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湖南科技大學(xué) 2015 屆畢業(yè)設(shè)計(jì)（論文）開題報(bào)告
題 目
分 離 叉 工 藝 及 夾 具 設(shè) 計(jì)
作者姓名
劉鑫鑫
學(xué)號(hào)
1103010509
所學(xué)專業(yè)
機(jī)械設(shè)計(jì)制造及其自動(dòng)化
1、 研究的意義，同類研究工作國內(nèi)外現(xiàn)狀、存在問題（列出主要參考文獻(xiàn)）
研究的意義：隨著全球制造產(chǎn)業(yè)的區(qū)域轉(zhuǎn)移整個(gè)制造行業(yè)競(jìng)爭(zhēng)的加劇，導(dǎo)致機(jī)械加工生產(chǎn)單位都面臨提高生產(chǎn)效率的問題。而在機(jī)加過程中作為裝夾工件的工藝裝備的夾具，在提高生產(chǎn)效率方面有其顯著的優(yōu)勢(shì)。特別是在在切削過程中，配以適當(dāng)?shù)募庸ぽo助工具。（如夾具）等有力于提高企業(yè)生產(chǎn)效率，使得許多復(fù)雜零件的加工成為可能，常規(guī)零件加工的質(zhì)量進(jìn)一步提升，并降低勞動(dòng)強(qiáng)度，在保證產(chǎn)品質(zhì)量加工精度的同時(shí)批量生產(chǎn)，從而降低生產(chǎn)成本，從而夾具的使用在某種長度上提高實(shí)際生產(chǎn)企業(yè)的效益。因而對(duì)夾具知識(shí)的認(rèn)識(shí)和學(xué)習(xí)，在今天顯的尤為更重要起來。?
結(jié)合目前實(shí)際生產(chǎn)，常常發(fā)現(xiàn)僅用通用夾具不能滿足生產(chǎn)要求，用通用夾具裝夾工件生產(chǎn)效率低勞動(dòng)強(qiáng)度大，加工質(zhì)量不高，而且往往需要增加劃線工序，而專門設(shè)計(jì)的銑床夾具，主要包括夾具的定位方案、夾緊方案、對(duì)刀方案，夾具體與定位鍵的設(shè)計(jì)及加工精度等方面的分析?？梢杂行У臏p少工件的加工基本時(shí)間和輔助時(shí)間，大大提高了勞動(dòng)生產(chǎn)力，從而可以有效地減輕工人的勞動(dòng)強(qiáng)度和增加勞動(dòng)效率。不論是傳統(tǒng)制造，還是現(xiàn)代制造系統(tǒng)，夾具都是十分重要的。因此，好的夾具設(shè)計(jì)可以提高產(chǎn)品勞動(dòng)生產(chǎn)率，保證和提高加工精度，降低生產(chǎn)成本等，還可以擴(kuò)大機(jī)床的使用范圍，從而使產(chǎn)品在保證精度的前提下提高效率，降低成本。
國內(nèi)外現(xiàn)狀: 近些年來，隨著數(shù)控機(jī)床、加工中心、柔性制造單元、柔性制造系統(tǒng)等現(xiàn)代化加工設(shè)備的廣泛應(yīng)用，使傳統(tǒng)的機(jī)械加工的制造方法發(fā)生了重大變革，人們對(duì)夾具的功能已經(jīng)從過去的裝夾、定位、引導(dǎo)刀具定位為裝夾、定位。而數(shù)字化的設(shè)備加工功能的擴(kuò)大化，已經(jīng)將夾具的引導(dǎo)刀具的功能完全替代，給今后夾具的快速定位、快速裝夾提出了更高的要求。目前國內(nèi)外已開始將夾具設(shè)計(jì)和數(shù)字化、現(xiàn)代化加工技術(shù)相結(jié)合，研究和推廣?KBV?夾具，即基于知識(shí)的工程。?把知識(shí)、技能、經(jīng)驗(yàn)、原理、規(guī)范等結(jié)合到三維?CAD?系統(tǒng)中，使得設(shè)計(jì)人員只要輸入工程參數(shù)或應(yīng)用要求，系統(tǒng)就能依據(jù)相關(guān)的知識(shí)，推理構(gòu)造出符合特定要求的工程設(shè)計(jì)結(jié)果?KBV?夾具。
我國對(duì)分離叉類不規(guī)則零件的加工處于效率低，加工成本高的階段，大批量生產(chǎn)正逐漸成為現(xiàn)代機(jī)械制造業(yè)新的生產(chǎn)模式，在這種模式中，要求加工機(jī)床和夾具裝備具有更好的柔性，以縮短準(zhǔn)備時(shí)間，降低生產(chǎn)成本，所以手動(dòng)夾緊的方式已經(jīng)過時(shí)，氣動(dòng)，液壓夾緊夾具正是適應(yīng)這一生產(chǎn)模式的工裝準(zhǔn)備。國外為了適應(yīng)這一生產(chǎn)模式，也把柔性制造系統(tǒng)作為開發(fā)新產(chǎn)品的有效手段。
