垫板冲压模具设计【说明书+CAD】
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紫琅职业技术学院毕业设计(论文)题 目:垫板冲压模具设计学 生 姓 名:周竟成所在系、专业: 机电系 模具设计与制造班 级:模具5083指 导 教 师:彭少清日 期:6.9I摘 要摘 要本设计为一垫板的冷冲压模具设计,根据设计零件的尺寸、材料、批量生产等要求,首先分析零件的工艺性,确定冲裁工艺方案及模具结构方案,然后通过工艺设计计算,确定排样和裁板,计算冲压力和压力中心,初选压力机,计算凸、凹模刃口尺寸和公差,最后设计选用零、部件,对压力机进行校核,绘制模具总装草图,以及对模具主要零件的加工工艺规程进行编制。其中在结构设计中,主要对凸模、凹模、凸凹模、定位零件、卸料与出件装置、模架、冲压设备、紧固件等进行了设计,对于部分零部件选用的是标准件,就没深入设计,并且在结构设计的同时,对部分零部件进行了加工工艺分析,最终才完成这篇毕业设计。 关键词:冲压、模具、制造。I目 录目 录1 零件的工艺分析 11.1 结构与尺寸 11.2 精度 11.3 材料 12 确定冲裁工艺方案23 确定模具总体结构方案 23.1 模具类型 23.2 操作与定位方式 23.3 卸料与出件方式23.4 模架类型及精度 24 工艺设计计算 24.1 排样设计与计算24.2 计算冲压力与压力中心,初选压力机44.3 计算凸、凹模刃口尺寸及公差55 设计选用零件、部件,绘制模具总装草图65.1 凹模设计 65.2 凸模设计75.2.1 凸模的结构形式与固定方法75.2.2 凸模长度计算75.2.3 凸模的强度与刚度校核85.2.4 凸模材料和技术条件85.3 凸凹模的设计95.3.1 凸凹模的结构形式与固定方法95.3.2 校核凸凹模的强度105.3.3 凸凹模尺寸的确定105.3.4 凸凹模材料和技术条件105.4 定位零件 105.5 卸料与出件装置115.6 模架及其它零件的选用135.6.1 模柄135.6.2 模座145.6.3 垫板145.6.4 冲压设备的选择165.6.5 紧固件的选用166 压力机的校核166.1 公称压力166.2 滑块行程166.3 行程次数166.4 工作台面的尺寸 166.5 滑块模柄孔尺寸 176.6 闭合高度17 7 模具主要零件加工工艺规程的编制177.1 冲压模具制造技术要求 177.2 总装工艺 17总结 19致谢 19参考文献 19I附 录1 零件的工艺分析如图1所示零件:垫扳生产批量:大批量材料:08F t=2mm图11.1 结构与尺寸该零件结构简单,形状对称。 硬钢材料被自由凸模冲圆形孔,查冷冲压工艺及模具设计表3-8,可知该工件冲孔的最小尺寸为1.3t,该工件的孔径为:61.3t=1.32=2.6。由于该冲裁件的冲孔边缘与工件的外形的边缘不平行,故最小孔边距不应小于材料厚度t,该工件的空边距(20)t=2,(10)t=2,均适宜于冲裁加工。1.2 精度零件内、外形尺寸均未标注公差,属自由尺寸,可按IT14级确定工件尺寸的公差,经查表得,各尺寸公差分别为:零件外形:58, 38, 30, 16, 8 零件内形:6 孔心距:180.215, 利用普通冲裁方式可以达到零件图样要求。1.3 材料08F,属于碳素结构钢,查冷冲压工艺及模具设计附表1可知抗剪强度=260MPa,断后伸长率=32。此材料具有良好的塑性和较高的弹性,其冲裁加工性能好。根据以上分析,该零件的工艺性较好,可以进行冲裁加工。2 确定冲裁工艺方案该零件包括落料、冲孔两个基本工序,可以采用以下几种工艺方案:(a)先落料,再冲孔,采用单工序模生产;(b)采用落料冲孔复合冲压,采用复合模生产;(c)用冲孔落料连续冲压,采用级进模生产。方案(a)模具结构简单,但需要两道工序,两套模具才能完成零件的加工,生产效率低,难以满足零件大批量生产的要求。由于零件结构简单,为了提高生产效率,主要采用复合冲裁或级进冲裁方式。采用复合冲裁时,冲出的零件精度和平直度好,生产效率高,操作方便,通过设计合理的模具结构和排样方案可以达到较好的零件质量。根据以上分析,该零件采用复合冲裁工艺方案。3 确定模具总体结构方案3.1 模具类型根据零件的冲裁工艺方案,采用复合冲裁模。复合模的主要结构特点是存在有双重作用的结构零件凸凹模,凸凹模装在下模称为倒装式复合模。采用倒装式复合模省去了顶出装置,结构简单,便于操作,因此采用倒装式复合冲裁模。3.2 操作与定位方式虽然零件的生产批量较大,但合理安排生产,可用手工送料方式能够达到批量要求,且能降低模具成本,因此采用手工送料方式。考虑到零件尺寸大小,材料厚度,为了便于操作和保证零件的精度,宜采用导料板导向,固定挡料销挡料,并与导正销配合使用以保证送料位置的准确性,进而保证零件精度。为了保证首件冲裁的正确定距,采用始用挡料销,采用使用挡料销的目的是为了提高材料利用率。3.3 卸料与出件方式采用弹性卸料的方式卸料,弹性卸料装配依靠橡皮的弹力来卸料,卸料力不大,但冲压时可兼起压料作用,可以保证冲裁件表面的平面度。为了方便操作,提高零件生产率,冲件和废料采用由凸模直接从凹模洞口推下的下出件方式。3.4 模架类型及精度考虑到送料与操作的方便性,模架采用后侧式导柱的模架,用导柱导套导向。由于零件精度要求不是很高,但冲裁间隙较小,因此采用I级模架精度。4 工艺设计计算4.1 排样设计与计算零件外形近似矩形,轮廓尺寸为5830。考虑操作方便并为了保证零件精度,采用直排有废料排样。如图2所示:图2查冷冲压工艺及模具设计表3-13,工件的搭边值a=2,沿边的搭边值a1=2.2。级进模送料步距为S=30+2=32mm条料宽度按表3-14中公式计算:B -0=(Dmax+2a1)-0 查表3-15得:=0.6B=(58+22.2)=62.4 ()由零件图近似算得一个零件的面积为1354.82,一个进距内的坏料面积BS=62.432=1996.82。因此一个进距内的材料利用率为: =(A/BS)100=67.8查冷冲压工艺及模具设计附表3选用板料规格为71020002。采用横裁时,剪切条料尺寸为62.4。一块板可裁的条料为32,每间条可冲零件个数22个零件。则一块板材的材料利用率为:=(nA0/A)100 =(22321354.8/7102000)100=67.2采用纵裁时,剪切条料尺寸为62.4。一块板可裁的条料为11,每条可冲零件个数62个零件,则一块板材的材料利用率为:=(nA0/A)100 =(11621354.8/7102000)100=59.2根据以上分析,横裁时比纵裁时的板材的材料利用率高,因此采用横裁。4.2 计算冲压力与压力中心,初选压力机冲裁力:根据零件图可算得一个零件外周边长度:L1=16+8+28+382=162.27 内周边长度之和:L=23=18.84查冷冲压工艺及模具设计附表1可知:MPa;查冷冲压工艺及模具设计附表3可知:Kx=0.05, KT=0.055.落料力:F落=KL1 t T =1.3162.272260=109.69KN 冲孔力:F孔=KL2 t T =1.362260=12.74KN卸料力:Fx=KxF落 =0.05109.69=5.48KN推件力:根据材料厚度取凹模刃口直壁高度h=6, 故:n=h/t=3 FT=nKtF孔=30.05525.47=4.20KN总冲压力:F= F落+ F孔+Fx+ FT则F=109.69+12.74+5.48+4.20 =132.11KN应选取的压力机公称压力:25t.因此可初选压力机型号为J23-25。当模具结构及尺寸确定之后,可对压力机的闭合高度,模具安装尺寸进行校核,从而最终确定压力机的规格。确定压力中心:画出凹模刃口,建立如图3所示的坐标系:图3由图可知,该形状关于X轴上下对称,关于Y轴左右对称,则压力中心为该图形的几何中心。即坐标原点O。该点坐标为(0,0)。4.3 计算凸、凹模刃口尺寸及公差由于模具间隙较小,固凸、凹模采用配作加工为宜,由于凸、凹模之间存在着间隙,使落下的料或冲出的孔都带有锥度。落料件的尺寸接近于凹模刃口尺寸,而冲孔件的尺寸接近于凸模刃口尺寸。固计算凸模与凹模刃口尺寸时,应按落料与冲孔两种情况分别进行。由此,在确定模具刃口尺寸及其制造公差时,需遵循以下原则:(I)落料时以凹模尺寸为基准,即先确定凹模刃口尺寸;考虑到凹模刃口尺寸在使用过程中因磨损而增大,固落料件的基本尺寸应取工件尺寸公差范围较小尺寸,而落料凸模的基本尺寸则按凹模基本尺寸减最小初始间隙;(II)冲孔时以凸模尺寸为基准,即先确定凸模刃口尺寸,考虑到凸模尺寸在使用过程中因磨损而减小,固冲孔件的基本尺寸应取工件尺寸公差范围内的较大尺寸,而冲孔凹模的基本尺寸则按凸模基本尺寸加最小初始间隙;(III)凸模与凹模的制造公差,根据工件的要求而定,一般取比工件精度高23级的精度,考虑到凹模比凸模的加工稍难,凹模比凸模低一级。