TAPCHlKHOAHpC&CdNGNGHfcAC TRITONG B.^ HPC Kt THU4T*s690-20I2 DYNAMICALLY STABLE MILLING TOOLS WITH INTEGRATED CUT- SPLITTING NOHlfiN COXJ PHAT TRifiN DAO PHAY C6 TtNH N DJNH D()NG HOC CAO V6l NGUYEN TAC PHAN CHIA CHlfeU SAU C A T Nguyen Trong Hieu', T Emma', Nguyen Dac Trung' 'Hanoi University of Science and Technology ^Olto-von-Guericke University Magdeburg Received April 10, 2012; accepted August 14, 2012 ABSTRACT 7/ie principle of cut-splitting can guarantee an effective cutting even under the difficult conditions of stability To divide ttie chip In two or more places, ttte gaometric relations of the cutting area of every clilp are ciianged This change is caused by the cutting forces and therefore by the dynamic behaviour of the whole process The advancement of the prindpie of cut-splitting obviously Improves the dynamic behaviour In pattlcuiar, under unstable conditions of machine processing currently In practice, these new milling tools outclass the ordinary milling heads because of their fewer vibrations and less noise Key words: plane milling heads, cut splitting T6M TAT Nguyen /^c phSn chia chi^u sSu c^t ddm bdo quA trinh c4t sS diin hi^u qu6 cA nhOng iS^u est kem 6n ^nh Bihg c6ch chia phoi thinh hai ho$c nhiiu minh nhd, m6t quan hi hlnh hQC cCia khu vvc cit ddi vdi moi minh phoi s6 bi thay Oil Si/ thay Oil giy rabdilfjKck vi Mi chit ddng hoc cOa toin bi qui trinh Diim vur?t trii cOa nguyin tic phin chia chiiu siu dtlidi thi$n duvc tinh chit ding hoc cOa qui trinh cit Die bi^t Mi v6i cic (Siu kiin gia dng kim in d ^ & thi/c ti, nhOng dao phey niy si vuryt trii hin nhung dao phay binh thuimg It rung ding vi It in hon TCr kh6a: Dao phay m$t ddu, phdn chia chi6u sSu c i t 1, INTRODUCTION have especially proved themselves when For the chipptog technology of planar and right^gled Zeis, theie is a varied and high-performance assortment of milling heads wWi clamped inserts, taserts made of carbide metal are used in most cases Tliey arc ci±er clamped direcdy in die body material or mounted in extra caskets [I] For practical processing, predominantly planar milling heads (K, < 90°) are used, but in some cases angled milling heads (ic= 90°) as well [2],[3] hi diese cases, uiseits with a regular geometrical form are used, for angle nulling heads a rhombic and triangular form, for planar milling heads mostly a quadrangular form with K, = 75° or K, = 45° In terms of a better exploitation of cutting material and decreasing material allowances, multi-angled insert forms, such as 8- and 12: angled-fonns and also round forms, have prevailed in the last years The round* forms ^ f " ? ' * ""^ ^ r "1? '"'l!'' ™ f ' T f ^^°' '"V prospects of new, spectacular developments Infeet,the tool manufactures are tryingtomeet the demands of ^ customers by optimising and matching M milling heads The exploitation of basic cuH^ T4P CHt KHOA Hpc & CdNG NGH? CAC TRlTdNG D ^ HOC K? THUAT • S6 9« - 2012 principals can he very helpfiil Tlie splitting of the material allowance in two different chips will lead to a changed cutting state with very important effects in respect to the cutting forces and the dynamic behaviour, Referring to Fig.la, the allowance gets cut with the total depth apo, at which time edges and are cut with the cutting profile ba x ho If you split the depth of cut {Fig lb) in two sequential edges, then the tooth feed rate doubles with the same angle of setting KK) of the chip thickness The gage gets halved at the same time And with the cutting profile, which is generally knovm to have a higher dynamic stability, there is an obvious change of the cutting proportion b/h (Fig.m Fig.l Principle ofcul-spliiting According to Kienzle's force equation the also the cutting depth It is very important to cutting forces are lower with larger chip combine the cut splitting and the decrease of the thickness Because of this equation, power