Design of Ultrasonic automatic weld cartridge ring welding joint flaw detecting system

1. Weld cartridge ring welding joint ultrasonic detecting method

1.1  weld cartridge profile

Weld steel cartridge is  gun cartridge case that developed by state-run 753 factory。Its cylinder bottom and barrel body is produced by welding of circumferential weld machine。 At the welding place,the cylinder bottom thickness is 2.6mm,barrel body thickness is 1.6mm,forming 4--6mm wide circumferential welding joint after welded,and internal surface is ups and downs,   and irregular，when fire a shell,the pressure in cartridge is heavy,flaw in the welding joint may lead to a serious result。The military requests        detection on welding joint，In the welding joint ,it will exist air hole，transverse cracks、weld misalignment，to adapt to requirements of production line  volume production and automatic detection,combined to costs and other factors,adopting water immersion ultrasonic automatic testing method。

1.2  circumferential welding joint ultrasonic orthogonal scanning detecting scheme

Flaw has dot shape and line shape。By analyzing on cartridge case and circumferential welding joint，adopting like graph 1 scheme，from two directions to do quadrature detection on welding joint，cause this will not miss inspection, and also according to information achieved by two directions to do qualitative analysis on flaw，in graph 1,Three probes set on a probe frame，all adopt water immersion focusing probe。 The whole probes and cartridge that detected parts is immersed in water。

In graph1(a),probe 1 is launching probe,launched longitudinal wave transmission in water oblique incidence to cartridge,and produce A1 model plate wave。Plate wave will spread along with the direction that perpendicular to welding joint , at the same time of transmission,partly energy radiate o water as a form of longitudinal wave，the plate wave that cross welding joint up to a point,its radiation longitudinal wave energy received by probe 2。When plate wave acoustic beam crosses welding joint with air hole or weld misalignment,The signal that Probe 2 received will be decreased。

In graph 1(b),the longitudinal wave that launched by probe 3 oblique incidence to welding joint，and produces surface wave on welding joint，spread along with welding joint, when there are transverse flaws 、air hole in certain distance from the point of incidence on weld pass,surface wave along welding joint to reflect,the partial energy of reflecting echo radiate to water in the form of longitudinal wave,and received by probe 3 and formed flaw reflection echo signal。

By analyzing and comprehensive analysis on two sets probe signal ,can get welding condition of weld pass,this is basic principle and method of detecting。

2  automatic detecting system genera design

According to detecting scheme,detecting system should equipped with following function:

Two sets probe detect on the same place one after another,and deal with respective echo signal

Exact main features of echo signal so as to analyze and judge

For achieving whole weld pass information, cartridge and  probe must have relative motion,   Make the system detect the entire circumferential weld 

The whole system is controlled by microcomputer and data deal,according to detecting data to make conclusion automatically；

Meet unqualified cartridge case will alarm,and automatically mark at unqualified place,so as to be convenient to operators to do X ray inspection verification 。

According to above designed detecting system chart,as shown in graph2, microcomputer is monitoring center，it observes and controls as well as deals circuit to combine with other parts。Observing and controlling and dealing circuit including two sets launching circuit,echo signal preprocessing circuit, material position detecting circuit,marking controlling circuit,condition indicating circuit。Data collecting circuit is used for feature extract to processed echo signal,the whole work process of detecting system is :

1.   Firstly detect on cartridge case is place or not,if not in place then waiting ,giving indicating condition if in place;

2.   The double probes that Perpendicular to welding joint launch ultrasonic,receiving probe receives signal and then amplify 、 detection、sampling and save the data、signal probe launch ultrasonic and deal with useful signal and save;

3.  Under the control of microcomputer ,stepping motor rotates angle,by transmission system correspond to cartridge case to rotate to the next position;

4.  Repeat number 2 detection until cartridge rotates a round,At present,whole welding pass two sets probe detected data has been saved;

5. After data dealing and giving a conclusion ,if not qualified then alarming with marking at the place of unqualified,needing further processing,and then waiting for the next cartridge case ,repeat above steps 

3   multiple input -single output matching circuit 

Quadrature detection scheme requests to do two sets probe measurement on same point。For two sets ultrasonic is not aliasing,two sets probe should detect respectively one after another,later processor of two echos is basically same,but factory currently has CTS-23 type single channel detector,for using a channel to process two signals (adopt single channel flaw detector) ,designing matching circuit that multiple input-single output。   Electrical block diagram like graph 3,working principle is:under the control of computer,controlling unit first to let double probes launch,delay some time,open double probes multiplex switching channel,make signal received by double probes being preprocessing ,and use multiplex convertor enters flaw detector and process and extract later feature,then close double probes channel,let single probe launches,delay certain time,open single probe multiplex convertor,let flaw signal that received by single probe being preprocessing ,and do later treatment by multiplex convertor,then close single probe channel to accomplish this detecting job。Its working time series like graph 3 (b) shown,in echo signal,1  is wave in beginning ,2 is useful signal wave,3 is disturbing signal, disturbing signal amplitude is big and small ,sometimes  not exist,single probe crack flaw is gradually move to wave in beginning along with cartridge rotation,When move to some point ,its amplitude is the biggest.

4. Crack flaw feature extract circuit design

For double probes receive signal,when it has crack ,it shows signal amplitude decreased,waveform has little change,its main features is amplitude,by analyzing its frequency spectrum, the frequency spectrum will be wider when it has crack,according this  speciality,in the process of signal dealing,designing a band pass filter that suitable for signal that absence of defect ,thus when it has defect ,amplitude keeps decreasing。For single probe echo signal,when it has transverse crack ,appears crack signal,its strength is related to the size of crack,so its properties is also   signal amplitude,therefore ,for simplifying processing circuit and reducing dealing time,the function of feature extract circuit is collect peak value of useful echo signal 。 Due to echo signal after being dealt by flaw detector is pulse signal that has quick change on time domain，after signal passed,to keep signal peak value to do A/D transformation,designing shown in graph 4 two levels adaptation and protection circuit,the first level is consist of discrete component,take advantage of capacitance charge to collect peak value,when signal comes,using D1 charge C2,due to D1 single direction conductivity,after signal passed,the voltage in both ends of C2 is equal to signal peak value,but C2 has bad ability to maintain,so has little requirements on sampling speed,its maintaining properties is good,satisfying A/D transformation requirements。

Due to echo signal of single 、double probe group not only has useful signal,but also wave in beginning and disturbing signal,so it is necessary to control peak protection circuit according to  ultrasonic transmission time ,make it maintainedpeak value of useful signal ,and make disturbing signal not affect its output,before next sample,it is necessary to put off the electricity capacitor C2。