Arc Welding Process Monitoring And Analysis System

Arc welding is the most widely used and important type of welding methods,widely used in aviation,aerospace,ship,vehicle,construction,boiler and pressure vessel manufacturing, and other industrial sectors.Being a Processing method,arc welding must also use product quality as evaluation criteria.However,in the actual production process, even if the welding process is strictly controlled and comply with the WPS,it is still impossible to ensure that there is no quality problem. Therefore artificial quality inspection is widely used in practical production,however, there are some defects which can not be overcome.In recent years,welding process automated monitoring technology get more and more attention in academic circles and industrial community.In some industrialized countries,welding process automated monitoring devices have been utilized by automobile industry.The application of welding process automated monitoring technology is increasingly extensive in China.This article takes welding current and voltage as signal sources to develop arc welding process monitoring and analysis system.The system includes hardware design and software design.System hardware consists of sensors,sensor power supply,data acquisition card, twin-core cable with metal shielding layer,PC with ISA slot.Sensors adopted by system is Hall current sensor(HDC-500EK) and Hall voltage sensor(HNV500T). HDC-500EK is a new generation of Hall current sensor.It can survey DC,AC,pulse current and irregular waveform current under the electrical isolation condition.HNV500T is a kind of Hall voltage sensor with high insulation level.It adopts the principle of magnetic compensation,and it can survey each kind of voltage. These two sensors have the advantage of small volume, fast response speed, high precision,and they are easy to install and use.This system chooses the PCL-818L data acquisition card.PCL-818L uses the ISA bus,therefore this system must select a computer with ISA slot. PCL-818L which is produced by Advantech company has the advantage of high-performance,multi-function,low cost.This card whose data acquisition capability is powerful integrate the A/D converter,D/A converter,DI0 and timer/counter on a board,and it is well suited to the field of automatic monitoring and control which is based on PC. The part of system software design uses Visual C++ which is included by Visual Studio. NET 2003 programming development tool bag to carry on software development.Visual C++ is the most powerful programming tool in Windows platform,and its function covers all areas of Windows programming.When system starts to carry on the software design,it's necessary to use virtual instrument software to display data.Virtual instrument adopted by system is Measurement Studio which is an integrated package of Visual C + + environment.It provides a user interface component for measurement.Users can drag-and-drop and extend it so as to create a custom interface for measurement application.The system achieves some functions such as current and voltage signal monitoring,waveform playback,signal analysis and quality assessment and so on.When author attempts to achieve the current and voltage signal monitoring function,author finds that computer's memory is inadequate for long time monitoring.Arc welding process usually works for a long time,and the sampling frequency of data acquisition card is set to 20kHz for dual-channel collection.Each datum is stored in the type of float (single precision real number) which occupies 4 bytes in the memory,thus each data acquisition process gets two data which occupy 8 bytes totally.So data are sent to the memory at the speed of 160K bytes per second. If the system start to run and data are stored in a computer whose memory capacity is 256M,it's well known that the number of available memory is less than 130M under normal condition,even only 50M under special condition,so the system will cause dead halt fault only after 10 minutes due to insufficient memory.In order to solve the problem at zero cost,the system uses multithread technology.After the system uses multithread techonology,if the system run on a computer whose hard disk capacity is 80G,the problem of insufficient memory and hard disk capacity will not appear even if after 100 hours.Of course,any welding process doesn't works for 100 hours.This shows that the system has successfully solved the problem of insufficient memory capacity.This system can monitor arc welding process for a long time.When author attempts to achieve the waveform playback function,author finds that the screen only can show part of the waveform data because of the limited size.So author set the current and voltage waveform playback graph control to display only 2000 data each time.The system survey welding current and voltage at the sampling frequency of 20kHz,namely 20,000 data per second.Because graph control only can display 2000 data each time,so graph control must circularly display.At this time the system must confirm displaying time of each screen.If displaying time is very short,the refresh speed is too fast.The data's refreash speed is so quick that users have not enough time to observe them.If displaying time is very long,the refresh speed is too slow,and the playback efficiency is low.Because even if the data instantly refreash,refreash spead still can't reach sampling speed.Long displaying time means long interval between each screen.It is very time-consuming and inconvenient for users.To solve this problem, the system allows the users to set playback speed, playback speed can be adjusted very easily.This system's signal analysis function can obtain statistical graphics and statistical parameters which reflect welding quality by carrying on statistical analysis of welding current and voltage. System uses welding current and voltage to calculate the probability density of voltage,current,frequency of arcing time and short-circuit time and so on.The system displays these statistics in statistics graphics. In addition, the system shows current and voltage cycle map.This system's quality assessment function can obtain average short circuit time, average arcing time,variation coefficient of short-circuit and variation coefficient of arcing time as basic information of quality assessment.System adopts the sum of average short circuit time and average arcing time as fundamental criterion(the smaller,the better).On this basis,system adopts average value of variation coefficient of short-circuit and variation coefficient of arcing time as secondary criterion(the smaller,the better).If the sums of average short circuit time and average arcing time of two welding processes are very close(the difference does not exceed 2.5% of greater value),system uses secondary criterion as the ultimate criterion.The system can achieve the following applications:Users can optimize process parameters by using waveform playback function and signal analysis function;This system's quality assessment function may evaluate quality of welding processes,it can also be extended to evaluate welder's operation skill, welding equipment's performance,welding material's performance.In order to verify the reliability of the system, author uses CO2 arc welding equipment to do experiment.Experimental results show that system works well and can achieve each functional effectivelly.