Properties of Micro-Holes for
Nozzle by Micro-EDM
微細放電加工之微噴孔的特性
碩研機械一甲
M9910114
林泓緯
1
• Abstract
• The micro Electrical Discharge Machining (EDM) technique is used for
machining hard conductive materials and achieves holes from 0.05 to 1.8 mm
in diameter. The holes are machined with a high repeatability,without burrs
and material alteration. The technology currently in production in the
automotive industry is used to drill diesel and gasoline nozzles coming from
the direct injection technology.
• One of the most important features,
• with respect to diesel nozzle requirements
• , is the drilling of positive tapered holes.
• This positive taper is mechanically set up,
• and offers more possibilities and
• better stability compared to
• using EDM set up parameters.
由於EDM可加工硬度較高之材料，孔徑
能達0.05mm至1.8mm，且具高重複性，
無毛邊與材料性質變更，該技術目前在
汽車產中運用於柴油與汽油噴嘴技術，
對於柴油噴嘴的要求是為錐形孔，此錐
度可提供噴嘴更多的可能性與穩定性。
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The Electrical Discharge Machining (EDM) technique is widely used for machining hardened steel. The
most frequently used application is die-sinking EDM for mold steel fabrication [1]. Electrical discharges
occur between an electrode and the conductive material work piece. The electrode and the work
piece are immersed in a dielectric liquid, which is de-ionized water (< 0.8mSiemens) and the process is
carried out without mechanical forces. Each spark melts and vaporizes aterial from both the work
piece and the electrode, which exhibit a wear phenomenon. The EDM ablated material is flushed away
from the spark gap by the dielectric liquid. The hole diameters are determined by both the electrode
size and the gap extension. A high level of quality in shape and surface texture (< 0.5 Ra), is obtained
without burrs. In Europe, this direction has led to specialized roduction applications, such as the
drilling of nozzles for diesel and gasoline injection. The introduction of die-sinking in the 90s to process
small mechanical parts and micro pharmacy applications allowed for a superior level of precision.
Roughness in the region of 0.1 Ra and spark
由於在（EDM）技術廣泛用於加工高
gaps of about 5 μm could be obtained. Nowadays, high
硬材料，其電極與工件都沉浸於介電
液中，過程無機械力量，火花融化與
quality EDM drilling procedures use rotating electrodes
蒸發的廢料由電解液帶走，形成一個
and axial flushing through hollowed electrodes. At
高層次和質量的表面精度（0.5 RA），
present, EDM drilling is well established in the field of
manufacturing metal pieces with complicated geometries. 在歐洲此技術影響了專業生產化的應
EDM drilling remains the method of choice for diameters 用程序，如鑽孔噴射柴油及汽油噴射。
above 50 μm. The geometry of the holes is very important 在目前EDM鑽孔是公認製造複雜幾何
形狀的金屬工件技術，其直徑超過
to the injection nozzle market [2], which has improved
50μm，幾何形狀的孔洞為噴嘴市場的
quality and product performances. Tapered holes allow for
重要技術，不但提升了其品質與產品
better spray efficiency [3], reduction of cavitation
性能，圓錐孔有更好的噴霧效率，減
phenomena [4] and self-cleaning of the nozzle holes [5].
少氣泡現象和自行清潔的噴嘴孔，此
The goal of this article is to show how to control the
文章為展示如何控制錐形形狀與特色
3
conical shape and characteristics of the holes.
的孔洞。
2 EXPERIMENTAL
• Research activities are
mainly focused in the field
of pulse generator
technology, which is used
in order to generate
• small spark durations, fine
craters and to avoid idle
• discharge pulses or short
circuits. The rotation of
the electrode, which is
maintained by shifting
collets and passes through
the guiding collets, is done
in order to optimize
quality and drilling speed
(see Figure 1).
傾斜頭部
可調節環
轉移夾頭：
侵蝕軸
引導夾頭
2 EXPERIMENTAL 實驗
研究主要集中在該領域的脈衝發電
機技術，用於以產生小火花持續時
間，細坑，避免閒置的放電脈衝或
短路。旋轉電極是安置於轉移夾頭
穿過引導夾頭，是為了其高品質和
鑽孔速度（圖1）。
4
實驗與量測設備規範
• Nozzles made of hardened steel (HRC
57-63), Cr-Ni are drilled using microEDM technologies on Posalux’s FP1
• (One spindle machine for flexible batch
production) and Posalux’s HP4 (Four
spindles machine for mass production).