a): 落料凹模刃口尺寸。按磨损情况分类计算:i)凹模磨损后增大的尺寸,按冷冲压工艺及模具设计公式:DA=(Dmax-X);计算,取 A=/4,制件精度为IT14级,故X=0.558: DA1 =(58-0.50.74 )=57.63 () 38: DA2=(38-0.50.62)=37.69 ()30: DA3=(30-0.50.52)=29.74 ()16: DA4=(16-0.50.43)=15.785()8: DA5=(8-0.50.36)=7.18()ii)凹模磨损后不变的尺寸,按冷冲压工艺及模具设计公式:CA=(Cmin+X)0.5A: 计算,取A=/4 ,制件精度为IT14级,故X=0.5180.215: Cd1=(17.785+0.50.43)0.43/8=180.05375() 冲裁间隙影响冲裁件质量,在正常冲裁情况下,间隙对冲裁力的影响并不大,但间隙对卸力、推件力的影响却较大。间隙是影响模具寿命的主要因素。间隙的大小则直接影响到摩擦的大小,在满足冲裁件质量的前提下,间隙一般取偏大值,这样可以降低冲裁力和提高模具寿命。查冷冲压工艺及模具设计表3-3可知Zmax=0.360 , Zmin=0.246相应凸模按凹模实际尺寸配作,保证最小合理间隙为0.246mm冲孔凸模刃口尺寸。冲孔凸模为圆形,可按冷冲压工艺及模具设计公式dT=(dmin+x) 计算,取T=/4,制件精度为IT14级,故X=0.512: dT1=(6+0.50.30)=6.155 设计选用零件、部件,绘制模具总装草图5.1 凹模设计凹模的结构形式和固定方法:凹模采用矩形板状结构和通过用螺钉、销钉固定在凹模固定板内,其螺钉与销钉与凹模孔壁间距不能太小否则会影响模具强度和寿命,其值可查冷冲压工艺及模具设计表3-23。凹模刃口的结构形式:因冲件的批量较大,考虑凹模有磨损和保证冲件的质量,凹模刃口采用直刃壁结构,刃壁高度取6mm, 漏料部分沿刃口轮廓单边扩大0.5 mm凹模轮廓尺寸的确定:查冷冲压工艺及模具设计表3-24,得:K=0.28;查冷冲压工艺及模具设计表3-25, 得: s2=36; 凹模厚度H=ks=0.2858=16.24() B=s+(2.54.0)H=58+(2.54.0)16.24=98.6122.96 () L=s1+2s2=30+236=102 ()根据算得的凹模轮廓尺寸,选取与计算值相接近的标准凹模板轮廓尺寸为LBH=12512528.5()凹模材料和技术要求:凹模的材料选用T10A。工件部分淬硬至HRC5862。外轮廓棱角要倒钝。如图4所示: 图4 落料凹模5.2 凸模设计5.2.1 凸模的结构形式与固定方法冲孔部分的凸模刃口尺寸为圆形,为了便于凸模和固定板的加工,将冲孔凸模设计成台阶式。为了保证强度、刚度及便于加工与装配,圆形凸模常做成圆滑过渡的阶梯形,小端圆柱部分。是具有锋利刃口的工作部分,中间圆柱部分是安装部分,它与固定板按H7/m6配合,尾部台肩是为了保证卸料时凸模不致被拉出,圆形凸模采用台肩式固定。5.2.2 凸模长度计算凸模的长度是依据模具结构而定的。采用弹性卸料时,凸模长度按公式L=h1+h2+h3计算,式中 L-凸模长度,mm; h1-凸模固定板厚度,mm; h2-卸料板厚度,mm ; ?h3-卸料弹性元件被预压后的厚度L=22mm+10mm+18.5mm=50.5mm5.2.3 凸模的强度与刚度校核一般情况下,凸模强度与刚度足够,由于凸模的截面尺寸较为积适中,估计强度足够,只需对刚度进行校核。对冲孔凸模进行刚度校核:凸模的最大自由长度不超过下式:有导向的凸模Lmax1200,其中对于圆形凸模Imin=d4/64则Lmax1200=24.00mm由此可知:冲孔部分凸模工作长度不能超过24.00mm,根据冲孔标准中的凸模长度系列,选取凸模的长度:50.55.2.4 凸模材料和技术条件凸模材料采用碳素工具钢T10A,凸模工作端(即刃口)淬硬至HRC 5660,凸模尾端淬火后,硬度为HRC 4348为宜。如图5所示: 图5 冲孔凸模 5.3 凸凹模的设计5.3.1 凸凹模的结构形式与固定方法凸凹模的结构简图如图6所示: 图6 凸凹模 凸凹模与凸凹模固定板的采用H7/m6配合。5.3.2 校核凸凹模的强度冲孔边缘与工件外开边缘不平行时,凸凹模的最小壁厚不应小于材料厚度t=2mm,而实际最小壁厚为5mm,故符合强度要求。5.3.3 凸凹模尺寸的确定凸凹模的外刃口尺寸按凹模尺寸配作并保证最小间隙为Zmin=0.246mm,内形刃口尺寸按凸模尺寸配做并保证最小间隙为Zmin=0.246mm。5.3.4 凸凹模材料和技术条件凸凹模材料采用碳素工具钢T10A,淬硬至5660HRC。5.4 定位零件定位零件的作用是使坯料或工序件在模具上相对凸、凹模有正确的位置。 选用固定挡料销一个。挡料销的作用是挡住条料搭边或冲件轮廓以限定条料送进的距离,固定挡料销固定在位于下模的凸凹模上,规格为GB/T7694.10-94,材料45号钢,硬度为4348HRC选用导料销两个。导料销的作用是保证条料沿正确的方向送进,位于条料的后侧(条料从右向左送进)尺寸规格为6X2,如图7所示: 图7 导料销5.5 卸料与出件装置出件方式是采用凸模直接顶出的下出料方式。由于卸料采用弹性卸料的方式,弹性卸料装置由卸料板、卸料螺钉和弹性元件组成。卸料板:弹性卸料板的平面尺寸等于或稍大于凹模板的尺寸,厚度取凹模厚度的0.60.8倍, 卸料板与凸模的单边间隙按冷冲压工艺及模具设计表3-32选取,t1mm时,单边间隙为0.15mm。为了便于可靠卸料,在模具开启状态时,卸料板工作平面应高出凸模刃口尺寸端面0.30.5,卸料板的尺寸规格为:125mmX125mmX10mm,材料为:45#钢。如图8所示: 图8 卸料板 卸料螺钉:卸料螺钉采用标准的阶梯形螺钉,根据卸料板的尺寸选择4个卸料螺钉,规格为,JB/T7650.5-94。如图9所示: 图9 卸料螺钉卸料装置:由于橡皮允许承受的负荷较大,安装调整方便,因此选用橡皮作为弹性元件,卸料橡皮的选择原则: 为了保证卸料正常工作,应使橡皮工作时的弹力大于或等于卸料力FXFXY=APFX=5.48KN式中FXY橡皮工作时的弹力,A橡皮的横截面积,P与橡橡皮压缩量有关的单位压力,一般预压时压缩量为10%15%。由冷冲压工艺及模具设计图3-64知,取P=0.6MPa,求得A=91.3cm2,由冷冲压工艺及模具设计表3-33中的公式求得橡皮尺寸规格为352624根据工件材料厚度为2mm,冲裁时凸模进如凹模的深度为1mm,模具维修时刃磨留量为2mm,开启时卸料板高于凸模1mm,则求得总工作行程:h工件=6mm, 使用橡皮时,不应使最大压缩量超过橡皮自由高度的35%45%否则是皮的自由高度应为: H=h/(0.250.30) =6/(0.250.30) =2024mm模具组装时的预压缩量为: H预=(10%15%)H =2.43.6mm取H预=3mm由此可知:安装橡皮高度尺寸为21mm,式中的H所需的工作行程。由上式所得的高度,还在按下式进行校核: 0.5H/B1.5如果H/D超过1.5,应把橡皮分成若干段,并在橡皮之间垫上钢圈。由冷冲压工艺及模具设计表3-33中的公式求得橡皮尺寸规格为3526245.6 模架及其它零件的选用5.6.1 模柄模柄的作用是把上模固定在压力机滑块上,同时使模具中心通过滑块的压力中心,模柄的直径与长度与压力机滑块一致,模柄的尺寸规格选用凸缘模柄,用34个螺钉固定在上模座上。如图10所示: 图10 模柄 5.6.2 模座标准模座根据模架类型及凹模同界尺寸选用,上模座:125mm 125mm35mm;下模座:125mm125mm45mm;模座材料采用灰口铸铁,它具有较好的吸震性,采用牌号为HT200。5.6.3 垫板垫板的作用是承受并扩散凸模或凹模传递的压力,以防止模座被挤压损伤。是否要用板,可按下式校核:P=F12/A式中P凸模头部端面对模座的单位面积压力;F12凸模承受的总压力; A凸模头部端面与承受面积。由于计算的P值大于冷冲压工艺及模具设计表3-34模座材料的许应压力,因此在工作零件与模座之间加垫板。 垫板用45号钢制造,淬火硬度为HRC4348,其尺寸规格为:125mm125mm10mm。上下面须磨平,保证平行。如图11所示: 图11 垫板模架选用后侧导柱标准模架:上模座:LBH =125mm125mm35mm下模座:LBH=125mm125mm45mm导柱:DL=22mm150mm导套:dLD=35mm85mm38mm模架的闭合高度:160190mm垫板厚度:10mm;凸模固定板厚度:22 mm上模底板厚:35 mm,凹模厚度:28.5mm橡皮厚:24mm 卸料板厚度10 mm凸凹模固定板厚度:45 mm,下模底板厚:45 mm模具的闭合厚度:Hd=35+10+22+28.5+2+1+45+45=188.5mm5.6.4 冲压设备的选择选用开式双柱可倾压力机J23-25。