Parameter acquisition and quality management syste

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Parameter acquisition and quality management system of CNC pneumatic rail welding machine

rail welding is the technical key to realize the laying of seamless rail, and the use of small-scale pneumatic welding is the preferred process for on-site construction [1, 2]. The welding process principle of rail gas pressure welding is to heat the clean end faces of the two closely bonded rails through the gas flame. When the rails near the bonding surface are heated to the plastic state, and the metal atoms have enough activation energy to spread rapidly through the bonding surface, that is, the bonding surface is pressed and upset. Under the condition of high temperature and high pressure, apply sufficient extrusion force to shorten the distance between welding surfaces to the interaction radius between atoms, achieve the metal bond connection between molecules, and complete recrystallization, so as to obtain the welded joint with two rails firmly connected [3]. At present, China's new CNC small pneumatic rail welding machine has the ability to automatically control the production of biodegradable shopping bags, lunch boxes and other products. However, due to the poor environmental conditions at the construction site and many influencing factors, the actual process of rail welding construction cannot be tracked and monitored

therefore, it is very necessary to collect and analyze parameters such as oxygen, acetylene flow, pressure and displacement of gas pressure welding in real time. At present, the common method of industrial parameter acquisition is board card acquisition, that is, inserting some boards into the computer host to collect parameters. This acquisition method requires many accessories and takes up a large space, which is very inconvenient for pneumatic welding in field operation. This paper uses the parameter acquisition module with USB interface and the powerful function of visual basic software to develop a parameter acquisition system suitable for on-site pneumatic welding. The system is used in conjunction with the CNC pneumatic welding control box. The required parameters are obtained by the USB module. Using the USB transmission line as the communication cable between the acquisition module and the notebook computer, the pneumatic welding parameters can be collected in real time, and the data can be processed in time, which is very convenient to use

1 system hardware design

1.1 working principle of acquisition module

the core part of the system hardware is the data acquisition module with hot plug and play functions. The operating system adopts the current popular windows series, high stability UNIX and other operating systems, as well as professional data acquisition and analysis system LabVIEW and other software environments. During hardware installation, it is only necessary to insert the module interface into the interface socket in the computer, and the signal cable is directly connected from the interface provided by the module. The acquisition module allows 16 channels of single ended input or 8 channels of double ended input in the late 1990s. The data acquisition module is mainly composed of analog multi-channel switch gating circuit, differential amplification circuit, analog-to-digital conversion circuit, switching input and output circuit and interface control logic circuit. The analog signal selected by the channel switch is amplified by the differential amplifier, transformed and processed by the 12 bit APD converter, and finally transmitted to the computer through the USB transmission line

1.2 hardware composition

the data acquisition module is installed in the numerical control pneumatic welding control box, and the module is connected with the notebook computer through the transmission line (Figure 1). The quality of pneumatic welding mainly depends on the heat input, pressure and upsetting amount (i.e. displacement) in the welding process. Therefore, this system mainly collects the flow, pressure and displacement of oxygen and acetylene in the process of pneumatic welding, converts these four parameters into voltage signals through sensors, and inputs the signals into the analog signal input end of the acquisition module after filtering and amplification. At the same time, in order to realize the automatic start and stop of the parameter acquisition system and facilitate the later data processing, this system also sets up the acquisition of switching value signals. The hardware structure is shown in Figure 2

the flow of oxygen and acetylene in the system is obtained through the gas flow control valve, the pressure is detected by the pressure sensor on the oil pump, and the displacement is obtained by the sliding resistance displacement sensor added to the welding machine

2 system software design

2.1 DLL technology

dynamic link library DLL is a Windows based program module, which is loaded and connected at runtime. The dynamic link library only contains the relevant information about the DLL when the supply program runs, not the copy of the source code. Therefore, using the dynamic link library can enable multiple applications to share code and resources, so as to improve the running speed. When calling library functions from VB, first declare the library functions to be used in the global module or form description part with declare, and then call these functions like using VB's own functions [4]. Usb7KC. DLL is a dynamic link library configured for data acquisition module, which works in Windows 95p98p2000pnt environment. The functions it encapsulates can be called directly by other applications at runtime

2.2 programming

visual basic (hereinafter referred to as VB) is a visual programming language, which has been favored by the majority of programmers since its appearance. The program design part of the system adopts a functional modular structure, and the main functional modules are shown in Figure 3

1) parameter setting module: This module is mainly used to set some main conditions of the welding site, including rail model, material, welding machine model and site environment

