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1、Unit 13 Jigs and Fixtures,Introduction Definition of a Drill Jig Typical Jigs and Fixtures,Jigs incorporate means of tool guiding during the actual cutting operation, and fixtures do not. Fixtures may incorporate means of setting the cutting tools relative the location system.,Introduction,Jigs and
2、fixtures are alike in that they both incorporate 包含 devices to ensure that the workpiece is correctly located and clamped, but they differ in that :,marking out and other measuring and setting out methods are eliminated; unskilled workers may proceed confidently and quickly in the knowledge that the
3、 workpiece can be positioned correctly, and the tools guided or set; the assembly of pairs is facilitated, since all components will be identical within small limits, and “trying” and filing of work is eliminated; the pairs will be interchangeable, and if the product is sold over a wide area, the pr
4、oblem of spare parts will be simplified.,The advantages of jigs and fixtures can be summarised as follows:,The location of workpiece Fig.1 represents a body that is completely free in space. In this condition it has six degrees of freedom.,The clamping 夹持 of the workpiece The clamping system must be
5、 such that the workpiece is held against the cutting forces, and the clamping forces must not be so great as to cause the workpiece to become distorted or damaged.,Fig.1 The six degrees of freedom,2. Definition of a Drill Jig,Basically it consists of a clamping device to hold the part in position un
6、der hardened-steel bushings through which the drill passes during the drilling operation.,A drill jig is a device for ensuring that a hole to be drilled, tapped, or reamed in a workpiece will be machined in the proper place.3,3. Typical Jigs and Fixtures,Fig.2 illustrates a drilling jig for drilling
7、 four holes in the flange 凸缘 of a work-piece that has been completed expect for the four holes.,Fig.2 Drilling jig,Typical drill jig,Typical milling fixture,Fig.3 illustrates a simple milling fixture for milling the slot in the oterwise complited workpiece shown.The workpiece is clamped in position,
8、and cutter is located against the setting block,which provides setting or cutter position and depth of cut .The fixture must be positioned relative to the machine table,this is done by engaging the two tenons at the bottom of the fixture in the slot in the machine table8 .the fixture is secured to t
9、he machine table with T-bolts,also engaging in the slots in the table (Fig.3).,Fig.3 Milling fixture,Notes,1. In practice,the only cutting tools that can be guided while actually cutting are drills,reamers,and similar cutters;and so jigs are associated with drilling operations,and fixtures with all
10、other operations. 句意：实际上，在切削时惟一的能被引导的切削刀具是钻头、铰刀和类似的铣刀；因此钻模适用于钻削加工，而夹具则用在其他加工工艺中。 2. When a clearance is specified,it is better to ensure its observance,rather than to allow careless marking out and machining to encroach upon it. 句意：当确定一个间隙时，最好能保证它的习惯要求，而不是超出正常界限地随便划出和加工出来。,3. A dill jig is a device
11、for ensuring that a hole to be drilled,tapped,or reamed in a workpiece will be machined in the proper place. 句意：钻模是一种确保在工作的正确位置上钻孔、攻螺纹或铰孔的装置。 分析：这里，that引出的从句是动名词ensuring的宾语，to be drilled,tapped是动词不定式的被动式，做定语，说明hole。 4. as在这里是副词，意为“同样”。,5. Responsibility for the accuracy of hole location is taken fro
12、m the operator and given to the jig. 句意：孔的定位精度不是靠操作者，而是靠钻模来保证。 6. A fixture holds the work during machining operations but does not contain special arrangements ofr fuiding the cutting tool,as drill jigs do. 句意：夹具在机加工时夹持工件，但与钻模不同的是，它没有专门引导刀具的装置。,7. There is no need to control the rotational position
13、 about the axis of the bore,because up to the time when the holes are drilled,it is symmetrical about that axis. 句意：没有必要限制围绕孔腔轴线的圆周位置，因为直到各孔被加工时，它都是相对于该轴心对称的。 8. The fixture must be positioned relative to the machine table,this is done by engaging the two tenons at the bottom of the fixture in the slot in the machine table. 句意：夹具必须相对于机器的工作台定位，这是通过把夹具底部的两个榫头嵌入机器工作台上的开槽来达到的。,
