0420-SSCK20A數(shù)控車床主軸及主軸箱的數(shù)控加工工藝及數(shù)控編程【含5張CAD圖】
0420-SSCK20A數(shù)控車床主軸及主軸箱的數(shù)控加工工藝及數(shù)控編程【含5張CAD圖】,含5張CAD圖,ssck20a,數(shù)控車床,主軸,數(shù)控,加工,工藝,編程,cad
附錄1專題部分
數(shù)控五軸技術(shù)及數(shù)控編程
隨著科學(xué)技術(shù)的發(fā)展，制造技術(shù)的進(jìn)步，以及社會(huì)對(duì)產(chǎn)品質(zhì)量和品種多樣化的要求越來(lái)越加強(qiáng)烈。中、小批量生產(chǎn)的比重明顯增加，要求現(xiàn)代數(shù)控機(jī)床成為一種高效率、高質(zhì)量、高柔性和低成本的新一代制造設(shè)備。同時(shí)，為了滿足制造業(yè)向更高層次發(fā)展，為柔性制造單元，柔性制造系統(tǒng)，以及計(jì)算機(jī)集成制造系統(tǒng)提供基礎(chǔ)設(shè)備，也要求數(shù)控機(jī)床向更高水平發(fā)展。這些要求主要由數(shù)字控制技術(shù)的發(fā)展來(lái)實(shí)現(xiàn)。數(shù)控技術(shù)體現(xiàn)在數(shù)控裝置、伺服驅(qū)動(dòng)系統(tǒng)、程序編制、機(jī)床主機(jī)和檢測(cè)監(jiān)控系統(tǒng)等方面。
一、數(shù)控加工技術(shù)
近代，大工業(yè)生產(chǎn)大量采用了剛性自動(dòng)化。在汽車工業(yè)、拖拉機(jī)以及輕工業(yè)消費(fèi)品生產(chǎn)方面。采用了大量的組合機(jī)床自動(dòng)線、流水線；在標(biāo)準(zhǔn)件生產(chǎn)中采用了凸輪控制的專用機(jī)床和自動(dòng)機(jī)床。這類機(jī)床適合于大批量生產(chǎn)，但是建立制造過(guò)程很難，所以更換產(chǎn)品，修改工藝要較長(zhǎng)的時(shí)間和比較多的費(fèi)用。
由于產(chǎn)品多樣化和產(chǎn)品更新，解決單件，小批量生產(chǎn)自動(dòng)化迫在眉睫。航空、宇航、造船、電子等工藝對(duì)解決復(fù)雜型零件加工和高精度零件加工要求越來(lái)越高。這就使剛性自動(dòng)化不能滿足要求，柔性加工和柔性自動(dòng)化也就迅速發(fā)展起來(lái)。
數(shù)控機(jī)床是新型的自動(dòng)化機(jī)床，它具有廣泛通用性和很高的自動(dòng)化程度。數(shù)控機(jī)床是實(shí)現(xiàn)柔性自動(dòng)化最重要的裝置，是發(fā)展柔性生產(chǎn)的基礎(chǔ)。數(shù)控機(jī)床在下面一些零件的加工中，更能顯示出它的優(yōu)越性。它們是：1）批量小而又多次生產(chǎn)的零件；2）幾何形狀復(fù)雜的零件；3）在加工過(guò)程中必須進(jìn)行多種加工零件；4）切削余量大的零件；5）必須控制公差（即公差帶范圍?。┑牧慵?；6）工藝設(shè)計(jì)會(huì)變化的零件；7）加工過(guò)程中的錯(cuò)誤回造成嚴(yán)重浪費(fèi)的貴重零件；8）需全部檢測(cè)的零件，等等。
數(shù)控加工技術(shù)的特點(diǎn)：
1、提高生產(chǎn)率。數(shù)控機(jī)床能縮短生產(chǎn)準(zhǔn)備時(shí)間，增加切削加工時(shí)間的比較。采用最佳切削參數(shù)和最佳走刀路線能縮短加工時(shí)間，從而提高生產(chǎn)率。
2、穩(wěn)定產(chǎn)品質(zhì)量。采用數(shù)控機(jī)床可以提高零件的加工精度，穩(wěn)定產(chǎn)品質(zhì)量。它是按照程序自動(dòng)加工不需要人工干預(yù)，而且加工精度還利用軟件進(jìn)行校正及補(bǔ)償，因此，可以獲得比機(jī)床本身精度還要高的加工精度及重復(fù)精度。
3、有廣泛的適應(yīng)性和較大的靈活性。通過(guò)改變程序，就可以加工新品種的零件。能夠完成很多普通機(jī)床難以完成，或者根本不能加工的復(fù)雜型面的零件的加工。
4、可以實(shí)現(xiàn)一機(jī)多用。一些數(shù)控機(jī)床，例如加工中心，可以自動(dòng)換刀。一次裝卡后，幾乎能完成零件的全部加工部位的加工，節(jié)省了設(shè)備和廠房面積。
5、提高經(jīng)濟(jì)效益?？梢赃M(jìn)行精確的成本計(jì)算和生產(chǎn)進(jìn)度安排，減少在制品，加速資金周轉(zhuǎn)，提高經(jīng)濟(jì)效益。
