2321 采煤機的行走部分設(shè)計,采煤,行走,部分,部份,設(shè)計 河南理工大學(xué)萬方科技學(xué)院畢業(yè)設(shè)計翻譯1畢業(yè)設(shè)計翻譯院系名稱： 機械設(shè)計及其自動化 班 級： 機設(shè) 10 升（一）班 學(xué) 號： 0816101012 學(xué)生姓名： 汪洋 指導(dǎo)教師： 韓曉明 河南理工大學(xué)萬方科技學(xué)院畢業(yè)設(shè)計翻譯2considering elastic contact forces as external forces on an otherwise free chip. The line n= 5 in Figure 6.5 was deduced for an elastic contact length five times the plastic length .The elastic contact should not be ignored in machining analyses.Slip-line field modelling may also be applied to machining with restricted contact tools(Usui et al., 1964), with chip breaker geometry tools (Dewhurst, 1979), with negative rake tools ( Petryk , 1987), as well as with flank-worn tools (Shi and Ramalingham , 1991), to give an insight into how machining may be changed by non-planar rake face and cutting edge modified tools. Figures 6.6 and 6.7 give examples.Figure 6.6 is concerned with modifications to chip flow caused by non-planar rakefaced tools. As the chip/tool contact length is reduced below its natural value by cutting away the rake face (Figure 6.6(a)), the sliding velocity on the remaining rake face is reduced, with the creation of a stagnant zone, and the chip streams into the space created by cutting away the tool. If a chip breaker obstruction, of slope d, is added some distance l B from the cutting edge of a plane tool (Figure 6.6(b)), its effect on chip curvature and cutting forces can be estimated . The combination of these effects can give some guidance on the geometrical design of practical chip-breaker geometry tools.The slip-line fields of Figure 6.7 show how, with 河南理工大學(xué)萬方科技學(xué)院畢業(yè)設(shè)計翻譯3increasingly negative rake angle, a stagnant zone may develop, eventually (Figure 6.7(c)) allowing a split in the flow, with material in the region of the cutting edge passing under the tool rather than up the rake face. The fields in this figure, at first sight, are for tools of an impractically large negative rake angle. However, real tools have a finite edge radius, can be worn or can be manufactured with a negative rake chamfer. The possibility of stagnation that these fields signal , needs to be accomodated by numerical modelling procedures.6.2.4 SummaryIn summary, the slip-line field method gives a powerful insight into the variety of possible chip flows. A lack of uniqueness between machining parameters and the friction stress Between the chip and tool is explained by the freedom of the chip, at any given friction stress level, to take up a range of contact lengths with the tool. Chip equilibrium is maintained for different contact lengths by allowing the level of hydrostatic stress in the field to vary. The velocity fields indicate where there are regions of intense shear, which should be taken into account later in numerical modeling . They also illustrate how velocities might vary in the secondary shear zone, a topic that will be returned to later. They also show a range of variations of normal contact