碳纤维增强塑料的铣削破坏和尺寸精度设计实验

1、瞄芹纸贺轨昔象浼去羟帝芷擐硎Damage and dimensional precision on milling carbonfiber-reinforced爿缤恩履芩巳髦客绅访溲脊弈瑗plastics using design experiments饱毛纽荬吲秦嘛倨概忿树街猥碎J. Paulo Davim, Pedro Reis橇墩斡形寺蔗鬈欲盅堡鲍驽敖砟Department of Mechanical Engineering, University of Aveiro, Campus Santiago, 3810-193 Aveiro, Portugal呙匍惴纬坡佐拓循舢圃逸陆吩析Rec

2、eived 24 June 2002; received in revised form 10 May 2004; accepted 8 June 2004籀魄泛轹紊疳雁马捧孝离甫俜蝉Abstract骗渚吉螵渑辞凄亩卵缌怂滔缌郜Milling composite materials is a rather complex task owing to its heterogeneity and the number of problems, such as surface delamination, that appear during the machining process, associ

3、ated with the characteristics of the material and the cutting parameters.踔铠谈鳝浯奄诊濞洮坎呃蘸渎抵With the purpose of understanding and reducing these problems, this paper presents a study that evaluates the cutting parameters (cutting velocity and feed rate) under the surface roughness, and damage in milling

4、laminate plates of carbon fiber-reinforced plastics (CFRPs). A plan of experiments, based on the Taguchis method, was established considering milling with prefixed cutting parameters in an autoclave CFRP composite material. An analysis of variance (ANOVA) was performed to investigate the cutting cha

5、racteristics of CFRP composite material using cemented carbide (K10) end mills. The objective was to establish a model using multiple regression analysis between cutting velocity and feed rate with the surface roughness and damage in a CFRP composite material. 狯疟北园揎氨俺惧蟮咸飘晤噍很 2004 Elsevier B.V. All r

6、ights reserved.堪黯圩歌滏惑向屉阔徜渺钮槟怊Keywords: Milling; Carbon fiber-reinforced plastics (CFRPs); Dimensional precision; Taguchis method; Orthogonal arrays; Analysis of variance (ANOVA)晃舢享云蜃灿绦弋鸵悯嬷九抢门1. Introduction咀犟漶饼蒉剔梦亲惊筘择来母堑1.1. Milling fiber-reinforced plastics (FRPs)颓镄沥舍赁疲经攒倮稹朗逗晦柏Milling is the machin

7、ing operation most frequently used in manufacturing parts of fiber-reinforced plastics, because components made of composite materials are commonly produced by net-shape that often require the removal of excess material to control tolerances, and milling is used as a corrective operation to produce

8、a well defined and high quality surfaces 1.男迮沉聩顿草奋佟茑弭捡割统推The machinability of fiber-reinforced plastics is strongly influenced by the type of fiber embedded in the composite and by its properties. 笕乍舣焐啾司以搴赁鹤忘悚痧筮Mechanical and thermal properties have an extremely importance on machining FRP. 书功斥擅裟迄冉耽

9、础昶喔反靡羿The fiber used in the composites has a greater influence in the selection of cutting tools (cutting edge material and geometry) and machining parameters.岱纤移侮您扒灭放夹溲督呢骛常It is fundamental to ensure that the tool selected is suitable for the material. 鞫沿疽拦敕嵇堀靴惭歹蛘扣浣倒The knowledge of cutting mechani

10、sms is indispensable in view of cutting mechanics and machinability assessment in milling 1,2.缛枢很蒜爬乡咣闹浯督盐龋册鼬Composite materials such as carbon fiber-reinforced plastics (CFRPs) made by using carbon fibers for reinforcing plastic resin matrices, such as epoxy, are characterised by having excellent pr

11、operties as light weight, high strength and high stiffness.逊谝戢括睽入莱骡铬俘荻虏髅倮These properties make them especially attractive for aerospace applications 2.缘谝澜唁酊估娜镑飘哧鏊蔡疴黍Surface roughness is a parameter that has a greater influence on dimensional precision, performance of mechanical pieces and on product

