Kyowa Electric Wire

Development of Ultra-Thin Wall Welded Metal Pipe andIts Applications
by Hisakazu Ishibashi *, Satoshi Inada * and Shinjiro Konishi *Recently, there has been a year-by-year growing need for weight reduction inmetal pipes aimed at cost reduction and energy saving, centering on the automotive industry. It has been difficult for the conventional welded pipe manufacturing technology
to manufacture ultra-thin wall metal pipes having a thickness to diameter (t/D) ratio of not morethan 1 %, so that such pipes have normally been manufactured using handicraft means. On theother hand, utilizing a special forming technology of our development and our proprietary manufacturing technology, we have established a continuous, high-speed manufacturing technology
for ultra-thin wall metal pipes having a t/D ratio of not more than 1 %. The development of ultrathin wall metal pipes will be described in this paper, including those for the automotive industry.

ABSTRACT1.

INTRODUCTION

The Kanagawa Plant of Kyowa Electric Wire has beendeveloping, since it was established in 1972 as a plant
specialized in corrugated metal sheath, various products
such as thin-wall welded metal pipes for automotive
exhaust gas and home appliance applications, as well as
corrugated cables (see Table 1 and Figure 1).

Table 1Main product items.

Corrugated cable for power use

Stainless steel pipe for automotive exhaust gas

Corrugated cable for communications use Magnet cover for motors in home appliances
Stainless steel corrugated cable

Corrugated metal tube (flexible tube)

Aluminum corrugated cable

Various special pipes (perforated pipe, deformed pipe)

Figure 1

In out plant, an automatic continuous manufacturingmachine (see Figure 2) is employed to manufacture thethin-wall welded metal pipes from metal strips in a complete inert gas atmosphere, using special welding techniques such as tungsten inert gas (TIG) arc welding orplasma welding. This manufacturing process provides themetal pipes with flat and smooth weld beads on the innersurface as well as complete air- and water-tightness,making it possible to apply these pipes for use in corrosive atmospheres and complicated secondary machining
processes.

2.

FEATURES AND SPECIFICATIONS OFTHIN-WALL WELDED METAL PIPES

2.1 Features
The metal pipes have a uniform wall thickness except for
the weld bead portion, because strip stock is used asThin-wall metal pipe products.

* The Kanagawa Plant, Kyowa Electric Wire

Figure 2

Automatic continuous manufacturing machine forthin-wall metal pipes.

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Development of Ultra-Thin Wall Welded Metal Pipe and Its Applications

their mother material. While the weld bead portionachieves the equivalent mechanical strength as for themother material, the strength and shape of the weldbeads can be controlled in accordance with the intended
use. The integrity of the pipes that has been achieved issuch that its circularity, one of the measures representing
the pipe precision, is ±0.3 mm or better; the straightness
is 1 mm/m or better; and the pipe ends are cut using aclear-cut technique with circumferential uniformity, realizing a burr- and dust-less cut ends. Moreover, special
products and processing are available including flaring
work for the pipe ends and piercing work for the double
pipes, in addition to manufacturing deformed pipes suchas thin-wall rectangular pipes and semi-circular pipes,
which were difficult to manufacture conventionally.
2.2 Specifications
In response to diversified customers’ needs, a variety ofproducts are available as shown in Table 2 and Figure 3.
They are: in terms of material, stainless steel which is amultipurpose material for automobiles as well as titan,copper and aluminum; as for wall thickness, 0.1~2.0 mm;
and as for pipe diameter, 5~130 mm.

3.

DEVELOPMENT OF STAINLESS STEEL
THIN-WALL WELDED PIPES FOR
AUTOMOBILES

steel pipes have been employed by many automobile
manufacturers as a mother material for components ofautomotive exhaust gas pipe systems comprising exhaust
manifold, flexible tube and catalytic converter casing (seeFigure 4). We succeeded in developing in-house a manufacturing machine for stainless steel mufflers in 1979, andwe have delivered a sum total of approximately 10,000
tons of these products since then. In particular, manufacturing of double tubes consisting of two thin-wall metal
pipes was made possible for the first time, by using thismetal pipe with superior circularity and straightness torealize a small clearance between the inner and outerpipes. And the bulge processed products using this double tube as a mother material have acquired a high reputation for their heat-insulating effects together with thedamping and vibration absorption effects due to flexibility.
3.2 Advantages of Wall Thickness Reduction
Figure 5 illustrates the advantages of wall thickness
reduction, taking different manufacturing processes forcatalytic converter casing for example. Conventionally,
bent sheet pipes were manufactured by a method suchthat a metal strip having the specified length for the final
product is bent to form a circular tube, and the matingedge is seam welded, and in this case, the required mini-

3.1 Development History and Track Record
Automotive exhaust gas pipes are required to be thinwalled from the standpoint of energy saving and weight
reduction, and yet they have to satisfy stringent requirements such as endurance, corrosion resistance and heatresistance. Our products of thin-wall welded stainless

Table 2

Specifications for standard thin-wall metal pipes.
Wall thickness(mm)Material

Outer diameter(mm)

Converter

Length (m)Titan

Exhaust manifold

Stainless steel

0.1~2.0

Copper5~130

0.01~6.0

Figure 4

Flexible tuber

Schematic of automotive gas exhaust pipe system.

