Y3150E滾齒機滾齒刀架設(shè)計【含10張CAD圖紙】
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附錄一
PLC模塊控制回轉(zhuǎn)工作臺在三軸數(shù)控銑床銑削螺旋傘齒輪中的應(yīng)用
S. Mohsen Safavi & S. Saeed Mirian & Reza Abedinzadeh & Mehdi Karimian
Received: 25 November 2008 / Accepted: 23 November 2009 # Springer-Verlag London Limited 2009
摘要
當(dāng)今，數(shù)控機床在機電一體化領(lǐng)域中得到了日益廣泛的應(yīng)用。機械、電氣和數(shù)據(jù)處理系統(tǒng)與數(shù)控技術(shù)相結(jié)合，引領(lǐng)了新的生產(chǎn)加工理念。近年來，數(shù)控技術(shù)的發(fā)展已將非線性校正技術(shù)在切削弧齒錐齒輪中的應(yīng)用變?yōu)榭赡?。在本文中，我們將嘗試采用帶有外加PLC模塊分度臺的三軸數(shù)控銑床，運用帶有索引工作界面的通用銑床的傳統(tǒng)連續(xù)多重切削方法來加工制造出這個螺旋傘齒輪。該研究包括(a)弧齒錐齒輪的幾何建模，(b)運用CAD/CAE系統(tǒng)進行傳統(tǒng)或新型非傳統(tǒng)方案的模擬仿真，(c)數(shù)控加工工藝的設(shè)計與PLC編程，(d)通過三軸數(shù)控銑床的實驗切削來探索新方案的正確性。結(jié)果表明，開發(fā)的螺旋傘齒輪實驗切削方案不僅與先進數(shù)控加工相比成本更低，而且相比傳統(tǒng)切削，加工齒輪的時間也較短。因此，在螺旋傘齒輪加工領(lǐng)域，這是一個很經(jīng)濟的方案。
關(guān)鍵詞：齒輪加工，螺旋傘齒輪，CAD/CAM/CAE，數(shù)控技術(shù)，PLC，交流電動機，逆變，接近傳感器，光電傳感器，旋轉(zhuǎn)編碼器
1 引言
齒輪是工業(yè)機械領(lǐng)域中重要的精密機構(gòu)，在平行軸、橫向交叉或非交叉軸之間用于傳遞機械功率和機械運動。雖然有時會看不見，但齒輪仍是我們工業(yè)文明中最重要的機械元件之一。在各式各樣的條件下，齒輪會以幾乎達到無限的速率運轉(zhuǎn)。得到發(fā)展的齒輪加工設(shè)備與工藝流程已經(jīng)非常先進與成熟。無論大批量生產(chǎn)還是小批量生產(chǎn)，無論在小型車間還是分批處理的加工車間，加工齒輪的流程按順序都需要以下四步操作
1.下料
2.切齒
3.熱處理
4.研磨
根據(jù)它們的類型、應(yīng)用范圍及強度和剛度要求，通常經(jīng)過鑄造、擠壓、鍛造、粉末冶金、注塑加工和滾齒加工來完成齒輪的加工制造。在這一系列加工流程中，螺旋傘齒輪是最復(fù)雜的一種齒輪，在成角度的橫軸之間，它用來傳遞回轉(zhuǎn)運動。
沿齒長方向，螺旋傘齒輪有徑向彎曲的齒廓曲線。這類齒輪之所以能夠保證與配合齒輪有光滑的嚙合，主要是因為它們有勝過直齒輪的曲型齒廓，這樣它們同一時間接觸并嚙合的齒數(shù)會更多。螺旋傘齒輪的設(shè)計與制造仍然是一個熱門的研究課題，在直升機運輸齒輪系、摩托車齒輪減速器及其他工業(yè)分支中都得到十分重要的應(yīng)用。對于制造而言，這種齒輪通常由一種特殊機床加工而成，如滾齒機、成型機。目前，基于輪齒加工的特種數(shù)控加工機床已運用于工業(yè)實踐中。這也許就是輪齒加工的相關(guān)文獻在公開的研究領(lǐng)域稀少的原因所在。最近，基于齒輪加工的數(shù)控加工機床已得到長足發(fā)展并逐漸運用于工業(yè)實踐。然而，它們的運動結(jié)構(gòu)與工業(yè)數(shù)控銑床還是有著內(nèi)在的差異，前者是為一種特種刀具而設(shè)計的。
