外文翻譯---高速銑削加工淬硬模具模具鋼的優(yōu)化策略

1、Journal of University of Science and Technology BeijingVolume 13, Number 3, June 2006, Page 240Corresponding author: Ying Tang, E-mail: tangydl@public3.bta.net.cnMaterialsOptimization strategy in end milling process for

2、high speed machining of hardened die/mold steelYing TangMechanical Engineering School, University of Science and Technology Beijing, Beijing 100083, China(Received 2005-02-21)Abstract: An optimization strategy for high s

3、peed machining of hardened die/mold steel based on machining feature analysis wasstudied. It is a further extension of the previously presented study on the thermal mechanism of end milling and constant cutting forcecont

4、rol. An objective function concerning machining cost and associated optimization algorithm based on machining time and cuttinglength calculation was proposed. Constraints to satisfy specific machining strategies when hig

5、h speed machining the hardened die/moldsteel, trochoid tool path pattern in slot end milling to avoid over-heat and feed rate adaptation to avoid over-load, were also discussed.As a case study, the tool selection problem

6、 when machining a die part with multiple machining features was investigated.Key words: optimization algorithm; hardened die/mold steel; machining cost; machining feature1. IntroductionThe introduction of advanced cuttin

7、g tools like AlTiN-coated micro-grain carbide end mill since the 1990s has changed the trend in die/mold manufacturing towards hard machining both in roughing and finishing [1]. Nowadays, high speed machining of hardened

8、 die and mold steels is a proven technology already, where many specific machining concepts and strategies are developed to facilitate it [2]. Representatively, ma- chining features that are defined as distinctive volume

9、tric shape to be removed by distinctive ma- chining operations (i.e. cutting tool and tool path pat- tern), is put forward to ease NC (numerical control) programming [3]. Usually tool path pattern for each feature type c

10、an be standardized and fixed.Once machining features and relevant tool path pat- tern are fixed, it becomes absolutely necessary to opti- mize other operation parameters because when we consider both productivity and too

11、l cost, the latter contributes to as much as 20% of the total cost of die and mold manufacturing. Such optimization is made possible with machining feature and fixed tool path pattern analysis, which reduces the number o

12、f variables that have to be considered at the same time. Productiv- ity and tool cost can be treated as functions of these independent cutting condition variables so that the impact of these variables on the productivity

13、 and tool cost or the combined objective function of these two can be calculated and optimized.This paper is organized as follows: an objective function concerning machining cost and its associated optimization algorithm

14、 is proposed in Section 2, fol- lowed by a case study to use the proposed algorithm for tool selection in end milling die part with multiple machining features in Section 3. Constraints faced in attempting to satisfy spe

15、cific machining strategies when high speed machining the hardened die/mold steel are discussed in the same section. Conclusions are presented in Section 4 based on the results of the case study.2. Optimization strategyAs

16、 concerning productivity, the time involved in machining process needs to be calculated. The ma- chining time m T considered includes the cutting timec T and the air cutting time nc T . Basically, the exact cutting t

17、ime c T is calculated by adding the times spent on every chip and the air cutting time nc T is the total time of air cutting in the tool path, which can normally be calculated with ease based on fixed tool path patte

18、rn,m c nc nc zeii iL T T T T f = + = + ∑(1)where the cutting length i L of the i-th chip is calculat- ed based on the engagement geometry between the workpiece and the cutting tool, and zei fis the instant feed of too

19、l when cutting the chip. In the case of end milling concave contour, i L , zei fand other parameters242 J. Univ. Sci. Technol. Beijing, Vol.13, No.3, Jun 2006process presented in previous works [4-5]. It becomes essent

20、ial to seek a specific machining strategy to re- duce cutting heat accumulation for improving tool life. The key issue lies in the limitation of contact between the tool and the part per revolution.Trochoid tool path pat

21、tern with successive trochoid cycles of the same pitch, shown in Fig. 3, is such a substitute designed for end milling a slot into the hardened steel at high speed [6]. By maintaining a limited pitch, the arc of contact

22、is minimized. In con- junction with proper feeds and speeds, end milling in this manner can remove a large amount of material without the generation of excessive heat.Fig. 3. Slot end milling with trochoid tool path pa

23、ttern. B isa slot of given width.(2) Feed rate adaptation to keep constant cutting force.Another concept taken as a basis for hardened die steel end milling is to maintain the cutting force con- stant under a safety limi

24、t especially in roughing or intermediate roughing operation, because chipping occurs soon if excessive cutting forces at the cutting edge are present. Chipping on one cutting edge can cause a cascade effect of successive

25、 chipping on the remaining intact cutting edges. This makes the tool unusable very quickly.A straightforward approach to keep constant cutting force is to adapt feed rate along tool path. The basic principle of the strat

26、egy is to solve the instant feed rate according to tool-work engagement geometry with a second order force model, which was presented in previous works [7-8],2 2 0 1 1 2 2 11 1 22 2 12 1 2 Y X X X X X X β β β β β β = + +

27、 + + +(4)where Y denotes the average cutting force value in XY-plane xy F . The control target force Y is deter- mined from experiences. 1 X and 2 X are the normal- ized maximum uncut chip thickness mi tand chip

28、cut- ting length i L respectively. The six coefficients ( 0 12 , , β β ??? ) are identified by conducting a set of pre-process experiments of straight cut by using least squares method.Under these constraints, the simu

29、lation was con- ducted firstly to seek the optimal cutter diameter D when a machining feature, a slot of given width B, needed to be machined. Fig. 4 is the B-D plane of the contour plot of machining cost when machined w

30、ith a pitch of 0.5 mm and a spindle speed of 9600 r/min. The target cutting forces are equal to the values measured in cutting experiments with different diameter cutters to cut along straight contours at the same pitch

31、and spin- dle speed. The tool life f L =112 mm/blade and cost per machining time m c =750 yuan RMB/h were deter- mined according to our industrial partners’ experience. Cutter costs were named according to their market

32、 prices.Fig. 4. Machining cost C on B-D plane in the case of one-slotend milling with trochoid tool path.The black dotted line across machining cost con- tours on the B-D plane in Fig. 4 indicates the optimal tool diame

33、ter D to the minimum cost achievement for the given slot width B. For example, a φ10 mm cutter should be used to cut the 50 mm-width slot, while a φ6 mm cutter to cut the 15 mm-width slot. In other words, two cutters are

34、 needed if cutter diameter selection is considered separately for each machining feature. As also seen in the figure, the black dotted line located in the left end of the B-D plane implies that small end mill cutters of

35、6, 8 and 10 mm in diameter are preferred in slot end-milling machining. It has to be pointed out that the simulation is conducted under the assumption that the slot can be removed in one layer with all end mill cutters.

36、In the case of deep slot, more layers will be needed if a smaller diameter cutter is used. The result- ing machining cost increase will push optimal cutter diameter positions to the right end in Fig. 4. Further- more, th