Precise Extrusion Technology by Conform Process for Irregular

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Precise Extrusion Technology by Conform Process for
Irregular Sectional Copper
Tatsuya Tonogi*                                      ABSTRACT: Various forms of copper extrusion exist for which the importance of near
Kazuhiko Okazato**                                   net shapes is increasing because of the need to reduce costs and the number of
                                                     intermediate processes.
Saburou Tsukada**
                                                         Conform extrusion, which is a continuous extrusion, is limited in that the range of
                                                     extruded forms has been restricted to rectangular shapes, and there have been very few
                                                     examples of its application to irregularly shaped sections.
                                                         We examined the die strength, metal flow, and internal defects of copper irregular
                                                     sectional extrusion. Consequently, we were able to extrude irregular sections and
                                                     significantly reduce the number of process steps by using a near net shape.
                                                         We also found ways of replacing cutting processes with extrusion processes.

                                                                       a shoe which puts a lid on the groove, an abutment which dams
                                                                       the material to be extruded, an extrusion die, and a die
    Conform extrusion was developed as a continuous                    chamber, which contains the die.
extrusion method by the United Kingdom Atomic Energy                       For direct extrusion, billets of about 250 mm in diameter
Authority (UKAEA) in 1971, and has a history of 30 years. Its          are used as the material to be extruded. In contrast, conform
merits are that it can extrude products continuously and make          extrusion uses copper wires 10-20 mm in diameter. Since this
near net shapes, and it has been used for the production of            copper wire is manufactured by continuous cast and rolling, it
aluminum coverings for steel wire and multiport tubes.                 is cheap and it is easy to make a large coil of two tons or more.
    On the other hand, for metals harder than aluminum,
problems, such as insufficient tool strength and inferior product
quality, have limited conform extrusion’s range of application.
However, improvements to machinery in recent years have
made it possible to use conform extrusion for mass production                                                                         die
of copper objects.
    At Hitachi Cable, Ltd., conform extrusion of copper was
introduced about ten years ago, and it has been applied to the
manufacture of copper strips for electrical supplies.                                                 shoe
    Although in early stages it was only possible to extrude
                                                                                                                    abutment    die-chamber
simple square products, improvements to the metal flow and
die strength have recently made possible near net extrusion of
irregular sections and have contributed to a large reduction in          Wire rod
the number of process steps.
    This paper describes the technology of conform extrusion
developed for irregular sectional copper and examples of
products to which it can be applied.                                    groove
                                                                                                                         extruded product
 2 PRINCIPLE OF CONFORM EXTRUSION                                                                                   die-chamber
    The outline of a conform extrusion machine is shown in
Fig. 1. The machinery consists of a rotary wheel with a groove,        Fig. 1 Conform extrusion machine
                                                                       It generates extrusion pressure by the frictional force of the rotating

* Research and Development Center, Hitachi Cable, Ltd.
** Tsuchiura works, Hitachi Cable, Ltd.

                                                                                         HITACHI CABLE REVIEW No.21 (August 2002)           77
The principle of conform extrusion is as follows. A copper wire                 3.1 Increasing the strength of the extrusion die
inserted in the groove of a wheel is drawn by friction against                     Fig. 3 shows the change in temperature of the extrusion die
the wheel. The drawn material is dammed by an abutment                          and extrusion pressure at the start of conform extrusion.
inserted in the groove, and the extrusion pressure is generated                    In direct extrusion, since the die and the billet are heated
as the shoe covers the groove. The material flows into the die                  beforehand, the die’s cold strength is not important. On the
chamber and can be extruded from the die in any form.                           other hand, in conform extrusion, the friction heat and the
    Since the material generates frictional heat and
modification heat, temperatures of up to 500 degrees or more
can be reached, without using a heater.
    The material is in a high plastic flow state due to the
modification to the shear direction at the abutment and the high
temperature. Thus, near net shapes of irregular sections become
    In addition, since the extruded material is completely re-
crystallized, it is in a tempered state, and since the form of
supplied material is a wire rod, it is possible to extrude
continuously, without having to stop the machine in order to
join pieces of material together. This is advantageous because
large coils of product can be made.

