KAYABA TECHNICAL REVIEW No. 66 APR. 2023

TechnologyIntroduction

Incorporation of Processing of Base Plates for Piston Motors
into FMS Lines
HANAEDA Ken

1 Introduction

2 Purpose

As excavators in the Chinese construction equipment
market have become larger, there has been a demand forboosting production of large excavators. Under this situation, KYB Corporation has received more orders forpiston motors (Fig. 1) manufactured in its Sagami Plant(Fig. 2). It was decided to establish a plant-wide production system in Sagami Plant, requiring enhanced production capacity for the base plate (the part in red shown inFig. 1). Another demand was to reduce the selling pricewhile needing to develop competitive products. To increase the profit margin, it is essential to carry out activity to reduce the cost of the base plate that accounts for a
substantial proportion of the product cost.

To achieve the target manufacturing cost of the cost
reduction activity and to establish a new production system for base plates.

3 Targets- Manufacturing cost
- Base plate production capacity

Down 22%
Up 66%

4 Requirements[1] To cut back capital investment by optimizing production lines.
[2] To implement preventive maintenance using sensing
technology and internal automatic evaluation of machining centers.
[3] To ensure the process capability for precision deephole drilling.

5 Overview of Lines

Fig. 1 Piston motor
Production system established(two-shift operation)

Production [units/month]

Shortage of capacity

Production
Capacity with overtime
Capacity without
overtime

Target capacity

FY19

FY20

FY21

FY22

FY23

FY24

Fig.2 Projected production of base plates and production
capacity

The base plate processing line consists of a machining
process with machining centers (hereinafter the "MC")and a finishing process including deburring, inspection,honing, surface grinding, and jet cleaning. Among these,
the MC machining process may use the serial (Fig. 3) orparallel (Fig. 4) processing line configuration dependingon the number of types of work. These lines have the following features:[1] Serial line
Fast processing line with less set-ups for limited typesof work.
[2] Parallel line
FMS-based Note1) line with less set-ups for a variety ofwork. The use of FMS allows the production of manydifferent parts and unattended operation. Fig. 5 shows theFMS operation screen.
Note 1) Acronym for Flexible Manufacturing System.

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Incorporation of Processing of Base Plates for Piston Motors into FMS Lines

Fig. 3

Table 1Comparison of proposed approaches

ItemMark

Mark

Proposal [2] Parallel line

Characteristics―

Fast line with less set-ups―

FMS-based line with lessset-ups for a variety of work

Machine model―MSF-340 *One model―MAG-14 to MSF-340 *11models

×

Positioning is required in eachprocess. Some processes cannot
be divided to ensure theprecision requirements.

○Single-chuck machining. Not so
affected by the positioning
accuracy.

Quality Quality

Overview of serial processing line for base plates

Cost

Additionalequipment

×3 units○2 units

Extra personnel―+1 person/shift―+1 person/shift

Division of processing timecauses time loss○

Manufacturing cost

×

Processing time

×

Productivity Set-up

Initial and final
pieces check
Piecework

OthersOverview of parallel processing line for base plates

Fig. 5

FMS operation screen

6 Implementation
6. 1 Optimization of Production Lines
6. 1. 1 Overview of Improvement
To establish a base plate production system, an approach was introduced that added two more MCs to theexisting parallel line to achieve the target cost and thetarget production capability. Before deciding on the approach, two proposed approaches were compared witheach other: one was to add equipment to the existing serial line and the other to add equipment to the existing
parallel line, because building a brand new line requiredhuge capital investment.
6. 1. 2 Results of Comparison of Proposed Approaches
Table 1 shows the results of the comparison. The serialand parallel line approaches had their own advantagesand disadvantages and both approaches could satisfy thetarget production capability. In this project, the parallel
line approach was selected because it was judged to beable to satisfy the target cost with a minimum number ofequipment units with no time loss for dividing the processing time.

○
No division of processing time,
no time loss
Minimum tool changes○

A single product requires noextra set-up

×Extra small set-ups in finishingprocess○

Only parts machined in therelevant process to be measured

×All machined parts to bemeasured in each equipment unit―

Less vulnerable to process
trouble―Relatively easy to increase
capacity with additionalequipment―

Simple physical and information
flows

―

Easy to implement unattended
operation due to long processingtime○Advantages

Total evaluation

Fig. 4

Proposal [1] Serial line××○

 utomation of Jig Inclination Measurement and6. 2 A
Automatic Internal Evaluation
6. 2. 1 Current Problems
The base plate is subject to a stringent tolerance for thesquareness between the reference plane and the bearing
bore. To maintain the accuracy, it is essential to always
achieve the squareness of work to the MC spindle (Fig.
6). Conventionally, operators have tried to ensure the accuracy by manually measuring the accuracy of the MC
spindle and jig. However, such manual measurement involves destabilizing factors including misadjustment,
mismeasurement and forgetting to measure.
6. 2. 2 Automatic Measurement Using Touch Sensor
Higher capital investment leads to higher cost. Then,
we built a software program to automatically measuredisplacement and evaluate equipment accuracy by using
the touch sensor installed in the MC process. The following describes the measurement flow and Fig. 7 shows theflow chart of the measurement program.
[1] If the last accuracy measurement was in the previous
month or earlier, proceed to the measurement sequence (monthly measurement)[2] Using the touch sensor, measure the reference planeof the jig that is clamping work (Fig. 8).

