机械制造技术课程设计-张力装置底架加工工艺及铣V型槽夹具设计

设计说明书 题目：张力装置底架零件的工艺规程及铣V型槽的钻床夹具设计全套图纸加扣 3346389411或3012250582摘 要本次设计内容涉及了机械制造工艺及机床夹具设计、金属切削机床、公差配合与测量等多方面的知识。张力装置底架加工工艺规程及铣槽的夹具设计是包括零件加工的工艺设计、工序设计以及专用夹具的设计三部分。在工艺设计中要首先对零件进行分析，了解零件的工艺再设计出毛坯的结构，并选择好零件的加工基准，设计出零件的工艺路线；接着对零件各个工步的工序进行尺寸计算，关键是决定出各个工序的工艺装备及切削用量；然后进行专用夹具的设计，选择设计出夹具的各个组成部件，如定位元件、夹紧元件、引导元件、夹具体与机床的连接部件以及其它部件；计算出夹具定位时产生的定位误差，分析夹具结构的合理性与不足之处，并在以后设计中注意改进。关键词：工艺、工序、切削用量、夹紧、定位、误差。ABSTRCTThis design content has involved the machine manufacture craft and the engine bed jig design, the metal-cutting machine tool, the common difference coordination and the survey and so on the various knowledge.The reduction gear box body components technological process and its the processing hole jig design is includes the components processing the technological design, the working procedure design as well as the unit clamp design three parts. Must first carry on the analysis in the technological design to the components, understood the components the craft redesigns the semi finished materials the structure, and chooses the good components the processing datum, designs the components the craft route; After that is carrying on the size computation to a components each labor step of working procedure, the key is decides each working procedure the craft equipment and the cutting specifications; Then carries on the unit clamp the design, the choice designs the jig each composition part, like locates the part, clamps the part, guides the part, to clamp concrete and the engine bed connection part as well as other parts; Position error which calculates the jig locates when produces, analyzes the jig structure the rationality and the deficiency, and will design in later pays attention to the improvement.Keywords: The craft, the working procedure, the cutting specifications, clamp, the localization, the error目 录序言1一. 零件分析 21.1 零件作用 21.2零件的工艺分析 2二. 工艺规程设计32.1确定毛坯的制造形式 42.2基面的选择 52.3制定工艺路线 52.4机械加工余量、工序尺寸及毛坯尺寸的确定 62.5确定切削用量及基本工时 7三 夹具设计 123.1问题的提出123.2定位基准的选择143.3定位误差分析163.4切削力及夹紧力计算183.5定向键与对刀装置设计223.6夹具设计及简要操作说明22总 结23致 谢24参考文献 25序 言机械制造业是制造具有一定形状位置和尺寸的零件和产品，并把它们装备成机械装备的行业。