   Fig. 2 shows examples of irregular sectional copper
manufactured by the conventional process.
   These samples were formed by repeating the drawing and
annealing two or more times after direct extrusion.
   For near net shapes to be made by conform extrusion, we
had to improve the strength of the extrusion die and metal flow,                Fig. 2 Examples of irregular sectional copper created by the usual
and prevent interior defects from occurring.                                    manufacturing process
                                                                                The usual manufacturing process has many stages.
  (pressure/steady state pressure)

     ratio of extrusion pressure




                                      400    temperature
                      temperature (

                                                           start of extrusion
                                                                                                         Fig. 3 Change in die temperature and
                                                                     steady state                        extrusion pressure at start of extrusion
                                        0                                                                Die experiences extrusion pressures over
                                                           time                                          a large temperature renge.

78 HITACHI CABLE REVIEW No.21 (August 2002)
modification heat of the material causes the extrusion die to                temperature. Inconel 718 loses strength while still cold,
receive pressure over a broad temperature range. Thus the die                although its softening-proofing is sufficient. Tool steel has
material’s strength must be well balanced in terms of hot and                comparatively well balanced hot and cold strengths. However,
cold.                                                                        since conform extrusion dies are exposed to temperatures of
    Proper choice of die material is an especially important for             about 600 for a long time, water cooling of dies made from
extrusion dies of non-flat bars, because the die’s strength is               this material is indispensable.
affected by stress concentration.                                                A stress analyses using the finite element method are used
    Fig. 4 shows the change in measured hardness of AISI-H13                 to design stress-resistant dies, an example of which is shown in
(a common tool steel), Inconel718 (a super heat-resistant                    Fig. 5.
alloy), and heat-resistant tool steel X at temperatures
maintained for 5 hours.                                                      3.2 Improvement of metal flow
    For AISI-H13, softening starts abruptly at 600 ; this is                    The supplied material of conform extrusion is 10-20 mm in
why it can only be used for aluminum with a low extrusion                    diameter, and the width of the extruded material is about 40



    vichers hardness (Hv)



                            200                                            AISI-H13
                                                                           Hot tool steal A

                                  20   500                           600                      700    Fig. 4 Change in hardness of die materials
                                                                                                     Balance of both cold and hot hardness is
                                             keeping temperature (   )

                                                                             mm at most. Thus it is necessary to extrude while expanding
                                                                             the width of the material.
                                                                                 Fig. 6 shows a simulation of the metal flow in the material
                                                                             gathering chamber by using black and white Plasticine.
                                                                             Although material gathering chamber is cone-like and material
                                                                             spreads easily, the flow is poor. The flow of material
                                                                             concentrating in the thicker parts means that there is not
                                                                             enough material flow into the thinner parts. For this reason,
                                                                             cracks occur in thin irregular sectional copper, especially in
                                                                             sections with thin edges and thick centers, as shown in the
                                                                             Fig. 7 (a).
                                                                                 To solve this problem, a flow guide by which the flow to an
                                                                             end or edge can be increased was installed before the die.
                                                                             Fig. 7 (b) shows an example of form improvement after
                                                                             installation of a flow guide. The extruded material has a width
Fig. 5 Example of die stress analysis                                        of 50 mm, whereas the supplied material had a diameter of 12
It is possible to design a die for which the stress is reduced.              mm. The flow guide had a thickness of 6 mm. No cracks are

                                                                                              HITACHI CABLE REVIEW No.21 (August 2002)      79
    wheel                                         chamber

                                                                                      Fig. 6 Simulation of metal flow by Plasticine
                            abutment                           die                    Center flow is strong, where as edse flow is weak.

