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INTERNATIONAL JOURNAL OF PRECISION ENGINEERING AND MANUFACTURING Vol. 13, No. 7, pp. 1101-1106 JULY 2012 / 1101 DOI: 10.1007/s12541-012-0144-x NOMENCLATURE R m = tensile strength A 11.3 = percentage elongation 1. Introduction Light weight auto-body and passive safety of passengers become trend of automotive industry, while energy saving and environment protecting deeply wised. Application of ultra-high strength steel with dual advantages of weight-light and safety improvement performance grows rapidly, also with characteristics of both high-strength and high-precision, has become a industry hotspot. On one hand, the forming process parameters are the key points of hot stamping technology, on the other hand, hot stamping die needs to set cooling system to ensure the die function of stamping and quenching, which is quite different from the common stamping mold. The main parameters including heating temperature, holding time, forming speed, impulse pressure, holding time, open mold temperature, flow velocity and etc., should be optimized during hot stamping process primarily for guaranteed high-intensity and high- precision of forming parts. Taking a Chinese independent brand car door beam as an example, ultra-high strength steel hot stamping technology and lightweight design were studied in this paper. 1-3 2. Development of hot stamping die for ultra-high strength steel door beam 2.1 Material optimization of hot stamping die During hot stamping process, phase transformation strengthening of parts after forming is completed through the dies, so the dies require creation of cooling pipes inside to realize a cooling quenching function. 4,5 From the point of view for material properties, die material must have high thermal conductivity coefficient in order to achieve rapid and uniform cooling effect, better thermal fatigue performance and high heat strength to work under long-term alternation of heating and cooling state, strong wear-resistance to bear thermal friction of high temperature blank and its oxidation skin. 6-8 Hot working die steel material of HHD containing high chromium in the composition (shown in Table 1) to enhance its corrosion-resistance was used. Under normal temperature, the Hot Stamping Die Design for Vehicle Door Beams using Ultra-High Strength Steel Chao Jiang 1 , Zhongde Shan 1,# , Bailiang Zhuang 1 , Milan Zhang 1 , and Ying Xu 1 1 State Key Lab. of Advanced Forming Technology with increasing of pipe diameter, the average cooling rate linearly increases. And the greatest influence factor on cooling effectiveness is depth of pipe from the surface, followed by pipe spacing, and finally pipe diameter, that is, calculative determination of depth from die surface to cooling pipe should be considered first during design of die cooling system, and it is also the basis of the reasonable design of pipe spacing and pipe diameter. The depth from die surface to cooling pipe of 10mm, pipe spacing of 15mm and pipe diameter of 10mm was the optimized result of the simulation. The design of cooling pipe should make sure that the die could