TECHNICAL REPORT

Development of a Small-scale CVJ Forging LineT. MISHIMA

We have improved the global standard forging line for the CVJ outer race by transforming it into a smaller linethat is simple and versatile. This line achieves a lower manufacturing cost with cost down technologies such aspress downsizing and integration of transfer equipment. Furthermore, to maintain forging quality, this line has ahigh precision sizing method and new lubrication system.
With this line regarded as the Global Standard Line, we are expanding the same concept line overseas.
Key Words: CVJ, forging, downsizing, transfer, global standard line

1. Introduction
The environment surrounding the automobile industry
over the past few years, while remaining sluggish
regarding demands in Japan, has seen a gradual shift inproduction to overseas locations as demands within Asia
have risen. Furthermore, forging processes have until
now focused mainly on large-lot production on large size
equipment, requiring a large amount of WIPs (work inprocess) due to the length of production lead time. The
global development of JTEKT, however, requires theconstruction of a small-scale production line with low
investment which incorporates downsizing, simplicity,versatility, and easy changeover of work number. We havetherefore focused our efforts towards the “development ofa small-scale CVJ forging line” for the outer race, a CVJ
component.

CVJ (constant velocity joint)

Fig. 1 CVJ installation position
InboardClamp

Square snap ring

2. 1 CVJ installation position and components* CVJ: Constant Velocity Joint

Clamp
Intermediate
shaft

Round snap
ring×3Retainer×3
Needle (multiple)
Roller×3
TripodOuter race

2. About the CVJ
The CVJ, which transmits drive force to the tire,is installed inside the vehicle in the positions shownin Fig. 1. Within each vehicle, there are two CVJs inthe front of FF vehicles, two CVJs in the rear of FRvehicles, and four CVJs within AWD vehicles. The CVJ
is comprised of four components, including the outer race
(inboard, outboard), inner race, and tripod (Fig. 2).

Boot

Outboard
Round snap ringDeflector

Clamp

Boot

Clamp
Intermediate
shaft

Outer race

Cage

Inner race

Ball×6Fig. 2 CVJ components

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−Development of a Small-scale CVJ Forging Line−

2. 2 CVJ forging process
As shown in Fig. 3, the outer race is warm forgedfrom steel and completed within the cold sizing
process. Production conditions, which are specified foreach process, are maintained and operated using theappropriate measuring devices.
Steel material

CuttingHeating

Air cooling

Shot blasting

Warm forging

Single process lubrication

Cold sizing

Fig. 3 Process flow chart for outer race forging

3. Construction of a small-scale forging lineand refer to our ideal state to pinpoint issues which shallbe resolved before implementing global application.
By doing so, we shall create a versatile line that can beoperated without experience, intuition or know-how.
The results in Fig. 4 show that for the GSL for CVJs,
we have halved the total length of the conventional line
22and reduced space by 58% from 304 m to 127 m . Thishas been achieved by directly connecting processes fromthe heater up until cold sizing, and decreasing the sizeof equipment. This has consequently achieved a 10%
increase in space productivity, from the conventional 585
2products per month per m to 636 products per month2
per m . In particular, the elimination of WIPs has greatly
reduced production lead time from the conventional twodays, to 0.03 days.

Conventional line CT: 4.5 sec./workpiece

3. 1 Line concepts

Shear cutting

As stated previously, the conventional forging processused for the outer race consisted of a long production
line which included a large size forging press, requireda large amount of WIPs due to large-lot production, andhad a long production lead time. To resolve these issues
within the Global Standard Line (GSL) for the CVJ, wehave conducted an investigation based on the following
concepts:(1) Forging line that enables added value at one half theproduction scale(2) Small-scale line suitable for small-lot production(Simplification and downsizing, no changeover)(3) Utilization as mother line and global application

3. 2 Goal setting and results
To promote global application of the line, we have set
the following goals (Table 1) which include improvementof operational availability and shorter production leadtime (reduction in WIPs) through line scale downsizing.
We also plan to establish the developed line as the GSL

Total length: 80 m
Material loading device
Billetheater Warm forging press
Cooling conveyor
Loading
Shot
blasting conveyor

Single processlubrication

Production lead time: 2.0 days

WIPs for0.3 days

23 000 products within line

GSL

Sizing press

WIPs for1.6 days

CT: 11.5 sec./workpiece
Total length: 40 m
Saw cutting machine
Material loading
deviceBilletheaterWarm forging 600-ton press
Warm forging 1 000-ton press
Cooling
conveyor Inline shot
blasting

Single processlubrication/
Sizing press

Production lead time: 0.03 days (32 min.)Table 1 Setting goals
ConventionalGSLline

Item

130 products within line

Aim/Target①Investment
amount％10050−②Production
capacity％

10050

Reduce production
scale by half

③Reduce production％
lead time

10025

Reduce WIPs

④Operational
availability

7085

Improveproductivity

78％

Fig. 4 Comparison of conventional line and global
standard line

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3. 3 Simplification and downsizing of forging press

3. 4 Robotization of transfer between processes

To create a simpler and more compact warm forging
press, we have optimized the internal mechanism of thepress, thereby achieving a more compact structure andreduction in number of parts, and contributing to lower
investment.
Furthermore, while the conventional line required a
2 000-ton press, we have achieved downsizing suitable
for small lots by a tandem press combining a 600-ton anda 1 000-ton press. We have also increased the speed ofstrokes from 40 spm (strokes per minute) to 60 spm, andabolished the deceleration mechanism by employing aservo motor. Table 2 shows the effects of investment andthe items optimized within the internal mechanism. Inaddition, Fig. 5 shows the parts of the forging press whichhave been optimized.

