【機械類畢業(yè)論文中英文對照文獻翻譯】單刃刀具
【機械類畢業(yè)論文中英文對照文獻翻譯】單刃刀具,機械類畢業(yè)論文中英文對照文獻翻譯,機械類,畢業(yè)論文,中英文,對照,對比,比照,文獻,翻譯,刀具
南華大學(xué)機械工程學(xué)院畢業(yè)論文
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單刃刀具
刀具有切削部分（或產(chǎn)生切屑的部分）和刀桿，常用于車床、轉(zhuǎn)塔車床、龍門刨床、牛頭刨床、鏜床及類似的機床。圖2.30為一典型的單刃刀具，其最重要的特征是切削刃及相鄰的刀面。如圖所示，可定義如下：
1. 前刀面是切屑流經(jīng)的表面；
2. 后刀面是與工件已加工面相對的表面；
3. 切削刃是刀面擔(dān)負切削任務(wù)的邊緣，主刀刃是切削刃中擔(dān)負工件過渡表面上切削任務(wù)的部門，其余是副刃；
4. 刀尖是主、副刃相連接處的以小段刀刃，它可以是曲線或直線，也可以是主副刀刃的交點。
一般而言，刀具切削時，相對于工件的運動有兩個方面：
1. 來自機床主運動的相對運動，可以稱為刀具的主運動。
2. 來自于機床進給運動的相對運動（如圖2.31）
這兩個運動的合成就稱為合成切削運動，定義為機床主運動和進給運動而產(chǎn)生的合成運動
應(yīng)該注意，機床作進給運動時，如刀具并不接觸工件，則合成切削運動就等于主運動。當(dāng)連續(xù)進給運動時，主運動與合成運動間的夾角叫做切削速度角。這個角度通常很小，多數(shù)情況下可以假設(shè)為零。另外，切削速度v-主刀刃上不同選頂點相對于工作的瞬時速度，沿主切削刃可能時變化的，而進給速度刀刃
上不同選定點相對于工件的進給運動的大小是固定不變的，總之，合成速度-刀刃上選頂相對于工作瞬時合成切削運動的大小可以表示:，但因為對大多數(shù)實際加工很小，通?？梢约僭O(shè)，考慮切削刀具幾何角度時，一個很重要的角度就是主偏角。在刀刃上選定點切下的切削層厚度——未變形切削厚度，極大地影響著切削功率，嚴格地說，應(yīng)在既垂直切削刃又垂直合成切削運動方向上地測量。然而實際如前所述，因為很小，就在垂直于主運動方向測量，因此在圖2.32和后續(xù)各圖中，就按此測量。所以，由圖2.32可知，其中為進給量，即沿進給運動方向測量地切削層參數(shù)。單刃刀具切削時，就等于進給量f。
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切削層地橫截面積A近似表示為，其中為背吃刀量，以前叫切削度，背吃刀量是在包含主運動與進給運動所在平面地垂直方向測量地切削層尺寸（圖2.31），一般而言，背吃刀量決定單刃刀具從工件切下材料地厚度。
*圖2.30 典型單刃刀具。刀柄， 切削部分，刀具軸線，副切削刃，基面，副后刀面，主切削刃，刀尖，前刀面，主后刀面。*
*圖2.31 外圓車削時合成切削運動。刀具主運動矢量，合成切削速度角，合成切削運動矢量，刀刃上選定點，刀具進給運動矢量。*
*圖2.32 單刃刀具切削。 進給量，刀桿，主偏角，切削層截面，前刀面，背吃刀量（切削深度），主切削刃，副切削刃，未變形切削厚度，刀尖，包括主運動及進給運動地平面。
夾具
如前所示，工件必須相對于刀具在一定的位置定位并夾緊。工件在劃線以后加工之前，還必須確定出相對于機床運動的位置，并將其夾緊。
當(dāng)需要加工若干相同工件時，通過使用夾具，可無須對每個工件進行劃線。但如果加工的是鑄件或者鍛件，則仍需要對工件進行劃線，以確保加工出合格的工件，而不至于造成肋條、內(nèi)孔等位置便宜。
鉆模和其它夾具相似，都是確保工件正確定位和夾緊裝置，但也有不同之處，鉆模具有在實際加工過程能導(dǎo)引刀具裝置，而其它夾具則沒有。實際上，在切削過程中，只有對鉆頭、絞刀以及類似刀具才能進行引導(dǎo)，所以與鉆削加工有關(guān)的夾具是鉆模，而與其它加工有關(guān)的則是夾具。夾具可裝有調(diào)整刀具相對于定位工件位置的裝置。
夾具的優(yōu)點可概括如下：
可以省去劃線及其它測量、調(diào)整等手續(xù)；由于能使工件正確定位，刀具能正確地導(dǎo)引和調(diào)整，不熟練的工人也能有把握地快速進行操作；
便于零件的裝配，因為所有零件的一致性好，尺寸公差的范圍較小，所以可以省去“試裝”和“銼配”工作；零件具有互換性，如果產(chǎn)品廣銷各地，備件的供應(yīng)問題將為之簡化。用于裝螺栓的螺栓孔通常有1.5～3.0mm的間隙，讀者可能懷疑，對這樣的零件是否有必要制造精密夾具。應(yīng)該牢記，夾具一經(jīng)制造出來，便可用以加工廠許多零件精密制造夾具的附加成本可分攤給為數(shù)眾多的工件。此外，在機構(gòu)的裝配過程中，即使是很小的誤差，累積起來也是很大的。公差一經(jīng)規(guī)定，最好確保其要求，而不允許隨意劃線使尺寸超出規(guī)定值。
（1） 工件的定位。圖2.27表示在空間完全不受約束的剛體，此時，它具有6個自由度?？紤]這些自由度時，可用三個互相垂直的坐標(biāo)軸XX、YY、ZZ來表示。物體可沿任一坐標(biāo)軸移動，因此，它具有三個移動自由度。它還可以繞任一坐標(biāo)軸轉(zhuǎn)動，因此，又有三個轉(zhuǎn)動自由度，故共有6個自由度。工件定位時，必須限制盡可能多的自由度，以確保加工時獲得所需的精度。應(yīng)盡可能提前加工出合適的定位面來保證精度，并用它人微言輕所有加工面的定位基面，除非有其它原因必須使用另外的定位面。而即使是要用另外的定位面，也必須根據(jù)原有的定位面加工新的定位面。
（2） 工件的夾緊。夾緊機構(gòu)必須夾緊工件，使之能承受切削力，但夾緊力不可過大，以免造成工件變形或損壞。工件夾緊點下方應(yīng)有支承，以確保力由夾具的主體承受，然后轉(zhuǎn)由機床的工件臺和床身承受。設(shè)計夾具時，應(yīng)保證其夾緊機構(gòu)既能施加合適的夾緊力，又能使夾緊操作迅速、安全。
