1、Dimensioning 零件圖的尺寸標注,Datum features 尺寸基準的選擇 Direct specifications of important dimensions 重要的尺寸直接注出 Avoiding close dimension chains 避免出現(xiàn)封閉的尺寸鏈 Producing dimensions in accordance with machining sequence 標注尺寸應符合加工順序 Only one link allowed between machined and non-machined surfaces 同一個方向只能有一個非加工面與加工面聯(lián)系

2、 Exercises 練習題,請點擊相應標題顯示其內(nèi)容,請點擊鼠標左鍵顯示后面內(nèi)容,Datum features 尺寸基準的選擇,When selecting a datum, one must consider the part position, function, assembling, position setting and measurement. Therefore, datum features should be determined according to the designs requirements, machining conditions, and measur

3、ements. 在選擇尺寸基準時, 必須考慮零件在機器或部件中位置、作用、零件之間的 裝配關系以及零件在加工過程中的定位和測量等要求。因此, 基準應根據(jù)設計要求、加工情況和測量方法確定。,Design datum This class includes datum planes or datum lines used to locate a given part inside other parts. 設計基準 是用于確定零件在部件中工作位置的基準面或線。,Process datum This class includes datum plane or datum line used to m

4、achine or measure the parts. 工藝基準 是零件在加工、測量時的基準面或線。,Determining datum features 尺寸基準的確定,請 點 擊 鼠 標 左 鍵 顯 示 后 面 內(nèi) 容,Datum features 尺寸基準的選擇,This section focuses on some general issues of dimensioning and some commonly used structures so that the dimensions will not only meet the design requirements but

5、also other requirements to facilitate machining, measurement and inspection. 使所標注的尺寸既能滿足設計要求,又符合生產(chǎn)實際, 便于加工、測量和檢驗。,Select the bottom surface D as the datum for the dimension of the center height of the brackets axle hole. 標注支架軸孔的中心高，應以底 面D為基準,The dimensions of the two threaded holes select datum face

6、 B、C. 底板兩螺孔的 定位尺寸,以B、C為基準,It is easy to use datum E to measure the depth of the threaded hole. 以E為基準測 量螺孔的深 度比較方便,Process datum 工藝基準,Design datum 設計基準: B、C、D,Length datum 長度基準 B,D Height datum 高度基準zzzz,Width datum 寬度基準 C,Process datum 工藝基準: E,Bracket 支架,The dimensions of the threaded holes select da

7、tum face C. 螺孔的 定位尺寸以C為基準,請 點 擊 鼠 標 左 鍵 顯 示 后 面 內(nèi) 容,Direct specifications of important dimensions 重要的尺寸直接注出,Important dimensions include the ones used to mount other parts, key relative positions and any other information related to the function of the part. All of them should be directly specified

8、when drawing parts. 重要尺寸是指與其他零件相配合的尺寸、重要的相對位置尺寸、影響零件使用性能的其他尺寸，這些尺寸都應在零件圖上直接注出。,Bracket 支架,The center height of the axle hole is an important dimension. So it should be directly specified. 軸孔的中心高是重要尺寸應直接注出,Appropriate 標注合理,Inappropriate 標注不合理,As shown in Fig, dimensions A, B ,C and L form a close dim

9、ension chain. Since L=A+B+C, if dimension L has a constant error, dimensions for A，B and C must have very little error, which may lead to difficulties in machining. Therefore, close dimension chains should be avoided and the dimension with less importance should be removed. 圖中的尺寸A、B、C和 L 構成一個封閉的尺寸鏈。

10、 由于L=A+B+C，若尺寸L的誤差一定, 則A 、B、C每個尺寸的誤差就要定得很小。這樣，就會使加工困難，所以應當避免封閉的尺寸鏈，將一個不重要的尺寸去掉。,Avoiding close dimension chains 避免出現(xiàn)封閉的尺寸鏈,請 點 擊 鼠 標 左 鍵 顯 示 后 面 內(nèi) 容,Avoiding close dimension chains 避免出現(xiàn)封閉的尺寸鏈,Process datum 工藝基準,Length datum 長度基準,Height and width datum 高度、寬 度基準,Length subsidiary datum 長度輔助基準,The clos

11、e dimension chains should be avoided and the dimension with less importance should be removed. 避免封閉的尺寸鏈，將軸的一個不重要尺寸去掉,(1)Dimensions should also be specified in accordance with machining sequence 標注尺寸應符合加工順序,請 點 擊 鼠 標 左 鍵 顯 示 后 面 內(nèi) 容,Producing dimensions in accordance with machining sequence 標注尺寸應符合加工

12、順序,Precise dimensions 標注合理,Imprecise dimensions 標注不合理,Determine the location of the escape according to the dimension 36, and then machine the escape. 按尺寸36mm 定退刀槽的位置, 加工退刀槽尺寸4mm,Turn the external diameter 18 and chamfer the end of the shaft . 用車刀加工18mm的外圓和軸端倒角,a) Escape加工退刀槽,b) External diameter加工外

13、圓,(2) Dimensions should be specified for easy inspection 標注尺寸應便于測量,請 點 擊 鼠 標 左 鍵 顯 示 后 面 內(nèi) 容,Producing dimensions in accordance with machining sequence 標注尺寸應符合加工順序,Precise dimensions 標注合理,Imprecise dimensions 標注不合理,Dimensioning C is not convenient for measurement. 尺寸C不便于測量,請 點 擊 鼠 標 左 鍵 顯 示 后 面 內(nèi) 容,

14、Only one link allowed between machined and non-machined surfaces 同一個方向只能有一個非加工面與加工面聯(lián)系,Precise dimensions 標注合理,Imprecise dimensions 標注不合理,There are three non-machined surfaces along the height line: B, C, and D, in which only surface B and machined surface A have a link of dimension 8, which is appro

15、priate. 沿鑄件的高度 方向有三個非加工面B、C 和D，其中 只有B 面與加工面A有尺寸8的聯(lián)系， 這是合理的,If dimensions are specified with three non-machined surfaces linked to A, it would be difficult to ensure the precision of linked dimensions 8, 34 and 42 while machining the surface. 三個非加工面B、C和D都與加工面A有聯(lián)系,那么在加工A面時,就很難同時保證三個聯(lián)系尺寸8,34和42的精度,請點擊題目顯示其內(nèi)容,Exercises 練習題,1. Find out imprecise dimensions and correct it. 找出標注不合理的尺寸，并更正之。,2. Fully dimension the drawing of bearing bracket， take the 、 as the design datum. 注出軸承架全部尺寸,已知.為設計基準。,本 小 節(jié) 結 束,謝謝您的認真學習！,退出,前一頁,1. Find out imprecise dimensions and co