The influence of the welding circuit cable routing on reproducible welding results is often underestimated. The following points must be considered when planning a welding system:
Possible setup errors and how to optimize them |
Possible setup errors and how to optimize them: e.g., separate current paths |
The influence of the welding circuit cable routing on reproducible welding results is often underestimated. The following points must be considered when planning a welding system:
Possible setup errors and how to optimize them |
Possible setup errors and how to optimize them: e.g., separate current paths |
The welding circuit contains different materials and cross-sections, as well as contact resistances at the coupling points.
In a series circuit, the resistances add up; large power losses and voltage drops can occur.
The contact resistances at coupling points vary greatly with the contact force and the surface condition.
Resistances of the different materials | Resistances of the coupling points |
R1 HP Con | Interconnecting hosepack | R C1 | Welding positive lead to power source |
R2 HP | Torch hosepack | R C2 | Extension hosepack |
R3 GD | Return lead cable | R C3 | Torch hosepack |
R4 WP | Workpiece, work table | R C4 | Torch body |
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| R C5 | Welding table or clamp |
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| R C6 | Welding negative lead to power source |
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R | Total resistance (= sum of all individual resistances) |
The welding circuit contains different materials and cross-sections, as well as contact resistances at the coupling points.
In a series circuit, the resistances add up; large power losses and voltage drops can occur.
The contact resistances at coupling points vary greatly with the contact force and the surface condition.
Resistances of the different materials | Resistances of the coupling points |
R1 HP Con | Interconnecting hosepack | R C1 | Welding positive lead to power source |
R2 HP | Torch hosepack | R C2 | Extension hosepack |
R3 GD | Return lead cable | R C3 | Torch hosepack |
R4 WP | Workpiece, work table | R C4 | Torch body |
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| R C5 | Welding table or clamp |
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| R C6 | Welding negative lead to power source |
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R | Total resistance (= sum of all individual resistances) |
The welding circuit contains different materials and cross-sections, as well as contact resistances at the coupling points.
In a series circuit, the resistances add up; large power losses and voltage drops can occur.
The contact resistances at coupling points vary greatly with the contact force and the surface condition.
Resistances of the different materials | Resistances of the coupling points |
R1 HP Con | Interconnecting hosepack | R C1 | Welding positive lead to power source |
R2 HP | Torch hosepack | R C2 | Extension hosepack |
R3 GD | Return lead cable | R C3 | Torch hosepack |
R4 WP | Workpiece, work table | R C4 | Torch body |
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| R C5 | Welding table or clamp |
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| R C6 | Welding negative lead to power source |
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R | Total resistance (= sum of all individual resistances) |
The resistance of a current-carrying cable depends on the cross-section, material, and length.
A high resistance causes a voltage drop and thus a power loss in the welding circuit.
Adequate dimensioning of the cable cross-sections can counteract this.
Recommended minimum cable cross-sections for uncooled copper cables and 100% duty cycle:
Welding current | Cable length up to 10 m | Cable length up to 50 m |
---|---|---|
150 A | 16 mm² | 25 mm² |
200 A | 25 mm² | 35 mm² |
250 A | 35 mm² | 50 mm² |
300 A | 50 mm² | 70 mm² |
400 A | 70 mm² | 95 mm² |
500 A | 95 mm² | 120 mm² |
600 A | 120 mm² | 2 x 95 mm² |
IMPORTANT! Position and fix components isolated to earth potential to avoid parallel resistances and current flows.
Every current-carrying conductor generates a magnetic field. If the amperage changes, the changing magnetic field induces a voltage. The voltage counteracts the change in current.
The inductance corresponds to the resistance to a change in current.
If the effective area between two conductors increases, the area of the magnetic flux increases and so does the inductance.