entering angle KT because m this combination an requirements are lower in practical operation optimal use of this technique without negative On the other hand, the doubling of the tiuckness effects is possible of chip leads to a higher specific stress for the CONSTRUCTIVE FORMATION OF tootii feed rate and inevitably to higher wear of THE CUT SPLITTING the cutting edge (Ab) The decrease of the entering angle K, compensates this, because Tlie cut splitting in milling head can be a achieved at the edges in the upper line-up b =—£— andh=/xsinKhigher (axial) and in a bigger diameter sinx-^ compared to the lower edge line-up leads to a bigger chip gage and to a smaller chip The edges of the milling head are \ thickness The state of stress is relaxed alternating; high —* low —* high —*^ Hie enlargement of the chip gage is not The techiuque of cut splitting can be used critical, because splitting tiie cut length of the by milling heads with directiy embedded inserts growing cutting edge can be better exploited as well as for casket constructions It can be ! Fig.Ic shows that it is possible to change used for all types of inserts, such as round or tiie entering angle of edge I and and also the squared Combinations with different types are cutting deptii It is very important to combine also possible the cut splitting and the decrease of the entering 3.1 Cut splitting with squared inserts \ angle K, because in this combination an optimal ^ use of this technique without negative effects is Fig.2 shows the cut splitting of squared ' possible the growing cutting edge can be better inserts It is combined with smaller entering K exploited Fig.Ic shows that it is possible to angles KTI and K^^ which are compared to K^) By < change the entering angle of edge I and and choosing i ^ < KJI the inserts wear out in TJM* CHt KHOA Hpc & CdNG NGHI^ CAC TRU'dNG DAI HpC Kf THUAT *S690- 2012 different areas, x and y Edge wears out at the edge comer (x) Edge in a other part (y) That allows a increased usage by changing the tips around 3.2 Cut splitting with round inserts A better solution is to combine the cut splitting with round inserts (Fig.3) The round insert is used often in manufacturing, especially for materials which are hard to mill Especially when cutting at large depths, the susceptibility to vibrations rises because of the long depthing arc In this case the technique of cirt splitting highly improves the cutting performance Hie smaller depthing arches (pi and tpi lead to a better dynamic behaviour by woridng widi larger cutting depths, which are ofien possible witii divided cuts X = wearcd part ofthc indexable lip Y = nonweared part oftiie indexable tip Fig Cut splitting with sqiujre edged tips Fig Cut-splitting with stixiightpolygon cutting eofecj 90 ^$^ T^P CHl KHOA HpC & C6NG NGHE CAC TRCPNG D ^ HOC K* THUAT * S6 90 - 2012 better material exploitation Unfortunately the cutting depth of these tips is strongly limited The insert with 12 cutting edges can be used only for cutting depths up to 1,3 mm, which is the result of the entering angles of primary and secondary edges With the principle of cut splitting, shown in Fig.4, the cutting depth can be enlarged up to a level which is used in practice today, In this case, the inserts oftiie lower edge line-up are also important when working at an extremely small pressure angle Therefore by working with a doubled tooth feed rate there is a beneficial specific cutting edge stress By working with squared inserts, the entering angles K,| of the lower edge line-up have to be bigger than tiiose of the higher edge line-up In regard to the edge stress, it is disadvantageous By working with round inserts it goes the other way The entering angle oftiie lower edge lineup is smaller than that of the upper line-up Also the absence of a distinctive edge comer protects against the danger of broken comers 