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1、Some key words related with reference datum （基準(zhǔn)）,Reference datum (基準(zhǔn)） Design reference (設(shè)計基準(zhǔn)） Process reference (工藝基準(zhǔn)） Location element (定位元件) Location datum(定位基準(zhǔn)) Datum Superposition (基準(zhǔn)重合) Non-superposition (不重合) Operational datum (工序基準(zhǔn)) Operational draft (工序圖）,reference,Design reference,Process r

2、eference,Defined as those points, lines or surfaces which act as references to determine other Points,lines or surfaces,The reference in design drawing,Used to locate the position of the workpiece in machining,1、rough reference 2、finish reference 3、auxiliary reference 4、main reference 5、assistant re

3、ference,Used to inspect the workpiece in machining,Used to determine the relative position between parts or components in assembling,The reference in operational draft,Used in machining Inspection or assembling,3.4 Selection of reference datum（基準(zhǔn)）,A reference is used to define the position of points

4、, lines or surfaces on the workpiece in relation to it . It is also called the positioning reference datum.,3.4.1 Classification of references,The reference can be classified into two categories according to the application purpose.,1 Design Reference: The reference used in design stage by designer

5、2 Process Reference: The reference used in machining or assembling,支座零件圖,3.4.1 Classification of references,1 Design Reference: The reference used in design stage by designer,Question: Could you tell what are the design references in the drawing?,2 Process reference (工藝基準(zhǔn)）,（1）Operation reference (工序

6、基準(zhǔn)）,In operational draft, the points, lines or surfaces that are used to determine the operation dimensions or positions relative to the machined surface are called the operation reference.,According to its application purpose, it can be further classified into 4 subcategories,Question: Could you te

7、ll what are the operation references in the drawing?,3.4.1 Classification of references,（2）locating reference(定位基準(zhǔn)）,The locating reference is used to determine the correct position of the points, lines or surfaces to be machined on the workpiece relative to the machine tool, fixture and cutting tool

8、. The process that finds the location is called positioning.,3.4.1 Classification of references-Process reference,Could you describe the locating process of the workpiece in relation with the fixture?,7,圖2-46 組合夾具,1加筋角鐵（2） 2槽用螺栓（6） 3平鍵（10） 4方形支承 5定位支承 6方形支承 7平墊圈 8六角螺母（8） 9 槽用螺栓 10鉆套螺釘 11快換鉆套 12鉆模板 1

9、3圓形定位銷 14工件 15方形支承 16角鐵 17壓緊螺釘 18基礎(chǔ)板,（3）inspection reference,The points, lines or surfaces which are used as a reference to inspect the position of machined surfaces are called the inspection reference. In most cases, the design reference is used as the inspection reference.,3.4.1 Classification of

10、references,(4) Assembling reference,In the process of assembling，the points, lines or surfaces which are used as a reference to determine the position of the parts or components relative to the product are called the assembling reference. For example, when a gear is to be installed on a shaft, its h

11、ole is used as the assembling reference.,3.4.1 Classification of references,3.4.2 Select the locating surface,locating surfaces,the first datum surfaces(粗基準(zhǔn)）,the accurate datum surfaces （精基準(zhǔn)）,the auxiliary datum surfaces （輔助基準(zhǔn)）,How to select the position reference is one of the main factors that dec

12、ides the reasonability of process design and fixture design, as well as the machining accuracy, productivity and cost.,also called starting datum surfaces, making use of the surfaces existing on the raw blank.,The machined surfaces are used as the datum surfaces in the following operations.,It is th

13、e auxiliary datum surfaces, for the purpose of easy machining,Sometimes the locating surface is specially reserved on the roughcast for locating,3.4.2 Select the locating surface,1 The criteria of selecting the accurate datum surfaces,When selecting the accurate datum surfaces, some aspects, such as

14、 convenience, accuracy and stability must be taken into consideration. The following general principles should be followed.,（1）Principle of coincident locating surfaces（基準(zhǔn)重合）,（2）principle of locating datum surfaces unchangeable（基準(zhǔn)不變或統(tǒng)一）,（3）principle of being datum surfaces with each other and machin

15、ing time after time（互為基準(zhǔn)）,（4）principle of self-datum surface （自為基準(zhǔn)）,（5）Principle of stable and simple clamping （穩(wěn)定、易裝夾）,3.4.2 Select the locating surface,（1）Principle of coincident reference surfaces（基準(zhǔn)重合原則）,Select the operation datum surfaces (or design datum surface) as locating datum surfaces as

16、best as possible. It can reduce the manufacturing error caused by inaccurate location.,1 The criteria of selecting the accurate datum surfaces,3.4.2 Select the locating surface,（2）principle of datum surfaces unchanged（基準(zhǔn)不變原則）,The advantage of datum surfaces remaining unchanged: Different operations can be carried out using the same fixture. Thus it reduces the time and cost of fixture design and manufacture, speeds up the process of production preparation, and reduces the production cost. If mos