1. Project introduction
XKH series five-axis linkage blade processing center is a professional blade processing machine tool developed by Beijing Mechanical and Electrical Research Institute Machine Tool Co., Ltd. with independent technology, combined with the processing characteristics of blade parts, and has been successfully implemented in batches in China. Users include Dongfang Turbine Factory and Wuxi Blade Plant, Liming Engine Company and other OEMs, as well as professional blade processing plants for supporting OEMs.
The five-axis blade machining center introduced in this article is part of the national science and technology major project "Demonstration application of domestic high-end CNC machine tools in blade processing" led by Wuxi Turbine Blade Factory. The machine tool model is XKH800Z, and the appearance of the machine tool is shown in Figure 1.
XKH800Z five-axis linkage blade machining center adopts a column moving structure, five-axis linkage, all coordinates are fully closed-loop control, the machine tool table moves left and right along the X axis, the column moves back and forth along the Y axis, and the spindle moves up and down along the Z axis and swings around the center of rotation (B-axis), Z-axis is driven synchronously by double screws (Z1, Z2), and B-axis is directly driven by torque motor; headstock (A1 axis) and tailstock (A2 axis) are installed on the worktable, both using torque The motor is directly driven and rotates synchronously. At the same time, the tailstock can be adjusted according to the size of the parts through the U-axis on the worktable, and the head and tailstock are locked by hydraulic pressure during cutting.
Figure 1: Appearance of XKH800Z
2. CNC system configuration
The XKH800Z five-axis linkage blade machining center has 5 linear axes (X, Y, Z1, Z2, U), 3 rotary axes (A1, A2, B) and 1 main shaft (SP1). A total of 9 axes need to be controlled. The machine tool uses SINUMERIK 840D sl CNC system. Due to the large number of control axes, the design enhances the drive control performance of the system by connecting the NX module. Therefore, the control is divided into two parts. One is to realize the Y-axis, U-axis and X-axis control through NCU720.3. The control of axis, B axis, SP axis, the second is to realize the control of Z1 axis, Z2 axis, A1 axis, A2 axis through the NX15.3 module, the control frame diagram is shown in Figure 2.
1. Control unit NCU720.3
The control unit NCU720.3 controls 5 axes, and communicates between modules and between modules and motor encoders through the DRIVE-CLiQ interface. Because the Y-axis, U-axis, X-axis and B-axis use 1FT7 series standard motors, the motor itself has a DRIVE-CLiQ interface, which can be directly connected to the motor module; while the spindle motor uses a third-party motor, the encoder signal needs to be equipped with an SMC20 module Connect with the motor module after signal conversion.
2. Control unit NX15
The control unit NX15 controls 4 axes, of which the A1 and A2 axes use 1FW6 series torque motors, use HEIDENHAIN RCN226 encoder for position detection, and add an external encoder module SME125 to convert encoder signals and motor temperature sensor signals into DRIVE-CLiQ signals , Connect to the motor module.
Figure 2: Connection topology diagram
3. Realization of head and tailstock motion control
1. Synchronous control
The blade is a thin-walled structure, and its rigidity is weak, and its bending rigidity and torsion rigidity are very poor. During processing, the head of the blade is clamped by the head frame, and the tail is clamped by the tail frame. If the swing of the part is only driven by the head frame, when the part is processed to the tail of the blade, the rigidity of the part is weak, and the machining error is relatively large. In order to ensure the machining accuracy, the design uses a torque motor to drive the headstock (A1 axis) and the tailstock (A2 axis) for synchronous drive, which improves the rigidity of the blade in the cutting state. At the same time, a high-precision angle encoder is used for closed-loop control. To improve movement accuracy.
When the product was initially designed, the headstock (A1 axis) and the tailstock (A2 axis) were controlled by the GANTRY axis, which required the two axes to ensure the same position at all times. In theory, this position synchronization control is the most accurate type of synchronization. However, there are two problems found in actual processing. The first is that when the workpiece is clamped, since the head and tailstock motor is the control mode of the GANTRY axis, the tailstock motor cannot follow the moment the tailstock is clamped by the vise. Rotation will cause the blade to twist, which will affect the subsequent processing accuracy, and the torque of the tailstock motor will increase, which will affect the service life of the motor over time. The second problem is that it is easy to spring back during the blade processing. In addition, during processing The original residual stress in the blade will gradually be released, and it will also cause the blade processing deformation. Because the tailstock motor cannot follow the rotation, the torque of the head and tailstock motor is inconsistent, which affects the precision of the blade finishing.