3.4 Cut splitting in combination of straight and round cutting edges There arc a lot of options for combining different forms of inserts by using the principle of cut splitting It is possible to combine straight with straight and also straight with round cutting edges, whereby it is fi^e to choose whether it is mounted in the upper or lower edge line-up 3.3 Cut splitting with straight polygon cutting edges In the last years, inserts with or even 12 useable cutting edges were developed for a Fig Cut-splitting in combination ofstraight and round cutting edges ^ Fotc^6(AveraB»: " ^ (r:> "'1 f: 31BB 11/1- , Reduction , vi^'f:Z 'WZ- '" :,Reduction _; 2S19 100% as^M 3157 100% 2609 100% 82,6% 100% 1438 44.8% 1207 42.8% 84.5% 1351 42,8% S46 32.4% 62,6% FassivfrForce Fp [N] Z770 72,2« 1861 66.0% 82,0% 1821 57,7% 1355 51.9% 74,4% I ot Fofces 6886 5887 85.5% 6329 4610 CuttlnB-Force Fe [r4] FeettForeoFv (N] \ff\ Mlling-hMdi MjKhMil = 125inm: Number of cutting edges z ' 6; MBtenal42CrMo4 Ơ,"1BanVmin V, ã 500; 630; 800 mmftnln (averages of forces) ap-3mm:5mni a,-1D0mn 76% 1/1 • wiUiout cul-splHtinB K = 45" 1^2=withoul cul-splRllnBround012 mm |[/1- with cut-Bplittlng K=45'; 30° Ufi= wllh eut-iplilling inund/nHind Tab 1: Results qf the force behaviours of Milling with and without Cut-splitting Fig.5 shows a combination of a octahedron with a round insert The possibilities of the principle of cut splitting can be used for milling heads with caskets and also with direct holders RESULTS OF TESTING 4.1 Productivity and durability The main concern in cut splitting is the creation of beneficial chip profiles while keeping productivity at the same level Raising the speed of the feed rate would increase the already doubled tooth feed rate to critical point Section 4.3 shows the new milling cutters witii cut splitting allow much higher cutting values in normal practical instable working conditions TAP CHl KHOA HpC & C6NG NGHf CAC TRU'ONG D^I HpC Ki? THUAT • S6 90 - 2012 up to the "clattcring-border" This leads to a much higher productivity In temis of durability the doubled feed rate causes a higher parti^ stiress of the cutting edge Durability life tests have shown lifetimes of 65% - 70% compared to standard tools These tests were made without reduction of the entering angle or changing around the inserts for better material exploitation The tests showed that polygon inserts can only be used for relevant cutting depths if they are combined with the principle of cut splitting Comparing a milling head with 12-edged tips to a normal milling head with 8edged tips shows that at the same cutting depth, the milling head witii 12-edged tips has a 50% higher edge exploitation 4.2 Cutting force behaviour Experiments about cutting force behaviours were made under conditions shown Short protruding length {50 mm) in Table I The measurements of the forces were made with a Kistier-Three component measure platform The computer program Turbo-Lab was used to analyse the measurement results For better clarity, the results are displayed as the average of tiie stepped feed speeds and the cutting depth for the components of the cutting force comparing milling heads with and without cut splitting The expected change of the cutting forces is proved by the results of the experiments Overall a decrease of 15% - 25% is noticeable which also means a smaller required power rating By wotking with round mserts, die components of the cutting forces are upgraded, for example, the feed rate force decreases approximantly 40% which is very positive finpractical use l^rge protnjdng length (170 mm) a Without cul-spltttlng • With cut-spNHIng Fig Measured sound pressure by machining with and without cut splitting Fig 'Vlatter limit" with anciwithcmt cut splitting Cinstabletooiclan9}mg) 92 TAP CHt KHOA Hpc & CdNG NGHE C Ac TRXTPNG Di^I HOC K? THU AT « S6 90 - 2012 4.3 Dynamic