振動解析

振動解析でできること

振動特性（固有振動数や振動の大きさ）を得ることで、共振・騒音対策へ繋げることができます。

樹脂（ガラス繊維強化材）を用いた場合には、共振・騒音対策として、以下の方法が考えられます。
①固有振動数を使用範囲外の周波数にする
②振動増幅を抑える
ガラス繊維配向の検討やリブの追加・リブの厚みの変更によって、固有振動数を製品使用時の周波数帯から外すことが可能です（図4①）。 また、金属からの置き換えの場合、樹脂の粘弾性特性により制振効果が大きくなります（図4②）。

振動解析事例-1

Here is an example showing that the natural frequency can be changed by fiber orientation. As shown in Fig. 5, after forming a flat plate of 120mmx80mmx2mm, we cut it out in each direction and conducted a damping characteristic evaluation test using the central excitation method.

The experimental results are shown by the dashed line in Fig. 6. It can be seen that the natural frequency is higher in the 0° direction (= higher fiber orientation). Here, we can see that the primary natural frequency differs by several hundred Hz between the 0° direction and the 90° direction.

The solid line in Fig. 6 shows the results of a similar test reproduced by Vibration analysis. Here, Digimat was used to create material data considering anisotropy and reflected in the analysis. Similar to the experimental results, the results obtained from the analysis show that the higher the fiber orientation, the higher the natural frequency, and the difference between the natural frequencies obtained from the experiment and the analysis was only 5%.

振動解析事例-2

As mentioned above, the eigenfrequency can be changed by changing the fiber orientation, but we will introduce how to actually change the fiber orientation using an application example of Box parts.

Changing the injection molding gate position is an effective way to change the fiber orientation in the actual product. As shown in Fig. 7, when gate A (left) and gate B (right) were compared and evaluated, changing to gate B changed the natural frequency to a higher position, as shown in Fig. 8. This approach is possible with glass-fiber reinforcements if the desired natural frequency cannot be obtained.

振動解析事例-3

The natural frequency can be changed by adding ribs or changing the thickness of the ribs, in addition to glass-fiber orientation. As shown in Fig. 9, adding ribs increases the natural frequency, and reducing the thickness decreases the natural frequency (Fig. 10). In injection molding, it is relatively easy to change the shape like this, so it is effective to search for a better shape while analyzing.