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湘潭大學興湘學院
畢業(yè)論文（設計）鑒定意見
學號： 2010963142 姓名： 朱楊華 專業(yè)： 機械設計制造及自動化
畢業(yè)論文（設計說明書） 頁 圖 表 張
論文（設計）題目：自行車用無級變速器結構的設計
內容提要： 自信車用無級變速器進行對自行車的調速，現(xiàn)今對自信車是一種新型的研
發(fā)設計方案。本文首先介紹機械無級變速器的發(fā)展概述及其特征和應用，然后歸納了
現(xiàn)今幾種無級變速自行車的發(fā)展概況。在以上內容的基礎上，提出了兩個方案，經(jīng)過
仔細的分析與比較，選出了鋼球行星式無級變速器采用螺旋傳動實現(xiàn)球架左右移動為
最佳方案，并對該裝置的部分進行改進，以滿足該設計裝置能在自行車上使用的要求：
對該變速器的部分零件進行結構設計和尺寸計算，另外其中一部分零件還要進行壽命
計算和強度校核，以保證該無級變速自行車能夠滿足老師的設計要求；最后對該無級
變速器進行安裝，根據(jù)運動原理讓我們更加了解該裝置的調速過程。用CAD繪圖軟件
繪制出該裝配圖以及非標準零件的零件圖。
指導教師評語
該生在本次畢業(yè)設計中表現(xiàn)出基礎知識扎實、專業(yè)知識牢固，具有較強的獨立工作能力，有一定的創(chuàng)新性。計算機操作熟練。勞動紀律性強，工作認真扎實。能如期完成設計任務，設計方案正確可行，結構合理，圖面質量好。設計說明書撰寫認真、規(guī)范，具有較好的專業(yè)英文文獻閱讀與翻譯能力。同意其參加答辯。
建議成績評定為良好。
指導教師：
2014年 5 月26日
答辯簡要情況及評語
根據(jù)答辯情況，答辯小組同意其成績評定為 。
答辯小組組長：
年 月 日
答辯委員會意見
經(jīng)答辯委員會討論，同意該畢業(yè)論文（設計）成績評定為
答辯委員會主任：
年 月 日
湘潭大學興湘學院畢業(yè)論文
題 目： 自行車用無級變速器結構設計
專 業(yè)： 機械設計制造及其自動化
學 號： 2010963142
姓 名： 朱楊華
指導教師： 聶松輝
完成日期： 2014年5月29日
湘潭大學興湘學院
畢業(yè)設計說明書
題 目： 自行車用無級變速器結構設計
專 業(yè)： 機械設計制造及其自動化
學 號： 2010963142
姓 名： 朱楊華
指導教師： 聶松輝
完成日期： 2014年5月29日
湘潭大學興湘學院
畢業(yè)論文（設計）任務書
論文（設計）題目：自行車用無級變速器結構設計
學號： 2010963142 姓名： 朱楊華 專業(yè)： 機械設計制造及其自動化
指導教師： 聶松輝 系主任：
一、主要內容及基本要求
1、輸入功率P=0.15kw、最低轉速n=20rpm、調速范圍R=8；
2、裝配圖A0#1張、零部件圖總量不小于A0#1張；
3、設計說明書一份（含電子文檔）；
4、英文文獻翻譯資料一份，不少于3000Words。
二、重點研究的問題
1、機械式無級變速器的變速原理；
2、基于變速原理的傳動結構實現(xiàn)。
三、進度安排
各階段完成的內容
起止時間
1
熟悉課題與基礎資料
第1周
2
調研、收集資料
第2周
3
方案設計與論證
第3～4周
4
無級變速器各零件三維模型設計
第5～7周
5
無級變速器總裝配圖設計
第8周
6
無級變速器工程圖設計
第9周
7
無級變速器關鍵部件運動仿真
第10周
8
撰寫設計說明書
第11周
9
英文文獻翻譯\答辯
第12周
四、應收集的資料及主要參考文獻
應收集的資料：自行車無級變速器的類型和無級變速自行車的研究現(xiàn)狀，零件的設計與計算的方法，以及選型等。
主要參考文獻：
[1] 周有強. 機械無級變速器[M]. 成都:機械工業(yè)出版社,2001.
