Hardware

4.2.1.1 Computer

A laptop computer, the Sony PCG-FX109K running Microsoft Windows 2000, was used both for control software development and for program execution. This laptop computer is the centre point of the developed systems.

4.2.1.2 Welding Equipment

The welding equipment includes the mechanised motion system and the arc welding equipment. A description of the equipment used follows.

4.2.1.2.1 Power Supplies

Lincoln Electric Power Wave F355i power supplies (PSs) were used in this work. These are digital robotic PSs which can be used in constant current, constant voltage and pulse welding modes depending on the configurations within the PS [102]. These PSs are part of the robotic range of products from Lincoln Electric. They work in conjunction with the Power Feed 10 Robotic wire feeder using the “ArcLink” protocol. ArcLink is an open, digital communications protocol from Lincoln Electric. ArcLink differs from other communications protocols as it was developed by Lincoln Electric for the welding industry and can be applied to a range of welding systems from manual metal arc to complex robotic welding systems [103].

The Power Wave F355i PS has a current range of 5 to 425A and a rated output of 350A, 34V at 60% duty cycle. Its physical dimensions are 372 x 530 x 437 mm and weight 45.1kg.

Figure 4.3 – Power Wave F355i power supply [104].

The Power Wave F355i PSs, which were designed for robotic applications, have no control pendant as this task is usually performed by the robot control pendant. In order to control them is possible also to connect them to a computer through an Ethernet cable. This

communication allows the pulse waveform to be tailored to the application needs using Wave Designer. For a better understanding on the software capabilities and functioning the user manual or brochure can be analysed [105]. It also allows control by specially developed software, as in the case of this project. This was possible since Lincoln Electric has made the communication protocol available for this project. The ability to communicate with the PSs was made possible by the use of a DLL package previously developed in agreement with Lincoln Electric for this project [106]. The Power Wave F355i PS(s) can be used in single, dual and tandem applications. In the last two options it can be either in synchronised or unsynchronised mode. In order to use the synchronised mode the use of a phase generator (System Interface) module is required.

4.2.1.2.2 Phase Generator

The System Interface module (K2282-1) will be referred as the phase generator throughout this thesis, as that is the function it serves in the system. See Figure 4.4. The phase generator ensures that in pulsed GMAW using a dual or tandem torch, the PSs waveforms are synchronised. In this case the waveforms are in anti-phase (180º apart).

Figure 4.4 – Lincoln Electric system interface [107].

4.2.1.2.3 Wire Feeder

The wire feeder used is also part of the robotic range of products from Lincoln, the Power Feed 10R (Figure 4.5). This wire feeder communicates digitally with the PS using ArcLink

communication protocol. The wire feeder has an inbuilt tachometer which provides accurate digital feedback of the wire feed speed [108].

The wire output speed ranges from 1.27 to 20.3 m/min and is able to feed solid wires of diameters between 0.6 to 2.4 mm. Its physical dimensions are 226x261x206 mm and weight 10.2 kg [109].

Figure 4.5 – Lincoln Electric Power Feed 10R [110].

4.2.1.2.4 Consumables

The three main consumables used to perform the experiments were the parent metal, the welding wires and the shielding gas. They will be described below.

4.2.1.2.4.1 Parent Material

The parent material used was a high strength X100 steel. This choice of steel is based on its use in several projects at Cranfield University.

4.2.1.2.4.2 Wires

The GMAW welding wire used throughout the experimental work was the 1.0 mm diameter CARBOFIL NiMo1. This wire was supplied by Air Liquide.

4.2.1.2.4.3 Shielding Gas

The shielding gas used in the experiments was the standard BOC gas “Trimix”. The gas mix proportions are 82.5% Ar, 12.5% CO2 and 5% He.

4.2.1.3 Motion Equipment

4.2.1.3.1 Welding Head

The welding head’s main function is to accurately position the welding torch(es) in order to perform the weld. For this purpose a Serimax Saturmax 5 welding carrier was utilised. The Saturmax 5 is a “bug on band” system. By “bug on band” should be understood a welding carrier performing its motion around the pipe attached to a band that embraces the pipe. The carrier has three motion axes: translation (transverse to the weld); oscillation; and up/down.

The welding head also includes as standard an inclinometer which allows angular position measurement around the pipe. The gain from the use of the inclinometer is the possibility to control the welding carrier’s position around the pipe. By this it is the possible to place the

welding carrier at any specific location around the pipe or to home it with an accuracy of less than a tenth of a degree. Another advantage is the possibility to adjust the welding parameters according to the bug angular position. Further details concerning the inclinometer can be found in section 4.2.1.3.3.

The standard welding head can be seen in Figure 4.6. Some modifications were necessary in order to be able to accommodate one or two Cranfield tandem torches. It was also necessary to create a bracket to attach the sensor to the welding carrier (Figure 4.7). A description of the bracket and its manoeuvrability is given in section 6.1.1.2 (page 68).

