基于ug二次开发技术的麻花钻、扩孔钻、铰刀设计系统研究cutting forces in the end milling of inconel 718(刘斌).pdf

Journal of Materials Processing Technology 77 (1998) 153159 Cutting forces in the end milling of Inconel 718 M. Alauddin a, M.A. Mazida, M.A. El Baradib,*, M.S.J. Hashmib aDepartment of Mechanical Engineering, BIT Dhaka, Gazipur, Bangladesh bSchool of Mechanical and Manufacturing Engineering, Dublin City Uni6ersity, Glasne6in, Dublin 9, Ireland Abstract Inconel 718 is a nickel-base alloy that is diffi cult to machine, a high cutting force being generated in the machining of this advanced material. This paper presents a study of the infl uence of the machining conditions on the average cutting forces for half-immersion end milling in the up- and down-milling modes. The cutting tests were carried out under dry conditions using carbide inserts. 1998 Elsevier Science S.A. All rights reserved. Keywords:Cutting forces; Milling modes; Nickel-base alloy 1. Introduction Inconel 718 is a nickel-base alloy containing a nio- bium (columbium) age-hardening addition that pro- vides increased strength without decrease in ductility. This alloy is non-magnetic, oxidation- and corrosion- resistant and can be used at temperatures in the range of 217 to 700C 1. In the case of nickel-base alloys, the critical phase in the microstructure is the high volume fraction, micron-sized, coherent particles of Ni3 (Al, X)(g%) embedded within a solid-solution strength- ened nickel (g) matrix. In the case of Inconel 718, the g% phase X corresponds to the presence of columbium, titanium or tantalum, whereas the g matrix contain varying amounts of chromium, molybdenum or cobalt. The increased diffi culty of dislocation motion through the g%/g microstructure is responsible for the retention of its high strength at elevated temperature. Due to its good tensile, fatigue, creep and rupture strength, this advanced material is used in the manufacture of com- ponents for liquid rockets, parts for aircraft turbine engines, cryogenic tankage, etc. Hence, nowadays the ability to machine Inconel 718 is increasingly de- manded. Metal machining has a long history and good cutting tools have been developed, but still advanced materials such as Inconel 718 are diffi cult to machine. The basic reasons for the diffi culty in machining this alloy are as follows 24: (i) high work-hardening at machining strain rates; (ii) abrasiveness; (iii) toughness, gumminess and a strong tendency to weld to the tool and to form a built-up edge; (iv) low thermal properties leading to high cutting temperatures; and (v) a tendency for the maximum tool-face temperature to be close to the tool tip. This paper presents an approach to study the infl u- ence of the machining conditions (speed, feed and axial depth of cut) on the average cutting forces for half-im- mersion end milling in the up- and down-milling modes. The cutting tests were carried out under dry conditions using carbide inserts. 2. Workpiece material and machine tool The Inconel 718 workpiece material used in the ma- chining test was in the hot forged and annealed condi- tion. The chemical composition of the workpiece material confi rms to the following specifi cation (wt.%): 0.08 C; 0.35 Mn; 0.35 Si; 0.60 Ti; 0.80 Al; 1.00 Co; 3.00 Mo; 5.00 Nb; 17.00 Fe; 19.00 Cr; 52.82 Ni. The hard- ness of the workpiece material was measured and found to be 260 BHN. The tool material (insert) was uncoated tungsten carbide:ISO K20 or AISI M15 (Sandvik grade H13A) 5 with an approximate composition of 94% WC and 6% Co. The end mill with carbide inserts (Sandvik U-Max R215.44 5 used in this work was 25 mm * Corresponding author. Tel.: +353 1 704551; fax: +353 1 7045345; e-mail: baradiemdcu.ie 0924-0136/98/$19.00 1998 Elsevier Science S.A. All rights reserved. PIIS0924-0136(97)00412-3 M. Alauddin et al./Journal of Materials Processing Technology77 (1998) 153159154 diameter and right-hand helix (left-hand cut). The tool holder (end mill body) was similar to En 46/En 47 steel with a hardness range of 42 to 46 Rc. The number of indexable carbide inserts of the cutter was 2, the incli- nation angle was 5 and nose radius was 0.8 mm. The milling operations (up- and down-cutting) were carried out on a Cincinnati Universal Machine (8 kW). 