存在的問題：制造業(yè)是國民經(jīng)濟(jì)的基礎(chǔ)，隨著以計(jì)算機(jī)技術(shù)為主導(dǎo)的現(xiàn)狀科學(xué)技術(shù)的迅速發(fā)展，以‘時(shí)間驅(qū)動(dòng)’為特征的市場(chǎng)競(jìng)爭(zhēng)，產(chǎn)品更新?lián)Q代的加快，商品需求的多樣化等，是制造業(yè)面臨著巨大的挑戰(zhàn)。在現(xiàn)階段分離叉零件的加工還沒有達(dá)到現(xiàn)代自動(dòng)化的加工水平，它的加工工藝還需要人工畫線的加工方法來保證精度，而對(duì)工件的裝夾也是通過人工的方法進(jìn)行的。
參考文獻(xiàn)：
甘永立.幾何公差與測(cè)量.上海：上?？萍汲霭嫔?，2004
張福潤，徐鴻木主編.機(jī)械制造技術(shù)基礎(chǔ).武漢：華中科技出版社，2000
2、 研究目標(biāo)、內(nèi)容和擬解決的關(guān)鍵問題（根據(jù)任務(wù)要求進(jìn)一步具體化）
本設(shè)計(jì)是分離叉工藝規(guī)程及一些工序的專用夾具設(shè)計(jì);
分離叉內(nèi)側(cè)面銑夾具的主要加工表面是平面及孔，因此主要研究?jī)?nèi)容為基準(zhǔn)的選擇，加工工藝和零件主要部位的專用夾具的設(shè)計(jì)
工件定位是否正確，定位精度是否滿足要求，工件夾緊是否可靠等。工件在夾具中的定位精度，主要與定位基準(zhǔn)是否與工序基準(zhǔn)重合，定位基準(zhǔn)與定位元件的配合狀況等諸多因素有關(guān)，可以提高夾具的制造精度，減少配合間隙；夾緊必須可靠，但夾緊力不可過大，以免工件或夾具產(chǎn)生過大變形，可采用多點(diǎn)夾緊或在工件剛性薄弱部位安放適當(dāng)?shù)妮o助支撐。
3、 特色與創(chuàng)新之處
工件在夾具中的正確定位，是通過工件上的定位基準(zhǔn)與夾具上的定位元件相接觸而實(shí)現(xiàn)的，只需要找正便可將工件夾緊；
通過對(duì)夾具上的對(duì)刀位置，即可保證工件加工表面相對(duì)于刀具的正確位置；
裝夾基本上不受人工技術(shù)水平的影響，能比較容易和穩(wěn)定地保證加工精度；
裝夾迅速，方便，能減輕勞動(dòng)強(qiáng)度，顯著地減少輔助時(shí)間，提高勞動(dòng)生產(chǎn)率。
4、 擬采取的研究方法、步驟、技術(shù)路線
文獻(xiàn)資料法：通過各種途徑，翻閱大量文獻(xiàn)資料，擴(kuò)展自己知識(shí)，掌握一定的專業(yè)理論，為畢業(yè)設(shè)計(jì)打下理論基礎(chǔ)；
數(shù)據(jù)分析法:通過一定的數(shù)據(jù)，分析存在的現(xiàn)象情況，對(duì)結(jié)果作出定量和定性分析，說明現(xiàn)象存在的條件及可能性：
案例分析法：通過具體的實(shí)例，來說明論證自己得出的結(jié)論，這樣可以更形象客觀的來論證論文的觀點(diǎn)；
資料引證法：通過對(duì)大量資料的閱讀，掌握，引用其中有用的內(nèi)容來論證論文的觀點(diǎn)。
擬定工藝路線:表示零件的加工順序及加工方法，分出工序，安裝或工件及工步等，并選擇各工序所使用的機(jī)床，刀具，夾具及量具等。
步驟及技術(shù)路線：制訂工藝規(guī)程、確定加工余量、工藝尺寸計(jì)算、工時(shí)定額計(jì)算、定位誤差分析等。在整個(gè)設(shè)計(jì)中也是非常重要的,通過這些設(shè)計(jì),不僅讓我們更為全面地了解零件的加工過程、加工尺寸的確定,而且讓我們知道工藝路線和加工余量的確定,必須與工廠實(shí)際的機(jī)床相適應(yīng)。工序的劃分和定位基準(zhǔn)的選擇，在開始的時(shí)候，要認(rèn)真分析零件圖，了解分離叉的結(jié)構(gòu)特點(diǎn)和技術(shù)要求。加工表面的粗糙度、平行度、垂直度，注意零件各孔系自身精度（同軸度，圓度，粗糙度等）和它們的相互位置精度，采用AutoCAD軟件繪制零件圖，一方面可以使我們對(duì)其零件有進(jìn)一步了解與認(rèn)識(shí)，另一方面可以增強(qiáng)我們對(duì)AutoCAD軟件的熟悉和運(yùn)用。?
工序的劃分確定加工順序和工序內(nèi)容，安排工藝的加重和分散程度，劃分工序階段，與生產(chǎn)綱領(lǐng)有密切聯(lián)系，具體可以根據(jù)生產(chǎn)類型，零件的結(jié)構(gòu)特點(diǎn)，技術(shù)要求和機(jī)床設(shè)備。定位基準(zhǔn)的選擇根據(jù)粗基準(zhǔn)的選擇原則：遵循基準(zhǔn)同意，基準(zhǔn)重合。
