Method for welding wire consumption optimization.

Sintea, Sorin ; Cooper, Edward ; Grebenisan, Dan 等

1. INTRODUCTION

In welding plants were welding process is made using automated welding machines or welding robots, the main concerning of operators is focused in monitoring quality of welding. For this they monitor arc welding parameters (welding voltage, welding current, welding gas pressure). Using these measured parameters the welding controller trying to keep welding current into preset domain of values (Joni N. & Trif N.2005).

We propose to monitor the wire parameters (wire speed and wire consumed quantity) and include them automation controlled process. Using wire speed control we can include a new major loop in welding process control. This new control loop can inform process about:

* Status of welding wire motor load;

* Status of welding wire mechanism;

* Any jam or obstruction of welding wire.

Monitoring this parameter we can warn operator about problems with welding wire, and stopping in time of a poor welding. Another important parameter is warning of welding wire drum limit. This parameter is important for inform welding engineers and supply department to prepare a new drum unit for welding unit (Schmidt, J. S. 2002).

All these features are provided by Wizard View 1 controller, produced by ELCo Enterprises Inc, USA (ELCo Enterprises Inc. 2008).

[FIGURE 1 OMITTED]

2. CONTROLLER

This controller is a new entry in welding automation line controllers. The controller measuring wire speed using ELCo's HHSS wire speed sensor and local display the current wire speed and consumed wire quantity (see Fig. 1.) (ELCo Enterprises Inc. 2008). The controller is able to measure values all the time or only in active welding interval, for this the controller can be enabled or disabled using a signal connected to automated welding machine (ELCo Enterprises Inc. 2008). The controller has two operating modes:

* Simply counter--in this mode the controller counts the total weight of wire consumed in welding process;

* Controller mode--in this mode the unit outputs through two relays. One relay indicates when wire speed exceeds a preset low limit value measured. The other one relay indicates when counted welding wire is overtaking the drum warning level.

All internal data of Wizard View Controller can be accessed through serial port.

We are using this Wizard View 1 controller in controller mode and both outputs connected with welding programmable logic controller (PLC).

3. SOLUTION

In most solutions we have a welding PLC associated with a welding unit (Joni, N. & Trif, N. 2005). This PLC is responsible with welding process. One solution is to add the Wizard View 1 controller outputs to the PLC inputs and to update the PLC software to monitor and get the right decisions in according with these inputs. In big welding plants it is not a problem, because there is "Software for Automation Department" and they can make this update.

In small plants, where we do not have possibility to change the software in controllers, we can addition a PLC to the welding unit, to monitor welding parameters (Margineanu, I. 2005). On this PLC we can add the normal welding parameters (welding voltage, welding current, welding gas and a signal from welder named RUN. The "RUN" signal is active when welding cell is welding or can be active when operator or robot is in welding interval.

3.1 Implementation

We can choose a PLC (see Fig. 2.) with one CPU, three modules (one 8 optoisolated digital inputs, one with four 0-10 Volts (or 0-5 Volts) isolated analogue inputs and one with 8 relays output digital module) and optional an Ethernet module (if CPU does not have Ethernet capabilities on board) (Direct Logic. 1998). For implementation we take Koyo PLC model DL-205 with DL-240 CPU unit.

To the PLC we add the following signals:

* digital inputs: RUN is the running signal which indicate that operator or robot is in welding process; SPD_OK is the "Normal Speed" digital output of Wizard View 1 controller and DRUM_WARN is the "Drum Warning" signal generate by Wizard View 1 controller

* analogue inputs: U is the analogue input connected to welding voltage through resistive divider (100:1), I is analogue input connected to welding current using a current transformer and GAS is analogue input connected to the gas pressure sensor.

* digital outputs: WELD_OK indicates that all welding parameters are in normal limits, WELD_NOK signal indicates that at least one parameter is out of limits and WIRE_WARN signal indicates that welding wire reach the preset value in Wizard View 1 controller.