keep ensuring sufficient strength during hot stamping process, so the overall strength intensity of the die needs to be checked firstly. The next numerical simulation boundary conditions were as friction coefficient of 0.03, forming speed of 50mm/s, the stress field and force were shown in Fig. 4. The results showed that there was no damage on die because the maximum deformation was only 0.027mm, which was in the elastic deformation range. The stress simulation results showed that the stress is far less Table 1 Composition of HHD (wt-%) C Cr Mo Ni V W Si Mn 0.20.35 8.013.0 1.02.0 0.71.3 0.41.0 0.31.0 0.71.3 0.21.0 Fig. 1 Door beam Fig. 2 Internal cooling pipes Table 2 Parameters of cooling pipe Depth from die surface to cooling pipe(mm) 5 10 15 20 25 Spacing between pipes (mm) 15 20 25 30 35 Dia. of cooling pipe (mm) 10 12 15 17 20 0 5 10 15 20 25 30 32.8 29.6 27.2 26.6 25.6 average cooling rare (/s) pip e de pth ( m m ) 10 15 20 25 30 35 40 p i p e ap ac e (mm ) Fig. 3 Influence of cooling parameters pipe depth: r=0.97 pipe space: r=0.98 INTERNATIONAL JOURNAL OF PRECISION ENGINEERING AND MANUFACTURING Vol. 13, No. 7 JULY 2012 / 1103 than that of the blank mechanical strength, cracking phenomena would not happen. The corresponding door beam die entities was shown in Fig. 5. 3. Hot stamping process applications 3.1 Hot stamping simulation Hot stamping process mainly concerns on high temperature deformation behavior of sheet, which is closely related to optimization of process parameters. In this paper, Baosteel hot- rolled BR1500HS (compositions shown in Table 3), with hardness of HV193, tensile strength of 666MPa, microstructure of ferrite and pearlite was in experimental measurement. From CCT curve (Fig. 6), it could be seen that, AC 3 was 811, AC 1 was 736, critical cooling rate of 15/s, martensite start point was between the 350380, the end point of was of 280300 . Experiments were conducted using Gleeble-3800 thermal simulator to study the rheological behavior. Sample part was heated to 950 under 15/s speed, persevered at this temperature for 5 minutes to obtain homogeneous austenite organization, then quickly cooled to experiment temperature under speed of 70/s to complete isothermal tension test. During process of data analysis, Norton-Hoffs law was used to build the models: ( ) 0.31 0.07 50.12 exp 2542 T= when keeping the length and the width dimension constant, while reducing the depth from 32 mm to 23.6 mm, weight of the beam decreased 9.32%, all led to energy conservation and emission reduction. Three-point bending experiments of door beams (Fig. 14) showed that, with the reduction of sheet thickness or the reduction of depth, bending property of hot stamping beam reduced synchronously, and thickness of sheet metal played less important role on the bending property, so automotive parts could achieve more lightweight from thinning thickness while achieving weight loss purpose. As shown as Fig. 14, the deformation of lightweight optimization door beam increases 15mm compared to 2mm that of thick 32mm deep door beam, 6.7% of the original deformation, the deformation increasing amount would have no effect on the automotive side impact test results, that was, the improved lightweight door beams satisfied double requirements of safety and lightweight. 