夾具設(shè)計(jì)要確定工件定位是否正確，定位精度是否滿足要求，工件夾緊是否可靠等等。工件在夾具中的定位精度，主要是定位基準(zhǔn)是否與工序基準(zhǔn)重合，定位基準(zhǔn)與定位元件的配合狀況等因素有關(guān)，可提高夾具的制造精度，減少配合間隙，就能提高夾具在機(jī)床上的定位精度，夾具中出現(xiàn)過的定位時(shí)，可通過撤銷多余定位元件，使多余定位元件失去限制重復(fù)自由度的能力，增加定位元件與定位基準(zhǔn)的配合間隙等辦法來解決，夾緊必須可靠，但夾緊力不可過大，一面工件或夾具產(chǎn)生過大變形，可采用多點(diǎn)夾緊或在工件剛性薄弱部位安放適當(dāng)?shù)妮o助支撐，夾具的設(shè)計(jì)必須要保證夾具的定位準(zhǔn)確的機(jī)構(gòu)合理，考慮夾具的定位誤差和安裝誤差。我們將通過對(duì)工件與夾具的認(rèn)真分析，結(jié)合一些夾具的具體設(shè)計(jì)事例，查閱相關(guān)的夾具設(shè)計(jì)資料，聯(lián)系在工廠看到的一些加工的夾具來解決這些問題。
5、 擬使用的主要設(shè)計(jì)、分析軟件及儀器設(shè)備
設(shè)計(jì)，分析軟件:Auto CAD，proe
儀器設(shè)備：機(jī)床，刀具，夾具等
6、參考文獻(xiàn)
陳宏鈞.實(shí)用金屬切削手冊(cè)【M】.北京：機(jī)械工業(yè)出版社，2005
楊黎明.機(jī)床夾具設(shè)計(jì)手冊(cè)【M】.國防工業(yè)出版社，2003
王力行.專用機(jī)床夾具安裝精度分析【J】.裝備制造技術(shù)，2008
趙生虎.夾具的優(yōu)化設(shè)計(jì)及經(jīng)濟(jì)性分析研究【J】.煤礦機(jī)械.2006
趙家齊.機(jī)床制造工藝學(xué)課程設(shè)計(jì)指導(dǎo)書【M】.第二版，北京：機(jī)械工業(yè)出版社，2008
注：
1、開題報(bào)告是本科生畢業(yè)設(shè)計(jì)（論文）的一個(gè)重要組成部分。學(xué)生應(yīng)根據(jù)畢業(yè)設(shè)計(jì)（論文）任務(wù)書的要求和文獻(xiàn)調(diào)研結(jié)果，在開始撰寫論文之前寫出開題報(bào)告。
2、參考文獻(xiàn)按下列格式（A為期刊，B為專著）
A：[序號(hào)]、作者（外文姓前名后，名縮寫，不加縮寫點(diǎn)，3人以上作者只寫前3人，后用“等”代替。）、題名、期刊名（外文可縮寫，不加縮寫點(diǎn)）年份、卷號(hào)（期號(hào)）：起止頁碼。
B：[序號(hào)]、作者、書名、版次、（初版不寫）、出版地、出版單位、出版時(shí)間、頁碼。
3、表中各項(xiàng)可加附頁。
3
英文原文
Cutting process and fixture design
Machine tools have evolved from the early foot-powered lathes of the Egyptians and John Wilkinson's boring mill. They are designed to provide rigid support for both the workpiece and the cutting tool and can precisely control their relative positions and the velocity of the tool with respect to the workpiece. Basically, in metal cutting, a sharpened wedge-shaped tool removes a rather narrow strip of metal from the surface of a ductile workpiece in the form of a severely deformed chip. The chip is a waste product that is considerably shorter than the workpiece from which it came but with a corresponding increase in thickness of the uncut chip. The geometrical shape of workpiece depends on the shape of the tool and its path during the machining operation.