Inductances | Calculation of inductances from |
L1 | Inductance of positive pole winding | N1 | Number of welding positive lead turns |
L2 | Inductance of return lead cable winding | N2 | Number of welding negative lead turns |
L3 | Inductance from total area | A1 | Welding positive lead winding area |
A2 | Welding negative lead winding area | ||
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| A3 | Effective area |
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| µr1-µr3 | Permeabilities due to material in the areas |
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L | Total inductance (= sum L1 + L2 + L3) |
The inductance L [µH] increases due to the surrounding materials with their permeability µr and squares with the number of turns N of a conductor.
With the included area A and the materials µr, the inductance can be approximated using the formula for the ring-shaped air coil µ0:
N | Number of turns [1] |
A | Effective area [m2] |
l | Conductor length [m] |
| Magnetic field constant [Vs/Am] |
| Relative permeability [Vs/Am] |
IMPORTANT! |
Every current-carrying conductor generates a magnetic field. If the amperage changes, the changing magnetic field induces a voltage. The voltage counteracts the change in current.
The inductance corresponds to the resistance to a change in current.
If the effective area between two conductors increases, the area of the magnetic flux increases and so does the inductance.
Inductances | Calculation of inductances from |
L1 | Inductance of positive pole winding | N1 | Number of welding positive lead turns |
L2 | Inductance of return lead cable winding | N2 | Number of welding negative lead turns |
L3 | Inductance from total area | A1 | Welding positive lead winding area |
A2 | Welding negative lead winding area | ||
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| A3 | Effective area |
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| µr1-µr3 | Permeabilities due to material in the areas |
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L | Total inductance (= sum L1 + L2 + L3) |
The inductance L [µH] increases due to the surrounding materials with their permeability µr and squares with the number of turns N of a conductor.
With the included area A and the materials µr, the inductance can be approximated using the formula for the ring-shaped air coil µ0:
N | Number of turns [1] |
A | Effective area [m2] |
l | Conductor length [m] |
| Magnetic field constant [Vs/Am] |
| Relative permeability [Vs/Am] |
IMPORTANT! |
When welding with high inductances, rapid current changes can no longer take place at the desired rate of change because the maximum voltage of a power source (= ULimit) is insufficient.
This is particularly noticeable with pulsed arcs and long hosepacks with high inductances in the welding circuit.
Low inductance | High inductance |
At high inductance, the current actual value Iact does not reach the target current flow Iset due to the limited socket voltage Uclamp.
Sequence A1 - A2: | Sequence B1 - B2: |
Same settings for sequence A1 - A2 and B1 - B2.
The welding circuit resistance and the welding circuit inductance are determined via the power source in the course of the R/L alignment.
After positioning the contact tip and starting the R/L alignment, the voltage drop and inductance in the entire welding circuit are determined. The ohmic resistance and the inductance are used to correctly document the arc voltage display and for process control.
IMPORTANT! |
Start R/L alignment:
The inductance in the welding circuit varies with the measuring position.
When the position is changed, the effective area of the welding circuit changes and, as a result, the inductance changes. The conditions for droplet detachment are not constant.
The power source calculates an instantaneous value of inductance for the pulse, PMC, and CMT welding processes, and the process controllers can better respond to inductance changes.
Position 1: | Position 2: |
IMPORTANT! |
Standard values of welding circuit resistance R and inductance L for possible process interference:
Welding process | R [mOhm] | L [μH] |
---|---|---|
Conventional dip transfer arc * | ≤ 50 | ≤ 30 |
Pulsed arc * | ≤ 25 | ≤ 40 |
Spray arc ** | ≤ 60 | ≤ 80 |
Assumptions:
* | Welding current 120 A, filler metal ø 1.2 mm, shielding gas M21 |
** | Spray arc with 300 A, filler metal ø 1.2 mm, shielding gas M21 |
Depending on the power source type, operating point, characteristic property, and interference, the recommendation may differ.
Spray arc
The spray arc is most insensitive to high currents due to its almost constant current flow.
Conventional dip transfer arc
The short-circuit behavior is event-oriented.
LSC (Low Spatter Control)
With its prediction-oriented dip transfer arc strategy, LSC is sensitive to high inductances.
