薄殼產品落地試驗之研究

Study on The Drop Test of Thin-Wall Product

黃鐳迪(Lei-Ti Huang)

指導教授 ： 陳夏宗

中原大學/工學院/機械工程研究所/博士(2003年)

https://doi.org/10.6840/cycu200300214

摘要

3C產品設計朝向輕、薄、短、小是未來產業不可避免的趨勢，落地衝擊實驗是評估該產品功能尤其是安全與品質評估的重要指標。以目前業界所使用的衝擊試驗準則，僅對一般產品作概括性實驗規範，對於3C產品而言，並無詳盡規範。另一方面，以電腦軟體模擬落地試驗來縮短產品開發時間是未來之趨勢，實際量測與模擬比對相互驗證已是重要課題；本研究的目的在於建立一套簡易可行且具重複性之落地試驗量測系統，對於產品落地方向、落地角度與速度的掌控和分析，以及對於加速規訊號的擷取能夠提供有效精確的數據，並且藉由落地實驗的結果來驗證模擬分析之正確性。
研究中之落地試驗平台是以一特殊夾具夾持測試物以使其落地角度具高度重複性，同時藉由一個CCD與一個反射鏡擷取落地瞬間測試物之實像與虛像，並經由電腦影像處理落地之畫面，推導出物體實際落地空間角度。
為評估系統量測之加速度g值與模擬g值之相符性，使用簡單幾何外型之電子翻譯機(CD-66)下蓋作實際落地測試，並對量測與模擬之加速度g值做適當之濾波處理。由量測之加速度g值與LS-DYNA模擬軟體之分析結果發現，由於LS-DYNA使用時間積分(Time Integration)求解的關係，當網格數固定時，輸出分析時距(Time Interval)越小則g值將趨於穩定，另一方面，當網格數增加時，輸出分析時距越小越有助於g值之判斷，因此資料分析輸出時距的設定對於落地分析的準確度具有相當大的敏感性與影響性。
本研究同時針對CD-66整體產品模型，並假設以ABS與PC為外殼基材作模擬分析，結果顯示，外殼為承受碰撞力最嚴重的地方，尤其在落地點。內部之PC Board、 IC 零件以及背光板承受之碰撞應力不大，且內部零組件模型之簡化對於分析結果影響不大。另外也針對CD-66上蓋作薄化分析發現，適當之局部薄化後之最大碰撞應力並不影響產品既有之機械性質。因此，簡化平板模型以預測落地實驗之最大碰撞應力值，不但可以節省模型建構之時間，結果亦能保有一定的精確度，同時對於產品薄化設計可提供有效之預測。

關鍵字

落地試驗模擬 ； 結構特性 ； 落地衝擊測試 ； 薄殼產品

並列摘要

Portable communication devices may easily suffer impact-induced failure in their usage. Drop/impact performance for portable products becomes one of the important concerns in both safety and quality view point. Because of the small size and compact design of these electronics devices, it is very expensive, time-consuming and difficult to conduct valuable drop tests to achieve directly detection for the failure mechanism and drop behaviors. At the present, the simple impact test standard in the industrial only is used for the general products but no detailed standard for the 3C products yet. In addition, using the simulation to shorten the design and development produce process becomes the trend for the future 3C industries. Therefore, to conduct reliable drop test experiment and the relevant simulations become very important for 3C products.
The purpose of this research is to build a simple and repeatable drop test platform, which can control the drop direction, drop velocity and drop angle in an accurate way. The system can also access the drop acceleration signals from accelerometer and use them to compare with the simulated predictions. The physical drop/impact test system consisting of impact orientation control mechanism, fast speed visual surveillance system, mirror image methodology and data acquisition/processing system is designed and established. A set of correlated spatial equations provides an accurate methodology to determine dropped product orientation upon drop instance, which is a key factor to structure design affecting impact damage.
Top housing of thin-wall computer dictionary (Model CD-66) top was used to carry out experiments and to verify the simulation results. The impact acceleration value represented in unit of g was measured from the accelerometer. It was found that the dominant frequency of the tested product was very important as the reference data for the simulation. The setup time interval for simulation output data extraction was also found to be the key parameter which must be suitable chosen so that accurate verification of the simulation with experiment can be achieved. As a result, validation test is indispensable assistance to the computer simulation.
Finally, numerical simulations for the drop test and bending strength were applied to a thin-wall computer dictionary (Model CD-66) housing to understand the key factors that affect the part drop test performance. The appropriate modeling that would affect simulation accuracy, the associated nodal degree of freedom and computer time were also investigated. A CD-66 housing of 1.6 mm thickness was redesigned to be 1 mm thick assuming molded with two different plastics: polycarbonate (PC) and acrylonitrile butadiene styrene (ABS), respectively. The simplification of the PC board and LCD backlight circuit in finite element modeling (FEM) only causes about a difference of less than 10% while saving many modeling costs. The numerical simulations also indicate that both bending strength and drop-impact strength were decreased only about 5%, i.e., the product remains its structure integrity, if only the top housing plate thickness was reduced whereas the sidewall thickness was kept unchanged. In general, the study indicates that an appropriate modeling saving computer cost can be used to forecast the precision impact stress for the design of the thin wall products.

並列關鍵字

structure performance ； drop test simulation. ； Thin wall products ； drop/impact test

參考文獻

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