汽车变速箱加工工艺及夹具设计【毕业设计资料】【CAD图纸和毕业论文】
收藏
资源目录
压缩包内文档预览:(预览前20页/共64页)
编号:316257
类型:共享资源
大小:1.17MB
格式:RAR
上传时间:2014-08-28
上传人:好资料QQ****51605
认证信息
个人认证
孙**(实名认证)
江苏
IP属地:江苏
45
积分
- 关 键 词:
-
a1
工艺
汽车
变速箱
加工
夹具
设计
- 资源描述:
-
【温馨提示】 购买原稿文件请充值后自助下载。
[全部文件] 那张截图中的文件为本资料所有内容,下载后即可获得。
预览截图请勿抄袭,原稿文件完整清晰,无水印,可编辑。
有疑问可以咨询QQ:414951605或1304139763
致 谢
摘要
本设计是汽车变速箱箱体零件的加工工艺规程及一些工序的专用夹具设计。汽车变速箱箱体零件的主要加工表面是平面及孔系。一般来说,保证平面的加工精度要比保证孔系的加工精度容易。因此,本设计遵循先面后孔的原则。并将孔与平面的加工明确划分成粗加工和精加工阶段以保证孔系加工精度。基准选择以变速箱箱体的输入轴和输出轴的支承孔作为粗基准,以顶面与两个工艺孔作为精基准。主要加工工序安排是先以支承孔系定位加工出顶平面,再以顶平面与支承孔系定位加工出工艺孔。在后续工序中除个别工序外均用顶平面和工艺孔定位加工其他孔系与平面。支承孔系的加工采用的是坐标法镗孔。整个加工过程均选用组合机床。夹具选用专用夹具,夹紧方式多选用气动夹紧,夹紧可靠,机构可以不必自锁。因此生产效率较高。适用于大批量、流水线上加工。能够满足设计要求。
关键词:变速箱;加工工艺;专用夹具
Abstract
The design is about the special-purpose clamping apparatus of the machining technology process and some working procedures of the car gearbox parts. The main machining surface of the car gearbox parts is the plane and a series of hole. Generally speaking, to guarantee the working accuracy of the plane is easier than to guarantee the hole’s. So the design follows the principle of plane first and hole second. And in order to guarantee the working accuracy of the series of hole, the machining of the hole and the plane is clearly divided into rough machining stage and finish machining stage. The supporting hole of the input bearing and output bearing is as the rough datum. And the top area and two technological holes are as the finish datum. The main process of machining technology is that first, the series of supporting hole fix and machine the top plane, and then the top plane and the series of supporting hole fix and machine technological hole. In the follow-up working procedure, all working procedures except several special ones fix and machine other series of hole and plane by using the top plane and technological hole. The machining way of the series of supporting hole is to bore hole by coordinate. The combination machine tool and special-purpose clamping apparatus are used in the whole machining process. The clamping way is to clamp by pneumatic and is very helpful. The instruction does not have to lock by itself. So the product efficiency is high. It is applicable for mass working and machining in assembly line. It can meet the design requirements.
Key words: Gearbox; machining technology; special-purpose clamping apparatus
目 录
第一章汽车变速箱加工工艺规程设计 ………………………………………(1)
1.1零件的分析 …………………………………………………………………(1)
1.1.1零件的作用…………………………………………………………………(1)
1.1.2零件的工艺分析……………………………………………………………(1)
1.2变速箱箱体加工的主要问题和工艺过程设计所应采取的相应措施 ……(2)
1.2.1孔和平面的加工顺序………………………………………………………(2)
1.2.2孔系加工方案选择…………………………………………………………(2)
1.3变速箱箱体加工定位基准的选择……………………………………………(5)
1.3.1粗基准的选择………………………………………………………………(5)
1.3.2精基准的选择………………………………………………………………(5)
1.4变速箱箱体加工主要工序安排………………………………………………(5)
1.5机械加工余量、工序尺寸及毛坯尺寸的确定………………………………(7)
1.6确定切削用量及基本工时(机动时间)……………………………………(12)
1.7时间定额计算及生产安排…………………………………………………(33)
附表1:机械加工工艺规程综合卡片……………………………………………(41)
第二章 专用夹具设计……………………………………………………………(47)
2.1加工工艺孔夹具设计………………………………………………………(47)
2.1.1定位基准的选择…………………………………………………………(47)
