Contribution to the achievement of SDGs
by Furukawa Electric Group

Development of the Wiring System Technology
to Realize its Weight-Reduction in Vehicles
Takanori Toyama*1, Kouhei Ikemoto*2, Akihisa Watanabe*3, Satoshi Hirose*3,
Yuji Tamura*3, Yasuharu Uchiyama*4, Akihiro Nagao*5,
Yukihiro Kawamura*6, Takashi Tonoike*5, Takuro Yamada*5
Looking at today’s vehicles, the number of system devices equipped in a vehicle, which offer safety, security, and comfort tends to increase. On the other
hand, the requirement for reduction in CO2 emission is growing every year as one of the means
to realize the carbon neutral society. Such requirement as to reduce the weight of automotive
components is growing further as one of the measures to achieve the reduction in CO2 emission.
Responding to this requirement, we have been promoting the development of the technology torealize not only the weight reduction of automotive wiring systems but also the mass productionof its components. In this paper, we are going to report an example of our successful results
implemented in a large size SUV launched in the market last year.

ABSTRACTINTRODUCTION
1.1.INTRODUCTION
The requirement for the reduction in CO2 emission has
been growing every year along with the growing awareness in global environmental conservation. On the other
hand, the weight of wiring system itself has been increasing caused by the growing number of automotive components required for safety, security, and comfort. Amongthese components, the weight of a set of Wire Harnesses(W/Hs), one of which is shown in Figure 1, installed allover a vehicle body is as heavy as approximately 50 kg
for a large-size SUV to make up approximately 2% of its
total weight. Further, the number of its components is as
many as approximately 2,000 pieces.

Figure 2 shows the weight percentage of each component group of the W/H. The total weight of wires is morethan 50% of that of the whole W/H. This trend has notchanged over the past several years.

Year 2015
Terminals
4%
Relay Boxes (R/Bs) equippedwith the power components
6%
Connectors
10%

Protectors & tape /Route guiding components
24%Year 2021
Terminals
4%
Relay Boxes (R/Bs) equippedwith the power components
8%Connectors
8%

Figure 1 Wire harness (W/H).
	Wiring System Engineering Dept. 5 Engineering Div. 1
Furukawa AS Co., Ltd.
*2	Wiring System Engineering Dept. 2 Engineering Div. 1
Furukawa AS Co., Ltd.
*3	EC Dept. 1 Engineering Div. 2 Furukawa AS Co., Ltd.
*4
	Furukawa Automotive Parts (Vietnam) Inc.
*5	EC Dept. 2 Engineering Div. 2 Furukawa AS Co., Ltd.
*6	SRC Dept. Engineering Div. 2 Furukawa AS Co., Ltd.
*1

Components for ﬁxing
3%

Other
components
1%

Wires
52%

Other components
3%

Components
for ﬁxing
2%

Wires
54%

Protectors & tape /Route guiding components
21%
Figure 2 The weight percentage of each component group in
the W/H.

It is essential to reduce the weight of wires in order tosatisfy the requirement for the weight reduction which has
been growing every year and we have to work on reducing the weight of other components of the W/H as well. In
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Development of the Wiring System Technology to Realize its Weight-Reduction in Vehicles

this paper, we are going to report an example of our successful results installed in a large-size SUV launched in
the market last year.

2.