2) data acquisition module: This module is the core part of the parameter acquisition system. After the equipment is connected, run the program to collect parameters. Using the timer control of VB, call the DLL function of the module 25 times per second to collect parameters

3) graphic display module: the function of this module is to process the collected pneumatic welding parameters, and output the welding process parameters and their change trend in the form of curves and graphics on the display screen or printer. The welding parameter curve is distinguished by four color lines. The red curve represents oxygen flow, the black curve represents acetylene flow, the Yellow curve represents pressure, and the blue curve represents displacement. The left coordinate is the gas flow and pressure, and the right coordinate is the displacement. The collection range of oxygen and acetylene is 0 ~ 200slm, the collection range of pressure is 0 ~ 100 MPa, and the collection range of displacement is - 5 ~ 45 mm

4) quality management module: the main function of this module is to count the experimental results, and compare the experimental results with the welding parameters of the rail joint to form a quality management platform, which is convenient for analyzing the experimental results and welding parameters, and finally realize the selection of the best welding parameters

5) report generation module: This module mainly saves and processes the data, and outputs the processed data to the display screen or printer in the form of reports. There are two kinds of reports in this system: joint report and table. Because there are many items in the table, it is realized by VB excel control

3 application effect of the system

3.1 field welding track measurement results

using this system, the field welding track measurement was carried out in Xidatan and other sections of the Qinghai Tibet plateau at an altitude of 4300 m, and the oxygen, acetylene flow, pre jacking pressure and time (P1, T1), low pressure pressure and time (P2, T2), upsetting pressure and time (P3, T3), upsetting amount, tumor pushing force P4 See Table 1 for the change law of parameters such as total welding time TM and the drop hammer results of welding head. It can be seen that the parameters of each stage are basically stable, so the drop hammer keeps three hammers, and the performance is good. This provides a basis for the selection of the best parameters: in the case of little difference in the construction environment, the U71Mn 60 kgpm rail can be welded with the parameters shown in Table 1, and a high-quality welded joint can be obtained

3.2 comparison between process test and on-site welding rail condition

the welding parameters of 50 kgpm rail passing the process test are used for construction site welding, and the parameters collected in real time are compared with the process test parameters (Table 2), and the differences between on-site pneumatic welding parameters and process test parameters are found

1) different gas ratios. Because the altitude of the process test site is higher than that of the on-site welding site, the thin air should be installed on the basis of concrete, so the oxygen flow of the process test is higher than that of the on-site welding

2) the values of pre jacking and low-pressure pressure are different. During on-site rail welding construction, due to the existence of special working conditions such as the gradient (3 ~ 20) of the line and the self weight component of the rail, bend resistance, etc., the pre jacking and low-pressure pressure values should be 2 ~ 3 MPa higher than those in the process test, so as to compensate the component force brought by the special working conditions and ensure the welding pressure

3) the heating time in the pre jacking stage is shortened. Because the on-site sunshine time is long and the rail temperature is high, the heating time in the pre jacking stage is shortened by 10 s on the basis of the type inspection test parameters. In addition, due to the manual intervention in the welding process, the actual welding parameters are different from the parameters set before welding. For example, for the No. 2 rail in the process test in the table, due to the artificial extension of the welding heating time in the low-pressure stage, the actual heating time in the low-pressure stage is changed from the set 125 s to 15514 S. the actual situation of these welding processes can be truthfully reflected in the parameters collected by this system

3.3 relationship between altitude and gas matching

due to the different altitude of the welding location, it was unknown in the past how to obtain good welding quality by welding gas ratio. For this reason, this system was applied to nanshankou, Xidatan and unfrozen spring to collect the changes of gas ratio during rail welding (Table 3). It was found that with the increase of altitude, the thinner the air is, the oxygen flow should be appropriately increased

4 conclusion

1) this system has the advantages of hot plug, plug and play, Chinese interface, easy to use and so on. The system is used in the harsh construction environment on the plateau, with good stability, and can fully meet the requirements of quality management of on-site rail welding work

2) the system automatically generates the parameter curve of pneumatic welding in real time, which can truly reflect the quality information of the actual welding rail, and can be used for the research and analysis of the influence of the on-site welding rail process on the quality under different working conditions, such as special environment, unit welding and lock welding

3) the system can automatically generate the daily, monthly and annual reports of pneumatic welding quality management, which provides an effective means for tracing the rail welding conditions, diagnosing the rail welding quality, and realizing the modern management of rail welding engineering quality

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