2.1.2切削力的计算与夹紧力分析……………………………………………(47)
2.1.3夹紧元件及动力装置确定………………………………………………(48)
2.1.4钻套、衬套、钻模板及夹具体设计………………………………………(49)
2.1.5夹具精度分析……………………………………………………………(51)
2.1.6夹具设计及操作的简要说明……………………………………………(52)
2.2粗铣前后端面夹具设计……………………………………………………(53)
2.2.1定位基准的选择…………………………………………………………(53)
2.2.2定位元件的设计…………………………………………………………(53)
2.2.3定位误差分析……………………………………………………………(55)
2.2.4铣削力与夹紧力计算……………………………………………………(55)
2.2.5定向键与对刀装置设计…………………………………………………(56)
2.2.6夹紧装置及夹具体设计…………………………………………………(57)
2.2.7夹具设计及操作的简要说明……………………………………………(59)
结束语……………………………………………………………………………(59)
参考文献…………………………………………………………………………(60)
致 谢……………………………………………………………………………(61)
附件1:毕业设计(论文)任务书…………………………………………………(62)
附件2:毕业设计(论文)指导教师评语…………………………………………(64)
附件3:毕业设计(论文)评阅人评语……………………………………………(65)
附件4:毕业设计(论文)答辩小组评语…………………………………………(66)
外国文献翻译……………………………………………………………………(67)







- 内容简介:
-
毕业设计(论文)任务书机制 专业 2001 年级2005 年3 月28 日批准专业负责人: 乔水明 发给学生: 李尚勤 1.毕业设计(论文)题目:汽车变速箱加工工艺及夹具设计2.学生完成全部任务期限:2005 年6 月17 日3.任务要求:(1)、设计内容:制订年产10万台汽车变速箱加工工艺,设计铣端夹具及加工工艺孔夹具各一套。 (2)、图纸要求:汽车变速箱零件工作图,两套夹具装配图,夹具专用零件图二到三张。 (3)、计算与说明:加工工艺分析、工艺尺寸计算、定位误差计算、切削用量、工时定额计算、夹具精度分析、说明书、工艺卡。 4.实验(调验)部分内容要求:_5.文献查阅及翻译要求:(1)、翻译有关机械制造方面10000个字符以上的外文资料,字数不得少于三千。 (2)、查阅资料:机械制造工艺学、机械加工工艺人员手册、机床夹具手册、机床夹具图册、金属切削手册、典型零件机械加工工艺、毕业设计指导资料等(不少于十五本资料)。 6.发出日期: 2005 年4 月5 日指导教师:陈广凌 (签名)指导教师:张彦博 (签名)完成任务日期:2005 年6 月17 日学生:李尚勤 (签名)攀枝花学院Panzhihua University本科毕业设计(论文)文献综述院 (系): 机电工程学院 专 业: 机械设计制造及其自动化班 级: 机制自动化一班 学生姓名: 伍钢 学 号: 200310621004 2007 年 4 月 26 日XXXXX学院毕业设计(论文)开题报告设计(论文)名称汽车变速箱加工工艺及夹具设计设计(论文)类型指导教师学生姓名学号院、专业、班级一、选题依据(简述研究现状或生产需求情况,说明该设计(论文)目的意义)制造业特别是机械制造业是国民经济的支柱产业,现代制造业正在改变着人们的生产方式、生活方式、经营管理模式乃至社会的组织结构和文化。由于中国潜在的巨大市场和丰富的劳动力资源,世界的制造业正在向中国转移,中国正在成为世界的制造大国. 现代制造技术是以传统制造技术与计算机技术、信息技术、自动控制技术等现代高新技术交叉融合的结果,是一个集机械、电子、信息、材料与管理技术于一体的新型交叉学科,它使制造技术的技术内涵和水平发生了质的变化。我所选择的题目就是通过优化工艺和设计专业夹具来达到提高生产率和减小加工误差的目的,这一课题可以把我三年来学到的机械制造知识应用于实践也是对我学习的一次检验。二、设计(论文研究)思路及工作方法(1)零件的工艺分析,毛坯的选择;主要表面和定位基准的选择;主要表面的加工;次要表面的加工(2)确定零件的工艺规程(3)钻模的设计(4)夹具装配图与零件图的设计(5)撰写毕业设计说明书(6)答辩三、设计(论文研究)任务完成的阶段内容及时间安排X月XX号开始进行毕业设计、熟悉题目及要求X月XX号设计资料的收集及借阅X月XX号分析研究所得到的设计资料X月XX号方案设计、比较X月XX号设计方案实施(设计、计算等)X月XX号设计、论文整理及修改X月XX号毕业设计答辩指导教师意见指导教师签字: 年 月 日教研室毕业设计(论文)工作组审核意见难度分量综合训练程度教研室主任: 年 月 日设计(论文)类型:A理论研究;B应用研究;C软件设计;D-其它等。攀枝花学院毕业设计(论文)摘要本设计是汽车变速箱箱体零件的加工工艺规程及一些工序的专用夹具设计。汽车变速箱箱体零件的主要加工表面是平面及孔系。一般来说,保证平面的加工精度要比保证孔系的加工精度容易。因此,本设计遵循先面后孔的原则。并将孔与平面的加工明确划分成粗加工和精加工阶段以保证孔系加工精度。基准选择以变速箱箱体的输入轴和输出轴的支承孔作为粗基准,以顶面与两个工艺孔作为精基准。主要加工工序安排是先以支承孔系定位加工出顶平面,再以顶平面与支承孔系定位加工出工艺孔。在后续工序中除个别工序外均用顶平面和工艺孔定位加工其他孔系与平面。支承孔系的加工采用的是坐标法镗孔。整个加工过程均选用组合机床。夹具选用专用夹具,夹紧方式多选用气动夹紧,夹紧可靠,机构可以不必自锁。因此生产效率较高。适用于大批量、流水线上加工。能够满足设计要求。关键词:变速箱;加工工艺;专用夹具AbstractThe design is about the special-purpose clamping apparatus of the machining technology process and some working procedures of the car gearbox parts. The main machining surface of the car gearbox parts is the plane and a series of hole. Generally speaking, to guarantee the working accuracy of the plane is easier than to guarantee the holes. So the design follows the principle of plane first and hole second. And in order to guarantee the working accuracy of the series of hole, the machining of the hole and