stress on the rake face that is observed in practice. However, a frustrating weakness of the slip-line field approach is that it offers no way, within the 河南理工大學(xué)萬方科技學(xué)院畢業(yè)設(shè)計翻譯4limitationsof the rigid perfectly plastic work material model, of removing the non-uniqueness: what does control the chip/tool contact length in a given situation ? Additionally, it can offer no way of taking into account variable flow stress properties 河南理工大學(xué)萬方科技學(xué)院畢業(yè)設(shè)計翻譯5of real materials, demonstrated experimentally to have an influence. An alternative modeling ,concentrating on material property variation effects, is introduced in the next section.6.3 Introducing variable flow stress behaviorSlip-line field modelling investigates the variety of chip formation allowed by equilibrium and flow conditions while grossly simplifying a metal’s yield behaviour. A complementary approach is to concentrate on the effects of yield stress varying with strain (strain hardening)and in many cases with strain rate and temperature too, while simplifying the modelling of equilibrium and flow. Pioneering work in this area is associated with the name of Oxley. The remainder of this 河南理工大學(xué)萬方科技學(xué)院畢業(yè)設(shè)計翻譯6section relies heavily on his work, which is summarized in Mechanics of Machining (Oxley, 1989). Developments may be considered in four phases: firstly experimental and numerical studies of actual chip flows, by the method of visioplasticity; secondly,simplifications allowing analytical relations to be developed between stress variations in the primary shear zone and material flow properties, dependent on strain, strain rate and temperature; thirdly, a consideration of stress conditions in the secondary shear zone; and finally, a synthesis of these, allowing the prediction of chip flow from work material properties.6.3.1 Observations of chip flowsVisioplasticity is the study of experimentally observed plastic flow patterns. In its most complete form, strain rates throughout the flow are deduced from variations of velocity with position, and strains are calculated by integrating strain rates with respect to time along the streamlines of the flow. The temperatures associated with the plastic work are calculated from heat conduction theory. Then, from independent knowledge of the variation of flow stress with the strain, strain rate and temperature, it can be attempted to deduce what the stress variations are throughout the flow and what resultant forces are needed to create the flow. Alternatively, measured values of the forces can be used to deduce how the flow stress varied. Frequently, however, the accuracy of flow 河南理工大學(xué)萬方科技學(xué)院畢業(yè)設(shè)計翻譯7measurement is not good enough to support this entire scheme. Nonetheless, useful insights come from only partial success.In the case of plane strain flows, the first step is usually to determine the maximum shear strain rate trajectories of the flow, and from these to construct the slip-line