OUR ACTIVITIES TO REDUCE THE
WEIGHT OF WIRES

2.1 Our Activities to Adopt Aluminum Wires for W/HConsidering that application of aluminum wires was oneof the best ways to reduce the weight of wires whichwere the heaviest among any components of W/H, wehave already been replacing the copper wires with thealuminum ones every year since 2010. Recently, the needfor the replacement with the aluminum wires has been
growing because the aluminum wires have advantages
against copper wires from the aspects of the global
depletion of resources and the rising prices as well.
As mentioned above, the application of aluminum wires
seems to have a lot of advantages. However, there are
big problems to install them in a vehicle. First, the aluminum wire needs larger diameter because its conductivity
is lower than that of copper. There is the problem thatlarger-diameter wires need more space when installingthem in the limited small space in a vehicle. Second, thestrength of conductor is lower than that of copper. The
aluminum wire, especially made of small-diameter conductor is easily broken because of insufficient tensile
strength of conductors. Third, a terminal crimped on theend of wire is made of copper alloy. When its contact partwith an aluminum wire gets soaked with water, the aluminum is corroded away caused by the bimetallic corrosion.
The following shows our technology and its impact onsolving those problems mentioned above.
2.1.1 Development of technology for aluminum wires
The first problem of the aluminum wire was that the aluminum conductor larger in its diameter is required whenloading the current equivalent to that of a copper wire,
because its conductivity is lower than that of copper. As aresult, its insulated overall outer diameter becomes larger.
We have solved this problem by offsetting the increased
size of conductor with a developed thinner insulation to
Table 1ALVSS

Insulation thickness

Insulation thickness

Outer dia.

AVS 3/5(Copper wire)

ALVSS 5/8
(Aluminum wire)

Figure 3 Comparison of AVS 3 / AVS 5 and ALVSS 5 / ALVSS 8.

Our product lineup of aluminum wires.

Wire type

ALVUS

make the insulated overall outer diameter equivalent withthat of the insulated copper wire.
We were concerned with the wear resistance of thethinner insulation. But we have satisfied it by applying our
PVC composition technology already developed for thethin insulation type wire in which copper wires werealready in mass production.
ALVSS 5 and ALVSS 8 were adopted in the large-size
SUV launched last year. We had solved the problem of
increased wire diameter by making the wire diameter of
ALVSS 5 to be equivalent with that of AVS 3 and also
ALVSS 8 with AVS 5 respectively by applying the technology mentioned above. (Figure 3)
The second problem of the aluminum wire was thelower strength of conductors. We have solved this problem especially for the small-diameter conductor which
required more tensile strength by developing a brand-new
aluminum alloy whose strength was equivalent with thatof copper, and which had sufficient conductivity toreplace copper based on making full use of our metallographic control technology 1). Applying this aluminum alloy,
for example, we have realized a 0.5 mm2 aluminum wire
which has sufficient tensile strength and shock absorption
value (toughness) equivalent with those of a 0.35 mm2
copper wire and good conductivity interchangeable with
it as well.
Solving these problems, the wide range of aluminum
wires from 0.35 mm2 to 8.0 mm2 could be carried in our
lineup of products. (Table 1)

Structure of the conductor
Number of strands /Strand diameter

Conductor
diameter
(mm)

0.35

7/Compressed in circular shape

0.70

0.5

7/Compressed in circular shape

0.85

Size
(mm2)

Finished outside
diameter(mm)

Insulationmaterial(–)

Conductor resistance@20℃ (mΩ/m)

Mass
(g/m)

1.10

PVC

107.7

1.7

1.25

PVC

77.0

2.3

0.75

11/Compressed in circular shape

1.00

1.40

PVC

43.4

3.1

1

16/Compressed in circular shape

1.20

1.60

PVC

32.0

4.0

1.25

16/Compressed in circular shape

1.40

1.80

PVC

25.3

4.8

2

17/Compressed in circular shape

1.70

2.20

PVC

16.3

7.5

2.5

17/Compressed in circular shape

2.00

2.50

PVC

12.0

9.9

2

19/0.36

1.80

2.50

PVC

16.3

8.7

2.5

19/0.42

2.10

2.80

PVC

12.0

11.2

5

19/0.56

2.80

3.60

PVC

6.76

18.9

8

19/0.73

3.65

4.45

PVC

4.08

29.9

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Development of the Wiring System Technology to Realize its Weight-Reduction in Vehicles

