畢業(yè)論文數(shù)控銑床孔類零件加工

1、天津?yàn)I海職業(yè)學(xué)院畢業(yè)設(shè)計(jì)（論文）數(shù)控銑床孔類零件加工 作者：管立宇 院系：天津?yàn)I海職業(yè)學(xué)院機(jī)電工程系 專業(yè)：機(jī)電一體化技術(shù) 年級(jí)：2010級(jí) 學(xué)號(hào)： 20100141309 指導(dǎo)教師：章黎麗 摘 要盤類零件是由多個(gè)端面、深孔、螺紋孔、曲面、溝槽、外輪廓組合而成的較復(fù)雜的盤形零件。其特點(diǎn)是零件基本形狀呈盤形塊狀，零件表面匯集了多種典型表面。加工時(shí)，裝夾次數(shù)一般較少，但所用刀具一般較多，編制程序較繁瑣。加工前需要做好充分的準(zhǔn)備，包括圖紙分析、確定加工工藝、選用機(jī)床型號(hào)、選用毛坯大小、確定走刀路線與加工順序等，其前期的準(zhǔn)備工作比較復(fù)雜。關(guān)鍵詞：盤類零件 圖紙分析 確定加工工藝 機(jī)床目 錄 一. 盤類

2、零件加工工藝性分析 11.1 選擇并確定數(shù)控加工中心加工盤類零件 11.2 盤類零件圖樣的工藝性分析 21.3 盤類零件的加工路線 3二. 盤類零件加工工藝的確定 32.1 工藝分析 32.2 工藝卡片 52.3刀具卡片 62.4 走刀路線 62.5 程序的編制 11三. 誤差分析15四. 結(jié)論15參考文獻(xiàn) 16 一 盤類零件加工的工藝性分析盤類零件加工工藝性分析是編程前的重要工藝準(zhǔn)備工作之一，根據(jù)實(shí)際加工，利用數(shù)控加工中心具有高精度、高柔性、高效率，且適合加工具有復(fù)雜輪廓、端面的零件等特點(diǎn)。通過(guò)對(duì)使用BV75型數(shù)控加工中心加工盤類零件，來(lái)闡述以下幾個(gè)方面的問(wèn)題： 1.1 選擇并確定數(shù)控加工中

3、心加工盤類零件在選擇加工盤類零件的設(shè)備時(shí)，應(yīng)充分發(fā)揮數(shù)控加工中心適用于加工復(fù)雜端面這一加工優(yōu)勢(shì)。選擇BV75數(shù)控加工中心的主要依據(jù)如下：BV75立式加工中心采用專業(yè)化廠家提供的數(shù)控系統(tǒng)，各直線運(yùn)動(dòng)軸、主軸及追加旋轉(zhuǎn)軸均采用伺服電機(jī)驅(qū)動(dòng)，三軸或四軸聯(lián)動(dòng)，可進(jìn)行各種銑削、鏜孔、鉆鉸孔、剛性攻絲等一般機(jī)械加工，并實(shí)現(xiàn)數(shù)字化精確定位，通過(guò)運(yùn)動(dòng)軸插補(bǔ)聯(lián)動(dòng)可實(shí)現(xiàn)旋切大螺紋、多種曲面加工，且同一臺(tái)機(jī)床上可實(shí)現(xiàn)工件一次裝夾過(guò)程中多種工序的粗、精加工。同時(shí)，數(shù)控系統(tǒng)中配備了多種典型循環(huán)程序供加工過(guò)程中編程選用。機(jī)床工作過(guò)程中的切削加工、冷卻液提供、刀具交換等均由預(yù)編制程序控制，且換刀過(guò)程中自動(dòng)實(shí)施主軸中心吹氣，

4、保持刀柄及主軸錐孔清潔。機(jī)床切削過(guò)程中產(chǎn)生的切屑根據(jù)配置不同或者由沖刷系統(tǒng)及排屑器等定向排送到集屑小車，或者人工清理。BV75立式加工中心主要技術(shù)參數(shù)如下：機(jī)床行程范圍X軸 mm762Y軸 mm510（帶A軸為450或490）Z軸 mm560工作臺(tái)參數(shù)工作臺(tái)尺寸 mm610*900T型槽尺寸 mm5-18*100*125工作臺(tái)最大承載能力（均布） kg500主軸端面直工作臺(tái)面距離 mm152712主軸中心至立柱導(dǎo)軌面距離 mm563.4移動(dòng)速度快速移動(dòng)速度 mm/min24000切削進(jìn)給速度 mm/min315000主軸參數(shù)主軸錐孔7：24主軸軸徑 mm70刀庫(kù)參數(shù)斗笠式刀庫(kù)機(jī)械手式刀庫(kù)刀庫(kù)容