                                                                     or the oxides of copper adhering to wheel slot may be involved
                                                                     into the product, creating internal defects such as a swelling
                                (a)                                  that break out. Fig. 8 (a) shows an example of an internal
                                                                         The conventional wisdom has been that it is difficult to
                                                                     eliminate such defects. However, by minimizing the amount of
                                                                     oil on the surface of the material and by optimizing the gap
                                                                     between the wheel and the shoe as shown in Fig. 9, scrap (the
                                                                     origin of the defects) can be discharged from the gap.
                          by no flow guide                           Consequently, we could obtain a micro-structure that does not
                                                                     have the defect shown in Fig. 8 (b).

                                                                      4   HIGHLY DEFORMED EXTRUSION
                                                                         Taking advantage of the high formability of our conform
                           by flow guide
                                                                     extrusion, we applied it to the manufacture of heat sinks for
                                                                     cooling electronic products.
                                                                         Extruded aluminum heat sinks have traditionally been used
Fig. 7 Improvement of metal flow by addition of a flow guide
                                                                     because they are cheap, but copper is more thermally
Metal flow to thin parts is improved by the flow guide.
                                                                     conductive. Fig. 10 shows the form of the copper heat sink
                                                                     extruded by conform extrusion. The aspect ratio (fin height /
                                                                     fin width) of the fin was 5. Although this is not as good as an
visible in the extrusion created with the flow guide. The flow       aluminum fin’s aspect ratio, very high fins can be extruded. We
guide can extrude an expanding cross-section area of about           are improving the aspect ratio and pitch of this application.
three times that of the supplied material, or an expanding width         Other applications of our conform copper extrusion include
of about four times the supplied material’s diameter.                the copper bar used in the commutator of an electric motor
                                                                     (Fig. 11 (a)) and the piping parts of air-conditioners (Fig. 11
3.3 Prevention of interior defects                                   (b)). Good results have been obtained with respect to reducing
    In conform extrusion, if the material’s surface becomes          the complexity of processes while maintaining the
dirty, air can be trapped between the material and wheel slots,      characteristics of the extruded product.

80 HITACHI CABLE REVIEW No.21 (August 2002)



                                                                      Fig. 10 Copper heat sink
                                                                      Fin height; 6 mm, fin width; 1.2 mm, pitch; 3.4 mm.

Fig. 8 Cross section of microstructure of conform product
(a) including internal defects (b) no internal defects


 clean material

                                                                      Fig. 11 Example of high deformed extrusion
                                                                      (a) copper strip for commutator
                                                                      (b) parts for air conditioner pipe
                                          material including defect

Fig. 9 Relative positions of wheel and shoe
Defects are discharged as scrap by narrowins the gap.

                                                                                    HITACHI CABLE REVIEW No.21 (August 2002)   81
                                                                  Tatsuya Tonogi
    Precision extrusion technology for copper using the           5th Dept., Research & Development Center.
conform extrusion method has been developed. This                 Received B. E. degree in Mechanical Engineering
                                                                  from University of Electro-Communications.
technology not only contributes to cost reductions by reducing    Currently reseach and developing conform extrusion
the number of intermediate processes, because with it, near net   method.
shapes can be created, but it also makes possible extrusion of
complex forms such as heat sinks without the need for cutting.
                                                                  Kazuhiko Okazato
                                                                  Electrical Copper Products Manufacturing Dept.,
                       REFERENCES                                 Tsuchiura Works.
                                                                  Received B. E. degree in Mechanical Engineering
(1) D. Green: J. Inst. Metals, 100 (1972)                         from Hitachi Ibaraki Technical College in 1991.
                                                                  Currently engaged in Engineering Work related to
(2) Nagai, et al.: The proceedings of 36th Japanese Joint         Extrusion process.
    Conference for the Technology of Plasticity (1985)
(3) Okuno, et al.: Journal of the Japan Society for Technology
    of Plasticity, the 40th volume, No. 465 (1999)                Saburou Tsukada
                                                                  Engineering Dept., Tsuchiura Works.
                                                                  Graduated from Nagano Technical High School.
                                                                  Currently engaged in design of Copper Products.

82 HITACHI CABLE REVIEW No.21 (August 2002)

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