6、不需要專用夾具。采用普通的通用夾具就能滿足數(shù)控加工的要求，節(jié)省了專用夾具設(shè)計(jì)制造和存放的費(fèi)用。
7、大大地減輕了工人的勞動(dòng)強(qiáng)度。
數(shù)控機(jī)床是具有廣泛的通用性而又具有很高自動(dòng)化程度的全新型機(jī)床。它的控制系統(tǒng)不僅能控制機(jī)床各種動(dòng)作的先后順序，還能控制機(jī)床運(yùn)動(dòng)部件的運(yùn)動(dòng)速度，以及刀具相對(duì)工件的運(yùn)動(dòng)軌跡。數(shù)控機(jī)床是計(jì)算機(jī)輔助設(shè)計(jì)和制造，群控，柔性制造系統(tǒng)，計(jì)算機(jī)集成制造系統(tǒng)等柔性加工和柔性制造系統(tǒng)的基礎(chǔ)。
但是，數(shù)控機(jī)床的初投資及維修技術(shù)等費(fèi)用較高，要求管理及操作人員的素質(zhì)也較高。合理地選擇及使用數(shù)控機(jī)床，可以降低企業(yè)的生產(chǎn)成本，提高經(jīng)濟(jì)效益和競(jìng)爭(zhēng)能力。
二、五軸加工技術(shù)
五軸加工是在數(shù)控鏜或數(shù)控銑的基礎(chǔ)上，增加了自動(dòng)換刀裝置，使工件在一次裝夾后，可以連續(xù)對(duì)工件自動(dòng)進(jìn)行鉆孔、擴(kuò)控、鉸孔、攻螺紋、銑削等多加工的機(jī)床。加工中心一般帶有自動(dòng)分度回轉(zhuǎn)工作臺(tái)或主軸箱可自動(dòng)改變角度，從而使工件一次裝夾后，自動(dòng)完成多個(gè)平面或多個(gè)角度位置的多工序加工，工序高度集中；加工中心能自動(dòng)改變主軸轉(zhuǎn)速、進(jìn)給量和刀具相對(duì)工件的運(yùn)動(dòng)軌跡；加工中心如果帶有交換工作臺(tái)，工件在工作位置的工作臺(tái)上進(jìn)行加工的同時(shí)，可在裝卸位置的工作臺(tái)上裝卸工件，工作效率高。五軸數(shù)控加工技術(shù)可以在一次裝夾中完成工件的全部機(jī)械加工工序，滿足從粗加工到精加工的全部加工要求，即適用于單件小批量生產(chǎn)也適用于大批量生產(chǎn)，減少了加工時(shí)間和生產(chǎn)費(fèi)用，提高了數(shù)控設(shè)備的生產(chǎn)能力和經(jīng)濟(jì)性。
目前國(guó)際上五軸高速切削加工技術(shù)主要應(yīng)用于汽車工業(yè)、模具行業(yè)、航空航天行業(yè)，尤其是在加工復(fù)雜曲面的領(lǐng)域、工件本身或刀具系統(tǒng)剛性要求較高的加工領(lǐng)域，顯示了強(qiáng)大的功能。國(guó)內(nèi)五軸高速切削加工技術(shù)的研究與應(yīng)用始于20世紀(jì)90年代，應(yīng)用于模具、航空航天和汽車工業(yè)。但采用的高速切削CNC機(jī)床、高速切削刀具和CAD/CAM軟件等以進(jìn)口為主。
數(shù)控五軸高速切削加工作為模具制造中最為重要的一項(xiàng)先進(jìn)制造技術(shù)，是集高效、優(yōu)質(zhì)、低耗于一身的先進(jìn)制造技術(shù)。在常規(guī)切削加工中備受困惑的一系列問(wèn)題通過(guò)五軸高速切削加工的應(yīng)用得到了解決。其切削速度和進(jìn)給速度比傳統(tǒng)的切削加工速度高，切削機(jī)理發(fā)生了根本的變化。與傳統(tǒng)切削加工相比，切削加工發(fā)生了本質(zhì)的飛躍。其單位功率的金屬切除率提高了30%—40%、切削力降低了30%、刀具的切削壽命提高了70%、留于工件的切削熱大幅度降低、低階切削振動(dòng)幾乎消失。隨著切削速度的提高，單位時(shí)間毛坯材料的去除率增加，切削時(shí)間減少，加工效率提高?？s短了產(chǎn)品的制造周期，增加了產(chǎn)品的市場(chǎng)競(jìng)爭(zhēng)力。同時(shí)高速加工的小量快進(jìn)使切削力減少，切屑的高速排除，減少了工件的切削力和熱應(yīng)力變形，提高了剛性差和薄壁零件切削加工的可能性。另外，由于切削力的降低，轉(zhuǎn)速的提高使切削系統(tǒng)的工作頻率遠(yuǎn)離機(jī)床的低階固有頻率，而工件的表面粗糙度對(duì)低階頻率最為敏感，由此降低了表面粗糙度。在模具的高淬硬剛件（45—65HRC）的加工過(guò)程中，采用高速切削可以取代電加工和磨削拋光的工序。避免了電極的制造和費(fèi)時(shí)的電加工時(shí)間，大幅度減少了鉗工的打磨與拋光量。一些市場(chǎng)上越來(lái)越需要的薄壁模具工件，高速銑削可順利完成。而且在高速銑削CNC加工中心上，模具一次裝夾可完成多工步加工。