The electrode is hardened steel
(WC/Co, 6% Co). The measurements of
the diameter, shape and position of the
hole are measured using a Werth Video
• Check IP machine. The variation and
control of the flow is performed by a
Sonplas machine with up to 138 bar
(2000psi), depending on customer
requirements.
淬硬鋼製成的噴嘴（HRC57-63），鉻鎳
的鑽孔使用瑞士Posalux公司的FP1的
（單軸撓性量產機具）和Posalux的HP4
（四軸質量製造機具）進行微細放電加
工製造。
電極是淬硬鋼（碳化鎢/鈷，6％鈷）。
測量的直徑，形狀和孔的位置均採用
Werth影像檢查 IP(image processing)機
台。該變化和控制流量由一個 Sonplas
機器達壓力138bar(2000psi ) ，根據客戶
的要求而定。
可用量測感測器
圖像處理影像感測器與固定聚焦鏡
變焦感測器
變焦感測器
光纖感測器
Werth機台規格圖表
5
Sonplas機台規格
Posalux-FP1
Posalux SA機台規格
Posalux-HP4
6
3 CONTROL OF TAPERED HOLE BY
MICRO-EDM
The “double clamping” (DC) unit is used to drill holes
with control on the geometry. The DC unit is
composed of shifting collets, a tilting head, guiding
collets and adjustable rings.
The shifting collets move along the Z-axis and provide
the in-feed of the electrode during machining.
The tilting head allows for control of the run-out of
the electrode, which modifies the diameter of the
hole.
The guiding collets are set-up to a short and fixed
protrusion
雙夾持頭(DC)裝置是用來控制錐形孔之幾何，其組合
有：轉移夾頭，傾斜頭部裝置，引導夾頭和調節環，
夾頭沿著Z軸進行移動，並提供進料加工之電極。
傾斜頭部(The tilting head)裝置能夠控制進出之電極，
修改孔之直徑。
引導夾頭(The guiding collets)是為了短而突出的水平
電極而設置的(如圖二所示) 。
調節環(The adjustable rings)可調節電極之斜率修改孔
的直徑。
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要獲得一個正錐度孔，電極必須以孔
入口為對正中心進行加工，負錐度孔
則以出口為對正中心進行加工。
正錐度孔
The adjustable rings set up the slope of the
electrode by mechanical adjustment.
To obtain a positive tapered hole, the electrode
must be centered at the hole entrance on the work
piece. For negative tapered hole the centering
must be done at the exit of the hole, which
corresponds to the protrusion and the wall
thickness (see Figure 4). A camera is used to
center the electrode.
The main advantages of the DC unit are:
· The control and the repeatability of the hole
diameter by fixing the protrusion and changing the
run-out.
· The feasibility of tapered hole by fixing a slope on
the electrode and rotating during erosion.
負錐度孔
雙夾頭之優點：
藉由前端凸出部分修正前端與改變其
擺動來進行孔控制與其重複性
錐形孔藉由修正電極斜度與旋轉進行
腐蝕
8
The hole is drilled in two steps, the dressing and the erosion. During the dressing
step, the polarity used is positive (electrode positive and work piece negative)
and the idea is to dress the electrode with the aim of obtaining a flat electrode
before beginning to erode. Thus the lateral wear of the electrode during erosion
will be compensated for and each hole machining will begin with the same
conditions. Then the polarity is changed (electrode negative and work piece
positive) for the erosion step. To guarantee good hole exit quality, the electrode
penetrates beyond the end of the hole.
鑽孔分兩步驟：披覆(敷料)與侵蝕鑽孔，披覆電極(電極為正 ，工件為負)目的為取
得扁平狀(面)的電極才開始腐蝕，因此橫向磨耗過程中的侵蝕電極將得到補償，對
於每個孔開始加工條件相同，然後極性改變(電極為負 ，工件為正)為腐蝕的步驟，
目的為保證孔洞的良好品質。
These two processes occur with a rotation between 500-1000 rev/min of the
electrode during machining. Rotation of the electrode allows for better
flushing of the eroded material and better control of the hole geometry.