12、ion costs. 噬砾杀戳柠壕戛踟氍侥劾讶滴畸For these reasons, research developments have been carried out with the purpose of optimising the cutting conditions to reach a specific surface roughness 3,4. 闲驯埔诫缱摩芒苍辙旖忄殆狴台For achieving the desired quality of the machined surface, it is necessary to understand the mechanis

13、ms of material removal, the kinetics of machining processes affecting the performance of the cutting tools 5.酵吞勘刊碛若哒斩木遭娱萌砟皮The works of a number of authors 612, 哓弊峰捣蹿金嘬曦梆缂啤讥奕晕when reporting on milling of FRP, have shown that the type and orientation of the fiber, cutting parameters and tool geometry

14、 have an essential paper on the machinability. 镀崇舴聒髻本鹨蹿诏眄肚呱字讳Everstine and Rogers 6 presented the first theoretical work on the machining of FRPs in 1971, since then the research made in this area has been based on experimental investigations.轾花奔锬鲦钋冗衾耆鸸普香瘾仞Koplev et al. 7, Kaneeda 8 and Puw and Hoch

15、eng 9 concluded that the principal cutting mechanisms correlate strongly to fiber arrangement and tool geometry. 腔框拇大墀笈亘翁铅袁膺歆砑扰Santhanakrishman et al. 10 and Ramulu et al. 11 carried out a study on machining of polymeric composites and concluded that an increasing of the cutting speed leads to a bet

16、ter surface finish. 晨绡篱墒豆缥曼庇帮类乇恨曹柒Hocheng et al. 12 studied the effect of the fiber orientation on the cut quality, cutting forces and tool wear on the machinability.茫瞧慢癌锘翕萋慈陟咸躺曷规睬 In summary, it can be noticed that the works carried out on the machinability of FRP, are basically related on the wear

17、 of cutting tools and the quality on the surfaces, as a function of the cutting conditions, the distribution of staple fibers in the polymeric matrix and the angle of inclination of staple fibers. 估雾且尿澈软敛旁旱鸾它眺阔尚The current paper investigates the influence of cutting parameters (cutting velocity and

18、feed rate) on the surface roughness (Ra), delamination factor (Fd), and international dimensional precision (IT), on CFRP composite material using cemented carbide end mills, with the purpose to establish a empirical relationship between cutting parameters (V and f) and surface roughness (Ra) and de

19、lamination factor (Fd).片抒刹裣华独咕勰顶烊忪姣掊科1.2. Autoclave process瓦娅噶判茎埠馆咎颈辞鸵簌揪极The autoclave process is widely used to produce high-performance laminates usually with fibers reinforced epoxy systems. 暖呓肥闳其夺递劐濠户克蕺吡恸Composite materials manufactured by autoclave are particularly important for aerospace appli

20、cations.嘟诏葡癜喟耙抿编盗襦戕笔翕堂This process uses a pressurised vessel to apply pressure and heat to both parts that have been sealed in a vacuum bag. Next it can be seen the several stages of this process. 扁好蛏饭碥僖籍揩氩鸥碗耿郗咦On the first stage, the prepreg carbon-fiberepoxy material is carefully laid out on a tab

21、le to ensure that fiber orientation meets the design requirement, where the prepreg material consists of unidirectional long carbon fibers in a partially cured epoxy matrix. On the second stage, pieces of the prepreg material are cut out and placed on top of each other on a shaped tool to form a lam

22、inate. 倍郛兰盔谛逼菝讲兄豫森奏硭汕The layers could be placed in different directions to produce the desired strength pattern since the highest strength of each layer is in direction parallel to the fibers.痘龉酉芳嘎玺锿石尾儇姜沙牯返After the required number of layers has been properly placed, the tooling and the attached lam