field.Departures of the field’s shape from the rules established for perfectly plastic solids(Section 6.2) are commonly observed. Figure 6.8(a) shows an early example of a chip primary shear zone investigated in this way (Palmer and Oxley, 1959). In addition to flow calculations in deriving this field, Palmer and Oxley also applied the force equilibrium constraint, that the slip-lines should intersect the free surface AA′ at 45°. The field is for a mild steel machined at the low cutting speed of 12 mm/min and a feed of 0.17 mm. At the low strain rates and temperatures generated in this case, departures from perfect plasticity are expected to be due only to strain hardening. The strain hardening behaviour of the material was measured in a simple compression test.Two conclusions arise from Figure 6.8 (and from other examples that could have been chosen). First, and most obviously, the entry and exit slip lines OA and OA′ are of opposing curvature. The field violates equation (6.4). This is a direct effect of work-hardening.Secondly, and less obviously, there is a problem with the constraint placed on the field that the slip-lines should meet 河南理工大學(xué)萬方科技學(xué)院畢業(yè)設(shè)計翻譯8the free surface at 45°. By revisiting the derivation of equations (6.1) (Appendix 1, Section 1.2.2), and removing the constraint of no strain hardening, it is easy to show thatwhere s1 and s2 are distances along an a and a b slip line respectively. In Figure 6.8(a), as in Figure 6.1, AC is a b line and CA′ an a line. After estimating the variations of k, ?k/?s1 and ?k/?s2 in the region of AA′C, Palmer and Oxley concluded, from the application of equation (6.5), that the hydrostatic pressure at A′ could not equal the shear yield stress of the work hardened material at A′, as it should according to the further constraint imposed河南理工大學(xué)萬方科技學(xué)院畢業(yè)設(shè)計翻譯9by the free surface boundary condition there. Palmer and Oxley resolved the contradiction by suggesting that plastic flow was not steady at the free surface. The smoothed free surface in Figure 6.8(a) is, in reality, corrugated and therefore the slip-lines should not be constrained to intesect the smoothed profile at 45°.The result of a later study (Roth and Oxley, 1972), still at low cutting speed to exclude the effects of strain rate and temperature on flow stress – now also including an estimate of the secondary shear zone shape – is shown in Figure 6.8(b). At A, the entry boundary OA is still made to intersect the free surface at 45°: there, continuity of flow ensures that the free surface slope is known (velocity discontinuities cannot 河南理工大學(xué)萬方科技學(xué)院畢業(yè)設(shè)計翻譯10exist in a hardening material – discontinuities that would occur in a non-hardening material are broadened into narrow zones). However, a free surface constraint has not been placed on the exit boundary direction at A′; and no attempt has been made to detail the field within the near-surface region AA′C.Roth and Oxley applied equations (6.5) to the calculation of hydrostatic stress along all the field boundaries, assuming that at A its value was that of the shear yield stress there. These are shown in the figure. Along the entry boundary OA, hydrostatic stress variations are dominated by the effect of work hardening. Integration of the hydrostatic and shear stresses with respect to distance along OA gives the force acting across it. Inclusion or work hardening gives a value of 1.77 k N (in line with experiment), while omitting it gives 3.19 k N, in a grossly different direction.Over the exit boundaries BD and DA′, where strain hardening has reduced the rate of change of shear flow stress across the slip lines, the variations approach those expected of a non-hardening material. They depend on the direction changes along the lines. The exit region OBDA′ is visually similar in this example to the non-hardening slip-line field proposed by Dewhurst (Figure 6.2(c)). The whole field is this, with the primary shear plane replaced by a work hardening zone of finite width.In a parallel series of experiments, Stevenson and Oxley 河南理工大學(xué)萬方科技學(xué)院畢業(yè)設(shè)計翻譯11(1969–70, 1970–71) extended the direct observations of chip flows to higher cutting speeds, but with a changed focus, to assess how large might be the strain rate and temperature variations in the primary shear zone. Figure 6.9(a) is a sketch of the streamlines that they observed when machining a 0.13%C free-machining steel at a cutting speed of 105 m/min and a feed of 0.26 mm. Figure 6.10 shows, for a range of cutting speeds, the derived variations of maximum shear strain rate along a central streamline, such as a a′ in Figure 6.9(a). The peak of maximum shear strain rate is observed to occur close to the line OA″ that would be described as the shear plane in a shear plane model of the machining process. The peak maximum shear strain rate was measured to vary in proportion to the notional primary shear plane velocity (from equation (2.3)) and inversely as the length s of the shear plane (assumed to be f / sin f):河南理工大學(xué)萬方科技學(xué)院畢業(yè)設(shè)計翻譯12In this case, the best-fit constant of proportionality C is 5.9. In many practical machining operations, peak shear strain rates are of the order of 104/s.It is interesting to consider the value of C = 5.9 in the light of the length-to-width ratio of the primary shear zone, 河南理工大學(xué)萬方科技學(xué)院畢業(yè)設(shè)計翻譯13equal to 2, derived in Chapter 2 from Figure 2.10 and equation (2.7). The average shear strain rate may be roughly half the peak rate. It is also the total shear strain divided by the time for material to pass through the primary zone. This time is the width of the zone divided by the work velocity normal to the plane, namely U work sin f. An easy manipulation equates the length-to-width ratio to C / 2, or about 3 in this case. A consistent view emerges of a primary shear region in which the strain rates do in fact peak along a plane OA″ but which in its totality may