In response to the above problems, combined with other multi-axis coupling functions of the SIEMENS 840D SL system, after repeated trials and experiments, it was decided to adopt a multi-strategy combination, and the control strategy of the head and tailstock was changed from a single GANTRY axis synchronous control to a clamping time Follow-up control, master-slave coupling during roughing, and machine tool coordinate system coupling during finishing are a combination of three ways to overcome the problems of a single strategy and meet the different needs of blades in the clamping, roughing and finishing processes , In order to improve the processing efficiency and processing accuracy of the machine tool.
The schematic diagram of blade processing is shown in Figure 3.
Figure 3: Schematic diagram of blade processing
2. Follow-up control (follow-up mode)
1) Introduction to follow-up control
In the general control state, after the servo motor is enabled, the motor is driven by the driver to generate torque and cannot be rotated by external force. The CNC system detects the position and speed of the motor. If there is a deviation, the system will give an alarm. But in the follow-up control mode, the servo motor can be rotated by external force. For example, if you manually rotate the servo motor by hand, the motor rotates, the motor measurement system is still effective, and its actual position value is also recorded. The screen can see the change of its coordinate value, the system will not alarm, and when the follow mode is cancelled, there is no need to return to the reference point for each feed axis.
2) Realization of follow-up control
During the blade clamping process, the control strategy adopts the follow-up control mode. When the tailstock motor is clamped by the tailstock vise, it can rotate with the headstock without causing the blade to twist; after the blade clamping is completed, cancel the follow-up Start processing in dynamic control mode.
The tailstock follow-up is mainly used when the blade is clamped. Through the PLC program, DB3*.DBX2.1 = "0", DB3*.DBX1.4 = "1", then the follow-up control can be realized; on the contrary, let DB3*.DBX2.1 = "1", DB3*.DBX1.4 = "0", the follow-up control can be cancelled.
3. Master-slave coupling (master-slave)
1) Brief introduction of master-slave coupling function
Using the master-slave coupling method, two sets of motor drives are mechanically coupled to the same follower axis. The master axis has both a position loop and a speed loop control, which can achieve precise positioning; but the slave axis has only a speed loop, which is realized according to the speed command of the master axis. The control of the speed loop completes the balance of the torque output between the two drives by adjusting the speed difference between the master and slave shafts. The master-slave coupling mode is an optional function, and the order number is 6FC5800-0AM03-0YB0. The master-slave control principle diagram is shown in Figure 4 below.
Figure 4: Schematic diagram of master-slave coupling control
In the blade roughing process, the master-slave coupling is selected. Although the slave shaft does not have position loop control, it does not require high machining accuracy due to roughing, so the impact is not great; the master-slave coupling method uses the torque compensation controller to control the head, The torque of the tailstock motor is distributed to ensure that the head and tailstock drive motors are in the best torque coupling state, which can well solve the problem of blade processing deformation in the rough machining process.
2) Realization of master-slave coupling control
In the process of blade rough machining, the control strategy adopts the master-slave coupling mode. Although the slave axis does not have position loop control, it has little effect because of rough machining and does not require high machining accuracy; the master-slave coupling mode is controlled by torque compensation The controller distributes the torque of the head and tailstock motors to ensure that the head and tailstock drive motors are in the best torque coupling state, which can well solve the problem of blade processing deformation during the rough machining process.
When the master-slave coupling mode is adopted, the main machine parameters are set as follows: (Note: The parameters need to be set on the slave axis)
MD37250 $MA_MS_ASSIGN_MASTER_SPEED_CMD = ”4”
The machine tool axis number of the speed-coupled master axis, the A1 axis is the 4th axis;
MD37252 $MA_MS_ASSIGN_MASTER_TORQUE_CTR = ”4”
The machine tool axis number of the driving axis of torque coupling, the A1 axis is the 4th axis;
MD37253 $MA_MS_FUNCTION_MASK = ”1”
Master-slave coupling setting, recommended setting on sl is 1, MD37256, MD37260 use the setting value;
MD37254 $MA_MS_TORQUE_CTRL_MODE = ”1”
The output mode of the torque compensation controller, 0: output to the master axis and the slave axis; 1: output to the slave axis;
2: Output to the master axis; 3: No output;
MD37255 $ MS_TORQUE_CTRL_ACTIVATION = "1"
The activation mode of the torque compensation controller, 0: through MD37254; 1: through signal DB3*.DBX24.4;
MD37256 $ MA_MS_TORQUE_CTRL_P_GAIN = "50"
P gain of the torque compensation controller, range: 0~100,
The setting value is the percentage of MD32000 (maximum speed of the shaft) / P2003 (rated torque of the driven shaft);
MD37258 $ MA_MS_TORQUE_CTRL_I_TIME = "0.1"
The integral time of the torque compensation controller. When the gain is greater than 0, the integral time is valid;
MD37260 $ MA_MS_MAX_CTRL_VELO= "100"
The maximum speed of the torque compensation controller, the percentage of MD32000, range: 0~100;
MD37262 $ MA_MS_COUPLING_ALWAYS_ACTIVE = "0"
Master-slave coupling activation mode, 0: temporary coupling, through NC command MASLON or interface signal DB3*.DBX24.7;
1: Permanent coupling, NC or PLC control is invalid.
