机械制造技术基础课件-chapter3-section6-2012

1、2021/4/16,SCUT,1,3.6 The method to clamp the workpiece and obtain the desired accuracy,3.6.1 The clamping (1) Positioning and clamping by direct location(直接找正定位） When putting the workpiece directly on the machine bed, the operator can locate the machined surface by using a micrometer（千分尺） inspecting

2、 instrument（测量仪）, marking dish（划线盘） or straight rules to adjust and find the desired machining position relative to the cutting tool.,It is usually used in single or small batch type production, or in the condition of high accuracy machining requirement to relative position when it is hard to meet b

3、y a fixture.,2021/4/16,SCUT,2,（2） Clamping according to the pre-marked trail of the outline（划线找正装夹）,This kind of clamping method is widely used in single or small batch type production ，and the error of the operation itself exists, the clamping accuracy is low, usually in the range 0.20.5mm. Before

4、the work is machined, the outline of the surface to be machined on the raw material is marked, then located and clamped on the machine tool according to the pre-drawn lines. When using this method, sufficient metal removal must be ensured.,3.6 The method to clamp the workpiece and obtain the desired

5、 accuracy,2021/4/16,SCUT,3,(3) Clamped with a fixture （夹具）,This kind of method is convenient, fast, precise and stable. It is widely used in batch type production and large quantity production. For example, in Fig.4-1, it is an operation of machining a key in a stepped shaft. For some parts in small

6、 batches, such as the connecting rod or crank shafts, even though the batch quantity is not large, some special fixtures are still required in order to meet the specific machining requirement.,3.6 The method to clamp the workpiece and obtain the desired accuracy,2021/4/16,SCUT,4,Fig3-6-2 the setup o

7、f the keyway machined by milling,Obviously, the relative positional accuracy among different surfaces in mechanical machining, such as parallel, the perpendicular and coaxial degrees of accuracy, can be obtained with the above clamping method using several clamping steps, and also it can be obtained

8、 by arranging the different surfaces to be machined in the same clamping. These two methods are both commonly used to obtain the relative positional accuracy in mechanical machining.,3D,2021/4/16,SCUT,5,（1） Methods of obtain the dimensional accuracy in mechanical machining,Trial cutting method,Setti

9、ng dimension method,Adjust method, Automatic control method,A tiny part of the surface to be machined is pre-cut, and the dimensions are inspected. Then,proper adjustment is made according to the desired requirement, and try cutting is tried again.,The accuracy of the machined surface is ensured by

10、applying a cutting tool with the required accuracy, such as a reamer, twist drill or core drill.,The accuracy is ensured by the cutting route setting device or pre-adjusted carriages,1）Automatic inspection the inspection device is integrated into the machine tool. When the dimensions are satisfied,

11、an instruction will be sent from the automatic inspection device to make the cutting tool recede or stop. 2）Numerical controla stepping motor, rolling screw or a whole numerical controlled device is used to control the movement of cutting tool or worktable precisely. The dimensions are achieved by p

12、re-programmed instructions to control the movement of carriages or worktable through a computer controlled numerical device.,3.6.2 Methods of obtaining the accuracy of the dimension,2021/4/16,SCUT,6,（2）Methods to obtain the desired geometrical shape by mechanical machining, path method, Forming meth

13、od,(4)Generating method,the geometrical shape of the part is formed by the movement of the cutting tool tip. The accuracy of this method is mainly dependent on the accuracy of the cutters movement.,the shape of the workpiece is formed by synthesis of two movements, one of which is the movement of the cutting tool, and another is the movement of the workpiece.,The geometrical shape of the workpiece is an exact counterpart of the cutting tool. The accuracy of this machining method is mainly depended on the geometrical accuracy of the cutting tool and its clamping accuracy.,（2