先前對齒輪的研究主要涉及齒輪的設(shè)計和分析。在對其幾何特征與設(shè)計參數(shù)進行研究的同時，Tsai和Chin基于切面方向上的齒輪傳動和漸開線齒輪幾何學(xué)，提供了一個關(guān)于錐齒（直齒輪、螺旋傘齒輪）的數(shù)學(xué)曲面模型。后來，這個方案與A-daccak等人和Shunmugan等人基于精密球面漸開線的齒輪曲面模型進行了比較，從而得出了一個截然不同的模型。依據(jù)標(biāo)稱偏差，其精確度（相比運用特種機床加工的螺旋傘齒輪）得到了驗證。
對于冠齒輪，一些結(jié)論是可行的。Litvin和Kim通過改良直齒輪的基圓提出了運用范成法獲得漸開曲線。運用斜齒輪傳動誤差的修正測定值，Umeyama在節(jié)圓上設(shè)計了一個標(biāo)準(zhǔn)剖面，在面齒輪的上下表面設(shè)計了一個改良剖面。Tamura等人對采用平面齒形的錐齒輪研究得出了一個點接觸模型。這些研究都與專為加工齒輪而特殊設(shè)計的那些特種齒輪加工機床（如滾齒機、成型機）返程齒剖面有關(guān)。Suh等人對螺旋傘齒輪加工的雕刻面加工方法的可行性做了研究，并驗證了運用帶有回轉(zhuǎn)擺動升降臺的四軸數(shù)控銑床生成加工軌跡的可能性。同時，一種螺旋傘齒輪基于模型的驗證法也得以提出。
在本文中，對于螺旋傘齒輪我們將嘗試采用一種新的加工流程，加工時運用帶有可用于控制分度臺的PLC模塊的三軸銑床。很明顯，這種加工方法的生產(chǎn)率不及特種加工機床?？沙松a(chǎn)率，這種加工方法的優(yōu)點有以下幾個方面：(1)傳統(tǒng)加工方法需要消耗大量投資成本來獲得各種特種機床，所選用刀具加工的齒輪種類、尺寸和幾何形狀也非常有限；(2)運用這種新的加工方法，各種類型的齒輪都可通過工業(yè)三軸數(shù)控銑床加工而成；(3)相比運用特種加工機床，采用該方法加工更為經(jīng)濟。一個不同于先前的工作重點是，為了模擬全部加工過程并獲得加工參數(shù)，需要開發(fā)自動計算機模型。所有先前的研究都在計算復(fù)雜的數(shù)學(xué)方程組和設(shè)計幾何模型。鑒于上述情況，我們的重點在于螺旋傘齒輪的加工實驗檢驗，而不在于提供螺旋傘齒輪的幾何或數(shù)學(xué)模型。這是第一次同時運用機電一體化機床和數(shù)控銑床來加工特殊齒輪，甚至一個機械元件。
2 螺旋傘齒輪的幾何規(guī)格
通常，一個齒輪的幾何參數(shù)都由工程圖給出。對于定義其幾何形狀而言，有些參數(shù)（主要參數(shù)）是必須有的。為此，我們采用名為“GearTrax”的驅(qū)動元件開發(fā)軟件來算得這些主要參數(shù)。
螺旋傘齒輪的設(shè)計要求高精度的數(shù)學(xué)計算，并且生產(chǎn)這種齒輪傳動機構(gòu)不僅需要高質(zhì)量的設(shè)備和加工此類齒輪傳動機構(gòu)的機床，而且還需要拓展適當(dāng)?shù)臋C床參數(shù)設(shè)置。這樣的設(shè)置雖然不合乎標(biāo)準(zhǔn)，但也需要由能夠保證符合高質(zhì)量齒輪傳動要求的每種情況的設(shè)計（根據(jù)齒輪傳動的幾何參數(shù)和展成工具）來確定。
3 加工螺旋傘齒輪