此兩個過程轉速為500-1000轉/分，旋轉電極可更佳的沖洗侵蝕材料與控制孔本
身的結構。
9
4 RESULTS AND DISCUSSIONS
4.1 Tapered holes
4.1圓錐孔
Tapered holes can be obtained naturally with EDM drilling parameters by varying the
electrode diameters. With the consistent run-out and with the energy level adapted to the
electrode chosen, the following observations can be made:
圓錐孔可自然的利用EDM鑽孔改變參數，電極直徑隨著一致的變化並與能階適應電極
的選擇。
With small electrode diameters (< 100 mm), the hole obtained has a natural positive cone.
小電極直徑（<100μm），獲得自然的正錐度孔。
For an electrode with a diameter of 100 mm, a cylindrical hole is obtained.
電極直徑為 100μm，獲得圓柱孔。
With large electrode diameters (> 100 mm), the cone obtained is negative.
大電極直徑（>100μm），獲得負錐度孔。
10
As shown in Figure 5, it is mechanically
possible to control the hole geometry with
the adjustable rings by changing the taper
set-up value. A slope is given to the
electrode through mechanical adjustment.
The rotation of the electrode allows a
round hole with the desired taper.
圖五 為可控制孔的幾何形狀與調節環錐
度之夾具
其斜度是考慮到電極旋轉加工時所需錐
度
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負錐度
圓柱孔
正錐度
正錐度
圖六 錐度和正向錐度的可行性
隨著各項目標，取得圓錐形幾何形狀，
從而錐形裝置的調節環進行調節
該電極直徑為110mm，管壁為1mm
第一張為負錐度孔
第二張為圓柱形
三和四為正錐度孔
In Figure 6, the cut of various machined holes can be
seen, with the goal of obtaining various conical geometries,
thus changing the taper set-up of the adjustable rings. The
electrode diameter is 110 mm and the thickness of the wall is
of 1 mm. The entrance hole is at the top of the image and the
exit hole at the bottom. In the first cross section, the taper is
negative, the second cylindrical and the two last are positive
cones with different conical values.
錐度變化為±30μm
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4.2 Small diameter
The study of the maximum hole depth for through holes has been made by varying the electrode
diameter. Graph 2 shows the erosion time for various electrode diameters as a function of the hole
depth. Increasing the electrode diameter allows for larger through hole depths. A change in the graph
slopes can be seen for all hole diameters,indicating a limit of the zone under control. The hole depth
corresponding to the change in graph slope is the hole thickness limit where the time and the hole
quality is guaranteed. For higher hole depth values, the time of erosion increases and the hole quality
is no longer under control in terms of repeatability. For small electrode diameter, the lateral gap is
small and the eroded particles are trapped which makes evacuation difficult. This explains the
increase in erosion time and lack of control over hole quality. The holes diameters are limited based
on hole depth, with a ratio of between 1/10 to 1/12 (hole diameter/hole depth). For identical hole
depths, the erosion time decreases when the electrode iameter increases. This is primarily due to the
increase in the supplied energy that could be
圖二顯示為各時間與電極直徑的比，提
applied to a larger electrode.
高電極允許通過直徑較大的孔深，圖中
可看見斜坡與各孔徑，表明限制區是受
到控制的，圖中的斜率是孔壁厚與品質
的保證，對於小孔徑來說，橫向差距小，
使得侵蝕粒子疏散困難，這解釋侵蝕時
間的增加和缺乏控制
在有限的孔深基礎上，介於1/10至
1/12(孔徑/孔深)，相對於相同的孔深，
當電極直徑增大時侵蝕時間減少，這主
要是增加提供的能量，較適用於較大的
電極
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4.3 Thickness of the white layer
Micro-drilling technologies have the capacity to minimize the thermal affected zone.
White layer thickness has been studied with various energies levels corresponding to
applications such as diesel nozzles, diesel adapter plates and gasoline nozzles. The
material drilled is hardened steel which is typically used for diesel nozzles. The drilled
plates have a thickness of 0.6 mm. Two cuts were achieved:
· A vertical cut in the axis of the holes.
· A horizontal cut, at 120 mm from the top of the surface.
The parts were etched in order to investigate the white layer.
