120kw电机软启动隔爆箱优化设计【含9张CAD图纸、说明书】
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Journal of Materials Processing Technology 211 (2011) 141149 Contents lists available at ScienceDirect Journal of Materials Processing Technology journal homepage: /locate/jmatprotec A new in-feed centerless grinding technique using a surface grinder W. Xua, Y. Wub aGraduate School, Akita Prefectural University, 84-4 Tsuchiya-ebinokuchi, Yurihonjo, Akita 015-0055, Japan bDepartment of Machine Intelligence and Systems Engineering, Akita Prefectural University, 84-4 Tsuchiya-ebinokuchi, Yurihonjo, Akita 015-0055, Japan a r t i c l ei n f o Article history: Received 15 April 2010 Received in revised form 15 September 2010 Accepted 16 September 2010 Keywords: Centerless grinding Surface grinder Ultrasonic vibration In-feed Roundness Shoe a b s t r a c t This paper deals with the development of an alternative centerless grinding technique, i.e., in-feed cen- terless grinding based on a surface grinder. In this new method, a compact centerless grinding unit, composed of an ultrasonic elliptic-vibration shoe, a blade and their respective holders, is installed onto the worktable of a surface grinder, and the in-feed centerless grinding operation is performed as a rotating grinding wheel is fed in downward to the cylindrical workpiece held on the shoe and the blade. During grinding, the rotational speed of the workpiece is controlled by the ultrasonic elliptic- vibration of the shoe that is produced by bonding a piezoelectric ceramic device (PZT) on a metal elastic body (stainless steel, SUS304). A simulation method is proposed for clarifying the workpiece rounding process and predicting the workpiece roundness in this new centerless grinding, and the effects of process parameters such as the eccentric angle, the wheel feed rate, the stock removal and the workpiece rotational speed on the workpiece roundness were investigated by simulation followed by experimental confi rmation. The obtained results indicate that: (1) the optimum eccentric angle is around 6; (2) higher machining accuracy can be obtained under a lower grinding wheel feed rate, larger stock removal and faster workpiece rotational speed; (3) the workpiece roundness was improved from an initial value of 19.90?m to a fi nal one of 0.90?m after grinding under the optimal grinding conditions. 2010 Elsevier B.V. All rights reserved. 1. Introduction In the manufacturing industry, for high accuracy and high productivity machining of cylindrical components such as bear- ing raceways, silicon-ingots, pin-gauges and catheters, centerless grinding operations have been extensively carried out on spe- cialized centerless grinders. Two types of centerless grinders are available commercially; one is with a regulating wheel and the otherwithashoe,andtheyaredifferentfromeachotherinhowthe workpiece is supported and how the workpiece rotational speed is controlled during grinding. Since the invention of the regu- lating wheel type centerless grinder by Heim in 1915 (Yonetsu, 1966), much research has been devoted to enhance machining accuracy and effi ciency. Rowe and Barash (1964) proposed a com- puter method for investigating the inherent accuracy of centerless grinding by taking into account the geometrical considerations and the elastic defl exion of the machine. Further, Rowe et al. (1965) experimentally obtained the machining elasticity parame- ter.Hashimotoetal.(1982)analyzedtheproblemofsafemachining operation by discussing the friction-drive function of regulating Corresponding author. Tel.: +81 184 272157; fax: +81 184 272165. E-mail addresses: d10s007akita-pu.ac.jp, xuwx66 (W. Xu). wheel. Miyashita et al. (1982) studied the deformation of con- tact area and built a dynamic model for selecting chatter free conditions. Rowe and Bell (1986) experimentally investigated the high removal rate grinding process and optimized the grinding conditions. Wu et al. (1996) clarifi ed the infl uence of grinding parameters on roundness error through a computer simulation method to optimize grinding conditions. Epureanu et al. (1997) analyzed the stability of grinding system through a linearized model that described the formation and evolution of the pattern on the ground surface. Guo et al. (1997) studied the geometri- cal rounding of above-center and below-center centerless grinding to assist in the selection of acceptable set-up conditions. Albizuri et al. (2007) proposed a