Unit 7 Lesson 22

1、Professional English for Mechanical Engineering Lecturer: Xiaobin CuiPart IV Manufacturing Technology and Machine ToolsLesson 22 Machine Tool FramesLesson 22 Machine Tool Frames The frame is a machines fundamental element. Most frames are made from cast iron, welded steel, composite, or concrete. Th

2、e following factors govern material choice. The material must resist deformation and fracture. Hardness must be balanced against elasticity. The frame must withstand impact, yet yield under load without cracking or permanently deforming. The frame material must eliminate or block vibration transmiss

3、ion to reduce oscillations that degrade accuracy and tool life. Definition & RequirementsFrame 床身welded steel 可焊接结构钢Composite 复合材料It must withstand the hostile shop-floor environment, including the newer coolants and lubricants. Material expansion must be understood (in order) to minimize forces

4、 needed to move slides. The material must not build up too much heat, must retain its shape for its lifetime, and must be dense enough to distribute forces throughout the machine. 1. Pros and ConsEither castings or welded sections can be used in most applications. Lesson 22 Machine Tool FramesDefini

5、tion & RequirementsPros and Cons另外材料不能聚积太多热量材料不能聚积太多热量，必须能在寿命周期内保持保持其外形外形不发生变化，还必须足够致密足够致密以承受整个机床的受力。Pros and Cons 优点和缺点The decision on which is best depends on the costs in a given design situation.Cast iron Almost all machine tool frames were traditionally made of cast iron because features di

6、fficult 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. Although cast iron is a fairly cheap material, each casting requires a pattern. Lesson 22 Machine

7、 Tool FramesPros and Cons 几乎所有的机床床身床身均由由铸铁制成由铸铁制成，因为通过其他方式难以获取的特征均可通过铸造获得。stiffness-to-weight ratio刚性与质量之比 damping qualities 阻尼特性Pattern 铸模Larger sizes are a limiting factor because of pattern cost, problems with bolted joints, and the need to anneal castings, which is difficult and costly with larg

8、er sections. Smaller, high-volume machines usually have cast iron frames because they more easily absorb pattern cost. Welded frames may be cheaper for lower volume machines.Lesson 22 Machine Tool FramesPros and Cons 大尺寸铸件的铸造大尺寸铸件的铸造受到受到铸模成本、螺栓连接和必要的退火处理（对于大尺寸铸件来说是技术难题，并且成本很高）等问题的制约制约。bolted joints

9、螺栓连接Anneal 退火high-volume 大批量Welded steel Machine builders fabricate steel frames from welded steel sections when casting is impractical. Because steel has a higher modulus, it is usually ribbed to provide stiffness. The number of welds is a design tradeoff: with welding, its easy to make large secti

10、ons and add features even after the initial design is complete, but the heat can introduce distortion and also adds cost. Lesson 22 Machine Tool FramesPros and Cons设计过程中，要对对焊点的数量数量进行权衡权衡：对焊接结构而言，很容易制造大的结构,即使在初始设计完成之后，也容易在原基础上以及增加特征，但是焊接产生的热会引起结构变形并增加成本。Welded steel 焊接结构钢 Rib 加筋板Welds also help block

11、 vibration transmission through the steel frame. Builders sometimes increase damping by circulating coolant through the welded structure or adding lead or sand to frame cavities. Composites Advanced forms of these materials, including those with polymer, metal, and ceramic matrices, may change machi

12、ne tool design dramatically.Lesson 22 Machine Tool FramesPros and Cons 聚合物基，金属基和陶瓷基的新形式新形式复合材料可能会引起引起机床设计机床设计的巨大改变改变。Both matrix and reinforcing material can be tailored to provide strength in specific axes. Ceramics The Japanese introduced experimental machine tools with ceramic frames in the 1980

13、s. Ceramics offer strength, stiffness, dimensional stability, corrosion resistance, and low surface roughness, but they are brittle and expensive. Their lack of conductivity can be an advantage or not. Both composite and ceramic use are limited.Lesson 22 Machine Tool FramesPros and ConsMatrix 材料基质re