13 4. Conclusions (1) The most influential factor on cooling effectiveness of pipe is depth of pipe from die forming surface, followed by pipe spacing and pipe diameter. Depth from die surface to cooling pipe should be basis of reasonable design of pipeline spacing and diameter. (2) Hot stamping die developed with optimized system and process parameters could guarantee full martensite microstructure and excellent mechanical performance, with average tensile strength of 1550Mpa, elongation of 6.5%, shape accuracy of 0.5mm; and the optimization process parameters were heating temperature of 930 , holding time of 4.5min, forming speed of 75mm/s, punching pressure of 7MPa, quenching time of 15s, flow velocity of 1.1m/s. (3) The ultra-high strength steel door beam was optimized to realize crash test full marks, with stiffness increased of 2.5 times, strength increased of 3.8 times, lightweight of 9.32% than that of original pipe, which achieved dual objectives of security and lightweight. ACKNOWLEDGEMENT This study was supported by a grant from National Basic Research Program of China (2012CB724301), Program of International S&T Cooperation (2011DFA50810). REFERENCES 1. Zhuang, B., Shan, Z., and Jiang, C., “Hot Stamping Technology and the Application in Automobile Body,” Machinist Metal Forming, No. 21, pp. 62-64, 2010. 2. Gu, Z.-W., Shan, Z.-D., Xu, H., and Jiang, C., “Hot forming technology of automotive high strength steel sheet stamping part,” Die & Mould Industry, Vol. 35, No. 4, pp. 27-29, 2009. 3. Sikora, S. and Lenze, F.-J., “Hot-Forming Important Parameters for the Production of High-Strength BIW Parts,” IDDRG, pp. 295-301, 2006. 4. Kim, Y.-J. and Choi, C.-H., “A study on life estimation of hot forging die,” Int. J. Precis. Eng. Manuf., Vol. 10, No. 3, pp. 105- 113, 2009. 5. Shan, Z., Zhang, M., Jiang, C., Xu, Y., and Rong, W., “Basic study on Die Cooling System of Hot Stamping Process,” Proc. of the Int. Conf. on Advanced Technology of Design and Manufacture, pp. 1-4, 2010. 6. Hoffmann, H., So, H., Steinbeiss, H., “Design of Hot Stamping Tools with Cooling System,” Annals of the CIRP, Vol. 56, No. 1, pp. 269-272, 2007. 7. Ahn, D.-G., “Applications of laser assisted metal rapid tooling process to manufacture of molding & forming tools state of the art,” Int. J. Precis. Eng. Manuf., Vol. 12, No. 5, pp. 925-938, 2011. 8. Merklein, M., Lechler, J., and Geiger, M., “Characterization of the Flow Properties of the Quenchenable Ultra High Strength Steel 22MnB5,” Annals of the CIRP, Vol. 55, No. 1, pp. 229- 232, 2006. 9. Woon, K.-S., Rahman, M., and Liu, K., “Numerical and experimental study of contact behavior in the tool-based micromachining of steel,” Int. J. Precis. Eng. Manuf., Vol. 11, No. 3, pp. 453-459, 2010. 10. Zhuang, B., Shan, Z., Jiang, C., and Rong, W., “Numerical Simulation of Hot Stamping Technology for Automotive Structural Parts,” Proc. of the Int. Conf. on Advanced Technology of Design and Manufacture, pp. 190-194, 2010. 