【機(jī)械類畢業(yè)論文中英文對(duì)照文獻(xiàn)翻譯】五軸數(shù)控加工復(fù)雜曲面時(shí)局部干涉的處理與避免

【機(jī)械類畢業(yè)論文中英文對(duì)照文獻(xiàn)翻譯】五軸數(shù)控加工復(fù)雜曲面時(shí)局部干涉的處理與避免,機(jī)械類畢業(yè)論文中英文對(duì)照文獻(xiàn)翻譯,機(jī)械類,畢業(yè)論文,中英文,對(duì)照,對(duì)比,比照,文獻(xiàn),翻譯,數(shù)控,加工,復(fù)雜,繁雜,曲面,時(shí)局,干涉,處理,避免,防止 五軸數(shù)控加工復(fù)雜曲面時(shí)局部干涉的處理與避免 摘要：刀具干涉問題是表面雕刻加工面臨的最關(guān)鍵問題，本文提出采用五軸數(shù)控加工復(fù)雜曲面時(shí)對(duì)干涉進(jìn)行處理和退避的一種方法 。采用這種方法加工出的表面被劃分成凸起區(qū)域和非凸起的地區(qū)。在凸起的區(qū)域沒有局部干涉存在，而對(duì)于非凸起區(qū)域，以對(duì)不同的局部干涉進(jìn)行分析為基礎(chǔ)，局部過切干涉可以通過選擇最佳的刀具取向而首先被得到解決和避免。后方過切干涉處理和避免的運(yùn)算法則分別是為了獲得簡(jiǎn)單的光滑表面和復(fù)雜形狀而被提出的。本文介紹的這種技術(shù)能夠用來產(chǎn)生無干涉刀具路徑。現(xiàn)實(shí)結(jié)果表明這種方法不僅切實(shí)可行而且很可靠。 關(guān)鍵詞: 環(huán)形刀具 · 五軸數(shù)控加工 局部刨削 后方刨削 被雕刻表面 1緒論 采用五軸數(shù)控加工技術(shù)進(jìn)行復(fù)雜曲面加工已經(jīng)廣泛應(yīng)用于航空航天，造船， 汽車工業(yè)，玻璃器皿，陶瓷，模子和模子產(chǎn)業(yè)。由于比三軸加工機(jī)器多了兩個(gè)旋轉(zhuǎn)自由度，五軸數(shù)控加工較之三軸加工更具優(yōu)勢(shì)。然而五軸的加工機(jī)制也面臨了一些問題，比如投資大，刀具干涉處理與避免的運(yùn)算法則過于復(fù)雜等等。刀具干涉問題是復(fù)雜曲面加工面臨的最關(guān)鍵問題。 采用五軸數(shù)控加工進(jìn)行復(fù)雜曲面的加工的刀具干涉主要可以分為兩類：（1）全局干涉——刀具側(cè)表面與被加工表面、加工環(huán)境中的機(jī)構(gòu)表面和工作夾具的碰撞干涉。（2）局部干涉——本文主要談的就是局部干涉。局部干涉包括局部過切干涉和后方過切干涉【1、2】如圖1所示。有時(shí)刀具主切削刃部分延伸到設(shè)計(jì)表面下面，這將比設(shè)計(jì)表面輪廓公差去除更多的材料。這就造成了局部過切干涉（圖1.a）。當(dāng)局部表面曲率比刀具半徑還小時(shí)就會(huì)出現(xiàn)局部過切干涉。后方過切干涉是刀具底部切口或者后緣造成的與局部干涉類似的效果（如圖1.b、c）。后方過切干涉可能是由采用了大號(hào)刀具或者選擇了不正確的切削刀定位造成的。 刀具干涉的處理與避免是一個(gè)很堅(jiān)韌的問題。很多研究員都研究了干涉問題，但是到多數(shù)都集中在三坐標(biāo)數(shù)控加工的干涉處理與避免上。由于刀具運(yùn)動(dòng)復(fù)雜和復(fù)雜曲面曲率分布不規(guī)則，使得采用五軸數(shù)控加工進(jìn)行復(fù)雜曲面加工時(shí)，刀具干涉問題尤其尖銳。Jensen 等傾向于采用平頭立銑刀作為正常的復(fù)雜曲面刀具接觸點(diǎn)，它是基于瞬時(shí)掏槽刀側(cè)面與復(fù)雜曲面刀具接觸點(diǎn)相匹配，來消除局部過切干涉的。Choi等提出了一種通過刀具接觸點(diǎn)產(chǎn)生最佳刀具位置的方法，這種方法藉由明確闡述一個(gè)基于刀具瞬間切割剖面而被迫減少到最小限度的難題。Li 等人為復(fù)雜曲面產(chǎn)生無干涉刀具路徑提供了一個(gè)有效的運(yùn)算法則。Lee等已經(jīng)開發(fā)了一種可以消除碰撞和后方過切干涉的運(yùn)算法則。他們還就預(yù)防局部過切干涉這一議題發(fā)表演說。Sarema提出了一種在采用平頭立銑刀進(jìn)行五軸數(shù)控加工復(fù)雜曲面中處理和消除后方過切干涉的新方法。這種方法是通過準(zhǔn)確地尋找刀具瞬間切削剖面來使得后方過切干涉能夠在兩維中實(shí)現(xiàn)偵測(cè)與消除運(yùn)算。Rao等人在刀具接觸點(diǎn)處接觸平面的各個(gè)方向?qū)φ５脑O(shè)計(jì)表面曲率和刀具剪切平面曲率進(jìn)行比較。通過對(duì)曲率進(jìn)行廣泛匹配，局部過切干涉在采用平頭立銑刀進(jìn)行五軸數(shù)控復(fù)雜曲面加工中得到處理和消除。這樣環(huán)形刀具刀具干涉的處理與避免就只需做很少一部分的工作，Lee等人所做的工作就是一個(gè)很好的例子。 圖【1】 本文我們?yōu)椴捎闷筋^立銑刀進(jìn)行五軸數(shù)控復(fù)雜曲面加工提供了一種系統(tǒng)的研究方法。加工出來的表面被分成了凸起區(qū)域和非凸起區(qū)域，在凸起區(qū)域沒有局部干涉存在，對(duì)于非凸起區(qū)域，刀具干涉根據(jù)三個(gè)特定情節(jié)分成三個(gè)階段被解決。在第一階段，最佳的剪切方位藉由刀具瞬間切削剖面與加工表面想匹配來決定，盡可能地使它們相互靠近以避免局部過切干涉。在第二個(gè)階段，對(duì)于簡(jiǎn)單光滑表面來說，后方過切干涉的處理與避免可以通過計(jì)算加工表面的偏移量與刀具柱面的偏移量的交集來實(shí)現(xiàn)。在第三階段，以復(fù)雜形狀表面為例，先找出可能出現(xiàn)后方過切干涉的地方，然后將加工表面分成一批三角形的小平面，后方過切干涉的處理可以通過將刀具平面底部和三角形小平面的至高點(diǎn)的相關(guān)位置分類來實(shí)現(xiàn)。如果刀具下方三角形的某個(gè)至高點(diǎn)在刀具底部平面之上，將會(huì)產(chǎn)生后方過切干涉。如果后方過切干涉被偵測(cè)到，刀具的方位將調(diào)整以消除過切干涉。這一過程將持續(xù)到所有的聯(lián)咯數(shù)據(jù)被核查。 刀具描述與刀具定位 磨床中運(yùn)用到尋多類型的刀具。成型銑刀常常被用來復(fù)雜曲面加工，用于五軸數(shù)控加工復(fù)雜曲面的成型銑刀主要有三種類型：平頭立銑刀、環(huán)型刀具 和 球頭銑刀。一種典型的平頭立銑刀可以很容易的替代平頭立銑刀和球頭立銑刀。因此，本文將考慮用環(huán)型銑刀、平頭立銑刀 和球頭立銑刀進(jìn)行五軸數(shù)控表面雕刻作為專門的案例。 一把環(huán)型銑刀由一個(gè)服務(wù)于下表面的平面和一個(gè)連接圓柱面的圓形環(huán)面組成，如圖【2】所示。