[2] 阮忠唐.機械無級變速器設計與選用指南[M].北京:化學工業(yè)出版社，1999.
外文翻譯
半固態(tài)成型：
競爭來自汽車復雜零件的鍛造機
Q. ZHU1, S. P. MIDSON2
1.英國康明斯渦輪增壓技術有限公司，圣安得烈路，哈德斯菲爾德，Hd1 6RA S；
2.美國鋁復雜組分公司，科羅拉多州丹佛賈森街道2211南，80223， 2010年5月13日收到; 2010年6月25日接受
摘 要
葉輪制造的最新技術被稱為半固態(tài)成型（SSM）。它是康明斯渦輪增壓技術有限公司與鋁復合元件公司一起開發(fā)，SSM壓縮機輪的一種方式。它能使鑄造和加工固體之間（MFS）鋁合金車輪，實現(xiàn)成本和耐久性的地方。實驗結果表明，SSM材料具有優(yōu)良的顯微組織和力學性能，這些都高于MFS材料。測試包括耐久性的組分測試，使用加速的速度周期測試，證明SSM壓縮機輪子比鑄造的等值更耐用和接近MFS葉輪。為了使半固態(tài)處理進一步挑戰(zhàn)of other complex components and other materials in automotive industry in terms of both cost and durability are also discussed.，對汽車行業(yè)中制造成本和其他成分復雜等材料的耐久性進行了討論。
關鍵詞： 鋁合金; 半固體造型; 耐久性; 汽車復雜組分; 蒸氣增壓器壓縮機輪子
1引言
柴油和汽油發(fā)動機是造成的排放和全球變暖的一個重要來源。為了提高燃油效率和減少排放，汽車輕量化是一種有效的方法.。半固態(tài)成型（SSM）已成功幫助，減輕汽車零部件的重量，明顯改善的機械性能。所以，可以用小或更薄的壁零件。汽車零部件已成功用SSM。達斯古普塔[ 1 ]總結了最普遍的應用如下： 1) A357-T5,2)自動傳輸使換中檔杠桿A357-T5， 3)發(fā)動機裝配A357-T5， 4)引擎托架1 800 g A357-T5， 5)上部控制臂A356-T6， 6)懸浮A357-T5， 7)引擎托架720 g A357-T5， 8)引擎托架2400 g A357-T5和9)柴油引擎A356- T5泵體加油路軌。
發(fā)動機技術發(fā)展的另一種有效的提高燃油效率和減少排放。增加氣壓比率到發(fā)動機方式能夠進一步提高燃油效率和減少排放的目的。增加氣壓可以通過在一個渦輪增壓器壓縮機輪來實現(xiàn)。壓縮機輪需要非常復雜的葉片，幾何實現(xiàn)高壓力比。應付250 °C和重大溫度差時，壓縮機輪承受的旋轉速度高達200 000轉/分鐘。除機械力量和溫度能力的要求之外，由于在速度周期上的刀片的變化和振動，疲勞是一種典型的失效模式。
這種組合的復雜的幾何形狀和堅韌操作條件,意味著調制解調器壓縮機輪子要求最佳的物質技術。幾十年來，壓縮機的車輪含有鋁，硅和銅的合金。要達到指定的耐久性目標，然而，制約他們的發(fā)行速度，即是必要的。由于鑄造缺陷，在操作過程中減少了發(fā)動機的效率。因此，固體(MFS)或鍛件壓縮機輪子的開發(fā)，克服鑄件瑕疵問題。在耐久性的改善也意味MFS輪子可能可靠地跑以更高的速度，增長的燃料效率和減少排放。缺點是MFS鑄造比較昂貴。
因此，半固態(tài)成形加工（SSM）應用開發(fā)的制造過程中，在鑄造和MFS鋁合金之間車輪，去實現(xiàn)成本和耐久性能。由于壓縮機輪幾何形狀復雜，精度控制的要求和嚴格的操作條件，制造壓縮機輪可能是SSM最困難的過程。在這項工作SSM應用的開發(fā)和結果在制造業(yè)壓縮機輪子在復雜幾何學汽車組分制造被提出，為例SSM應用。
2 渦輪增壓
最近渦輪增壓技術廣泛用于柴油發(fā)動機和汽油發(fā)動機，直接噴射技術也一起發(fā)展。對于新汽車渦輪增壓器的應用量（合適的）。如圖1所示，在過去10年1999年-2004年穩(wěn)定增長約10%和2004年-2009年約5%，平均年增長率約7%。在2004年-2009年較低的增長率，主要是由經(jīng)濟衰退引起的。自2008年以來，未來10年預計年增長率將有約8%。2007年蒸氣增壓器新車的世界總寬容量大約是20百萬個單位，相當于6.8十億USD。
圖1 全球渦輪增壓發(fā)動機市場（首次適應卷）
渦輪增壓器可以通過壓縮機輪子有效地增加氣壓，這是由通過廢氣渦輪軸排氣。圖2顯示了一個典型的廢氣旁通增壓器。壓縮機輪子的轉動速度可高達200 000 r/min。進一步增加的速度是提高效率和燃油經(jīng)濟性。然而，轉動速度由壓縮機和渦輪葉輪的材料物產生限制。渦輪增壓器故障主要是由壓縮機或渦輪機在高溫條件下引起疲勞。
圖2典型的廢氣旁通增壓器概述
3 SMM制造渦輪增壓器壓縮機輪的挑戰(zhàn)
渦輪增壓器壓氣機葉輪幾何的設計是非常復雜，為了滿足特定的效率和耐久性的要求。圖3給出了一個典型的壓縮機葉輪的設計。葉片長度與葉片厚度比約為25，這使得它在SSM難填補的葉片和中央集線器刀片的質量比可以達到80左右，同時這使得它很難獲得滿意的葉片和輪轂組織。此外，葉片的曲度在處理以后SSM模子難拆卸。因此，模具設計，澆注系統(tǒng)設計及模具溫度控制和流道系統(tǒng)是達到一個成功的結果的關鍵參量[2]。另外，材料也必須經(jīng)過仔細挑選，以滿足在嚴格操作條件下符合壓縮機輪子的耐久性的嚴密要求。
圖3概述（a）、剖面圖（b）典型的壓縮機w heel砂輪
4 材料的選擇
材料的選擇是決定開始的物理性能如熱導率，熱系數(shù)和合金密度保證當前組分設計有效性。認為3XX鑄造鋁合金可用于目前壓縮機輪的設計?？捎盟衃 3-33 ] 數(shù)據(jù)的SSM的力學性能和鑄鋁合金比較后，319s合金被選擇制造壓縮機輪子。圖4顯示319s合金具有合理最好的和一致的拉伸強度和伸長率。從純粹的拉伸性能的觀點，SSM A201也顯示了可喜的成果。因此，SSM A201試驗，更好的實現(xiàn)了文學強度和延性比。然而，SSM A201沒有市售的。所以用于制造壓縮機輪仍然是SSM 319s合金。
圖4 SSM鋁合金的拉伸性能比較永久模鑄造的（PM）
5 結果
在表1中給出了SSM壓縮機輪選擇合金319s化學成分。圖5顯示SSM 319s壓縮機輪有優(yōu)越的抗拉伸強度和延展性。在2618鍛造熱處理T61的條件下用于壓縮機輪的c355和目前354接近。單軸疲勞試驗結果表明，試樣從一個平行的方向鍛造2618合金的金屬流動具有優(yōu)良的耐疲勞性，而在垂直方向有類似的疲勞性能抵抗熔鑄355（6）。金屬化流程樣品的取向之間這個區(qū)別主要出現(xiàn)從粗第二個階段微粒的對準線。改善疲勞在圖6小應變中可以看到SSM 319s在鑄造355的屬性。如圖7所示，已被證明組件的磁盤疲勞試驗，是由單軸的壓縮應力與R> O在從壓縮機輪子的后面面孔用機器制造的盤樣品進行。在渦輪增壓器組件測試中，檢測的細胞受康明斯渦輪增壓技術的限制，結果列于圖8。圖8顯示了鑄造c355，2618和SSM 319s相比的耐久性。SSM 319s和偽造2618壓縮機輪之間，雖然他們都優(yōu)越鑄造c355的耐久性。SSM 319s和偽造的2618的這重大改善主要來自材料的改善和鑄件瑕疵的排除，例如氧化物。除對材料的完整性，鍛造和SSM的改進清潔。鍛造2618和SSM 319s比鑄造的C355和354.0的晶粒結構細化和顯微組織是對壓縮機輪子的耐久性改善的另一貢獻(圖9)。