11. Shim, H. B., “Improving formability to develop miniature stamping technologies,” Int. J. Precis. Eng. Manuf., Vol. 10, No. 2, pp. 117-126, 2009. 0 2000 4000 6000 8000 10000 12000 14000 16000 0 102030405060 Displacement (mm) F o r ce （ N ） Fig. 14 Three-point bending test comparison curves of 4 kinds of door beam 2mm thickness with depth of 32mm 1.6mm thickness with depth of 32mm 1.6mm thickness with depth of2 5mm cold bending pipe 1106 / JULY 2012 INTERNATIONAL JOURNAL OF PRECISION ENGINEERING AND MANUFACTURING Vol. 13, No. 7 12. Park, C. W., Kwon, K. S., Kim, W. B., Min, B. K., Park, S. J., Sung, I. H., Yoon, Y. S., Lee, K. S., Lee, J. H., and Seok, J., “Energy Consumption Reduction Technology in Manufacturing - A Selective Review of Policies, Standards, and Research,” Int. J. Precis. Eng. Manuf., Vol. 10, No. 5, pp. 151-173, 2009.
任 務(wù) 書
課題名稱： 汽車車門外板
沖壓模具設(shè)計(jì)
課題名稱
汽車車門外板沖壓模具設(shè)計(jì)
主要內(nèi)容(包括設(shè)計(jì)參數(shù))與要求
一、本設(shè)計(jì)的主要內(nèi)容：
汽車車門屬大型汽車覆蓋件，通常采用冷沖壓的方式加工而成。本次設(shè)計(jì)題目即為汽車車門沖壓模具結(jié)構(gòu)設(shè)計(jì)，設(shè)計(jì)者可以參考任一款車型的轎車車門，進(jìn)行產(chǎn)品結(jié)構(gòu)設(shè)計(jì)和模具結(jié)構(gòu)設(shè)計(jì)，要求完成以下幾項(xiàng)工作：
1、 完成該沖壓模具結(jié)構(gòu)設(shè)計(jì)與計(jì)算，并完成設(shè)計(jì)說(shuō)明書。
2、 完成過(guò)程材料的編寫，包括工作計(jì)劃、開題報(bào)告、讀書報(bào)告、外文翻譯、階段總結(jié)、工作總結(jié)和工作記錄本等。
3、用CAD相關(guān)軟件完成三維車門結(jié)構(gòu)繪制，完成三維模具結(jié)構(gòu)設(shè)計(jì)，可將部分三維圖片插入畢業(yè)設(shè)計(jì)說(shuō)明書中。
4、用AutoCAD軟件進(jìn)行沖壓模具的二維結(jié)構(gòu)圖繪制，要求畫出模具總裝圖1張以及主要結(jié)構(gòu)零件圖3張。
二、畢業(yè)設(shè)計(jì)基本要求：
（1） 畢業(yè)論文應(yīng)符合高校畢業(yè)生的畢業(yè)論文格式、內(nèi)容要求規(guī)范，論文應(yīng)包括選題的研究或者開發(fā)意義，技術(shù)理論綜述，系統(tǒng)架構(gòu)和研究結(jié)果展示以及分析評(píng)價(jià)等。
（2） 設(shè)計(jì)說(shuō)明書應(yīng)有計(jì)算分析數(shù)據(jù)，并保證數(shù)據(jù)真實(shí)可信，字?jǐn)?shù)達(dá)到1萬(wàn)字。
（3） 完成時(shí)間嚴(yán)格按照學(xué)院要求執(zhí)行；
（4） 設(shè)計(jì)文件在答辯完成后進(jìn)行裝訂；
（5） 設(shè)計(jì)文件電子文稿和打印文稿一并上交；
（6） 設(shè)計(jì)文件嚴(yán)禁雇人代做、抄襲，一旦發(fā)現(xiàn)，無(wú)畢業(yè)設(shè)計(jì)成績(jī)；
（7） 時(shí)間要求在 年 月中旬前完成。
工 作 進(jìn) 程 及 需 完 成 工 作 量
1、開題論證階段：查找資料，確定畢業(yè)設(shè)計(jì)實(shí)施方案。 2周（共2周）
2、分析、研究、設(shè)計(jì)、實(shí)施、報(bào)告編寫階段。 3～11周（共9周）
3、論文審核修改階段：指導(dǎo)教師審閱論文，提出修改意見，學(xué)生編輯修論文，學(xué)生論文打印稿經(jīng)指導(dǎo)老師評(píng)定之后交給評(píng)閱教師評(píng)閱。 12～14周（共3周）
4、畢業(yè)答辯階段： 15周（共1周）
5、畢業(yè)設(shè)計(jì)工作總結(jié)階段。 16～17周（共2周)
應(yīng) 遵 守 的 法 紀(jì) 法 規(guī)
1、 國(guó)家和實(shí)習(xí)所在地的政府機(jī)關(guān)的各種法律、法規(guī)；
2、 學(xué)校和實(shí)習(xí)單位的規(guī)章制度；
3、 校紀(jì)校規(guī)；
4、 實(shí)習(xí)法律；
5、 保護(hù)知識(shí)產(chǎn)權(quán)；
畢業(yè)設(shè)計(jì)(論文)完成日期： 年 月 日
指導(dǎo)教師： (簽字)
教研室主任： (簽字)
譯文：
利用超高強(qiáng)度鋼設(shè)計(jì)車門橫梁熱沖壓模具
摘要：節(jié)能與安全是汽車行業(yè)發(fā)展的永恒主題。熱沖壓超高強(qiáng)度鋼擁有在減少車輛重量的同時(shí)提高安全性能這一雙重優(yōu)點(diǎn)，使其被廣泛地應(yīng)用于汽車車身結(jié)構(gòu)設(shè)計(jì)中。本文以車門橫梁作為例子對(duì)成形和淬火一體化模進(jìn)行了研究，尤其是整個(gè)模具結(jié)構(gòu)和熱沖壓過(guò)程的研究，通過(guò)數(shù)值模擬對(duì)凹模強(qiáng)度、冷卻管布置和其他相關(guān)因素進(jìn)行了優(yōu)化，并且用該模具生產(chǎn)出了拉伸強(qiáng)度為1550Mpa，伸長(zhǎng)率為6.5％和形狀精度為±0.3mm的橫梁。此外，橫梁的剛度和強(qiáng)度比原來(lái)的分別提高了2.2倍和3.8倍，在C-NCAP碰撞測(cè)試中得到了滿分。通過(guò)減小橫截面的厚度和拉深深度，橫梁的重量減輕了9.32％，并且提高了節(jié)能和減排效果。
關(guān)鍵詞：熱成形，超高強(qiáng)度鋼，機(jī)械特性，汽車輕量化
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1 引言
視曲梁enfan