Most machining operations produce parts of differing geometry. If a rough cylindrical workpiece revolves about a central axis and the tool penetrates beneath its surface and travels parallel to the center of rotation, a surface of revolution is produced, and the operation is called turning. If a hollow tube is machined on the inside in a similar manner, the operation is called boring. Producing an external conical surface uniformly varying diameter is called taper turning, if the tool point travels in a path of varying radius, a contoured surface like that of a bowling pin can be produced; or, if the piece is short enough and the support is sufficiently rigid, a contoured surface could be produced by feeding a shaped tool normal to the axis of rotation. Short tapered or cylindrical surfaces could also be contour formed.
Flat or plane surfaces are frequently required. They can be generated by radial turning or facing, in which the tool point moves normal to the axis of rotation. In other cases, it is more convenient to hold the workpiece steady and reciprocate the tool across it in a series of straight-line cuts with a crosswise feed increment before each cutting stroke. This operation is called planning and is carried out on a shaper. For larger pieces it is easier to keep the tool stationary and draw the workpiece under it as in planning. The tool is fed at each reciprocation. Contoured surfaces can be produced by using shaped tools.
Multiple-edged tools can also be used. Drilling uses a twin-edged fluted tool for holes with depths up to 5 to 10 times the drill diameter. Whether the
drill turns or the workpiece rotates, relative motion between the cutting edge and the workpiece is the important factor. In milling operations a rotary cutter with a number of cutting edges engages the workpiece. Which moves slowly with respect to the cutter. Plane or contoured surfaces may be produced, depending on the geometry of the cutter and the type of feed. Horizontal or vertical axes of rotation may be used, and the feed of the workpiece may be in any of the three coordinate directions.