1、五軸高速加工切削的優(yōu)點(diǎn)
五軸高速加工切削系統(tǒng)主要由高速加工中心、高性能的刀具夾持系統(tǒng)、高速切削刀具、安全可靠的高速切削CAM軟件系統(tǒng)，因此五軸高速加工是一項(xiàng)大的系統(tǒng)工程。隨著切削刀具技術(shù)的進(jìn)步，高速加工已應(yīng)用于加工合金鋼（硬度大于30HRC），廣泛地應(yīng)用在汽車和電子元件產(chǎn)品中的沖壓模，注射模零件。高速加工的定義依賴于被加工的工件材料的類型。例如，高速加工合金鋼采用的切削速度為500m/min，而這一速度在加工鋁合金是常采用順銑。
2、五軸高速銑削加工機(jī)床
五軸超高速切削技術(shù)是切削技術(shù)是切削加工的方向，也是時(shí)代發(fā)展的產(chǎn)物。高速切削技術(shù)是切削加工技術(shù)的主要發(fā)展方向之一，它隨著CNC技術(shù)、微電子技術(shù)、新材料和新結(jié)構(gòu)等基礎(chǔ)技術(shù)的發(fā)展而邁尚更高的臺(tái)階。然而高速切削技術(shù)自身也存在著一些急待解決的問(wèn)題，如高硬度材料的切削機(jī)理、刀具在載荷變化過(guò)程中的破損、建立高速切削數(shù)據(jù)庫(kù)、開發(fā)適用于高速切削加工狀態(tài)的監(jiān)控技術(shù)和綠色制造技術(shù)等等。同時(shí)高速切削所用的CNC機(jī)床，車、銑、鉆等刀具，CAD/CAM軟件等技術(shù)含量高，價(jià)格昂貴，使得高速切削投資大，這在一定程度上制約了高速切削技術(shù)的推廣應(yīng)用。高速切削的高效應(yīng)用要求機(jī)床系統(tǒng)中的部件都必須先進(jìn)，主要表現(xiàn)在以下幾個(gè)方面：
a、機(jī)床結(jié)構(gòu)的剛性。提供高速進(jìn)給的驅(qū)動(dòng)器（快進(jìn)速度約40m/min，3D輪廓加工速度為10m/min），能夠0.4—10m/s的加速度和減速度。
b、主軸和刀柄的剛性。10000—50000轉(zhuǎn)/min的轉(zhuǎn)速，通過(guò)主軸壓縮空氣或冷卻系統(tǒng)控制刀柄和主軸間的軸向間隙不大于0.005mm。
c、控制單元2和4位并行處理器，高的數(shù)據(jù)傳輸率，能夠自動(dòng)加減速。
d、可靠性與加工工藝。提高機(jī)床的利用率和無(wú)人操作的可靠性，工藝模型有助于對(duì)切削條件和刀具壽命之間關(guān)系的理解。
常見(jiàn)國(guó)內(nèi)外五軸高速加工中心與傳統(tǒng)普通數(shù)控機(jī)床相比，其機(jī)床結(jié)構(gòu)、加工速度和性能更優(yōu)秀，如德國(guó)的DMC85高速加工中心，采用直線電機(jī)和電主軸，其主軸轉(zhuǎn)速達(dá)到30000轉(zhuǎn)/min，進(jìn)給速度達(dá)到120m/min，加速度超過(guò)1g（重力加速度）。五軸高速機(jī)床要求高的主軸單元和冷卻系統(tǒng)、高剛性的機(jī)床結(jié)構(gòu)、安全裝置和監(jiān)控系統(tǒng)、以及優(yōu)良的靜動(dòng)力特性等，其技術(shù)含量高，機(jī)床制造難度大等特點(diǎn)。目前國(guó)內(nèi)的高速機(jī)床其性能與國(guó)外相比還存在一定的差距。
三、數(shù)控編程
數(shù)控機(jī)床是按照事先編制好的工程序自動(dòng)對(duì)工件進(jìn)行加工的高效自動(dòng)化設(shè)備。在數(shù)控機(jī)床上加工零件時(shí)，要把加工零件的全部工藝過(guò)程、工藝參數(shù)和位移數(shù)據(jù)，以信息的形式記率在控制介質(zhì)上，用控制介質(zhì)上的信息來(lái)控制機(jī)床，實(shí)現(xiàn)零件的全部加工過(guò)程。這里，我們把從零件圖紙到獲得數(shù)控機(jī)床所需控制介質(zhì)的全部過(guò)程，稱為程序編制。
程序編制是數(shù)控加工的一項(xiàng)重要、工作，理想的加工程序不僅應(yīng)保證加工出符合圖紙要求的合格工件，同時(shí)應(yīng)該能使數(shù)控機(jī)床的功能得到合理的應(yīng)用與充分的發(fā)揮，以使數(shù)控機(jī)床安全可靠及高效地工作。
數(shù)控機(jī)床程序編制的內(nèi)容主要包括：分析零件圖紙、工藝處理、數(shù)學(xué)處理、編寫程序單、制備控制介質(zhì)及程序校驗(yàn)。其具體步驟與要求如下：
1、分析零件圖紙