環(huán)型銑刀的切削面T (φ, θ)能通過兩個(gè)表面參數(shù)聯(lián)立得到等式1： R是圓形底部的半徑，r是刀具的環(huán)形半徑，φ是部分環(huán)形的角度，且φ ∈ 【0, π/2】 , θ角是X軸的夾角，且θ ∈ [0, 2π] 五軸加工除了可以沿著數(shù)控機(jī)床的三個(gè)平移軸平移外，刀具還可以繞著三個(gè)軸中的兩個(gè)軸旋轉(zhuǎn)。 圖【3】 如圖【3】所示，在刀具接觸點(diǎn)建立了局部調(diào)整系統(tǒng)（XL-YL-ZL）。XL軸的方向沿著刀具瞬間切削的路徑方向，ZL軸的方向則沿著刀具接觸點(diǎn)所在表面的法線，而YL軸則是根據(jù)XL軸和ZL軸通過右手法則確定。首先刀具以接觸點(diǎn)為支點(diǎn)繞著YL軸旋轉(zhuǎn)，第一個(gè)旋轉(zhuǎn)角度定義為傾斜角度α，然后刀具以接觸點(diǎn)為支點(diǎn)繞著ZL軸旋轉(zhuǎn)，第二個(gè)旋轉(zhuǎn)角定義為傾斜角β，這樣刀具的定位就被這兩個(gè)角度完全限制了。 Marciniak提出了一個(gè)結(jié)論：當(dāng)?shù)毒呓佑|點(diǎn)沿著曲線的最小曲率法則移動(dòng)，直到停留在傾斜角β = 0的位置，將會(huì)得到最大的加工帶寬度（或者最大的材料去除量）。因此我們選擇了XL軸作為刀具運(yùn)動(dòng)和通過與YL軸的傾斜角α旋轉(zhuǎn)的方向，這都是通過以下的旋轉(zhuǎn)矩陣Ry的不斷相乘來完成的。 這就給出了一個(gè)關(guān)于刀具繞著YL軸旋轉(zhuǎn)的方程式，如等式（2） Local interference detection and avoidance in five-axis NC machiningof sculptured surfaces Abstract ：The tool interference problem is the most critical problemfaced in sculptured surface machining. This paper presentsa methodology for interference detection and avoidance in five axis NC machining of sculptured surfaces with a filleted-end cutter. The surfaces to be machined are divided into convex and non-convex regions. There is no local interference inside the convex regions. For the non-convex regions, based on the analysis of the different local interference, local gouging is first detected and avoided by determining optimal cutter orientations. Rear gouging detection and avoidance algorithms are then proposed for simple smooth surfaces and complex shaped surfaces, respectively. The techniques presented in this paper can be used to generate interference-free tool paths. The realistic results indicate that the proposed method is feasible and reliable. Keywords ：Filleted-end cutter · Five-axis NC machining · Local gouging · Rear gouging · Sculptured surfaces 1 Introduction Five-axis numerically controlled (NC) machining of sculptured surfaces has been widely applied in the aerospace, shipbuilding, automotive, glassware, ceramics, and dies and moulds industries. Because of the two additional degrees of freedom, five-axis NC machining offers some advantages over 3-axis machining. However, five-axis machining suffers from some problems such as a large investment, and complex algorithms for tool interference detection and avoidance, etc. The tool interference problem is the most critical problem faced in sculptured surface machining. Tool interference in five-axis NC machining of sculptured surfaces can be classified into two types: (1) global interference – the tool flank surface collides with the machined surfaces and fixtures in the machining environment and (2) local interference. In this paper, the focus is on local interference. Local interference includes local gouging and rear gouging [1, 2] as shown in Fig. 1. Portions of the cutter’s leading edge sometimes extend below the designed surface, removing more material than is allowed by the designed surface profile tolerance. This leads to local gouging (Fig. 1a). Local gouging occurs when the radius of the local surface curvature is smaller than that