组合夹具系统的设计英文文献和中文翻译(4)
workpiece at the correct locating position without even a slight movement under external forces.
3.6. Fasteners
Fasteners include hex nuts, hex nuts with shoulders, round nuts, rectangular nuts, spherical head bolts, square head bolts, set screws, regular washers, concave and convex washers. They are about 48*52% of the total ®xture elements. Fasteners are used to put different types of elements together to create a ®xture nut. The M1261:5mm bolts and nuts are used in M12 UMJFS series.
3.7. Other elements
Other elements are connecting plates, spherical and ¯at auxiliary supports, set screws for drill bushings, screws for keys, support caps, measurement shafts, balance blocks and handles. They are about 3*4% of the total ®xture elements. Other elements are considered as accessories; they do not belong to any element group stated above.
3.8. Combination elements
A combination element is an assembly, such as rotation support element or movable V-block, which contains a couple of inpidual parts. It is usualy treated as a single element when used in a ®xture. Each of these types of elements has its unique function, which cannot be substituted by any combination of the other available elements. Therefore, it is particularly helpful when designing a ®xture with special requirements. In most cases, combination elements simplify the structure of the ®xture and improve its accuracy.
4. UMJFS speci®cation and design
4.1. Terminology conventions
The speci®cation and design of UMJFS utilize certain technical terms and vocabulary that are explained in this system. That terminology facilitates communication between both designers and users of UMJFS.
384 Kakish, Zhang and Zeid
4.1.1. One-point surface The term refers to the surface of the workpiece where one locating point can be applied to eliminate one degree of freedom of the workpiece.
4.1.2. Two-point surface The term refers to the surface of the workpiece where two locating points can be applied to eliminate two degrees of freedom of the workpiece.
4.1.3. Three-point surface The term refers to the surface of the workpiece where three locating points can be applied to eliminate three degrees of freedom of the workpiece.
4.1.4. Sine angular structure This is an angle structure often used in ®xtures with high angle accuracy demand.
4.1.5. Self clamping This term checks the correctness of the clamping point of a ®xture. A steady and ®rm clamp to the workpiece is always assumed with a clamp of this type.
4.1.6. Compound-angle milling ®xture The term refers to an angle structure with two or more angles along different axes. Some cases require complicated geometric calculations to ®nd out the exact elevation of the machining surface with respect to certain datum.
4.1.7. Up-right milling The term refers to a type of milling with a milling machine tool, which has a vertical power head spindle where the milling cutter mounts.
4.1.8. Horizontal milling In contrast with the Up-right milling, the term refers to a type of milling by using a machine tool with a horizontal power head spindle. It is important to distinguish these two milling methods as one ®xture for one cannot be used for the other.
4.1.9. Multi-workpiece clamping This is a term for the technique of clamping more than one workpiece by single clamping operation. There are few ways to achieve this depending on the situation. For example, thin pieces could be placed on top of each other and then clamped together.
4.1.10. V-block locating This is a popular method for locating cylindrical surfaces. The term can also refer to the following:
(a) Short V-block locating, which is treated as a two-point locating to the workpiece. In other words, it restricts two degrees of freedom of the workpiece. (b) Long V-block locating, which provides fourpoint locating to the workpiece, thus restricting fourdegrees of freedom.
4.1.11. Pin and diamond pin locating Pin locating is suitable for those workpieces with existing machined bores. The locating accuracy depends upon the accuracy of the bores, whether they are ground or reamed, or produced by other means. The round pin usually serves as two-point locating by restricting the displacement on a ®xed surface in either direction. The workpiece can still rotate around the pin axis. The diamond pin is often used as a one-point locating, because the pin, machined to a diamond shape, can be offset from the bore center to some extent that it would not interfere with the other locating points. The combination of the two is always used to provide complete locating with two parallel holes in a workpiece.
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