首先要分析零件圖紙。根據(jù)零件的材料、形狀、尺寸、精度、毛坯形狀和熱處理要求等確定加工方案，選擇合適的數(shù)控機(jī)床。
2、工藝處理
工藝處理涉及問(wèn)題較多，需要考慮如下幾點(diǎn)：
1）確定加工方案 此時(shí)應(yīng)按照能充分發(fā)揮數(shù)控機(jī)床功能的原則，使用合適的數(shù)控機(jī)床，確定合理的加工方法。
2）刀具工夾具的設(shè)計(jì)和選擇 數(shù)控加工用刀具由加工方法、切削用量及其它與加工有關(guān)的因素來(lái)確定。數(shù)控機(jī)床具有刀具補(bǔ)償功能和自動(dòng)換刀功能。
數(shù)控加工一般不需要專用的復(fù)雜的夾具。在設(shè)計(jì)和選擇夾具時(shí)，應(yīng)特別注意要迅速完成工件的定位和夾緊過(guò)程，以減少輔助時(shí)間。使用組合夾具，生產(chǎn)準(zhǔn)備周期短，夾具零件可以反復(fù)使用，經(jīng)濟(jì)效益好。此外，所用夾具應(yīng)便于安裝，便于協(xié)調(diào)工件和機(jī)床坐標(biāo)系的尺寸關(guān)系。
3）選擇對(duì)刀點(diǎn) 程序編制時(shí)正確地選擇對(duì)刀點(diǎn)是很重要的?！皩?duì)刀點(diǎn)”是程序執(zhí)行的起點(diǎn)，也稱“程序原點(diǎn)”。對(duì)刀點(diǎn)的選擇原則是：所選對(duì)刀點(diǎn)，應(yīng)使程序編制簡(jiǎn)單；對(duì)刀點(diǎn)應(yīng)選擇在容易找正、并在加工過(guò)程中便于檢查的位置；引起的加工誤差小。
對(duì)刀點(diǎn)可以設(shè)置在被加工零件上，也可以設(shè)置在夾具或機(jī)床上。為了提高零件的加工精度，對(duì)刀點(diǎn)應(yīng)盡量設(shè)置在零件的設(shè)計(jì)基礎(chǔ)或工藝基準(zhǔn)上。
4）確定加工路線 加工路線的選擇主要應(yīng)該考慮：盡量縮短走刀路線，減少空走刀行程，提高生產(chǎn)率；保證加工零件的精度和表面粗糙度的要求；有利于簡(jiǎn)化數(shù)值計(jì)算，減少程序段的數(shù)目和編程工作量。
5）確定切削用量 切削用量即切削深度和寬度，主軸轉(zhuǎn)速及進(jìn)給速度等。切削用量的具體數(shù)值應(yīng)根據(jù)數(shù)控機(jī)床使用說(shuō)明書的規(guī)定，被加工工件材料，加工工序以及其它工藝要求，并結(jié)合實(shí)際經(jīng)驗(yàn)來(lái)確定。
3、數(shù)學(xué)處理
在工藝處理工作完成后，根據(jù)零件的幾何尺寸，加工路線，計(jì)算數(shù)控機(jī)床所需的輸入數(shù)據(jù)。一般數(shù)控系統(tǒng)都具有直線插補(bǔ)、圓弧插補(bǔ)和刀具補(bǔ)償功能。對(duì)于加工由直線和圓弧組成的較簡(jiǎn)單的平面零件，只需計(jì)算出零件輪廓的相鄰幾何元素的交點(diǎn)或切點(diǎn)（稱為基點(diǎn)）的坐標(biāo)值。對(duì)于較復(fù)雜的零件或零件的集合形狀與數(shù)控系統(tǒng)的插補(bǔ)功能不一致時(shí)，就需要進(jìn)行較復(fù)雜的數(shù)值計(jì)算。
4、編寫零件加工程序單
在完成工藝處理和數(shù)值計(jì)算工作后，可以編寫零件加工程序單，編寫人員根據(jù)所使用數(shù)控系統(tǒng)的指令、程序段格式，逐段編寫零件加工程序。編程人員要了解數(shù)控機(jī)床的性能、程序指令代碼以及數(shù)控機(jī)床加工零件的過(guò)程，才能編寫出正確的加工程序。
5、制備控制介質(zhì)及程序檢驗(yàn)
程序編好后，需制作控制介質(zhì)。控制介質(zhì)有穿孔紙帶、穿孔卡、磁帶、軟磁盤和硬磁盤等。早期為穿孔紙帶，現(xiàn)在已被磁盤所代替。但是，規(guī)定的穿孔紙帶代碼標(biāo)準(zhǔn)沒(méi)有變。
在單件和多品種小批量產(chǎn)品生產(chǎn)模式下，產(chǎn)品品種復(fù)雜多樣，個(gè)性化要求高，沒(méi)有統(tǒng)一的流程。數(shù)控加工技術(shù)在這種生產(chǎn)模式中日益發(fā)揮巨大作用人。數(shù)控加工技術(shù)不僅可以提高產(chǎn)品的加工精度和品質(zhì)，而且可以大大縮短產(chǎn)品的生產(chǎn)周期。一般來(lái)講，數(shù)控加工技術(shù)中包括了數(shù)控加工機(jī)床、數(shù)控編程軟件和數(shù)控設(shè)備管理軟件。數(shù)控編程軟件（ＣＡＭ 軟件）在提高機(jī)床加工精度和加工效率方面起著至關(guān)重要的作用。從目前數(shù)控加工設(shè)備的普及和發(fā) 展情況來(lái)看，數(shù)控編程軟件要具有如下特性。