14、inforcing material强化材料 tailorto使适合（满足）的要求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 polymer matrix, is more popular. Lesson 22 Ma

15、chine Tool FramesPros and Cons虽然传统的钢筋混凝土在简单的部件结构上能增加质量，减小振动，但实际上另一种形式另一种形式，即聚合物基复合材料如今使用更加广泛使用更加广泛，这种复合材料将压缩混凝土和花岗岩结合在聚合物基体中制作而成。 Reinforced concrete钢筋混凝土 Crushed 压缩 挤压Granite 花岗岩The composite has better damping characteristics than cast iron, can be cast into almost any shape, needs no stress relie

16、ving, and can accommodate fasteners and rails if inserts are used. However, it isnt as strong as metals and diffuses heat less efficiently. Lesson 22 Machine Tool FramesPros and Cons 相对于铸铁来说，这种复合材料复合材料的阻尼特性阻尼特性更好更好，基本上可被浇筑成任何外形可被浇筑成任何外形，不需要进不需要进行应力消除行应力消除，可容纳可容纳嵌入的紧固件和筋板紧固件和筋板。stress relieving 应力消除F

17、astener 紧固件Rail 筋板Diffuse 散发Designers must consider the different expansion coefficients between the composite and the metal sections to which it is joined. The most common applications for this material are high-accuracy machine tools and grinders. 2. Foundations Foundations ensure the machines sti

18、ffness, shock absorption and isolation are secondary considerations. If the machine isnt stiff enough, the foundation may have to supply the stiffness necessary. Lesson 22 Machine Tool FramesPros and ConsFoundationsGrinder 磨床Foundation 底座In selecting a foundation, designers must consider the machine

19、s weight, the forces it generates, accuracy requirements, and the loads being transmitted to the ground by adjacent machines. Soil condition can be a problem because long-term changes can influence machine stability. Lesson 22 Machine Tool FramesFoundations 在选择底座时，设计设计者者必须考虑考虑机床自重自重，工作过程产生的力力，精度要求要求

20、和周围机床传递到地面的载荷载荷。If a small machine tool is rigid enough, it doesnt need the extra stiffness supplied by a base. For light loads, machines need only a 6-8”(152203 mm) thick concrete floor. Usually an elastic mount in the machine base helps isolate it from other forces in the plant or shop. An indepen

21、dent mounting slab cast into the plant floor supports heavier machines. The most complex arrangement is a mounting slab isolated from the rest of the shop with passive or active shock-isolation elements.Lesson 22 Machine Tool FramesFoundations 最复杂的布置形式是布置形式是采用主动或被动的振动隔离元件与车间内的其余部分隔离开的安装板安装板。Slab 厚板

22、板材3. Frame Design Major considerations in frame design are loads, damping, apertures, heat distortion, noise.Loads Understanding the static and dynamic loads a machine generates is essential. The basic load is static: the mass of the machine and its workpiece. The dynamic load adds all that happens

23、once the machine is running. Lesson 22 Machine Tool FramesFrame DesignAperture 空隙This includes the forces of acceleration, deceleration, tool action, irregular loads caused by an unbalanced condition, or self-exciting loads from load and vibration interaction.Damping Though frame material and design

24、 should handle damping, dampers are sometimes built into frame sections to handle specific problems. Lesson 22 Machine Tool FramesFrame Design 它包括它包括机床运行时加速和减速的惯性力力，刀具切削力力，不平衡条件引发的不规则载荷不规则载荷，及载荷与振动相互作用产生的自激载荷自激载荷。They work best in machine areas where little dynamic force is at work and are effective

25、 only when the designer has a good understanding of all the loads involved. For example, a damper that works well under static conditions may do more harm than good under dynamic conditions.Lesson 22 Machine Tool FramesFrame Design所设计的阻尼器阻尼器在机床几乎没有动态力的位置处表现表现最最好好，且仅当设计者对机床承受的所有负载都有深刻理解时阻尼器阻尼器方能有效有效。Apertures Each frame face should be solid, but the machine needs openings for assembly and maintenance. The designer balances aperture number and size against stiffness and strength requireme