Construction of Case Machining Line for Piston Pump

TechnologyIntroduction

Construction of Case Machining Line for Piston Pump
ITOU Yuusuke1Note 1) An abbreviation for piston pump motor
Note 2) A system that controls the pump discharge to supply theflow as much as needed

Introduction

PPM Note 1) products manufactured in KYB Sagami Plant
include piston pumps (Fig. 1). The piston pump is used as
a component of hydraulic excavators. One of the components of the piston pump is a pump case (Photo 1) (hereinafter "the case"), which is the core part of the pump.
With the recent rising market demand for environmental measures and energy saving, the demand for piston
pumps with a load sensing control Note 2) is expected toincrease (Fig. 2). We are thus required to manufacturecompetitive products of this kind. Among the piston pump
manufacturing processes, the one involving the highest
manufacturing cost ratio is case machining. It is therefore
indispensable to reduce the cost. Then, in preparation for
the establishment of a new production line, we have successfully established a level of quality, which had been
hardly accomplished before, to achieve higher availability
and shorter cycle time (hereinafter "CT"). We have finallybuilt a production line that can realize lower manufacturing costs.

Production volumeFig. 1

Piston pump

Photo 12

2.1 Case Machining LineThe pump case machining line consists of machining
centers (hereinafter "MC"), deburring, rough cleaning,inspection, and jet cleaning (Fig. 3).

Note 3)

Material

Fig. 3

Inspection

Jetcleaning

Finishedproduct

Manufacturing process

2.2 Problems
The MCs can provide an integrated process Note 4). EachMC can deliver finished products by itself. The problem isthat, after products have been machined, they are measured on the same MC, resulting in a long cycle time.
Dimensional correction is conducted as the necessity
arises, which leads to lower availability. In addition, thepump case is a heavy workpiece (18 kg) to be lifted using
a crane. This dangerous work is a factor in the long manual
handling operation.
Note 4) A single MC can support all related processes.

Production 1.4 times
the benchmark3

PurposeTo improve productivity to build a production line forlower manufacturing costs.

2021 2022 2023 2024 2025 2026
Fiscal year

Fig. 2

Deburring

Roughcleaning

Note 3) Machined product

Pump case

BenchmarkLine Overview and Challenges

4

Objective

Table 1 shows the target values.

Estimated production volume of piston pumps― 38 ―KAYABA TECHNICAL REVIEW No. 64 APR. 2022
Table 1
Item

Target (from theconventional level)

Production volume

33% upAvailability

6% up

Cycle time

27% down

Personnel

1 person reducedCase
Spindle180-degree turn
Bore on the front (a)SpindleMisalignment

Bore on the back (b)Overview of front/back machining of caseFig. 4

Requirements

Variations in outside
air temperature

Displacement① The machining accuracy shall be improved to ensure
the required quality without relying on human operation.
② The machining rate shall be increased to reduce themachining time (hereinafter "MT").
③ Work handling shall be achieved without using a crane
to remove dangerous tasks.

Outside air temperature (°C)

5

Target values

Displacement
6

Achievements

Equipment displacement

6.1 No more 100% measurement in MCs
6.1.1 Conventional Quality Problems
The case has two holes as its critical parts: one is on thefront and the other on the back (Photo 2). In fact, alignment of these holes (coaxiality) was difficult to beobtained (Fig. 4), resulting in 100% manual measurementand dimensional adjustment. These additional tasks
degraded the availability and productivity. The casemachining was conducted by turning the machining tableby 180 degrees to machine the front or the back or viceversa. Naturally, the machining quality was affected by
the equipment accuracy. This was found to be attributableto variations in outside air temperature superimposed by
the heat generated during continual machining, whichdisplaced the equipment, resulting in unstable machining
positions (Figs. 5 and 6). To follow any displacement of
the equipment due to temperature variations, temperature
sensors and temperature control systems needed to beadded, which meant even higher capital investment.

(a) Front(b) Back
Photo 2BoreFig. 5External temperature

Equipment displacement due to outside airtemperature
SpindleOrigin ofmachine

Table

Center ofrotation

Reference
position
Displacement

Equipment is displaced withoutside air temperature.