圖5顯示了SSM 319s鑄造優(yōu)越的抗拉性能C355, 354.0 and 319 while comparable with forged 2618c355，354和319，與鍛造2618
圖6通過鑄造SSM 319s顯示出c355與鍛造2618優(yōu)越的耐疲勞性
圖7 SSM 319s顯示出在鑄造c355阻力優(yōu)越的單軸疲勞resistance over cast C355
圖8 SSM 319s壓縮機輪表現(xiàn)出在鑄造c355壓縮機輪與forged 2618鍛造2618優(yōu)越的耐久性
圖9晶粒結構的鑄造c355（a），2618（b）和鍛造SSM 319s (c), indicating comparable grain size between forgedSSM 319s（c），表明類似的晶粒尺寸之間鍛造and SSM alloys, while both significant finer than cast alloy和SSM合金，而顯著小于鑄造合金。
5 執(zhí)行總結
1）渦輪增壓是實現(xiàn)大幅減排和燃油經(jīng)濟一個最成功的技術。渦輪增壓發(fā)動機在過去10年已經(jīng)取得大約7%的體積增加，并且未來10年預測增長8%。
2）SSM已被成功地應用于生產極其復雜的幾何渦輪增壓器的壓縮機車輪。
3）SSM壓縮機輪取得了拉伸，疲勞性能和部件的耐久性。所以，它接近2618鍛造，優(yōu)于鑄造c355。
6 未來的挑戰(zhàn)
雖然制造業(yè)的SSM汽車零部件已取得重大進展，研究人員努力開發(fā)新的合金和工藝，仍有需要更多的努力來滿足工業(yè)要求。這些措施包括：
1）更多選擇的合金
有汽車的工業(yè)應用不同要求，一些需要高強度，而有些人可能需要高的熱性能，疲勞性，耐腐蝕性和耐磨性。這些都需要不同的合金系統(tǒng)滿足一個或多個工業(yè)應用的要求。
2）高熔點合金系統(tǒng)
發(fā)展SSM是最大的努力過程歷史上以相對較低的熔化點、合金如鋁和鎂合金。一些努力和成功取得了高熔點點合金如鋼[ 34 ]，但進一步的研究需要發(fā)展的材料系統(tǒng)的鑄鐵，鋼鎳基合金。這些材料具有顯著的比鋁和鎂合金密度更高，所以有更大的潛在節(jié)省更多的重量汽車零部件，從而更多的燃油經(jīng)濟性，和提高質量和性能，耐久性在SSM過程改進的光比合金。
3）復雜的幾何部件
一些汽車零部件的復雜幾何，例如一個渦輪增壓器壓氣機輪和發(fā)動機缸頭，使得它很難實現(xiàn)嚴格的性能要求，在鑄造鍛坯加工效率/成本。因此，SSM幾何組成有制造復雜的巨大潛力。非常低的剪切強度在半固態(tài)狀態(tài)合金使它實現(xiàn)制造復雜的幾何部件時澆注系統(tǒng)的合理設計與模具結構在低剪切強度達到可容納相對較高的抗壓強度。
4）還原電流SSM元件成本
在使用SSM加工過程中減少零件的制造成本實現(xiàn)鍛坯。然而，由于成本高制造原料棒料，復雜性澆注系統(tǒng)和模具結構以及相對高成本，SSM組件的成本仍然顯著高于鑄造。因此，應作出努力，進一步達到降低成本棒料的原材料，設計和制造澆注系統(tǒng)和模具結構和工藝。
致謝
作者想表達他們的感謝，在康明斯渦輪增壓邁克爾鳳博士對批判性閱讀和科技有限公司本文的評論。多虧了安得烈.杰克遜的鋁成分復雜，開發(fā)工具和一般支持successfully manufacturing the SSM impelle成功地生產的SSM葉輪。
參考文獻
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Semi-solid moulding: Competition to cast and machine from forging in making automotive complex components Q. ZHU 1 , S. P. MIDSON 2 1. Cummins Turbo Technologies Limited, St. Andrews Road, Huddersfield, HD1 6RA, UK; 2. Aluminium Complex Components Inc, 2211 South Jason Street, Denver, Colorado 80223, USA Received 13 May 2010; accepted 25 June 2010 Abstract： The very latest technique for impeller manufacture is called semi-solid moulding (SSM). Cummins Turbo Technologies Limited, together with Aluminum Complex Components Inc, developed SSM compressor wheels as a way of achieving cost and durability performance somewhere between that of cast and machined from solid (MFS) aluminium alloy wheels. Experimental results show SSM material has a superior microstructure and mechanical properties over cast and comparable to MFS materials. Component testing including durability testing, using accelerated speed cycle tests, proves SSM compressor wheels emerge as being significantly more durable than cast equivalents and approaching that of MFS impellers. Further challenges for semi-solid processing in manufacture of other complex components and other materials in automotive industry in terms of both cost and durability are also discussed. Key words: aluminum alloys; semi-solid moulding; durability; automotive complex component; turbocharger compressor wheel 1 Introduction Diesel and gasoline engines are one of the most important sources to cause emission and global warming. To increase fuel efficiency and to reduce emission, vehicle weight