机械制造业的产品既可以直接供人们使用，也可以为其它行业的生产提供装备，社会上有着各种各样的机械或机械制造业的产品。我们的生活离不开制造业，因此制造业是国民经济发展的重要行业，是一个国家或地区发展的重要基础及有力支柱。从某中意义上讲，机械制造水平的高低是衡量一个国家国民经济综合实力和科学技术水平的重要指标。张力装置底架的加工工艺规程及其钻的夹具设计是在学完了机械制图、机械制造技术基础、机械设计、机械工程材料等进行课程设计之后的下一个教学环节。正确地解决一个零件在加工中的定位，夹紧以及工艺路线安排，工艺尺寸确定等问题，并设计出专用夹具，保证零件的加工质量。本次设计也要培养自己的自学与创新能力。因此本次设计综合性和实践性强、涉及知识面广。所以在设计中既要注意基本概念、基本理论，又要注意生产实践的需要，只有将各种理论与生产实践相结合，才能很好的完成本次设计。本次设计水平有限，其中难免有缺点错误，敬请老师们批评指正。一、 零件的分析1.1 零件的作用张力装置底架的作用，待查1.2 零件的工艺分析张力装置底架有2个加工面他们相互之间没有任何位置度要求。1.宽12的左右端面为基准的加工面，这组加工面主要是90x25端面和10的孔，2.以10孔为基准的加工面，这组加工面主要是铣9x60v型槽和钻2-M8孔。二. 工艺规程设计2.1 确定毛坯的制造形式零件材料为HT200，考虑到运行时经常需要挂倒档以倒行或辅助转向，因此零件在工作过程中经常受到冲击性载荷，采用这种材料零件的强度也能保证。由于零件成批生产，而且零件的轮廓尺寸不大，选用砂型铸造，采用机械翻砂造型，铸造精度为2级，能保证铸件的尺寸要求，这从提高生产率和保证加工精度上考虑也是应该的。2.2 基面的选择粗基准选择应当满足以下要求：（1）粗基准的选择应以加工表面为粗基准。目的是为了保证加工面与不加工面的相互位置关系精度。如果工件上表面上有好几个不需加工的表面，则应选择其中与加工表面的相互位置精度要求较高的表面作为粗基准。以求壁厚均匀、外形对称、少装夹等。（2） 选择加工余量要求均匀的重要表面作为粗基准。例如：机床床身导轨面是其余量要求均匀的重要表面。因而在加工时选择导轨面作为粗基准，加工床身的底面，再以底面作为精基准加工导轨面。这样就能保证均匀地去掉较少的余量，使表层保留而细致的组织，以增加耐磨性。（3） 应选择加工余量最小的表面作为粗基准。这样可以保证该面有足够的加工余量。（4） 应尽可能选择平整、光洁、面积足够大的表面作为粗基准，以保证定位准确夹紧可靠。有浇口、冒口、飞边、毛刺的表面不宜选作粗基准，必要时需经初加工。（5） 粗基准应避免重复使用，因为粗基准的表面大多数是粗糙不规则的。多次使用难以保证表面间的位置精度。基准的选择是工艺规程设计中的重要工作之一，他对零件的生产是非常重要的。先选取宽12的端面作为定位基准，。精基准的选择精基准的选择应满足以下原则：（1）“基准重合”原则 应尽量选择加工表面的设计基准为定位基准，避免基准不重合引起的误差。（2）“基准统一”原则 尽可能在多数工序中采用同一组精基准定位，以保证各表面的位置精度，避免因基准变换产生的误差，简化夹具设计与制造。（3）“自为基准”原则 某些精加工和光整加工工序要求加工余量小而均匀，应选择该加工表面本身为精基准，该表面与其他表面之间的位置精度由先行工序保证。（4）“互为基准”原则 当两个表面相互位置精度及自身尺寸、形状精度都要求较高时，可采用“互为基准”方法，反复加工。（5）所选的精基准 应能保证定位准确、夹紧可靠、夹具简单、操作方便。以已经加工好的10孔和一端面为定位精基准，加工其它表面及孔。主要考虑精基准重合的问题，当设计基准与工序基准不重合的时候，应该进行尺寸换算，这在以后还要进行专门的计算，在此不再重复2.3 制定工艺路线制订工艺路线的出发点，应当是使零件的几何形状、尺寸精度及位置精度等技术要求能得到合理的保证。在生产纲领已确定为成批生产的条件下，可以考虑采用万能型机床配以专用夹具，并尽量使工序集中在提高生产率。除此以外，还应当考虑经济效果，以便使生产成本尽量降下来。 制定以下两种工艺方案：方案一1铸造铸造2时效处理时效处理3铣铣12mm上端面4铣铣12mm下端面5钻铣90x25端面6铣钻2-10孔7镗铣9x60v型槽8钻钻2-M8孔9检验检验，入库方案二1铸造铸造2时效处理时效处理3铣铣12mm上端面4铣铣12mm下端面5钻钻2-10孔6铣铣90x25端面7镗铣9x60v型槽8钻钻2-M8孔9检验检验，入库工艺方案一和方案二的区别在于方案二把钻2-10孔放在铣90x25端面的前面，而方案一把铣90x25端面放在钻2-10孔的前面，这样我们做钻孔的时间就可以利用加工好的面作为定位基准，这样能能更好地保证工件钻孔时的位置度要求。