The disruption of the inductive decay behavior is significantly improved with the aid of an electronic switch in the welding circuit (e.g., hardware, TPS 400i LSC ADV).
CMT
Due to the cyclic process adjustment with each forward and backward movement of the wire electrode, CMT is between LSC and LSC ADV.
Pulsed arc
Pulsed arc variants are the most sensitive because high pulsed currents require low resistances and low inductances.
Adjusted PMC multi-arc characteristics with reduced rates of change and reduced current levels can be used as a remedy.
If an electrical conductor is in a magnetic field, a resultant force acts on it.
This is known as the Lorentz force and it depends on the current direction, magnetic field direction, and their orientation to each other.
Even the smallest magnetic force effects generate a geometric deflection of the arc.
This undesirable interaction is referred to as "magnetic arc blow".
MIG/MAG weldability depending on magnetic flux density:
Very good | Good | Average | Poor | Impossible |
≤ 2 mT | 2-4 mT | 4-6 mT | 6-8 mT | ≥ 8 mT |
≤ 20 Gauss | 20-40 Gauss | 40-60 Gauss | 60-80 Gauss | ≥ 80 Gauss |
Magnetized components can deflect an arc and interfere with droplet detachment.
The current-carrying wire electrode and the arc plasma also generate concentric magnetic fields, which are distorted at component ends and uneven air gaps and also exert a deflecting force on an arc.
Current-carrying parts of a clamping device retain a residual magnetism (= remanence) if they are made of a ferritic material. Aluminum, copper, and austenitic steels do not retain remanence.
Force effect on the arc due to magnetic fields:
The strength of the magnetic field in the component depends on the current level, the magnetic conductivity (material), the cross-section, and the number and size of the air gaps in the magnetic circuit.
Welding over the premagnetized current path can have a negative effect on stability.
Arc blow away from the ground connection:
The position of the earthing clamp is crucial for the current flow direction and its magnetic field in the component.
The electric current always chooses the shortest distance, with the same materials and cross-sections, and determines the arc deflection direction opposite to the earthing clamp.
Determination of the force effect on the arc:
by means of the right-hand rule
Thumb in welding current direction
Index finger in the direction of the magnetic field lines
Middle finger points in force direction
If an electrical conductor is in a magnetic field, a resultant force acts on it.
This is known as the Lorentz force and it depends on the current direction, magnetic field direction, and their orientation to each other.
Even the smallest magnetic force effects generate a geometric deflection of the arc.
This undesirable interaction is referred to as "magnetic arc blow".
MIG/MAG weldability depending on magnetic flux density:
Very good | Good | Average | Poor | Impossible |
≤ 2 mT | 2-4 mT | 4-6 mT | 6-8 mT | ≥ 8 mT |
≤ 20 Gauss | 20-40 Gauss | 40-60 Gauss | 60-80 Gauss | ≥ 80 Gauss |
Magnetized components can deflect an arc and interfere with droplet detachment.
The current-carrying wire electrode and the arc plasma also generate concentric magnetic fields, which are distorted at component ends and uneven air gaps and also exert a deflecting force on an arc.
Current-carrying parts of a clamping device retain a residual magnetism (= remanence) if they are made of a ferritic material. Aluminum, copper, and austenitic steels do not retain remanence.
Force effect on the arc due to magnetic fields:
The strength of the magnetic field in the component depends on the current level, the magnetic conductivity (material), the cross-section, and the number and size of the air gaps in the magnetic circuit.
Welding over the premagnetized current path can have a negative effect on stability.
Arc blow away from the ground connection:
The position of the earthing clamp is crucial for the current flow direction and its magnetic field in the component.
The electric current always chooses the shortest distance, with the same materials and cross-sections, and determines the arc deflection direction opposite to the earthing clamp.
Determination of the force effect on the arc:
by means of the right-hand rule
Thumb in welding current direction
Index finger in the direction of the magnetic field lines
Middle finger points in force direction
Two adjacent arcs with the same current direction attract each other.
