机械专业英语课件3.ppt

1、1n单词复习：nLubrication wear weld viscositynFriction contaminant corrosionnDampen sealing asperityn边界润滑 绝缘体 黄油 上一课回顾2Lesson 18 Machine Tool Frames机床床身机床床身n重点词汇：nframe/bednimpact/yield/hostile/densenvolumenfabricatenimpractical/practicalndramaticallynmass/granite/diffuse3Paragraph 1nThe frame is a machin

2、es fundamental element.Most frames are made from cast iron,welded steel(可焊接的结构钢),composite,or concrete.The following factors govern(决定)material choice.n机身是机器的基础部件。大多数机身是铸铁（机身是机器的基础部件。大多数机身是铸铁（cast iron）、焊接结构钢、复合材料、混凝土）、焊接结构钢、复合材料、混凝土（concrete）材料制作而成。材料选择由下列因素）材料制作而成。材料选择由下列因素来决定。来决定。4Paragraph 2:nTh

3、e material must resist deformation and fracture.Hardness must be balanced against elasticity(必须解决硬度合弹性之间的矛盾).The frame must withstand impact,yet yield(产生)under load without cracking(裂纹)or permanently deforming(永久性变形).n材料必须能够抵抗变形和断裂。硬度必须与其弹性相材料必须能够抵抗变形和断裂。硬度必须与其弹性相平衡。机身必须能承受冲击且在载荷作用下不能裂缝平衡。机身必须能承受冲击且

4、在载荷作用下不能裂缝和永久性变形。和永久性变形。5nThe frame material must eliminate or block vibration transmission to reduce oscillations(震荡)that degrade accuracy and tool life(降低精度和刀具寿命).It must withstand the hostile(恶劣的)shop-floor environment,including the newer coolants(冷却液)and lubricants(润滑剂).n机身材料具有消除或阻止振动（机身材料具有消除或阻

5、止振动（oscillation）传递的性）传递的性能。以减轻降低精度和刀具寿命的振荡。它必须面对不能。以减轻降低精度和刀具寿命的振荡。它必须面对不利的车间环境，包括冷却液和润滑剂。利的车间环境，包括冷却液和润滑剂。6nMaterial expansion must be understood(in order)to minimize forces needed to move slides.The material must not build up(聚集)too much heat,must retain its shape for its lifetime,and must be dens

6、e enough to distribute forces throughout the machine.n材料的膨胀不能妨碍滑动部件的运动。在正常工作期间材料的膨胀不能妨碍滑动部件的运动。在正常工作期间材料不能产生太多的热量，应能保护其形状，且具有足材料不能产生太多的热量，应能保护其形状，且具有足够大的密度以支承机床的其它部件。够大的密度以支承机床的其它部件。7Pros and Cons 优缺点优缺点 Paragraph 3:nEither castings or welded sections(焊接结构)can be used in most applications.The decisi

7、on on which is best depends on the costs in a given(一定的)design situation.n铸件和焊接件应用都很广泛，哪种形式最好由给定条铸件和焊接件应用都很广泛，哪种形式最好由给定条件下的成本来决定。件下的成本来决定。8Paragraph 4:nCast iron.Almost all machine tool frames were traditionally made of cast iron because features difficult to obtain any other way can be cast in.Cast

8、ings have a good stiffness-to-weight ratio and good damping qualities.Modifying wall thickness and putting the metal where its needed is fairly easy.n铸铁：几乎所有传统机床的床身都是由铸铁制成，因铸铁：几乎所有传统机床的床身都是由铸铁制成，因为其他方式难以获得的形状都能铸造而成。铸件有好为其他方式难以获得的形状都能铸造而成。铸件有好的刚度与重量比和好的减震的刚度与重量比和好的减震(damp)性能。各种壁厚都性能。各种壁厚都容易浇注而成。容易浇注而

9、成。9Paragraph 5nAlthough cast iron is a fairly cheap material,each casting requires a pattern(模型).Larger sizes are a limiting factor because of pattern cost,problems with bolted joints,and the need to anneal(将退火)castings,which is difficult and costly with larger sections.n尽管铸铁是一种便宜的材料，但是每个铸件都需要一个尽管铸铁