Basic Machine Tools
Machine tools are used to produce a part of a specified geometrical shape and precise I size by removing metal from a ductile material in the form of chips. The latter are a waste product and vary from long continuous ribbons of a ductile material such as steel, which are undesirable from a disposal point of view, to easily handled well-broken chips resulting from cast iron. Machine tools perform five basic metal-removal processes: I turning, planning, drilling, milling, and grinding. All other metal-removal processes are modifications of these five basic processes. For example, boring is internal turning; reaming, tapping, and counter boring modify drilled holes and are related to drilling; bobbing and gear cutting are fundamentally milling operations; hack sawing and broaching are a form of planning and honing; lapping, super finishing. Polishing and buffing are variants of grinding or abrasive removal operations. Therefore, there are only four types of basic machine tools, which use cutting tools of specific controllable geometry: 1. lathes, 2. planers, 3. drilling machines, and 4. milling machines. The grinding process forms chips, but the geometry of the abrasive grain is uncontrollable.
The amount and rate of material removed by the various machining processes may be I large, as in heavy turning operations, or extremely small, as in lapping or super finishing operations where only the high spots of a surface are removed.
A machine tool performs three major functions: 1. it rigidly supports the workpiece or its holder and the cutting tool; 2. it provides relative motion between the workpiece and the cutting tool; 3. it provides a range of feeds and speeds usually ranging from 4 to 32 choices in each case.
Speed and Feeds in Machining
Speeds, feeds, and depth of cut are the three major variables for economical machining. Other variables are the work and tool materials, coolant and geometry of the cutting tool. The rate of metal removal and power required for machining depend upon these variables.
The depth of cut, feed, and cutting speed are machine settings that must be established in any metal-cutting operation. They all affect the forces, the power, and the rate of metal removal. They can be defined by comparing them to the needle and record of a phonograph. The cutting speed (V) is represented by the velocity of- the record surface relative to the needle in the tone arm at any instant. Feed is represented by the advance of the needle radially inward per revolution, or is the difference in position between two adjacent grooves. The depth of cut is the penetration of the needle into the record or the depth of the grooves.
Turning on Lathe Centers
The basic operations performed on an engine lathe are illustrated. Those operations performed on external surfaces with a single point cutting tool are called turning. Except for drilling, reaming, and lapping, the operations on internal surfaces are also performed by a single point cutting tool.
All machining operations, including turning and boring, can be classified as roughing, finishing, or semi-finishing. The objective of a roughing operation is to remove the bulk of the material as rapidly and as efficiently as possible, while leaving a small amount of material on the work-piece for the finishing operation. Finishing operations are performed to obtain the final size, shape, and surface finish on the workpiece. Sometimes a semi-finishing operation will precede the finishing operation to leave a small predetermined and uniform amount of stock on the work-piece to be removed by the finishing operation.
Generally, longer workpieces are turned while supported on one or two lathe centers. Cone shaped holes, called center holes, which fit the lathe centers are drilled in the ends of the workpiece-usually along the axis of the cylindrical part. The end of the workpiece adjacent to the tailstock is always supported by a tailstock center, while the end near the headstock may be supported by a headstock center or held in a chuck. The headstock end of the workpiece may be held in a four-jaw chuck, or in a type chuck. This method holds the workpiece firmly and transfers the power to the workpiece smoothly; the additional support to the workpiece provided by the chuck lessens the tendency for chatter to occur when cutting. Precise results can be obtained with this method if care is taken to hold the workpiece accurately in the chuck.
Very precise results can be obtained by supporting the workpiece between two centers. A lathe dog is clamped to the workpiece; together they are driven by a driver plate mounted on the spindle nose. One end of the Workpiece is mecained;then the workpiece can be turned around in the lathe to machine the other end. The center holes in the workpiece serve as precise locating surfaces as well as bearing surfaces to carry the weight of the workpiece ?and to resist the cutting forces. After the workpiece has been removed from the lathe for any reason, the center holes will accurately align the workpiece back in the lathe or in another lathe, or in a cylindrical grinding machine. The workpiece must never be held at the headstock end by both a chuck and a lathe center. While at first thought this seems like a quick method of aligning the workpiece in the chuck, this must not be done because it is not possible to press evenly with the jaws against the workpiece while it is also supported by the center. The alignment provided by the center will not be maintained and the pressure of the jaws may damage the center hole, the lathe center, and perhaps even the lathe spindle. Compensating or floating jaw chucks used almost exclusively on high production work provide an exception to the statements made above. These chucks are really work drivers and cannot be used for the same purpose as ordinary three or four-jaw chucks.