reduction is one of the effective ways. Semi-solid moulding (SSM) has successfully helped to reduce weight of automotive components due to the significant improvement of mechanical properties over cast, so, smaller or thinner wall parts can be used. Automotive components have been successfully manufactured by SSM. DASGUPTA1 has summarized the most popular applications as: 1) fuel rail of A357-T5, 2) automatic transmission gear shift lever of A357-T5, 3) engine mount of A357-T5, 4) engine bracket 1 800 g of A357-T5, 5) upper control arm of A356-T6, 6) suspension of A357-T5, 7) engine bracket 720 g of A357-T5, 8) engine bracket 2 400 g of A357-T5, and 9) diesel engine pump body of A356-T5. Engine technology development is another effective way increasing fuel efficiency and to reduce emission. Increasing the air pressure ratio to the engine is a way to achieve the objective of further improving fuel efficiency and reducing emission. One way to increase air pressure can be achieved by a compressor wheel in a turbocharger. The compressor wheel needs very complex blade geometry to achieve high pressure ratios. Compressor wheel withstands rotational speeds up to 200 000 r/min but must do so while coping with up to 250 C and a significant temperature gradient. In addition to the requirements of mechanical strength and temperature capability, fatigue is a typical failure mode of a compressor wheel in application due to changes in speed cycles and vibration of blades. This combination of sophisticated geometry and tough operating conditions means that the modern compressor wheels demand the best material technology. Compressor wheels for decades have been cast from alloys containing aluminum, silicon and copper. To achieve the specified durability targets, however, it is necessary to restrict their release speed, i.e. to reduce efficiency of an engine during operation due to cast defects. Therefore, the machined from solid (MFS) or forging compressor wheels have been developed to overcome the casting defect problem. The improvement in durability also means MFS wheel can run reliably at the higher speeds, increasing fuel efficiency and reducing emission. The downside is that MFS is significantly more expensive than casting. Therefore, semi-solid moulding (SSM) processing is applied to develop a manufacturing process that is a Corresponding author: Q. ZHU; +44-1484-832567; E-mail: Qiang.zhuC; Q Trans. Nonferrous Met. Soc. China 20(2010) s1042-s1047 Q. ZHU, et al/Trans. Nonferrous Met. Soc. China 20(2010) s1042-s1047 s1043 way of achieving cost and durability performance somewhere between that of cast and MFS aluminum alloy wheels. Due to the complex geometry, precision control requirement and severe operation condition of a compressor wheel, manufacturing compressor wheel may be one of the most difficult processes for SSM. In this work, development and results of SSM application in manufacturing compressor wheels are presented, as an example of SSM application in manufacture of complex geometric automotive components. 