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1、基于刀具状态的切削力模型研究（常州铁道高等职业技术学校、常州昌成铁路机械厂 江苏 常州 213011）张宝金 摘 要：建立适用于变工况加工的切削力模型，将切削力信号用于切削过程监控。建立基于切削参数（切削速度、进给量、切削深度）与刀具状态（主要考虑后刀面磨损量）的切削力模型，通过试验值与模型的预测值之间的比较，进一步验证模型的准确性。关键词：切削力；刀具状态监控；金属切削；模型1 引言目前，加工中心（MC）、柔性制造单元（FMC）、柔性制造系统（FMS）及计算机集成制造系统（CIMS）逐渐成为现代机械制造业的主流，为实现制造系统的高度自动化提供了先决条件。自动化生产的实现，依赖于加工过程中切削
2、刀具状态的自动监控，国内外学者在切削力模型方面进行了大量的研究工作。其中，切削力法被认为是一种具有实际应用前景的监控方法1。但以往基于切削力信号的研究大多是通过单因素试验2确定特定情况下切削力的阈值，从而对刀具状态进行识别。这类方法存在监控阈值难以确定以及监控参数特征信息不能适应切削参数的变化即监控的柔性差等问题，仅适用于不改变或较少改变切削参数的刚性加工生产线。随着计算机技术的发展，建立可适应变工况加工的刀具状态监控系统十分必要。影响切削力的因素有很多，其中切削用量三要素：切削速度、进给量、切削深度对切削力的影响最为显著3。本文以外圆车削为例，建立了基于切削参数（切削速度、进给量、切削深度）
3、与刀具状态（主要考虑后刀面磨损量）的切削力简化模型，并通过试验值与模型的预测值之间的比较，进一步验证模型的准确性。2 切削试验系统及方案 （1）试验装置本试验在一台型号为CA6140的普通车床上进行，切削力信号由Kistler测力仪（传感器）检测，测出的力信号经电荷放大器放大、经过数据采集卡后可直接将信号传送到计算机。再用Kistler测力仪的配套软件Dynoware对测得的力信号进行分析和处理。试验系统组成如图1-1 所示。试验中刀面磨损状况及磨损值随时刻进行测量，使用Keyence的VH-8000系列数码显微镜对车刀后刀面的磨损状况拍照，通过测量软件测量车刀后刀面的磨损量以及刀具的破损情况
4、。（2） 试验方案切削力试验分为三部分进行：使用新刀片（磨损量为零）进行切削试验；使用不同状态的刀片（变化的磨损量）进行切削试验；使用不同状态的刀片（变化的磨损量）验证已建立的刀具磨损状态下的切削力模型。采用正交试验法安排试验，使用L9()正交表，为三因素、三水平试验。具体试验正交表如表1：表1试验计划试验号试验因素（切削三要素）试验结果记录切削速度Fx（N）Fy（N）Fz（N）主轴转速r/min线速度m/ min进给量mm/ r切削深度mm1320600.10.12500950.20.137101350.30.14320600.20.25500950.30.267101350.10.2732
5、0600.30.38500950.10.397101350.20.3刀具后刀面磨损量VB（）3 基于刀具状态的切削力模型（1）切削力模型的简化由于切削力经典理论模型过于繁琐的局限，难以在实际生产进行有效应用。因此，研究人员常常通过大量试验，由测力仪得到切削力后，将所得数据进行数学方法处理，即可得到切削力的试验模型。如采用指数模型计算切削力，在金属切削加工中得到广泛的应用。常用的指数模型形式如下 :（1） R.Uehara和F.Kiyosawa4的研究表明主切削力能更准确的反映刀具磨损的程度，并建立了切削参数、后刀面磨损量与主切削力的模型。式（1）切削力简化模型如下： （2）式中：F为切削力（N
6、）；为车削深度（mm）；f为进给量（mm/r）；v为车削速度（m/min）；k、x、y、z分别为待定系数和指数，需要通过试验建立回归方程确定。（2）基于刀具状态的切削力模型在实际的生产过程中，切削用量为已知量，刀具的磨损量未知。参考已建立的切削力模型，考虑到刀具磨损量的与切削用量之间的相互影响，建立一个以刀具的磨损量和切削三要素为自变量、切削力为因变量的函数方程（即切削力模型）。在原有切削力模型的基础上引入VB因素，试验数据表明，当VB0.3mm, 切削力上升较平缓；当VB在0.3mm附近, 切削力上升较陡峭；当VB0.3mm, 切削力上升有趋于平缓。因此，VB=0.3mm是一个突变点，对切削
7、力模型有重大影响。切削力模型如下： （3）式中：F为切削力（N）；为车削深度（mm）；f为进给量（mm/r）；v为车削速度（m/min）；k、x、y、z分别为待定系数和指数，需要通过试验建立回归方程确定。4 试验结果与讨论（1）正交试验数据的处理切削试验获得刀具处于不同状态的切削力信号，选择具有代表性的VB=0、VB=0.07、VB=0.38等三组试验处理结果（见表2表4）。表2 试验结果一顺序号组别第一组磨损量VB（mm）0切削用量切削力主轴转速r/min切削速度r/min进给量mm/r切削深度mmFx（N）Fy（N）Fz（N）1-1320600.10.112.330019.016417.9