Fig. 6

X-axisConceptual rendering of displacement

6.1.2 Internal Measurement using TouchSensors
High capital investment leads to high manufacturingcosts. So, a software program has been developed tomeasure displacement or deviation from the reference
position using the touch sensors already mounted on theequipment and compensate for any displacement toachieve the machining target values (Fig. 7).
① Measure the position of holes provided in the jigs andthen establish reference values as initial settings forequipment introduction② Before mass production, measure the position of theholes in the jigs before machining and add any deviation from the reference value to the machining target
value
If the equipment is displaced during mass production,
the hole position in the jig changes. That is, the deviation― 39 ―

Construction of Case Machining Line for Piston Pumpfrom the initially set reference value will be the displacement of the equipment.
This measurement has made it possible to satisfy thecoaxial front and back machining capability. The 100%
measurement during mass production is no longer necessary to achieve shorter CT. The dimensional adjustment
has been also abolished to eliminate any adjustment loss,
thus improving the availability.

Down milling→ Resistance applied in a direction
opposite to the direction of travel
ResistanceResistance

Rotation
Up milling→ Resistance applied inthe direction of travel

Equipment
preparation

Record the position
as reference

ResistanceResistance

Feed

Cutterrotation

Up milling

Resistance

Jig hole(positionsensing)

Measure the positionof jig holes
Massproduction

Down milling

Rotation

Resistance
Measure the positionof jig holes

PathFeed

Resistance occurs in two directions,which is likely to cause chattering

WorkFig. 9

Calculate deviationfrom the reference

Milling (before change)

Add the deviation to
the coordinate system

Down milling

CutterrotationFig. 7 Program flow and machining jig

Resistance

6.2 MT Reduction with Optimal Milling Path
Among the case machining processes, milling is themost time-consuming one (Fig. 8). In the conventional
milling technique, the milling cutter moves along theshortest path to accomplish the required machining. Since
50% of the perimeter of the cutter was used for milling,
the cutter involves mixed operation of up milling anddown milling. In fact, this resulted in unstable cutting
resistance, which might cause chattering (Fig. 9). Themilling machine eventually machined work at a lower
speed, resulting in a prolonged MT.
To solve the problem, an optimal milling path has beendeveloped to be suited to the complex geometry of thecase (Fig. 10). The cutter has then become able to machine
only with down milling being applied with cutting resistance in a fixed direction, successfully suppressing chattering. The machining speed has been doubled to reduce
the MT.

PathConstant resistance to suppress chatteringFig. 10

Milling (after change)

6.3 Reduction of Manual Handling Time byImproving Jig Installability
The horizontal MC uses cross jigs for machining thecase. Work must be set in position horizontally (Fig. 11).
Lifting the heavy work involves danger tasks. The use ofa crane makes it difficult to accurately position work,
taking more time to complete attaching or detaching. As aresult, the target manual handling time cannot be met.

WorkJig

Machining time

Install・May drop・No support

ø100 milling cutterø25 reamer
ø40 milling cutter
ø4.8 drill
M6 formed tool
Touch sensor
ø12.5 reamer
ø16.0 end mill
ø24.97 burnisher
M6 tapø10.3 drill
M12＊1.75 tap
ø32.8 formed toolR-chamfered drill
PF 3/4 formed tool
ø24 T-slot cutter
ø25 formed tool
PF 1/4 formed toolFig. 11Fig. 8

Machining time of individual processes

Conventional way of setting work

To solve the problem, a jig that can allow the operator toset heavy work without lifting using a crane has beendeveloped (Photo 3).
When loading, the work is slid into the jig from thecarrier cart and guided by the jig for temporary positioning. The operator can just push the work to the end toaccomplish final positioning with the aid of tapered pins
― 40 ―KAYABA TECHNICAL REVIEW No. 64 APR. 2022

(Photo 4). With improved operability of jig setting, thework attach/detach time has been reduced by 50% and themanual handling time in the total production line has been
reduced by 20%.

7Results

The target values have been achieved. The results areshown in Table 2.
Table 2

Fall prevention

Tapered pin(positioning)

Results

ItemAchievements (from theconventional level)

Production volume

36% upAvailability

14.7% up

Cycle time

27% down

Personnel

1 person reduced

Guiding8

Jig overview

Photo 3A new measurement method has been developed toachieve the process capability for the machining accuracy
that was difficult to be achieved before. A new production
line has been built to no longer involve dangerous tasks or
no longer put a load on operators.
We will deploy this technique to realize new products atlower costs in future.

Work is slid into position
JigCarrier cart

Cart can slide
up to jig

Photo 4Conclusions

9In Closing

I would like to take this opportunity to thank all thoseconcerned from related functions who extended cooperation to the building of this production line as well as all
those who gave guidance and support to us.

Work in position

Author 
ITOU Yuusuke
Joined the company in 2017.
Production Engineering Sect.,
Production Engineering Dept.,
Sagami Plant, Hydraulic Components
Operations
Mainly in charge of design of pump
manufacturing process for PPM
products― 41 ―