of the cutter. Rear gouging is a similar effect caused by the trailing edge or the cutting bottom of the cutter (Fig. 1b,c). Rear gouging may be caused by using a large size cutter or by choosing an improper cutter orientation. The detection and avoidance of tool interference is a tough problem. Many researchers have studied the interference problem, but most concentrate on interference detection and avoidance in three-axis NC machining. In five-axis NC machining of sculptured surfaces, the tool interference problem is much more acute because of the complex tool movements and the irregular curvature distributions of sculptured surfaces. Jensen et al. [3] inclined a flat-end cutter to the normal at the cutter contact (CC) point on a sculptured surface based on matching the curvature of the instantaneous cutting profile of the cutter to that of the sculptured surface at the CC point, to eliminate local gouging. Choi et al. [4] proposed a method for generating optimal cutter location (CL) points from CC points by formulating a constrained minimization problem based on the instantaneous cutting profile of the cutter. Li et al. [5] presented an efficient algorithm for generating interference-free tool paths for sculptured surfaces. Lee et al. [6–8] have developed algorithms to eliminate collisions and rear gouging. They also address issues of local gouging prevention [9]. Sarma [1] presented a new method to detect and eliminate rear gouging in the five-axis NC machining of sculptured surfaces with flat-end cutters. The method is based on finding accurately the instantaneous cutting profile of the cutter that enables rear gouging detection and elimination calculations to be done in two dimensions. Rao et al. [10] compared the normal curvatures of the machined surface and the cutter swept surface, in all directions in the tangent plane of the machined surface at the CC point. Based on this comprehensive curvature matching, local gouging in the five-axis machining of sculptured surfaces using flat-and cutters is detected and eliminated. Very little work has been done on tool interference detection and avoidance of the filleted-end cutter. Lee et al.’s work [8] is one example. In this paper, we present a systematic methodology for investigating the tool interference in five-axis NC machining of sculptured surfaces using filleted-end cutters. The surfaces to be machined are divided into convex and non-convex regions. There is no local interference inside the convex regions. For the nonconvex regions, the tool interference is solved in three phases according to three scenarios. In phase I, an optimal cutter orientation is first determined by matching the instantaneous cutting profile of the cutter and the machined surface, as close as possible to avoid local gouging. In phase II, rear gouging detection and avoidance is implemented by calculating the intersection between the offset surface of the machined surface and the offset cylinder of the cutter, for simple smooth surfaces. In phase III, for cases of