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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.


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:

  1. Insufficient pressure application
  2. Unstable pressure application
  3. Too large output power
  4. Oxidized (dirty) material
  5. Too sharp electrode tips
  6. 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".

MTI MicroWelding
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