2.1.2 Development of the technology for the closed
anticorrosion terminal (α Terminal)
The bimetallic corrosion is one of the problems when
adopting the aluminum wires in the W/H. It occurs underthe environment where all of three factors, water, salt, andoxygen exist. Therefore, such process as to isolate thedissimilar metal interface from these factors, that is, thecorrosion protection process is required.
Until now, resin molding was applied as the corrosion
protection process to prevent the aluminum conductors
from contacting water by covering the whole crimped
part with resin. However, this process has not been
adopted widely because a terminal with resin molding
over the crimped area occupies too much space to fit in
the same housing cavity with that for a current terminal
with no resin molding process. Furthermore, the individual corrosion protection process required time and equipment and the cost grew much higher.
Therefore, as a method to solve the problems mentioned above at once, we have developed the α terminal
which is a closed anticorrosion terminal giving a corrosion
protection function by itself without requiring any additional materials or process for corrosion protection.
(Figure 4)
The α terminal is such a terminal formed in the processof stamping press and welding to have on one-side anopen tube at the wire end instead of the open wire barrel
and insulation barrel. When crimping to have electric connection with conductor, the tube-shaped part of the terminal is crimped tightly over the insulation to remove any
room against water intrusion. The corrosion protection isrealized by preventing water intrusion. Because its structural components are only a terminal and a wire, theexpansion of occupying space, which was a problem incase of molding is controlled.

Figure 4 The α terminal.

Furthermore, it is excellent in cost as well, because no
additional process or equipment are required as the corrosion resistance process is completed at the same timewith the crimping. (Figure 5)
To realize the corrosion-free closed structure of the αterminal, it is required to bond the edges of the tubeshaped barrel of the terminal with a laser welding freefrom any defects, which is formed in the stamping press.
It is important for reducing defects in the welding to minimize the clearance at the edges to be bonded by applying our technology of highly accurate stamping press
forming. It is also important to control the effect of springing-back which always occurs at any metal processing.
To solve this problem, we have carried out such stamping
die design as adopting the springing-go which would
generate the process counterforce to the side ofsqueezed clearance by re-bending it from the excessive
bending condition. As a result, we have realized thestamping press process to minimize the clearance
between the edges to be welded.

Manufacturing process of the terminal(1) Form the tube shapewhen pressing the terminal(2) Welding on
contact area

W/H process(3) Wire insertion & crimping
Welding

Overlap welding

Fiber laser welding

Tube-shaped
terminal crimping

Aluminum conductor

Insulation
Terminal

Wire

Cross-section of compressed insulation
Close the crimped part tightly withthe tube structure + the compressed wire-insulation

Figure 5 The manufacturing process and structure of the α terminal.

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Development of the Wiring System Technology to Realize its Weight-Reduction in Vehicles

Furthermore, as for the welding, we have developed a
combination of the fiber laser and the 3D optical unit
exclusively for the manufacturing of the α terminal, which
is able to control the 3-dimensional trace of welding torealize the welding speed and the process accuracy tosynchronize with the stamping process speed. As aresult, we have built our high-speed manufacturing process synchronized with the stamping process. (Figure 6)
Further, it is necessary to prevent the bimetallic corrosion for this joint as well. We have applied the same water
protection for the welding joint of copper wires against
the corrosion.
We had a problem in the crimping process in which aterminal was connected with a conductor where thecrimping form of a current open-barrel type terminal(F-Crimp) could not be applied to the α terminal which
was a tube type one. To solve this problem, we haveexamined crimping forms optimized to combinations of
the aluminum wires and the welded-tube type terminals
and successfully developed the crimping form in which
the tube type barrel with a wire inside was shoved fromthe top side and the bottom side. (Figure 7)
This shoved shape of the crimp seldom causes thestress relaxation and avoids partial damages to the conductor by the barrel edges to bite through the insulation.