１． 軟件要操作簡(jiǎn)單，易學(xué)易用
隨著國(guó)內(nèi)企業(yè)數(shù)控設(shè)備使用的不斷普及，對(duì)數(shù)控編程人員的需求量也不斷增加。那種需要長(zhǎng)時(shí)間培訓(xùn)才能要輸入或設(shè)置很多選項(xiàng)，過(guò)多的操作會(huì)給編程人員帶來(lái)很大的壓力，也帶 來(lái)了更多的出錯(cuò)幾率。因此，操作簡(jiǎn)單、易學(xué)易用是數(shù)控編程軟件普及的關(guān)鍵。要做到操作簡(jiǎn)單，易學(xué)易用不僅僅是軟件界面的問(wèn)題，更多涉及到的是軟件的智能化處理算法。
２．軟件產(chǎn)生的刀具軌跡要保證高速、高精度和高效率
數(shù)控加工技術(shù)是提高產(chǎn)品生產(chǎn)效率，縮短生產(chǎn)周期的關(guān)鍵手段。高速不僅僅是要求編程軟件支持高速加工機(jī)床，也要求編程軟件產(chǎn)生的刀具軌跡能夠發(fā)揮普通數(shù)控機(jī)床的最高切削速度。在保證高精度的前提下盡量減少空走刀和重復(fù)走刀。這樣才能縮短加工時(shí)間。畢竟在中國(guó)市場(chǎng)上普通數(shù)控機(jī)床還占絕大多數(shù)，讓這些機(jī)床充分發(fā)揮加工能力是關(guān)鍵。
３．軟件要匹配各種數(shù)控系統(tǒng)
在中國(guó)市場(chǎng)上，存在著各種各樣的數(shù)控機(jī)床。因此，機(jī)床控制系統(tǒng)也是五花八門的，這就要求數(shù)控編程軟件要能夠匹配各種機(jī)床控制系統(tǒng)。
４．軟件要能與整個(gè)生產(chǎn)流程集成
隨著中國(guó)企業(yè)的信息化程度不斷加深，數(shù)控編程已經(jīng)不再是一個(gè)獨(dú)立的信息化孤島，而是整個(gè)企業(yè)生產(chǎn)流程中的一個(gè)環(huán)節(jié)和數(shù)據(jù)源。對(duì)數(shù)控編程軟件的要求也不僅僅是生成數(shù)控代碼，而是要求數(shù)控編程軟件要能夠與ＰＤＭ集成以快速得到設(shè)計(jì)數(shù)據(jù)，能夠產(chǎn)生工藝數(shù)據(jù)并與工藝管理系統(tǒng)集成，能夠與數(shù)控設(shè)備管理系統(tǒng)集成使數(shù)控設(shè)備能夠得到加工所需要的信息，這樣才能在某種程度上做到設(shè)計(jì)、工藝和制造過(guò)程的并行，縮短制造周期。
數(shù)控五軸加工技術(shù)及數(shù)控編程是數(shù)控機(jī)床應(yīng)用的基礎(chǔ)，機(jī)加工工藝是數(shù)控五軸加工技術(shù)和數(shù)控編程的基礎(chǔ)，要充分發(fā)揮數(shù)控機(jī)床的能力，需要刀具、材料、計(jì)算機(jī)、高等數(shù)學(xué)等多學(xué)科知識(shí)，還應(yīng)不斷進(jìn)行編程實(shí)踐，總結(jié)經(jīng)驗(yàn)教訓(xùn)，在實(shí)踐中不斷得到提高。
附錄2 外文翻譯（外文部分）
ADVANCED MACHINING PROCESSES
As the hardware of an advanced technology becomes more complex, new and visionary approaches to the processing of materials into useful products come into common use. This has been the trend in machining processes in recent years.. Advanced methods of machine control as well as completely different methods of shaping materials have permitted the mechanical designer to proceed in directions that would have been totally impossible only a few years ago.