the plane is clearly divided into rough machining stage and finish machining stage. The supporting hole of the input bearing and output bearing is as the rough datum. And the top area and two technological holes are as the finish datum. The main process of machining technology is that first, the series of supporting hole fix and machine the top plane, and then the top plane and the series of supporting hole fix and machine technological hole. In the follow-up working procedure, all working procedures except several special ones fix and machine other series of hole and plane by using the top plane and technological hole. The machining way of the series of supporting hole is to bore hole by coordinate. The combination machine tool and special-purpose clamping apparatus are used in the whole machining process. The clamping way is to clamp by pneumatic and is very helpful. The instruction does not have to lock by itself. So the product efficiency is high. It is applicable for mass working and machining in assembly line. It can meet the design requirements.Key words: Gearbox; machining technology; special-purpose clamping apparatus 目 录第一章 汽车变速箱加工工艺规程设计 (1)1.1零件的分析 (1)1.1.1零件的作用(1)1.1.2零件的工艺分析(1)1.2变速箱箱体加工的主要问题和工艺过程设计所应采取的相应措施 (2)1.2.1孔和平面的加工顺序(2)1.2.2孔系加工方案选择(2)1.3变速箱箱体加工定位基准的选择(5)1.3.1粗基准的选择(5)1.3.2精基准的选择(5)1.4变速箱箱体加工主要工序安排(5)1.5机械加工余量、工序尺寸及毛坯尺寸的确定(7)1.6确定切削用量及基本工时(机动时间)(12)1.7时间定额计算及生产安排(33)附表1:机械加工工艺规程综合卡片(41)第二章 专用夹具设计(47)2.1加工工艺孔夹具设计(47)2.1.1定位基准的选择(47)2.1.2切削力的计算与夹紧力分析(47)2.1.3夹紧元件及动力装置确定(48)2.1.4钻套、衬套、钻模板及夹具体设计(49)2.1.5夹具精度分析(51)2.1.6夹具设计及操作的简要说明(52)2.2粗铣前后端面夹具设计(53)2.2.1定位基准的选择(53)2.2.2定位元件的设计(53)2.2.3定位误差分析(55)2.2.4铣削力与夹紧力计算(55)2.2.5定向键与对刀装置设计(56)2.2.6夹紧装置及夹具体设计(57)2.2.7夹具设计及操作的简要说明(59)结束语(59)参考文献(60)致 谢(61)附件1:毕业设计(论文)任务书(62)附件2:毕业设计(论文)指导教师评语(64)附件3:毕业设计(论文)评阅人评语(65)附件4:毕业设计(论文)答辩小组评语(66)外国文献翻译(67) V文献综述:拨叉C的加工工艺及其夹具设计1 前言夹具设计作为高等工科院校教学的基本训练科目,在毕业设计中占极其重要的位置。夹具结构设计在加深我们对课程基本理论的理解和加强对解决工程实际问题能力的培养方面发挥着极其重要的作用。因此,选择拨叉的夹具设计能很好的综合考查我们大学四年来所学知识。本次所选设计内容主要包括:拨叉C工艺路线的确定,夹具方案的优选,各种图纸的绘制,设计说明书的编写等。本次综述的目的就是分析研究夹具在国内外的研究现状及拨叉类夹具的发展趋势。夹具是工艺装备的主要组合部分,在机械制造中占有重要地位,夹具对保证产品质量,提高生产率,减轻劳动强度,缩短产品生产周期等都具有重要意义。随着先进制造技术的发展和市场竞争的加剧,传统的夹具设计方式已成为企业中产品快速上市的瓶颈,企业迫切需要提高夹具设计的效率。目前,大批量生产正逐渐成为现代机械制造业新的生产模式。在这种模式中,要求加工机床和夹具装备具有更好的柔性,以缩短生产准备时间、降低生产成本,所以,按手动夹紧的方法已不能满足生产发展的要求,而气动、液压夹紧等夹具正是适应这一生产模式的工装设备。它对缩短工艺装备的设计、制造周期起到至关重要的作用。国外为了适应这种生产模式,也把柔性制造系统作为开发新产品的有效手段,并将其作为机械制造业的主要发展。2 正文今日五金网站一篇关于机床夹具发展趋势的文章上指出,夹具技术正朝着高精、高效、模块、组合、通用、经济方向发展,夹具的通用性直接影响其经济性。采用模块、组合式的夹具系统,一次性投资比较大,只有夹具系统的可重组性、可重构性及可扩展性功能强,应用范围广,通用性好,夹具利用率高,收回投资快,才能体现出经济性好。同时也指出,为了提高机床的生产效率,双面、四面和多件装夹的夹具产品越来越多。为了减少工件的安装时间,各种自动定心夹紧、精密平口钳、杠杆夹紧、凸轮夹紧、气动和液压夹紧等,快速夹紧功能部件不断地推陈出新。新型的电控永磁夹具,加紧和松开工件只用12秒,夹具结构简化,为机床进行多工位、多面和多件加工创造了条件。河北工业大学学报2002年05期夹具设计技术发展综述一文中提到, 随着科学技术的发展,和社会市场需要,夹具的设计在逐步的超向柔性制造系统方向发展。迄今为止,夹具仍是机电产品制造中必不可缺的四大工具之一,刀具本身已高度标准化,用户只需要按品种、规格选用采购。而模具和夹具则和产品息息相关,产品一有变化就需重新制作,通常是属于专用性质的工具,模具已发展成为独立的行业;夹具在国内外也正在逐渐形成一个依附于机床业或独立的小行业。 组合夹具不仅具有标准化、模块化、组合化等当代先进设计思想,又符合节约资源的原则,更适合绿色制造的环境保护原理。所以是今后夹具技术的一个重要发展方向单位。 同时在夹具设计过程中,对于被加工零件的定位、夹紧等主要问题,设计人员一般都会考虑的比较周全,但是,夹具设计还经常会遇到一些小问题,这些小问题如果处理不好,也会给夹具的使用造成许多不便,甚至会影响到工件的加工精度。