Stamping die
and punch
FeederMain body of thestamping press

It has easily realized both a stable electrical connection
and a sufficient mechanical strength to achieve a highreliability in the connection.
As for the corrosion protection process implemented at
the same time with the electrical connection, we haveanalyzed the physical properties of the insulation and its
behavior at the crimping process to find the necessary
conditions of repulsion force to guarantee the water tightness between the terminal and the insulation. We haveestablished the required specifications for the design torealize these necessary conditions in the crimping process.
Further, we have examined this crimping technology in
its implementation in automated equipment to improve
the productivity and the quality of the W/H. The first problem found was that it was required to insert a wire very
accurately into an uncovered mouth of the tube-type terminal. We have developed both the crimping applicatorand the automatic crimping machine combined together
and equipped the applicator with both a terminal holding
mechanism and a wire guiding mechanism to solve thisproblem.
The second problem was found that the projected
length of conductor after crimping could not be checkedby its appearances, and the quality of the crimping could

Fiber-laser welding

Inspection of
tube forming

Inspection of
welding condition

100% inspectionof the gap
RewindingreelMaterial

SupplyAutomatic
rewinding machineHigh speed stamping press

Control the welding trace
along the 3D shape of the terminal
with the 3D optical unit

Figure 6 Manufacturing process of the α terminal.

Crimped shape ofthe α terminal

Crimped shape ofa current terminal

Figure 7 Crimped shape of the α terminal.

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Development of the Wiring System Technology to Realize its Weight-Reduction in Vehicles

not be guaranteed in the process. We put a marking on
the insulation for image inspection and linked the wirecondition before crimping to the crimped condition after
crimping to realize the crimping with high reliability andhave solved the second problem.
The α terminal realized by the technologies mentioned
above has made it possible to use the aluminum wire
under the same environment as the copper wire and has
made a great contribution in expanding the adoption of
the aluminum wire in the W/H.
Further, we have also been making efforts in developing
the larger-size α terminal applicable to the larger aluminum wires of 5 to 8 mm2 in cross-section. It would realize
the replacement of larger-size copper wires, which would
produce larger effects in the weight reduction.
We had another problem that it was difficult to weld thethick plate material with high conductivity selected for theterminal by laser, when applying the α terminal to largesize aluminum wires. We had aimed at welding it by alaser with higher output but could not apply it actually,
because the unstable melting behavior caused by excessive energy input was too much to control. Then, weapplied the beam mode control technology to the conversion of the laser beam into the optional energy profile,which was developed by Furukawa Electric aiming to
expand the welding range of the fiber laser. Then, we
have established the welding technology to stabilize themelting behavior even under the high output and realized
the mass production of the α terminal for a large-size aluminum wire.
2.1.3 Development of welding technology for jointing
aluminum wires
With the increasing number of automotive system devices, the number of wires for power, grounding, and signals, which make up these systems, has been also
increasing. Along with it, the number of joints which connect these wires together has been increasing as well.
There are two techniques to joint circuits, one is to connect wires with a connector, and another is to connect
wires directly. From the viewpoint of weight reduction, thewelding joint which connects wires directly is more effective for the weight reduction than that with a connector.
In such a situation as mentioned above and aluminum
wires are adopted more and more, the development of a
new joint technology is required not only to connect aluminum wires themselves but also to connect aluminum
wires and copper ones combined together as well.
One of the difficulties to connect different metals of aluminum and copper is difference in their physical properties. We already have two techniques for the joint, crimping and resistance welding. It is difficult to secure therobustness in either the crimping because of their different tensile strength or the resistance welding because of
their different thermal conductivity. Considering the difference of physical properties, especially that of melting
point between them, we have selected the ultrasonicbonding as our joint technique, which would connect

them without melting. During our development, a problem
was found that an aluminum wire was bonded to theequipment by frictional heat generated by the ultrasonicvibration. To solve this problem, we carried out the ultrasonic bonding with inserting wires in a copper tube toprevent aluminum from bonding and have solved the
problem. With this solution, we have established the joint
technology between the aluminum wires and the copper
ones, which had never been applied to its mass production. (Figure 8) The bimetallic corrosion protection isrequired for this joint as well. And the conventional water
protection treatment for copper wires welding joint isapplied.

Figure 8 Welding joints between the aluminum wires and thecopper ones.