23、inate are vacuum-bagged, for removing the entrapped air from the laminated part.娶庀缡皑韵倌鲁蕊埠祠猬侮鞘笺Finally, the vacuum bag and the tooling is put into an autoclave for the final curing of the epoxy resin.供南蛸赛焚阢多囡鸱馅佑犄嘧After removed from the autoclave, the composite material is ready for further finishing

24、operations 2,13.览鋈铩雍癞褊皈钱四失楹磉馁鸷2. Experimental procedure菁题榆孳趁戚逻覆袄蜊溜铘眚戎2.1. Method and materials褪靡怀膛洞醯媵趣葚獍朴屯僚士In order to reach the objective of this experimental work, mainly the establishment of the correlations between cutting parameters (V and f) and surface roughness (Ra) and delamination factor

25、(Fd), machining issues were performed under different cutting conditions on the CFRP composite material.揶港泛曝厶镤患索恕戏剑彻遁碲 The composite material used in the tests (epoxy matrix reinforced with 55% of carbon fiber), supplied by INEGI, was produced by autoclave with a fiber orientation of 0/90, as can be

26、 observed in Fig. 1.擀鞍默吁甚烦菩诮烤仿瑁奴襻吮The experiments have been carried out in a laminate plate, made up with 16 alternating layers of fibers with 4mm of thickness, using two cemented carbide (K10) end mills, presented in Fig. 2, with 6mm of diameter. Both cemented carbide end mills, two-flute (R216.32-

27、06030-AC10P-1020) and six-flute (CCT-GSR-D0635), were manufactured according to ISO. 甾婶蒯西步作让瓶曰吕蹭现蜣徙The two-flute end mill presents the following geometry: a helix angle of 30, a rake angle of 1030_, a clearance angle of 9 and a flute length of 10 mm. 靼气簇喔伏瀑赛醅表镢余馥髋霹The six-flute end mill presents a n

28、eutral helix and 20mm of flute length. The depth of the cut on CFRP composite material was 2 mm. 螬芥救娄卫叭鲋豚日寡遒栽庖洳A milling machine “LC-11/2VS First” with 2.2kW spindle power and a maximum spindle speed of 2500 rpm was used to perform the experiments. 洽均僳巍瘿谰样埴敞噻祉谣揆址The fixation of the composite materia

29、l (plate) was made as observed in Fig. 3, to make sure that vibrations and displacement did not exist. 涪崆锁糊晋车恋氐轸程醵碴挹元The surface roughness was evaluated (according to ISO 4287/1) with a Hommeltester T1000 profilometer, as can be observed in Fig. 4.鬓熬埴哧郎外垭萁逭岂劬钟鳐吁For each test five measurements were m

30、ade over milling surfaces, according to Fig. 5. Considering the number of measurements to be carried out, a programmable technique was used, by previously selecting a roughness profile, the cut-off (0.8 mm) and the roughness evaluator parameter (Ra) according to ISO. 吮洮学羰例忝兰沂蹲曜痦嬉殄蝶Data acquisitions

31、were made through pro-filometer, by interface RS-232 to PC using the software欷门餐悠缭数剔醚除倔俣萏番谂Hommeltester Turbo-Datawin.液呻欹跞钡寨璁蕞取腐鲆泌伽埚The damage caused on the composite material was measured with a shop microscope, Mitutoyo TM 500, with 30 magnification and 1 _m resolution.肜皇泪樟范窍涉箍钲印陈返莼已2.2. Plan of e

32、xperiments荏濮稷苦堤昧蟹呗郸罨暖娜驶呐Taguchis method has been widely used in engineering analysis and consists of a plan of experiments with the objective of acquiring data in a controlled way, in order to obtain information about the behaviour of a given process. 苡焚锑拇撒井甏钯加握鲴庸射廖The Taguchis method for two factor

33、s at three levels was used for the elaboration of the plan of experiments. Table 1 indicates the factors studied and the assignment of the corresponding levels. By levels is meant the values taken by the factors. 且健鳔鳏娼琮昆腿揭着玢醯鸿郫The orthogonal array L9 (24), was selected as shown in Table 2, which has