Figure 4.6 – Saturmax 5 (standard torch configuration)

Figure 4.7 – Saturmax 5 (adapted tandem torch and laser sensor)

Legend Figure 4.6

1. Single Wire Torches.

Legend Figure 4.7

1. Tandem Wire Torch;

2. Laser Vision Sensor.

The standard welding head motion controller was specific to the Serimax head control package. In order to ease the portability of the system across different manufacturers a commercial motion controller was acquired and applied to the system. An in depth description of motion controller system is given in 4.2.1.3.4 (page 36).

4.2.1.3.2 Band-On-Pipe System

The band-on-pipe system used to perform the first part of the experimental work was the Serimax system. The system constitutes a pipe band for 38 inch outside diameter pipes and the Saturmax 5 welding head. The welding head is described in section 4.2.1.3.1. The pipe band can be seen in Figure 4.8.

1 1

1

2

Figure 4.8 – Serimax pipe band.

4.2.1.3.3 Inclinometer

The inclinometer hardware inside the Saturmax 5 is a SX 42400 Series tilt sensor from Sensorex. This tilt sensor has a working range of two times hundred and forty degrees and cannot retrieve values in the entire circumference. To overcome this limitation two tilt sensors are used. The use of two of these sensors combined and an algorithm to calculate the angle, allows having precise positioning control around the entire pipe.

Connections in the welding head were made to the motion controller analogue inputs so that the values could be transmitted to the computer. In order to develop the algorithm several trials were made to collect data from the sensors. These algorithms are described in 4.2.3.1.1 page 43.

4.2.1.3.4 Motion Controller

The motion controller utilised for this work is a DMC-2280 from Galil Motion Control. This equipment is an eight axes motion controller with two methods of communication to the PC, Ethernet (10/100 Base-T) and Serial Port (RS-232). The connection used during this project was Ethernet.

Figure 4.9 – Galil motion control DMC-2280 [111].

4.2.1.3.5 Amplifiers

Two types of amplifiers were used, the Galil Motion Control ICM/AMP 1900 and the Advanced Motion Controls 12A8K. The Galil amplifier (Figure 4.10) has four on board servo drivers. For the band-on-pipe phase of the experiments one of these drivers was required and two for the second phase. As two of the welding head motors have an inductance outside the amplifier working range two Advanced Motion Control amplifiers (Figure 4.11) were required for the initial phase. For the second phase of the experiments the travel direction is controlled by the sliding table motor. This new motor has a higher inductance than the welding head one, so the new motor was wired to the Galil Motion Control amplifier and one of the Advanced Motion Control amplifiers was no longer required.

Figure 4.10 – Galil motion control ICM/AMP 1900 amplifier [112].

Figure 4.11 – Advanced Motion Controls 12A8K [113].

4.2.1.3.6 Calibration

4.2.1.3.6.1 Welding Carrier Axes

In order to calibrate the three welding head axes, different distances were measured against the encoder steps moved using a measuring tape. This way the accurate length of the encoder step was obtained for each of the three axes.

During the development of the control software it was noticed that there was a physical limitation in the oscillation motion. If the oscillation width was over 5mm there was a limit to the oscillation speed. On further investigation it was observed that there was a compromise between the oscillation speed and width in this equipment. This compromise was converted into a relationship that was embedded in the control software. In order to verify the accuracy of oscillation motion, a linear resistor was attached to the main body of the welding head with the shaft attached to the oscillation arm (Figure 4.12). This resistor was then inserted in a voltage divider circuit (see Figure 4.13) and the voltage at the linear resistor was measured with the digital oscilloscope mentioned in section 7.1.1.3.

Figure 4.12 – Linear resistor attached to the welding head.

Legend:

1. Resistor;

2. Oscillation Arm

Figure 4.13 – Voltage divider circuit.

1

2

4.2.1.3.6.2 Inclinometer

The inclinometer built-in the welding head includes two tilt sensors, SX 42490 from Sensorex.

In order to utilise the inclinometer the signals from both tilt sensors had to be connected to the motion controller terminals. This was achieved by a pull-down 470 resistor and a 4.7µF capacitor to the GND pin. From there the signals can be accessed by the computer where they are appropriately processed to obtain the welding head angular position. This was developed with the intent of controlling the parameter based on the bug’s angular position around the pipe.

Each of the tilt sensors outputs a current between 4 to 20mA that corresponds to the hundred and forty degrees range that they can measure. This current is then converted into a voltage in the motion controller. The obtained voltage ranges from 1.88 to 9.37 V. The combination between the voltage range limits and the values of both sensors will indicate the welding head angular position around the pipe. The algorithm developed to achieve the angular position value will be explained in 4.2.3.1.1 (page 43). As can be seen in Figure 4.14, each of the tilt sensors covers two 140º regions. According to [114] the tilt sensor has an accuracy higher than 1º. The combination of both tilt sensors resulted in the experimentally confirmed resolution of 0.1º. This value was confirmed with a digital inclinometer that has a precision of 0.1º.

Figure 4.14 – Inclinometer coverage diagram [115].