MD37264 $ MA_MS_TENSION_TORQUE = "0"
The tension between the main and slave shafts, the tension is the percentage of the reference torque, the positive and negative values adjust the direction of expansion and tightening, the range: -100~100;
MD37266 $ MA_MS_TENSION_TORO _FILTER_TIME = "0"
Tension adjustment filter time constant, value>0, tension adjustment filter is valid, range: 0~100, unit: second;
MD37268 $ MA_MS_ TORQUE_WEIGHT_SLAVE = "50"
The percentage of the slave shaft torque to the total torque, if the master and slave motors are the same, set it to 50, range: 0~100;
MD37270 $ MA_MS_ VELO_TOL_COARSE = ”5”
The coarse positioning window of the master-slave speed difference, the window setting value is the percentage of MD32000, the range: 0~100;
MD37272 $ MA_MS_ TORQUE_ VELO_TOL_FINE = ”1”
The precision positioning window of the master-slave speed difference, the window setting value is the percentage of MD32000, the range: 0~100;
MD37274 $ MA_MS_ MOTION_ DIR_REVERSE = "0"
Reverse the movement direction of the slave axis. 0: The coupling direction of the slave axis remains unchanged; 1: The coupling direction of the slave axis is reversed.
4. Machine coordinate system coupling
1) Introduction to machine tool coordinate system coupling
In a machine tool, if there are two or more relatively independent machine tool heads that need to complete the same action, but they cannot be achieved through the standard coupling function, the machine coordinate system coupling function can be used to achieve synchronized actions, that is, to establish their own independence. In the coordinate system, several axes under their respective coordinate systems realize the position synchronization between the coordinate axes through functions such as position detection and compensation during movement. The axis under the coupling control of the machine tool coordinate system has the function of displacement and speed synchronization. It moves at the same speed. The speed direction can be the same or opposite, and the position error of the two axes can be controlled within the set range.
The master axis under the coupling of the machine coordinate system can have one or more slave axes, but the slave axis and the master axis cannot be interchanged; for the slave axis, it cannot be a PLC axis, nor can it be used as a control axis. And in JOG mode, the slave axis cannot act alone. In addition, to apply the machine tool coordinate system coupling function, it is required that the master axis and the slave axis must be the same rotary axis or the same linear axis, and the master axis and the slave axis cannot be conversion axes, and the spindle cannot use the machine tool coordinate system coupling function.
It is important to note that the activation and deactivation of the machine coordinate system coupling function cannot be controlled by the PLC interface signal. It can only be turned on or off through the NC commands CC_COPON and CC_COPOFF. After activating the machine coordinate system coupling function, you can see in the axis diagnosis screen that the control state of the slave axis is changed from speed control to position control.
The machine coordinate system coupling is an optional function. The order number is 6FC5800-0AM72-0YB0. This is an option package. When activating the authorization, you need to select this order number and 6FC5800-0AM23-0YB0 to make the function effective.
In the following figure 5, the machine head 1 and machine head 2 are driven by 5 coordinate axes respectively, which are indirectly connected mechanically and have their own independent coordinate systems. The two coordinate systems are Y and Y2, Z and Z2, W and W2, A and A2 and C and C2, these 5 pairs of coordinate axes can all be controlled by the machine coordinate system.
Figure 5: Schematic diagram of machine tool coordinate system coupling
2) Realization of the coupling function of the machine coordinate system
When blade finishing, there are strict requirements on the positioning accuracy of the head and tailstock motors, so the machine coordinate system coupling function is adopted, but this function cannot be controlled by the PLC interface signal. It can only be turned on or off by the NC commands CC_COPON and CC_COPOFF. It is troublesome to input these instructions in the program every time, so use M code to call. In addition, for safety reasons, except during the blade clamping process, the tailstock can follow-up. In other states, the head and tailstock are in a synchronized state, so use the M code to open or close the machine coordinate system coupling. At the same time, the master-slave coupling function should be closed or opened accordingly.
The general parameter settings are as follows:
MD10715 [5] $ MN_M_NO_FCT_CYCLE = ”65”
MD10715 [6] $ MN_M_NO_FCT_CYCLE = ”66”
MD10716 [5] $ MN_M_NO_FCT_CYCLE_NAME = "L65_MCSON"
MD10716 [6] $ MN_M_NO_FCT_CYCLE_NAME = "L66_MCSOFF"
Then copy the following two programs into the manufacturer's cycle directory.