The smaller the angle and the shorter the distance between the wire electrodes, the greater the mutual attraction.
I1 | Welding current of leading electrode |
I2 | Welding current of trailing electrode |
B1 | Magnetic flux due to the leading electrode |
B2 | Magnetic flux due to the trailing electrode |
F1 | Deflection force due to the leading electrode |
F2 | Deflection force due to the trailing electrode |
An arc in the pulsed phase exerts a strong magnetic field on the second arc.
Welding away from ground is advantageous because both arcs are forced forward.
Synchronized characteristics with high plasma pressure at high amperage have been developed for TWIN welding.
Demagnetizing components reduces the arc blow and is achieved by means of cyclic remagnetization. Lifting magnets or demagnetizing devices can be used for cyclic remagnetization.
Applications include in pipeline construction or for components with production- or transport-related residual magnetism.
Simple alternative if the lifting magnet has no demagnetizing function:
Use of a TIG AC power source (e.g., iWave AC/DC) + short-circuited grounding cables on the wrapped component while reducing the current amplitude.
Demagnetizing with iWave AC/DC:
If several arcs are being used to weld one component or in one welding cell, the routing of the hosepacks and grounding cables is a decisive factor in their mutual interference.
The following figure shows two parallel grounding cables.
The red cable (a) has current flowing through it and induces a voltage in the gray cable (b).
The magnitude of the induced voltage is described by the coupling factor (M).
The coupling factor is inversely proportional to the distance (d). The greater the distance, the lower the induced voltage.
A minimum distance of 30 cm is recommended.
Routing the return lead cables together in a ferritic channel (e.g., iron rail) strengthens the coupling.
Avoid routing the return lead cables together in a ferritic channel!
If several arcs are being used to weld one component or in one welding cell, the routing of the hosepacks and grounding cables is a decisive factor in their mutual interference.
The following figure shows two parallel grounding cables.
The red cable (a) has current flowing through it and induces a voltage in the gray cable (b).
The magnitude of the induced voltage is described by the coupling factor (M).
The coupling factor is inversely proportional to the distance (d). The greater the distance, the lower the induced voltage.
A minimum distance of 30 cm is recommended.
Routing the return lead cables together in a ferritic channel (e.g., iron rail) strengthens the coupling.
Avoid routing the return lead cables together in a ferritic channel!
I1 | Target welding current power source 1 |
I2 | Target welding current power source 2 |
U1 | Required voltage welding circuit 1 |
U2 | Required voltage welding circuit 2 |
Uc | Coupling voltage |
The figure shows the idealized current waveforms (I) in red and the idealized voltage waveforms (U) in blue of two power sources.
Power source 1 induces a coupling voltage (Uc) into the welding circuit of power source 2 during welding.
This coupling voltage adds to or subtracts from the arc voltage and distorts the actual ratios of arc length and droplet detachment and their measured values for the second power source.
As a result of this interference, a cyclic change in arc length occurs.
The figure also shows a typical setup with parallel hosepacks and return lead cables, which couple mutually induced voltages. Separating the welding circuits or having a sufficient distance between the current-carrying conductors does away with this magnetic coupling (see also page (→)).
Simplest way to check coupling in the event of welding process instabilities:
Weld with only one arc at a time on the component and compare the welding result.
Uneven seam progression with interference voltage coupling into the welding circuit:
The arc changes that lead to this undesirable welding result are visible in the high-speed image and also to the naked eye.
Remedial measures as described in the optimization examples starting on page (→) reduce the arc length disruption.
A good welding result with a stable arc length is achieved.
Start welding circuit coupling:
IMPORTANT! The work steps must be performed on both power sources!
0 mOhm / 0%
Two completely separate welding circuits
High mOhm value
A great deal of static coupling, e.g., through shared grounding cables
High % value
A great deal of dynamic coupling, e.g., due to closely positioned, parallel hosepacks or return lead cables of external power sources
If two return lead cables or hosepacks are routed or wound together in one ferritic rail, this increases the mutual interference and thus the dynamic coupling.