8、8911-2500950.20.114.170926.984527.65001-37101350.30.115.670937.798234.19821-4320600.20.218.811837.567341.50911-5500950.30.216.600938.289148.17361-67101350.10.220.190941.849134.19361-7320600.30.328.946457.345571.12451-8500950.10.321.875534.230033.45551-97101350.20.324.299143.391862.0082表3 试验结果二顺序号组别第
9、二组磨损量VB（mm）0.07切削用量切削力主轴转速r/min切削速度m/min进给量mm/r切削深度mmFx（N）Fy（N）Fz（N）2-1320600.10.112.382719.090918.01732-2500950.20.114.510028.368228.32272-37101350.30.114.799136.307339.15902-4320600.20.222.993645.780941.58452-5500950.30.221.147345.970950.08822-67101350.10.218.469136.092736.26092-7320600.30.329.060
10、956.366472.38272-8500950.10.325.115539.247335.77912-97101350.20.326.716458.306464.5118表4 试验结果三顺序号组别第三组磨损量VB（mm）0.38切削用量切削力主轴转速速/min切削速度m/min进给量mm/r切削深度Fx（N）Fy（N）Fz（N）3-1320600.10.113.143621.617324.87183-2500950.20.116.200938.184537.31453-37101350.30.116.388262.777349.76913-4320600.20.225.56050.28365
11、3.59003-5500950.30.223.379158.609167.30553-67101350.10.217.896464.573648.64363-7320600.30.331.530964.178278.40093-8500950.10.322.286438.782746.32553-97101350.20.326.509176.900973.3764在相同的切削用量，不同的切削刀具后刀面磨损量下，切削力随磨损量变化而变化。变化有增大的趋势，但并不完全对应，在初始阶段上升较快，随后又缓缓上升, 至VB=0.38mm时上升较突然，然后又开始缓升。（2） 基于刀具状态的切削力模型拟合对
12、式（3）两边同时取对数，可得： （4）则切削力的对数同切削用量及磨损量的对数关系就变成为线性关系，成为多元线性回归方程。利用表2中的数据，拟合出基于切削用量和刀具状态的切削力模型如下： （5）式中已含有后刀面磨损量。刀具磨损量作为切削力模型的参数，更能反映出切削用量和刀具后刀面磨损量与切削力的的内在关系，为切削刀具状态的检测打下了坚定基础。（3） 基于刀具状态的切削力模型检验表5中试验值Fzs用于模型拟合，预测值Fzc用式（5）计算出的切削力Fz值。显然，预测值与试验值的相对误差很小，多数在-5%5%之间，最大不超过10%，相对误差平均为0.03861，显示出该回归模型具有较好的拟合度。切削力
13、Fz、预测值Fzc与试验值Fzs符合程度较高，能比较准确地反映切削力Fz与切削用量和刀具后刀面磨损量的内在联系，各切削用量指数客观地体现各因素在切削力模型中的作用或影响，特别是后刀面磨损量作为切削力模型的重要参数，建立起刀具后刀面磨损量VB与主切削力Fz的模型，确立了后刀面磨损量与切削力Fz的内在关系，探索出磨损量影响切削力的内在规律；为建立基于切削力模型的刀具状态检测做好准备。表5 试验数据及预测值序号切削用量刀具磨损量VB试验值Fzs预测值FzcFzs/Fzc相对误差切削速度进给量背吃刀量1600.10.1017.98917.3921.034310.034312600.20.20.0741
14、.58540.9641.015150.015153600.30.30.1373.20368.5111.068490.068494600.10.10.1719.57719.9690.98037-0.01965600.20.20.2347.87546.3081.033820.033826600.30.30.3878.40181.6850.9598-0.04027600.20.20.4455.46353.1991.042550.042558950.20.1027.6527.5821.002470.002479950.20.10.0728.32329.2740.9675-0.032510950.20.
