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在EDM內的再鋳層描述與電極消耗率
Black layer characterisation and electrode wear ratio
inelectrical discharge machining (EDM)
Journal of Materials Processing Technology 184 (2007) 27–31
J. Marafona
授課老師 :
學生
戴子堯 教授
: 方立凱
中 華 民 國 九 十 七 年 五月
大綱
介紹
實驗設備與方法
再鋳層描述
等碳量與電極消耗率
結論
介紹
Some researchers have study the surface modification of the tool
and Chen et al show that there is a migration of work piece elements
to the tool surface when high and low current intensities are used.
許多研究員研究修改電極的表面、、然而學者Chen et al等人研究
使用高、低強度電流則能使工件元素轉移到電極表面上。
Mohriet al.observed, in the surface of a copper tool ,a black layer
consisting of “a bi-dimensional laminate of carbon crystals with
random phases”.
學者Mohri等人注意到在銅質電極的表面上有一層黑層，組織結構
是由一種大尺寸的碳晶組織薄片和隨機相位所組成的。
Soni and Chakraverti also reveal that there is a migration of
iron and chromium to the tungsten–copper (80/20) tool using
the IS-T215 steel work piece.
學者Soni and Chakraverti等人研究指出在使用IS T215的工
件，材料上的鐵元素和鉻元素會游走到鎢銅電極上(80/20)。
Mohri et al. refers that the EWR is very small in the beginning of the
machining and tends to a certain value, depending on the machining
conditions.
Mohri et al.等人談論機台開始加工時的EWR非常小並傾向於某
些值，這是取決於機器加工條件。
According to Marafona and Wykes , the decrease of the tool wear is
obtained with the increase of carbon on the tool surface in the
beginning of machining.
根據Marafona and Wykes指出在機器開始加工時，電極表面上的
碳量會增加相對使得電極消耗率的減少。
Moreover, these authors mentioned that this increase of carbon on the
tool surface is due to the use of a predetermined set in the beginning of
the machining.
然而，作者提到電極表面上碳量的增加是由於預先測定的機台加工
參數得知的。
實驗設備與方法
The experiments were conducted with a square-sided (50mm×50mm× 25
mm), work pieces in high carbon steel (BS 4695 D2) and square-sided
(25mm×25mm×75 mm) tungsten–copper (75/25) tools positively polarised.
本實驗進行是在一方形內 (50mm×50mm× 25 mm)做處理，工件材
料選用高碳鋼(BS 4695 D2)，，電極則是方形鎢銅(75/25)的極
化工具鋼(25mm×25mm×75 mm)
The composition of the black layer was evaluated by qualitative energy
dispersive spectroscopy (EDS) on scanning electron microscope (SEM)
and a transverse section tool was evaluated by electron probe microanalyser (EPMA).
使用一台(SEM)電子掃描式顯微鏡內的能量分散性分光學(EDS)元
件來評估黑層的成分以及使用電子探針微量分析儀(EPMA)來評估
一橫向剖面的電極。
The EPMA X-ray images are from the tool with a EWR of 0.18%.
EPMA X射線影像是來自於0.18%的電極消耗率
Fig1. (a) Energy X-ray spectrum (original electrode material)
Two of the three EDS patterns are from tools having high and low EWR.
3 種分光學圖案中有兩種是來自電極消耗率的高低
(b) energy Xray spectrum (electrode (c) energy X-ray spectrum (electrode with
with EWR= 3.48%)
EWR= 0.26%)
黑層描述
The results of the previous section show that there are elements of the
work piece composition at significant quantities on the tool surface. The
black layer is formed by large quantities of carbon and iron deposited on
the tool surface.
以往的剖面結果顯示，在電極表面上由工件轉移的組成元素是存
在的，大量的碳和鐵沉澱在工具表面上就形成了所謂的黑層。
The EDS patterns an Fig. 2(a)–(d) were obtained using the microscope
JOEL J6400 with low and high magnification.
圖(2)(a)~(d)的EDS圖像是使用JOEL J6400的顯微鏡經由鏡頭放
大及縮小得來的。
Fig. 2(a) and (b) shows the black layer in a transversal section of the tool while
Fig. 2(c) and (d) shows the circled areas in (a) and (b), respectively.
圖(二)a.b顯示磨耗電極的橫向剖面黑層， c.d顯示圖像分別來自a.b的圓圈區域
Fig. 3.
(a) View of the black layer,
(黑層影像顯示圖)
(b) tungsten X-ray image,
(鎢x放射線)
(c) copper X-ray image,
(銅x放射線)
(d) carbon X-ray image,
(碳x放射線)
and (e) iron X-ray image.
(鐵x放射線)
The layer composition was evaluated in five different areas of the top tool
surface, four areas near the square corners and one at its centre.
組織層的工具表面頂端有5塊不同的區域被評估，4區塊靠近在方形
角落和一塊在中心。
This irregular distribution of migrated elements may be due to nonuniform current density or temperature distribution in the discharge
channel as mentioned by Mohri et al.
在Mohri et al.的排流道文獻中有敘述到，元素的轉移呈現不規則
的分散有可能是密度或溫度分配不均勻所致。
The EDS analyses show the quantity of elements migrated to the tool
surface, some of them contributing to the equivalent carbon of the
black layer.
EDS分析顯示元素轉移到工具表面上的數量，對於黑層內的部分
碳組織是有幫助的。
The value of this parameter was calculated using the Eq. (1), which is used
to evaluate the equivalent carbon for steels:
這套參數的理論推導是被用來因應圖一的解析並用來作為鋼的等碳
量評估。
等碳量與電極消耗率
The author concludes that the existence of high percentages of iron
and carbon on the tool surface forms the black layer in the beginning
of machining, but that does not necessarily decrease the EWR
本文作者認為電極表面上鐵和碳所存在高百分比是機械開始加工
時形成的黑層，但是那不一定會減少EWR。
The analysis of the previous section guides the author to a relationship
between the equivalent carbon in the end of machining and the electrode
wear ratio.
作者將先前切片分析與機台加工結束時的等碳量和電極消耗率之間
做關聯。
表格(一)顯示碳，鐵和等碳量及電極消耗率之百分比
sample no. 5 shows a EWR of 0.22% that corresponds to an increase
of the amount of equivalent carbon of 9.79% during erosion time.
樣本5顯示在侵蝕的這段期間內0.22%的EWR與等碳量總差9.79%
是相符合的。
On the other hand, sample no. 16 presents a EWR of 0.65% and
it looses an amount of equivalent carbon of 16.3% during erosion
time.
另一方面，樣本16在侵蝕時間內有0.65%的EWR和總計等碳量遺
失的16.3%也是符合的。
作者斷定在侵蝕期間內的工具表面上總計等碳量的增加和減少量與
EWR這兩者之間的關係。
Fig. 4 displays the increase of the equivalent carbon that corresponds
to a decrease of the electrode wear ratio.
圖四 顯示等碳量的增加符合電極消耗率的減少
置入不同加工參數的等碳量和EWR之趨勢圖
結論
再鑄層是由於放電過程中在電解時碳分子轉移所造成的。
在加工時間內增加等碳量的百分比同時也減少了電極消耗
率的百分比，兩者是相符的。
碳的轉移和工具表面的觸媒物機台在加工參數與EWR皆
有一定的關聯。
研究證實再鑄層內不僅只有碳成分而且還有其他成分
如鐵、鉻、釩、鉬元素。
研究證實電極消耗率的減少是決定於機台加工一開始的
加工參數。