10、是一种便宜的材料，但是每个铸件都需要一个铸型。铸型要用螺栓紧固联接，且铸件需要退火处理使铸型。铸型要用螺栓紧固联接，且铸件需要退火处理使得大尺寸铸件受到限制，这些条件也使得大尺寸铸件制得大尺寸铸件受到限制，这些条件也使得大尺寸铸件制作困难，花费大。作困难，花费大。10nSmaller,high-volume(大批量的)machines usually have cast iron frames because they more easily absorb pattern cost.Welded frames may be cheaper for lower volume machines.n

11、尺寸小，大批量生产的机床由于分担的铸型费用较低，尺寸小，大批量生产的机床由于分担的铸型费用较低，常使用铸铁床身。单件小批生产的机床结构用焊接或常使用铸铁床身。单件小批生产的机床结构用焊接或许是经济的。许是经济的。11Paragraph 6nWelded steel.Machine builders fabricate steel frames from welded steel sections when casting is impractical.Because steel has a higher modulus(弹性模量),it is usually ribbed(加筋)to prov

12、ide stiffness.The number of welds is a design tradeoff。n焊接钢结构：当铸件不容易实现时，常用焊接钢结构焊接钢结构：当铸件不容易实现时，常用焊接钢结构制作床身。由于钢具有高的模数，常设置肋提高刚度。制作床身。由于钢具有高的模数，常设置肋提高刚度。焊接件的数量是设计时需权衡的因素。焊接件的数量是设计时需权衡的因素。12nwith welding,its easy to make large sections and add features even after the initial design is complete,but the h

13、eat can introduce distortion and also adds cost.Welds also help block vibration transmission through the steel frame.n焊接容易得到大尺寸零部件，而且既使最初的设计完焊接容易得到大尺寸零部件，而且既使最初的设计完成后也可以添加一些特征，但是（焊接产生的）热量成后也可以添加一些特征，但是（焊接产生的）热量会引起变形，增加费用。焊件也有助于削弱振动传递。会引起变形，增加费用。焊件也有助于削弱振动传递。13nBuilders sometimes increase damping by

14、circulating coolant through the welded structure or adding lead or sand to frame cavities.n制造有时通过冷却液循环和在床身空腔内加铅和沙子，制造有时通过冷却液循环和在床身空腔内加铅和沙子，来抑制热变形和减振。来抑制热变形和减振。14nParagraph 7:nComposites.Advanced forms of these materials,including those with polymer,metal,and ceramic matrices,may change machine tool

15、design dramatically.Both matrix and reinforcing material can be tailored to provide strength in specific axes(某个方向上).n复合材料：包括高分子材料、（优质）金属材料、陶复合材料：包括高分子材料、（优质）金属材料、陶瓷在内的这些新材料引起了机床设计的显著变化。基瓷在内的这些新材料引起了机床设计的显著变化。基体和强化材料都能满足某一具体轴线方向的强度要求。体和强化材料都能满足某一具体轴线方向的强度要求。15Paragraph 8nCeramics.nThe Japanese intro

16、duced experimental machine tools with ceramic frames in the 1980s.nCeramics offer strength,stiffness,dimensional stability,corrosion resistance,and low surface roughness,but they are brittle and expensive.n陶瓷：二十世纪八十年代，日本制作了陶瓷床身的试验陶瓷：二十世纪八十年代，日本制作了陶瓷床身的试验机床。陶瓷具有足够的强度、刚度，尺寸稳定，耐腐蚀，机床。陶瓷具有足够的强度、刚度，尺寸稳定，耐腐蚀，低表面粗糙度，但脆性大，费用高。低表面粗糙度，但脆性大，费用高。16nTheir lack of conductivity can be an advantage or not.Both composite and ceramic use is limited.n低的传导率有时是优点，有时是缺点。复合材料和陶低的传导率有时是优点，有时是缺点。复合材料和陶瓷的应用是有限的。瓷的应用是有限的。