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MTI MicroWelding offers
the Optimum System to meet your specific requirements.
From initinal consultation to extended service - Take advantage
of our vast experience in the micro spot welding field to help
you select the most suitable welding technique and system for
your individual needs.
How to select a micro
spot welding system.
Use this flow chart to help determine the micro
spot welding system which best suits your product and process
requirements.
Determining
your welding requirements.
First you must consider the construction of the weldments,
including material composition, configuration, and thermal
capacity. The desired weld quality must be examined in
terms of accuracy, thermal effects, productivity and cost.
|
 Determine
type of current path
First, determine the welding current path based on the physical
characteristics of the weldments and production process. There
are three types of resistance welding based upon current path.
Direct Welding
This is often the most commonly used type of resistance welding.
The welding current flows directly from one electrode to the
other, through the weldments.
Indirect Welding
This is often used when the weldments are configured in such
a way that only one side of the weldments is accessible with
an electrode. The welding current flows from the first electrode,
along one weldment, through the area of the weld, and into
the other electrode.
Series Welding
Series welding is also used when only one side of the weldments
is accessible with electrodes. This form of welding has the
advantage of making two weld nuggets at one time. However,
series welding is less controllable because of the many shunt
paths available to the welding current.
Welding Conditions
There are three major welding conditions to consider in selection
of a welding system.
1) Shape and composition of the welding electrodes.
2) The amount of force applied during welding.
3) The amplitude and duration of the welding current.
Selection of welding head design
The force and energy necessary to weld the workpieces can be
estimated by considering the properties of the weldments and
the desired weld quality. By considering the necessary welding
force, type of required current path, required size of electrodes,
and process area available, you can determine the weld head
that is best suited to your specific application. A wide variety
of welding head designs and configurations are available from
Seiwa. Pneumatic or manual foot pedal operated systems can
be used to drive the welding heads. Seam welding and hand held
welding heads are also available.
|
Selection of welding power supply
The ideal current duration is determined by carefully studying
the thermal capacity of the weldments, the thermal effects
of the weld, and the quality of finish required. The amplitude
of the current required to form the weld nugget is then calculated.
Considering these requirements, the most suitable type of welding
power supply is chosen. To aid in this process, the four available
types of welding power supplies are listed on the bottom graph.
The power supply is the heart of a restance welding system.
In addition to the desired weld, other factores such as cost,
weld duration, incoming power fluctuations, labor costs, and
potential for future automation must be taken into account
when selecting a power supply.
Selection of electrode shape and composition
 The
welding electrodes play three different roles in resistance welding,
maintaining uniform current density, concentrating current at
welding points, and maintaining thermal balance during welding.
The most commonly used electrode materials are copper chrome,
copper tungsten, tungsten, and molybdenum. Electrodes are available
in many shapes, the most common above. Electrode material and
shape are determined by considering the force nessary for welding
and the thermal conductivity of the weldments. Electrodes require
maintenance to prolong their usefulness, and will periodically
need to be replaced.
Advantages of projections in micro
spot welding
 By
providing a projection on the surface of one of the weldments,
the welding current and force can be focused into the small area
of the projection efficiently producing heat at the desired weld
location. Projection welding is effective even if the weldments
are thick. Projection welding can also extend electrode life
by increasing the electrode contact area and decreasing the current
density at the surface of the electrodes.
METHOD OF SETTING WELDING CONDITIONS:
General conditions are given in the Table below. The final setting
is determined after completion of testing.
| Steps
to be taken |
|
|
|
|
Especially
in the case of AC welder |
|
|
| |
Increase |
Decrease |
Increase |
Reduce |
|
Change |
Change |
| |
prsssure |
pressure |
output |
output |
Current
passing time |
Heat
Scale |
electrode |
electrode |
| Welding
material & condition |
|
|
|
|
Lenghten |
Shorten |
Raise |
Lower |
material |
shape |
| Thick metal |
O |
|
O |
|
O |
|
O |
|
|
|
| Thin metal |
|
O |
|
O |
|
O |
|
O |
|
|
| Hard metal |
O |
|
|
O |
O |
|
|
O |
|
|
| Soft metal |
|
O |
O |
|
|
O |
O |
|
|
|
| Metal with low electric resistance |
|
O |
O |
|
|
O |
O |
|
O |
|
| Metal with high electric resistance |
O |
|
|
O |
O |
|
|
O |
|
|
| When welding is weak |
|
|
O |
|
O |
|
O |
|
|
|
| Firm contact is not made (hard metal) |
O |
|
|
|
|
|
|
|
|
|
| Material deforms excessively |
|
O |
|
O |
|
O |
|
O |
O |
O |
| Material discolors excessively (#1) |
|
|
|
O |
|
O |
|
O |
|
O |
| Sticking occurs (#2) |
O |
|
|
O |
O |
|
|
O |
O |
|
| Material becomes porous |
O |
|
|
O |
O |
|
|
O |
O |
|
| Violent splash occurs (#3) |
O |
|
|
O |
O |
|
|
O |
O |
O |
| Welded wire becomes too flat (#4) |
|
O |
|
O |
|
O |
|
O |
|
O |
| Note
#1: |
Discoloration increases as
the welding time increases, however, spattering and surface
roughness is reduced. Since heat is diffused throughout
the welding material, electrodes and secondary conductor,
a lot of energy is required. Avoid the over heating of
the unit. The difficulty in welding combination materials
that have large variances in thermal conductivity and heat
capacity will also increase the welding time required.
|
| Note
#2: |
Electrode materials usually
have a larger thermal conductivity than the material being
welding. In order to prevent an extreme rise in temperature
of the electrode tips, either lengthen the welding time
or increase the heat capacity of the electrode tips (i.e.,
thicken the electrode tips).
|
| Note
#3: |
 Some
examples of conditions that cause violent splash:
- Insufficient pressure application
- Unstable pressure application
- Too large output power
- Oxidized (dirty) material
- Too sharp electrode tips
- Roughened electrode tips
A counter measure for unstable pressure application would
be to use a "cushion electrode" to improve the
follow-up characteristics of the electrode. See Drawing.
|
| Note
#4: |
The movement of electrodes
is larger when welding wire material than when welding
plate material increasing the likelihood of unstable pressure
application (Note 3-b). To overcome this difficulty, improve
the follow-up characteristic of the head by reducing the
weight of the moving parts or use the "cushion electrode".
|
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