Without proper electrode design, it’s impossible to achieve weld consistency and weld quality. This is even more of a challenge for micro-resistance welding, due to the typically more complex part design. More than anything, the design of the parts, especially the materials selected, dictates the electrode and tip design. There are three major factors that must be considered when selecting or designing a welding electrode:
• The part’s base metal
• The part’s plating material and thickness of the plating
• The part weld geometry
There is no such thing as a perfect electrode design. Rather, the process of electrode design is a series of compromises, seeking the best balance of features to meet the multiple needs of the welding process. Designing for only one factor will reduce the weld quality or electrode life. Therefore, to achieve the best balance, one must take all of the factors into consideration.
Electrode Selection and Design:
The base metal determines the electrical conductivity of the parts to be welded. This, in turn, determines the electrode material. High conductivity metals need low conductivity electrodes, so that the extra heat generated by the electrodes can augment the weld heat. Conversely, low conductivity metals need electrodes with a high conductivity, to minimize heat buildup in the electrode.
A lot of miniature welding is electronics related, so it’s not uncommon to be welding two parts together that have dissimilar base materials. In these cases, it may be necessary to use electrodes that are of different materials as well, matching each electrode to the base material for the part it is coming in contact with.
It is helpful to use a larger electrode tip area than the actual contact area needed for the weld. The additional tip area helps dissipate heat created by the welding process, prolonging electrode life.
Tip Selection and Design:
Tip geometry is largely dependent upon the part geometry. The most important factor to consider when selecting tip geometry is ensuring consistent contact area between the tip and the part. Rectangular tips are much more likely to provide a consistent contact area than round ones, as the positioning of the part may cause the actual contact point to be off center. In those cases, a round tip would have a smaller contact area with the part than it would if the part was centered, creating an inconsistent weld. However, a rectangular tip would maintain the same amount of contact area.
The plating of the part affects how easily the tip sticks to the part. This sticking lowers electrode life. Thinner plating helps reduce this, by reducing sticking. Electrode tips which are made of materials that don’t alloy easily with the plating material are less likely to stick. Likewise, a larger electrode tip reduces the tip temperature, reducing sticking as well.
Electrode tips come in a variety of materials. The tip material hardness affects the life of the electrode. Softer materials groove more easily than harder ones. Unfortunately, this changes the contact surface area, affecting the quality of the weld. In cases where grooving is likely, such as with a cylindrical part (electronic part leads), a pre-grooved tip will help maintain weld consistency.
Many electrode tips are designed with a long tip length, in comparison to the tip width. This is done so that the tip can be resurfaced several times before having to dispose of the electrode. However, the longer the tip length, the lower the weld quality. To maintain good weld quality, the tip length should be no more than twice the tip’s width.
Conclusion
Of course, there are other factors besides the electrode and tip design which affect the quality of the weld. Some common factors are the current used for welding and the pressure applied to the electrodes. Once again, a balance needs to be found, between too much and too little. The ideal current and pressure will provide a solid weld, without causing undue damage to the electrode and tip.
In many cases, some experimentation with weld electrodes may be necessary. It is necessary to start with the best combination of factors, based upon the criterion listed above, and test for weld consistency and electrode life. Adjustments may need to be made to find the perfect combination for the application.
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• The part’s plating material and thickness of the plating
• The part weld geometry
There is no such thing as a perfect electrode design. Rather, the process of electrode design is a series of compromises, seeking the best balance of features to meet the multiple needs of the welding process. Designing for only one factor will reduce the weld quality or electrode life. Therefore, to achieve the best balance, one must take all of the factors into consideration.
Electrode Selection and Design:
The base metal determines the electrical conductivity of the parts to be welded. This, in turn, determines the electrode material. High conductivity metals need low conductivity electrodes, so that the extra heat generated by the electrodes can augment the weld heat. Conversely, low conductivity metals need electrodes with a high conductivity, to minimize heat buildup in the electrode.
A lot of miniature welding is electronics related, so it’s not uncommon to be welding two parts together that have dissimilar base materials. In these cases, it may be necessary to use electrodes that are of different materials as well, matching each electrode to the base material for the part it is coming in contact with.
It is helpful to use a larger electrode tip area than the actual contact area needed for the weld. The additional tip area helps dissipate heat created by the welding process, prolonging electrode life.
Tip Selection and Design:
Tip geometry is largely dependent upon the part geometry. The most important factor to consider when selecting tip geometry is ensuring consistent contact area between the tip and the part. Rectangular tips are much more likely to provide a consistent contact area than round ones, as the positioning of the part may cause the actual contact point to be off center. In those cases, a round tip would have a smaller contact area with the part than it would if the part was centered, creating an inconsistent weld. However, a rectangular tip would maintain the same amount of contact area.
The plating of the part affects how easily the tip sticks to the part. This sticking lowers electrode life. Thinner plating helps reduce this, by reducing sticking. Electrode tips which are made of materials that don’t alloy easily with the plating material are less likely to stick. Likewise, a larger electrode tip reduces the tip temperature, reducing sticking as well.
Electrode tips come in a variety of materials. The tip material hardness affects the life of the electrode. Softer materials groove more easily than harder ones. Unfortunately, this changes the contact surface area, affecting the quality of the weld. In cases where grooving is likely, such as with a cylindrical part (electronic part leads), a pre-grooved tip will help maintain weld consistency.
Many electrode tips are designed with a long tip length, in comparison to the tip width. This is done so that the tip can be resurfaced several times before having to dispose of the electrode. However, the longer the tip length, the lower the weld quality. To maintain good weld quality, the tip length should be no more than twice the tip’s width.
Conclusion
Of course, there are other factors besides the electrode and tip design which affect the quality of the weld. Some common factors are the current used for welding and the pressure applied to the electrodes. Once again, a balance needs to be found, between too much and too little. The ideal current and pressure will provide a solid weld, without causing undue damage to the electrode and tip.
In many cases, some experimentation with weld electrodes may be necessary. It is necessary to start with the best combination of factors, based upon the criterion listed above, and test for weld consistency and electrode life. Adjustments may need to be made to find the perfect combination for the application.