5、量（把）2124換刀方式任選隨機(jī)換刀時(shí)間（秒）62.5最大刀具直徑 mm8075相鄰無(wú)刀最大刀具直徑 mm160120最大道具長(zhǎng)度 mm304290最大單刀重量 kg6.86刀庫(kù)承載能力 kg68801.2 盤類零件圖樣的工藝性分析根據(jù)BV75數(shù)控加工中心加工盤類零件的特點(diǎn)，對(duì)零件圖紙進(jìn)行工藝分析時(shí)，應(yīng)著重考慮如下幾點(diǎn)：（1） 盤類零件圖紙的尺寸分析根據(jù)盤類零件圖紙的分析，應(yīng)首先確定零件上各端面的相互位置、相距尺寸，保證加工時(shí)刀具的走刀路線不會(huì)干涉到零件的各個(gè)端面。例如，在加工時(shí)刀具直徑為10mm，零件兩端面距離為9mm，若在加工前發(fā)現(xiàn)這一點(diǎn)便會(huì)在保證加工精度的情況下更換合適的刀具。相反，如果

6、在實(shí)際加工前對(duì)圖紙的分析不夠透徹，便有可能出現(xiàn)上述錯(cuò)誤，造成零件加工失敗，不僅浪費(fèi)時(shí)間，還提高了加工成本，得不償失。（2） 順銑和逆銑對(duì)加工的影響 在銑削加工盤類零件時(shí)，采用順銑還是逆銑方式是影響加工表面粗糙度的重要因素之一。逆銑時(shí)切削力F的水平分力FX的方向與進(jìn)給運(yùn)動(dòng)Vf方向相反，順銑時(shí)切削力F的水平分力FX的方向與進(jìn)給運(yùn)動(dòng)Vf的方向相同。銑削方式的選擇應(yīng)視零件圖樣的加工要求，工件材料的性質(zhì)、特點(diǎn)以及機(jī)床型號(hào)、刀具規(guī)格等條件因素綜合考慮。通常，由于數(shù)控加工中心傳動(dòng)采用滾珠絲杠結(jié)構(gòu)，其進(jìn)給傳動(dòng)間隙很小，順銑的工藝性就優(yōu)越于逆銑。為了降低表面粗糙度值，提高刀具的耐用度，對(duì)于鋁鎂合金、鈦合金和耐熱

7、合金等材料，盡可能采用順銑加工。但如果盤類零件的毛坯為黑色金屬鍛件或鑄件，表皮較硬而且余量一般較大，這時(shí)采用逆銑較為合理。1.3 盤類零件的加工路線（1） z軸方向走刀路線在加工盤類零件時(shí)，Z軸的切削深度尤為重要。必須要看清圖紙的標(biāo)注，并在深度上也要保證高精度。銑削外輪廓時(shí)，盡量選擇在工件外下刀。銑削內(nèi)輪廓時(shí)，要選好下刀點(diǎn)，必須保證不能干涉工件的尺寸精度。（2）x、y軸方向走刀路線在加工盤類零件時(shí)，x、y軸方向走刀路線是否正確直接影響到零件加工的質(zhì)量。x、y軸方向在走刀路線正確的情況下基本能保證零件成型正確。若x、y軸方向走刀路線錯(cuò)誤，則直接導(dǎo)致工件作廢，成為廢品。如果走刀路線偏差較大，不僅會(huì)

8、導(dǎo)致零件作廢，更會(huì)威脅到操作人員的人身安全。（3）對(duì)于二維輪廓加工通常采用以下幾個(gè)步驟：(1)從起刀點(diǎn)下刀到下刀點(diǎn)；(2)沿切向切入工件； (3)輪廓切削； (4)刀具向上抬刀，退離工件； (5)返回起刀點(diǎn)。二 盤類零件加工工藝的確定2.1 工藝分析圖1 盤類零件需要加工的盤類零件如圖1所示，零件的材料為45號(hào)鋼，毛坯選為100mm×80mm×27mm的方形毛坯料。且底面和四個(gè)輪廓面均已加工好，要求在BV75立式加工中心上加工頂面及孔。（1） 加工部位分析加工頂面；加工32孔；加工60沉孔；加工4×M87H螺紋孔；加工2 × 12孔；加工3 ×