2 Turbocharging Turbocharging technology is widely used for diesel engine and recently also for gasoline engine together with direct injection technology development. The volume of turbocharger application for new vehicles (first fit) has steadily increased by about 10% between 1999 and 2004 and 5% between 2004 and 2009, leading to about 7% average annual increase rate in the past 10 years (Fig.1). The lower increase rate between 2004 and 2009 has been mainly caused by the economic recession since 2008 and it is expected that annual increase rate in the next 10 years will be about 8%. The total world wide volume of turbochargers in 2007 was about 20 million units for new vehicles, which was equivalent to 6.8 billion USD. Fig.1 Global turbocharged engine market (first fit volume) Turbocharger can effectively increase air pressure ratio through a compressor wheel, which is driven by turbine wheel through a shaft by exhaust gas. Fig.2 shows a typical wastegated turbocharger. The speed of rotation of the compressor wheel can reach as high as 200 000 r/min. Further increasing speed is desirable for improved efficiency and fuel economy. However, the rotation speed is limited by materials properties of the compressor and turbine wheels. Failure of a turbocharger is mainly caused by fatigue of the compressor or turbine wheel operated at high temperatures. Fig.2 Overview of typical wastegated turbocharger 3 Challenges of manufacturing turbocharger compressor wheels by SSM The geometry of a turbocharger compressor wheel is designed to be very complex in order to meet specific efficiency and durability requirement. Fig.3 presents a typical design of a compressor wheel. The ratio of blade length to blade thickness is about 25, which makes it difficult to fill the blade during SSM process, and the ratio of mass at central hub to blade can be about 80, which makes it difficult to get satisfied microstructure for both blade and hub simultaneously. In addition, the curvature of the blades makes it difficult to disassemble the SSM die after processing. Therefore, die design, runner system design and temperature control of the die and runner system are the key parameters to achieve a successful result2. In addition, materials must be also selected very carefully to meet the stringent requirements of durability of a compressor wheel under the severe operation conditions. Fig.3 Overview (a) and section view (b) of typical compressor wheel Q. ZHU, et al/Trans. Nonferrous Met. Soc. China 20(2010) s1042-s1047 s1044 4 Materials selection Materials selection was started from determining the physical properties such as thermal conductivity, thermal coefficient and alloy density to ensure the validity of current component design. It was recognized that all 3XX cast aluminum alloys can be applied for currently designed compressor wheels. After comparison of all available data3-33 of mechanical properties for SSM and cast aluminum alloys, the 319s alloy was selected to manufacture compressor wheels. Fig.4 shows that SSM 319s alloy has reasonably the best and consistent tensile strength and elongation. From purely tensile property point of view, SSM A201 also shows promising results and therefore, trials were also conducted. Better strength and