随着机械工业的迅速发展,对产品的品种和生产率提出了愈来愈高的要求,使多品种,中小批生产作为机械生产的主流,为了适应机械生产的这种发展趋势,必然对机床夹具提出更高的要求。综合以上参考资料它主要表现在以下几个方面:2.1 加强机床夹具的三化工作 为了加速新产品的投产,简化设计工作,加速工艺装备的准备工作,以获得良好的技术经济效果,必须重视机床夹具的标准化,系列化和通用化工作。2.2 大力研制推广实用新型机床夹具 在单件,小批生产或新产品试制中,应推广使用组合夹具和半组合夹具。在多品种,中小批生产中,应大力推广使用可调夹具,尤其是成组夹具。2.3 提高夹具的机械化,自动化水平 近十几年来,高效,自动化夹具得到了迅速的发展。主要原因是由于数控机床,组合机床及其它高效自动化机床的出现,要求夹具能适应机床的要求,才能更好的发挥机床的作用。3 总结利用更好的夹具,可以提高劳动生产率,提高加工精度,减少废品,可以扩大机床的工艺范围,改善操作的劳动条件。因此,夹具是机械制造中的一项重要的工艺装备。一个好的夹具是加工出合格产品的首要条件,为了让夹具有更好的发展,夹具行业应加强产、学、研协作的力度,加快用高新技术改造和提升夹具技术水平的步伐,创建夹具专业技术网站,充分利用现代信息和网络技术,与时俱进地创新和发展夹具技术。主动与国外夹具厂商联系,争取合资与合作,引进技术,这是改造和发展我国夹具行业较为行之有效的途径。参 考 文 献1李旦等机床专用夹具图册M,哈尔滨:哈尔滨工业大学出版社,20052机床夹具发展趋势,今日五金网 /china/exhibition_info.do?ID=170673张龙勋机械制造工艺学课程设计指导书M.,北京:机械工业出版社,19934李德红等夹具设计技术发展综述J,河北工业大学学报2002年05期5朱耀祥夹具发展综述J,机电产品市场2002年05期6王启平机床夹具设计M,哈尔滨:哈尔滨工业大学出版社,1988.7林文焕,陈本通机床夹具设计M,北京:国防工业出版社,1987.8邱宣怀机械设计第四版M,北京:高等教育出版社,19979柯明扬机械制造工艺学M,北京:北京航天航空大学出版社,1995第一章 汽车变速箱加工工艺规程设计1.1零件的分析1.1.1零件的作用1.1.2零件的工艺分析1.2变速箱箱体加工的主要问题和工艺过程设计所应采取的相应措施1.2.1孔和平面的加工顺序1.2.2孔系加工方案选择1.3变速箱箱体加工定位基准的选择1.3.1粗基准的选择1.3.2精基准的选择1.4变速箱箱体加工主要工序安排1.5机械加工余量、工序尺寸及毛坯尺寸的确定1.6确定切削用量及基本工时(机动时间)1.7时间定额计算及生产安排第二章 专用夹具设计2.1加工工艺孔夹具设计2.1.1定位基准的选择2.1.2切削力的计算与夹紧力分析2.1.3夹紧元件及动力装置确定2.1.4钻套、衬套、钻模板及夹具体设计2.1.5夹具精度分析2.1.6夹具设计及操作的简要说明2.2粗铣前后端面夹具设计2.2.1定位基准的选择2.2.2定位元件的设计2.2.3定位误差分析2.2.4铣削力与夹紧力计算2.2.5定向键与对刀装置设计2.2.6夹紧装置及夹具体设计2.2.7夹具设计及操作的简要说明参考文献致 谢攀枝花学院毕业设计(论文)附件1:外语文献翻译摘自: 制造工程与技术(机加工)(英文版) Manufacturing Engineering and TechnologyMachining 机械工业出版社 2004年3月第1版 美 s. 卡尔帕基安(Serope kalpakjian) s.r 施密德(Steven R.Schmid) 著原文:20.9 MACHINABILITYThe machinability of a material usually defined in terms of four factors:1、 Surface finish and integrity of the machined part;2、 Tool life obtained;3、 Force and power requirements;4、 Chip control. Thus, good machinability good surface finish and integrity, long tool life, and low force And power requirements. As for chip control, long and thin (stringy) cured chips, if not broken up, can severely interfere with the cutting operation by becoming entangled in the cutting zone.Because of the complex nature of cutting operations, it is difficult to establish relationships that quantitatively define the machinability of a material. In manufacturing plants, tool life and surface roughness are generally considered to be the most important factors in machinability. Although not used much any more, approximate machinability ratings are available in the example below.20.9.1 Machinability Of SteelsBecause steels are among the most important engineering materials (as noted in Chapter 5), their machinability has been studied extensively. The machinability of steels has been mainly improved by adding lead and sulfur to obtain so-called free-machining steels.Resulfurized and Rephosphorized steels. Sulfur in steels forms manganese sulfide inclusions (second-phase particles), which act as stress raisers in the primary shear zone. As a result, the chips produced break up easily and are small; this improves machinability. The size, shape, distribution, and concentration of these inclusions