9、 6孔（2） 工步設(shè)計(jì)工步號(hào)工步內(nèi)容刀具號(hào)刀具規(guī)格1粗銑頂面T1端面銑刀1252鉆32、 12孔中心孔T2中心鉆23鉆32、 12孔至11.5T3麻花鉆11.54擴(kuò)32孔至30T4麻花鉆305鉆3×6孔至尺寸T5麻花鉆66粗銑60沉孔T6立銑刀18，2刃7鉆4×M8底孔至6.8T7麻花鉆6.88鏜32孔至31.7T8鏜刀31.79精銑頂面T1端面銑刀12510鉸12孔至尺寸T9鉸刀1211精鏜32孔至尺寸T10微調(diào)精鏜刀3212精銑60沉孔至尺寸T11立銑刀18，4刃1312孔口倒角T13倒角刀20143×6、M8孔口倒角T3麻花鉆11.515攻4×M8

10、螺紋T12絲錐M82.2工藝卡片序號(hào)加工工序刀具刀具名稱主軸 速度進(jìn)給 速度mm/min刀具長(zhǎng)度補(bǔ)償?shù)毒甙霃窖a(bǔ)償?shù)毒哐a(bǔ)償值1粗銑頂面 T1端面銑刀125240300H01實(shí)測(cè)值2鉆32、 12孔中心孔 T2中心鉆21000100H023鉆32、 12孔至11.5 T3麻花鉆11.5550110H034擴(kuò)32孔至30 T4麻花鉆3028085H045鉆3×6孔至尺寸 T5麻花鉆61000220H056粗銑60沉孔 T6立銑刀18，2刃3701000H06D0630.57鉆4×M8底孔至6.8 T7麻花鉆6.8950140H078鏜32孔至31.7 T8鏜刀31.7830120

11、H089精銑頂面 T1端面銑刀125320280H0110鉸12孔至尺寸 T9鉸刀1217042H0911精鏜32孔至尺寸 T10微調(diào)精鏜刀3294075H1012精銑60沉孔至尺寸T11立銑刀18， 4刃4601000H11D11301312孔口倒角 T13倒角刀2030050H13143×6、M8孔口倒角 T3麻花鉆11.530050H0315攻4×M8螺紋 T12絲錐M8100125H122.3刀具卡片刀具選擇與加工目的轉(zhuǎn)速r/min進(jìn)給量mm/min背吃刀量mm端面銑刀125 240300中心鉆2 10001002麻花鉆11.555011030麻花鉆30 28085

12、35麻花鉆6100022015立銑刀18，2刃370100010麻花鉆6.895014030鏜刀31.783012027鉸刀121704230微調(diào)精鏜刀329407527立銑刀18，4刃460100010倒角刀2030050麻花鉆11.530050絲錐M8100125272.4走刀路線1）粗銑頂面2）鉆32、 12孔中心孔3）鉆32、 12孔至11.54）擴(kuò)32孔至305）鉆3×6孔至尺寸6）粗銑60沉孔7）鉆4×M8底孔至6.88）鏜32孔至31.79）精銑頂面10）鉸12孔至尺寸11）精鏜32孔至尺寸12）精銑60沉孔至尺寸13） 12孔口倒角14） 3×6、

13、M8孔口倒角15）攻4×M8螺紋2.5程序的編制如圖所示為本文數(shù)控程序編制的流程圖。加工工藝參數(shù)輸入部分以人機(jī)交互對(duì)話方式輸入盤類零件銑削加工的有關(guān)工藝參數(shù)，如刀具半徑，起刀點(diǎn)、加工走向，主軸轉(zhuǎn)速、進(jìn)給速度等。NC 數(shù)據(jù)處理部分根據(jù)幾何形狀數(shù)據(jù)及加工工藝參數(shù),對(duì)數(shù)據(jù)文件中的實(shí)體(直線、圓弧、列表點(diǎn)) 的數(shù)據(jù)重新排序,列表點(diǎn)先以三次B 樣條曲線進(jìn)行擬合，再用雙圓弧法進(jìn)行插補(bǔ)，形成標(biāo)準(zhǔn)的G 代碼格式。刀具軌跡仿真部分主要是檢驗(yàn)數(shù)控程序語(yǔ)法錯(cuò)誤，加工時(shí)是否有干涉現(xiàn)象或刀具軌跡不合理等，可以減少實(shí)際加工中試切次數(shù)和防止設(shè)備、刀具、工件的損壞。加工程序編制如下：O0001;N3 G17 G90