15、10.1328.62230.7140.93189-0.068111950.30.20.1755.95760.2690.92846-0.071512950.20.10.2332.03633.0930.96803-0.03213950.20.10.3837.31536.621.018970.0189714950.20.10.4440.58538.0171.067520.06752151350.10.2034.19431.2991.092490.09249161350.20.30.0764.51261.7461.04480.0448171350.20.30.1365.01264.7821.00354
16、0.00354181350.20.30.1767.03266.7961.003530.00353191350.20.30.2368.08669.8010.97542-0.0246201350.30.10.3849.76948.7491.020920.02092211350.20.30.4474.2680.1880.92608-0.0739Fz平均值及平均误差47.97347.951.000480.038615结论建立了基于切削参数和刀具状态的车削力简化模型, 通过对试验值与模型的预测值进行比较，验证模型的准确性。基于多因素试验建立的模型可适应变工况的加工，模型的试验验证成功为建立可适应变工况加
17、工的刀具状态监控系统提供了一种较准确的监控方法，同时为多传感器信号耦合(切削力、切削功率、声发射等)提供了基础。以外圆车削试验建立的力模型为基础，可以尝试为其他常见的加工过程如铣削加工、钻削加工等建立类似的力模型，以解决变工况加工的刀具状态监控问题。参考文献1 Dimla E. Dimla Snr. Sensor signals for tool-wear monitoring in metal cutting operationsa review of methods J.International Journal of Machine Tools & Manufacture. 40 (20
18、00) 107310982 刘敦焰，邵华. 基于切削参数和刀具状态的车削力模型J. 上海交通大学学报 2000,10(34)：1434-1436.3 吴道全，万光珉，林树兴，等.金属切削原理及刀具M. 重庆大学出版社，1994.4 R.Uehara,F.Kiyosawa. Automatic tool wear monitoring in NC turningJ. CIRP,1989,38(1):39-42.Editors note: Judson Jones is a meteorologist, journalist and photographer. He has freelanced
19、with CNN for four years, covering severe weather from tornadoes to typhoons. Follow him on Twitter: jnjonesjr (CNN) - I will always wonder what it was like to huddle around a shortwave radio and through the crackling static from space hear the faint beeps of the worlds first satellite - Sputnik. I a
20、lso missed watching Neil Armstrong step foot on the moon and the first space shuttle take off for the stars. Those events were way before my time.As a kid, I was fascinated with what goes on in the sky, and when NASA pulled the plug on the shuttle program I was heartbroken. Yet the privatized space
21、race has renewed my childhood dreams to reach for the stars.As a meteorologist, Ive still seen many important weather and space events, but right now, if you were sitting next to me, youd hear my foot tapping rapidly under my desk. Im anxious for the next one: a space capsule hanging from a crane in
22、 the New Mexico desert.Its like the set for a George Lucas movie floating to the edge of space.You and I will have the chance to watch a man take a leap into an unimaginable free fall from the edge of space - live.The (lack of) air up there Watch man jump from 96,000 feet Tuesday, I sat at work glue
23、d to the live stream of the Red Bull Stratos Mission. I watched the balloons positioned at different altitudes in the sky to test the winds, knowing that if they would just line up in a vertical straight line we would be go for launch.I feel this mission was created for me because I am also a journa
24、list and a photographer, but above all I live for taking a leap of faith - the feeling of pushing the envelope into uncharted territory.The guy who is going to do this, Felix Baumgartner, must have that same feeling, at a level I will never reach. However, it did not stop me from feeling his pain wh
25、en a gust of swirling wind kicked up and twisted the partially filled balloon that would take him to the upper end of our atmosphere. As soon as the 40-acre balloon, with skin no thicker than a dry cleaning bag, scraped the ground I knew it was over.How claustrophobia almost grounded supersonic skyd
26、iverWith each twist, you could see the wrinkles of disappointment on the face of the current record holder and capcom (capsule communications), Col. Joe Kittinger. He hung his head low in mission control as he told Baumgartner the disappointing news: Mission aborted.The supersonic descent could happ
27、en as early as Sunday.The weather plays an important role in this mission. Starting at the ground, conditions have to be very calm - winds less than 2 mph, with no precipitation or humidity and limited cloud cover. The balloon, with capsule attached, will move through the lower level of the atmosphe
28、re (the troposphere) where our day-to-day weather lives. It will climb higher than the tip of Mount Everest (5.5 miles/8.85 kilometers), drifting even higher than the cruising altitude of commercial airliners (5.6 miles/9.17 kilometers) and into the stratosphere. As he crosses the boundary layer (ca
29、lled the tropopause), he can expect a lot of turbulence.The balloon will slowly drift to the edge of space at 120,000 feet (22.7 miles/36.53 kilometers). Here, Fearless Felix will unclip. He will roll back the door.Then, I would assume, he will slowly step out onto something resembling an Olympic di
30、ving platform.Below, the Earth becomes the concrete bottom of a swimming pool that he wants to land on, but not too hard. Still, hell be traveling fast, so despite the distance, it will not be like diving into the deep end of a pool. It will be like he is diving into the shallow end.Skydiver preps f
31、or the big jumpWhen he jumps, he is expected to reach the speed of sound - 690 mph (1,110 kph) - in less than 40 seconds. Like hitting the top of the water, he will begin to slow as he approaches the more dense air closer to Earth. But this will not be enough to stop him completely.If he goes too fa
32、st or spins out of control, he has a stabilization parachute that can be deployed to slow him down. His team hopes its not needed. Instead, he plans to deploy his 270-square-foot (25-square-meter) main chute at an altitude of around 5,000 feet (1,524 meters).In order to deploy this chute successfull
33、y, he will have to slow to 172 mph (277 kph). He will have a reserve parachute that will open automatically if he loses consciousness at mach speeds.Even if everything goes as planned, it wont. Baumgartner still will free fall at a speed that would cause you and me to pass out, and no parachute is g
34、uaranteed to work higher than 25,000 feet (7,620 meters).It might not be the moon, but Kittinger free fell from 102,800 feet in 1960 - at the dawn of an infamous space race that captured the hearts of many. Baumgartner will attempt to break that record, a feat that boggles the mind. This is one of those monumental moments I will always remember, because there is no way Id miss this.
