Unit 7 Lesson 22

stiffness-to-weight ratio 刚性与质量之比 damping qualities 阻尼特性 Pattern 铸模
and putting the metal where it's needed is fairly
easy. Although cast iron is a fairly cheap material, each casting requires a pattern.
高分子材料，金属和陶瓷等新形式的复合 材料可能会引起机床设计的巨大改变。
Lesson 22
Hale Waihona Puke Machine Tool Frames
Both matrix and reinforcing material can be Pros and Cons tailored to provide strength in specific axes. Matrix 材料基质 Ceramics The Japanese introduced reinforcing material experimental machine tools with ceramic 强化材料 frames in the 1980 s. Ceramics offer strength, tailor…to… 使…适合（满足）… stiffness, dimensional stability, corrosion 的要求 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.
Rib 加筋板
而言，即使在初始设计完成之后，也很容易在原基础
上制造大的结构以及增加特征，但是焊接产生的热会 引起结构变形并增加成本。
Lesson 22
Machine Tool Frames
Welds also help block vibration transmission Pros and Cons 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 machine tool design dramatically.
Lesson 22
Machine Tool Frames
Welded steel Machine builders fabricate steel frames
Pros and Cons
from welded steel sections when casting is impractical. Welded steel 焊接结构钢 Because steel has a higher modulus, it is usually ribbed to provide stiffness. The number of welds is a design tradeoff: with welding, it’s 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. 设计过程中，要对焊点的数量进行权衡：对焊接结构
Designers must consider the different Pros and Cons 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 Grinder 磨床 and grinders. Foundations 2. Foundations Foundations ensure the machine's Foundation 底座 stiffness, shock absorption and isolation are secondary considerations. If the machine isn’t stiff enough, the foundation may have to supply the stiffness necessary.
Machine Tool Frames
The frame is a machine’s fundamental element. Most frames are made from cast iron, welded steel, composite, or concrete. The 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 transmission to reduce oscillations that degrade accuracy and tool life.
Definition & Requirements
Frame 床身 welded steel 可焊接结构钢 Composite 复合材料
Lesson 22
Machine Tool Frames
It must withstand the hostile shop-floor environment,
Lesson 22
Machine Tool Frames
Reinforced concrete Though conventional Pros and Cons reinforced concrete in simple sections Reinforced concrete increases mass and reduces vibration, 钢筋混凝土 another form, actually a polymer matrix composite made of crushed concrete or Crushed 压缩 挤压 granite bound in a polymer matrix, is more Granite 花岗岩 popular. 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，
Cast iron Almost all machine tool frames were traditionally made of cast iron because features
difficult to obtain any other way can be cast in.
几乎所有的机床床身均由由铸铁制成，因为通 过其他方式难以获取的特征均可通过铸造获得。 Castings have a good stiffness-to-weight ratio and good damping qualities. Modifying wall thickness
更好，基本上可被浇筑成任何外形，不需要进
行应力消除，可容纳嵌入的紧固件和筋板。 However, it isn't as strong as metals and diffuses heat less efficiently.
Diffuse 散发
Lesson 22
Machine Tool Frames
Lesson 22
Machine Tool Frames
Larger sizes are a limiting factor because of Pros and Cons pattern cost, problems with bolted joints, and bolted joints 螺栓连接 the need to anneal castings, which is difficult Anneal 退火 and costly with larger sections. 大尺寸铸件的铸造受到铸模成本、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。 Smaller, high-volume machines usually have
high-volume 大批量
cast iron frames because they more easily absorb pattern cost. Welded frames may be cheaper for lower volume machines.
Professional English for Mechanical Engineering