Wall thickness（mm）

Aluminum

2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0

Production capacity: 200 ton/month

Conventional product(wall thickness≧1.5 mm)
To secondary
process

0102030405060 708090 100 110 120 130 140 150

Pipe diameter（mm）

Figure 3

Manufacturable range by wall thickness and pipe
diameter.

Catalytic converter casing

Developed product(wall thickness≦1.5 mm)

Figure 5

Manufacturing process for catalytic converter casing,comparing the conventional and developed methods.

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200745Development of Ultra-Thin Wall Welded Metal Pipe and Its Applications

mum wall thickness is generally 1.5 mm or more. In contrast, in our manufacturing process a coiled strip is formed
into a tubular shape through our proprietary forming
method, continuously welded, and cut into the specified
lengths for the final product, and in this case, sufficient
weld strength can be obtained even for a wall thickness ofnot more than 1.5 mm.
The advantages of wall thickness reduction include aweight reduction of 20~40 % and a cost reduction due tomaterial costs of 10~20 %. Based on our proprietary
forming method, the thin-wall metal pipes allow a freechoice of the weld bead shapes without impairing themechanical characteristics of the mother material, so thatthe pipes are suitable for severe-conditioned secondary
processing such as bending, bulging, drawing and continuous corrugating.

4.

DEVELOPMENT OF SPECIALPERFORATED ALUMINUM PIPES

embedding is allowed for, 2) provided with superiormechanical characteristics, together with high compression strength and high inner pressure strength, 3) provided with light weight and high bendability, permitting easeof laying work, 4) complete anti-ant and anti-rodent
effects are offered, and 5) large electromagnetic shielding
effect is offered.
5.2 Specifications of Corrugated Cables
Table 3 shows available forms of corrugation. Depending
on applications, corrugated pipes having spiral grooves
are used in applications where strength is emphasized,
while corrugated pipes having independent bellows-type
grooves in such applications as various piping where flexibility is of much importance. Moreover, partially corrugated pipes combining straight sections and corrugated sections can also be manufactured.
In terms of material and wall thickness, various customized specifications are available as shown in Table 4, andWe have been successful in developing a pipe manufacturing technology using TIG welding for thin perforated
Al-Mg-based aluminum strips, thereby releasing theproducts (see Figure 6). Since the product allows for customizing the hole diameter, hole number and pattern ofthe perforation, in addition to a free choice of materials
including stainless steel, copper and copper alloys aswell as aluminum, we are planning to expand its applications to commodities related with the housing industry,
such as watering pipes and the like.

5.

CORRUGATED CABLES ANDAPPLICATION OF THEIRMANUFACTURING TECHNOLOGY

5.1 Features of Corrugated Cable
Figure 7 shows the structure and the cross section of typical corrugated cables. The structure of corrugated cables
is such that an inner cable is covered with a corrugatedmetal pipe, over which an outer sheath of PVC or polyethylene is applied as a corrosion protection layer. The features of corrugated cable include: 1) direct underground

Inner cable

Corrugated sheath

Figure 7

Outer sheath(corrosion protection layer)

Structure of typical corrugated cable.

Table 3Available corrugation forms.
Spiral corrugation

Form of corrugation

Bellows-type corrugation
Partial corrugation

Table 4
Material

Standard specifications of corrugated pipes.
Wall thickness(mm)

Inner diameter(mm)

Outer diameter(mm)

0.3~0.6

10.0~47.4

13.5~53.0

0.5~1.5

10.0~37.4

14.7~42.9

Steel
Stainless steel
CopperFigure 6

Perforated aluminum pipe.

Aluminum

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Development of Ultra-Thin Wall Welded Metal Pipe and Its Applications

with respect to the depth of corrugations that constitutes
an important factor for determining the bendability andmechanical strength, the deep groove-type corrugation(corrugation height/pitch > 0.25) is also available besides
the standard-type corrugation (corrugation height/pitch≦0.25).
5.3

Company’s Share in the Corrugated Cable
MarketAs of March 2007, we have produced 30,000 km of corrugated cables since the start of production in 1972, equivalent to three quarters of the circumference of the earth.
Such being the case, thanks to the long-cultivated technology for corrugated cables, our performance is highly
appreciated in terms of quality, delivery time and costeffectiveness, and we enjoy the highest domestic market
share of corrugated cable production (i.e., as of January
2007, according to our study). We are developing newtechnology innovations targeted at achieving a 100 %share in manufacturing corrugated cable sheathing
domestically.

