Keywords Engine Manufacturing Pressing CNC Machine Tool Linux

In the manufacturing process of the engine, pressurization is an indispensable process. According to the type of engine, the number and location of pin holes vary. The core of the traditional press machine is a lever mechanism. Its working process is as follows: (1) clamping the engine blank on the workbench; (2) placing the preselected pin in the pin hole; (3) passing the rocker arm; Rotate the screw, move the table, align the presser head with the pin, and (4) use the lever to force the pin into the pin hole. There are two difficulties in this process: the precise positioning of the first table, the axial deviation of the indenter and the pin hole must not exceed 30μm; secondly, the depth of the indentation of the pin is 5±0.5mm from the upper end of the pin hole. With the use of traditional pinching machines, the degree of achievement of these two indicators is closely related to the operating experience and physical conditions of the operators and is a labor-intensive type of work.

In view of the labor intensity of traditional presses, and the fact that production units often change product types, it is difficult to match with other processing links when the processing volume is large and the lead time is short. We have developed the ATHD-030 type CNC press machine.

Figure 1 shows the schematic structure of the pinching machine. Considering the positioning accuracy, load condition and cost required by the control object, a stepping motor direct-connect ball screw is used as the open-loop drive unit of the work table. The machine tool control core adopts an industrial PC and is installed in the control cabinet (1). During work, the workpiece is mounted on the X slide (3) and clamped using a matching jig. The position of the workpiece in the plane relative to the axis of the indenter (5) is controlled by the X, Y slides. The cylinder is used to control the pressing and lifting of the indenter. Hall elements are used to capture the position of the indenter at both ends of the stroke of the indenter.

With this design scheme, two difficult-to-control links in the pressurization process are effectively controlled: First, the positional deviation between the indenter axis and the pinhole axis is controlled by the numerical control system and the ball screw The transmission accuracy of the bar is guaranteed; secondly, the depth of the pin pressed into the pin hole can be ensured by adjusting the pressure of the cylinder and the holding time after being pressed into place. Once the test is qualified, the accuracy of the machine tool is maintained, and human error is eliminated in these two key links, which can effectively guarantee the quality of the workpiece.

See Figure 2 for the hardware architecture of the CNC system. The IPC is the core control unit of the CNC system. It is responsible for the scheduling management of the entire system, and controls the position control card and the I/O card so as to realize the position control and discrete logic control functions of the CNC system. The host computer is equipped with a network card that can link with other hosts through the LAN to implement DNC ​​group control or exchange data.

(1) Position Control [1]

Advantech PCL839 intelligent position control card is used to generate command pulses to control the position of the stepper motor. The card has the function of automatic trapezoidal acceleration and deceleration. The positive and negative limit switches and zero switch signals of the machine axes are sent directly to the PCL839. The industrial control host realizes the monitoring function by directly reading and writing the register bank of the PCL839 position control card. The kick frequency, the maximum frequency, and the acceleration of the output pulse can be set. These parameters determine the basic characteristics of the axis operation; the PCL839 can be instructed to generate Continuous operation, fixed-length operation pulse, control the machine zero return action.

The host computer generates a position command and writes it into the PCL839 command register to generate a command pulse and send it to the stepper motor driver to control the position of the machine tool.

(2) Logical control

The industrial control host cooperates with the PW24-24 optically isolated input/output card to implement a built-in PLC to scan the input signal from the control panel at a high speed, isolate the output signal and amplify it, and then directly drive the relay to realize the discrete logic control function. [2].

CNC system software development is based on the Linux operating system, Linux is free software, so that it can develop a proprietary digital control system. The system is divided into the following modules according to the function: man-machine interface management, manual machine control, teaching function, machine tool automatic control, and workpiece parameter backup. The man-machine interface adopts the Chinese-like Windows-like interface, and the setting and modification of the machine structure parameters and technological parameters are realized through the universal keyboard. Under the manual control mode, the coordinate axes of the machine tool can be jogged and returned to the origin. Manually control the output point; use the teaching function to record the manually controlled trajectory and use it to automatically control the movement of the machine tool; in the automatic mode, the workpiece is processed according to a previously set trajectory. When the workpiece type is changed, the workpiece with the set process parameters can be backed up so that it can be taken out and used again in the future.

Figure 3 is a flowchart of automatic processing. For each pin hole position, the position in the machine coordinate system can be calculated according to the design dimension of the workpiece, and directly filled in the table provided by the numerical control system to achieve accurate positioning.

After the installation and function debugging of the ATHD-030 CNC pinching machine, the HP5528A dual-frequency laser interferometer was used to test its positioning accuracy and repeatability. The test results show that the machine tool is calculated with 3s accuracy at a running speed of 6m/min. Method: Positioning accuracy is 12μm, repeatability is 25μm, and it meets the design requirements of machine tools.

During the trial period of up to one month, the machine tool is stable and reliable, with high control accuracy, and one workpiece per minute is processed. When replacing the product, only the pin hole position needs to be reset, and the operator is not required to retrain. Fully able to adapt to the actual needs of many projects, large quantities, and short lead times.

1. PCL-839 3-axis High Speed ​​Stepping Motor Control Card PC-LabCard Series User's Manual

2. Li Bingcao, Zhang Dengju, Fu Shouying, etc. Microcontroller interface technology and its application in industrial control Shaanxi Electronic Editing Department.

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