34、 nine rows corresponding to the number of tests (8 degrees of freedom) with two columns at three levels. The factors and the interactions are assigned to the columns. 兢崾笪糁铆秆姹懂祺圬坏抟亭鲨The plan of experiments was made of nine tests (array rows), where the first column was assigned to the cutting velocit

35、y (V) and the second column to the feed rate (f) and the remaining were assigned to the interactions. 蒗笼邬荟意嗣淖慵赖院铲擘没攻The outputs studied were surface roughness (Ra) and delamination factor (Fd), in the CFRP composite material. 骠灸静踅兄削葶裹叮瞍遗蹿触摆The treatment of the experimental results was based on the a

36、nalysis average and the analysis of variance (ANOVA) 1417.关阐掩叠禧蛮凄寄蛄瞿舁飓侄笾An analysis of variance of the data with the surface roughness and delamination factor, on the CFRP composite material was done with the objective of analysing the influence of the cutting velocity, and the feed rate on the tota

37、l variance of the results.懵胄蘸宦蓿团胪悔轿杌连羰订3. Results and discussion散愣脔媳醴腱腐阽惬箬棣垃咫笔The results of milling tests allowed the evaluation of the CFRP composite material manufactured by autoclave, using two cemented carbide (K10) end mills. 湍掩晾狼钴辰苤冯夫逃慧接踺膣The machinability was evaluated by surface roughness (

38、Ra), delamination factor (Fd) and international dimensional precision (IT).笪濯焕井撙毋镍乘骥馕彭鳐绎堋3.1. Influence of the cutting parameters on the surface烩麾踢鳋劲锤防蓬苜葆轷钰钫跎roughness翻赞挹泪效蚁鍪剔陇枯处十臾洎The surface roughness (Ra) was evaluated with a Hommeltester T1000 profilometer, according to ISO 4287/1. Tables 3 and

39、4 show the results of the surface roughness (Ra) as a function of the cutting parameters, for both end mills, two- and six-flute, respectively. In Fig. 6, the evolution of the surface roughness (Ra) can be seen with the feed rate, for the different cutting speed values. From Fig. 6, it can be realis

40、ed that the value of Ra increases with feed rate and decreases with the cutting velocity, i.e. with a higher cutting velocity and a lower feed rate it is possible obtain a better surface finish. It can also be observed that the two-flute end mill provides a better surface than the six-flute end mill

41、. Table 5 shows the results of the analysis of variance with the surface roughness (Ra) for both end mills. 恿瞩样涔刃够悄骣良黢鳐页雀氟This analysis was carried out for a level of significance of 5%, i.e. for a level of confidence of 95%. The last column of the previously shown tables indicates the percentage of

42、 contribution (P) of each factor on the total variation indicating then, the degree of influence on the result.锖鬈笼遣颖仗襟炽译魉割棍芋箴From Table 5, it can be realised that the feed rate factor (P = 77.5%), have statistical and physical significance on the obtained surface roughness (Ra), for two-flute end mi

43、ll. The factor cutting velocity (P= 9.5%) does not present statistical and physical significance on the surface roughness, because Test F F = 5% and P (percentage of contribution) F = 5% and P (percentage of contribution) error associated. 鹭谣龄呋尖讨恨挫杆笥和勺巛跬Notice that the error associated to the table

44、ANOVA for the Ra was approximately 1.7%. The value of international dimensional precision (IT) can be obtained by the following empirical equation according to UNI ISO 3963/2: IT= 30Ra (1)孑恫怪饕恳酗烙哺惜扪廖腿洄短Ra being the surface roughness in _m. Table 6 shows the results of the dimensional precision (IT),

45、 obtained by Eq. (1), as a function of the cutting parameters In Fig. 7 the evolution of the dimensional precision (IT) can be seen with the feed rate, for the different cutting speed values. According to the graph, it is evident that the IT increases with the feed rate, and decreases with the cutti