由引言中的討論，我們知道所有類型的齒輪都能通過加工手法來獲得所需要的所有規(guī)格，其中高精度齒輪的加工手法仍然非常卓越的。成型銑削是加工任意類型齒輪的最常見的加工工序。所使用的道具都具有類似相鄰輪齒間隙的相同形狀。標(biāo)準(zhǔn)刀具通常用于齒輪的成型切削。在美國，這些刀具的每個徑節(jié)都是原來的8倍，用于加工標(biāo)準(zhǔn)表上指示的多齒齒輪。格利森公司基于為補充冠齒輪范成原理而產(chǎn)生的錐齒輪范成的普遍概念：相互嚙合的大小齒輪可分別考慮，運用了表面滾齒的加工手法。
由公式(1)可知，表面滾齒加工的速率比應(yīng)取決于工具齒輪與展成齒輪的齒數(shù)比：
（1）
其中，和分別為工具齒輪與展成齒輪的扭轉(zhuǎn)角速度；和分別為工具齒輪和展成齒輪的齒數(shù)。
展成齒輪與工具齒輪的基圓半徑由公式(2)、(3)確定：
（2）
（3）
其中，s為機床徑向設(shè)定值。
范成的冠齒輪可考慮為螺旋角為90度的特殊斜齒輪。因此，出現(xiàn)了“形齒輪”這個通用術(shù)語。當(dāng)已生成的大小齒輪的配合吃面共軛時，可以考慮對范成冠齒輪的概念進行補充。在實踐中，為了使失配的輪齒表面得以匹配，形齒輪的大小齒可能互不相同。形齒輪的旋轉(zhuǎn)由戟齒輪上的搖架旋轉(zhuǎn)體現(xiàn)。
用三軸數(shù)控銑床加工螺旋傘齒輪，我們首先應(yīng)該對開發(fā)的CAD/CAM系統(tǒng)的幾何建模和仿真模塊盡享程序測試。運用商業(yè)軟件Solidworks創(chuàng)建CAD模型和MSC。運用Visual NASTRAN 4D軟件（運用3D模型的CAE機械運動分析系統(tǒng)）模擬齒輪加工并得到分析結(jié)果。
對于機床的結(jié)構(gòu)而言，很明顯，螺旋傘齒輪的數(shù)控機床上，工件的回轉(zhuǎn)運動史必要的?；谄淝邢鞯男阅芊治?，通過一步安裝，螺旋傘齒輪的數(shù)控加工至少也可達到四軸控制的要求。因此，對于三軸銑床具備回轉(zhuǎn)工作臺是必要的。成型切削或成型銑削都會在測試中用到。刀具從齒輪毛坯中心想要得到的齒高徑向進給，然后穿過齒面，而回轉(zhuǎn)工作臺繞其中心旋轉(zhuǎn)工件來獲得所需的齒寬。當(dāng)加工完成一個齒間時，刀具后退，分度頭指示齒輪毛坯，繼續(xù)切削下一個齒間。從根本上說，這種方法是一種簡易而靈活的螺旋傘齒輪加工方法。所需的設(shè)備和刀具都相對簡單，并且只運用標(biāo)準(zhǔn)三軸數(shù)控銑床。然而，防止出現(xiàn)任何的工件損壞，就每一工步為短程的刀具進給而言，我們有必要做到謹(jǐn)慎考慮。
我們在GearTrax環(huán)境下創(chuàng)建螺旋傘齒輪用以模擬操作工序并估算一些加工參數(shù)，如端銑刀的原始高度、接近傳感器的位置、電動機轉(zhuǎn)矩、電動機轉(zhuǎn)速及轉(zhuǎn)動頻率。例如，在Solidworks環(huán)境下，端銑刀與螺旋傘齒輪的齒頂間距為14.7mm，這是我們沿Z軸用來垂直定位主軸的。
同時，根據(jù)我們使用的CAE系統(tǒng)所提供的圖形報告，電動機的角速度和轉(zhuǎn)矩分別為1rpm和48Nm。
Mastercam是一種可以生成刀具加工軌跡的機械專業(yè)軟件。根據(jù)齒輪的總深度和表面寬度，在我們的切削程序中可設(shè)計出加工輪廓線為矩形的刀具軌跡。
其它加工參數(shù)和刀具的規(guī)格也應(yīng)錄入軟件的刀具軌跡菜單。在加工輪廓線窗口，我們要用到以下兩個選項：
考慮到對切削量的較大控制，在多通道口允許刀具多工步進給。
2、在沒有額外的幾何尺寸條件下，在入口/出口位置變動之前，導(dǎo)入/導(dǎo)出拉長的或縮短的刀具軌跡，這樣有助于我們控制加工補償，并能使短時間編制固定加工輪廓線變?yōu)榭赡堋?