The evaluation of the measurement results is divided into four ranges. If the measurement results fall within the lower two ranges, the welding circuits on one component should be optimized.
If several arcs are being used to weld one component, the coupling values of the individual welding circuits in relation to each other should be determined. The individual coupling values add up when all arcs magnetically influence each other.
Recording the individual current paths and measuring, analyzing, and modifying them in pairs simplifies optimization of the welding circuits.
How to perform a coupling measurement:
To achieve reproducible welding results, the electric welding circuit must be planned and optimized if necessary.
In addition to the position and length of the return lead cables, their attachment is also crucial to achieving welding results of consistent quality.
To achieve reproducible welding results, the electric welding circuit must be planned and optimized if necessary.
In addition to the position and length of the return lead cables, their attachment is also crucial to achieving welding results of consistent quality.
To achieve reproducible welding results, the electric welding circuit must be planned and optimized if necessary.
In addition to the position and length of the return lead cables, their attachment is also crucial to achieving welding results of consistent quality.
A high contact force or surface pressure is required to ensure low contact resistances:
Screw terminals have the highest contact forces (> 1000 N).
Frequently used clamping elements and toggle clamps are usually not precisely defined, especially with regard to tolerances.
The figure shows point-shaped grounding point variants.
The pneumatic version with two grounding points has additional spring-loaded clamping cylinders for different forces and diameters.
The second figure shows sliding grounding contact variants, used on or in rail systems.
A high surface pressure is also of great importance for these systems. Therefore, it must be ensured that the sliding block cannot lift off.
In many cases, a circuit is designed with two spring-loaded sliding blocks to stop this happening.
Dirt deflectors or wiper systems keep the rail free of dust and insulating grease.
Each welding circuit requires its own grounding point or grounding rail, which must be sufficiently dimensioned.
IMPORTANT!
There are variants with sliding grounding contacts for rotating devices and components:
Important features of grounding contacts for rotating devices:
Planning multiple grounding points can significantly reduce the length of the current paths and inductance areas. Shared grounding cables are avoided and current paths are separated.
To obtain approximately equal resistance values, return lead cables should be of equal length and run parallel to the welding positive hosepack for as long as possible.
The figure shows the grounding cables routed in a net shape on the hall floor.
Large longitudinal chassis would have very high resistances and inductances with long drag chains for the hosepack and return lead cable.
In the case of compact welding systems with an integrated wire drive and without an interconnecting hosepack, short torch hosepacks are usually also used.
Here, the routing of the return lead cable in particular must be taken into account:
This results in:
Poorly clamped ground connections or dirty workpiece surfaces have large, changing contact resistances.
In the case of compact welding systems with an integrated wire drive and without an interconnecting hosepack, short torch hosepacks are usually also used.
Here, the routing of the return lead cable in particular must be taken into account:
This results in:
Poorly clamped ground connections or dirty workpiece surfaces have large, changing contact resistances.
In split welding systems, a separate wirefeeder is connected to the power source via an interconnecting hosepack.
The length of the interconnecting hosepack and its arrangement are decisive factors in the inductance in the welding circuit.
Winding the interconnecting hosepack on the trolley or, in the worst case, around the gas cylinder multiplies the total inductance in the welding circuit.
Remedy
Wind return lead cables and interconnecting hosepacks in opposite directions:
The figure shows how the interconnecting hosepack is picked up in the middle and then wound up.
Compensated interconnecting hosepacks
With compensated interconnecting hosepacks, the welding positive lead and return lead cable are routed in one hosepack.
Almost the entire magnetic field is compensated for by means of an internal "4-strand arrangement".
In shipbuilding and pipeline construction in particular, this special solution can be a variant for short return lead cables and low inductances.
Especially in automated systems or robot applications, the welding circuit must be planned first in order to exclude or reduce process interference in advance.
Subsequent planning and also optimization can often only be implemented at great expense.