comparable ductility of SSM A201 than those in literature was achieved. However, SSM A201 was not commercially available so SSM 319s was still the alloy used to manufacture compressor wheels. Fig.4 Tensile properties of SSM aluminum alloys compared with permanent mould (PM) cast ones 5 Results Chemical composition of the selected alloy 319s for SSM compressor wheel is given in Table 1. Fig.5 shows that the SSM 319s compressor wheel had superior tensile strength and ductility over cast C355 and 354.0 currently used on compressor wheels and approaching those of the forged 2618 under the condition of heat treatment T61. Uniaxial fatigue testing results showed that samples cut from forged 2618 alloy in a parallel direction to the metal flow had superior fatigue resistance whereas in the perpendicular direction it had similar fatigue resistance to cast 355 (Fig.6). This difference between orientations of sample to metal flow mainly arises from the alignment of coarse second phase particles. Improvement of fatigue property of SSM 319s over cast 355 can also be seen at Table 1 Chemical composition of 319s (mass fraction, %) Element Min. Max. Copper (Cu) 2.0 3.0 Magnesium (Mg) 0.25 0.35 Silicon (Si) 5.0 6.0 Iron (Fe) 0.15 Nickel (Ni) 0.03 Zinc (Zn) 0.05 Titanium (Ti) 0.20 Manganese (Mn) 0.03 Lead+Tin (Pb+Sn) 0.05 Strontium (Sr) 0.01 0.05 Others (Each) 0.03 Others (Total) 0.1 Aluminium (Al) Bal. Fig.5 SSM 319s showing superior tensile properties over cast C355, 354.0 and 319 while comparable with forged 2618 Fig.6 SSM 319s showing superior fatigue resistance over cast C355 while comparable with forged 2618 small strains in Fig.6. This has been proven by component disk fatigue test, where uniaxial compressive stress with R0 on the disk samples machined from back face of compressor wheel was performed, as shown in Fig.7. Component testing in a turbocharger was carried out on gas stand testing cells at Cummins Turbo Technologies Limited and the results are given in Fig.8. Q. ZHU, et al/Trans. Nonferrous Met. Soc. China 20(2010) s1042-s1047 s1045 Life comparison between cast C355, forged 2618 and SSM 319s in Fig.8 shows a comparable durability between SSM 319s and forged 2618 compressor wheels, while they both have superior durability over cast C355. This significant improvement of SSM 319s and forged 2618 arises mainly from improvement of material integrity and the elimination of casting defect such as oxides. In addition to the material integrity and cleanliness improvement by forging and SSM, refinement of grain structure and thus microstructure of forged 2618 and SSM 319s compared with cast C355 and 354.0 is another contribution to the durability improvement of compressor wheels (Fig.9). Fig.7 SSM 319s showing superior component uniaxial fatigue resistance over cast C355 Fig.8 SSM 319s compressor wheel showing superior durability over cast C355 compressor wheel while comparable with forged 2618 5 Executive summary 1) Turbocharging is one of the most successful technologies to achieve significant emission reduction and fuel economy. About 7% volume increase of turbocharged engines has been achieved in the past 10 years and 8% increase in the next 10 years is predicated. 