1、数控机床加工精度异常故障的诊断和处理生产中经常会遇到数控机床加工精度异常的故障。此类故障隐蔽性强，诊断难度比较大。形成这类故障的原因主要有五个方面：1机床进给单位被改动或变化。2 机床各个轴的零点偏置 NULL OFFSET异常。3轴向的反向间隙BACK LASH异常。4电机运行状态异常，即电气及控制部分异常。5机械故障，如丝杠，轴承，轴联器等部件。另外加工程序的编制，刀具的选择及人为因素，也可能导致加工精度异常。1 系统参数发生变化或改动 系统参数主要包括机床进给单位，零点偏置，反向间隙等。例如SIMENS，FANUC 系统，其进给单位有公制和英制两种。机床修理过程中某些处理，常常影响到零点
2、偏置和间隙的变化，故障处理完毕后应作适时的调整和修改；另一方面，由于机械磨损严重或连结松动也可能造成参数实测值的变化，需要对参数做相应的修改才能满足机床加工精度的要求。2 机械故障导致的加工精度异常 一台THM6350立式加工中心，采用SIMENS 840D系统。在加工联杆模具过程中，忽然发现Z轴进给异常，造成至少1毫米的切削误差量（ Z向过切） 。调查中了解到：故障是忽然发生的。机床在点动，MDI（手动数据输入方式）操作方式下各个轴运行正常，且回参考点正常；无任何报警提示，电气控制部分硬故障的可能性排除。分析认为，主要应对以下几个方面逐一进行检查。 1检查机床精度异常时正在运行的加工程序段，
3、特别是刀具长度补偿，加工坐标（G54G59）的校对和计算。 2在点动方式下，反复运动Z轴，经过视，触，听对其运动状态诊断，发现Z向运动噪 音异常，特别是快速点动，噪音更加明显。由此判断，机械方面可能存在隐患。3检查机床Z轴精度。用手摇脉冲发生器移动 Z轴， （将其倍率定为1X100的挡位，即每变化一步，电机进给0.1毫米） ，配合百分表观察Z轴的运动情况。在单向运动精度保持正常后作为起始点的正向运动，脉冲器每变化一步，机床Z轴运动的实际距离d=dl=d2=d3.=0.1mm ，说明电机运行良好，定位精度也良好。而返回机床实际运动位移的变化上，可以分为四个阶段：机床运动距离d1d=0.1mm(斜
4、率大于1)； 表现出为d1=0.1d2d3(斜率小于1)；机床机构实际没移动，表现出最标准的反向间隙；机床运动距离与脉冲器给定数值相等（斜率等于1） ，恢复到机床的正常运动。 无论怎样对反向间隙（参数1851）进行补偿，其表现出的特征是：除了阶段能够补偿外，其他各段变化依然存在，特别是 阶段严重影响到机床的加工精度。补偿中发现，间隙补偿越大，阶段移动的距离也越大。 分析上述检查认为存在几点可能原因：一是电机有异常；二是机械方面有故障；三是丝杠存在间隙。为了进一步诊断故障，将电机和丝杠完全脱开，分别对电机和机械部分进行检查。检查结果是电机运行正常；在对机械部分诊断中发现，用手盘动丝杠时，返回运动
5、初始有非常明显的空缺感。而正常情况下，应能感觉到轴承有序而平滑的移动。经过拆卸检查发现其轴承确实受损，且有滚珠脱落。更换后机床恢复正常。3 机床电气参数未优化电机运行异常 有一台北京产的立式数控铣床，配备SIMENS840D系统。在加工过程中，发现X轴精度异常。检查发现X轴存在一定间隙，且电机启动时存在不稳定的现象。有手触摸X轴电机时感觉电机抖动比较厉害，停止是抖动不明显，尤其是点动方式下比较明显。分析认为，故障原因有两点，一是丝杠反向间隙很大；二是X轴电机工作异常。利用SIMENS系统的参数功能，对电机进行调试。首先对存在的间隙进行补偿；调整伺服增益参数及脉冲抑制功能参数，X 轴电机的抖动消
6、除，机床加工精度恢复正常。4 机床位置环异常或控制逻辑不妥 一台TH61140加工中心，系统是FANUC18I，全闭环控制方式。加工过程中，发现该机床Y轴精度异常，精度误差最小为0.006mm ，最大为1.4mm。检查中，机床已经按照要求设置了G54工件坐标系。在MDI （手动数据输入方式）方式下，以G54坐标系运行一段程序即“G00G90G54Y80F100 ；M30；”，待机床运行结束后显示器上显示的机械坐标值为“-1046.605”，记录下该数值。然后在手动方式下，将机床点动到其他任意位置，再次在MDI方式下运行上次的程序段，待机床停止后，发现此时机床机械坐标数值显示为“-1046.99
7、2”，同第一次执行后的数值相比差了0.387mm。按照同样的方法，将Y 轴点动到不同的位置，反复执行该程序段显示器上显示的数值不定。用百分表对Y 轴进行仔细检查，发现机械位置实际误差同数显显示出的误差基本一致，从而认为故障原因为Y 轴重复定位误差过大。对Y轴的反向间隙及定位精度进行检查，重新做补偿，均无效果。因此怀疑光栅尺及系统参数等有问题。但为什么产生如此大的误差，却未出现相应的报警信息呢？进一步检查发现，次轴为垂直方向的轴，当Y 轴松开时主轴箱向下掉，造成了误差。 对机床的PLC 逻辑控制程序做了修改，即在Y轴松开时，先把Y 轴使能加载，再把Y轴松开；而在夹紧时，先把轴夹紧后，再把 Y轴使
8、能去掉。调整后机床故障得以解决。CNC machining accuracy of the abnormal fault diagnosis and treatmentProduction often encounter unusual precision CNC machining of the fault. Such failure concealed strong, and the diagnosis more difficult. Such a failure of the main reasons there are five areas: (1) machine tool unit
9、 to be altered or changed. (2)-axis machine tools all the 0.1 bias NULL OFFSET anomaly. (3) axial reverse the gap BACK LASH anomaly. (4) abnormal motor running, electrical and control of the anomaly. (5) mechanical failure, such as the screw, bearings, shaft and other components for the. In addition
10、 the establishment of procedures for processing, tool selection and human factors, may also lead to abnormal processing accuracy1. System parameters change or alterationSystem parameters including machine feeding units, 0.1 bias, such as reverse gap. For example, SIMENS, FANUC system, feeding its me