The system design should use the same return lead cable lengths and cross-sections for the different grounding points.
The effective area between the hosepack and the grounding cable determines the inductance and should be kept as small as possible.
Component or device should be isolated from ground potential to avoid parallel ground currents and voltage potential shifts.
Especially in automated systems or robot applications, the welding circuit must be planned first in order to exclude or reduce process interference in advance.
Subsequent planning and also optimization can often only be implemented at great expense.
The system design should use the same return lead cable lengths and cross-sections for the different grounding points.
The effective area between the hosepack and the grounding cable determines the inductance and should be kept as small as possible.
Component or device should be isolated from ground potential to avoid parallel ground currents and voltage potential shifts.
Systems with one grounding point
Example – rotating unit with longitudinal chassis
Remedy:
Setup with multiple grounding points
The second figure shows the longitudinal chassis with an additional grounding contact.
The areas between the welding positive lead and the return lead cable across the component become significantly smaller and also more constant over the travel path.
Both manual and automated processes can use multiple arcs on a single component, which can lead to magnetic coupling effects.
Both manual and automated processes can use multiple arcs on a single component, which can lead to magnetic coupling effects.
If several arcs are being used to weld one component simultaneously, all welding circuits must be separated from each other:
A | Welding system with setup errors (a) Crossing current paths Shared ground potential Current path routed under the second arc (b) |
B | Correctly set up welding system – power and return lead cables compensate each other (d) Separated grounds and non-overlapping current paths (e) |
Result of optimization:
Interference voltages from neighboring welding circuits influence the arc length control and lead to instabilities in the welding process (see also from page (→)).
Remedy:
Direct voltage measurement by means of sensor cable (c) from component to the next system bus interface (e.g., wirefeeder (b), SplitBox, or SB 60i)
From this interface, the voltage potential is transmitted to the power source without interference.
(a) | Power source |
(b) | Wirefeeder, SplitBox, or SB 60i |
(c) | Sensor cable |
(d) | Distance, min. 30 cm |
(e) | SpeedNet bus communication |
The figure shows the circuit diagram of the sensor interfaces (a) and (b).
The sensor cable is routed separately from the SpeedNet bus communication (e) but in the same multipole robot cable in the hosepack.
The physical effects of resistance and inductance due to the welding circuit arrangement do not change, since these are determined by the current-carrying cables (hosepack and return lead cable).
The measurement of the arc voltage is improved, and interferences in the voltage measurement are eliminated.
IMPORTANT!
Improving the hosepack arrangement is always the first optimization choice.
The distance (d) from the sensor cable to the return lead cable or hosepack should be at least 30 cm, if possible, to avoid coupled voltages in the sensor cable.
Single-wire welding systems usually do not require a sensor cable.
If several arcs are being used to weld one component, the sensor cable brings a significant improvement in the voltage measurement and thus the arc stability, if the hosepack and ground wiring has not been optimally designed.
Example: Rotary table with the welding area behind a partition wall
Multiple welding positions require multiple grounding contacts and sensor cables on the device. These must also be arranged with sufficient spacing to avoid coupling.
Several sensor cables can be routed together in one cable harness, since they do not carry welding current and do not cause mutual coupling.
With long welding gantries, a sensor cable does not bring any advantages. Therefore, short welding circuit lengths should be planned when designing the system.
The sensor cable can be used as a retrofit solution, e.g., for existing systems.
Ideally, the expected current flow is already taken into account during system planning.
The following optimization examples are described in the next sections:
The following optimization examples are described in the next sections:
The following optimization examples are described in the next sections:
The images from before and after optimization are shown in an enlarged view underneath.
Multiple individual welding systems on one component – before optimization |
Multiple individual welding systems on one component – after optimization |
The images from before and after optimization are shown in an enlarged view underneath.
TWIN setup before optimization |
TWIN setup after optimization |
The images from before and after optimization are shown in an enlarged view underneath.
Multi-TWIN system before optimization |
Multi-TWIN system after optimization |