2) SSM has been successfully applied to produce extremely complex geometric turbocharger compressor wheels. Fig.9 Grains structure of cast C355 (a), forged 2618 (b) and SSM 319s (c), indicating comparable grain size between forged and SSM alloys, while both significant finer than cast alloy 3) SSM compressor wheel has achieved tensile and fatigue properties, and so component durability, approaching forged 2618 and superior over cast C355. 6 Future challenges Although significant progress of manufacturing automotive components by SSM has been achieved and extensive efforts to develop new alloys and processes have been made by researchers, there are still needs for more efforts to satisfy requirements from the industry. These include: 1) More choices of alloys There are different requirements for automotive industrial applications, some need high strength, while some may need high thermal capability, fatigue resistance, corrosion resistance and/or wearing resistance. These need different alloy systems to meet one or more requirements for industrial applications. 2) High melting point alloy systems The greatest efforts of developing SSM processes historically are on alloys with relatively low melting Q. ZHU, et al/Trans. Nonferrous Met. Soc. China 20(2010) s1042-s1047 s1046 points such as aluminum and magnesium alloys. Some efforts and success have been achieved on high melting point alloys such as steels34, but further studies are desirable to develop material systems of cast iron, steels and nickel base alloys. These materials have significant higher density than aluminum and magnesium alloys, so there is greater potential to save more weight of automotive components, and thus more fuel economy, and to improve durability by quality and property improvement in terms of SSM processes than for light alloys. 3) Complex geometric components Complex geometry of some automotive components, such as compressor wheels of a turbocharger and cylinder head in an engine, makes it difficult to achieve the stringent property requirements in cast and efficiency/cost in machining from forged billets. SSM has, therefore, great potential to manufacture complex geometric components. The very low shear strength of alloys at semi-solid status makes it achievable to manufacture complex geometric components when a proper design of runner system and die configuration can be achieved in accommodating the low shear strength but relatively high compressive strength. 4) Cost reduction of current SSM components Cost reduction of manufacturing components has been achieved using SSM process over machining from forged billets. However, due to the high cost of manufacturing raw material bar stock, complexity of runner system and die configuration as well as relatively high process costs, the costs of SSM components are still significantly higher than those of casting. Therefore, efforts should be made to further achieve cost reduction of raw material bar stock, of design and manufacture of runner system and die configuration and of processes. 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