3. Cutting-force components in end milling The cutting-force components acting on one tooth of the end mill cutter are shown in Fig. 1, where the table system of cutting forces 6 is: Fx=instantaneous feed component (the projection of resultant cutting force in the X direction); Fy=instantaneous normal component (the projection of resultant cutting force in the Y direc- tion); Fz=instantaneous vertical component (the pro- jection of resultant force in the Z direction); and FR=instantaneous resultant cutting force (table sys- tem) acting on the workpiece. The table system of cutting forces does not depend on the kinematics of the cutting and is, therefore, stationary. The cutter system of cutting forces is: Ft=instanta- neous tangential component (force passing through the tangent to the circle circumscribed on the contour of the cutter cross-section); Fr=instantaneous radial com- ponent (perpendicular to the cutter axis and acting along the radius of the cutter or tip of the tooth; Fa=instantaneous axial component of the cutting force (passing through the axis of the cutter); FR% =instanta- neous resultant cutting force (cutter system) acting on the cutter. 3.1.A6erage cutting force in multi-tooth end milling Although the average cutting forces are not the max- imum cutting forces encountered in an end-milling op- eration, it is still useful for engineers to have a knowledge of their levels in designing machine tools and setting up the cutting system. In multi-tooth end milling, if several teeth are cutting simultaneously then the total average cutting forces acting on the teeth of the cutter (table system) per cut are: FXT= % zc i=1 d(i)Fxi(ci)(1) FYT= % zc i=1 d(i)Fyi(ci)(2) FZT= % zc i=1 d(i)Fzi(ci)(3) where: d(i)=1 =0 if c15c2 otherwise and where FXT, FTYand FZTare the total average cutting forces acting on the teeth of the cutter per cut in X, Y and Z directions respectively, Fx, Fyand Fzare the instantaneous cutting forces on an individual tooth per cut in the X, Y and Z directions respectively, ciis the instantaneous (cutting) angle of the cutter, c1is the entry angle of the cutter, c2is the exit angle of the cutter and zcis the number of teeth cutting simulta- neously. Note that zcis not rounded off to the nearest whole number and can be determined as: zc=zcs 360 (4) Thus, for a multi-tooth milling cutter of uniform tooth pitch the average cutting forces (table system) per tooth are: Fxa=FXT zc (5) Fya=FYT zc (6) Fza=FZT zc (7) Where z is the number of teeth (inserts) in the cutter, and csis the swept angle (=c2c1) which can be determined in terms of the cutting parameters 6. In multi-tooth milling, the average tangential force, Ftaper tooth and the average radial force per tooth, Fra are: Fta=Ftzc(8) Fra=Frzc(9) where Ftand Frare the instantaneous tangential and radial cutting forces acting per tooth of the cutter per cut, respectively.Fig. 1. Cutting-force components acting on one tooth of an end mill. M. Alauddin et al./Journal of Materials Processing Technology77 (1998) 153159155 3.2.Relationship between the table and the cutter system of cutting forces From Fig. 1, the averge resultant cutting force (table system), FRaacting on the workpiece can be shown to be: FRa=?(F2 xa+F2ya+F2za) (10) whilst the average resultant cutting force (cutting sys- tem), FRa% , acting on the cutter can be shown to be: FRa% =?(F2 ta+F2ra+F2aa) (11) For static equilibrium it is assumed that FR=FR% (or FRa=FRa% )and that when the cutter is correctly mounted, the cutter axis and spindle axis coincide, so that then Fz=Fa(or Fza=Faa) is usually assumed. The relationship of the cutting forces in end milling with a cutter having a straight tooth (neglecting the helix angle for a small axial depth of cut) is assumed as a plane system in which the axial forces are equal to zero in both the up- and down-milling mode, so that Fig. 1 is possible to relate the forces on the milling table to those on the cutter for both modes of milling: Fxa=Ftacos(ci)+Frasin(ci) Fya=Ftasin(ci)Fracos(ci)“ up milling(12) Fxa= Ftacos(ci)Frasin(ci) Fya=Ftasin(ci)+Fracos(ci) “ down milling(13) 4. Experimental set-up The milling machine was equipped with a table-type 3-component piezoelectric transducer. Data acquisition of the average cutting force (table system) was performed by a computer via an A/D converter. The cutting-force signals were also recorded on a UV recorder to confi rm the results obtained by the computer. The tangential cutting force was obtained using Eqs. (12) and (13) while the resultant cutting force was obtained using Eq. (10). 