Parallel development in other technologies such as electronics and computers have made available to the machine tool designer methods and processes that can permit a machine tool to far exceed the capabilities of the most experienced machinist.
In this section we will look at CNC machining using chip-making cutting tools. CNC controllers are used to drive and control a great variety of machines and mechanisms, Some examples would be routers in wood working; lasers, plasma-arc, flame cutting, and waterjets for cutting of steel plate; and controlling of robots in manufacturing and assembly. This section is only an overview and cannot take the place of a programming manual for a specific machine tool. Because of the tremendous growth in numbers and capability of computers ,changes in machine controls are rapidly and constantly taking place. The exciting part of this evolution in machine controls is that programming becomeseasier with each new advanced in this technology.
Advantages of Numerical Control
A manually operated machine tool may have the same physical characteristics as a CNC machine, such as size and horsepower. The principles of metal removal are the same. The big gain comes from the computer controlling the machining axes movements. CNC-controlled machine tools can be as simple as a 2-axis drilling machining center (Figure O-1). With a dual spindle machining center, the low RPM, high horsepower spindle gives high metal removal rates. The high RPM spindle allows the efficient use of high cutting speed tools such as diamonds and small diameter cutters (Figure O-2). The cutting tools that remove materials are standard tools such as milling cutters, drills, boring tools, or lathe tools depending on the type of machine used. Cutting speeds and feeds need to be correct as in any other machining operation. The greatest advantage in CNC machining comes from the unerring and rapid positioning movements possible. A CNC machine does dot stop at the end of a cut to plan its next move; it does not get fatigued; it is capable of uninterrupted machining error free, hour after hour. A machine tool is productive only while it is making chips.