complex shaped surfaces, a search for possible rear gouging is conducted by first dividing the machined surfaces into a set of triangular facets. Rear gouging is then detected by classifying the relative position of the bottom plane of the cutter and the vertices of the triangular facets. If one of the vertices of the triangles under the cutter shadow is above the bottom plane of the cutter, rear gouging will occur. If any rear gouging is detected, the cutter orientation is adjusted to eliminate gouging. The process continues until all the CC data are checked. 2 Cutter description and cutter orientation There are many types of cutters used in milling applications. An end-mill cutter is often the choice for sculptured surface machining. Basically three types of end-mill cutters are used in the 5-axis NC machining of sculptured surfaces: the flat-end cutter, the fillet-end cutter and the ball-end cutter. A model of a filletend cutter can easily represent both the flat-end cutter and the ball-end cutter. For this reason, this paper will consider 5-axis sculptured surface machining with a fillet-end cutter, and with the flat-end cutter and the ball-end cutter as special cases. A filleted-end cutter consists of a plane that serves as the bottom surface, and a piece of a torus connected to a cylinder, as shown in Fig. 2. The cutting surface T (φ, θ) of a filleted-end cutter can be represented by a two parameter surface with continuous derivatives as in Eq. 1: where R is the radius of the bottom portion, r is the fillet radius of the cutter, φ describes the corner portion and φ ∈ 【0, π/2】 , and θ is the angle from the Xt -axis and θ ∈ [0, 2π]. In 5-axis machining, besides the translations along the three translation axes of an NC machine, the cutter can be rotated about two of the three translation axes. As shown in Fig. 3, the local coordinate system (XL ?YL ? ZL ) is set up at the CC point. The XL -axis is along the tangent of the tool path in the instantaneous cutting direction and the ZL -axis is along the normal of the surface at the CC point. The YL -axis is defined by the XL -axis and ZL -axis, using the right-hand rule. First, the cutter is rotated around the YL -axis, while the CC point is the pivot. The first rotation angle is defined as the inclination angle α. Secondly, the cutter is rotated around the ZL -axis, while the CC point is the pivot. The second rotation angle is defined as the tilt angle β. These two angles completely define the orientation of the cutter [2]. Marciniak [11] concluded that the largest machined strip width (or the largest material removal) is obtained when the CC point moves along a curve of the smaller principle curvature, and the tool position is at the tilt angle β = 0. Thus, we choose the XL -axis as the direction of tool motion and rotate the cutter by an inclination angle α about the YL -axis. This is accomplished by pre-multiplying by the following rotation matrix Ry: ???? which gives an equation for the cutter rotated about the YL -axis as shown in Eq. 2: ??? ? 9