KAYABA TECHNICAL REVIEW No. 65 OCT. 2022

TechnologyIntroduction

Making Plating Thickness Constant by Simulation
MIZUNO Yuuki, TERADO Ayuko

Introduction

2This chapter describes the major characteristics of electroplating including hard chrome plating. For electroplating, the film thickness is generally proportional to thequantity of electricity (current × time) (Faraday's 1st law).
When applying plating to workpieces, the current islikely to concentrate at the edges of them, resulting inthicker films (Fig. 2). This phenomenon can be prevented
by the use of shorter electrodes. In facilities where workpieces of different lengths are plated, however, just changing the length of the electrode would not be enough. Then,jigs can be installed at the edges of a workpiece to suppress the concentration of the current at the edges, curbing
the increase in plating thickness.

PlatingWork

Surface of plating solution

ElectrodeNote 1) M asking jigs used to prevent plating or limit the film
thicknessNote 2) Three to four tries were needed before completion: 2weeks/try(according to interviews with operators)

Work

Surface of plating solution

Plating

Recent years have seen the promotion of digital technologies including artificial intelligence (AI) and Internetof Things (IoT) in virtually all fields. Even techniques thathave long been conveyed as craftmanship are becoming
subject to standardization with digital technologies.
KYB Corporation frequently applies hard chrome
plating to sliding parts of shock absorber piston rods andother components. This plating requires masking jigs
(hereinafter "jigs") Note 1) because of its characteristics.
Conventional jig design relies on work learned only
through actual experience (so-called knack or intuition) ofoperators. It is difficult to achieve constant deposition ofplating (hereinafter "film thickness"). Since jig fabricationand plating prototyping are needed for each try, many
man-hours are spent to discuss and determine the form ofjigs Note 2) (Fig. 1). With this background, KYB has developed a jig design methodology requiring no knack orintuition by utilizing simulation software. This paper
introduces a case study of our efforts to achieve constantplating thickness of industrial hydraulic equipment products by means of simulation.

Characteristics of Electroplating

Electrode1

Jig

Fig. 2 Illustration of effects of jigs

Designerror

3
Jig fabrication

Form modification

Trial platingCompletion
Fig. 1Repeatedtrial and error

Conventional jig design flow

Preliminary Test on Stepped Work

Before redesigning the jig through simulation, a preliminary test was conducted using a stepped workpiece.
Fig. 3 shows the front view of the preliminary test equipment. The workpiece and electrodes are vertically inserted
into the plating bath. In total four electrodes are installedaround the workpiece. This stepped workpiece consists ofthick and narrow sections: the former has a diameter ofø22 and the latter ø10. All of these sections, regardless ofthe diameter, are 100 mm long. The test conditions areshown in Table 1. As mentioned in the previous chapter,―3―

Making Plating Thickness Constant by Simulation

High

ElectrodeCurrent

Work

The trends of film thickness distribution of sections A,
B and C obtained through simulation almost match thoseobtained through actual measurement. Therefore, the use← density →the edges or corners of the workpiece are likely to havehigher current density which builds thicker films. The test
was carried out to verify whether this phenomenon can be
reproduced in simulation.

Plating bath

Low

Table 1

Plating conditions for preliminary test

Item
Plating bath
Plating solution temperature
Plating area
Current density
Current setting
Plating timeSettings
Sargent bath
50°C
1.7 dm2
40 A/dm2
70 A
30 min.

Analysis results (current density distribution)
Measurement
Analysis

Distance from solution surface [mm]The simulation software used for this research isintended to be used for analysis of current density (A/dm2). Since analysis results cannot be directly comparedwith film thickness measurements, the analysis results (A/dm2) have been converted into the film thickness (μm)
using Equation (hereinafter "Eq.") (1):Film thickness μm = Deposition speed μm/min·A·dm-2 ×
Current density A/dm2 × Plating time min × Current
efficiency
(1)Fig. 5Film thickness

Sketch of preliminary test equipment
Film thickness

Fig. 4
Fig. 3Comparison in section A

Measurement
Analysis

Distance from solution surface [mm]―4―Fig. 6

Film thickness

A contour diagram of the analysis results is shown inFig. 4. For convenience, the top section of ø22 is called A,
the middle section of ø10 called B, and the bottom sectionof ø22 called C. The edges of sections A and C as well as
the central part of section B have a higher current density,
while the edges of section B have a lower current density.
Comparison between the analysis results and the measurements are shown in Figs. 5 to 7. For the purpose ofthis paper, the "film thickness" (vertical axis) in theFigures indicates individual measurements that havebeen divided by the mean value of the film thickness ofthe flat parts (A: 10 mm to 60 mm, B: 130 mm to 170 mm,C: 230 mm to 270 mm) of the workpiece and then madedimensionless.