5. Analysis of results 5.1. Infl uence of the cutting speed on the cutting forces in the end milling of Inconel718in the up- and down-mode The measured (experimental) cutting forces (Fxa, Fya and Fza) and the calculated tangential and resultant cutting forces (Ftaand FRa) are plotted against cutting speed for an axial depth of cut of 1.2 mm in the up- and down-milling modes in Fig. 2. From this fi gure, it is observed that all of the cutting forces decreases as the cutting speed increases, which may be attributed to the following: (i) it is usually observed that as the cutting speed decreases, the shear angle also decreases, a small shear angle giving a long shear plane, for a fi xed shear strength, an increase in shear-plane area increasing the shear forces required to produce the stress required for deformation; (ii) at low cutting speed the friction coeffi - cient increases, hence increasing cutting forces. From Fig. 2, it is seen in the case of up milling that the Fxacomponent is the highest in the table system of cutting force. The reason may be analyzed from Eq. (12), in which Fxais the sum of two resolved components of the cutter system of cutting forces, whilst Fyais the subtraction of two resolved components of the cutter system of cutting forces. However, from Fig. 2, it is seen that in the case of down milling, the Fyacomponent is the largest amongst the table system of cutting forces. The reason may be analysed from Eq. (13) in which Fya component is the sum of two resolved components of the cutter system of cutting forces whilst Fxacomponent is the subtraction of two resolved components of the cutter system of cutting forces. There is no signifi cant difference observed in the case of other components of cutting forces at up and down milling. 5.2. The infl uence of feed on the cutting forces in the end milling Inonel718in the up- and down-milling mode The measured (experimental) cutting forces (Fxa, Fya and Fza) and the calculated tangential and resultant cutting forces (Ftaand FRaare plotted against feed for an axial depth of cut of 1.2 mm in the up- and down-milling mode in Fig. 3, from which fi gure it is observed that all of the cutting forces increase as the feed rate increases. The reason for this increase of cutting force with the increase of feed is due to an increase of chi load per tooth as the feed rate increases. From Fig. 3, it is observed that in the case of up-milling, the Fxa component of cutting forces is the highest in the table system of cutting forces, whilst in the case of down milling, the Fyacomponent is the largest in the table system of cutting forces (the reason is mentioned in Section5.1).Therearenosignifi cantdifferencesobserved in the case of other components of cutting forces for up- and down-milling. 5.3. The infl uence of the axial depth of cut on the cutting forces in the end milling of Inconel718in the up- and down-milling mode The measured (experimental) cutting forces (Fxa, Fya and Fza) and the calculated tangential and resultant cutting forces (Ftaand FRa) are plotted against axial depth of cut for cutting speed of 16.17 m min1in the up- and down-milling mode in Fig. 4, from which fi gure it is observed that all of the cutting forces increase almost linearly with the increase of axial depth of cut. This is due to the size of cut per tooth increasing as the axial depth of cut increase. From Fig. 4, it is observed M. Alauddin et al./Journal of Materials Processing Technology77 (1998) 153159156 Fig. 2. Infl uence of the cutting speed in up- and down-milling. M. Alauddin et al./Journal of Materials Processing Technology77 (1998) 153159157 Fig. 3. Infl uence of the feed rate in up- and down-milling. M. Alauddin et al./Journal of Materials Processing Technology77 (1998) 153159158 Fig. 4. Infl uence of the axial depth of cut in up- and down-milling. M. Alauddin et al./Journal of Materials Processing Technology77 (1998) 153159159 that in the case of up-milling the Fxacomponent of that in the case of up-milling the Fxacomponent of that in the case of up-milling the Fxacomponent of that in the case of up-milling the Fxacomponent of cutting forces is the highest in the table system of cutting forces, whilst in the case of down-milling, the Fyacomponent is the largest in the table system of cutting f