14、 G40 G80 G49 G21;G91 G28 Z0.;N5 M06 T01;N8 G90 G54 G00 X120. Y0.;N9 M03 S240;N10 G43 Z100. H01;N11 Z0.5;N12 G01 X-120. F300;N13 G00 Z100. M05;N14 G91 G28 Z0. M05;/ M00；N16 M06 T02;N19 G90 G54 G00 X0. Y0.;N20 M03 S1000;N21 G43 Z100. H02;N22 G99 G81 Z-5. R5. F100;N23 X-36. Y26.;N24 G98 X36. Y-26.;N25

15、G80 G91 G28 Z0. M05;/ M00;N27 M06 T03;N30 G90 G54 G00 X0. Y0.;N31 M03 S550; N32 G43 Z100. H03;N33 G99 G81 Z-30. R5. F110;N34 X-36. Y26.;N35 G98 X36. Y-26.;N36 G80 G91 G28 Z0. M05;/ M00;N38 M06 T04;N41 G90 G54 G00 X0. Y0.;N42 M03 S280;N43 G43 Z100. H04;N44 G98 G81 Z-35. R5.0 F85;N45 G80 G91 G28 Z0. M

16、05;/ M00;N47 M06 T05;N50 G90 G54 G00 X40. Y0.;N51 M03 S1000;N52 G43 Z100. H05;N53 G99 G81 Z-15. R5. F220;N54 Y15.;N55 G98 Y30.;N56 G80 G91 G28 Z0. M05;/ M00;N58 M06 T06;N61G90G54G00 X0. Y0.;N62 M03 S370;N63 G43 Z5. H06;N64 G01 Z-10. F1000;N65 G41 X8. Y-15. D06 F110;N66 G03 X23. Y0. R15.;N67 I-23.;N6

17、8 X8. Y15. R15.;G00 G40 X0 Y0;N69 G01 G41 X15. Y-15. D06;N70 G03 X30. Y0. R15.;N71 I-30.;N72 X15. Y15. R15.;N73 G01 X-16. Y0.;N74 Z-4.7 F1000;N75 X-61. F110;N76 X-56.5 Y-41.586;N77 X-12.213 Y-16.017;N78 X15. Y-15. F1000;N79 G03 X30. Y0. R15. F110;N80 G01 Y51.;N81 X0.;N82 Y16.;N83 G40 Y0. F1000;N84 G

18、00 Z100. M05;N85 G91G28 Z0.;/ M00;N87 M06 T07;N88 G90 G54 G00 X23. Y0.;N91 M03 S950;N92 G43 Z100. H07;N93 G98 G81 Z-30. R5. F140;N94 X0. Y23.;N95 X-23. Y0.;N96 G98 X0. Y-23.;N97 G80 G91 G28 Z0. M05;/ M00;N9 M06 T08;N102 G90 G54 G00 X0. Y0.;N103 M03 S830;N100 G43 Z100. H08;N101 G98 G76 Z-27. R5. Q0.1

19、 F120;N102 G80 G91 G28 Z0. M05;/ M00;N106 M06 T01;N107 G90 G54 G00 X120. Y0.;N108 M03 S320;N109 G43 Z100. H01;N110 Z0;N111 G01 X-120. F280;N112 G00 Z100. M05;N113 G91 G28 Z0.;/ M00；N115 M06 T09;N118 G90 G54 G00 X-36. Y26.;N119 M03 S170;N120 G43 Z100. H09;N121 G99 G82 Z-30. R5. P1000 F42;N122 G98 X36

20、. Y-26.;N123 G80 G91 G28 Z0. M05;/ M00;N9 M06 T10;N102 G90 G54 G00 X0. Y0.;N103 M03 S940;N100 G43 Z100. H10;N101 G98 G76 Z-27. R5. Q0.1 F75;N102 G80 G91 G28 Z0. M05;/ M00;N134 M06 T11;N137 G90G54G00 X0. Y0.;N138 M03 S460;N139 G43 Z5. H11;N140 G01 Z-10. F1000;N141 G41 X8. Y-15. D11 F80;N142 X15. ;N14

21、3 G03 X30. Y0 R15.;N144 I-30.;N145 X15. Y-15. R15.;N146 G01 X-16. Y0. ;N147 Z-5. F1000;N148 X-61. F110;N149 X-56.5 Y-41.586.;N150 X-12.213 Y-16.017 ;N151 X15. Y-15. F1000;N152 G03 X30. Y0 R15. F150;N153 G01 Y51.;N154 X0. ;N155 Y16. ;N156 G40 Y0. F1000;N157 G00 Z100. M05;N158 G91 G28 Z0;/ M00;N185 M0

