2014/12/17 Yokohama laboratory Section 2

Study for practical use of conductive titanium material (developed by NSSMC) for AC64Report No.1Forming of cathode separator with thin titanium plate

1 Purpose of this trialThis development is an extension of localization of anode separator production as joint development with SMILE and the purpose of the development are as follow.

For FCV volume production, improvements of performance and reliability and cost reduction Acquisition of thin plate (t=0.1) process technology and in-house production of separators

Production of cathode separator requires higher precise process technology due to its 3D forming than anode separator process. And if the material is changed, design of cell and production process need to be optimized. Through some optimizations, we would like to acquire the knowledge related to design and production internally. Schedule and contents to be implemented are as follow.

Technical reportContentMaterialTarget date

First report (this report)Process trialRoller forming, re-strikeStandard titaniumEnd of October, 2014

Second reportProcess trialTrimming of manifold partElectric TestAC64, 6 cellsDevelopment titaniumEnd of March,2015

After third reportDurability testAC64, 6 cellsImprovement of process accuracyRoller formingDevelopment titaniumEnd of September, 2015

2 DeviceChart 1 shows trial process. Tooling for process 1 and 2 have been purchased and evaluated. Both tooling for roller forming and re-strike were produced by Miyoshi for internal review in order to give SMILE quotation about 2 years ago.

Chart 1. Trial process of cathode separator and required toolingProcessToolingStatus

Process 1Tooling for Roller forming Purchased

Process 2Tooling for re-strikePurchased

Process 3Tooling for trimming Thomson bladeTo be purchased To be confirmed

5.1 Tooling for roller forming 2 gears make preforming of 0.1mm thin plate. The gears have a flat area to preform one cathode plate by one cycle.

Lower gearUpper gear

Figure 1 Roller forming machine produced by Miyoshi (Leftoverall view, Upper right : Engagement of upper and lower gear on process, Lower right : Enlarged view of gear)

5.2 Tooling for restrikePreformed thin plate by using above machine is pressed into corrugated form. It was done by 80t press machine (owned by Miyoshi).

Figure 2 Tooling for re-strike (Left : Lower tooling, Right : upper tooling)

3 Condition of process6.1 MaterialStandard titanium (JIS1, 0.1mm thickness)4 sheets

Conductive titanium developed by NSSMC has superior electric conductive to standard titanium due to its surface treatment on their rolling line. As this conductive titanium does not need dedicated surface treatment process and expensive special material (gold for Nano-clad), it has advantages regarding total material cost and recyclability. According to NSSMC, conductive titanium developed by them has the same press formability as standard JIS1 titanium. For this time, we would like to confirm whether we can use the tooling for SUS316L as well as for standard JIS1 titanium.As Chart 2 as below shows, SUS316L and standard titanium have different characteristics of press forming in terms of n figure and R figure. However, this level of gap can allow us to have trials of press forming with the same tooling. Thus, we decided to observe dimension accuracy of standard titanium formed with tooling made for SUS316L.

Chart 2. Characteristics of press formingMaterialnR

SUS316L0.401.00

Standard titanium0.155.28

6.2 Process of forming1 Standard titanium plate is inserted from the left side, which should be flat area of both gears. 2 Edges of gears are matched to the right position of the material, which are inserted lightly to make initial forming.3 Handle of lower gear is turned clockwise at stable speed to make the material sin-curve.4 Sin-curved material is set on the press-machine (80t) with the tooling for re-strike and weighted four corners with magnets. 5 Press forming is done to complete the process.

Current parts (made by Brandauer) are formed by 2 roller-forming processes. On the other hand, this prototype needs only one time roller-forming process.

4 Result of forming7.1 Roller formingWider pitch of corrugation by 4 mm was found compared with the forming of SUS316L. It is mainly due to the difference of spring-back.

Difference of pitch width

Figure 3Comparison of products after roller forming (First process)Upper:SUS316L, Lower: Titanium

Deformations of corrugation were also found when the material was mildly sloped during the process.

Diagonal deformation

Figure 4 Deformed corrugation7.2 RestrikeDue to greater spring back of Titanium after roller forming, the length was longer than the restrike tooling size. In order to set it onto the restrike tooling, we shrunk the pitch of corrugation by hand. When we shrunk it too much, we needed to slightly extend it again to fit it on the tooling. It was found that the length of corrugation area was shorter than the one of SUS316L. The reason for it would be that we shrunk it too much to adjust into the restrike tooling. Difference of pitch width

Figure 5 Comparison of products after restrike (Second process)Upper:SUS316L, Lower: Titanium

5 Result of precise measurementPrecise measurement was conducted for 4 prototypes made with Titanium sheets as described as above. The measurement points are Pitch of corrugation Height of corrugationFlatness and parallelismas below.

1 PitchHeightFlatnessParallelism

Figure 6 Specified dimension on IE drawing (Cathode separator)

8.1 Pitch of corrugationAll corrugations of a prototype made from standard titanium (yellow line) were out of specification due to shorter pitch compared with a prototype of SUS316L made with the same tooling and cathode plate purchased from IE (Nano clad). Figure 7 Comparison of corrugation pitch

8.2 Height of corrugationThe corrugation made from standard titaniumshow a trend of higher corrugation compared with the one made from SUS316L and Nano clad.

Figure 8 Comparison of corrugation height

8.3 Flatness and parallelismSUS316L and Nano clad could meet the specification. Regarding standard titanium, 2 out of 4 prototypes could meet the specification. It is probably because roller-formed parts were forced to put into the re-strike tooling by shrinking it by hand.

Chart 3. Comparison of flatness and parallelismMeasured FiguremmTolerancemmNote

SUS316LTooling made by MiyoshiFlatness0.0261 0.05

Parallelism0.0288 0.05

Nano cladMade by BrandauerFlatness0.0283 0.05

Parallelism0.0312 0.05

Standard titaniumTooling made by MiyoshiFlatness0.0353 0.05Prototypes to meet the specification

Parallelism0.0370 0.05

6 ReviewIssues related to process operations On the tooling of roller-forming, it is difficult to have flatness. It is required to have a guide to forward the material properly. While the process of roller-forming, it is preferable to turn the gear at the stable speed. However it is difficult to do it by hand. So it should be considered to add motors on these gears to adjust the speed of turning gears.

Issues related to process accuracy Due to the difference of spring back and processing by hand, prototypes made from standard titanium could not meet the specification. It is required to modify the gear of roller forming to fit it into the restrike tooling. Regarding flatness and parallelism, 2 out of 4 samples can meet the specification.

Conclusion On the process of titanium material with the tooling made by Miyoshi, significant issues, such as cracking on the materials and huge deviation of the specification could not be found though prototypes made from standard titanium cannot meet some specifications. Thus, for the initial material evaluations and electric tests, cathode plates made in this method can be useful.

Future action We are going to prepare Thomson blade for Trial Process 3. (As in 2. Device) In order to procure development samples from NSSMC, we are going to conclude NDA. Then, we produce prototypes and conduct material evaluations and electric tests on test-rigs. We are going to have precise measurement of the tooling to have a drawing of it. (Miyoshi declined Suzukis request to buy drawings of the tooling.) After completion of drawings, we are going to modify the tooling for titanium.

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