雖然這種齒輪的成型切削一般運用萬能銑床上的分度頭來完成，但其加工過程緩慢并需要技術(shù)熟練的工人師傅和操作者。刀具安裝在刀柄軸上，運用分度頭來旋轉(zhuǎn)（切削輪齒）并指示齒輪毛坯。工作臺設(shè)置在螺旋角為35度的角度上，并且分度頭也應(yīng)與工作臺的縱向絲杠相適應(yīng)，以便使齒輪毛坯得以縱向回轉(zhuǎn)運動。
針對上述提供的方法，我們采用了連接了蝸輪蝸桿變速箱的交流電動機。蝸輪蝸桿變速箱用來減小交流電動機的輸出速度，并將齒線也節(jié)圓錐面間的角度設(shè)置為螺旋角大小。
只要刀具軌跡編制與蝸輪蝸桿變速箱輸出軸的旋轉(zhuǎn)運動間的同步性達到要求，機電一體化系統(tǒng)便可同時控制四根軸（一軸用于工作臺的回轉(zhuǎn)運動，三軸用于刀具的切削運動）。
同時，在機電一體化系統(tǒng)中我們運用梯形圖和通用編程語言來操作PLC。
基于梯形圖，PLC的操作步驟如下：
第一步 讀取外部輸入信號，例如傳感器與旋轉(zhuǎn)編碼器的地址。
第二步 根據(jù)第一步中的輸入信號值，計算輸出信號并將其傳送給變頻器（反相器），從而驅(qū)動交流電動機正反轉(zhuǎn)或通過旋轉(zhuǎn)編碼器使電動機旋轉(zhuǎn)一定的角度（齒距）。配置數(shù)控銑床的同時，所有系統(tǒng)的程序按以下五個階段完成：
第一階段 成型刀抵達第一個接近傳感器，傳感器一旦檢測到成型刀，就向PLC發(fā)送一個+5V的信號，正如前面提到的，PLC接收信號并向變頻器發(fā)送一個輸出信號來驅(qū)動電動機正轉(zhuǎn)。
第二階段 以Mastercam中生成的刀具加工軌跡用成型刀加工旋轉(zhuǎn)的工件。
第三階段 刀具抵達第二個接近傳感器，傳感器通過檢測刀具來向PLC傳送第二個信號，同時PLC接收并向變頻器發(fā)送一個停止指令。
第四階段 銑刀從停止的工件退刀并回到起始位置。同時，變頻器驅(qū)動電動機反轉(zhuǎn)直到輸出軸回到第一工位，在這個位置，光電傳感器的接收器可可通過輸出軸的縱向裂紋接收傳輸光線。
第五階段 重復(fù)一至四階段直到第一個齒間切削完成。PLC根據(jù)運行上述四階段的次數(shù)計數(shù)直到達到加工程序中的預(yù)設(shè)次數(shù)。然后，PLC向變頻器發(fā)送信號指示齒輪毛坯達到加工直徑尺寸，接著上述所有階段重復(fù)運行。加工直徑由1024脈/轉(zhuǎn)的旋轉(zhuǎn)編碼器測定。
在本次創(chuàng)新的加工方法的有利體現(xiàn)里，加工時間是主要關(guān)注的指標(biāo)之一。例如，加工完成一個齒間只需2分鐘。相比較，運用傳統(tǒng)方法加工同樣的齒間需要花費半個多小時。
在本次創(chuàng)新關(guān)于手工切削的深遠有利體現(xiàn)里，切削刀頭的瞬間角度補償是在跳轉(zhuǎn)程序結(jié)束之前立即設(shè)置的。
4 加工策略
工件為木料，通過車削加工將坯料預(yù)加工為錐狀（齒頂錐角）。用于實驗的5號標(biāo)準(zhǔn)刀安裝在機床主軸上，齒輪毛坯安裝在蝸輪蝸桿變速箱的輸出軸上。隨后，刀具向齒輪毛坯的中心進給以達到所需齒深（圍繞30條加工程序以避免次品出現(xiàn)）。加工完成一個齒間，退刀；根據(jù)已編譯的程序由交流電動機指引齒輪毛坯接著切削下一個齒間。
5 結(jié)論
在本文中，我們嘗試運用三軸數(shù)控銑床通過成形銑削的方法加工螺旋傘齒輪。為了達到這一目的，我們對CAD/CAM模具的切削步驟和刀具軌跡算法做了研究。運用復(fù)雜的數(shù)學(xué)程序，所有的預(yù)先工作都與設(shè)計息息相關(guān)，并沒有依靠經(jīng)驗加工理論。從根本上說，成形切削用于加工齒輪簡單而靈活。所需的設(shè)備和刀具相對簡單、廉價，一臺標(biāo)準(zhǔn)數(shù)控銑床即可。因而，并不需要技術(shù)熟練的操作者來創(chuàng)建加工系統(tǒng)。與運用專業(yè)機床加工齒輪的常規(guī)方法相比，本文所采用的加工方法用于加工各種規(guī)格的螺旋傘齒輪或其它類型的齒輪，改進起來也很容易。與手動切削加工相比，這種加工方法又是一個全自動的，因為所有的加工參量都通過電腦模塊得到。這種加工理念同時也是一個多變的系統(tǒng)（運用機電一體化和數(shù)控系統(tǒng)），并且會源源不斷地發(fā)展下去。
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附錄二
Use of PLC module to control a rotary table to cut spiral bevel gear with three-axis CNC milling
S. Mohsen Safavi & S. Saeed Mirian & Reza Abedinzadeh & Mehdi Karimian
Received: 25 November 2008 / Accepted: 23 November 2009 # Springer-Verlag London Limited 2009
Abstract