Since the chip-making process is controlled by the proper feeds and speeds, time savings can be achieved by faster rapid feed rates. Rapid feeds have increased from 60 to 200 to 400 and are now often approaching 1000 inches per minute (IPM). These high feed rates can pose a safety hazard to anyone within the working envelope of the machine tool.
Complex contoured shapes were extremely difficult to product prior to CNC machining .CNC has made the machining of these shapes economically feasible. Design changes on a part are relatively easy to make by changing the program that directs the machine tool.
A CNC machine produces parts with high dimensional accuracy and close tolerances without taking extra time or special precautions, CNC machines generally need less complex work-holding fixtures, which saves time by getting the parts machined sooner. Once a program is ready and production parts, each part will take exactly the same amount of time as the previous one. This repeatability allows for a very precise control of production costs. Another advantage of CNC machining is the elimination of large inventories; parts can be machined as needs .In conventional production often a great number of parts must be made at the same time to be cost effective. With CNC even one piece can be machined economically .In many instances, a CNC machine can perform in one setup the same operations that would require several conventional machines.
With modern CNC machine tools a trained machinist can program and product even a single part economically .CNC machine tools are used in small and large machining facilities and range in size from tabletop models to huge machining centers. In a facility with many CNC tools, programming is usually done by CNC programmers away from the CNC tools. The machine control unit (MCU) on the machine is then used mostly for small program changes or corrections. Manufacturing with CNC tools usually requires three categories of persons. The first is the programmer, who is responsible for developing machine-ready code. The next person involved is the setup person, who loads the raw stork into the MCU, checks that the correct tools are loaded, and makes the first part. The third person is the machine and unloads the finished parts. In a small company, one person is expected to perform all three of these tasks.
CNC controls are generally divided into two basic categories. One uses a ward address format with coded inputs such as G and M codes. The other users a conversational input; conversational input is also called user-friendly or prompted input. Later in this section examples of each of these programming formats in machining applications will be describes.
CAM and CNC
CAM systems have changed the job of the CNC programmer from one manually producing CNC code to one maximizing the output of CNC machines. Since CNC machine tools are made by a great number of manufacturers, many different CNC control units are in use. Control units from different manufacturers use a variety of program formats and codes. Many CNC code words are identical for different controllers, but a great number vary from one to another.
To produce an identical part on CNC machine tools with different controllers such as one by FANCU, OKUMA or DYNAPATH, would require completely different CNC codes. Each manufacturer is constantly improving and updating its CNC controllers. These improvements often include additional code words plus changes in how the existing code works.
A CAM systems allows the CNC programmer to concentrate on the creation of an efficient machining process, rather then relearning changed code formats. A CNC programmer looks at the print of a part and then plans the sequence of machining operations necessary to make it (Figure O-3). This plan includes everything, from the selection of possible CNC machine tools, to which tooling to use, to how the part is held while machining takes place. The CNC programmer has to have a thorough understanding of all the capacities and limitations of the CNC machine tools that a program is to be made for. Machine specifications such as horsepower, maximum spindle speeds, workpiece weight and size limitations, and tool changer capacity are just some of the considerations that affect programming.
Another area of major importance to the programmer is the knowledge of machining processes. An example would be the selection of the surface finish requirement specified in the part print. The sequence of machining processes is critical to obtain acceptable results. Cutting tool limitations have to be considered and this requires knowledge of cutting tool materials, tool types, and application recommendations.
A good programmer will spend a considerable amount of time in researching the rapidly growing volume of new and improved tools and tool materials. Often the tool that was on the cutting edge of technology just two years ago is now obsolete. Information on new tools can come from catalogs or tool manufacturers' tooling engineers. Help in tool selection or optimum tool working conditions can also be obtained from tool manufacturer software. Examples would be Kennametal's "TOOLPRO", software designed to help select the best tool grade, speed, and feed rates for different work materials in turning application. Another very important feature of "TOOLPRO" is the display of the horsepower requirement for each machining selection. This allow the programmer to select a combination of cutting speed, feed rate, and depth of cut that equals the machine's maximum horsepower for roughing cuts. For a finishing cut, the smallest diameter of the part being machined is selected and then the cutting speed varied until the RPM is equal to the maximum RPM of the machine. This helps in maximizing machining efficiency. Knowing the horsepower requirement for a cut is critical if more than one tool is cutting at the same time.