Fig. 6― 14 ―Positional relation between work and MC spindle

KAYABA TECHNICAL REVIEW No. 66 APR. 2023

[3] If the measurement result is within the specification
limits, proceed to the machining sequence. If the result is out of the limits, issue an alarm to urge operators to take remedies.

Fig. 7

 nsuring Process Capability by Improving the6. 3 E
Honing Stone
6. 3. 1 Current Problems
The spool bore, which is an important part of the baseplate, is roughly machined in the MC process and thenfinished by the honing machine. In the initial quality
check, however, the process failed to meet the spool bore
cylindricity requirements. A comparison of cylindricity
before and after honing revealed that the cylindricity actually worsened after honing (Figs. 10 and 11).

Flow of measurement program

Fig. 10Fig. 11

Fig. 8Measuring point of touch sensor

6. 2. 3 Verification of Proposed Approaches
We compared the measurements of actual work withthe jig specifications because we could not directly measure actual work. We determined that the measurements
satisfied the work specifications when they met the jigspecifications (Fig. 9).

Fig. 9Before honing

After honing (before improvement)

6. 3. 2 Causes of Lower Honing Accuracy
A cause investigation identified two possible causes oflower honing cylindricity:[1] Bore profile specific to the base plate
Fig. 12 shows the cylindrical section of the spool bore.
Problems occurred in the parts c and d in Fig. 12. In therelevant parts, the circumference of the circle is partiallygrooved. The presence of the machined grooves affects
the processing area, resulting in substantial variations in
cutting load.

Fig. 12

Relation of measurements between jig and actual work

Section view of spool bore

[2] Hardness of the bond of honing stones
Adjustment work must be carried out every time thehoning stone is replaced. So, a relatively hard bond has― 15 ―

Incorporation of Processing of Base Plates for Piston Motors into FMS Lines

been conventionally used to extend the stone change cycle. While the service life of the stone has certainly beenlonger, the self-sharpening effect has been reduced, worsening the honing performance.
6. 3. 3 Improvement of Working Accuracy by Changing the Stone Bond
As mentioned above, there has been a conventionaltendency that relatively hard bond is used to extend thestone life. To address the problem that dull stones areused to hone the parts with substantially variable cutting
load, it was decided to use a softer bond. The use of softer stone bond improved the self-sharpening to ensure that
new abrasives are always exposed. This has improved thehoning performance, achieving stable processing not depending on the work profile.
6. 3. 4 Verification of the Proposed Approaches
A verification of the accuracy after improvement hasdetermined that the cylindricity has been substantiallyimproved (Fig. 13). Furthermore, a quality check after
continuous processing (N = 20) has determined that thecylindricity, which had been around the upper limit of thespecifications, was substantially improved, satisfying theprocess capability requirements (Fig. 14). Despite theconcern with the softer bond, the stone adjustment time
per replacement has been shorter. The total tool change
time has remained the same because the frequency ofstone replacement has increased.

7 Results
Table 2 shows the results of the improvement.
Table 2

Results of improvement

Item

TargetResultManufacturing cost

Down 22%

Down 19%

Evaluation
×Production volume

Up 66%Up 64%△

Possible causes of failing to achieve the targets are:[1] Higher manufacturing cost due to lower availability
A major cause of lower availability was that work
waiting for finishing had to be temporarily placed at
the point where several types of work join after theFMS area. To improve the situation, we plan to install
shelves for work waiting for finishing. This improvement is expected to help achieve the target.
[2] Deviation from the initial production plan
The reason for failing to achieve the target production
volume was that the initial production plan for the target month for evaluation was not achieved. Still, thetarget production capacity was achieved.

8 Conclusions
Fig. 13

We have successfully implemented stable preventive
maintenance using a new measurement method, thereby
establishing a product satisfying the process capability
which was conventionally difficult to achieve. From now
on, we will carry out activities that can develop preventive maintenance into predictive maintenance based on
accumulated data and will also continuously improve theavailability whose target has not yet been achieved.

After honing (after improvement)

9 In Closing

Fig. 14

Finally, I would like to take this opportunity to express
my appreciation to the related functions that extendedcooperation in building the production line as well as
those who extended guidance and support to us.

Cylindricity before and after improvement

Author 
HANAEDA Ken
Joined the company in 2008.
Production Engineering Dept., Sagami Plant, Hydraulic Components
Operations
Mainly engaged in machining process engineering for PPM products.

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