CNC machining nowadays makes more use of "Mechatronics" increasingly. Combining numerical control with mechanic, electric, and data processing systems can lead to new methods of production. In recent years, the development of CNC has made it possible to perform nonlinear correction motions for the cutting of spiral bevel gears. In this paper, we attempt to manufacture the spiral bevel gear using a three-axis CNC milling machine interfaced with an additional PLC module based on traditional discontinuous multi-cutting method accomplished by using a universal milling machine interfaced with an indexing work head. This research consists of (a) geometric modeling of the spiral bevel gear, (b) simulating the traditional and our new nontraditional method using a CAD/CAE system, (c) process planning for CNC machining and PLC Programming, (d) experimental cuts with a three-axis CNC milling machine were made to discover the validity of the presented method. The results demonstrate that invented experimental cutting method of SBGs not only is less expensive than advanced CNC machining but also produces gears in a shorter time in comparison with the traditional cutting. Thereby, it is an economical method in manufacturing of SBGs.
Keywords：Gear manufacturing . Spiral bevel gear .CAD/CAM/CAE . CNC . PLC . AC motor . Inverter .Proximity sensors . Photoelectric sensors . Rotary encoder
1 Introduction
Gears are important and precision mechanisms for industrial machinery as a means for mechanical power or motion transmission between parallel, intersecting and nonintersecting cross-axis shafts. Although hidden from sight, gears are one of the most important mechanical elements in our civilization. They operate at almost unlimited speeds under a wide variety of conditions. The machines and processes that have been developed for producing gears are among the most existing ingenious ones. Whether produced in large or small quantities, in cell, or job shop batches, the sequence of processes for gear manufacturing requires four sets of operations:
1. Blanking
2. Gear cutting
3. Heat treatment
4. Grinding
Depending on their type and application or required strength and resistance, gears are manufactured by casting, extruding, forging, powder metallurgy, plastic molding, gear rolling, and machining. Among these processes, machining is more frequently used for high-precise gears. Among the various types of gears, the spiral bevel gears (SBG) are the most complex type and are used to transmit the rotational motion between angularly crossed shafts.