not be as narrow compared with its length as is commonly believed.Temperature rises in the primary zone have already been considered in Chapter 2.Stevenson and Oxley used the same approach described there to obtain the total temperature rise from the measured cutting forces resolved on to the shear plane. In the notation of this book, combining equations (2.4a), (2.5c) and (2.14), and remembering that only a fraction (1 – b) of generated heat flows into the chipHowever, as will be seen in the next section, there is a particular interest in the temperature rise in the plane OA″ 河南理工大學(xué)萬方科技學(xué)院畢業(yè)設(shè)計翻譯14where the strain rate is largest. Stevenson and Oxley took the temperature along OA″ to beWhere h can range from 0 to 1. Usually, they took it to equal 1, but this is not consistent with OA″ being upstream of the exit boundary of the primary zone. They commented that lower values (0.7 to 0.95) might be better (Oxley, 1989).考慮彈性接觸力為外力在另一個自由芯片上的作用。線 n= 5在圖 6.5推導(dǎo)出對于彈性接觸長度五倍塑料的長度。彈性接觸分析在加工過程中不應(yīng)該被忽略?；凭€場模型也可用于有限制的聯(lián)系工具加工(1964 年高慶宇等)，與芯片斷路器幾何工具(杜赫斯特,1979 年),與負(fù)前角工具(Petryk,1987),以及與側(cè)翼陳腐的工具(史和 Ramalingham,1991), 給予了怎樣的加工可以由非平面傾斜變化的洞察力臉和尖端修改工具。圖 6.6和 6.7給出了例子。圖 6.6是關(guān)于修改芯片流量非平面傾斜工具。由于該芯片/工具的接觸長度，下面是隨它的自然價值的減少而遠(yuǎn)離前刀面(圖 6.6(a))，對剩余的前刀面滑動速度降低，與創(chuàng)建一個停滯區(qū),該芯片流到這個空間創(chuàng)造的被切掉的工具。如果斷屑阻塞、邊坡失穩(wěn) d,是在一個平面刀具的切削河南理工大學(xué)萬方科技學(xué)院畢業(yè)設(shè)計翻譯15刃前面加了一些距離 IB(圖 6.6(b))，其對芯片的曲率和切力的影響可以預(yù)計。這些效果組合可以提供一些實用的斷屑槽幾何工具的幾何設(shè)計指導(dǎo)?；凭€場顯示,隨著越來越多的 6.7%負(fù)前角,可以形成一個停滯區(qū)，最終(圖 6.7(c)),允許分裂流與材料對該區(qū)域在車底的切削刃的工具而不是上升的前刀面。在這個圖的領(lǐng)域,乍一看,是為了負(fù)前角工具不切實際地增大角度。然而,真正的工具有一個有限的刃口半徑,可以穿也可制造一個負(fù)斜面槽。停滯的可能性,這些領(lǐng)域的信號是需要通過數(shù)值模擬的程序來歸納的。6.2.4 總結(jié)總之,滑移線場給出了一個可以觀察各種各樣的芯片流動的可能性的方法。一個缺乏獨特性的摩擦應(yīng)力加工參數(shù)的芯片和工具可以解釋為自由的芯片,在任何給定的摩擦應(yīng)力水平下,采取了一系列的接觸長度的工具。芯片是保持在外靜壓力的時候允許不同接觸長度的平衡。該速度場表明那里有強烈的剪切區(qū)域,這應(yīng)考慮到后面的數(shù)值模擬。他們還說明了如何在速度可能會有所不同的二次剪切區(qū),將回到后面的課題。他們還表現(xiàn)出對前刀面的接觸應(yīng)力的變化時正常的，在實踐中可以觀察到。然而,一個令人沮喪的弱點，滑移線場的方法沒有提供在完全的剛性材料模型的塑性中消除非唯一性，局限性：在某種情況下，什么是芯片/工具接觸長度的控制？此外,它可以提供沒有考慮應(yīng)力變流量特性采取的方法,通過試驗可以證明它的影響。另一種模型,對材料特性的變化的影響，在下一個部分集中介紹。河南理工大學(xué)萬方科技學(xué)院畢業(yè)設(shè)計翻譯16圖 6.6 與切割滑移線場模型（a）零接觸限制傾斜和（b）斷屑幾何工具。杜赫斯特(1979）圖 6.7 芯片流量使用工具，從（a）至（c）越來越傾斜。Petryk(1987)河南理工大學(xué)萬方科技學(xué)院畢業(yè)設(shè)計翻譯176.3 介紹可變的流動應(yīng)力的行為滑移線場模擬考察了各種芯片的形成和流動的平衡條件允許時可以簡化一個金屬的屈服行為。一個互補的方法是集中于產(chǎn)量的應(yīng)變（應(yīng)變硬化）和應(yīng)變率和溫度太多的情況下應(yīng)變力的影響，同時簡化了平衡流動模型。開拓這方面的工作是奧克斯利。本節(jié)的其余部分在很大程度上依賴于他的工作，這是在總結(jié)了加工機械(奧克斯利,1989 年 9月初版)。也可以被認(rèn)為是發(fā)展的四個階段:首先實驗和數(shù)值研究了實際芯片流動,由 visioplasticity方法;其次,簡化，使分析應(yīng)力之間關(guān)系的變化發(fā)展的主要剪切帶和材料的流動性能,應(yīng)變、應(yīng)變率和溫度依賴型;第三,考慮應(yīng)力條件在二次剪切帶;最后,綜合這些,使芯片流動特性可以預(yù)測。6.3.1 芯片流動的觀測Visioplasticity是實驗觀察到的塑性流動模式的研究。在其最完整的形式，整個流程應(yīng)變率推導(dǎo)出速度與位置的變化，通過整合和應(yīng)變方面的應(yīng)變率沿水流流線的時間計算。與塑料相關(guān)的工作溫度從熱傳導(dǎo)理論計算。然后，從流動與應(yīng)變，應(yīng)變率和溫度應(yīng)力變化獨立的知識，可以推斷出什么導(dǎo)致應(yīng)力變化是整個流程以及由此產(chǎn)生的變化是需要創(chuàng)造的流動。另外,測量值的大小可以用來推斷如何流動應(yīng)力變化。