novel method to reduce chatter vibra- tions by using actively controlled piezoelectric actuators. Krajnik et al. (2008) developed an analytical mode that assists in effi cient centerless grinding system set-up for higher process fl exibility and productivity. Shoe type centerless grinding has also attracted attention from both industrial and academic researchers. Yang and Zhang (1998) designed a fl at vacuum-hydrostatic shoe to increase the load capacity and stiffness for high precision applications of shoe centerless grinding. Then Yang et al. (1999) and Zhang et al. (1999) analyzed the process stability in vacuum-hydrostatic shoe centerless grinding. In addition, Zhang et al. (2003) devel- oped a geometry model to predict the lobing generation in shoe 0924-0136/$ see front matter 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2010.09.009 142W. Xu, Y. Wu / Journal of Materials Processing Technology 211 (2011) 141149 Fig. 1. Three types of centerless grinding using a surface grinder: tangential-feed type (a), in-feed type (b) and through-feed type (c). centerless grinding and used the model for the analysis of grinding processes. From the viewpoint of production cost, the two types of centerless grinders are highly suitable for small-variety and large- volume production because the loading/unloading of workpieces is extremely easy and fast. However, the centerless grinder is a special-purpose machine and relatively costly, putting it at a disadvantage for large-variety and small-volume production, the demand for which has increased rapidly in recent years. As a solu- tion to this problem, one of the authors Wu et al. (2005) proposed a new centerless grinding technique that can be performed on a surface grinder (rather than a centerless grinder) previously. This methodisbasedontheconceptofultrasonicshoecenterlessgrind- ing developed by Wu et al. (2003, 2004). In the method, a compact unit consisting mainly of an ultrasonic elliptic-vibration shoe, a blade,andtheirrespectiveholdersisinstalledontheworktableofa multipurposesurfacegrinder.Thefunctionoftheultrasonicshoeis toholdthecylindricalworkpieceinconjunctionwiththeblade,and to control the workpiece rotational speed with the elliptic motion on its upper end-face. According to the relative motion of the workpiece to the grinding wheel, three types of centerless grinding operations can be performed in the proposed method as shown in Fig. 1: (a) tangential-feed type in which initially the grinding unit is located in the down-left side of the grinding wheel with a distance that is large enough for loading the workpiece on the upper end face of ultrasonic shoe, and then the workpiece is fed rightward along the tangential direction of the grinding wheel at a feed rate ofvf (Fig. 1(a) to perform the grinding action until the unit reaches the down-right side of the grinding wheel with a distance that is large enoughforunloadingthegroundworkpieceofftheultrasonicshoe; (b) in-feed type in which initially the grinding wheel is located above the grinding unit with a distance that is large enough for loading the workpiece on the upper end face of ultrasonic shoe, and then the grinding wheel is fed downward in radial direction into the workpiece at a feed rate ofvfr(Fig. 1(b) to perform the grinding action until the required stock removal has been attained, and after a short period for “spark-out” the grinding wheel is lifted up from the ground workpiece with a distance that is large enough to unloading the workpiece off the ultrasonic shoe; (c) through- feed type in which initially the grinding wheel is set at a given distance from the upper end face of ultrasonic shoe (as shown in Fig. 1(c), and then the workpiece is loaded on the loading guide and fed into the space between grinding wheel and ultrasonic shoe along its axial direction at a feed rate ofvfato perform the grinding action until it loses the contact with the grinding wheel but being supported on the unloading guide for the subsequent unloading. Inourpreviousworks,simulationandexperimentalworkshave been conducted for the tangential-feed type (Xu et al., 2010). The obtained results showed that the workpiece roundness can be Fig. 2. Schematic illustration of in-feed centerless grinding using a surface grinder. W. Xu, Y. Wu / Journal of Materials Processing Technology 211 (2011) 141149143 improved greatly from the initial value of 23.9?m to the fi nal one of 0.8?m, thus validating this new method. The objective of the present paper is to confi rm the in-feed type of centerless grind- ing carried out on a surface grinder. For this purpose, a simulation method is proposed to clarify the workpiece rounding process and to investigate the effects of process parameters, such as the workpiece eccentric angle, the grinding wheel feed rate, the stock removal, and the workpiece rotational speed on the workpiece roundness. Then a series of grinding experiments are carried out to confi rm the simulation results. 