Development of Technology to Produce the
Ultra-thin Copper Wire (0.13 mm2 wire)
Responding to the requirement for the weight reductionof wires, we have developed such technology as not only
replacing copper wires with aluminum ones but also producing ultra-thin copper wires.
There was a problem for the ultra-thin copper wire where
the wire itself and the crimped part made up with a thinner conductor had less tensile strength and the wire waseasily broken at the crimped part during the pulling operation in the W/H assembling process. This problem wassolved by applying a conductor made of harden copper
alloy with high tensile strength. With it, we have improved
the mechanical resistance against the broken conductorsof the wire even for the ultra-thin wire of 0.13 mm2 andalso the crimped part as strong as that of AVSS 0.3.
We have found a further advantage in the ultra-thin wireof 0.13 mm2. When loaded with the same tensile force,the electrical characteristic of the current AVSS 0.3 deteriorated (increase of electrical resistance of the conductors) a lot but the ultra-thin wire of 0.13 mm 2 had lesselongation of the conductors and maintained the electrical characteristics at this condition with less deterioration.
2.2

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Development of the Wiring System Technology to Realize its Weight-Reduction in Vehicles

We had to consider the decline in the bending resistance when applying the hard copper alloy and haveselected the hard copper alloy with high bending resistance, which was already applied in the robot cable 3), andit has enabled the ultra-thin copper wire to be used at any
bending part as well.
The downsizing in diameter of the conductor was carried out for the ultra-thin copper wire of 0.13 mm2 bycompressing its conductor. Furthermore, its insulator
could be thinned by using a material with excellent wear
resistance. We have realized the further downsizing in
diameter with this insulation. (Figure 9)

the number of functional components installed in these
R/Bs with that of the previous model (2015 Model), it
increased from 107 pieces to 125 pieces as shown in
Figure 11, that is by 16.2% and the total input current
increased from 277 A to 371 A, that is by 34%.

2015 Model

2021 Model

Main
R/B

1.40 mm0.85 mm0.80 mm

Hard copper
alloy

CHFUS0.13

Figure 9 The ultra-thin copper wire of 0.13 mm2 .

3.

Sub
R/B

OUR ACTIVITIES TO REDUCE THE
WEIGHT OF COMPONENTS

3.1 Weight Reduction of Exterior Components
As shown in Figure 2, the protectors & tape / route guiding components are the 2nd heaviest next to the wires
and the weight of tape with which wires are banded
together and a lot of components which are fixed isremarkably heavy. Therefore, we have changed the tapefrom the normal one with 0.13 mm in thickness to anotherwith 0.07 mm in thickness, and further, we have changed
the design to reduce the tape volume by less taping on
the areas of protectors where the less taping would notaffect any quality issue. As a result, we have realized theweight reduction by approximately 300 g per vehicle.
3.2 The Downsizing and the Weight Reduction of
the Power Supply BOX by Integration
Not only the W/H but also the Relay Box (R/B) which carries functions of circuit protection and circuit switchingshows a trend of upsizing caused by new automotivefunctions and equipment added every year.
The targets of our development in this project were
those for the large-size SUV. It was equipped with a lot offunctions and equipment in it because of its wider diversity in uses. Inevitably, the number of functional components installed in the R/B increased and further, it was
designed as capable of installing potential equipment forsuch as automatic driving and so on for future demandbecause of its longer model life. So, it has become one of
the largest R/B in the world.
In this vehicle, two R/Bs (main R/B and sub R/B) areinstalled under hood as shown in Figure 10. Comparing

Figure 10 Relay BOX (R/B).

Number of components / Pieces

AVSS0.3

Tough pitch copper(electrolytic copper)

0.45 mm

140
120

PI (Power Integration)µ-ISO Relay
Hi CURRENT RelayPWR MIN Relay
MULTI Slow Blow Fuse
A1-Ⅱ Fuse
MINI Fuse

100
80
60
40
20
0

2015 Model

2021 Model

Figure 11 Comparison of the number of components between
the new model and the previous model.