22、6 T12;N187 G90 G54 G00 X23. Y0.;N188 M03 S100;N190 G43 Z100. H12;N192 G98 G84 Z-27. R10. F125;N193 X0. Y23.;N194 X-23. Y0.;N195 X0. Y-23.;N196 G80 G91 G28 Z0.;N198 G28 X0. Y0.;M30; 三 誤差分析在數(shù)控加工的整個(gè)過(guò)程中，經(jīng)常會(huì)產(chǎn)生以下幾種誤差：(1) 近似計(jì)算誤差：主要產(chǎn)生在加工列表曲線、曲面輪廓時(shí)，采用近似計(jì)算法所發(fā)生的逼近誤差。(2) 插補(bǔ)誤差：這是由于用直線段或圓弧段逼近零件輪廓曲線所產(chǎn)生的誤差。減少插補(bǔ)誤差的方

23、法是密化插補(bǔ)點(diǎn)，但這會(huì)增加程序段數(shù)目，增加計(jì)算和編程的工作量。(3) 尺寸圓整誤差：這是將計(jì)算尺寸換算成機(jī)床的脈沖當(dāng)量時(shí)由于圓整化所產(chǎn)生的誤差。數(shù)控機(jī)床能反映出的最小位移量是一個(gè)脈沖當(dāng)量，小于一個(gè)脈沖當(dāng)量的數(shù)據(jù)只能四舍五入，于是就產(chǎn)生了誤差。(4) 操作誤差在加工過(guò)程中，操作者在操作過(guò)程中，工件的安裝引起的誤差和尋找工件坐標(biāo)原點(diǎn)過(guò)程中容易引起誤差。首先安裝過(guò)程中，可能會(huì)產(chǎn)生工件面與定位面之間靠不緊，解決辦法：在安裝過(guò)程中四個(gè)壓板要同時(shí)壓緊，不能其中某個(gè)壓緊。先讓四個(gè)螺栓稍微擰一下但是不要徹底擰緊，并且用尼龍棒或者木棒在工件上輕輕敲打，使工件底面與定位面之間靠實(shí)。并且擰緊順序?yàn)閷?duì)角擰緊。尋找坐標(biāo)

24、原點(diǎn)過(guò)程中，由于使用的設(shè)備的精度不同，會(huì)帶來(lái)不同的誤差。解決辦法：使用精度高的儀器，如：千分表、尋邊器等等。四 結(jié)論通過(guò)對(duì)盤類零件的工藝分析，合理制定了其加工工藝過(guò)程，選擇了合適的加工刀具及切削參數(shù)，合理的編制了加工盤類零件的數(shù)控程序，經(jīng)過(guò)獨(dú)立的分析、計(jì)算及改善加工過(guò)程，避免了可能產(chǎn)生的各種誤差，使用BV75數(shù)控加工中心加工出的盤類零件，精度較高，尺寸符合圖紙要求。即提高了產(chǎn)品的加工質(zhì)量和效率，又降低了工人的勞動(dòng)強(qiáng)度。 對(duì)我個(gè)人的數(shù)控技術(shù)及獨(dú)立完成加工的技能有了很大的幫助，并且使我更加喜歡數(shù)控技術(shù)專業(yè)，我充分看到了自己的不足，使我的技術(shù)有了一次跨越性的提高。參考文獻(xiàn)1.徐宏海 數(shù)控加工工藝 學(xué)

25、工業(yè)出版社，2003，7-50252.徐嘉元、曾家駒 機(jī)械制造工藝學(xué) 機(jī)械工業(yè)出版社，1999，7-1113.華茂發(fā) 數(shù)控機(jī)床加工工藝 械工業(yè)出版社，2000，7-1114.陳日曜 金屬切削原理 機(jī)械工業(yè)出版社 2002.45.李善樹 數(shù)控機(jī)床及其應(yīng)用 機(jī)械工業(yè)出版社 2001.16.延波 加工中心的數(shù)控編程與操作技術(shù) 機(jī)械工業(yè)出版社 2001.1ag an employment tribunal clai Emloyment tribunals sort out disagreements between employers and employees. You may need to ma

26、ke a claim to an employment tribunal if: you don't agree with the disciplinary action your employer has taken against you your employer dismisses you and you think that you have been dismissed unfairly. For more informu, take advice from one of the organisations listed under Fur ther help.

