*Online Measurements in Welding Processes DOI: http://dx.doi.org/10.5772/intechopen.91771*

its implementation in an embedded device. The actual application area is automatic

Automatic welding is affected by disturbances in the production parameters and welding conditions. Variations in components' position and dimensions, weld joint misalignment, oil in the surface and other improprieties in materials, instability in welding wire speed, and shielding gas flow are examples of disturbances. However, by adding measuring systems, the control system may have a better performance when disturbances are found. For this purpose, the disturbances and affected variables must be measured or estimated online, to counteract the effects of the disturbances through the control actions. These variables can be different in each process type or change your significance in the process. Some variables can be measured directly from the welding power source or using indirect measuring techniques, and others need to be estimated from measured variables. This last group includes the

In welding processes, the variables can be classified depending on whether they can be measured or modified and if these actions can be done online or offline. Responding to this classification, the variables in welding processes can be divided

• Fixed, which cannot be modified by the operator but defined in the process

• Adjustable offline, which can be modified only before starting the process

• Quantifiable offline, which is measurable only after the process ended

The most common measurement variables in welding are related to the power supplied to the process by the unit of material length or area, and most are defined or measured by the power source. In conventional arc welding processes, these variables are *electric voltage*, *intensity of electric current* (also called simply *amperage* or *welding current*), and *wire feed speed* in processes with material addition. The parameters to control the waveform of voltage or electric current in the advanced arc welding process are important also. Other variables can be necessary to define and know, as *gas flow*, *pre-gas time* and *post-gas time*, *source impedance*, and time or position when the arc is open and closed (*arc status*). In laser welding processes, *laser power*, *pulse rate*, *focal distance*, and *spot size* are

The modern welding power sources have one or various microcontrollers or

microprocessors to control source operations, data acquisition, and

An example of variables and groups for the constant voltage GMAW orbital process is shown in **Figure 1**, and some measurement techniques are described in

• Adjustable online, which can be modified during the process

• Quantifiable online, which is measurable during the process

control, arc welding, and sensor fusion research.

**2. Measurements in welding processes**

*Welding - Modern Topics*

weld bead depth or penetration.

into five basic groups [8]:

design

the following sections.

important too.

**80**

**2.1 Measurement of welding variables**






#### **Figure 1.**

*Variables and classification groups to conventional constant voltage gas metal arc welding (GMAW) process (adapted from [8]).*

communications. The communication interface usually implements a serial protocol or digital and analogical inputs and outputs to obtain or send information from an external supervisory control system (computer, programmable logic controller, and robotic system, among others). This interface can be used to synchronize work between power sources and robotic systems, other machines, control levels, or factory management. The welding variables, as voltage, electric current, and wire feed speed, can be measured and modified using this interface. Some commonly used standard network protocols are RS-232, RS-485, Modbus (RTU, TCP, or UDP), CAN Bus, DeviceNet, Field Bus, and Ethernet. Other companies define their protocol such as the Arclink developed by Lincoln Electric and SpeedNet by Fronius.

The communication protocol can be "open" or "proprietary." In the first case, the user can communicate his control system directly with the power source using the communication protocol description. In the second case, he needs to buy and use proprietary software or hardware. The implementation of protocols used in

The *forehand angle* or *attack angle* is the torch angle side view relative to the base

The *contact tip-to-work distance (CTWD)* can be obtained from the robot control system related to torch or piece position, or it can be measured with a laser distance sensor. Other variables, such as *electrical stick-out* or *electrode extension* and *arc length* (see **Figure 4**) need more complex procedures to obtain a measurement because they depend on the fusion rate. All these variables are expressed in longitude unit,

The first method to obtain the *CTWD* is more economical but has low accuracy. The zero references of the robotic system are calibrated with the workpiece position, but the surface variations and thickness of the material can affect the accuracy of the value. In arc welding processes, small variations in CTWD can affect the electric resistance of the arc, and consequently, the welding current and the heat input can be significantly affected. For example, reduction of the arc length causes

*Contact tip-to-work distance and electrical stick-out (or electrode extension) differences (adapted from [11]).*

metal surface, which is the angle in direction of torch travel. The *work angle* is defined by the torch angle end view relative to the base metal surface as shown in **Figure 3**. These angles can be fixed before starting the welding and staying constant or can be controlled by the robotic system. In the second case, the angles can be

calculated or obtained from the robotic system also.

*Online Measurements in Welding Processes DOI: http://dx.doi.org/10.5772/intechopen.91771*

**2.3 Measurement of contact tip-to-work distance**

*Welding speed, torch angles, and orbital angle (adapted from [10]).*

such as *mm*.

**Figure 3.**

**Figure 4.**

**83**

#### **Figure 2.**

*Fronius interface to translate the information between serial protocol and data acquisition system with digital and analogical inputs and outputs.*

modern power sources is serial<sup>2</sup> , and information is obtained or sent in digital format.

The old welding power sources can have an interface with digital and analogical inputs and outputs, to let the monitoring and control of the source. These power sources need a dedicated data acquisition and control system to convert the analog values in digital information and vice versa. The user, using this system, can monitor and control the power source operation partially or fully. To design or select the system, the sampling time, resolution and range of analogical inputs and outputs, and range and type of digital inputs and outputs, based on the power source characteristics and application requirements, should be considered.

Some manufacturers offer hardware interfaces to translate the information from serial protocol to digital and analogical inputs and outputs. If you do not have conditions to use a serial protocol, these interfaces can help to get and send information to power sources. These systems can be more slow, inaccurate, and inefficient than serial protocol, because of the sequential conversions from analogical to digital (on the source), from digital to analogical (on the interface), and from analogical to digital again (on the acquisition system). The ROB 5000 of Fronius, shown in **Figure 2**, is an example [9].
