MechanicalDesign機(jī)械設(shè)計(jì)

1、Introduction：The basic elements of the machine are Mechanical Parts。In this course, we introduce mainly about the basic knowledge of mechanical design of the whole machine, especially about the design of the common parts in general dimensions(一般尺寸) and under common operating parameters(常用工作參數(shù))，inclu

2、ding Basic design theory and method，technical data and Standard applications. Basic design theoryThe composition of a machineprime mechanism，Transmission mechanism，Executive mechanism，other parts(like: auxiliary system輔助系統(tǒng)、Control System)可以舉例說明：a car engine（prime mechanism）；Drive shaft and Gearbox (

3、Transmission part); wheel (Executive part);Fatigue strength of materials1) Definition：Fatigue is the weakening of a material caused by repeatedly applied loads(載荷). The maximum stress values that cause such damage may be much less than the yield stress limit(屈服應(yīng)力極限).So we use the sN fatigue curve an

4、d equal-life fatigue curve to show the Anti-fatigue properties(抗疲勞特性) of materials.2)Maximum stress max 、Number of stress cycles N 應(yīng)力循環(huán)次數(shù)、Stress amplitude a 應(yīng)力幅值、Mean stress m 平均應(yīng)力（under the fatigue limit）、static stress靜應(yīng)力Figure Error! Main Document Only. equal-life fatigue curveFigure Error! Main D

5、ocument Only. S-N fatigue curveSymmetry cyclic對稱循環(huán)variable stress 可變應(yīng)力:m=0,pulse cyclic脈動循環(huán) variable stress: m=a =0 /2,Known:A(0，-1) ,D (0 /2，0 /2);C ( 0, s ) ,Any point of line C represent the yield limit屈服極限When the parameter of cycle stress（ m，a ）is in OAGC，the materials dont break。When the param

6、eter is out OAGC，the materials must break。When the parameter is on OAGC，the materials reach fatigue limit 。Wear 磨損（Friction摩擦）1) Definition：the material of element surface disappeared or removed because of friction。2) Wear curve:run-in wear period-It results from the roughness of processing surface(

7、加工表面的粗糙度)。stable wear period-The wear speed of element is steady and slow。sharp wear period-the gap of pair increase and cause the vibration（振動） of machine 。The element may be rejected （遺棄，報(bào)廢）。（可以舉例：The running-in period of a new car,···········

8、··，················） Mechanical jointClassification：mechanical Dynamic joint（聯(lián)系到知識點(diǎn)：kinematic pair運(yùn)動副）mechanical static joint（Relative movement相對運(yùn)動 is not allowed）Screw joints and screw drive：1) Classification

9、of Screw thread(螺紋)：According to the type of tooth牙型 of screw threadRectangle矩形 screw thread；Triangle三角形 screw thread；Trapezium梯形 screw thread；Hackle鋸齒形 screw threadexternal thread外螺紋；internal thread內(nèi)螺紋2) Basic types of screw thread joint:Bolted joint螺栓連接；Screw joint螺釘連接；Stud joint雙頭螺柱連接；holding scr

10、ew joint緊定螺釘連接3) pre-tightening force 預(yù)緊力：the majority of screw thread joint need to be tightened while fitting裝配 before 8supporting service load負(fù)載. This load is called pre-tightening force.To enhance the reliability and tightness of joint, to prevent appearance of gap or relative move after bearing

11、 load.4) Screw drive：Function: to change rotating motion回轉(zhuǎn)運(yùn)動 to rectilinear movement直線運(yùn)動 and transferring power in the same time.Classification：According to purposeTransferring power screw（car jack汽車千斤頂）；Transferring movement screw (in machine tool機(jī)床)；Adjusting screwThe coupling between the axle（軸）

12、and the hub（輪轂）1) The key joint鍵連接Function：hoop location(固定) and transfer torque（傳遞力矩） between the axle and the hubType（多畫圖解釋）：straight key平鍵（主要記）, woodruff key半圓鍵, taper key楔鍵, tangent key切向鍵.2) The spline coupling花鍵連接Component（一對零件）：external spline, internal splineAdvantage：uniform pressure均勻受力；hi

13、gh load carrying ability；improve working accuracyDisadvantage：Working cost highlyWelding焊接（聯(lián)系“工程材料”相關(guān)）Mechanical drivesSummaryAim：To transmit power and change the state of motion between prime mechanism and Executive mechanismClassification：by friction，mesh（嚙合），······&#

14、183;······；By electric driveBelt drives1. Type（多畫圖，圖見書P144）: Friction belt driveFlat belts平帶；Round belts圓帶； V belts（It is now the basic belt for power transmission. because Greater contact area接觸面積，bigger friction）；Multi-groove belts多楔帶Mesh belt drive2. Features：Belt dr