27、Employment tribunals are less formal than some other courts, but it is still a legal process and you will need to give evidence under an oath or affirmation. Most people find making a claim to an employment tribunal challenging. If you are thinking about making a claim to an employment tribunal, you

28、 should get help straight away from one of the organisations listed under Further help. ation about dismissal and unfair dismissal, see Dismissal. You can make a claim to an employment tribunal, even if you haven't appealed against the disciplinary action your employer has ta

29、ken against you. However, if you win your case, the tribunal may reduce any compensation awarded to you as a result of your failure to appeal. Remember that in most cases you must make an application to an employment tribunal within three months of the date when the event you are complaining about h

30、appened. If your application is received after this time limit, the tribunal will not usually accept i. If you are worried about how the time limits apply to you If you are being represented by a solicitor at the tribunal, they may ask you to sign an agreement where you pay their fee out of your com

31、pensation if you win the case. This is known as a damages-based agreement. In England and Wales, your solicitor can't charge you more than 35% of your compensation if you win the case. You are clear about the terms of the agreement. It might be best to get advice from an experienced ad

32、viser, for example, at a Citizens Advice Bureau.  To find your nearest CAB, including those that give advice by e-mail, click on nearest CAB. For more information about making a claim to an employment tribunal, see Employment tribunals. The (lack of) air up there Watch m Cay man Islan

33、ds-based Webb, the head of Fifa's anti-racism taskforce, is in London for the Football Association's 150th anniversary celebrations and will attend City's Premier League match at Chelsea on Sunday. "I am going to be at the match tomorrow and I have asked to meet Ya ya Toure," h

34、e told BBC Sport. "For me it's about how he felt and I would like to speak to him first to find out what his experience was." Uefa has opened disciplinary proceedings against CSKA for the "racist behaviour of their fans" during City's 2-1 win. Michel Platin

35、i, president of European football's governing body, has also ordered an immediate investigation into the referee's actions. CSKA said they were "surprised and disappointed" by Toure's complaint. In a statement the Russian side added: "We found no racist insults from fans o

36、f CSKA." Age has reached the end of the beginning of a word. May be guilty in his seems to passing a lot of different life became the appearance of the same day; May be back in the past, to oneself the paranoid weird belief disillusionment, these days, my mind has been very messy, in my mind co

37、nstantly. Always feel oneself should go to do something, or write something. Twenty years of life trajectory deeply shallow, suddenly feel something, do it.一字開頭的年齡已經(jīng)到了尾聲?；蛟S是愧疚于自己似乎把轉(zhuǎn)瞬即逝的很多個(gè)不同的日子過(guò)成了同一天的樣子；或許是追溯過(guò)去，對(duì)自己那些近乎偏執(zhí)的怪異信念的醒悟，這些天以來(lái)，思緒一直很凌亂，在腦海中不斷糾纏。總覺得自己似乎應(yīng)該去做點(diǎn)什么，或者寫點(diǎn)什么。二十年的人生軌跡深深淺淺，突然就感覺到有些事情，非

38、做不可了。The end of our life, and can meet many things really do?而窮盡我們的一生，又能遇到多少事情是真正地非做不可？ During my childhood, think lucky money and new clothes are necessary for New Year, but as the advance of the age, will be more and more found that those things are optional; Junior high school, thought to have a

39、crush on just means that the real growth, but over the past three years later, his writing of alumni in peace, suddenly found that isn't really grow up, it seems is not so important; Then in high school, think don't want to give vent to out your inner voice can be in the high school children

40、 of the feelings in a period, but was eventually infarction when graduation party in the throat, later again stood on the pitch he has sweat profusely, looked at his thrown a basketball hoops, suddenly found himself has already can't remember his appearance. Baumgartner the disappointing news: M

41、ission aborted. r plays an important role in this mission. Starting at the ground, conditions have to be very calm - winds less than 2 mph, with no precipitation or humidity and limited cloud cover. The balloon, with capsule attached, will move through the lower level of the atmosphere (the troposph

42、ere) where our day-to-day weather lives. It will climb higher than the tip of Mount Everest (5.5 miles/8.85 kilometers), drifting even higher than the cruising altitude of commercial airliners (5.6 miles/9.17 kilometers) and into the stratosphere. As he crosses the boundary layer (called the tropopause),e can expect a lot of turbulence. We often close ourselves off when traumatic events happen in our liv