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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

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• 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

• gaps of about 5 μm could be obtained. Nowadays, high• quality EDM drilling procedures use rotating electrodes• and axial flushing through hollowed electrodes. At• present, EDM drilling is well established in the field of• manufacturing metal pieces with complicated geometries.• EDM drilling remains the method of choice for diameters• above 50 μm. The geometry of the holes is very important• to the injection nozzle market [2], which has improved• quality and product performances. Tapered holes allow for• better spray efficiency [3], reduction of cavitation• phenomena [4] and self-cleaning of the nozzle holes [5].• The goal of this article is to show how to control the• conical shape and characteristics of the holes.

由於在（ EDM ）技術廣泛用於加工高硬材料，其電極與工件都沉浸於介電液中，過程無機械力量，火花融化與蒸發的廢料由電解液帶走，形成一個高層次和質量的表面精度（ 0.5 RA ），在歐洲此技術影響了專業生產化的應用程序，如鑽孔噴射柴油及汽油噴射。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50μm ，幾何形狀的孔洞為噴嘴市場的重要技術，不但提升了其品質與產品性能，圓錐孔有更好的噴霧效率，減少氣泡現象和自行清潔的噴嘴孔，此文章為展示如何控制錐形形狀與特色的孔洞。

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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).

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 ）。

傾斜頭部

轉移夾頭：侵蝕軸可調節環

引導夾頭

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實驗與量測設備規範• Nozzles made of hardened steel (HRC 57-

63), Cr-Ni are drilled using micro-EDM 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.

可用量測感測器變焦感測器 光纖感測器

圖像處理影像感測器與固定聚焦鏡變焦感測器Werth 機台規格圖表

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。

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Sonplas 機台規格

Posalux SA 機台規格

Posalux-FP1

Posalux-HP4

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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 fixedprotrusion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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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 tocenter 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.

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。

負錐度孔

正錐度孔

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

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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 sameconditions. 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。

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。

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.

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4 RESULTS AND DISCUSSIONS4.1 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（ <100 ），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 100 ，獲得圓柱孔。With large electrode diameters (> 100 mm), the cone obtained is negative. 大電極直徑（ >100 ），獲得負錐度孔。

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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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In Figure 6, the cut of various machined holes can beseen, 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.

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

錐度變化為±30μm

負錐度 圓柱孔 正錐度 正錐度

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4.2 Small diameterThe 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 beapplied to a larger electrode. 圖二顯示為各時間與電極直徑的比，提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 layerMicro-drilling technologies have the capacity to minimize the thermal affected zone. White layer thickness has been studied with various energies levels corresponding toapplications such as diesel nozzles, diesel adapter plates and gasoline nozzles. The material drilled is hardened steel which is typically used for diesel nozzles. The drilledplates 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

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Low energyLow energy levels (~ 6 mJ per spark) are typically used todrill diameters from 50 mm up to 150 mm, whichcorresponds to the diesel nozzles currently beingproduced. The white layer studied here was producedusing a 70 mm electrode diameter. The thickness of thewhite layer along the hole varies between 1 and 1.5 mm.

High energyHigh energy levels (~ 10 mJ per spark) are used to drilldiameters from 150 mm to 300 mm and correspond toapplications such as diesel adapter plates. The whitelayer obtained has a thickness up to 3.5 mm and wasproduced using an electrode diameter of 150 mm.

It is possible to reduce the white layer thickness usinglower energy, but the machining time will increasedrastically and further tests need to be done in order tounderstand the white layer thickness and its influence in terms of nozzle spray efficiency.

In conclusion, no differences were observed due to theelectrode type. Therefore, the white layer remaining afterthe micro-EDM process is dependent exclusively on theenergy 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 RoughnessThe topography of a work piece can be characterized by four distinct components: form, waviness, roughness and micro-roughness.

Form is a component of surface finish with a long wavelength on the work piece.

Waviness is a surface texture component varying slowly,depending on the horizontal position.

Roughness is a of surface texture component varying rapidly, depending on the horizontal position.

Micro-roughness is the fine variation component of surface texture.

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)

型態 (Form) 為工件表面上的表面處理後的長波紋波紋 (waviness) 是根據不同水平位置，表面變化較慢的紋理

粗糙度 (Roughness)則是根據水平位置，迅速變化的紋理

微粗糙度 (micro- Roughness) 是優良成分的表面紋理

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4.5 Shape measurementsThe Werth machine is used in order to control the positionand the geometry of the hole. Recognition of the hole ismade by CCD camera and a fiber probe composed of anoptical fiber with a ball at the end. This probe makespossible precise measurements of weak geometries. Thedetection of very small elements can be obtained withmaximum 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 Zvalue measurement dependent on the hole depth due tolow light emission from the bottom of the hole. The resultsshow an average of variation of ± 2 mm at the holeentrance and of ± 4 mm at the hole exit. But these shapemeasurements can not be performed in process due to itsduration.

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。

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4.6 Flow measurementsThe 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 machineperforms 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 CONCLUSIONAt 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

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6 ACKNOWLEGMENTSAuthors are grateful to Neode for their scientific resultsand 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 ofCombustion in International Combustion Engines(COMODIA 2001), 493-498

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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

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Various measurements have been performed on workpieces machined with different energy levels. Roughnessis an indication of the type of machining used. In fact,given the same electrode diameter, the change of energyis visible in the roughness values. For lower energy levels,the roughness is smaller (around 0.3 Ra), than for higherenergy levels. This is essentially due to the fact that theenergy per pulse is higher and that the material removalrate is a priority. This implies that the roughness dependsessentially on the energy used for erosion.Traditional surface finish analysis consists of studyingsurface texture roughness and waviness. This implies thatform and micro-roughness components do not need to be evaluated.A study of roughness can give an indication on thevariability of the flow measured. The friction due to theroughness can be one of the major factor for thisvariability. A study on roughness needs to be undertakento 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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