11、tric and English units of two. Machine repair in certain treatment, often affecting 0.1 gap and offset the change, fault should be disposed of after timely adjustments and amendments on the other hand, due to mechanical wear or link may also be caused by loose parameters measured the changes , The p
12、arameters need to be revised accordingly to meet the requirements of precision machining.2. Mechanical failure caused by abnormal processing precisionTHM6350 a vertical machining centers, used SIMENS 840D system. Die-processing in the process, suddenly found Z-axis feed anomaly, at least one millime
13、ter of error of cutting (Z to the cut-off). In that survey: the fault is all of a sudden. Machine tools to move in, MDI (manual data input method) mode of operation under normal operation of the shaft, and the reference point back to normal without any warning tips, electrical control of the hard ru
14、le out the possibility of failure. Analysis, the main one by one the following aspects should be checked1 check accuracy of abnormal machine is running at the processing procedures, the length of particular tool compensation, processing coordinates (G54-G59) the proof-reading and computing. 2 to mov
15、e in the way, the Z-axis movement repeatedly, through visual, touch, listen to their campaign of state, found that the noise Z to the abnormal movement, in particular to move fast, noise more pronounced. This judgement, machinery possible hidden dangers3 Z-axis precision machine tool inspection. Usi
16、ng hand-cranked generator mobile Z-axis, (its rate set at the Shift 1 X100, which is in step, the electrical feed 0.1 mm), with Bai Fenbiao observe the movement of Z-axis. In a one-way movement to maintain normal accuracy of the positive movement as a starting point, every change in pulse-step machi
17、ne Z-axis movement of the actual distance d = dl = d2 = d3 .= 0.1 mm, that motor running well and also positioning accuracy Good. Back to the actual movement and displacement of the machine changes, can be divided into four stages: machine movement distance d1 d = 0.1mm (slope greater than 1); show
18、for d1 = 0.1 d2 d3 (slope less than 1); machine actually did not move bodies, showing the most standard reverse gap ; movement from the machine and pulse for a given numerical equivalent (slope equal to 1), return to the normal movement of the machineNo matter how the reverse gap (parameters 1851) c
19、ompensation to their performance characteristics: In addition to stage to compensation, all of the other changes still exist, especially stage seriously affect the accuracy of the processing machine. Compensation found that the greater the compensation gap, stage of moving from the greaterAnalysis o
20、f the inspection that there may be a few reasons: First, motor abnormalities and the other is in a mechanical fault; three screw there is space. In order to further diagnose problems, and the screw will be fully undocked from the electrical, mechanical and electrical were part of the inspection. Ins
21、pection results of the electrical operating normally in the diagnosis of the mechanical parts that move hand-screw, to return to the initial campaign have a very clear sense of vacancy.And under normal circumstances, should be able to feel bearing orderly and smooth movement. After the demolition in