（3） 內(nèi)容提要。
1）小批量生產(chǎn)時要對工件進行劃線，并用它作為切削的標(biāo)志線，對鑄件、鍛件毛坯也要進行劃線，以檢驗是否有足夠的加工余量。
2）如果批量允許，工件采用夾具定位夾緊，而不采用劃線。夾具上有使工件定位和夾緊的機構(gòu)，鉆模還有切削過程中對刀具導(dǎo)引的元件，而其它夾具則有可在切削前調(diào)刀的裝置。
譯文:
Single –Point Tools
Single-point tools are cutting tools having one cutting part (or chip producing element) and one shank. They are commonly used in lathes, turret lathes, planers, shapers, boring mills, and similar machine tools. A typical single-point tool is illustrated in Fig.2.30. The most important features are the cutting edges and adjacent surfaces. These are shown in the figure and defined as follows:
the face is the surface or surface over which the chip flows.
The flank is the tool surface or surfaces over which the surface produced on the work-piece passes.
The cutting edge is that edge of the face which is intended to perform cutting. The tool major cutting edge is that entire part of the cutting edge which is intended to be responsible for the transient surface on the work-piece. The tool minor cutting edge is the remainder of the cutting edge.
The corner is the relatively small portion of the cutting edge at the junction of the major and minor cutting edges; it may be curved or straight, or it may be the actual intersection of these cutting edges.
In general, when a tool is applied to a work-piece, its motion relative
to the work-piece has two components:
The motion resulting form the primary motion of the machine tool, which can be called the primary motion of the tool.
The motion resulting form the feed motion of the machine (Fig.2.31).
The resultant of these two tool motions is called the resultant cutting motion and is defined as the motion resulting from simultaneous primary and feed motions.
It should be noted that in machine tools where the feed is applied while the tool is not engaged with the work-piece (as in shaping or planning, for example ),the resultant cutting motion is identical to the primary motion. When the feed motion is applied continuously, the angle between the direction of primary motion and the resultant cutting direction is called the resultant cutting-speed angleη. This angle is usually extremely small and for most practical purposes can be assumed to be zero. Further, the cutting speed , the instantaneous velocity of the primary motion of the selected point on the cutting edge relative to the work-piece, can vary along the major cutting edge. The feed speed , the instantaneous velocity of the feed motion of the selected point on the cutting edge relative to the work-piece, is constant.
