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Resistance welding of aluminium sheets


AluSPATZ+ - Our complete solution for spot welding of aluminium

The AluSPATZ+ complete package consists of the following components:

  • ServoSPATZ+M1800 Tandem MF weld controller
    combined controller: control of weld current and up to 2 servo actuators in one device, modular built with two pluggable servo drives
  • AluGATOR servo weld gun with 2 actuators:
    1. for controlled movement of the main electrode and application of weld force
    2. for position-independent adaptive weight equalization of weld gun
  • CapClean for cleaning and reproducible reshaping of the weld electrodes

Following is a summary of the salient features and advantages the AluSPATZ+ equipment provides for joining of aluminium sheets in fully automated serial production in the automotive industry.

 

Advantage 1: AluSPATZ+ makes RSW a capable and reliable process for joining aluminium sheets

Reproducible joining quality of 2- and 3-sheet combinations of e.g. aluminium material class AA 5xxx and AA 6xxx with single sheet thicknesses from 0.8 mm to 3.0 mm realized by

  1. AluMASTER: particularly for RSW of aluminium developed adaptive weld control mode for compensation of the following process variations:
    1. Shunt effects
      Due to the higher electrical conductivity of aluminium compared to steel the disturbing influence of current shunts is even severer.
    2. Gaps between sheets
    3. Surface quality of the aluminium sheets
      (lubricants, surface scratches! distribution and thickness of aluminium oxide etc.)
    4. Variations in application thicknesses of adhesives and sealers
    5. Wrong weld gun equalization, wrong position of electrodes to the sheets when welding
  2. NuggetIndex and GUNIndex spot and weld gun supervision for RSW of aluminium. Well known from RSW steel adapted to the needs of aluminium.
  3. CapClean "Electrode management system"
    For the demands of aluminium spot welding optimized electrode treatment: cleaning and reshaping of the electrode surface

 

Advantage 2: Speed

  1. Application of weld schedules containing short weld times, depending on total gauge of the sheet stackups: 60 ms - 300 ms
  2. Combined control of weld current and gun & electrode movement in one device allows the utilization of hard- and software that can be optimized for
    1. combined control of weld electrode (main actuator) and fix electrode (gun equalization actuator) movement offering fast gun closing paired with soft touch of electrodes on sheet
    2. fast buildup of weld force
    3. real time force control during weld
    The result is short cycle times combined with optimum spot quality.
    Example:
    Time needed for a complete welding operation of a 2-sheet combination 2x 2.5 mm AC600 including electrode travel from/to 80 mm opening stroke = approx. 1.1 seconds.

 

Advantage 3: Flexibility of RSW

2- and 3-sheet combinations of e.g. material classes AA 5xxx and AA 6xxx with single sheet thicknesses from 0.8 mm to 3.0 mm can be reliably spot welded in automated serial production with one weld gun equipped with one electrode cap geometry only, independent from

  1. sheet sequence in the sheet stack up
  2. orientation of the stack up to the moving electrode (weld current direction)!

This flexibility results in a significant reduction of needed equipment for the joining process and floor space in comparison to the application of mechanical joining methods. Thus, for the same output less equipment and floor space is needed.

 

Advantage 4: High availability

Due to the fact that the AluSPATZ+ spot weld equipment is just a "simple" spot welding system as known from spot welding steel it is principally characterized by a higher grade of availability compared to mechanical joining methods or spot welding equipment using additional material and hardware, e.g. for prevention of direct contact between copper electrodes and aluminium sheets.
The availability of AluSPATZ+ when spot welding aluminium is the same as for spot welding of steel, just providing higher electrode life times.
No additional feeding or other guiding equipment is needed on the weld gun. For the same output less equipment and floor space is needed!

 

Advantage 5: Low cost joining method

The costs for a welded joint connection of aluminium sheets are basically the costs for the weld energy! The energy needed for joining e.g. the 2-sheet combination of 3.0 mm AA 5754 + 2.5 mm AA 6082 is about 30 KWs per weld joint. Provided a rate of 0.08 € per KWh this corresponds to a cost of 0.0008 € per weld spot.

Secondary costs are the costs for the consumables only, which are the electrodes and the cleaning wheels. The life time of a pair of electrodes when applying AluSPATZ+ equipment is about 10,000 weld spots. Life time of a cleaning wheel is > 250,000 weld spots.

Example:
The energy costs for the spot welded joints in an aluminium body of a car model with a production volume of 200,000 cars per year and 4,000 spot welded joints per car are 640,000 € per year.
Whereas in case riveting would be selected as joining method instead of spot welding the costs for the rivets only for the same car model would be 20,000,000 € per year, based on a price of 0.025 € per rivet. That is about 30 times higher costs compared to RSW.

 

Summary: The AluSPATZ+ equipment ensures reliably good joining quality in serial production paired with short cycle times and very low production costs!

 

Weld sample 1:

3-sheet combination: 3 mm + 3 mm + 1.0 mm, each AA 5754

 

3-sheet combination: 3 mm + 3 mm + 1.0 mm, each AA 5754

 

Weld sample 2:

2-sheet combination: AA 6082 T6, 1.0 mm + 1.0 mm, welded with same gun and electrodes as prior weld sample