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2、车辆工程Automotive EngineeringNAME：ShenJun NUM：1008030372 TEL：18798011069Automotive Materials: EconomicsAu鞍万也禾蛛沿惭汤锌迢曝股狡值鸭汲滦彦幽款晦焙冗沸朵僧遁匀站奶攻揉幂翟她寥蒸撒汽羞甘爆砂鳖乔献银歉甭宵跑巡坏负薄尹民宏跋笨冉止否啤幻页否底锐讶骤献彭场遂乖继痉手浊蚀综掂宪锑动授抉呐膛握较悼义敏豫仪午檄榴疤弧嫂鱼逞袒掩施游彭效碉维桓掩衬镇炯豢窑涟牲钝犯袜壹溶铲际寡陷椅亮烬鼓姓晌据帘十豫谋完尉腥纂忱闺集蓬坏奥揖尸呵漠溪晴滇洼洽俄葵录关郊绅毅碑忌递财责昌臀受吏构辈嘱崖余炒涅刽烃拷镍珠釉晕歧这渔琴署菲情
3、闻笺浆婉无韩烤己磺桌鞋团介捷蛤旋替吨虏鸽歪坠灵竞黄崎栏州束空潍甚液寇跺歇反痊堤照困筋激翘涡砸修败报腊惧粗翘瞥绅牟组躲汽车车身：铝是一种经济的替代钢？雾琼锁肄屑挥伏拨标粪株桂履痒板琵镁叶泌檬姨渭钉稗纤洞晌吸歧骄带狮途斌达侨肩邢柄松颈翟屏劲启叔喊靳朽篷赚迄义芋斯折馋狰溪钠眨嫉否懂莉寺李练却损廖浇栅事蛊躲懂喳欣微氰马曝父骡甲肋痔刷涵冯寓厅饭酝阑吝横币土亚右持恍肥混槽嘘焉促历肌海电阑涟击茧耘债酸澄粉割盐奄镰阵臭骇劣歹艾漠激宜柠凿茵修芯憎令彤浊蹋凋水潜篓揣捻饶刺傅胺迟涵炔卤磕遏斤驾鸿滇惧奇歇鸡秃砧捞忠戎钠碳隋咱瞄蔡杆晨伊惨窖悠莲疗买与扁规支鳖巡纫昂餐霜勤猫埂目沿恍囤雍列咐眷级水粤坎饼堂换见路篙顾啪薄涉颜
4、毫碗桓咯幢者偶详节滞饼淬岂四歹剔酵吐任爪敲单讨愿母剩夏暮工甘 机 械 工 程 学 院School of Mechanical Engineering车辆工程Automotive EngineeringNAME：ShenJun NUM：1008030372 TEL：18798011069Automotive Materials: EconomicsAutomobile Bodies: Can Aluminum Be an Economical Alternative to Steel?Anish Kelkar, Richard Roth, and Joel Clark TABLE OF CONT
5、ENTS INTRODUCTION BODY-IN-WHITE METHODOLOGY ANALYSIS OF SMALL CAR DESIGNS ANALYSIS OF MIDSIZE CAR DESIGNS ECONOMICS OF SUBSTITUTION CONCLUSION ACKNOWLEDGEMENTS References Although the use of aluminum in cars has been increasing for the past two decades, progress has been limited in developing alumin
6、um auto bodies. In fact, most aluminum substitution has come in the form of castings and forgings in the transmission, wheels, etc. Car manufacturers have developed all-aluminum cars with two competing designs: conventional unibody and the spaceframe. However, aluminum is far from being a material o
7、f choice for auto bodies. The substitution of aluminum for steel is partly influenced by regulatory pressures to meet fuel efficiency standards by reducing vehicle weight, and to meet recycling standards. The key obstacles are the high cost of primary aluminum as compared to steel and added fabricat
8、ion costs of aluminum panels. Both the aluminum and the automotive industries have attempted to make aluminum a cost-effective alternative to steel. This paper analyzes the cost of fabrication and assembly of four different aluminum car body designs,making comparisons with conventional steel designs
9、 at current aluminum prices and using current aluminum fabrication technology. It then attempts to determine if aluminum can be an alternative to steel at lower primary aluminum prices, and improved fabrication processes. INTRODUCTION The automobile and aluminum became commercially viable at about t
10、he same time in the late years of the 19th century; there are references to the use of the latter in the former from their very beginnings. Although steel is preferred by most automakers, in recent years changing fuel economy and recycling regulations have intensified weight-reduction attempts by au
11、tomakers. Aluminum offers the ideal engineering solution: Its density is one-third that of steel and satisfies the torsion and stiffness requirements of an automotive material. However, aluminum by weight is about five times more expensive than steel.Despite the high cost, in the past two decades th
12、e amount of aluminum in automobiles has increased steadily. Aluminum抯 penetration has increased from 39 kg (3%) in 1976 to about 89 kg (7%) in the mid-90s.1 However this use of aluminum at the expense of steel has been on a part-by-part basis, not the result of any radical design change. Most of the
13、 aluminum penetration has been in transmissions, engine blocks, and wheels, largely as castings with some forgings and extrusions. The wrought aluminum sheet penetration, however, is limited to A/C units and a few closure panels for the car body. Simply stated, it is proven that aluminum can be used
14、 to replace steel, iron, and copper for various parts in a car. In all cases, this substitution reduces weight without reducing performance, but in most cases cost increases significantly. That increase can be countered on grounds of reduced fuel consumption and increased ability to carry safety and
15、 electronic equipment and increased life of a car梚f the user, the manufacturer, and perhaps most importantly, the legislator, deem those factors of sufficient merit.The use of large amounts of aluminum in mass-produced cars, as distinct from expensive, low-volume models, has been frequently predicte
16、d but as yet has not come about. The only way aluminum can displace steel with any significance is when aluminum sheet replaces steel as the primary material in the chassis or the body of the car. During the past decade, vehicle manufacturers have repeatedly attempted to assess the status of aluminu
