臺灣大學: 機械工程學研究所蘇侃王敬仁Wang, Jin-JenJin-JenWang2013-04-012018-06-282013-04-012018-06-282011http://ntur.lib.ntu.edu.tw//handle/246246/255931磨削是精密加工中常見的加工方式，通常被用來製作高精密度與品質的產品。在製造高精密產品時，尺寸精密度與幾何精密度的控制都是很重要的目標，因為這會影響產品的功能與品質。然而，在一般金屬磨削過程中，會因為金屬切削與磨擦而產生大量的熱量，這會使得加工表面發生明顯的溫度上升現象，進而使加工表面發生嚴重的熱變形。在表面磨削加工過程中，熱變形通常會令加工表面在冷卻後產生凹陷變形；切削力則會造成砂輪與工件表面的彈性變形，如果在加工時不增加磨削深度(depth of cut)的情況下，則彈性變形部份會逐漸回復。因此在某些加工場合中，彈性回復的現象會被利用來改善尺寸精密度，一般將這種加工方式稱作火花消失加工(spark-out)。 本文中以磨削過程中的表面熱變形與彈性變形量來計算實際的磨削深度，並以此來模擬加工表面在磨削後的表面變形情形。一般而言，熱變形會使得實際切除深度增加，但是砂輪與工件之彈性變形則會減少實際切除量，因此在火花消失加工階段的模擬中，如果某次加工中彈性回復量與當時的熱變形量所造成的切削深度超過先前切削的深度，則判斷會發生磨削並且最終切除深度會增加至該次加工的切削深度。透過這個計算過程則可模擬加工後之表面形狀。 本研究也做了一系列磨削實驗，用來驗證模擬結果的正確性。在一般磨削加工部分，我們分別以10μm與20μm兩種磨削深度對工件表面做了一至四次的磨削加工。火花消失加工則分別做了三組實驗：磨削深度影響、砂輪性質影響與切削液影響的實驗。將這些實驗結果與模擬結果做比較後，顯示模擬結果只有在砂輪切削方向上與大磨削深度的條件下，可以做出較準確的預測。另外，由實驗結果中顯示，在乾磨削條件下，若以較小的磨削深度則可能在第八次火花消失加工後得到最小的表面凹陷。在濕磨削條件下，加工表面在第四次火花消失加工後則會發生表面由凹陷變形轉為凸起變形。因此最好的表面平坦度可以在濕磨削的第四次火花消失加工後達成。Grinding is a common process used for high quality part production. The dimensional and geometrical precision is the major concern to such parts. In metal grinding, enormous heat is generated due to the material removal and friction as well, this usually leads to prominent temperature rise on a ground surface. The thermal deformations on the ground surface usually lead to concave distortion. The cutting forces also cause elastic deformations on wheel and workpiece surfaces, which will recover gradually if there is no increase in depth of cut. The elastic recovery is also used to improve the dimensional accuracy in some grinding process, and such process is called spark-out. In this study, an analytical model is proposed to simulate the distortions in dry grinding by taking both thermal deformation in workpiece and elastic deformations on wheel and workpiece into consideration. The thermal deformation usually causes overcut and the elastic deformations will decrease the depth of cut. In the simulations of spark-out process, the cut will be made only when the sum of the thermal deformation and elastic deformations are greater than the cutting depth made by previous passes, and then the new cutting depth is found. By this mechanism, the surface profiles after grinding and spark-out will be found. The grinding experiments were also conducted for the depth of cut of 10μm and 20μm for up to 4 rounds on a surface. The experiments for spark-out were conducted with different depth of cut, wheel types and coolant application methods. The results were compared with the analytical results, and it showed the analytical prediction was only good for the profiles along the grinding direction and with larger depth of cut. The experiments showed the smallest concavity was obtained after 8 spark-out passes when small depth of cut and a softer wheel were used. It also showed the distortion on ground surface were concave in dry grinding and might turn convex after 4 spark-out passes in wet grinding. Thus, the best flatness in wet grinding may be achieved for 4 spark-out passes.7363547 bytesapplication/pdfen-US磨削火花消失表面變形熱變形GrindingSpark-outSurface DeformationsThermal Deflectionsthesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/255931/1/ntu-100-D92522025-1.pdf