公称压力为25t,滑块行程为65mm,最大闭合高度270mm,滑块中心线至床身距离200 mm,工作台尺寸:370 mm560 mm,垫板厚度:50 mm,模柄孔尺寸:40 mm60 mm.5.6.5 紧固件的选用上模螺钉:螺钉起联接紧固作用,上模上6个,45钢,尺寸为M8X70下模螺钉:6个,45钢,尺寸为M6X55.销钉起定位作用,同时也承受一定的偏移力.上模3个,45钢,尺寸为6X60.6 压力机的校核6.1 公称压力 根据公称压力的选取压力机型号为J23-25,它的压力为25t15.79t,所以压力得以校核;6.2 滑块行程 滑块行程应保证坯料能顺利地放入模具和冲压能顺利地从模具中取出.这里只是材料的厚度t=2mm,卸料板的厚度H=10mm,及凸模冲入凹模的最大深度2mm,即S1=2+10+2=14mmS=65mm,所以得以校核.6.3 行程次数 行程次数为105次/min.因为生产批量为中批量,又是手工送料,不能太快,因此是得以校核.6.4 工作台面的尺寸 根据下模座LB=125mm125mm,且每边留出60100mm,即L1B1=325mm325mm,而压力机的工作台面L2B2=560mm370mm,冲压件和废料从下模漏出, 漏料尺寸小于58mm30mm,而压力机的孔尺寸为250250,故符合要求,得以校核;6.5 滑块模柄孔尺寸 滑块上模柄孔的直径为40mm,模柄孔深度为60mm,而所选的模柄夹持部分直径为30mm,长度为48mm,故符合要求,得以校核;6.6 闭合高度 由压力机型号知Hmax=270mm M=80 H1=70Hmin=HmaxM= 270-80=190(M为闭合高度调节量/mm,H1为垫板厚度/mm)由公式得:( HmaxH1)-5H( HminH1)+10,得(27070)-5188.5(19070)+10即 195188.5120 ,所以所选压力机合适,即压力机得以校核.7 模具主要零件加工工艺规程的编制7.1 冲压模具制造技术要求模具精度是影响冲压件精度的重要因素之一,为了保证模具精度,制造时应达到以下技术要求:a、组成冲压模具的所有零件,在材料加工精度和热处理质量等方面均应符合相应图样的要求。b、组成模架的零件应达到规定的加工要求,装配成套的模架应活动自如,并达到规定的平行度和垂直度要求c、模具的功能必须达到设计要求.d、为了鉴别冲压件的质量,装配好的模具必须在生产条件下试模,并根据试模存在问题进行修整,直至试出合格的冲压件为止。7.2 总装工艺总装图如图12所示: 图12 总装图1 下模座 2导柱 3内六角螺钉870 4内六角螺钉860 5导套 6凸模固定板 7冲孔凸模 8垫板 9上模座 10销钉 11模柄 12打料杆 13连接推杆 14凸凹模 15卸料板 16推件块 17凹模 18活动挡料销 19推板 20弹性橡胶 21凸凹模固定板 22卸料螺钉 23导料销加工工艺路线:1备料2 把导柱2安装在下模座1上。3 把凸凹模14放在下模座1上面,按中心线装上凸凹模固定板21,用螺钉4把凸凹模固定在下模座上。4 通过卸料螺钉22把橡皮20和卸料板15固定好,在卸料板上装好导料销23和挡料销18。5 把导套安装在上模座上。6 把4个冲孔凸模通过凸模固定板6和垫板8一起固定到上模座9上,连同凹模17一起用螺钉3和销钉10紧固。7 把模柄11装在上模座9上,用螺钉紧固,装上打杆12。8把组装好的上模座和下模座通过导柱导套组装起来,中间装上2mm厚的材料。9试模10调整到合格11入库8 总结经过这次的毕业设计,使我受益匪浅。不仅使自己的专业技能有所发挥并且更为熟练,也加强了在大学阶段所学到专业理论知识的巩固。我在经过半年的在外实习明白模具设计和模具制造间的差别,才让我更加有勇气去搞这个毕业设计在毕业设计的过程中,在设计方面遇到了一些问题,经过老师和同学、厂里师傅的指导,再加上自身不懈的努力,问题得到了解决。这次的毕业设计使我对模具设计有了一定的认识,在模具设计过程中,不仅把大学五年所学到知识加深了,还能够把各科灵活的运用到设计中去。这次的毕业设计不仅是对自己大学五年的考核,也是在工作之前对自身的一次全面、综合型的测试。这为今后想从事模具设计的我做好铺垫。致谢 这次毕业设计顺利完成,首先要感谢我的指导老师彭少清,在毕业设计装配图及其说明书编制过程中,给予了精心的指导,并讲解了各项专业要领,特别要感谢我在外实习教我知识技术的师傅们,还有五年来所有的老师特别是我们班主任。是他们的精心指导才使我的毕业设计能够按期完成,感谢学校给予的支持和机会,感谢同学的无私帮助。同时要感谢百忙之中参加毕业答辩的评审老师们。参考文献1 曾霞文 徐政坤主编.冷冲压工艺及模具设计.长沙:中南大学出版社,20062 王 芳主编.冷冲压模具设计指导.北京:机械工业出版社,19993 付宏生主编.冷冲压成形工艺与模具设计制造.北京:化学工业出版社,20054 肖景容 姜奎华主编.冲压工艺学.北京:机械工业出版社,19995 徐茂功 桂定一主编.公差配合与技术测量.北京:机械工业出版社,20006 王孝培主编.冲压手册(修订本).北京:机械工业出版社,19887 催忠圻主编.金属学与热处理.北京:机械工业出版社,20008 谭海林 陈勇主编.模具制造工艺学.长沙:中南大学出版社,20069 廖念钊 莫雨松等主编.互换性与技术测量.北京:中国计量出版社,200010 张定华主编.工程力学.北京:高等教育出版社,200011 梁耀能主编.工程材料及加工工程.北京:机械工业出版社,2001 21INEEL/CON-2000-00104 PREPRINT Spray-Formed Tooling for Injection Molding and Die Casting Applications K. M. McHugh B. R. Wickham June 26, 2000 June 28, 2000 International Conference on Spray Deposition and Melt Atomization This is a preprint of a paper intended for publication in a journal or proceedings. Since changes may be made before publication, this preprint should not be cited or reproduced without permission of the author. This document was prepared as a account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, or any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for any third partys use, or the results of such use, of any information, apparatus, product or process disclosed in this report, or represents that its use by such third party would not infringe privately owned rights. The views expressed in this paper are not necessarily those of the U.S. Government or the sponsoring agency. BECHTEL BWXT IDAHO, LLC 1 Spray-Formed Tooling For Injection Molding and Die Casting Applications Kevin M. McHugh and Bruce R. Wickham Idaho National Engineering and Environmental Laboratory P.O. Box 1625 Idaho Falls, ID 83415-2050 e-mail: kmm4inel.gov Abstract Rapid Solidification Process (RSP) Tooling is a spray forming technology tailored for producing molds and dies. The approach combines