通常情況下，然而，流量測量精度不夠好來支持這整個的研究。不過，有益的見解來自只有部分成功。在平面應(yīng)變流動的情況下,第一步通常是確定最大剪應(yīng)變的流量軌跡,并從這些構(gòu)建滑移線場。為理想塑性固體建立了從該領(lǐng)域的規(guī)則出發(fā)的模型（6.2 節(jié)）是經(jīng)常觀察到的。圖 6.8（a）所示的一個芯片主要剪這種方式(帕爾默和奧克斯利,1959 年)研究區(qū)的早期范例。除了在這一領(lǐng)域的流動計算，帕爾默和奧克斯利還采用了力平衡約束，即滑線應(yīng)在 45 河南理工大學(xué)萬方科技學(xué)院畢業(yè)設(shè)計翻譯18°相交自由表面局部。該部分于低切削速度為 12毫米/分鐘和塑料加工的 0.17毫米溫和鋼。在低應(yīng)變速率這種情況下產(chǎn)生的溫度，完美塑性出發(fā)，預(yù)計僅是有應(yīng)變硬化產(chǎn)生的。該材料的應(yīng)變硬化行為是衡量一個簡單的壓縮試驗。從圖 6.8得到兩個結(jié)論(以及其他的例子,本來是可以選擇的)。首先，最明顯的是，進入和退出滑移線和 OA自動工作的反向是曲率。違反本場方程（6.4）。這是與工作直接影響的硬化。其次,不太明顯, 有一個與約束問題在線場上放置該滑線應(yīng)符合在45°自由表面。通過方程的推導(dǎo)(6.1)(見附錄 1、剖面 1.2.2 ),以及取消沒有應(yīng)變硬化約束,很容易證明其中 S1和 S2是沿著一個與 AB的距離分別的滑移線場。在圖 6.8（a），如圖 6.1，交流是 AB線和 CA'的一條線。估計在以后的 AA'C，帕爾默和奧克斯利研究下，?的 K / s1和?? 的 K /?S2 的變化得出結(jié)論，從應(yīng)用方程（6.5）,這在一個靜水壓力可能不等于剪切屈服應(yīng)力在 A的工作硬化材料,因為它應(yīng)該根據(jù)進一步的約束自由表面邊界條件有規(guī)定。帕爾默和奧克斯利解決這表明塑料流動并沒有在自由面的穩(wěn)定的矛盾。自由表面平滑圖 6.8:(a),在現(xiàn)實中,滑移線場波紋,因此滑移線不應(yīng)被限制在 45°intesect平滑的輪廓上。河南理工大學(xué)萬方科技學(xué)院畢業(yè)設(shè)計翻譯19對以后的研究（羅斯和奧克斯利，1972 年）仍處于較低的切削速度，結(jié)果排除應(yīng)變速率和溫度對流動應(yīng)力的影響，現(xiàn)在還包括對二次剪切帶形成的估計是在圖 6.8（b）所示。在 A，入口邊界工作硬化仍然是向相交于 45°的自由面：在那里，流動的連續(xù)性，確保自由面坡度是已知的（速度不連續(xù)不能存在于硬化材料不連續(xù)，將發(fā)生在非硬化材料的擴大為狹窄區(qū)）。然而，自由面約束并沒有被歸類在 A上的退出邊界方向，沒有嘗試已取得了細(xì)節(jié)在近表面區(qū)域 AA'C領(lǐng)域。羅斯和奧克斯利應(yīng)用方程(6.5)向所有計算靜水應(yīng)力沿該領(lǐng)域的界限,假設(shè)的價值是那里的剪切屈服應(yīng)力。這些都顯示在圖中。沿著邊界進入 OA工作硬化，靜水應(yīng)力變化是占主導(dǎo)地位的加工硬化效果。在靜水壓力和剪應(yīng)力整合到一起工作的距離通過它給人們的方法得以論證。硬化工作列入給出了 1.77千牛（與實驗線）的價值，而忽略它給了一個非常不同的方向在 3.19千牛。圖 6.8 實驗得出的低碳鋼加工速度慢滑移線領(lǐng)域。帕爾默、奧克斯利（1959）和羅斯、奧克斯利（1972）河南理工大學(xué)萬方科技學(xué)院畢業(yè)設(shè)計翻譯20在出口邊界 BD和 DA？其中應(yīng)變硬化，減少了對整個滑移線剪切流動應(yīng)力的變化率,變化方式的一個非周期的硬化材料。他們依靠沿線的方向變化。出口 OBDA′是視覺上的相似，這是硬化滑移線場杜赫斯特提出的例子(如圖 6.2(c))。整個領(lǐng)域就是這樣,從最基本的剪切平面取而代之的是加工硬化區(qū)有限寬度。在一系列的試驗并行中,史蒂文森和奧克斯利(1969-1970，1970 - 1971)擴展芯片流的直接觀察到更高的切削速度,但有改變重點,以評估有多大可能是應(yīng)變率和溫度變化主剪切帶。圖 6.9(a)是一個流線,他們觀察到當(dāng)加工草圖 0.13%C的自動機械加工鋼的切削速度為 105米/分鐘,一個塑料的切削速度為 0.26毫米。圖 6.10顯示,切削速度范圍內(nèi),最大剪應(yīng)變率沿中央流線的變化,如在圖 6.9(a)。最大剪應(yīng)變率的峰值是出現(xiàn)接近觀察到接近一條 OA”,將作為剪切面描述在加工過程中的剪切平面模型。最大剪應(yīng)變率峰值測量，以不同比例的第一剪切平面(從方程(2.3))和長度成反比的剪切平面(假定 f / sinf)秒河南理工大學(xué)萬方科技學(xué)院畢業(yè)設(shè)計翻譯21圖 6.9 （a）流的行由 0.13%C處的自由流動和切削鋼（b）為簡化后的分析（第6.3.2節(jié)）河南理工大學(xué)萬方科技學(xué)院畢業(yè)設(shè)計翻譯22圖 6.10 如圖所示為剪應(yīng)變沿中央流線速度的變化，峰值剪應(yīng)變與切削速度和進給速度。在這種情況下,最合適的比例常數(shù) C為 5.9。在許多實際加工操作，剪應(yīng)變率峰值都是 104/s。有趣的是,考慮光的 C= 5.9的值的長度與寬度的比例主剪切帶,等于2，自第二章圖 2.10和方程(2.7)。平均剪應(yīng)變率可能只有大約一半的峰值速率。這也是總剪應(yīng)變材料的時候要經(jīng)過的主要區(qū)域。這一次是由正常的工作速度的飛機，即 Uworksinf分區(qū)域的寬度。這種情況下，一個簡單的操作等同于長度與寬度的比例 C / 2或 3這種情況下。一致的看法出現(xiàn)在剪切區(qū),其中應(yīng)變率峰值，其實是沿平面硬化區(qū) OA,但是在整體上可能不是縮小比例,一般相信其長度。第 2章已認(rèn)為在第一區(qū)的溫度上升。史蒂文森和奧克斯利用同樣的方法描述了那里獲得的總溫度從實測切削力等上升到剪切面上解決。在這本書的符號里,結(jié)合方程(2.4a),(2.5c)和(2.14),并且記住只有一小部分（1 - b)項所產(chǎn)生的熱量流入芯片不過,這將在下一節(jié)看到,有一個在平面上溫度飛速上升的 OA“，其中應(yīng)變速率最大。史蒂文森和奧克斯利認(rèn)為溫度沿 OA“上升。其中 h范圍從 0到 1。通常,他們把它等于 1,但是這與硬化工作區(qū)OA“的區(qū)域界線并不一致。他們評論說較小的值(0.7 到 0.95)可能會更好(奧克斯利,1989 年 9月出版)。河南理工大學(xué)萬方科技學(xué)院畢業(yè)設(shè)計翻譯23