[FIGURE 2 OMITTED]

3.2 Programming

In PLC software we implement the algorithm for welding monitoring. Our implementation is made on KOYO Direct Logic-205 PLC with DL240CPU (Direct Logic, 2008). For implementation we declare the following constants in CPU memory:

* voltage sensor constant in location V2100,

* current sensor constant in location V2101,

* gas pressure sensor constant in location V2101,

* lower preset value for welding current in location V2103,

* lower and upper value of welding voltage in locations V2104 and V2105,

* lower level of gas pressure in location V2106.

The algorithm is based on following mathematical and logic relations:

* converting the input analogue signals in decimal floating point format (Zaciu, R. 2002):

V2110 = K0 x V2100 (1)

V2111 = K1 x V2101 (2)

V2112 = K2 x V2102 (3)

where, relations describe the conversions for voltage, current and gas pressure measures.

* comparing of analogue signals with presets and establish the values for internal Boolean variables which describe the status of welding:

C1 = V2111 > V2102 (4)

C2 = V2110 > V2104 (5)

C3 = V2110 < V2105 (6)

C4 = V2112 > V2106 (7)

C5 = X0 & C1 & C2 & C3 & C4 & X1 (8)

where, C5 variable describe the correct status of welding.

* generating normal and correct welding output signal:

Y0 = X0 & C5 (9)

* generating out of limits welding output signal:

Y1 = X0 & ! C5 (10)

* generating drum warning signal in time of welding:

Y2 = X0 & X2 (11)

and optional, we can generate a drum warning signal

Y3 = X2 (12)

The PLC can be equipped with an Ethernet module, to be able to send an e-mail when quantity of consumed wire reaches the preset value. The e-mail is send to a central server or direct to "Service Team" or to the "Supply Department" to minimize the time request for supplying with welding wire drum.

4. RESULTS

By introducing the wire speed factor in welding analysis we can monitor the status of wire supplying mechanism; and we can detect problems quickly. Detecting wire supplying mechanism problems in time, we can avoid other unexpected stopped time in welding process and eliminated death time.

By adding this new feature to welding units we can short the time with supplying with wire of welding automated machines. This can increase the productivity and can automate the supplying process in the entire plant.

5. CONCLUSIONS

This system presents a new vision in optimising the welding wire consumption and minimizing the time request for supplying with wire welding in automated plants.

The system can be developed in future by adding new features in PLC and introducing the fuzzy logic algorithms in detecting of the correct generating of WELD_OK signal. Also the PLC can be programmed to send data over Ethernet port to a central server, for creating of central welding monitor system. All data centralized on the server level can be accessed by anyone who is involved with welding process from the plant.

Another changing in presented system can be obtained by replacing the DL240CPU with WinPLC CPU for Direct Logic 205 PLC. The WinPLC CPU is based on WindowsCE operating system. All software can be made using Microsoft Visual Basic or Microsoft Visual C and the most important advantage is possibility to present all data and welding status on internal web site. The WinPLC system has internal web server integrated.

6. REFERENCES

Direct Logic. (1998) DL205 User Manual, Koyo, PLC Direct Inc, D2-USER-M, USA

ELCo Enterprises Inc. (2008). Wizard View 1. User Manual, rev. D., ELCo Enterprises Inc, -, Jackson, Michigan, USA,

Joni, N. & Trif, N. (2005). Automated Electrical Arc Welding, LUX Libris, ISBN 973-9495-34-3, Brasov, Romania,

Margineanu, I. (2005). Programmable Controllers, Blue Editor, ISBN 973-650-156-6, Cluj Napoca, Romania

Schmidt, J. S. (2002). Protocols for interconnecting the components of a welding system, -, IIW DOC XII-1697-02, Lisboa

Zaciu, R. (2002). Signals Digital Editing, Blue Editor, ISBN 973-650-095-0, Cluj Napoca, Romania