rapid solidification processing and net-shape materials processing in a single step. The ability of the sprayed deposit to capture features of the tool pattern eliminates costly machining operations in conventional mold making and reduces turnaround time. Moreover, rapid solidification suppresses carbide precipitation and growth, allowing many ferritic tool steels to be artificially aged, an alternative to conventional heat treatment that offers unique benefits. Material properties and microstructure transformation during heat treatment of spray-formed H13 tool steel are described. Introduction Molds, dies, and related tooling are used to shape many of the plastic and metal components we use every day at home or at work. The process involves machining the negative of a desired part shape (core and cavity) from a forged tool steel or a rough metal casting, adding cooling channels, vents, and other mechanical features, followed by grinding. Many molds and dies undergo heat treatment (austenitization/quench/temper) to improve the properties of the steel, followed by final grinding and polishing to achieve the desired finish 1. Conventional fabrication of molds and dies is very expensive and time consuming because: Each is custom made, reflecting the shape and texture of the desired part. The materials used to make tooling are difficult to machine and work with. Tool steels are the workhorse of industry for long production runs. Machining tool steels is capital equipment intensive because specialized equipment is often needed for individual machining steps. Tooling must be machined accurately. Oftentimes many individual components must fit together correctly for the final product to function properly. 2 Costs for plastic injection molds vary with size and complexity, ranging from about $10,000 to over $300,000 (U.S.), and have lead times of 3 to 6 months. Tool checking and part qualification may require an additional 3 months. Large die-casting dies for transmissions and sheet metal stamping dies for making automobile body panels may cost more than $1million (U.S.). Lead times are usually greater than 40 weeks. A large automobile company invests about $1 billion (U.S.) in new tooling each year to manufacture the components that go into their new line of cars and trucks. Spray forming offers great potential for reducing the cost and lead time for tooling by eliminating many of the machining, grinding, and polishing unit operations. In addition, spray forming provides a powerful means to control segregation of alloying elements during solidification and carbide formation, and the ability to create beneficial metastable phases in many popular ferritic tool steels. As a result, relatively low temperature precipitation hardening heat treatment can be used to tailor properties such as hardness, toughness, thermal fatigue resistance, and strength. This paper describes the application of spray forming technology for producing H13 tooling for injection molding and die casting applications, and the benefits of low temperature heat treatment. RSP Tooling Rapid Solidification Process (RSP) Tooling, is a spray forming technology tailored for producing molds and dies 2-4. The approach combines rapid solidification processing and net- shape materials processing in a single step. The general concept involves converting a mold design described by a CAD file to a tooling master using a suitable rapid prototyping (RP) technology such as stereolithography. A pattern transfer is made to a castable ceramic, typically alumina or fused silica (Figure 1). This is followed by spray forming a thick deposit of tool steel (or other alloy) on the pattern to capture the desired shape, surface texture and detail. The resultant metal block is cooled to room temperature and separated from the pattern. Typically, the deposits exterior walls are machined square, allowing it to be used as an insert in a holding block such as a MUD frame 5. The overall turnaround time for tooling is about three days, stating with a master. Molds and dies produced in this way have been used for prototype and production runs in plastic injection molding and die casting. Figure 1. RSP Tooling processing steps. 