was the 16 mm × 1.9 mm × 11 channel design. Maximum pressure is predicted within about 2%.

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Fig. 9

Graphs show ram velocity, ram force, and temperature data for two constant force extrusion trials. Temperature at the entrance of the die was ∼740 °C and the force was constant at 200 kN (45,000 lbs). The extrusion profile was the 16 mm × 1.9 mm × 11 channel design.

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Fig. 10

Ram force and temperature data are shown for three extrusion tests. The temperature at the entrance of the die was ∼740  °C and the ram velocity was constant at 9 mm/min (0.006 in/s). The profile was the 16 mm × 1.9 mm × 11 channel design. Maximum pressure was predicted within about 4%.

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Fig. 11

Graphs show ram velocity, ram force, and temperature data for a constant force extrusion trial. Temperature at the entrance of the die was ∼748 °C and the force was constant at 220 kN (50,000 lbs). The extrusion profile was the 7.9 mm × 4.2 mm × 2 channel tube.

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Fig. 12

Ram force and temperature data are shown for three extrusion tests. The temperature at the entrance of the die was ∼745 °C and the ram velocity was constant at 9 mm/min (0.006 in/s). The profile was the 7.9 mm × 4.2 mm × 2 channel design. Maximum pressure is predicted within 5%.

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Fig. 13

Photos of the 11-channel and 2-channel copper tubes produced in this research

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Fig. 14

Photomicrographs from a section of 11-channel tube, showing the solid state weld regions. The tube section was taken 152 mm (6 in.) from the start of extrusion. Figure (a) shows an internal wall and Figure (b) shows an external end-wall.

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