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1、1,单词复习： Lubrication wear weld viscosity Friction contaminant corrosion Dampen sealing asperity 边界润滑 绝缘体 黄油,上一课回顾,2,Lesson 18 Machine Tool Frames 机床床身,重点词汇： frame/bed impact/yield/hostile/dense volume fabricate impractical/practical dramatically mass/granite/diffuse,3,Paragraph 1,The frame is a machi
2、nes 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. 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（concrete）材料制作而成。材料选择由下列因素来决定。,4,Paragraph 2:,The material must resist deformation and fracture.
3、 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). 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和永久性变形。,5,The frame material must eliminate or block vibration transmission to
4、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). 机身材料具有消除或阻止振动（oscillation）传递的性能。以减轻降低精度和刀具寿命的振荡。它必须面对不利的车间环境，包括冷却液和润滑剂。,6,Material expansion must be understood (i
5、n 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 dense enough to distribute forces throughout the machine. 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，且具有足够大的密度以支承机床的其它部件。,7,Pros and Cons 优缺点 Para
6、graph 3:,Either castings or welded sections(焊接结构) can be used in most applications. The decision on which is best depends on the costs in a given(一定的) design situation. 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。,8,Paragraph 4:,Cast iron. Almost all machine tool frames were traditionally made of cast iron beca
7、use features difficult to obtain any other way can be cast in. Castings have a good stiffness-to-weight ratio and good damping qualities. Modifying wall thickness and putting the metal where its needed is fairly easy. 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。铸件有好的刚度与重量比和好的减震(damp)性能。各种壁厚都容易浇注而成。,9,
8、Paragraph 5,Although 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. 尽管铸铁是一种便宜的材料，但是每个铸件都需要一个铸
9、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作困难，花费大。,10,Smaller, 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. 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许是经济的。,11,Paragraph 6,Weld
10、ed 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 provide stiffness. The number of welds is a design tradeoff。 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。焊接件的数量是设计时需权衡的因素
11、。,12,with welding, its easy to make large sections and add features even after the initial design is complete, but the heat can introduce distortion and also adds cost. Welds also help block vibration transmission through the steel frame. 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）热量会引起变形，增加费用。焊件也有
12、助于削弱振动传递。,13,Builders sometimes increase damping by circulating coolant through the welded structure or adding lead or sand to frame cavities. 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。,14,Paragraph 7: Composites. Advanced forms of these materials, including those with polymer, metal, and ceramic matrices,
13、may change machine tool design dramatically. Both matrix and reinforcing material can be tailored to provide strength in specific axes(某个方向上). 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。基体和强化材料都能满足某一具体轴线方向的强度要求。,15,Paragraph 8,Ceramics. The Japanese introduced experimental machine tools with ceram
14、ic frames in the 1980s. Ceramics offer strength, stiffness, dimensional stability, corrosion resistance, and low surface roughness, but they are brittle and expensive. 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，低表面粗糙度，但脆性大，费用高。,16,Their lack of conductivity can be an advantage or not. Both com
15、posite and ceramic use is limited. 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。,17,Paragraph 9,Reinforced concrete. Though conventional reinforced concrete in simple sections increases mass and reduces vibration, another form, actually a polymer matrix composite made of crushed concrete or granite bound in a po
16、lymer matrix, is more popular. 钢筋混凝土：尽管普通预应力混凝土在简易零件中增大了质量，减轻了振动，另一种形式应用更广，这是一种碾碎的混凝土或花岗石粘接到高分子基体上而成的高分子基复合材料。,18,The composite has better damping characteristics than cast iron, can be cast into almost any shape, needs no stress relieving, and can accommodate fasteners and rails if inserts are used. However, it isnt as strong as metals and diffuses heat less efficiently. 这种复合材料较铸铁有好的减震性能，几乎能浇注成各种形状，不需消除应力处理，可以嵌入紧固件和设置横档。但它强度不如金属高、散热性能较差。,19,Paragraph 10,Designers must consider the differ