3 An important benefit of RSP Tooling is that it allows molds and dies to be made early in the design cycle for a component. True prototype parts can be manufactured to assess form, fit, and function using the same process planned for production. If the part is qualified, the tooling can be run in production as conventional tooling would. Use of a digital database and RP technology allows design modifications to be easily made. Experimental Procedure An alumina-base ceramic (Cotronics 780 6) was slurry cast using a silicone rubber master die, or freeze cast using a stereolithography master. After setting up, ceramic patterns were demolded, fired in a kiln, and cooled to room temperature. H13 tool steel was induction melted under a nitrogen atmosphere, superheated about 100C, and pressure-fed into a bench-scale converging/diverging spray nozzle, designed and constructed in-house. An inert gas atmosphere within the spray apparatus minimized in-flight oxidation of the atomized droplets as they deposited onto the tool pattern at a rate of about 200 kg/h. Gas-to-metal mass flow ratio was approximately 0.5. For tensile property and hardness evaluation, the spray-formed material was sectioned using a wire EDM and surface ground to remove a 0.05 mm thick heat-affected zone. Samples were heat treated in a furnace that was purged with nitrogen. Each sample was coated with BN and placed in a sealed metal foil packet as a precautionary measure to prevent decarburization. Artificially aged samples were soaked for 1 hour at temperatures ranging from 400 to 700C, and air cooled. Conventionally heat treated H13 was austenitized at 1010C for 30 min., air quenched, and double tempered (2 hr plus 2 hr) at 538C. Microhardness was measured at room temperature using a Shimadzu Type M Vickers Hardness Tester by averaging ten microindentation readings. Microstructure of the etched (3% nital) tool steel was evaluated optically using an Olympus Model PME-3 metallograph and an Amray Model 1830 scanning electron microscope. Phase composition was analyzed via energy- dispersive spectroscopy (EDS). The size distribution of overspray powder was analyzed using a Microtrac Full Range Particle Analyzer after powder samples were sieved at 200 m to remove coarse flakes. Sample density was evaluated by water displacement using Archimedes principle and a Mettler balance (Model AE100). A quasi 1-D computer code developed at INEEL was used to evaluate multiphase flow behavior inside the nozzle and free jet regions. The codes basic numerical technique solves the steady- state gas flow field through an adaptive grid, conservative variables approach and treats the droplet phase in a Lagrangian manner with full aerodynamic and energetic coupling between the droplets and transport gas. The liquid metal injection system is coupled to the throat gas dynamics, and effects of heat transfer and wall friction are included. The code also includes a nonequilibrium solidification model that permits droplet undercooling and recalescence. The code was used to map out the temperature and velocity profile of the gas and atomized droplets within the nozzle and free jet regions. 