46、ng speed. 乎掘储纹茑檀锎贪爽杠阕吃折钬It can also be observed that for both end mills (two- and six-flute) the surface presents ITs between 35 and 80 _m, and 40 and 80 _m, respectively, i.e. it is possible to get surfaces of quality of mechanics current construction, nominated qualities of IT 9 and 11.矫昊利架茛戍镩村冯怏豌

47、瘾及渡3.2. Influence of the cutting parameters on the delamination factor颧螳着磐蝤汉嬗尸撕娃捕柃淡糜The damage caused on the laminate plate (CFRP composite material) was measured perpendicular to the feed rate with a shop microscope Mitutoyo TM 500, as can be observed in Fig. 8. 涟酣尾耨鹦莱泸酋础效蕉嫒均蘑The composite material

48、 (laminate plate) was positioned and fixed on the XY stage glass of the microscope, then the alignment of an initial measuring point with one of the cross-hairs was made on the machined fea ture.柁觞啄瓢弄潮肇怆癖褐弓袒粽十 Moving the XY stage glass by turning the micrometer head with a Digital Counter to the fin

49、al point with the same cross-hair has been measured the damage (maximum width). 咸铄搅樊踢赧簖蛰婵韶宰蜕悔瀚After the measurement of the maximum width of damage (Wmax) suffered by the material, the damage normally assigned by delamination factor (Fd) was determined. 漂秽耔螵炷獍飕杀蘸檎呒媚苷延This factor is defined as the quo

50、tient between the maximum width of damage (Wmax), and the width of cut (W). The value of delamination factor (Fd) can be obtained by the following equation: Fd = Wmax W筹晷谋阌救掎熬握炽蓠稳愣闯狄(2)Wmax being the maximum width of damage in _m and W the width of cut in _m珀怂申共化币地醉镁暹芊懒刘逅Table 7 shows the results of

51、 the delamination factor (Fd) for the two end mills, obtained as Eq. (2) as a function of the cutting parameters. In Fig. 9 the evolution of the delamination factor (Fd) can be seen with feed rate, for different cutting speed values. 碣翅鹣褡天其蹬壮蜕逑璐淌孺惺From Fig. 9, it can also be noticed that the Fd incr

52、eases with the feed rate. It can also be observed a significant variation on the delamination factor (Fd) for the six-flute end mill with the increase of the cutting speed. 嫡霪轮要游疗嘈滢蚯圣漂迦劫手Finally, it can be realised that two-flute end mill presents a lower delamination factor than the six-flute end m

53、ill, i.e. the two-flute end mill leads to a smaller damage on the CFRP composite material. Table 8 shows the results of the analysis of variance with the delamination factor (Fd) for both end mills. From Table 8, it can be realised that the feed rate factor (P = 83.9%), have statistical and physical

54、 significance on the obtained delamination factor (Fd), for two-flute end mill. 将钙彷蚁僧狩喷鸠友赳睾钳嘲咏The factor cutting velocity (P = 0.6%) does not present statistical and physical significance on the delamination factor (Fd), because Test F F = 5% and P (percentage of contribution)N F = 5% and P (percent

55、age of contribution) error associated. Notice that the error associated to the table ANOVA for the Fd was approximately 4.3%.衫曹唇税呀烨经斛朕迷荬晕田契3.3. Multiple regression analysis (MRA)胨恫挪匆趸屿匆蝈撰盍冢吭娃停The correlation between factors (cutting velocity, feed rate) and surface roughness (Ra) and delamination fa

56、ctor (Fd), for both end mills on the CFRP composite material were obtained by multiple linear regression with a sample size (n) of 9. 蛩脶搪剂差屉恨卫传疏肥宓尴辕The equations obtained for both end mills were as follow: Two-flute end mill: Ra = 1.76 2.40 102V + 1.71 103f, R = 0.93 (3)必颊胄含镞倡赐推憩罹脘瑚苋则Fd = 1.00 6.58 105V + 2.34 105f, R = 0.89 (4)渴蹴形弗槔示苘策鼢钐聃到峄琢Six-flute end mill:优廒祭龠耿庋