2. Operation principle of in-feed centerless grinding using a surface grinder Fig. 2 shows the operation principle of in-feed centerless grind- ing using a surface grinder. A grinding unit, composed of an ultrasonic elliptic-vibration shoe and its holder, a blade and its holder,astopper,andabaseplate,isinstalledontotheworktableof a surface grinder at an angle of (hereafter called eccentric angle) (see Fig. 2(a). The workpiece is constrained between the blade, the shoeandthestopper.Asthegrindingwheelisfedinradialdirection intotheworkpieceatfeedrateofvfr,anin-feedtypedown-grinding operationisperformed,wheretheworkpieceisrotatedintheoppo- site direction to the wheel. As shown in Fig. 2(b), once the required stock removal has been attained, the wheel in-feed is stopped fol- lowed by a dwell for several seconds to allow “spark-out”. During grinding, the workpiece rotational speed nwis controlled by the elliptic motion on the upper end-face of the shoe and the stop- per is used to prevent workpiece from jumping away the grinding area. In addition, the blade is wedge-shaped with a tilt angle of ? (usually called blade angle) and the value of ? is in general set at around 60in terms of the optimum workpiece rounding condition demonstrated by Harrison and Pearce (2004). In the grinding unit, the shoe is constructed by bonding a piezo- electric ceramic device (PZT) with two separated electrodes onto a metal elastic body (stainless steel, SUS304). When two amplifi ed alternating current (AC) signals (over 20kHz) with a phase differ- ence of , generated by a wave function generator, are applied to the PZT, bending and longitudinal ultrasonic vibrations are excited simultaneously.Thesynthesisofthevibrationdisplacementsinthe two directions creates an elliptic motion on the end-faces of the metal elastic body. Consequently, the workpiece rotation is con- trolled by the frictional force between the workpiece and the shoe, so that the peripheral speed of the workpiece is the same as the bending vibration speed on the shoe end-face. The workpiece rota- tional speed can be adjusted by changing the value of parameters such as the amplitude Vppand frequency f of the voltage applied to the PZT, because the shoe bending vibration speed varies with thevariationoftheappliedvoltage(seeXuetal.,2009).Inaddition, a pre-load is applied to the shoe at its lower end-face in its longitu- dinal direction using a coil spring to prevent the PZT from breaking due to resonance. 3. Geometrical rounding analysis Fig.3showsthegeometricalarrangementoftheshoe,theblade, the workpiece and the grinding wheel in an in-feed centerless grinding operation using a surface grinder after grinding for time t. At this moment, the eccentric angle and the workpiece radius become (t) and ?(t), respectively, from their respective initial val- uesof0and?0.Inthemeantime,theworkpieceisheldbytheblade (with a tilt angle of ?) and the shoe at points B and C, respectively, and ground at point A by the grinding wheel rotating at the rota- tional speed of ngas the wheel is fed downward into the workpiece at a feed rate ofvfr. Fig. 3. Geometrical arrangements in in-feed centerless grinding using a surface grinder. 3.1. Geometrical rounding modeling In the simulation model (see Fig. 3), several assumptions are made: (1) the workpiece is in constant contact with the blade and the shoe at points B and C, respectively, during grinding; (2) the vibration of the entire machine is too small to be regarded, and no chatter occurs on the machine due to the ultrasonic elliptic- vibrationoftheshoe;(3)theworkpiecerotationalmotionisalways stable, and no variation of rotational speed occurs during grinding; (4) the wear of the grinding wheel is too small to be recognized, and the grinding wheel radius Rgis kept constant during grinding. Let a XY-coordinate system be located on the worktable. An optionalpointOontheworktableisdeterminedastheoriginofthe coordinate system. The X-axis is taken in the horizontal direction and the Y-axis in the vertical direction. Before grinding, the initial XY-coordinatesofthegrindingwheelcenterOg0andtheworkpiece center Ow0are (XOg0, YOg0) and (XOw0, YOw0), respectively. Thus, the XY-coordinates of the initial blade contact point B (XB0, YB0) and the shoe contact point C (XC0, YC0) can be obtained from the initial geometrical arrangement, as follows: ? XB0= XOw0 ?0sin? YB0= YOw0+ ?0cos? ? XC0= XOw0 YC0= YOw0 ?0 Then, the linear equations representing the blade end-face and the shoe upper end-face in this coordinate system can be written as: For the blade end-face: Y YB0= tan?