significantly influence machinability. Elements such as tellurium and selenium, which are both chemically similar to sulfur, act as inclusion modifiers in resulfurized steels.Phosphorus in steels has two major effects. It strengthens the ferrite, causing increased hardness. Harder steels result in better chip formation and surface finish. Note that soft steels can be difficult to machine, with built-up edge formation and poor surface finish. The second effect is that increased hardness causes the formation of short chips instead of continuous stringy ones, thereby improving machinability.Leaded Steels. A high percentage of lead in steels solidifies at the tip of manganese sulfide inclusions. In non-resulfurized grades of steel, lead takes the form of dispersed fine particles. Lead is insoluble in iron, copper, and aluminum and their alloys. Because of its low shear strength, therefore, lead acts as a solid lubricant (Section 32.11) and is smeared over the tool-chip interface during cutting. This behavior has been verified by the presence of high concentrations of lead on the tool-side face of chips when machining leaded steels.When the temperature is sufficiently high-for instance, at high cutting speeds and feeds (Section 20.6)the lead melts directly in front of the tool, acting as a liquid lubricant. In addition to this effect, lead lowers the shear stress in the primary shear zone, reducing cutting forces and power consumption. Lead can be used in every grade of steel, such as 10xx, 11xx, 12xx, 41xx, etc. Leaded steels are identified by the letter L between the second and third numerals (for example, 10L45). (Note that in stainless steels, similar use of the letter L means “low carbon,” a condition that improves their corrosion resistance.)However, because lead is a well-known toxin and a pollutant, there are serious environmental concerns about its use in steels (estimated at 4500 tons of lead consumption every year in the production of steels). Consequently, there is a continuing trend toward eliminating the use of lead in steels (lead-free steels). Bismuth and tin are now being investigated as possible substitutes for lead in steels.Calcium-Deoxidized Steels. An important development is calcium-deoxidized steels, in which oxide flakes of calcium silicates (CaSo) are formed. These flakes, in turn, reduce the strength of the secondary shear zone, decreasing tool-chip interface and wear. Temperature is correspondingly reduced. Consequently, these steels produce less crater wear, especially at high cutting speeds.Stainless Steels. Austenitic (300 series) steels are generally difficult to machine. Chatter can be s problem, necessitating machine tools with high stiffness. However, ferritic stainless steels (also 300 series) have good machinability. Martensitic (400 series) steels are abrasive, tend to form a built-up edge, and require tool materials with high hot hardness and crater-wear resistance. Precipitation-hardening stainless steels are strong and abrasive, requiring hard and abrasion-resistant tool