運用五軸加工技術於弧形手機玻璃基板導角磨削之研究

A Study of the Chamfer Grinding on Glass Substrate of a Mobile-Phone with Arc Type by Five-Axis Machining Technique

詹民歆(Min-Xin Jan)

指導教授 ： 林盛勇

國立虎尾科技大學/工程學院/機械與機電工程研究所/碩士(2015年)

https://doi.org/10.6827/NFU.2015.00185

摘要

從早期舊型的一般非智慧型手機發展至平面或弧形面的智慧型觸控手機。弧形手機曲面的設計因較符合人體工學，通話時機身可與通話者的臉頰契合良好，聲音品質比一般平面手機更為清晰，並擁有一定程度的可撓性，已成為新一代手機的熱門話題。觸控面板經裁切後，其輪廓邊緣將留下無數的細微崩裂裂紋，而形成高度的應力集中，此有賴倒角研磨加工予以改善。但一般玻璃基板進行機械切削加工時由於其硬度高及脆性大，表面易產生裂紋及邊緣崩裂。又因其高強度與低熱傳導係數等性質，加工難度更為提高，是一典型的難切削材。再者，弧形手機因彎曲曲面的關係，倒角加工又比平面手機增加許多的困難度。為因應手機造型式樣的變化及突破業者於相關產品曲面倒角加工所遭遇之瓶頸，尋求相關倒角關鍵技術之開發與建立，儼然已成為相關業者亟需努力的一項重要課題。
本文使用CAD/CAM軟體建立弧型手機玻璃基板之幾何模型，並使用專業切削軟體規劃設計創新的切削路徑與加工工法，針對所生成的路徑程式進行切削路徑移動模擬，檢視磨輪與工件相互接觸作動情形，確認符合五軸倒角加工之所需。首先，設計製作符合曲面幾何之真空吸盤夾治具，架設於五軸加工中心機之工作台。接著，使用全因子規劃倒角磨削實驗相關參數（磨輪幾何、磨削速率、進給率、倒角寬度及潤滑條件）組合。同時利用兩種輪廓之鑽石砂輪(平面及圓弧)及傳統磨棒，搭配兩種五軸控制器進行弧形玻璃倒角研磨實驗。使用高倍率顯微鏡觀測倒角磨削完成面之形貌、邊緣崩裂及倒角寬均勻度，並進行實驗結果之交叉比對與分析。最後，以加工完成面之邊緣崩裂為目標函數，同時受制於倒角表面破裂的拘束條件，以求得最佳的製程參數，期能加工出合乎業界表面品質及邊緣崩裂缺陷之要求。
結果顯示，國產控制器與新開發機台尚未能匹配良好，促使B軸在加工旋轉時產生了微小的誤差，造成倒角寬度均勻度不佳。平面輪廓砂輪在磨削凹面倒角時，砂輪兩側於弧形底部形成過切的現象，於工法設計上需設定刀軸偏角以避開此干涉點，兩種輪廓砂輪所加工出來的倒角表面破損並無太大差異。高倒角磨削速率及低進給率有著較輕微的表面破損。水溶性切削液提供磨削加工區良好的冷卻及潤滑，其相較於吹氣冷卻減少了邊緣崩裂。創新的磨削工法相較於傳統磨棒的磨削方式，可提供較快的倒角速率，得到較輕微的表面破損及邊緣崩裂。

關鍵字

弧形玻璃 ； 倒角研磨 ； 加工工法 ； 邊緣崩裂 ； 表面破損

並列摘要

The non-smart phones from early times have developed into flat-surfaced and arc-shaped smart phones nowadays. Arc-shaped phones serve ergonomic in design, so when on the calls, speakers' cheeks can adjust closely with the phones. The audio quality of arc-shaped phones is much clearer than the flat-surfaced ones. They have flexibility, and have become a hit of new generation smart phones. The touch glass panel left countless micro-crack after its outer-edge profile cutting and a high stress concentration is deduced around there. Hence, this defect should be improved by chamfer grinding technique. But the hardness and brittleness of the glass substrate are too high to easily induce surface crack and edge-indentation while performing the mechanical machining. Also, a lot of difficulties encountered during the machining process due to its natures of high strength and low thermal conductivity. It belongs to a typically difficult-to-cut material. Furthermore, the chamfer of the outer-edge profile with arc-surface is more difficult to process than that of the flat-surface due to its bent surface configuration. In order to comply with the variations of geometrical style of phones and breakthrough the embarrassment in chamfer machining of the related curved-surface products in industry, seeking the development and establishment of the key technique for chamfer has become an important concern that the industry needs to strive.
This study used CAD/CAM software to construct the geometrical model of a mobile-phone with arc type. Appropriate cutting-path and machining strategy are designed and planned, and confirmed by a simulation pertaining to cutting-tool moving path. Furthermore, a commercial software for cutting simulation is used to verify the numerical control program generated from the above plan and to check the correctness of the proposed methodology in a virtual reality cutting environment. The contact situations between the wheel and workpiece during the chamfer grinding processes are investigated and these actions whether fulfill a five-axis chamfer machining manipulation requirement are further confirmed. Vacuum chuck fulfilling this arc-surface geometry is designed and fabricated and used to clamp the thin glass substrate on a jig platform. A five-axis machining center associated with grinding wheel is used to perform the experiment for the chamfer grinding of the glass substrate. Full-factorial experiment of process parameter combinations such as wheel profile, grinding velocity, feed rate, chamfer width and working environment was organized for chamfer grinding. Grinding wheels with flat or round profile along the peripheral direction, and a traditional diamond electroplated burs were used as chamfer grinding tools. In addition, the bent-surface glass substrate chamfer experiments were conducted by two kinds of five-axis controller, respectively. Tool maker microscope was used to detect the chamfer surface morphology, edge-indentation and dimension uniformity on the chamfer width zone, and the experimental results are analyzed thoroughly and compared crossly with each other. The chamfer surface edge-indentation is used as an objective function for better process parameter determination, which is subjected to surface damage constraint. It is expectedly that the quality of surface damage and edge-indentation may fulfill the requests for industry.
The results show that the controller made in Taiwan may not work properly in pair with a newly developed machine-tool in the laboratory, a small rotation error is deduced accompanied by B-axis, which results in worse dimension uniformity on chamfer width grinding. An undercut phenomenon occurred at the bottom of the arc-surface when the chamfer grinding on the concave surface side of the arc-glass by using a flat profile grinding wheel. An inclination angle of the grinder-axis should be adjusted in machining strategy design to avoid the interference point between the grinding wheel and arc-surface. But the results pertaining to chamfer surface damage has only a little difference by using these two geometrical profile wheel. Smaller chamfer surface damage is obtained under the condition of higher grinding velocity and lower feed rate. Water soluble cutting fluid offers a better cooling and lubrication actions in the primary grinding zone, the edge-indentation is thus reduced as compared with that of blowing air. Smaller surface damage and edge-indentation are obtained from the innovative strategy of chamfer grinding used in this study as compared with that of the traditional diamond electroplated burs due to a higher grinding velocity attained in the former grinding technique.

並列關鍵字

arc-surface glass substrate ； chamfer grinding ； machining strategy ； dge-indentation ； surface damage.

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