【正文】 Electrical discharge machiningElectrical discharge machining has proved especially valuable in the machining of supertough, electrically conductive materials such as the new spaceage alloys. These metals would have been difficult to machine by conventional methods, but EDM has made it relatively simple to machine intricate shapes that would be impossible to produce with conventional cutting tools. This machining process is continually finding further applications in the metalcutting industry. It is being used extensively in the plastic industry to produce cavities of almost any shape in the steel molds. Electrical discharge machining is a controlled metal removal technique whereby an electric spark is used to cut (erode) the workpiece, which takes a shape opposite to that of the cutting tool or electrode. The cutting tool (electrode) is made from electrically conductive material, usually carbon. The electrode, made to the shape of the cavity required, and the workpiece are both submerged in a dielectric fluid, which is generally a light lubricating oil. This dielectric fluid should be a nonconductor (or poor conductor) of electricity. A servo mechanism maintains a gap of about to in. ( to mm) between the electrode and the work, preventing them from ing into contact with each other. A direct current of low voltage and high amperage is delivered to the electrode at the rate of approximately 20 000 hertz (Hz). These electrical energy impulses bee sparks which jump the dielectric fluid. Intense heat is created in the localized area of the park impact, the metal melts and a small particle of molten metal is expelled from the surface of the workpiece . The dielectric fluid, which is constantly being circulated, carries away the eroded particles of metal and also assists in dissipating the heat caused by the spark.In the last few years, major advances have been made with regard to the surface finishes that can be produced. With the low metal removal rates, surface finishes of 2 to 4 um. ( to ) are possible. With high metal removal rates finishes of 1 000uin. (25um) are produced.The type of finish required determines the number of amperes which can be used, the capacitance, frequency, and the voltage setting. For fast metal removal (roughing cuts), high amperage, low frequency, high capacitance, and minimum gap voltage are required. For slow metal removal (finish cut) and good surface finish, low amperage, high frequency, low capacitance, and the highest gap voltage are required.Electrical discharge machining has many advantages over conventional machining processes.1. Any material that is electrically conductive can be cut, regardless of its hardness. It is especially valuable for cemented carbides and the new supertough spaceage alloys that are extremely difficult to cut by conventional means.2. Work can be machined in a hardened state, thereby overing the deformation caused by the hardening process.3. Broken taps or drills can readily be removed from workpieces. 4. It does not create stresses in the work material since the tool (electrode) never es in contact with the work.5. The process is burrfree.6. Thin, fragile sections can be easily machined without deforming.7. Secondary finishing operations are generally eliminated for many types of work.8. The process is automatic in that the servomechanism advances the electrode into the work as the metal is removed.9. One person can operate several EDM machines at one time.10. Intricate shapes, impossible to produce by conventional means, are cut out of a solid with relative ease.11. Better dies and molds can be produced at lower costs.12. A die punch can be used as the electrode to reproduce its shape in the matching die plate, plete with the necessary clearance. 第51頁(yè) / 共25頁(yè) 葫蘆島渤海船舶職業(yè)技術(shù)學(xué)院。 。 9 .一個(gè)人可同時(shí)操作幾臺(tái)電火花加工機(jī)床。 7 . 對(duì)許多類型的工件，一般不需第二次精加工。 5 . 加工出的零件無(wú)毛刺。 3 . 很容易將斷在工件中的絲錐和鉆頭除。對(duì)用常規(guī)方法極難切削的硬質(zhì)合金和超韌性的太空合金，電火化加工特別有價(jià)值。 與常規(guī)機(jī)加工方法相比，電火花加工有許多優(yōu)點(diǎn)?？焖偾谐饘伲ù智邢鳎r(shí)，用大電流,低頻率,高電容和最小的間隙電壓。用高的金屬切除率[如高達(dá)15in3/h()]時(shí)，表面粗糙度為1000vin.(25vm)。 在最近幾年，電火花加工的主要進(jìn)步是降低了它加工后的表面粗糙度。在火花沖擊的局部區(qū)域，產(chǎn)生了大量的熱量，金屬融化了，從工件表面噴出融化金屬的小粒子。 ~（~）的間隙，以阻止他們相互接觸。工件與電極都浸在不導(dǎo)電的液體里，這種液體通常是輕潤(rùn)滑油。切削刀具用導(dǎo)電材料（通常是碳）制造。塑料工業(yè)已廣泛使用這種方法，如在鋼制模具上加工幾乎是任何形狀的模腔。這些金屬很難用常規(guī)方法加工，用常規(guī)的切削刀具不可能加工極其復(fù)雜的形狀，電火花加工使之變得相對(duì)簡(jiǎn)單了。1． 分段概述：1． 1分段在船體所處位置：206P/S處于主船體貨艙區(qū)舷側(cè)平行中體部分，由頂邊柜和部分雙層舷側(cè)結(jié)構(gòu)組成；1．2分段的外形尺寸：11800mm(長(zhǎng))*3200mm(寬)*9200（高）；1．3分段重量：55噸；1．4分段的結(jié)構(gòu)形式：混合骨架式；2．分段建造方法及胎架的選擇：：：以舷側(cè)外板為基準(zhǔn)段進(jìn)行側(cè)造；：無(wú)；：5碼頭分段預(yù)制區(qū)；:：立柱式胎架；：，肋板位置輔助線，接縫位置線；、縱方向，在每隔1200mm位置交點(diǎn)上垂直豎立支點(diǎn)角鋼；，來(lái)保證胎架的剛性。由于本船較長(zhǎng)，船體重量大，船體結(jié)構(gòu)采用高強(qiáng)度鋼多，中直及部分曲面分段采用了無(wú)余量建造，船臺(tái)合攏及焊接時(shí)應(yīng)注意，船體分段船臺(tái)安裝定位時(shí)的各種測(cè)量數(shù)據(jù)應(yīng)綜合優(yōu)化，定位必須準(zhǔn)確，在船體建造過(guò)程中各種數(shù)據(jù)應(yīng)隨時(shí)監(jiān)測(cè)，控制好焊接收縮量，保證建造精度。i. 艙口圍板，保證圍板的寬度、長(zhǎng)度、方正度及高度，～，應(yīng)保證其直度和圍板結(jié)構(gòu)的連續(xù)性。g. 首部4040403分段，平臺(tái)甲板的平度，高度，首部總長(zhǎng)前后中心及肋距，并兼顧線型光順。保證左右分段位置與底部分段在一個(gè)循環(huán)面，并且結(jié)構(gòu)應(yīng)重合。c. 機(jī)艙底部311分段，分段定位必須考慮主機(jī)座各數(shù)據(jù)精度。6. 船體精度控制要點(diǎn)：a. 底部分段左右平度，縱向坡度，長(zhǎng)度數(shù)據(jù)，大口焊接收縮控制。b. 機(jī)艙區(qū)至尾部的密性實(shí)驗(yàn)結(jié)束。4. 分段上臺(tái)順序：