Experimental analysis of the machinability in the thermally assisted milling process of zirconia ceramics
Experimental analysis of the machinability in the thermally assisted milling process of zirconia ceramics
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氧化锆陶瓷热辅助铣削加工性能实验分析
DOI：
10.1016/j.precisioneng.2016.02.010
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发表时间：
2016
期刊：
影响因子：
--
通讯作者：
Mamoru Mitsuishi
中科院分区：
文献类型：
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作者：
Toru Kizaki;Naohiko Sugita;Mamoru Mitsuishi
氧化钇稳定的四方氧化锆多晶(Y-TZP)是一种很有前途的牙科修复材料。牙科修复体的制备方法通常为：(1)氧化锆粉热压；(2)预烧氧化锆机加工；(3)烧结。然而，目前的方法存在几何精度低、加工时间长等缺点。之所以采用它，是因为全烧成的Y-TZP极难加工。如果能够建立一种适合于全烧结Y-TZP的球磨工艺，它将能够实现准确、高效和成本效益高的工艺。对于制造牙科修复体所需的三维自由形状制造来说，铣削过程是很重要的。在这项研究中，我们提出了一种热辅助铣削工艺，在该工艺中，完全烧结的Y-TZP工件通过加热器直接加热到几百度，以使其软化并增强其可加工性。在实际情况下，必须事先预测可加工性，以确定适当的加工条件，包括工件温度。为了做出这样的预测，必须了解在热辅助加工过程中发生的加工现象。此外，还必须描述工件温度、切割条件和由此产生的可加工性之间的定量关系。在本研究中，我们进行了一系列的直切实验，观察了Y-TZP的加工现象，并获得了加工条件与Y-TZP的可加工性之间的定量关系。采用中心组合设计方法进行了一系列试验。实验结果表明，提高工件温度可显著降低刀具的耐切削力和刀具磨损。虽然在加热时发生了更多的断裂，但由此产生的沟槽底部表面的粗糙度并没有增加。用曲线拟合法建立了加工条件(包括工件温度)与可加工性之间的定量关系。
Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) is a promising material for dental restoratives. The fabrication method of such dental restoratives is usually as follows: (1) hot pressing of zirconia powder (2) machining of pre-sintered zirconia (3) sintering. However, the current method has disadvantages such as low geometrical accuracy and long process time. It was adopted since the fully sintered Y-TZP is extremely difficult to machine. If a suitable milling process for fully sintered Y-TZP can be established, it will enable an accurate, efficient, and cost-effective process. The milling process is important for three-dimensional free-form fabrication, which is required for manufacturing dental restoratives. In this study, we propose a thermally assisted milling process in which a fully sintered Y-TZP workpiece is directly heated to several hundred degrees by a heater to soften it and enhance its machinability. In a practical situation, the machinability must be predicted in advance to determine the proper machining conditions, including the workpiece temperature. In order to make such predictions, the machining phenomena occurring during thermally assisted machining must be understood. In addition, the quantitative relationships between the workpiece temperature, cutting conditions, and the resulting machinability must be characterized. In the present study, we conducted a series of straight-milling experiments to observe the machining phenomena and obtain the quantitative relationships between the machining conditions and the machinability of Y-TZP using the proposed thermally assisted milling process. A series of experiments were performed using the central composite design method. The results of the experiments revealed that raising the workpiece temperature significantly reduces cutting resistance and the tool wear. Although a greater amount of fracturing occurred when the workpiece was heated, the resulting roughness of the bottom surface of the grooves did not increase. Quantitative relationships between the machining conditions, including the workpiece temperature, and the machinability were established using a curve-fitting method.