behaviour The principle of cut splitting produces chips with a smaller proportion b/h The doubling of the chip thickness causes a decrease in the cutting forces It is also well known, that a decrease in the chip gage and an enlargement of ±e chip thickness lead to a higher dynamic stability of the cutting process This effect was proved in an other experiment First, the emitted acoustic pressure was measured when working with duplicate milting tool FCT, both with and witiiout cut splitting Fig.6 shows the results for a compact clamped stabile woricpiece in diSerent work-piece fixtures with short (50 mm) and long (170 mm) overhang The experiments showed that there are no differences in acoustic pressure when woridng with a short oveihang The resiUts for a long overfiang were totally different By using cut sphtting, there is always, for every combination, a normal acoustic behaviour ('' -^ ^-.,-• ^ rln) tticu splW Ins "^^ >" wil loulc ' '^ ^^^ ^, • MabiBtod wMl culipllteig-r igtoalwMioutculvllil'ig- round (Morudlng langin • M I Fig "Clatter limit" with and without cut splitting (instable work-piecel clamping) CONSIDERATIONS The principle of splitting the cut in two sequenced edges leads to a favourable chip profile with a chip proportion b/h four times smaller The constructive realization of this principle allows a large multitude of possibilities in design to vary and combine the used inserts (squared, round), the entering angles and the cutting depths of the upper and lower edge line-up Cut splitting is suited especially for nulling tools with round inseris The e^^cted reduction of the cutting forces was verified in cjqKriments The electric power used by the machine decreases by 75 - 85% The most important advantage of the principle of cut splitting is the highly inqiroved cutting TAP CHl KHOA HpC & C6NG NGH? CAC TRU'dNG D-^I HpC K* THU>4T S6 90 • 2012 behaviour Especially when working with unaable processing conditions, these new milling tools are supenor because of low vibrations and noise The "clatter limit" is then raised up to mnch higher cutting values Thereby productivity raises up to more than 150%, Working with extremely unstable processing conditions can only be realized with muling tools using the pnnciple of cut sphtting The results show, that the new milling tools with cut splitting are good for problematic tasks Tlie potential of their capabilities are not yet fully achieved Further developments will show usable reserves NOMENCLATURE a,: Cutting depth [mm] ' a t- i J a,: Cutting width fmmj ^ : Chip width [mm] ^ '• •' / , Feed per revolution [mm/rev] j ^^^^ ,^^,j [mm/tooth] ji r i J h : Chip thickness [mm] K, j j r / • , "' ' F^'d speed [mm/mm] v^ : Cutting Speed [tn/min] „ , , M Kr : Entering angle / REFERENCES Albrecht P - New Developments in Theoiy of the Metal Cutting Process, Part I, Tlie Ploughing Process in Metal Cutting, ASME 82 (1960) 348-35S BoDJour, Ch - Erweiterung eines Fraeswerkzeugsortiments, Technische Rundschau 78 (1987) 36-39 Boehm, M - Averzahnter Plattensitz filer WSP Praedsionsschnittstclle sotgt fiier ruhige Bearbeitung, Technica Aarau 56 (2007) 34-35 Btaeuning, H - Fraesen mit der Lochplatte Positive und negative Scfaneikeilgeometiie auf demselben Werkzeug-Grundkoeper, VDI-Naehiichten 31 (1977) 20-25 Buschka, M - Neue Trends bei Spanenden Werkzeugen, VDI-Z Intergrierte Pioduktion 18 (1997) Cus, F - Inclusion of geometrical shape of cutter into optimization of milling process, Intemationale Faehzeitschrift filer Metallurgie 52 (1998) 604-«10 Falger, F - Kassetten weehseta Zerspanleistung und Standzeit optimieren beim UmfangsstimiraesenmitHartmetallwendeplatten, Der Maschinenmaikt 93 (1987)44-50 Author's address: Nguyen Trong Hieu - Email: hieunt-mtd@mail.hutedu.vn Department of Manuaiacturing Technology Hanoi University of Science and Technology No Dai Co Viet Road, Ha Noi, Viet Nam