4 Results and Discussion Spray forming is a robust rapid tooling technology that allows tool steel molds and dies to be produced in a straightforward manner. Examples of die inserts are given in Figure 2. Each was spray formed using a ceramic pattern generated from a RP master. Figure 2. Spray-formed mold inserts. (a) Ceramic pattern and H13 tool steel insert. (b) P20 tool steel insert. Particle and Gas Behavior Particle mass frequency and cumulative mass distribution plots for H13 tool steel sprays are given in Figure 3. The mass median diameter was determined to be 56 m by interpolation of size corresponding to 50% cumulative mass. The area mean diameter and volume mean diameter were calculated to be 53 m and 139 m, respectively. Geometric standard deviation, d =(d 84 /d 16 ) , is 1.8, where d 84 and d 16 are particle diameters corresponding to 84% and 16% cumulative mass in Figure 3. 5 Figure 3. Cumulative mass and mass frequency plots of particles in H13 tool step sprays. Figure 4 gives computational results for the multiphase velocity flow field (Figure 4a), and H13 tool steel solid fraction (Figure 4b), inside the nozzle and free jet regions. Gas velocity increases until reaching the location of the shock front, at which point it precipitously decreases, eventually decaying exponentially outside the nozzle. Small droplets are easily perturbed by the velocity field, accelerating inside the nozzle and decelerating outside. After reaching their terminal velocity, larger droplets (150 m) are less perturbed by the flow field due to their greater momentum. It is well known that high particle cooling rates in the spray jet (10 3 -10 6 K/s) and bulk deposit (1- 100 K/min) are present during spray forming 7. Most of the particles in the spray have undergone recalescence, resulting in a solid fraction of about 0.75. Calculated solid fraction profiles of small (30 m) and large (150 m) droplets with distance from the nozzle inlet, are shown in Figure 4b. Spray-Formed Deposits This high heat extraction rate reduces erosion effects at the surface of the tool pattern. This allows relatively soft, castable ceramic pattern materials to be used that would not be satisfactory candidates for conventional metal casting processes. With suitable processing conditions, fine 6 Figure 4. Calculated particle and gas behavior in nozzle and free jet regions. (a) Velocity profile. (b) Solid fraction. 7 surface detail can be successfully transferred from the pattern to spray-formed mold. Surface roughness at the molding surface is pattern dependent. Slurry-cast commercial ceramics yield a surface roughness of about 1 m Ra, suitable for many molding applications. Deposition of tool steel onto glass plates has yielded a specular surface finish of about 0.076 m Ra. At the current state of development, dimensional repeatability of spray-formed molds, starting with a common master, is about 0.2%. Chemistry The chemistry of H13 tool steel is designed to allow the material to withstand the temperature, pressure, abrasion, and thermal cycling associated with demanding applications such as die casting. It is the most popular die casting alloy worldwide and second most popular tool steel for plastic injection molding. The steel has low carbon content (0.4 wt.