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1、3.3 Location principle of workpiece,In order to fulfill the machining requirement of a certain job, a relatively accurate position of the workpiece in a machine tool in relation to the cutting tool during the metal cutting movement must be ensured. The following three conditions must be satisfied wh
2、en fulfilling such a practical function, which are（1）The accurate position of a batch of workpieces in relation to the jigs or fixtures； (2) The accurate position of the jigs or fixtures in relation to the machine tool;（3）The accurate position of the cutting tool in relation to the jigs or fixtures.
3、 In this section, the main attention is directed to the accurate positioning of workpieces in jigs or fixtures.,Relative position between workpiece, fixture and machine tool,3.3 Location principle of workpiece,（1）move along axis X, denoted by （2） move along axis Y, denoted by （3） move along axis Z,
4、denoted by （4）rotate around axis X， denoted by （5） rotate around axis Y, denoted by （6） rotate around axis Z，denoted by,3.3 Location principle of workpiece,3.3,1 The 6-point location principle of the workpiece,3.3 Location principle of workpiece,任一物体在空间都有六种宏观运动的可能性，称为六个自由，即沿X、Y、Z轴的移动和绕此三轴的转动，欲使工件在空间
5、取得唯一位置，则必须限制六个自由度。这就是六点定位原理,There are 6 possible movements for any object in space, which is called 6-degree of freedom. If the only one position for the object is designated, the 6-degree of freedom must be limited, which is the principle of 6-point location.,Principle of six-point location,Questio
6、n: How to decide the position of the object in space ?,Answer: limit the 6 degrees of freedom,3.3 Location principle of workpiece,The six-point location principle,Fig.3-4 six degrees of freedom cancelled for a workpiece,3.3 Location principle of workpiece,Concepts:,Complete location(完全定位）：all the si
7、x degrees of freedom have been cancelled. Incomplete location（不完全定位）：not all the 6 degrees of freedom have been cancelled, but still satisfy the requirement. Redundant location（过定位）: two location elements have both cancelled the same degree of freedom for a workpiece. Insufficient location（欠定位）：the
8、number of location points is less than the degrees of freedom which must be cancelled, the workpiece is insufficiently located .,3.3 Location principle of workpiece,Complete location and incomplete location,3.3 Location principle of workpiece,Insufficient location,3.3 Location principle of workpiece
9、,Redundant location,3.3 Location principle of workpiece,Redundant location,Definitiona degree of freedom(or several degrees of freedom) is limited by two (or above two) points.,Allowable or not? it must be decided according to the practical condition:1）if the locate surface has been machined, and it
10、s shape, dimension, position have high accuracy, then redundant location is allowable. Sometimes it is necessary, since not only it would not influence the machining accuracy, but also reinforce the stiffness of the machining system and stability of location 2）otherwise，it is prohibited, because it
11、will cause inaccurate location or unstable location, or location interference,3.3 Location principle of workpiece,Redundant location and elimination,Case study: 齿轮坯以内孔和一大端面定位，车削外圆和大端面。加工后检测发现大端面与内孔垂直度超差。试分析原因，提出改进意见。,Case study: redundant location,Deformation caused by clamping,Analysis of redundant
12、 location,3.3.2 The location ways and elements,On the one hand, the distribution of the location elements in jigs or fixtures must conform to the six-point principle. On the other hand, the distribution envelope of the location elements should be as large as possible so as to make the weight of the
13、workpiece and the cutting force fall within the area formed by the support points.,location elements,Fixed location elements,adjustable location elements,Auxiliary support element,floating location support,support post,support plate,location pin,centering shaft,V-shaped block,3.3.2 The location ways
14、 and elements,（1） Positioned with plain surface on workpiece,3.3.2 The location ways and elements,Support pin,Support plate,（a) plain head (b) spherical head (c) meshed head,3.3.2 The location ways and elements,Adjustable support pin,1screw adjustable 2- secure nuts,Question： how many degrees of fre
15、edom are canceled by each location element?,（1） Positioned with plain surface on workpiece,(1) Positioned with plane on the workpiece,3.3.2 The location ways and elements,Self-adjustable location pin,Question： how many degrees of freedom are canceled by each location element?,(2) Positioned with cyl
16、indrical holes on the workpiece,3.3.2 The location ways and elements,Note: these location elements are standardized , and utilized with other location elements,Question： how many degrees of freedom are canceled by each location element?,(2) Positioned with cylindrical holes on the workpiece,3.3.2 Th
17、e location ways and elements,There are 3 types of cylindrical pins, which are long pin (l/d0.81), short pin(l/d0.4) and rhombic pin (削边销）,Question： how many degrees of freedom are canceled for each location element?,rhombic pin,(3) Positioned with external cylindrical surface on the workpiece,3.3.2
18、The location ways and elements,Question： how many degrees of freedom are canceled for each location element?,3.3.3 Symbol of location and marking,3.3.3 Symbol of location and marking,3.3.3 Symbol of location and marking,3.3.3 Symbol of location and marking,3.3.3 Symbol of location and marking,(3) Cy
19、lindrical location pin（圆柱形定位销）,Fitting tolerance between pin and the fixture body is H7/r6 ,or H7/n6 between the bush and the fixture body. fitting tolerance between the location pin and the location bore is K7/g6 or H7/f7.,Tapered location pin,The application of rhombic pin（菱形销）,（4）Location centeri
20、ng (centering shaft，定位心轴）),The fit tolerance between the bore and the centerings is H7/h6 or H7/g6,（5）V-shaped block,5.2.2.3 adjustable location element,5.2.2.4 Auxiliary support element（辅助支撑）,5.2.2.5 floating locating element（浮动支撑）,Question: Does this kind of element cancel any freedom degree?,Question: Does this kind of element cancel any freedom degree? If it does, how many have been cancelled?,floating locating element,