These functional components are generating heat and
we always have a thermal problem when installing themtightly in the R/B. We have adopted thermal components
to suppress the heat generation such as heat pipes andpower plates until today, and on the other hand, we haverealized the downsizing and the weight reduction of our
R/B, by using our thermal simulation technology having
been developed in these 20 years.
Regarding the thermal simulation, the amount of heatgeneration by each component such as a fuse and a relay
was calculated, and a heat transfer coefficient was
obtained by calculating the amount of heat transferred
between the internal and external atmospheres. In addition, loading the heat transfer coefficient actual current
value as a condition to the thermal simulation modelcomposed with 3D modeled components, we have carried out the thermal analysis and Joule thermal analysis
reflected with self-heat generated from wires and bus
bars composing the circuit. And we have got the accuracy within ± 5 ˚C compared with an actual measured data.
(Figure 12)
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Development of the Wiring System Technology to Realize its Weight-Reduction in Vehicles

Repair W/H <Section of crimp area A>
Aluminum wire(copper wire)(vehicle side)
Crimp area A

Crimp sleeve(with insulation)

Aluminum wire(vehicle side)

Copper wire
Aluminum wire
Crimp sleeve

Repair W/H(copper wire)<Section of crimp area B>

Crimp area B Crimp area C

Figure 12 3D contour view of the R/B thermal analysis.

Feeding the result of the simulation mentioned above toour design, we have optimized the arrangement of components in the R/B to uniform the temperature in it. As aresult, we have satisfied the specified requirement without adding any thermal components.
Considering the functional difference of components,
the new model has accomplished the downsizing (projected area / number of functional components) by 5.3%
and the weight reduction (total weight / number of functional components) by 19.5% compared with those of2015 model.
3.3 The Technology Development of Aluminum
Repair Sleeves
In addition to our activities for the weight reduction ofcomponents, considering the spread of aluminum wires,we have developed the aluminum repair sleeve as our
support to an end user, which is used when repairing avehicle and contributed to the weight reduction by supporting the spread of aluminum wires.
The current repair sleeve used for copper wires inrepairing the W/H is not good enough in securing theelectrical performance of aluminum wires to be applied
for the W/H which includes aluminum wires. We havedeveloped the repair sleeve applicable for repairing theW/H including aluminum wires to solve the problem mentioned above. (Figure 13)
The structure of the aluminum repair sleeve is adequate
for its application to both aluminum wires and copper
wires. A ratchet type tool is in use to be sure to make thenecessary crimping shape and compression rate. A heat
shrink tube containing the adhesive free from any negative effects to the electrical performance is applied forelectrical insulation and water protection. With thosementioned above, we have successfully developed therepair sleeve for aluminum wires capable of securing theelectrical performance of aluminum wires.

Crimp sleeveheat shrinkable tube
(for water protectionand electrical insulation)

Aluminum
wire

Crimp
sleeveFigure 13 The repair sleeve for copper wires (top) and the repair
sleeve for aluminum wires (bottom).

4.

RESULTS

Until now, we have explained about the technology of theweight reduction of W/H to satisfy the requirement to
reduce CO2 aiming toward a carbon neutral society. With
these mass-produced technologies, approximately 11%
of W/H weight was reduced in the SUV released last year.
Among them, for the seat-harness, which has a large
weight reduction effect, we have replaced 115 circuits outof total 152 circuits at the maximum specification withaluminum wires (aluminum wire rate: 75%) to reduce theweight by 44%.

5.

CONCLUSION

Considering the global trend toward the sustainable environment, we have forecasted that our environmental
responsive technologies and products would be continuously required more and more by our society. Responding
to further requirements for the weight reduction, ouractivities to develop the weight reduction technology forthe future is essential. We will continue our developmentof new weight reduction technologies including aluminum
wires, in order to respond to needs for weight reduction,and contribute to the realization of the carbon neutral
society by the reduction in CO2 emission.

REFERENCES
1) Sho Yoshida, Shigeki Sekiya and Kengo Mitose: “TheDevelopment of the High Strength Aluminum Alloy Wire” P. 16 to
P. 22, Furukawa Review, No.49, 2018.
2) New Products “Aluminum Wire Harness”, P.6 to P.8, Furukawa
Review, No. 41, 2012.
3) Furukawa Electric Product Catalog “Copper and Copper Alloy
Wire Materials” 5th ed., 2021.

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