(X XB0)(1) For the shoe upper end-face: Y YC0= 0(2) Substituting coordinates of point B and C into Eqs. (1) and (2), respectively, gives: PX + QY + R = 0(3) Y YOw0+ ?0= 0(4) whereP = tan?,Q = 1,R = YOw0+ ?0cos? tan?(XOw0 ?0sin?).During grinding, the coordinates of the workpiece center Owtand the grinding wheel center Ogtwill vary as the material is removed. Let the instantaneous workpiece radius in the direction parallel to the X-axis after grinding for time t be ?(t) (see Fig. 3). 144W. Xu, Y. Wu / Journal of Materials Processing Technology 211 (2011) 141149 At this moment, the workpiece radius at points A, B and C can be expressed with ?(tTA), ?(tTB) and ?(tTC), respectively, where TA=?+2(t)/4?nw, TB=(?+2?)/4?nwand TC=3/4nw are the time delays for points A, B and C. Since the ?(tTB) and ?(tTC) are equal to the distances from the workpiece center Owt to the blade end-face and to the shoe upper end-face, respectively, they can be obtained from the geometrical arrangement in Fig. 3 by using Eqs. (3) and (4) as follows: ?(t TB) = |PXOw(t) + QYOw(t) + R| ? P2+ Q2 (5) ?(t TC) = YOw(t) YOw0+ ?0(6) Solving Eqs. (5) and (6) simultaneously yields the XY-coordinates of the workpiece center Owtat time t, as follows: XOw(t) = ?P2+ Q2?(t TB) QYOw(t) R P YOw(t) = ?(t TC) + YOw0 ?0 (7) In this moment, the XY-coordinates of the grinding wheel center Ogtare also obtained from the geometrical arrangement in Fig. 3 as: ? XOgt= XOg0= XOw0 (Rg+ ?0)sin YOgt= YOg0vfrt = YOw0+ (Rg+ ?0)cos vfrt (8) In addition, the following relationships are established from the geometrical arrangement in Fig. 3. ? XA(t) XOg(t)2+ YA(t) YOg(t)2= R2 g YA(t) YOw(t) = cot(t)XA(t) XOw(t) (9) where: cot(t) = YOg(t) YOw(t) XOg(t) XOw(t) (10) Subsequently,theXY-coordinatesofpointAareobtainedasfollow- ing by re-arranging Eqs. (9) and (10). XA(t) = (V ? V2 4UW) 2U YA(t) = cot (t)XA(t) XOw(t) + YOw(t) (11) whereU = 1 + cot2(t),V = 2cot(t)YOw(t) cot2(t)XOw(t) cot (t)YOg(t) XOg(t),W = X2 Og(t) + cot(t)XOw(t) YOw(t) + YOg(t)2 R2 gEventually, thework- piece radius ?(tTA) at the point A after grinding for time t is calculated from the XY-coordinates of the workpiece center Owt and the grinding point A as follows: ?(t TA) = ? XA(t) XOw(t)2+ YA(t) YOw(t)2(12) Consequently,theapparentwheeldepthofcutwouldbe ?=?(tTAT)?(tTA), where T is the time required for one revolutionoftheworkpiece.Ifthegrindingsystemhasanidealstiff- ness, the true wheel depth of cut would be equal to the apparent one.However,thegrindingsystemwithstandstheelasticdeforma- tion caused by the grinding force during actual grinding. Rowe et al. introduced a dimensionless parameter called machining elastic- ity parameter k as a measure to indicate the elastic deformation of centerless grinding system, which is defi ned as a quotient between the true depth of cut and the apparent depth of cut with Eq. (13) (Rowe and Barash, 1964; Marinescu et al., 2006). k = truewheeldepthofcut apparentwheeldepthofcut = ? ? (13) Following Rowe et al.s consideration, the true wheel depth of cut ? can be calculated as ? =k?in the current work, resulting in that the true workpiece radius at point A is: ?(t TA) = ?(t TA T) k?(t TA T) ? XA(t) XOw(t)2+ YA(t) YOw(t)2(14) However, the wheel depth of cut calculated using these equations is less than zero occasionally. Obviously, this phenomenon would not happen. Therefore, Eq. (14) should be modifi ed as: ? ?(t TA) = ?(t TA T) k(?(t TA T) ? XA(t) XOw(t)2+ YA(t) YOw(t)2)?(t TA) ?(t TA T) ?(t TA) = ?(t TA T)?(t TA) ?(t TA T) (15) 3.2. Determination of the machining elasticity parameter As described above, the machining elasticity parameter k depends on the stiffness of the grinding system. If the simulation result is to be trusted, the value of k should be determined for th
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