Finally, the resultant cutting speed ,the instantaneous velocity of the resultant cutting motion of the selected point on the cutting edge relative to the work-piece, is given by , ,but since for most practical operations is very small, it can generally be assumed that ,. One of the important tool angles when considering the geometry of a particular machining operation is the angle in Fig.2.32 called the major cutting-edge angle .The thickness of the layer of material being removed at the selected point on the cutting edge, known as the under-formed chip thickness chip thickness ,significantly affects the power required to perform the operation. Strictly, this dimension should be measured both normal to the cutting edge and normal to the resultant cutting direction. However, for all practical purposes, since is small, as described above, can be measured normal to the direction of primary motion; thus in Fig.2.32 and all subsequent figures, will be measured this way. From Fig.2.32, therefore, is given by , where is the feed engagement, the instantaneous engagement of the tool cutting edge with the work-piece measured in the direction of feed motion. For single-point cutting operations is equal to the feed, and therefore, .
The cross-sectional area of the layer of material being removed (cross-sectional area of the uncut chip) is approximately giver by, ,where is the base engagement, previously known as depth of cut. The back engagement is the instantaneous engagement of the tool with the work-piece, measured perpendicular to the plane containing the directions of primary and feed motion(Fig.2.31). In general the back engagement determines the depth of material removed from the workpiece in a single point cutting operation.
Jigs and Fixtures
It has already been stated the work-piece must be located relative to the cutting tool, and be secured in that position. After the work-piece has been marked out, it is still necessary to position it with respect to the machine movement, and to clamp it in that position before machining is started.
When several identical work-piece are to be produced the need to mark out each part is eliminated by the use of jigs and fixtures, but if a casting or forging is involve, a trail work-piece is marked out, to ensure that the work-piece can be produced from it, and to ensure that ribs, cores, etc. have not become misplaced.
Jigs and fixtures are alike in that they both incorporate devices to ensure that the work-piece is correctly located and clamped, but they fifer in that they both incorporate means of tool guiding during the actual cutting operation, and fixtures do not. In practice ,the only cutting tools that can be guided while actually cutting are drills, reamers, and similar cutters; and so jigs are associated with drilling operations, and fixtures with all other operations. Fixtures may incorporate means of setting the cutting tools relative to the location system.
The advantage of jigs and fixtures can be summarized as follows:
1. marking out and measuring and setting out methods are eliminated;
2. unskilled workers may proceed confidently and quickly in the knowledge that the work-piece can be positioned correctly, and the tools guided or set;
3. the assembly of parts is facilitated, since all components will be identical within small limits, and ‘trying’ and filing of work is eliminated;
4. the parts will be interchangeable, and if the product is sold over a wide area, the problem of spare parts will be simplified.
Bolt holes often have 1.5mm or even 3.0mm clearance for the bolt, and reader may doubt the necessity of making precision jigs for such work. It must remembered that the jigs, once made, will be used on many components, and the extra cost of an accurately made jigs is spare over a large output. Further more, it is surprising how small errors accumulate in a mechanism during its assembly. When a clearance is specified, it is better to ensure its observance, rather than allow careless marking out and machining to encroach upon it.
(1) the location of work-piece. Fig 2.27 represent a body that is completely free in space; in this condition it has six degrees of freedom. Consider these freedom, with respect to the three mutually perpendicular axes XX,YY and ZZ. The body can move along these axes; it therefore has three freedoms of translation. It can also rotate about any of the three axes; it therefore has three freedoms of rotation .the total number of freedoms is six. When work is located, as many of these freedoms as possible must be eliminated, to ensure that the operation is performed with the required accuracy. Accuracy is ensured by machining suitable location features as early as possible, and using them for all location, unless other considerations mean the other location features must be used. If it is necessary, the new location features must be machined as a result of location from the former location features.
(2) The clamping of the work-piece. The clamping system must be such that the work-piece is held against the cutting forces, and the clamping force must not be so great as to cause the work-piece to become distorted or damaged. The work-piece must be supported beneath the point of clamping, to ensure that the forces are taken by the main frame of the jig or fixture, and on to the machine table and bed. When jigs and fixtures are designed to ensure that the correct clamping force is applied, and that the clamps can be operated quickly but with safety.
(3) Summary
1) small quantity production involves marking out to produce guidelines for machining. Marking out is also done upon trial castings, and forgings, to check that there is enough metal allowed for “cleaning up”.
2) If the quantity permits, work-pieces are located and clamped in jigs or fixtures, instead of marking out each work-piece. Jigs and fixtures incorporate means of locating and clamping the work-piece. Jigs also include means of guiding the tool during the cutting, and fixtures include means of setting the tool before cutting.
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