机械制造作业考研题目答案分享——工件的定位
Week 8 CHAPTER 2
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文章目录
1．什么是机械加工工艺过程？什么叫机械加工工艺规程？工艺规程在生产中起什么作用？
- Machining process contains the whole process through which the dimensions, shapes and surface quality of a blank are directly changed into a qualified part step by step by means of the metal cutting methods.
- Machining process route is a kind of document expressed by charts, tables and words, which is relative to the manufacturing process of production.
- Process route has 4 main functions in production.
Main technological documents used to guide production course.
Basis of production preparation.
Important technical reference to build new factory or rebuild former factory.
Main means used to store and exchange technology
2．什么叫工序、工位和工步？
- Working operation can be defined as a part of process course which is completed continuously by one operator (or a group of workmen) who machines one workpiece (or several workpieces simultaneously) on a definite working place (or a definite machine tool).
- Working position can be described as a position occupied by the workpiece and fixture or the movable part of the machine tool together relative to the cutter or the fixed part of the machine tool after the workpiece is clamped.
- Working step can be defined as the part of process in which the machining surface, cutting tool and cutting amount, including the cutting speed, feed and back engagement, are kept unchanged.
3．如图所示零件，毛坯为Φ35mm棒料，批量生产时其机械加工过程如下所述，试分析其工艺过程的组成。
图3.61 （习题14图）
在锯床上切断下料，车一端面钻中心孔，调头，车另一端面钻中心孔，在另一台车床上将整批工件螺纹一边都车至Φ30mm，调头再调换车刀车削整批工件的Φ18mm外圆，又换一台车床车Φ20mm外圆，在铣床上铣两平面，转90˚后，铣另外两平面，最后，车螺纹，倒角。
什么是定位？简述工件定位的基本原理。
- Location is to locate the workpiece in a fixture is to have the batch of workpieces in the same operation occupying the correct position in relation to both the machine tool and the cutting tool.
- Six-point location principle. A workpiece can be considered as a free body. Any free body in space has six degrees of freedom (3 linear and 3 rotary) as shown in figure 1. Six locators (location and support points) constrain six degrees of freedom of the workpiece, thus making the workpiece have a definite position in space only. It can be seen in figure 2.
限制工件自由度与加工要求的关系如何？
The situation about location has complete location, incomplete location, redundant location, insufficient location.
对不需要限制的自由度，一般不设置定位支承点。一般不允许出现过定位，但当采用形位精度很高的工件表面作为定位面时，可采用过定位来提高工件定位的稳定性和刚度。欠定位无法保证加工精度要求，在夹具中是不允许的。
32．根据六点定位原理，分析图3.68中所示各定位方案中各定位元件所消除的自由度。
Question Restriction types Restricted degrees of freedom