Software for a machining center application would be Ingersoll Tool Company's "Actual Chip Thickness", a program used to calculate the chip thickness in relation to feed-per-tooth for a milling cutter, especially during a shallow finishing cut. Ingersoll's "Rigidity Analysis" software ealculates tool deflection for end mills as a function of tool stiffness and tool force.
To this point we looked at some general qualifications that a programmer should possess. Now we examine how a CAM system works. Point Control Company's SmartCam system uses the following approach. First, the programmer makes a mental model of the part to be machined. This includes the kind of machining to be performed-turning or milling. Then the part print is studied to develop a machining sequence, roughing and finishing cuts, drilling, tapping, and boring operations. What work-holding device is to be used, a vise or fixture or clamps? After these considerations, computer input can be started. First comes the creation of a JOBPLAN. This JOBPLAN consists of entries such as inch or metric units, machine type, part ID, type of workpiece material, setup notes, and a description of the required tools.
This line of information describes the tool by number, type, and size and includes the appropriate cutting speed and feed rate. After all the selected tools are entered, the file is saved.
The second programming step is the making of the part. This represents a graphic modeling of the projected machining operation. After selecting a tool from the prepared JOBPLAN, parameters for the cutting operation are entered. For a drill, once the coordinate location of the hole and the depth are given, a circle appears on that spot. If the location is incorrect, the UNDO command erases this entry and allows you to give new values for this operation. When an end mill is being used, cutting movements (toolpath) are usually defined as lines and arcs. As a line is programmed, the toolpath is graphically displayed and errors can be corrected instantly.
At any time during programming, the command SHOWPATH will show the actual toolpath for each of the programmed tools. The tools will be displayed in the sequence in which they will be used during actual machining. If the sequence of a tool movement needs to be changed, a few keystrokes will to that.
Sometimes in CAM the programming sequence is different from the actual machining order. An example would be the machining of a pocket in a part. With CAM, the finished pocket outline is programmed first, then this outline is used to define the roughing cuts to machine the pocket. The roughing cuts are computer generated from inputs such as depth and width of cut and how much material to leave for the finish cut. Different roughing patterns can be tried out to allow the programmer to select the most efllcient one for the actual machining cuts. Since each tool is represented by a different color, it is easy to observe the toolpath made by each one.
A CAM system lets the programmer view the graphics model from varying angles, such as a top, front, side, or isometric view. A toolpath that looks correct from a top view, may show from a front view that the depth of the cutting tool is incorrect. Changes can easily be made and seen immediately.
When the toolpath and the sequence of operations are satisfactory, machine ready code has to be made. This is as easy as specifying the CNC machine that is to be used to machine the part. The code generator for that specific CNC machine during processing accesses four different files. The JOBPLAN file for the tool information and the GRAPHICE file for the toolpath and cutting sequence. It also uses the MACHINE DEFINE file which defines the CNC code words for that specific machine. This file also supplies data for maximum feed rates, RPM, toolchange times, and so on. The fourth file taking part in the code generating process is the TEMPLATE file. This file acts like a ruler that produces the CNC code with all of its parts in the right place and sequence. When the code generation is complete, a projected machining time is displayed. This time is calculated from values such as feed rates and distances traveled, noncutting movements at maximum feed rates between points, tool change times, and so on. The projected machining time can be revised by changing tooling to allow for higher metal removal rates or creating a more efficient toolpath. This display of total time required can also be used to estimate production costs. If more then one CNC machine tool is available to machine this part, making code and comparing the machining time may show that one machine is more efficient than the others.
CAD/CAM
Another method of creating toolpath is with the use of a Computer-aided Drafting (CAD) file. Most machine drawings are created using computers with the description and part geometry stored in the computer database. SmartCAM, though its CAM CONNECTION, will read a CAD file and transfer its geometry represents the part profile, holes, and so on. The programmer still needs to prepare a JOBPLAN with all the necessary tools, but instead of programming a profile line by line, now only a tool has to be assigned to an existing profile. Again, using the SHOWPATH function will display the toolpath for each tool and their sequence. Constant research and developments in CAD/CAM interaction will change how they work with each
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