While very large diameter workpieces are sometimes mounted on two centers, they are preferably held at the headstock end by faceplate jaws to obtain the smooth power transmission; moreover, large lathe dogs that are adequate to transmit the power not generally available, although they can be made as a special. Faceplate jaws are like chuck jaws except that they are mounted on a faceplate, which has less overhang from the spindle bearings than a large chuck would have.
Introduction of Machining
Machining as a shape-producing method is the most universally used and the most important of all manufacturing processes. Machining is a shape-producing process in which a power-driven device causes material to be removed in chip form. Most machining is done with equipment that supports both the work piece and cutting tool although in some cases portable equipment is used with unsupported workpiece.
Low setup cost for small Quantities. Machining has two applications in manufacturing. For casting, forging, and press working, each specific shape to be produced, even one part, nearly always has a high tooling cost. The shapes that may he produced by welding depend to a large degree on the shapes of raw material that are available. By making use of generally high cost equipment but without special tooling, it is possible, by machining; to start with nearly any form of raw material, so tong as the exterior dimensions are great enough, and produce any desired shape from any material. Therefore .machining is usually the preferred method for producing one or a few parts, even when the design of the part would logically lead to casting, forging or press working if a high quantity were to be produced.
Close accuracies, good finishes. The second application for machining is based on the high accuracies and surface finishes possible. Many of the parts machined in low quantities would be produced with lower but acceptable tolerances if produced in high quantities by some other process. On the other hand, many parts are given their general shapes by some high quantity deformation process and machined only on selected surfaces where high accuracies are needed. Internal threads, for example, are seldom produced by any means other than machining and small holes in press worked parts may be machined following the press working operations.
Primary Cutting Parameters
The basic tool-work relationship in cutting is adequately described by means of four factors: tool geometry, cutting speed, feed, and depth of cut.
The cutting tool must be made of an appropriate material; it must be strong, tough, hard, and wear resistant. The tool s geometry characterized by planes and angles, must be correct for each cutting operation. Cutting speed is the rate at which the work surface passes by the cutting edge. It may be expressed in feet per minute.
For efficient machining the cutting speed must be of a magnitude appropriate to the particular work-tool combination. In general, the harder the work material, the slower the speed.
Feed is the rate at which the cutting tool advances into the workpiece. "Where the workpiece or the tool rotates, feed is measured in inches per revolution. When the tool or the work reciprocates, feed is measured in inches per stroke, Generally, feed varies inversely with cutting speed for otherwise similar conditions.
The depth of cut, measured inches is the distance the tool is set into the work. It is the width of the chip in turning or the thickness of the chip in a rectilinear cut. In roughing operations, the depth of cut can be larger than for finishing operations.
The Effect of Changes in Cutting Parameters on Cutting Temperatures
In metal cutting operations heat is generated in the primary and secondary deformation zones and these results in a complex temperature distribution throughout the tool, workpiece and chip. A typical set of isotherms is shown in figure where it can be seen that, as could be expected, there is a very large temperature gradient throughout the width of the chip as the workpiece material is sheared in primary deformation and there is a further large temperature in the chip adjacent to the face as the chip is sheared in secondary deformation. This leads to a maximum cutting temperature a short distance up the face from the cutting edge and a small distance into the chip.
Since virtually all the work done in metal cutting is converted into heat, it could be expected that factors which increase the power consumed per unit volume of metal removed will increase the cutting temperature. Thus an increase in the rake angle, all other parameters remaining constant, will reduce the power per unit volume of metal removed and the cutting temperatures will reduce. When considering increase in unreformed chip thickness and cutting speed the situation is more complex. An increase in undeformed chip thickness tends to be a scale effect where the amounts of heat which pass to the workpiece, the tool and chip remain in fixed proportions and the changes in cutting temperature tend to be small. Increase in cutting speed; however, reduce the amount of heat which passes into the workpiece and this increase the temperature rise of the chip m primary deformation. Further, the secondary deformation zone tends to be smaller and this has the effect of increasing the temperatures in this zone. Other changes in cutting parameters have virtually no effect on the power consumed per unit volume of metal removed and consequently have virtually no effect on the cutting temperatures. Since it has been shown that even small changes in cutting temperature have a significant effect on tool wear rate it is appropriate to indicate how cutting temperatures can be assessed from cutting data.