Comparison in section B

Measurement
Analysis

Distance from solution surface [mm]Fig. 7Comparison in section C

KAYABA TECHNICAL REVIEW No. 65 OCT. 2022of the simulation model and conditions developed for theresearch can be used to obtain a film thickness distribution similar to the actual phenomenon.
4Making Film Thickness Constant

Since the simulation model was validated through thepreliminary test, its utilization in mass production equipment was tried.
4.1 Target Product
The piston rods for forklift cylinders were selected as
the target product (Fig. 8).
Cylindertime and consumed extra electricity and chemicals.
While the central part of the rod has a constant film
thickness, the edges of the rod have uneven film thicknesses due to the concentrated current and the shielding
effect of the jig. Through comparison with the simulation
results, it was verified that the tendency of the film thickness distribution was successfully reproduced.
4.3 Redesigning the Jig
To make the current density distribution indicated by
the analysis results more uniform, we tried to find an
optimal form of the jig by repeatedly changing and analyzing the aspect ratio, hole diameter and the number ofholes of the jig model (Fig. 10). This redesigning was
carefully conducted because the current density distribution greatly varies with the jig form (Fig. 11). The authors
Analysis software
conditions
setting

Gear pump

Model creation
with CAD
softwareControl valve

Fig. 8Target productCalculation

4.2 Conventional Jig
Fig. 9 shows measurements of plating thickness
obtained with the conventional jig (Photo 1). An electromagnetic plating thickness gauge was used to measure thefilm thickness of workpieces longitudinally along astraight line. The Figure includes a sketch of the workpiece installed with the jig.
The jig design was based on operators' knack and intuition, resulting in uneven film thicknesses. In particular,
the masked portion had a substantially lower film thickness. To compensate for the film thickness in this portion,
thicker plating was made overall. This led to longer plating

Model modification

Result checking

Jig fabrication

Trial plating

Completion

Fig. 10

Jig design flow using simulation software
Design #3

Design #1

Photo 1

Design #2

Conventional jig

Current density

Film thickness

Measurement
Analysis

Distance from the top edge of plating

Fig. 9Final design

Design #1
Design #2
Design #3
Final design

Distance from the top edge of plating

Comparison between measurement and simulation(conventional jig)

Fig. 11―5―

Analysis results of various jig model versions

Making Plating Thickness Constant by Simulation

had no previous experience of jig form design. After about
two weeks of redesigning work, the "final design" includedin Fig. 11 was obtained through repetitive modification of
the jig model.
As indicated by the workflow in Fig. 10, the simulation
cycle was effectively used to successfully fabricate the jig
and verify the plating with a single try.
4.4 Verifying the Effect
The jig prototype obtained through the jig fabricationand trial plating processes was compared with the conventional jig. For the purpose of this paper, the prototype iscalled the "improved jig" (Photo 2). Fig. 12 shows film
thickness measurements with the conventional andimproved jigs. The film thickness variation {(Maximum
film thickness - Minimum film thickness) / Mean filmthickness} of the conventional jig was 57% of the mean
film thickness. In contrast, the film thickness distributionof the improved jig was as low as 11% of the mean value.

Analysis software
conditions
setting
Optimization software
Model creation
with CAD
softwareCalculation

Result checking

Jig fabrication

Completion

Film thickness

5

Jig design flow using optimization software

5.1 Conditions Setting
For the purpose of redesigning the jig, the five parameters listed in Table 2 were selected for conditions settingin the optimization software. 100 combinations of parameter settings were subjected to calculation by the software
to determine the jig form with the smallest variation infilm thickness. Fig. 14 shows what the parameters indicate
in the actual jig.