%) to promote toughness, medium chromium content (5 wt%) to provide good resistance to high temperature softening, 1 wt% Si to improve high temperature oxidation resistance, and small molybdenum and vanadium additions (about 1%) that form stable carbides to increase resistance to erosive wear 8. Composition analysis was performed on H13 tool steel before and after spray forming. Results, summarized in Table 1, indicate no significant variation in alloy additions. Table 1. Composition of H13 tool steel Element C Mn Cr Mo V Si Fe Stock H13 0.41 0.39 5.15 1.41 0.9 1.06 Bal. Spray Formed H13 0.41 0.38 5.10 1.42 0.9 1.08 Bal. Microstructure The size, shape, type, and distribution of carbides found in H13 tool steel is dictated by the processing method and heat treatment. Normally the commercial steel is machined in the mill annealed condition and heat treated (austenitized/quenched/tempered) prior to use. It is typically austenitized at about 1010C, quenched in air or oil, and carefully tempered two or three times at 540 to 650C to obtain the required combination of hardness, thermal fatigue resistance, and toughness. Commercial, forged, ferritic tool steels cannot be precipitation hardened because after electroslag remelting at the steel mill, ingots are cast that cool slowly and form coarse carbides. In contrast, rapid solidification of H13 tool steel causes alloying additions to remain largely in solution and to be more uniformly distributed in the matrix 9-11. Properties can be tailored by artificial aging or conventional heat treatment. A benefit of artificial aging is that it bypasses the specific volume changes that occur during conventional heat treatment that can lead to tool distortion. These specific volume changes occur as the matrix phase transforms from ferrite to austenite to tempered martensite and must be accounted for in the original mold design. However, they cannot always be reliably predicted. Thin sections in the insert, which may be desirable from a design and production standpoint, are oftentimes not included as the material has a tendency to slump during austenitization or distort 8 during quenching. Tool distortion is not observed during artificial aging of spray-formed tool steels because there is no phase transformation. An optical photomicrograph of spray-formed H13 is shown in Figure 5 together with an SEM image, in backscattered electron (BSE) mode. Energy dispersive spectroscopic (EDS) composition analysis of some features in the photomicrographs is also given. While exact quantitative data is not possible due to sampling volume limitations, results suggest that grain boundaries are particularly rich in V. Intragranular (matrix) regions are homogeneous and rich in Fe. X-ray diffraction analysis indicates that the matrix phase is primarily ferrite (bainite) with very little retained austenite, and that the alloying elements are largely in solution. Discrete intragranular carbides are relatively rare, very small (about 0.1 m) and predominately vanadium-rich MC carbides. M 2 C carbides are not observed. Element Si V Cr Mn Mo Fe Spot #1 (wt%) 0.61 32.13 6.68 0.17 2.05 58.36 Spot #2 (wt%) 1.59 0.79 5.35 0.28 2.28 89.72 Figure 5. Photomicrographs of as-deposited H13 tool steel. 3% nital etch. (a) Optical photomicrograph. (b) SEM image (BSE mode) near a grain boundary. Table gives EDS composition of numbered features. 9 Figure 6 illustrates the microstructure of spray-formed H13 aged at 500C for 1 hr. During aging, grain boundaries remain well defined, perhaps coarsening slightly compared to as- deposited H13 (Figure 5). The most prominent change is the appearance of very fine (0.1 m diameter) vanadium-rich MC carbide precipitates. The precipitates are uniformly distributed throughout the matrix and increase the hardness and wear resistance of the tool steel. Increasing the soak temperature to 700C results in prominent carbide coarsening, the formation of M 7 C 3 and M 6 C carbides, and a decrease in hardness. The photomicrographs of Figure 7 illustrate the dramatic change in carbide size. BSE imaging clearly differentiates Mo/Cr-rich carbides from V-rich carbides, shown as light and dark areas, respectively, in Figure 7. EDS analysis of these carbides is also given in Figure 7. Element Si V Cr Mn Mo Fe Spot #1 (wt%) 0.06 13.80 7.20 2.64 2.44 73.86 Spot #2 (wt%) 1.52 0.82 5.48 0.23 2.38 89.57 Figure 6. Photomicrographs of spray-formed/aged H13 tool steel. 