SBGs have teeth curved longitudinally along the length of the teeth. The main advantage of these gears over the straight-toothed varieties lies in the fact that more teeth are in contact at the same time because of the curve-shaped contour of the teeth and so a smoother meshing action between the mating pair is ensured. The design and manufacturing of spiral bevel gears is still a hot topic of research that is vital for application of such gears in helicopter transmissions, motorcycle gears, reducers, and in other branches of industry. As far as manufacturing is concerned, the gears are machined by a special type of machine tools, such as gear hobbing and shaping machines. Recently, special CNC-based gear manufacturing machine tools are used in industrial practice. This may be why literature on gear manufacturing is sparse in the open research domain. Recently, CNC-based gear manufacturing machine tools have been developed and increasingly used in industrial practice. However, their kinematic structure is still inherently different from the industrial CNC milling machine, as the former is designed for a special type of cutter.
Previous studies on gears have been mainly concerned with the design and analysis of gears. The geometric characteristics and design parameters of gears have been studied. Tsai and Chin presented a mathematical surface model for bevel gears (straight and SBGs) based on basic gearing kinematcis and involute geometry along the tangent planes. Later, this method was compared with another model based on exact spherical involute curves by Al-daccak et al. Shunmugan et al. presented a different model, and its accuracy (compared with the spiral bevel gear manufactured by special machine tools) was verified in terms of nominal deviation.
For crown gears, a few results are available. Litvin and Kim suggested a generation method for an involute curve from a modified base circle for a spur gear. Umeyama designed a standard profile at the pitch circle and a modified profile at the top/bottom face gear with a determination of the modification value for transmission error of helical gear. Tamura et al. studied a point contact model for a bevel gear using a flat surface tooth. These studies are concerned with the generation of the tooth profile for special gear machines, such as gear hobbing and shaping machines, which are specially designed for manufacturing gears. Suh et al. investigated the possibility of a sculptured surface-machining method for the manufacture of spiral bevel gears and verified the possibility by presenting tool-path generation using a four-axis CNC milling machine interfaced with a rotary-tilt table. A model-based inspection method for the spiral bevel gears was also presented.
In this paper, we attempt to present a new manufacturing procedure of SBGs by using a three-axis milling machine interfaced with a PLC module which operates as an indexing table. In terms of production rate, it is obvious that this method will be lower than that of the special machine tool. Other than production rate, this method is advantageous in the following respects: (1) the conventional method requires a large investment for obtaining various kinds of special machinery and cutters dedicated to a very limited class of gears in terms of gear type, size, and geometry; (2) by this method, various types of gears can be manufactured with the industrial three-axis CNC milling machine; (3) this method is more economical than using the special machine tool. One of the main points which separate our work from previous ones is developing an automatic computer model in order to simulate the process entirely and obtain machining parameter. All previous studies have been engaged in calculating complicated mathematical equations and designing geometric models. In view of the above, special attention is given to experimental tests rather than presenting geometrical or mathematical model of SBGs. This is the first time that mechatronic tools and a three-axis CNC milling machine are being used simultaneously in manufacturing a special gear and even a mechanical element.
2 Geometric specifications of the spiral bevel gears
Most of the time, the geometric parameters of a gear are provided with an engineering drawing. Some parameters (principal parameters) are required for defining the geometry. To calculate these parameters, we have used “drive component development software” called GearTrax.
The design of spiral bevel gear requires high-accuracy mathematical calculations, and the generation of such gear drives requires not only high-quality equipment and tools for manufacturing of such gear drives but also the development of the proper machine-tool settings. Such settings are not standardized but have to be determined for each case of design (depending on geometric parameters of the gear drive and generating tools) to guarantee the required quality of the gear drives.