L65_MCSON.SPF;
MASLOF(AA)
CC_COPON(A,AA)
M17
L66_MCSOFF.SPF;
CC_COPOFF(A,AA)
MASLON(AA)
M17
Axis parameter setting (Note: the parameter needs to be set on the driven shaft)
MD28090 $ MM_NUM_CC_BLOCK_ELEMENTS = "1"
The number of program segment elements (DRAM) used for the compilation cycle;
MD28100 $ MM_NUM_CC_BLOCK_USER_MEM = "100"
The program segment memory capacity (DRAM) used for the compilation cycle, in KB;
MD60946 $MN_CC_ACTIVE_IN_CHAN_MCSC = ”1”
General parameters, the option function is activated, PO reset is required after setting to 1, and the following parameters can be searched in the axis parameters after reset;
MD63540 $ MA_CC_MASTER_AXIS = "4"
The machine axis number of the active axis coupled to the machine coordinate system, the A1 axis is the 4th axis;
MD63541 $ MA_CC_POSITION_TOL = ”0.5”
The monitoring window of the driven axis, this window detects the absolute position;
MD63542 $ MA_CC_PROTEC_MASTER = "0"
For the active shaft corresponding to the collision protection, the head and tailstock will not collide, so there is no need to use the collision protection function;
MD63543 $ MA_ CC_PROTEC_OPTIONS = "0"
Configuration of collision protection function;
MD63544 $ MA_ CC_COLLISION_WIN = "-1"
Collision protection window;
MD63545 $ MA_ CC_OFFSET_MASTER = "0"
Zero offset for collision protection.
5. Switching the control mode
In summary, the control strategy of the head and tailstock simultaneously uses three control modes: follow-up, master-slave and coordinate system coupling. Taking into account the safety and convenience of machine tool operation, the user interface is designed with Easy Screen function. Click the vertical button in the interface to activate the corresponding control mode.
There are two folders under F:\HMI\hmisl\oem\sinumerik\hmi\ of the hard disk path of the SINUMERIK 840D sl CNC system. The folder cfg stores the framework files for interface control, and the folder proj stores the manufacturer's secondary Interface file for development.
1) Modify the configuration file easyscreen.ini, specify the storage location of the tailstock automatic control interface, under the system's diagnostic screen: [STARTFILES]
StartFile07 = area := AreaDiagnosis, dialog:=SlDgDialog, startfile := diag.com;
2) Prepare the interface program for switching the head and tailstock control mode, and store it in the folder prog, the file name is diag.com, because the machine coordinate system coupling must be activated by commands, so the file function "select program" is used when making the interface SP" sentence, for example, when the machine coordinate system coupling mode is activated, the corresponding sentence SP ("//NC/CMA.DIR/ L65_MCSON.SPF");
3) The program is transferred to the path F:\HMI\hmisl\oem\sinumerik\hmi\proj\. After the system restarts, the soft key "Head and Tail Frame Control" will appear under the system's diagnostic screen. Click this key to enter To switch the interface of the control mode of the head and tail frame, click the corresponding vertical button in the interface, and then press the cycle start key to activate the corresponding mode. At the same time, the control status of the head and tail frame can also be read out in the interface for easy operation Real-time monitoring. The control interface of the head and tailstock is shown in Figure 6.
Figure 6: Head and tailstock control status interface
Fourth, processing verification
After the design and development are completed, six XKH800Z machine tools embedded in the multi-strategy control mode have passed the small batch continuous processing test of blade parts in our company. The test blade blank is square steel, the size is 300×75×45mm, and the material is stainless steel. In the small batch continuous processing test of blades, the head and tailstock control mode combined with multiple coupling modes is convenient and effective in operation, stable and reliable in work, and the accuracy and surface roughness of the processed blades are qualified and passed the user's acceptance.
After the machine tool was shipped to Wuxi Turbine Blade Factory, the user used the machine tool to mass-produce various types of stainless steel square steel blades (blank length 200-580mm) and die forging blades (blank length 350-550mm). More than half a year The cutting process shows that the machine tool is stable and reliable, and the head and tailstock motion control is practical and effective, which has been praised by users, and played an important role in improving the blade machining accuracy and machining efficiency.
Five, application experience
Through the comprehensive application of the three functions of SINUMERIK 840D SL CNC system, master-slave coupling, follow-up control, and machine tool coordinate system coupling, a reliable and effective embedded control strategy is formed, and the head and tailstock synchronization control of the five-axis blade machining center is realized. It solves the problems of different requirements on the control of the head and tailstock during the blade clamping, roughing and finishing processes, improves the processing efficiency, satisfies the technological requirements of blade processing, and fully reflects the powerful functions of the SINUMERIK 840D SL CNC system And its good openness.