具体的加工路线如下1铸造铸造2时效处理时效处理3铣铣12mm上端面4铣铣12mm下端面5钻铣90x25端面6铣钻2-10孔7镗铣9x60v型槽8钻钻2-M8孔9检验检验，入库2.4 机械加工余量、工序尺寸及毛坯尺寸的确定壳体零件材料为HT200 重量为1生产类型为大批量生产，采用砂型机铸造毛坯。1、 不加工表面毛坯尺寸不加工表面毛坯按照零件图给定尺寸为自由度公差，由铸造可直接获得。2、 宽12两端面由于壳体底面要与其他接触面接触，同时又是10孔的中心线的基准。粗糙度要求为6.3，查相关资料知余量留2.5比较合适。3、孔毛坯为空心，铸造出孔。孔的精度要求介于IT7IT8之间，参照参数文献，确定工艺尺寸余量为2.5mm2.5 确定切削用量及基本工时工序1：铸造工序2：退火处理工序3：铣12mm上端面1. 选择刀具刀具选取不重磨损硬质合金套式面铣刀，刀片采用YG8,，。2. 决定铣削用量1） 决定铣削深度 因为加工余量不大，一次加工完成2） 决定每次进给量及切削速度 根据X51型铣床说明书，其功率为为7.5kw，中等系统刚度。根据表查出 ，则按机床标准选取1600当1600r/min时按机床标准选取3） 计算工时切削工时：，则机动工时为工序4：铣12mm下端面铣12mm下端面和铣12mm上端面的切削用量和计算工时相同，在此不再累述。工序5：铣90x25端面1. 选择刀具刀具选取不重磨损硬质合金套式面铣刀，刀片采用YG8,，。2. 决定铣削用量4） 决定铣削深度 因为加工余量不大，故可在一次走刀内铣完，则5） 决定每次进给量及切削速度 根据X51型铣床说明书，其功率为为7.5kw，中等系统刚度。根据表查出 ，则按机床标准选取1000当1000r/min时按机床标准选取6） 计算工时切削工时：l=90 ，则机动工时为工序6：钻2-10孔确定进给量：根据参考文献表2-7，当钢的，时，。由于本零件在加工10孔时属于低刚度零件，故进给量应乘以系数0.75，则根据Z525机床说明书，现取切削速度：根据参考文献表2-13及表2-14，查得切削速度所以 根据机床说明书，取，故实际切削速度为切削工时：，则机动工时为工序8：钻2-M8孔工步一：钻M8螺纹底孔， 选用高速钢锥柄麻花钻（工艺表3.16） 由切削表2.7和工艺表4.216查得 （切削表2.15） 按机床选取 基本工时： min工步二：攻螺纹M8mm： 选择M8mm高速钢机用丝锥 等于工件螺纹的螺距，即 按机床选取 基本工时：三、 铣床夹具设计3.1问题提出本夹具主要用来工序7：铣960v型槽，采用张力装置底架基准B和两个10H7孔定位。3.2 定位基准的选择拟定加工路线的第一步是选择定位基准。定位基准的选择必须合理，否则将直接影响所制定的零件加工工艺规程和最终加工出的零件质量。基准选择不当往往会增加工序或使工艺路线不合理，或是使夹具设计更加困难甚至达不到零件的加工精度（特别是位置精度）要求。因此我们应该根据零件图的技术要求，从保证零件的加工精度要求出发，合理选择定位基准。此零件图没有较高的技术要求，也没有较高的平行度和对称度要求，所以我们应考虑如何提高劳动效率，降低劳动强度，提高加工精度。3.3定位误差分析3.3.1移动时基准位移误差 （式3-1）式中： A型固定式定位销孔的最大偏差 A型固定式定位销孔的最小偏差 A型固定式定位销定位孔与定位销最小配合间隙代入（式3-1）得： =0.015+0+0.013 =0.028（mm) 3.3.2转角误差 （式3-2）式中： A型固定式定位销孔的最大偏差 A型固定式定位销孔的最小偏差 A型固定式定位销定位孔与定位销最小配合间隙 B型固定式定位销孔的最大偏差 B型固定式定位销孔的最小偏差 B型固定式定位销定位孔与定位销最小配合间隙其中： 则代入（式3-2）得：则：0.010033.4夹紧力计算3.4.1铣削力查简明机床夹具设计手册表3-3得切削力计算公式：由工时计算知，=0.3mm，由简明机床夹具设计手册表3-3知即 5101.8660.3820.0249.88N684N3.4.2夹紧力所需夹紧力，查表5得，安全系数K=式中为各种因素的安全系数，查表得：K=1.872，当计算K2.5时，取K=2.5孔轴部分由M6螺母锁紧，查参考文献2，P92，表3-16螺母的夹紧力为2903N=7257.5N由上计算得，因此采用该夹紧机构工作是可靠的。