Improved jig

Conventional
Improved

Parameter settings for optimization software

Table 2

Distance from the edge of plating

Fig. 12

Automatic model
modification &calculation

Trial plating

Fig. 13

Photo 2Model modification

Comparison of film thickness measurements

Further Efforts for Even Higher Efficiency

The company's traditional jig improvement relied on
operators' knack and intuition and the redesigning required
about six weeks. For the authors' jig improvement throughsimulation, the redesigning time was reduced to twoweeks. However, the model improvement through simulation involved repetitive trial and error and could notcompletely exclude the dependence on operators’ knackand intuition. The reduction of improvement time remains
a big challenge even after the introduction of simulation.
Then, we tried to reduce the redesigning time andeliminate the dependence on knack and intuition by introducing an optimization software product Note 3) to allow themodel modification and calculation processes to be done
automatically (Fig. 13).
Note 3) Software used: Simcenter HEEDS®

―6―Parameter settings
Outside diameterø47-85 mm
Height5-130 mm
Hole diameterø1-30 mm
Number of longitudi2-10
nally aligned holes
Number of circum4-20
ferentially alignedholes

100
combinationsof parametersettings wereanalyzed.

Work

Electrode
Electrode

No. ofcircumferentiallyaligned holes

HeightODWork
No. oflongitudinallyaligned holes
Upper surfaceof plating bathFig. 14

Front view of jig

Locations of parameters

Jig

KAYABA TECHNICAL REVIEW No. 65 OCT. 2022plating has been applied based on the film thickness at theedges, which is lower as shown in Fig. 16. Plating in thisway will provide an excessive film thickness on the flatpart that is away from the edges of the plated work. Then,the improved jig can be used to ensure work has a higher
film thickness at the edges than on the flat part, thereby
enabling the excess in film thickness to be eliminated (seethe shaded zone in Fig. 16). The plating time can also be
reduced by an amount corresponding to the film thickness
reduction, leading to lower processing cost and lower CO2emissions.

Film thickness

5.2 Film Thickness Measurements
The model obtained through calculation using the optimization software was used to fabricate a jig (Photo 3).
This jig was trial plated and then subjected to measurement of film thickness.
As shown in Fig. 15, the film thickness variations werereduced to about 1/3 (19%) of those of the conventional
jig, although this result was inferior to that of the improved
model (11%) obtained only through the simulation software. Furthermore, the redesigning time was reduced toas little as eight hours, which is about 1/10 of the timespent for the improved jig (i.e., two weeks: equivalent to80 working hours). Thus, "anyone" can now "easily"
design a jig in a "short time" just by entering the fiveparameters.

Improved Ver.2
Improved
Conventional

Reduceable plating time

Distance from the edge of plating

Film thickness

Photo 3Fig. 16

Improved jig Ver.2

7

Improved Ver.2
Improved
Conventional

Distance from the edge of plating

Fig. 15 Comparison of film thickness measurements #2

6

Future Prospects

Additional expected benefits from this effort include
lower processing costs (for electricity and chemicals) andlower CO2 emissions due to shorter plating time.
Plating should be applied to applicable products toensure that the thinnest part of the plating film meets thefilm thickness requirements. However, conventional

Expected benefits

In Closing

It was verified that the simulation is very effective forachieving constant plating films and higher productivity.
In addition, the utilization of the optimization software
was shown to enable jig redesigning that does not depend
on knack and intuition and a substantial reduction in redesigning time.
The simulation can also be expected to be utilized tofind causes of inappropriate film thickness or even for
discussion of the specifications for new plating lines (suchas throughput). KYB operates a variety of working processes including heat treatment and cutting as well as
plating. It is desirable to effectively apply the simulation
methodology not only to plating but also to various otherworking processes.
Finally, we would like to take this opportunity to sincerely thank all those concerned inside and outside KYB
who have extended cooperation to this development.

Author 
MIZUNO Yuuki

TERADO AyukoJoined the company in 2019.
R&D Sect. No.1, Production
Technology R&D Center,Engineering Div.
Engaged in development of surface
treatment technology

Joined the company in 2012.
R&D Sect. No.1, Production
Technology R&D Center,Engineering Div.
Engaged in development of surface
treatment technology―7―