In automated welding processes, especially arc and beam welding, reliable wire feeding is a key challenge. Increasingly, the welding wire is transported from logistically well-positioned wire drums to the main wire drive, which is located on a robot arm. The conveying distance can be more than 20 to 30 meters and often includes numerous bends. These lead to considerable friction within the wire feed hose, which hinders or, in extreme cases, blocks the wire feed. Each bend in the wire feed hose adds additional friction and, according to the Euler-Eytelwein rope friction formula
F2 = F1 – e(µ-α)
the tensile force with which the wire must be pulled through a hose increases exponentially with the wrap angle.
Symbol Meaning
F1 Tensile force on the loose side (for example at the wire drum)
F2 Tensile force on the pulling side (for example at the entry to the wire feeder)
µ Coefficient of friction between wire and hose or support
α Wrap angle in radians (not degrees!)
e Euler’s number ≈ 2.718
The coefficient of friction is also included exponentially in the formula. The coefficient of friction is a dimensionless number that indicates how much force is required to move two materials against each other – in relation to the normal force (i.e. the force with which they are pressed against each other). This is where modern wire conveyor hoses with pairs of rollers (roll liners) instead of plastic or steel spirals can show their advantages.
Due to the lower rolling friction compared to sliding friction, the coefficient of friction is considerably reduced and, as this enters the equation exponentially, the achievable effect is extremely significant. In large robot systems with a total wrap angle of more than 1000 degrees (e.g. wire guidance in several energy chains), the use of a roll liner is no longer sufficient to achieve process-stable wire guidance.
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Functional principle of the RoboFeed WireManager
The RoboFeed WireManager was developed to solve this problem. A continuously adjustable, constant feed force is used to press the wire electrode against the outside of the feed hose. This shifts the friction from the inside to the outside of the hose and the wire can no longer “tighten” on the inside of the hose. This works both with conventional wire conveyor hoses based on sliding friction and with the Rolliner. The bending angles that can be bridged increase to more than 2000 degrees and the lengths to more than 50 m. When optimally adjusted, the wire can be removed and checked at the end of the hose with minimal effort (two fingers). The robot’s wire feed unit therefore hardly needs to apply any feed force of its own to pull the wire through the preceding wire feed hose.
The decisive factor for the optimum function of such a wire drive is its sensitivity. The force with which the wire is pushed into the hose must be very finely adjustable in order to prevent the wire from clicking out, and the reaction to changes in speed on the part of the main drive must be very fast.
Autonomous operation without electrical coupling
A special feature of the system is its autonomous operation: the RoboFeed does not require an electrical connection to the robot or to the wire drive of the welding power source. It recognizes almost independently whether the main drive is running or stationary and automatically adjusts the wire feed. Regardless of whether the main drive is stationary or running at full speed, RoboFeed will always feed from behind with the same set force. However, an electrical interface (24 volts) is available for a start-stop signal.
Wire threading with a twist
The length of the wire feed hose can either be learned as part of a setup or set individually. In a threading process, the exact predetermined length is threaded at the push of a button and the drive then stops automatically. If the wire is blocked during threading (the wire feed hose is bent too tightly), the wire is automatically pulled back a certain length and then pushed forward again – until the preset distance has been reached or the operator stops the process.
Fill level control – avoid downtimes
The specific weight of the wire and the diameter can be used to calculate the quantity of wire transported by RoboFeed. This makes it possible to monitor the fill level of the container (wire drum or spool) and issue a warning if the quantity falls below a certain level. This warning is issued visually on the screen, via an electrical signal or by sending an email. In this way, the system operator is warned in good time before the wire runs out and is requested to prepare for the container change.
Prevent material mix-ups
A barcode scanner can be connected to the USB interface of RoboFeed WireManager. This allows the label of the wire electrode (Migal.Co label) to be read and the article number of the wire to be compared with a set article number. If they match, the wire is changed and the weight of the wire bundle is transferred to the settings. If the numbers are not the same, the wire change is rejected.
Determine arc times and wire consumption
The built-in stopwatch function can be used to determine the component-related wire consumption. It is also possible to measure the total welding time and the duty cycle (arc burning time) for a specific period of time.
Industry 4.0 functions
An Ethernet interface is available with the i4 version of the RoboFeed WireManager. This makes it possible to send an email if a minimum fill level is not reached. In addition, values for wire speed, wire charge, utilization, etc. can be transmitted to a higher-level computer at one-second intervals using the MQTT protocol.
Web:
www.migal.co