微鑽孔技術有能力盡量減少熱影響區，白層厚度被與不同能量等級對應噴嘴應用做
研究，例如：柴油噴嘴，柴油適配(配置)版(adapter plates) ，汽油噴嘴。柴油噴嘴
材料通常使用硬化鋼材(hardened steel)。
鑽孔版的厚度為0.6mm 兩板切銷結果為：
一個垂直的軸切割，一橫向切割再120mm的頂部表面
這些部件被腐蝕，進行白層調查
14
Low energy
Low energy levels (~ 6 mJ per spark) are typically used to
drill diameters from 50 mm up to 150 mm, which
corresponds to the diesel nozzles currently being
produced. The white layer studied here was produced
using a 70 mm electrode diameter. The thickness of the
white layer along the hole varies between 1 and 1.5 mm.
High energy
High energy levels (~ 10 mJ per spark) are used to drill
diameters from 150 mm to 300 mm and correspond to
applications such as diesel adapter plates. The white
layer obtained has a thickness up to 3.5 mm and was
produced using an electrode diameter of 150 mm.
It is possible to reduce the white layer thickness using
lower energy, but the machining time will increase
drastically and further tests need to be done in order to
understand the white layer thickness and its influence in
terms of nozzle spray efficiency.
In conclusion, no differences were observed due to the
electrode type. Therefore, the white layer remaining after
the micro-EDM process is dependent exclusively on the
energy level.
低能階
低能階(每火花約6 千分之一焦耳)
通常被使用於目前柴油噴嘴生產
之鑽頭直徑50mm至150mm。白
層的研究製作，使用電極直徑
70mm 白層厚度沿著洞口變化1和
1.5mm 。
高能階
高能階(約10 千分之一焦耳)通常
用於鑽頭直徑150mm至300mm，
適用於柴油適配(配置)版(adapter
plates)。電極直徑為150mm，白
層厚度可達3.5mm。
使用較低的能量可降低白層厚度，
但加工時間將增加，需大幅度的
進一步測試，以了解白層厚度與
其影響噴嘴效率。
總之，由於電極使用間無顯著差
異，故白層之形成完全取決於能
量等級
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4.4 Roughness
The topography of a work piece can be
characterized by four distinct components:
form, waviness, roughness and microroughness.
4.4粗糙度
加工後的表面，其特徵分別由四種不同的組
成：型態(Form)，波紋(waviness)，粗糙度
(roughness)，微粗糙度(micro-roughness)
Form is a component of surface finish with a 型態(Form)為工件表面上的表面處理後的長
波紋
long wavelength on the work piece.
Waviness is a surface texture component
varying slowly,depending on the horizontal
position.
波紋(waviness)是根據不同水平位置，表面
變化較慢的紋理
Roughness is a of surface texture
component varying rapidly, depending on
the horizontal position.
粗糙度(Roughness)則是根據水平位置，迅速
變化的紋理
Micro-roughness is the fine variation
component of surface texture.
微粗糙度(micro- Roughness)是優良成分的表
面紋理
16
4.5 Shape measurements
The Werth machine is used in order to control the position
and the geometry of the hole. Recognition of the hole is
made by CCD camera and a fiber probe composed of an
optical fiber with a ball at the end. This probe makes
possible precise measurements of weak geometries. The
detection of very small elements can be obtained with
maximum precision and minimum palpation pressure.
Theuncertainty of palpation is 0.5 μm and the uncertainty
of palpation pressure is 1μN. With the CCD camera, the
hole is centered and the probe is positioned in the optical
field and inserted into the hole at a specific Z value. At this
Z value a palpation is made. There is a limitation on the Z
value measurement dependent on the hole depth due to
low light emission from the bottom of the hole. The results
show an average of variation of ± 2 mm at the hole
entrance and of ± 4 mm at the hole exit. But these shape
measurements can not be performed in process due to its
duration.
4.5外型尺寸
本實驗為了控制位置和孔洞幾
何形狀，採用The Werth 機台
孔洞是由CCD相機與光纖探頭進
行量測，探頭末端由滾珠所組
成，因此可精確量測為小的集
合形狀，可獲得最大精度與最
低接觸壓力
此接觸量測誤差為0.5μm，CCD
相機以洞口為中心，並光場內，
差入指定的Z值作為量測之依據，
在探針觸診量測時，Z值隨著改
變。
17
4.6 Flow measurements
The way to control in process the reproducibility of the holes is a flow
measurement. The Sonplas machine performs static flow measurements on
nozzles. The high reproducibility of the holes drilled on Posalux machine
performs a flow variation in ± 3 % of a nominal value.