materials.The Effects of Other Elements in Steels on Machinability. The presence of aluminum and silicon in steels is always harmful because these elements combine with oxygen to form aluminum oxide and silicates, which are hard and abrasive. These compounds increase tool wear and reduce machinability. It is essential to produce and use clean steels.Carbon and manganese have various effects on the machinability of steels, depending on their composition. Plain low-carbon steels (less than 0.15% C) can produce poor surface finish by forming a built-up edge. Cast steels are more abrasive, although their machinability is similar to that of wrought steels. Tool and die steels are very difficult to machine and usually require annealing prior to machining. Machinability of most steels is improved by cold working, which hardens the material and reduces the tendency for built-up edge formation.Other alloying elements, such as nickel, chromium, molybdenum, and vanadium, which improve the properties of steels, generally reduce machinability. The effect of boron is negligible. Gaseous elements such as hydrogen and nitrogen can have particularly detrimental effects on the properties of steel. Oxygen has been shown to have a strong effect on the aspect ratio of the manganese sulfide inclusions; the higher the oxygen content, the lower the aspect ratio and the higher the machinability.In selecting various elements to improve machinability, we should consider the possible detrimental effects of these elements on the properties and strength of the machined part in service. At elevated temperatures, for example, lead causes embrittlement of steels (liquid-metal embrittlement, hot shortness; see Section 1.4.3), although at room temperature it has no effect on mechanical properties.Sulfur can severely reduce the hot workability of steels, because of the formation of iron sulfide, unless sufficient manganese is present to prevent such formation. At room temperature, the mechanical properties of resulfurized steels depend on the orientation of the deformed manganese sulfide inclusions (anisotropy). Rephosphorized steels are significantly less ductile, and are produced solely to improve machinability.20.9.2 Machinability of Various Other Metals Aluminum is generally very easy to machine, although the softer grades tend to form a built-up edge, resulting in poor surface finish. High cutting speeds, high rake angles, and high relief angles are recommended. Wrought aluminum alloys with high silicon content and cast aluminum alloys may be abrasive; they require harder tool materials. Dimensional tolerance control may be a problem in machining aluminum, since it has a high thermal coefficient of expansion and a relatively low elastic modulus.Beryllium is similar to cast irons. Because it is more abrasive and toxic, though, it requires machining in a controlled environment.Cast gray irons are generally machinable but are. Free carbides in castings reduce their machinability and cause tool chipping or fracture, necessitating tools with high