3 Manufacturing the SBG
As it was discussed in the introduction, by machining, all types of gears can be made in all sizes, and machining is still unsurpassed for gears having very high accuracy. Form milling is one of the most common machining processes used to manufacture any types of gears. The cutter has the same form as the space between adjacent teeth. Standard cutters usually are employed in form-cutting gears. In the USA, these cutters come in eight sizes for each diametral pitch and will cut gears having the number of teeth indicated in standard tables. Gleason works used the face hobbing process that is based on the generalized concept of bevel gear generation in which the mating gear and pinion can be considered respectively, generated by the complementary generating crown gears.
As it is shown in Eq. 1, velocity ratio of face hobbing process depends on tooth number of tool and generating gear:
（1）
where, wt and wc denote the angular velocities of the tool and generating gear; Nt and Nc denote the number of the blade groups and the tooth number of the generating gear.
The radii of the rolling circles of the generating gear and the tool are determined by Eqs. 2 and 3:
（2）
（3）
where s is the machine radial setting.
The generating crown gear can be considered as a special case of a bevel gear with 90° pitch angle. Therefore, a generic term “generating gear” is used. The concept of complementary generating crown gear is considered when the generated mating tooth surfaces of the pinion and the gear are conjugate. In practice, in order to introduce mismatch of the mating tooth surfaces, the generating gears for the pinion and the gear may not be complementarily identical. The rotation of the generating gear is represented by the rotation of the cradle on a hypoid gear generator.
To manufacture the SBGs with the three-axis CNC milling machine, we first test the process by developing a CAD/CAM system composed of geometric modeling and graphic simulation modules. The commercial software Solidworks is used for creating CAD model and MSC. Visual NASTRAN 4D (CAE system of the kinematic analysis of the mechanisms by means of their 3D models) is used for simulating the process of gear manufacturing and its analytical results.
As far as machine tool configuration is concerned, it is obvious that a rotational motion of the workpiece is required for NC machining of the SBGs. Based on the machinability analysis, at least four-axis controls are required for NC machining of SBGs by one setup. Thus, a rotary table to be interfaced with the three-axis milling machine is required. Form cutting or form milling is used in our tests. The tool is fed radially toward the center of the gear blank to the desired tooth depth, then across the tooth face, while the rotary table rotates the workpiece around its center to obtain the required tooth width. When one tooth space has been completed, the tool is withdrawn, the gear blank is indexed using a dividing head, and the next tooth space is cut. Basically, this method is a simple and flexible method of machining SBGs. The equipment and cutters required are relatively simple, and standard three-axis CNC milling machine is used. However, considerable care is required on the part of tool feed which should be a small value in each step to prevent any spoil.
We used spiral bevel gear created in GearTrax in order to simulate operating sequence and then estimate some machining parameters such as initial height of end mill, location of proximity sensors, motor torque, motor speed, and rotation frequency. For example, in SolidWorks, distance between end mill and the apex of SBG was 14.7 mm which we used to locate the spindle vertically along the z-axis.
Also, according to the graph report of CAE system which we used, motor angular velocity and motor torque are 1 rpm and 48 Nm, respectively.
Mastercam is a mechanical software that can be used to generate toolpaths for machining. According to whole depth and face width of the gear, a rectangular contour was designed as toolpath in our cutting procedure.
Other machining parameters and tool’s specifications were also submitted to the Tool Path menu of software. In contour window, there are two options which we use:
1. Multipasses which enable multiple stepovers of the tool, allowing for greater control of stock removal.
2. Lead in/out which extend or shorten the toolpath before making entry/exit moves without creating additional geometry, which is helpful when working with control compensation and makes it possible to program solid contours in less time.
Although the form cutting of this kind of gears is currently done on universal milling machine, using an indexing head, the process is slow and requires skilled labor and operator. The cutter is mounted on an arbor, and a dividing head is used to revolve (required to cut the gear tooth) and index the gear blank.
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