In contrast to conventional transfer between forging
processes, which mainly used a transfer unit, thedeveloped small-scale forging line utilized a robot
transfer system. A transfer unit requires transfer chuckchangeover and adjustment between each product numberand process, lengthening the time between changeoverand causing errors when adjustment is insufficient. These
factors cause reductions in line operational availability.
We therefore investigated transfer methods able totransfer products using the same chuck, regardless ofdifferences in forged shape or size. Through this study,
we were able to standardize a chuck for all productnumbers, shown in Fig. 6, thus eliminating the needfor adjustment and changeover. Furthermore, we haveestablished the optimum equipment layout, die design,process design and timing of lubricant coating by using
robot simulation analysis (Fig. 7) to optimize cycle timeand conduct preliminary verification of the interference
between the robot transfer unit and the peripheral
equipment. In particular, we have efficiently utilized
the space created by transfer robotization for lubricant
coating by optimizing the coating position of the moving
nozzle, which has greatly contributed to improving dielife (Fig. 8).

Table 2 Effects of investment and optimization ofinternal structure
Item

Conventional line

GSL

Pressing
capacity

2 000 tons

600 tons+1 000 tons

Deceleration Two-stage reduction
mechanismgear shaft

None

No. of strokes

40 spm60 spmMain motor

Inverter motor

Servo motor

Transfer

Transfer unit

Robot

Investment
amount100％

60% (two units)

Forgedshape

Irregular shape

Round shapeLarge

Conventional line press
Two-stage reduction gear

SmallInverter motor

Fig. 6 Robotized transfer between processes

GSL press
No reduction gear shaft

Servo motor

Fig. 7 Robot simulation analysis

Fig. 5 Optimized portions of forging press

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3. 6 Development of high precision sizing method
Punch

Coating fromoutside trajectoryof workpieceand punch

Lubricantdoes notreachdeeper areas

The conventional cold sizing method conductedpressing with the cup facing downwards, in which casethe stem area of the workpiece cannot be restricted.
This caused instability of the workpiece posture during
pressing. As a result, a large amount of variation occurredin stem runout. As a countermeasure, we have changed
the sizing method so that pressing is conducted withthe cup facing upwards. This restricts the stem area andmaintains stable workpiece posture, which suppresses
stem runout and successfully reduces stock removal.
Stem runout has been reduced from the conventional
standard of 2.0mm in diameter to 0.8mm in diameter, andstock removal has been reduced from 1.3mm on one side
to 0.8mm on one side. This has enabled a reduction inmaterial weight by 20 g.
This sizing method has also reduced the weight ofthe die set by 30% in comparison with the conventionaldie set, contributing the ease of mold replacement andmaintenance (Fig. 9).

Coating fromdirectly aboveand below using
moving nozzle

Moving nozzle
Die

Conventional lineGSL(Transfer unit transfer)(Robot transfer)

Fig. 8 Review of die lubrication method

Runout tolerance and stem stock removal

Weight of die set

ConventionallinePostureunrestrictedWorkpiece

1 100

Runout tolerance standard: 2.0
Stem stock removal: 1.3mm/side

Sizing die
Sizing punch

Runout tolerance standard: 0.8
Stem stock removal: 0.8mm/side

Sizing die750

GSL

Sizing punch

Posturemaintained

Workpiece

Restriction bystem O.D.
Shoulder backpressure control
Effect (Comparedwith conventional)

−20 g

−30％

Fig. 9 High precision sizing method

80

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−Development of a Small-scale CVJ Forging Line−

4. Results of implementation
The GSL was installed at the Tadomisaki Plant
in January 2013, achieving the pursued goal values(Table 3).
Table 3 Results
Conventional line

GSL

Aim/Target①Investment amount

Item％

10050

−Result Evaluation
60

×②Production capacity

％

10050

Reduce production scale by half

50○③Reduce production lead time ％10025

Reduce WIPs

0○④Operational availability

7085

Improve productivity

87○％○ : Goal achieved × : Goal not achieved

5. Conclusion
We have achieved the development of a small-scaleforging line with high versatility through the creationof new engineering methods, including a review ofspecifications of each unit of equipment. The developedline achieves 0.95 (CIM) compared to the 1 (CIM) ofthe conventional line, through accomplishments suchas halved production capacity and 40% reduction ininvestment amount. We will continue to downsize
production processes and further reduce investments inorder to lower costs.
*CIM: Cost Index of Manufacturing

T. MISHIMA**JTEKT ENGINEERING JOURNAL English Edition No. 1013E (2016)

Casting & Forging Production Engineering Dept.,
Production Engineering Headquarters

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