4.6 流體測量
要控制孔洞的重現性，方法是透過流體的量測
The Sonplas machine進行噴嘴靜態流體量測
Posalux machine進行鑽孔的高重現性流體變化在±3％的公差
5 CONCLUSION
At the moment, due to the technological control of the EDM process, it is possible to fully
answer the high pressure direct injection needs of the automotive industry.
However, current work indicates that there is considerable potential with regards to higher
geometrical hole control and reductions in erosion time. The production of tapered holes
for diesel nozzles is currently under control and the market of gasoline direct injection is
beginning to develop with very similar needs [6].
5.結論
目前由放電加工可充分滿足高壓直接注入需求的汽車行業，但目前
還有許多關於幾何控制(鑽孔外型)與侵蝕時間，生產圓錐柴油噴嘴
孔的市場與目前汽車直噴的發展有著非常相似的需求
18
6 ACKNOWLEGMENTS
Authors are grateful to Neode for their scientific results
and to Sarix for the micro-EDM technological support.
7 REFERENCES
[1] Ho K.H., Newman S.T., 2003, State of the art electrical discharge machining (EDM),
International Journal of Machine Tools and Manufacture, vol 43,issue 13, 1287-1300
[2] Diver C., Atkinson J., Helml H.J., Li L., 2004, Micro-EDM drilling of tapered holes for
industrial applications, Journal of Materials Processing Technology, vol 149, 296-303
[3] Prescher K., Astachow A., Krüger G., Hintze K.,1998, Effect on nozzle-geometry on
spray breakup and atomization in Diesel engines experimental investigations using model
nozzles and real injections nozzles, Cimac Congress Copenhagen,Band 3, 1073-1083
[4] Chaves H., Knapp M., Kubitzek A., Obermeier F.,Schneider T., 1995, Experimental Study
of Cavitation in the Nozzle Hole of Diesel Injectors Using Transparent Nozzles, SAE
Transactions, vol 104, n°3, 645-657
[5] Dürnholz M., Wintrich T., Polach W., 2001, Potenzial der Einspritzung zur Reduzierung
der Schadstoffemission von Diesel Motoren, Fortschritt Berichte, Reihe 12, Band 455
[6] Ishima T., Sukena R., Liu C., Obokata T., Kawachi K., Kobayashi K., 2001, The Fifth
International Symposium on Diagnostics and Modeling of
Combustion in International Combustion Engines
19
(COMODIA 2001), 493-498
參考資料：
1. 中國百科網-溶蚀钻孔进一步进步激光精度
http://www.chinabaike.com/z/jichuang/497192.html
2. DirectIndustry - The Virtual Industrial
http://www.directindustry.com/
3. Exhibition Micro Machining Microfor Division
http://www.posalux.net/microfor/f/company/
謝謝聆聽
20
Various measurements have been performed on work
pieces machined with different energy levels. Roughness
is an indication of the type of machining used. In fact,
given the same electrode diameter, the change of energy
is visible in the roughness values. For lower energy levels,
the roughness is smaller (around 0.3 Ra), than for higher
energy levels. This is essentially due to the fact that the
energy per pulse is higher and that the material removal
rate is a priority. This implies that the roughness depends
essentially on the energy used for erosion.
Traditional surface finish analysis consists of studying
surface texture roughness and waviness. This implies that
form and micro-roughness components do not need to
be evaluated.
A study of roughness can give an indication on the
variability of the flow measured. The friction due to the
roughness can be one of the major factor for this
variability. A study on roughness needs to be undertaken
to understand its importance.
加工能量不同，粗糙度是顯示該
加工的類型
事實上，由於同樣的電極直徑，
粗糙度值隨著能量跟著改變
相對於較低的能量水平，粗糙度
較小(約0.3RA)，低於較高之能量
水平，意味著粗糙度取決於侵蝕
時的能量高低
傳統表面光亮度分析包括表面紋
理(surface texture)的粗糙度
(roughness)與波紋度(waviness)這
意味著型態(form) and微粗糙度
( micro-roughness)不需要評估
表面粗糙度可指示出的流量測量
的變化，由於摩擦是粗糙度的一
個主要因素，所必須明白其重要
性
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