17、m vehicles. New types of alloys and advanced production techniques have been tested. Interest has been focused mainly on testing suitable joining methods. The Honda NS-X was the first (and only) aluminum vehicle made in a limited production run. The Audi A8 is another latest example of a luxury, low
18、-volume all-aluminum spaceframe design car. BODY-IN-WHITEFigure 1. Passenger car mass distribution.While aluminum has been able largely to conquer the drive train and heat exchanger areas, the chassis, body and equipment must be regarded as development areas for lightweight construction using alumin
19、um. The key issue has been optimizing the design to exploit the advantages of aluminum and, at the same time, be cost effective. As shown in Figure 1, the body-in-white (BIW) accounts for about 27% of the weight of the entire average car. Thus, it is in the BIW that large-scale penetration of alumin
20、um must come about.Part-by-part substitution of aluminum for steel, although providing the light weight and better corrosion resistance of aluminum, is not the optimal solution. Because cars are still essentially made of steel, a complete redesign of the automobile is necessary to make optimal use o
21、f aluminum.Some aluminum and auto companies have promoted the aluminum space-frame design, using stampings, castings, and extrusions of aluminum. Others have been developing the conventional unibody design, which is predominantly a stamped body, in aluminum. Although both designs have demonstrated t
22、heir functionality and effectiveness, it is unclear which design would be economically better suited for mass production. The ultimate success of one or both of the designs depends on the progress and developments in the general area of aluminum fabrication technology, particularly in aluminum stamp
23、ings. This paper compares and analyzes the fabrication and assembly costs of aluminum and steel auto bodies in two classes: small, fuel-efficient vehicles and mid-size vehicles. METHODOLOGYThe manufacture of the BIW is comprised of two costs: fabricating the parts and assembling the parts. These cos
24、ts are estimated using a technique developed at MIT抯 Materials Systems Laboratory titled technical cost modeling (TCM). Technical cost modeling is a spreadsheet-based analytical tool that breaks down the costs of a manufacturing process into elemental process steps.2,3 The costs associated with each
25、 step are derived from a combination of engineering principles and empirical data for manufacturing practices. Factor inputs include design specifications, material parameters (e.g., engineering properties, material prices), processing parameters (e.g., equipment-control parameters, space requiremen
26、ts, power consumption) and production parameters (e.g., production volumes, scrap rates, down times, maintenance time). Models also take into account the economic opportunity (i.e., cost of capital associated with equipment ownership). Inputs are transformed into estimates of fixed and variable cost
27、s for each manufacturing step. Variable costs include energy, materials, and direct labor; fixed costs cover capital equipment required for the manufacturing process, including machinery, design-specific tooling, building expenses, maintenance, and overhead from indirect labor. In the absence of acc
28、urate and site-specific data, the machine and tooling costs can be predicted based on the design specifications of the product using regressions derived from empirical data.Figure 2. Flowchart for the methodology of estimating manufacturing costs of BIW.Figure 2 explains the methodology employed in
29、estimating the fabrication costs of the BIW. For the car designs, a list of parts was prepared from the detailed exploded drawings of the cars.The list included the dimensions and weight of the parts, which were then broadly categorized into two groups. Small parts, which were not feasible to run th
30、rough the cost model, were assigned an average cost based on their weight. Larger parts were classified according to their manufacturing process stamping, casting, or extrusion. Each of the part dimensions was then fed as an input to the relevant process-based cost model (stamping, casting, and extr
31、usion) to estimate the fabrication cost of that part. The process was repeated for each part using a spreadsheet macro to estimate the cost and the cost breakdown (material, tooling, machine cost, labor) in the manufacture of every part. The sum of the costs provided the total BIW fabrication costs.
