- 學位論文
碳化鎢之線切割放電加工特性研究
The Study of the Machining Characteristics of WC-Co of Composite by Wire-EDM
摘要
碳化鎢具有高硬度、高強度、耐高溫、高耐磨耗等特性，因此難以使用傳統切削加工方法加工，而放電加工特殊的材料移除機制特別適合於碳化鎢的加工，因此本研究針對三種不同鈷含量的厚碳化鎢工件進行線切割加工實驗，觀察其加工速度、表面粗糙度、斷面鼓形量、放電延遲時間等性質，來了解不同的鈷元素含量對於加工的影響。本次實驗分為兩個部分： 第一部份主要討論不同鈷含量的材料彼此間的加工特性，使用上下沖水壓力相同的方式加工，其實驗結果發現，鈷含量較低者，其加工速度較快、表面粗糙度較好以及較短的放電延遲時間。而斷面鼓形量的影響，與鈷含量並沒有明顯的相關變化。 第二部份為探討不同的排渣模式對加工特性的影響，藉由不同的上下沖水壓力，改變排屑方向，故選擇了兩組沖水條件，分別為上水壓6 kg/cm2下水壓1 kg/cm2的向下沖水方式和上水壓1 kg/cm2下水壓6 kg/cm2的向上沖水方式，藉以了解改變沖水方式和排渣模式對不同鈷含量的加工影響。其結果發現使用向下沖水方式可以得到較好的加工速度以及表面粗糙度，鼓形量則是由中凸型轉變為中凹型。當使用向上沖水方式時，表面粗糙度有些微的改善情形，但加工速度卻是較其它種沖水方式低，鼓形量也是由原本中凸型轉變為中凹型。 最後觀察其波形圖，可以發現到隨著鈷含量的增加，週期時間逐漸增加，而放電頻率則是逐漸降低，因不同鈷含量所量測到的放電延遲時間皆不同，鈷含量越高其放電延遲時間越長，影響到頻率與週期。
並列摘要
Tungsten carbide (WC) has high hardness, high strength, high heat-resistant, high wear resistance and many other characteristics, it is difficult to deal with traditional cutting process. The special material removal mechanism of EDM is particularly suitable for tungsten carbide machining. Three thick tungsten carbide workpieces with different cobalt contents are used in this study. Processing speed, surface roughness, drum shape and discharge frequency are observed in the process in order to figure out the effects of different cobalt contents to the processing. The experiment is divided into two parts: The first part is focused on the effects of different cobalt contents of the material to the processing characteristics, the upper and lower flushing pressures are fixed in this part. According to the results, we found that when the cobalt content decreases, faster processing speed and better surface roughness degree are achieved. The change of the cobalt content does not significantly affect the drum shape of machined surface. The second part is mainly discussing that how do the different slagging type affect the processing characteristics results in different cobalt contents. Two flushing conditions are decided, respectively, downward flushing mode with upper flushing pressure 6 kg/cm2 and lower flushing pressure 1 kg/cm2, upward flushing mode with upper flushing pressure 1 kg/cm2 and lower flushing pressure 6 kg/cm2, in order to understand the effects of different flushing modes. The results show that the use of downward flushing method leads to a better processing speed and surface roughness, drum shape is changed from convex type into concave type, comparing to the first part. When using the upward flushing mode, the surface roughness slightly improves, but the processing speed is lower than other flushing types. The drum shape is also converted from convex type to concave type. When observing the waveforms, we can find that the higher cobalt content is, the higher period is, while the discharge frequency is gradually reduced. The delay time measured by different cobalt contents is different, which in turn affects the frequency and period.