8
the manufacturer’s (class I) safety system ineective and constitute
a serious risk to people (e.g. electric shock) and property (e.g. re).
WELDING CIRCUIT CONNECTIONS
WARNING! BEFORE CARRYING OUT THE FOLLOWING
CONNECTIONS MAKE SURE THAT THE WELDING MACHINE IS
SWITCHED OFF AND DISCONNECTED FROM THE POWER SUPPLY.
Table 1 (TAB. 1) shows the recommended sizes of the welding
cables (in mm2), according to the maximum current output from the
welding machine.
Connecting the welding gun and control cable (only for 66mF model
- Fig. C)
- Connect the DINSE connector to its socket.
- Insert the control cable connector into its socket.
Connecting the welding current return cable
Connect the welding current return cable to the piece to be welded, as
close as possible to the join being made.
Warnings:
- Screw the welding cable connectors right down into the quick
couplings (if any), so as to ensure a perfect electrical contact;
otherwise, the connectors will overheat, wear rapidly and become
inecient.
- Do not use metal structures that are not part of the workpiece to
substitute for the welding current return cable; this could endanger
safety and produce an unsatisfactory weld.
6. WELDING: DESCRIPTION OF PROCEDURE
Preparatory operations
Before carrying out any spot-welding operation it is necessary to carry
out a series of checks and adjustments, with the main switch in the “O”
position:
1- Make sure the electrical connections have been made correctly
according to the above instructions.
2- The welding machine should not be switched on and o repeatedly
because dissipation of the energy held by the capacitors could cause
heating and damage.
3- Preparing the gun.
Fig. D
- Choose the type, diameter and length of stud bolt (1) to be welded
then use and adjust the stud bolt holder (2) to the corresponding
diameter. For correct insertion see g. D (stud bolt holder 2).
- Insert the stud bolt to be welded (it should be held tightly); adjust its
protrusion to 0.8 - 1.2 mm using the screw (3) and lock the nut (4).
- Insert the stud bolt holder (2) into the gun’s chuck, push it in until you
feel it resting on the base and then lock the nut.
PRINCIPLES OF STUD WELDING OPERATIONS WITH IGNITION SPOT
STRIKE (Fig. E):
These welding systems work by extremely rapid discharge (2.3 ms) of a
battery of capacitors, enabling welding of studs ranging from Ø 3 mm to
Ø 8 mm according to the model used.
With this technology it is possible to weld stud bolts onto clean, non-
oxidised mild steel, galvanised steel, stainless steel, aluminium and brass
surfaces.
The process is so quick that it does not alter the surface on the other
side of the weld i.e. painted sheet, pre-paint treatments, plasticised and
galvanised surfaces. It is not possible to weld on hardened steel, or on
oxidised or painted metal.
The stud bolt is inserted into the stud holder clamp, after adjustment of
the pre-charge spring by means of the screw on the back of the gun (see
stage 1), and is positioned with its ignition strike directly on the surface
of the sheet being welded (see stage 2). Warning: the gun should be kept
perpendicular to the sheet being welded.
The gun is pressed against the metal until the four ns of the support
on the head of the gun are in perfect contact with the material; the start
control will cause the start of current passage, which will vaporise the
ignition strike and the electric arc will spread over the whole surface of
the stud bolt (stage 3), which is pressed onto the metal surface.
Warning: DO NOT apply excessive pressure to the stud.
The melted metal will solidify to weld the stud bolt (stage 4). The pistol
should be extracted in perfect alignment with the stud to prevent
deformation of the clamp and ensure it a long working life (stage 5 + Fig.
F).
Fig. F
STUD BOLT WELDING TESTS
Before starting production it is essential to make several test welds in
order to regulate the power source correctly and nd the correct pressure
to be applied to the gun. Proceed as follows:
- Insert the chosen stud bolt into the stud bolt holder (2) (which has
already been adjusted as described in Fig. D).
- start the power source by turning on light switch I.
- prepare the base sheet in conditions that are identical to working
conditions as regards thickness, earth connection area, piece size,
material quality; take the gun by the handgrip and press it onto the
sheet, making sure its axis is perpendicular to the surface.
- the earth clamp should be placed as close as possible to the welding
spot.
- make a number of test welds, adjusting the voltage and pressure until
you obtain a perfect weld.
Note (only for model 66mF): larger sized stud bolts (M5, M6), require
higher pressure to produce a correct weld, therefore the sheet to be
welded should have adequate mechanical properties. For this reason, in
the body shop, avoid using M5 and M6 stud bolts.
Before carrying out the next spot-weld, the gun should be extracted and
the new stud bolt inserted into the stud bolt holder.
The gun should be extracted, keeping it perfectly aligned with the stud to
prevent deformation of the clamp.
WELDABILITY OF TYPICAL COMBINATIONS OF STUD BOLT AND BASE
METAL IN CAPACITOR DISCHARGE WELDING.
It is important to make a careful study of strength and deformation at
the point where the stud bolt is welded to the base metal. For steel, you
should be beware of fragility due to hardening. The material and strength
of the stud bolt are subject to limited tolerance. The carbon content of
steel stud bolts should be ≤0.2% (cast analysis).The weldability of various
materials and the possible combinations of stud bolt and base metal are
shown in Tab. 2.
N.B. The base metal surface must be clean. Layers of paint, rust, slag,
grease and coatings in non-weldable metals should be removed from the
welding area. Do this adopting the method suited to the job. Base metals
with layers of slag and rust must be perfectly clean.
Fig. I (adjusting energy and spot-welding pressure) shows the values
of capacitance charge voltage (which can be adjusted with the
potentiometer) and of the pressure of the pre-charge spring, for the
dierent types of stud bolts being welded (M3, M4, M5, M6, faston pins).
Note: for ferrous materials, reduce the energy values in the table by 20-
30%.
IMPERFECTIONS AND REMEDIES DURING CAPACITOR DISCHARGE
STUD BOLT WELDING (FIG. H).
To help assessment of weld quality, the illustration shows possible
imperfections that may occur during the welding process, with the
corresponding remedies.
USING THE GUN
WARNING!
- To fasten accessories to the gun chuck, or remove them, use a xed hex
key.
- When working on doors, bonnets or boots, you must make the earth
connection on these parts so as to prevent current from passing
through the hinges, and in any case the connection must be near the
area being spot-welded (if the current has to travel long distances this
will reduce the eciency of the weld).
CONNECTING THE EARTH CABLE
- Bare the sheet as close as possible to the point where you intend to
work, then connect the earth clamp.
Spot welding threaded stud bolts ( Pos.6, Fig.G ), smooth pins (POS.5,
Fig.G ), rivets (POS.4, Fig.G ), faston holders (POS.7, Fig.G ).
Fit the gun with the appropriate stud bolt holder, insert the piece to be
spot-welded and place it on the sheet at the desired spot; adjust energy
and gun pressure appropriately and press the button on the gun.
Using the (optional) extractor (POS.1, Fig. G)
Coupling washers and traction
This is carried out by tting and locking the chuck (POS 3, Fig. G) to the
extractor and then working on the washer (POS.8 Fig. G) that has already