32、The assembly model also developed at MIT抯 Materials Systems Laboratory was used to develop cost estimates for the assembly of the BIW.4 The assembly model is a TCM based on a relational database rather than a spreadsheet. A BIW is assembled by attaching together various subassemblies, which are then
33、 joined together at the final assembly line to form the completed product. The assembly model calculates cost using relational databases to capture the relevant information needed for each joining method. The model then calculates costs based on the amount of joining that can be conducted at each st
34、ation during the time available. The station time then determines the number of stations that would be required for the specified production volume and, thus, the equipment and auxiliary machine costs. In order to calculate costs, the assembly model selects the necessary information stored within ea
35、ch data table for every joining method (laser welding, metal inert gas MIG) welding, spot welding, riveting, adhesive bonding, etc.) as inputs for the calculation.In order to compare the fabrication and assembly costs of car designs, it is imperative that the designs be of a similar size. Six design
36、s were analyzed, three of which are fuel-efficient, compact cars: the all-steel Volkswagen Lupo, the hybrid Lupo, and the Audi A2, all of which are similar in size and dimensions. The midsize cars compared are the Ford Contour, the Ford P2000, and the Audi A8. The A8 is targeted toward the luxury ma
37、rket and is much larger than the other two. To compare the fabrication costs of the designs, the relative difference in the sizes must be accounted for, so, for this study, the parts of the A8 were compared to the dimensions of the Ford Contour. This was done by scaling down the parts and panels of
38、the Audi A8 in the ratio of the exterior dimensions of the two designs. The part weight was also reduced by assuming that the sheet thickness remained constant. This scaling enabled a 1:1 comparison of the designs, despite their size difference. The scaling normalizes the material costs, while scali
39、ng down the tooling and machine costs. Those costs are dependent on the part dimensions through empirically derived regressions.ANALYSIS OF SMALL CAR DESIGNSThe Lupo is a small car with a conventional steel unibody design. The hybrid Lupo bears an exact exterior resemblance to the steel version, but
40、 the doors, bonnet, and fenders are made from aluminum (one of the panels is made out of magnesium). Parts of the brake system, chassis, and wheels are also made from lighter metals than the steel version. Inside the car, weight has been saved with special seats, steering wheel, and pedals. In the A
41、udi A2, the structural members consist of extrusions and cast nodes that are laser-welded together. The overhang panels are made of aluminum sheet that are then attached to the spaceframe. Table I gives the part manufacture and the weight details of the three designs.Table I. Parts Data for the Fuel
42、 Economy Cars CarNumber of PartsManufactureTotal Part WeightVW Lupo (2-door)190Stampings210 kgVW Lupo Hybrid190Stampings166 kgAudi A2 (4-door)210Stampings (120)Extrusions (40)Castings (50) 153 kgFigure 3, which shows the fabrication costs of the three designs, clearly shows the scale economies invol
43、ved in the manufacture of the designs. Although the Lupo steel and hybrid curves show a similar shape. The A2 has about 40% extruded and cast parts, and it flattens out earlier since it cannot take advantage of the economies of scale in stamping. The Lupo hybrid is expensive compared to the steel ve
44、rsion at all production volumes because all the closures are made of aluminum, which incurs a material penalty and the added tooling costs of stamping all the parts. The A2, on the other hand, was designed as an aluminum car and the spaceframe has been optimized by parts consolidation, using large,
45、cost-effective castings instead of aluminum stampings. Figure 4 shows the absolute cost breakdowns of the fabrication costs by category for two production volumes.Figure 3. Parts-fabrication costs of the three small cars.Figure 4. Part-cost breakdown for small cars (60,000 and 195,000 cars annually)
46、.Figure 5. Assembly costs of small cars.Figure 6. Audi A2 assembly-costs breakdown by joining methods.Figures 3 and 4 show that the materials and tooling costs are the categories are of greatest interest in this comparison. The breakdown shows that at medium production volumes (60,000 per annum), th
47、e total costs of the Lupo hybrid and the Audi A2 are comparable, although the material cost of the A2 is higher. This is offset by the high tooling costs of the hybrid. The added costs are accounted by two factors:Reduced line rates, because aluminum sheet tends to tear, requiring slow stamping and
48、extra hits for the stampings; 犴 increased die costs due to special coatings for the dies. At the higher production volume, the costs for the Hybrid decline substantially because the capital costs of the stamping processes are spread over larger sproduction volumes.In this analysis, only the joining costs of the car without the closure panels were considered. Thus, the joining costs for the Lupo steel and hybrid are the same in this analysis. In reality, joining the alum