Introduction

In this issue of SmartDO eNews, we will introduce how SmartDO was coupled with ABAQUS to optimize the O-Ring sealing of the steel bottle charger. In this real-world case, the optimum design provided by SmartDO was actually manufactured into real hardware product for verification. The result shows that, the sealing effect was improved by 30%.

The contents in this eNews is based on the Thesis for the Degree of Master in Engineering, Department of Mechanical Engineering, College of Engineering, National Chiao Tung University, Taiwan, June 2010. This is authored by Cheng-Yi Tsai, with advisor professor Ching-Hua Hung, Titled "Improving the O-ring Sealing of 8 gram Charger by Finite Element Analysis and Shape Optimization". The full text of the paper (in traditional Chinese only) can be downloaded from the following links (System ID GT079714504)http://140.113.39.130/cgi-bin/gs/tugsweb.cgi?o=dnctucdr

Description of the Problem

The subject of the current research is the 8 gram N2O bottle charger, which is commonly used in the cream whipper. This charger is made of steel, and filled with N20. A standard 8 gram charge can normally produce cream of 0.5L. However, the filled-in N2O can easily leak out if the sealing does not work well. The cross-section of the sealing mechanism for the charger is shown in Figure 1.

Figure 1 The Cross-Section of the Sealing Mechanism for the Charger

Currently the sealing of the charger was manufactured with one-step punch process, as shown in Figure 2.

Figure 2 One-Step Punching Process for the Sealing of the Charger

This one-step punching process can be accurately simulated by the nonlinear finite element method. Figure 3 shows the finite element mesh and analysis result of one specific dimension for the charger.

Figure 3 Finite Element Mesh and the Nonlinear Simulation Result for the One Punching Process of the Sealing

From literature and experience, it is known that the following factors have crucial impacts on the sealing performance.

• Larger contact stress on O-Ring will increase the sealing effect.
• Larger standard deviation for the contact stress on O-Ring will reduce the sealing effect.
• Larger contact area on O-Ring will increase the sealing effect.

From previous intensive research, it was found that all the above factors can be optimized through changing the shape of the punch. And the final sealing performance criteria can be calculated by finite element analysis. These numerical results and performance index criteria can then be coupled with SmartDO for numerical design optimization.

Design Optimization Modeling

The parametric model was created for the above problem in the commercial package ABAQUS. After the batch model was created using the Python language in ABAQUS preprocessor, it can be easily coupled with SmartDO. In the current research, we use four (4) design variables on the punch, DV1 to DV4, as shown in Figure 4. An existing charger (with specific dimension) was selected as the subject of the optimization process. This design is formulated as

Find : DV1, DV2, DV3, DV4
To Maximize : Maximum contact stress
Subjected To: Standard deviation of the contact stress<3 MPa
                              Contact area> 80%

Figure 4 The Four (4) Design Variables on The Punch

Final Results and Hardware Verification

After the numerical optimization by SmartDO and ABAQUS, the performance criteria for the final design are optimized as

• Maximum contact stress: increased from 1.85MPa to 17.6MPa
• Contact area : increased from 67% to 82.35%
• Standard deviation of the contact stress : changed from 0.516 to 2.067

The optimum design provided by SmartDO was actually manufactured into real hardware product for verification. Compared with the original design, the gas leaking rate was reduced from 0.004189 gram/day to 0.002846 gram/day, which was reduced by over 30%.

Conclusion and Remarks

In this issue of the SmartDO eNews, we show you how SmartDO can perform design optimization of nonlinear structure response with superior stability. With hardware test and verification, it was also proved that SmartDO can increase the performance of the product by over 30%. It is obvious that SmartDO not only has the leading edge technology of global optimization, but is also suitable for practical design purpose. In the future, we will continue to develop more Smart Global Optimization Technology, and will keep you posted in our eNews.