The most direct and accurate method for measuring temperatures in high -speed-steel cutting tools is that of Wright &. Trent which also yields detailed information on temperature distributions in high-speed-steel cutting tools. The technique is based on the metallographic examination of sectioned high-speed-steel tools which relates microstructure changes to thermal history.
Trent has described measurements of cutting temperatures and temperature ?distributions for high-speed-steel tools when machining a wide range of workpiece materials. This technique has been further developed by using scanning electron ?microscopy to study fine-scale microstructure changes arising from over tempering of the tempered martens tic matrix of various high-speed-steels. This technique has also been used to study temperature distributions in both high-speed -steel single point turning tools and twist drills.
Wears of Cutting Tool
Discounting brittle fracture and edge chipping, which have already been dealt with, tool wear is basically of three types. Flank wear, crater wear, and notch wear. Flank wear occurs on both the major and the minor cutting edges. On the major cutting edge, which is responsible for bulk metal removal, these results in increased cutting forces and higher temperatures which if left unchecked can lead to vibration of the tool and workpiece and a condition where efficient cutting can no longer take place. On the minor cutting edge, which determines workpiece size and surface finish, flank wear can result in an over sized product which has poor surface finish. Under most practical cutting conditions, the tool will fail due to major flank wear before the minor flank wear is sufficiently large to result in the manufacture of an unacceptable component.
Because of the stress distribution on the tool face, the frictional stress in the region of sliding contact between the chip and the face is at a maximum at the start of the sliding contact region and is zero at the end. Thus abrasive wear takes place in this region with more wear taking place adjacent to the seizure region than adjacent to the point at which the chip loses contact with the face. This result in localized pitting of the tool face some distance up the face which is usually referred to as catering and which normally has a section in the form of a circular arc. In many respects and for practical cutting conditions, crater wear is a less severe form of wear than flank wear and consequently flank wear is a more common tool failure criterion. However, since various authors have shown that the temperature on the face increases more rapidly with increasing cutting speed than the temperature on the flank, and since the rate of wear of any type is significantly affected by changes in temperature, crater wear usually occurs at high cutting speeds.
At the end of the major flank wear land where the tool is in contact with the uncut workpiece surface it is common for the flank wear to be more pronounced than along the rest of the wear land. This is because of localised effects such as a hardened layer on the uncut surface caused by work hardening introduced by a previous cut, an oxide scale, and localised high temperatures resulting from the edge effect. This localised wear is usually referred to as notch wear and occasionally is very severe. Although the presence of the notch will not significantly affect the cutting properties of the tool, the notch is often relatively deep and if cutting were to continue there would be a good chance that the tool would fracture.
If any form of progressive wear allowed to continue, dramatically and the tool would fail catastrophically, i. e. the tool would be no longer capable of cutting and, at best, the workpiece would be scrapped whilst, at worst, damage could be caused to the machine tool. For carbide cutting tools and for all types of wear, the tool is said to have reached the end of its useful life long before the onset of catastrophic failure. For high-speed-steel cutting tools, however, where the wear tends to be non-uniform it has been found that the most meaningful and reproducible results can be obtained when the wear is allowed to continue to the onset of catastrophic failure even though, of course, in practice a cutting time far less than that to failure would be used. The onset of catastrophic failure is characterized by one of several phenomena, the most common being a sudden increase in cutting force, the presence of burnished rings on the workpiece, and a significant increase in the noise level.
Mechanism of Surface Finish Production
There are basically five mechanisms which contribute to the production of a surface which have been machined. These are:
(l) The basic geometry of the cutting process. In, for example, single point turning the tool will advance a constant distance axially per revolution of the work price and the resultant surface will have on it, when viewed perpendicularly to the direction of tool feed motion, a series of cusps which will have a basic form which replicates the shape of the tool in cut.
(2) The efficiency of the cutting operation. It has already been mentioned that cutting with unstable built-up-edges will produce a surface which contains hard built-up-edge fragments which will result in a de