15、ive is simple, inexpensive, They need no lubrication潤滑 and minimal maintenance維護(hù).Slipping(打滑)the Friction of belt drive reached its maximumFriction, so wear of belt is a problem3. Calculate：機(jī)械設(shè)計(jì)課本P146P147三條公式Chain driveChain drive is Mesh drive(Sprocket鏈輪 and chain鏈條)Advantage：Chain drive has no sli

16、pping and is Mesh drive, so it has precise transmission ratio and high efficiency.Chain is made of metal, it can work in extreme environment.(machice of Coal transportation)Disadvantage: NoiseType: *Roller chain; Tooth Chain (Silent Chain)Calculate：機(jī)械設(shè)計(jì)課本p172公式1*Gear Drives機(jī)械原理+機(jī)械設(shè)計(jì)相關(guān)章節(jié)1. Advantage：

17、high efficiency( can reach 99)；compact structure結(jié)構(gòu)緊湊；high reliability and long life；2. Disadvantage：high precision request of installing高安裝精度；higher price。3. Type：spur gear；helical gear斜齒輪；（double- helical gear人字齒；）bevel gear錐齒輪；worm(蝸桿)and worm wheel；rack齒條 and pinion小齒輪4. 基礎(chǔ)知識（of Spur gear）：1) 見機(jī)械

18、設(shè)計(jì).pdf2) how can a pair of involute gears mesh?寫公式3) The pressure angles（）and the module（m） are equal ；the center distance between the gears is equal to the sum of Pitch radius4) Helix angle of helical gear(螺旋角)注意斜齒輪，錐齒輪，蝸輪蝸桿旋向（The direction of rotation）和力的方向的判斷。5. Produce gears:Gear milling銑齒；Gear

19、hobbing滾齒；Gear shaping插齒1) Gear millinguse the Milling cutter; machine the tooth one by one2) Gear hobbingGear hobbing is a multipoint machining process多點(diǎn)加工 in which gear teeth are machined by a series of cuts with a helical(螺旋的) cutter (hob). the hob and the workpiece Both revolve旋轉(zhuǎn) constantly3) Ge

20、ar shaping(畫運(yùn)動方向圖)Both the gear blank輪坯 and cutter are set in a vertical plane and rotated such as the two gears in meshing.; The cutter have Cutting movement切削運(yùn)動, Feed motion進(jìn)給運(yùn)動 ;the gear blank also have small movment.6. Types of gear failures：Breakage（崩齒）; Surface pitting點(diǎn)蝕Small piece off pitting

21、(麻點(diǎn)) ，increase the hardness of materialgear scoring膠合scoring（劃痕），increase the hardness of the tooth surfacewear磨損（聯(lián)系上面磨損相關(guān)知識）; plastic deformation塑性變形7. Gear design:（相關(guān)見機(jī)械設(shè)計(jì)課程設(shè)計(jì).doc）A. Choose gear type, precision grade精度等級and material Type: spur gear drive order bevel gear drivePrecision grade: 13 g

22、rade (0 to 12, 0 is the best)Material: 40 chrome (Cr鉻) to small gear and45 steel( 45號鋼)B.Design according to tooth contact strength（齒面接觸疲勞強(qiáng)度）C.Design according to tooth root bending strength（齒根彎曲疲勞強(qiáng)度）D.Compare the results from different method, choose the module, get the numbers of teeth（齒數(shù)z1, z2）E.

23、Calculate the size (pitch diameters節(jié)圓直徑, the distance centers between two ,width of the gear)Splash lubrication飛濺潤滑（浸油潤滑）BearingPlain bearing1. Definition：Bearings working under sliding friction；no rolling elements；The simplest example of a plain bearing is a shaft rotating in a hole.2. Feature：use

24、in High speed, harsh working environment, large impact and vibration, small space3. Structure：(畫剖面圖展示)the journal軸頸 (i.e., the part of the shaft in contact with the bearing)bushing軸瓦；（is inserted into a housing to provide a bearing surface for rotary applications）Bearing lining軸承襯（Friction-reducing

25、material layer）4. Material：Babbitt巴氏合金(a kind of alloy，make as bearing lining,expensive)Rolling Element bearing1. Definition：Bearings working under Rolling friction; Is standardized被標(biāo)準(zhǔn)化 and widely used；（畫圖表示）2. Structure: Inner ring, outer ring, rolling element, cage保持架（to Separating the rolling elements）3. Type：According to the shape of the rolling elementballs, cylind