toughness. Nodular and malleable irons are machinable with hard tool materials.Cobalt-based alloys are abrasive and highly work-hardening. They require sharp, abrasion-resistant tool materials and low feeds and speeds.Wrought copper can be difficult to machine because of built-up edge formation, although cast copper alloys are easy to machine. Brasses are easy to machine, especially with the addition pf lead (leaded free-machining brass). Bronzes are more difficult to machine than brass.Magnesium is very easy to machine, with good surface finish and prolonged tool life. However care should be exercised because of its high rate of oxidation and the danger of fire (the element is pyrophoric).Molybdenum is ductile and work-hardening, so it can produce poor surface finish. Sharp tools are necessary.Nickel-based alloys are work-hardening, abrasive, and strong at high temperatures. Their machinability is similar to that of stainless steels.Tantalum is very work-hardening, ductile, and soft. It produces a poor surface finish; tool wear is high.Titanium and its alloys have poor thermal conductivity (indeed, the lowest of all metals), causing significant temperature rise and built-up edge; they can be difficult to machine.Tungsten is brittle, strong, and very abrasive, so its machinability is low, although it greatly improves at elevated temperatures.Zirconium has good machinability. It requires a coolant-type cutting fluid, however, because of the explosion and fire.20.9.3 Machinability of Various MaterialsGraphite is abrasive; it requires hard, abrasion-resistant, sharp tools.Thermoplastics generally have low thermal conductivity, low elastic modulus, and low softening temperature. Consequently, machining them requires tools with positive rake angles (to reduce cutting forces), large relief angles, small depths of cut and feed, relatively high speeds, and proper support of the workpiece. Tools should be sharp.External cooling of the cutting zone may be necessary to keep the chips from becoming “gummy” and sticking to the tools. Cooling can usually be achieved with a jet of air, vapor mist, or water-soluble oils. Residual stresses may develop during machining. To relieve these stresses, machined parts can be annealed for a period of time at temperatures ranging from to (to), and then cooled slowly and uniformly to room temperature.Thermosetting plastics are brittle and sensitive to thermal gradients during cutting. Their machinability is generally similar to that of thermoplastics.Because of the fibers present, reinforced plastics are very abrasive and are difficult to machine. Fiber tearing, pulling, and edge delamination are significant problems; they can lead to severe reduction in the load-carrying capacity of the component. Furthermore, machining of these materials requires careful removal of machining debris to avoid contact with and inhaling of the fibers.The machinability of ceramics has improved steadily with the development of nanoceramics (Section 8.2.5) and with the selection of appropriate processing parameters, such as