6.

APPLICATION DEVELOPMENT OF
CORRUGATION TECHNOLOGY

6.1 Application to Automotive Fields
Figure 8 shows the schematics of the current and developed manufacturing processes for partially corrugatedpipes, which are used as flexible tube and EGR piping in

automotive exhaust gas piping. In the current manufacturing process, mother material is made into a pipe, cut to a
standard length, and bulging in applied, in a separate
process using an inner pressure, to the corrugation portion to swell the pipe outside. This method results in two
separate manufacturing processes, leading to a high process cost. In contrast, the corrugating technique isapplied to manufacture the developed product, where thecorrugation portion is formed by mechanically grooving
the raw pipe from the outside. This method allows for corrugating in-line with the pipe making process, resulting ina significant processing costs reduction. The number ofspiral corrugations can be changed as desired, and production lengths up to 2000 m are possible. Moreover, aluminum corrugated cables, which use aluminum of highshielding effect and light weight are drawing attention asprotection piping for harness cables used in hybrid cars,
where high-voltage power transmission is needed, whereby it is expected that the cables are particularly effective
not only for their shielding effect but also for their resistance against external damage and corrosion.
6.2 Application to Heatpipe Technology
Recently, heatpipe technology is drawing attention, fromthe standpoint of environmental issues and energy conservation, since heatpipes allow for maintenance-free
operation without using driving power. Figure 9 illustrates
the operating principle of heatpipe, which is a thermal
device taking advantage of the latent heat of a liquid atCurrent productDeveloped productCut to standard lengthPipe making
process

In-line single process from pipe
making to corrugating

Bulging
process

Figure 8Comparison of manufacturing processes of partially corrugated pipes for the current and developed products.

Working ﬂuid absorbs heat

Working ﬂuid vaporizes

Vapor moves tothe low-temperature end

Vaporized
working ﬂuid
High-temperature end
for heat absorption
Low-temperature end
for heat dissipation
Condensed
working ﬂuid

Condensation
Working ﬂuid

Working ﬂuid returns to
the high-temperature end

Figure 9

Operating principle of heatpipe.

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Development of Ultra-Thin Wall Welded Metal Pipe and Its Applications

the time of evaporation and condensation. When one end(high-temperature end) of a heatpipe containing a working fluid is heated, the working fluid vaporizes absorbing
heat. The vaporized working fluid diffuses in the pipe toreach the other end (low-temperature end) to condense
emitting latent heat there. In this way, heat is efficiently
transferred from the high-temperature end to the lowtemperature end.
At present heatpipes are extensively used in such applications as snow melting system using geothermal heat,temperature control in spacecraft, heat dissipation in electrical equipment, and home appliances. Because our corrugated pipes of stainless steel and copper possess, taking advantage of the manufacturing process in a completely inert gas environment in addition to continuous
long-length welding, perfect air- and water-tightness aswell as flexibility that make the pipes suitable for long distance piping, it is expected that the pipes find wide applications in the next-generation heatpipe systems.

7.

CONCLUSION

In response to the weight reduction requirements including those from the automotive industry, we have developed the manufacturing technology for ultra-thin wall

welded metal pipes that can endure, in spite of their
reduced thickness, in severe secondary processes andapplication environments. By combining it with corrugation technology, the pipe manufacturing technology
allows for making proposals for, and manufacturing of,next-generation commodities that can cope with environmental issues and energy conservation.

REFERENCES
1) Kazukiyo Kobayashi: Introduction to Welding Technology, 2nd edition, Rikogakusha Publisher (1999), 263. (in Japanese)
2) Kenzo Kato; Journal of the Japan Society for Technology ofPlasticity, 22 (1981), 1129. (in Japanese)
3) Kenzo Kato; Journal of the Japan Society for Technology ofPlasticity, 20 (1979), 859. (in Japanese)
4) Kenzo Kato; Journal of the Japan Society for Technology ofPlasticity, 23 (1982-8), 731. (in Japanese)5) Minoru Hasegawa: Mechanical Materials (4th edition), Rikogakusha
Publisher (1993). (in Japanese)
6) Yoshiro Siba: Journal of the Geothermal Research Society of Japan,
27 (2005). (in Japanese)
7) Geo-Heat Promotion Association of Japan: Brochure of Geo-Heat
Promotion Association of Japan. (in Japanese)

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