22、spection found that it really damaged bearings, and the ball is falling. After the replacement machine back to normal3. Machine did not optimize the electrical parameters of abnormal motor runningBeijing has a capacity of vertical milling machine, equipped with SIMENS840D system. In the process, we
23、found abnormal X-axis precision. X-axis inspection found that there are certain gaps, and the motor of instability at the start of the phenomenon. A hand touching the X-axis motor, sensory motor jitter relatively powerful, and stop dithering is not obvious, especially under way to move more obvious.
24、 Analysis of that failure for two reasons, First, screw reverse big gap and the other is abnormal X-axis electrical work. SIMENS system using the parameters of function, the motor debugging. First on the compensation gap, adjusting the servo gain parameters and pulse suppression parameters, X-axis m
25、otor to eliminate the jitter, precision machining back to normal4. Central location of machine control logic is nothing wrong or unusualTH61140 a processing center, the system is FANUC18I, closed-loop control the whole way. In the process, found that the Y-axis precision machine tools abnormal, the
26、smallest error for the accuracy of 0.006 mm, the largest to 1.4 mm. During the inspection, and machine tools have been set up G54 in accordance with the requirements of the workpiece coordinates. In MDI (manual data input method) mode, the G54 to coordinate procedures for running a section that is “
27、G00G90G54Y80F100; M30;“, machine tool operation to be displayed on the monitor after the end of the mechanical coordinates for the “-1046.605,“ a record of the numerical.Then in the manual mode, the machine will be to move to any other location, again running under way in the last MDI procedures, th
28、e question following the cessation of machine tools, machine tools found at this time numerical mechanical coordinates displayed as “-1046.992,“ with the first After the implementation of the numerical difference compared to the 0.387 mm. In accordance with the same methods, will move the Y-axis to
29、a different location and repeatedly monitor the implementation of the program displayed on the numerical uncertain. Bai Fenbiao with the Y-axis to double-check and found that mechanical error with the actual location of the show was basically the same error, the reasons for that failure to repeat Y-
30、axis positioning error too large.Y-axis on the reverse gap and positioning accuracy check and re-do of compensation, no effects. Therefore suspected grating device and system parameters such as a problem. But why have such a large error, the alarm has not been a corresponding information? Further in
31、spection found that the vertical axis of the shaft, when the Y-axis release me down when the spindle out, causing the error.The PLC logic of the machine tool control program made changes, that is, in the Y-axis release, the first Y-axis can be loaded, then release the Y axis and in clamping, the first axle clamp, then Y-axis can be removed. After adjusting machine fault is resolved.