ductile-regime cutting (Section 22.4.2).Metal-matrix and ceramic-matrix composites can be difficult to machine, depending on the properties of the individual components, i.e., reinforcing or whiskers, as well as the matrix material.20.9.4 Thermally Assisted MachiningMetals and alloys that are difficult to machine at room temperature can be machined more easily at elevated temperatures. In thermally assisted machining (hot machining), the source of heata torch, induction coil, high-energy beam (such as laser or electron beam), or plasma arcis forces, (b) increased tool life, (c) use of inexpensive cutting-tool materials, (d) higher material-removal rates, and (e) reduced tendency for vibration and chatter.It may be difficult to heat and maintain a uniform temperature distribution within the workpiece. Also, the original microstructure of the workpiece may be adversely affected by elevated temperatures. Most applications of hot machining are in the turning of high-strength metals and alloys, although experiments are in progress to machine ceramics such as silicon nitride. SUMMARYMachinability is usually defined in terms of surface finish, tool life, force and power requirements, and chip control. Machinability of materials depends not only on their intrinsic properties and microstructure, but also on proper selection and control of process variables.译文:20.9 可机加工性一种材料的可机加工性通常以四种因素的方式定义:1、 分的表面光洁性和表面完整性。2、刀具的寿命。3、切削力和功率的需求。4、切屑控制。以这种方式,好的可机加工性指的是好的表面光洁性和完整性,长的刀具寿命,低的切削力和功率需求。关于切屑控制,细长的卷曲切屑,如果没有被切割成小片,以在切屑区变的混乱,缠在一起的方式能够严重的介入剪切工序。因为剪切工序的复杂属性,所以很难建立定量地释义材料的可机加工性的关系。在制造厂里,刀具寿命和表面粗糙度通常被认为是可机加工性中最重要的因素。尽管已不再大量的被使用,近乎准确的机加工率在以下的例子中能够被看到。20.9.1 钢的可机加工性因为钢是最重要的工程材料之一(正如第5章所示),所以他们的可机加工性已经被广泛地研究过。通过宗教铅和硫磺,钢的可机加工性已经大大地提高了。从而得到了所谓的易切削钢。二次硫化钢和二次磷化钢 硫在钢中形成硫化锰夹杂物(第二相粒子),这些夹杂物在第一剪切区引起应力。其结果是使切屑容易断开而变小,从而改善了可加工性。这些夹杂物的大小、形状、分布和集中程度显著的影响可加工性。化学元素如碲和硒,其化学性质与硫类似,在二次硫化钢中起夹杂物改性作用。钢中的磷有两个主要的影响。它加强铁素体,增加硬度。越硬的钢,形成更好的切屑形成和表面光洁性。需要注意的是软钢不适合用于有积屑瘤形成和很差的表面光洁性的机器。第二个影响是增加的硬度引起短切屑而不是不断的细长的切屑的形成,因此提高可加工性。含铅的钢 钢中高含量的铅在硫化锰夹杂物尖端析出。在非二次硫化钢中,铅呈细小而分散的颗粒。铅在铁、铜、铝和它们的合金中是不能溶解的。因为它的低抗剪强度。因此,铅充当固体润滑剂并且在切削时,被涂在刀具和切屑的接口处。这一特性已经被在机加工铅钢时,在切屑的刀具面表面有高浓度的铅的存在所证实。当温度足够高时例如,在高的切削速度和进刀速度下铅在刀具前直接熔化,并且充当液体润滑剂。除了这个作用,铅降低第一剪切区中的剪应力,减小切削力和功率消耗。铅能用于各种钢号,例如10XX,11XX,12XX,41XX等等。铅钢被第二和第三数码中的字母L所识别(例如,10L45)。(需要注意的是在不锈钢中,字母L的相同用法指的是低碳,提高它们的耐蚀性的条件)。然而,因为铅是有名的毒素和污染物,因此在钢的使用中存在着严重的环境隐患(在钢产品中每年大约有4500吨的铅消耗)。结果,对于估算钢中含铅量的使用存在一个持续的趋势。铋和锡现正作为钢中的铅最可能的替代物而被人们所研究。脱氧钙钢 一个重要的发展是脱氧钙钢,在脱氧钙钢中矽酸钙盐中的氧化物片的形成。这些片状,依次减小第二剪切区中的力量,降低刀具和切屑接口处的摩擦和磨损。温度也相应地降低。结果,这些钢产生更小的月牙洼磨损,特别是在高切削速度时更是如此。不锈钢 奥氏体钢通常很难机加工。振动能成为一个问题,需要有高硬度的机床。然而,铁素体不锈钢有很好的可机加工性。马氏体钢易磨蚀,易
- 温馨提示:
1: 本站所有资源如无特殊说明,都需要本地电脑安装OFFICE2007和PDF阅读器。图纸软件为CAD,CAXA,PROE,UG,SolidWorks等.压缩文件请下载最新的WinRAR软件解压。
2: 本站的文档不包含任何第三方提供的附件图纸等,如果需要附件,请联系上传者。文件的所有权益归上传用户所有。
3.本站RAR压缩包中若带图纸,网页内容里面会有图纸预览,若没有图纸预览就没有图纸。
4. 未经权益所有人同意不得将文件中的内容挪作商业或盈利用途。
5. 人人文库网仅提供信息存储空间,仅对用户上传内容的表现方式做保护处理,对用户上传分享的文档内容本身不做任何修改或编辑,并不能对任何下载内容负责。
6. 下载文件中如有侵权或不适当内容,请与我们联系,我们立即纠正。
7. 本站不保证下载资源的准确性、安全性和完整性, 同时也不承担用户因使用这些下载资源对自己和他人造成任何形式的伤害或损失。

人人文库网所有资源均是用户自行上传分享,仅供网友学习交流,未经上传用户书面授权,请勿作他用。