3.5定向键与对刀装置设计根据GB220780定向键结构如图所示：图 1 夹具体槽形与螺钉图根据T形槽的宽度 a=18mm 定向键的结构尺寸如下： 图2 定位键的规格及主要尺寸铣壳体底面，为了防止铣刀铣到工件，故需要限制铣刀的位置，特制对刀块。 图3对刀平塞尺 图4 对刀平塞尺的规格及主要尺寸3.6夹具设计及操作简要说明如前所述，在设计夹具时，应该注意提高劳动生产率避免干涉。应使夹具结构简单，便于操作，降低成本。提高夹具性价比。本道工序为铣床夹具选择是用移动压板、可调支承钉、螺柱、六角螺母等组成的夹紧机构进行夹紧工件。本工序为铣削余量小，铣削力小，所以一般的手动夹紧就能达到本工序的要求。总 结这次设计是大学学习中最重要的一门科目，它要求我们把大学里学到的所有知识系统的组织起来，进行理论联系实际的总体考虑，需把金属切削原理及刀具、机床概论、公差与配合、机械加工质量、机床夹具设计、机械制造工艺学等专业知识有机的结合起来。同时也培养了自己的自学与创新能力。因此本次设计综合性和实践性强、涉及知识面广。所以在设计中既了解了基本概念、基本理论，又注意了生产实践的需要，将各种理论与生产实践相结合，来完成本次设计。 这次设计是培养学生综合运用所学知识,发现,提出,分析和解决实际问题,锻炼实践能力的重要环节,更是在学完大学所学的所有专业课及生产实习的一次理论与实践相结合的综合训练。这次设计虽然只有三个月时间，但在这三个月时间中使我对这次课程设计有了很深的体会。 这次毕业设计使我以前所掌握的关于零件加工方面有了更加系统化和深入合理化的掌握。比如参数的确定、计算、材料的选取、加工方式的选取、刀具选择、量具选择等； 也培养了自己综合运用设计与工艺等方面的知识； 以及自己独立思考能力和创新能力得到更进一步的锻炼与提高；再次体会到理论与实践相结合时，理论与实践也存在差异。回顾起此次设计，至今我仍感慨颇多，的确，从选题到完成定稿，从理论到实践，在整整一学期的日子里，可以说学到了很多很多的的东西，同时巩固了以前所学过的知识，而且学到了很多在书本上所没有学到过的知识。通过这次毕业设计使我懂得了理论与实际相结合是很重要的，只有理论知识是远远不够的，只有把所学的理论知识与实践相结合起来，从理论中得出结论，才能真正的实用，在生产过程中得到应用。在设计的过程中遇到了许多问题，当然也发现了自己的不足之处，对以前所学过的知识理解得不够深刻，掌握得不够牢固，通过这次毕业设计，让自己把以前所学过的知识重新复习了一遍。这次毕业设计虽然顺利完成了，也解决了许多问题，也碰到了许多问题，老师的辛勤指导下，都迎刃而解。同时，在老师的身上我也学得到很多额外的知识，在此我表示深深的感谢！同时，对给过我帮助的所有同学和各位教研室指导老师再次表示忠心的感谢！致 谢这次设计使我收益不小，为我今后的学习和工作打下了坚实和良好的基础。但是，查阅资料尤其是在查阅切削用量手册时，数据存在大量的重复和重叠，由于经验不足，在选取数据上存在一些问题，不过我的指导老师每次都很有耐心地帮我提出宝贵的意见，在我遇到难题时给我指明了方向，最终我很顺利的完成了毕业设计。这次设计成绩的取得，与指导老师的细心指导是分不开的。在此，我衷心感谢我的指导老师，特别是每次都放下她的休息时间，耐心地帮助我解决技术上的一些难题，她严肃的科学态度，严谨的治学精神，精益求精的工作作风，深深地感染和激励着我。从课题的选择到项目的最终完成，她都始终给予我细心的指导和不懈的支持。多少个日日夜夜，她不仅在学业上给我以精心指导，同时还在思想、生活上给我以无微不至的关怀，除了敬佩指导老师的专业水平外，她的治学严谨和科学研究的精神也是我永远学习的榜样，并将积极影响我今后的学习和工作。在此谨向指导老师致以诚挚的谢意和崇高的敬意。 参 考 文 献1. 切削用量简明手册,艾兴、肖诗纲主编,机械工业出版社出版，1994年2.机械制造工艺设计简明手册，李益民主编，机械工业出版社出版，1994年3.机床夹具设计，哈尔滨工业大学、上海工业大学主编，上海科学技术出版社出版，1983年4.机床夹具设计手册，东北重型机械学院、洛阳工学院、一汽制造厂职工大学编，上海科学技术出版社出版，1990年5.金属机械加工工艺人员手册，上海科学技术出版社，1981年10月6.机械制造工艺学，郭宗连、秦宝荣主编，中国建材工业出版社出版，1997年外文文献原文：Basic Machining Operations and Cutting TechnologyBasic Machining Operations Machine tools have evolved from the early foot-powered lathes of the Egyptians and John Wilkinsons 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 pre