500C soak for 1 hr. 3% nital etch. (a) Optical photomicrograph. (b) SEM image (BSE mode) near a grain boundary. Table gives EDS composition of numbered features. 10 Element Si V Cr Mn Mo Fe Spot #1 (wt%) 0 82.27 9.01 0 4.33 4.39 Spot #2 (wt%) 0 5.30 25.70 0 55.55 13.45 Spot #3 (wt%) 1.60 0.88 6.32 0.28 2.92 88.00 Figure 7. SEM Photomicrograph (BSE mode) of spray-formed/aged H13 tool steel showing adjacent V-rich (dark) and Mo/Cr-rich (light) carbides. 700C soak for 1/2 hr, 3% nital etch. Table gives EDS composition of numbered features. Material Properties Porosity in spray-formed metals depends on processing conditions. The average as-deposited density of spray-formed H13 was 98-99% of theoretical, as measured by water displacement using Archimedes principle. As-deposited hardness was typically about 59 HRC, harder than commercial forged and heat treated material (28 to 53 HRC depending on tempering temperature), and significantly harder than annealed H13 (200 HB). The high hardness is attributable to lattice strain due to quenching stresses and supersaturation. As shown in Figure 8, hardness can be varied over a wide range by artificial aging. 59 HRC as- deposited samples were given isochronal (1 hr) soaks at 50C increments from 400 to 700C, air cooled, and evaluated for microhardness. At 400C, a small decrease in hardness was observed, presumably due to stress relieving. As the soak temperature was further increased, hardness rose to a peak hardness of approximately 62 HRC at 500C. Higher soak temperature resulted in a drop in hardness as carbide particles coarsened. Peak age hardness in spray-formed H13 tool steel is notably higher than that of commercial hardened material. Normally, commercial H13 dies used in die casting are tempered to about 40 to 45 HRC as a tradeoff since high hardness dies, while desirable for wear resistance, are prone to premature failure via thermal fatigue as the dies surface is rapidly cycled from 300C to 700C during aluminum production runs. 11 Figure 8. Hardness of artificially aged spray-formed H13 tool steel following one hour soaks at temperature. Hardness range of conventionally heat treated H13 included for comparison. As-deposited spray-formed material was also hardened following the conventional heat treatment cycle used with commercial material. Samples of forged/mill annealed commercial and spray- formed materials were austenitized at 1010C, air quenched, and double tempered (2 hr plus 2 hr) at (538C). The microstructure in both cases was found to be tempered martensite with a few spheroidal particles of alloy carbide. Hardness values for both materials were very nearly identical. Table 2 gives the ultimate tensile strength and yield strength of spray-formed, cast, and forged/heat treated H13 tool steel measured at test temperatures of 22 and 550C. Values for spray formed H13 are given in the as-deposited condition and following artificial aging and conventional heat treatments. Values for the spray-formed material are comparable to those of forged and are considerably higher than those of cast tool steel. The spray-formed material seems to retain its strength somewhat better than forged/heat treated H13 at higher temperatures. 12 Table 2. H13 tool steel mechanical properties. Sample/Heat Treatment Ultimate Tensile Strength (MPa) Yield Strength (MPa) Test Temperature (C) Spray formed/as-deposited 1061 951
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