Author: Victor padilla

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Staying Safe during Resistance Welding

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https://www.aws.org/magazines-and-media/magazine-and-journal/welding-digest/welding-digest-staying-safe-during-resistance-welding/

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Resistance welding (RW) is a thermo-electric welding process in which the weld is made by a combination of pressure and current. The process involves the joining of metals by applying controlled pressure and passing current through the metal area to be joined. There are several different forms of RW (e.g., spot, seam, projection, single-sided, bonding, cross wire, micro, flash, and upset welding) that differ primarily by the types and shapes of weld electrodes used to apply the pressure and conduct the current.

Photo: Resistance welding is a thermo-electric process in which heat is generated at the interface of the parts to be joined by passing an electrical current through the parts. There are several different processes of resistance welding, including spot welding.

The electrodes, typically manufactured from copper-based alloys due to their superior conductive properties, are cooled by water flowing through cavities inside the electrode and the other conductive tooling of the RW machine.

There are several key advantages of the RW process, including the following:

-Very short process times;

-No consumables, such as brazing materials, shielding gas, solder, or welding rods/wires;

-Operator safety because of low voltage and fume emission;

-Cleanliness and environmentally friendliness; and

-Formation of a reliable electro-mechanical joint.

Safety Hazards

RW is not an open-arc process, and the weld is made inside or between the workpieces. As a result, several unique hazards must be considered during RW:

-Flying sparks can cause fire and explosion.

-Flying sparks and spatter can burn or injure eyes and skin.

-Electric shock can occur from live electrical parts.

-Hot metal and parts can cause burns.

-Moving electrode parts, such as tongs, tips, and linkages, can injure fingers and hands.

-Spot welding parts coated with cleaners, paints, or platings can create fumes.

How to Avoid the Hazards

The following lists several ways to stay safe during RW:

-Wear the appropriate personal protective equipment, including safety goggles or a face shield/safety glass; long-sleeved shirts made from nonmelting material; and dry, insulated gloves.

 

 

Figure 1-Feb-22-2022-02-39-49-24-PM

 

-Do not weld near flammables (move flammables away from the welding area). Also, keep a fire extinguisher nearby and know how to use it.

-Do not breathe the fumes. Use adequate ventilation and read safety data sheets for metals, coatings, and cleaners.

-Do not put your hands between tips. Keep away from linkages and pinch points. Keep all guards and panels in place.

-Do not touch hot workpieces, tips, or tongs with your bare hands. Allow tongs and tips to cool before touching. Wear proper insulating gloves when handling hot work or parts.

-Install and ground the unit according to electrical codes. Grounding should be provided to the secondary of all welding transformers for multispot, projection, and seam welding machines.

-Disconnect the input power before servicing. Ensure all equipment, with an appropriate safety disconnecting switch or circuit breaker, has been installed by qualified electricians.

-A thermal protection switch should be provided for ignition tubes used in RW equipment.

-Keep guards in place to mitigate activation of all automatic or air and hydraulic clamps, including foot pedals/switches.

-Use complete enclosures to insulate and protect stored energy or capacitor discharge types of RW equipment and control panels involving high voltage, including door interlocks that interrupt power and discharge capacitors.

-Use electronic eye, two-hand controls, or protection similar to punch press operation as guarding for all press welding machine operations when there is a possibility of the operator’s fingers being under the point of operation.

Adapted from American Welding Society (AWS) Safety and Health Fact Sheet No. 21, Resistance Welding. All of the AWS Safety and Health Fact Sheets are available through the AWS website at aws.org. Click on Standards on the home page and then on Safety & Health. AWS disclaims liability for any injury to persons or property, or other damages of any nature whatsoever, whether special, indirect, consequential or compensatory, directly or indirectly resulting from the publication, use of, or reliance on this information. AWS also makes no guaranty or warranty as to the accuracy or completeness of any information published herein.https://www.aws.org/magazines-and-media/magazine-and-journal/welding-digest/welding-digest-staying-safe-during-resistance-welding/

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Spot welding

The primary use of resistance spot welding is to join overlapping sheets of metal when the joint does not have to be gas or liquid tight.

Manufacturing using this process is inexpensive and fast as no separate fasteners are required.
Although commercial assembly production is generally limited to sheet thicknesses up to about 0,125 inches, plates of up to 0,25 inches or more.

Spot welding is used to manufacture many sheet metal products, like household appliances, car bodies, enclosures and furniture. The process can be easily automated and a variety of resistance welding machines are available from various sources.. Most metals can be resistance welded if required equipment is used and proper welding programs are followed.

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Protection for operators Punteadoras

Protection for operators Punteadoras

Operator Protection

Many companies are unaware that there is a way to protect the operator. He 90% accidents occur during alignment of the electrodes. It is because of this need to protect workers, the American Engineer, Roger Hirsch of Unitrol Electrodes, I believe that a system to detect other material other than metal, causes the pressure to drop to such a degree that would not hurt at some point the extremities of the operator, endorsed by OSHA. Alcavil system which S.A. The C.V. It is a distributor (It includes installation). This system is also used for pneumatic punching machines.

Operator Protection

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Projections welding Mexico

back up electrodes

Projection Welding Mexico

 

In the regular sheet to sheet welding we saw how size and shape of the weding electrodes was of great importance in determining the size, strength and quality of the Weld. It was also noted that all of the welding current is concentrated in the electrode tip. This current is in the order of thousands of amperes per square inch.

Therefore, electrode strength or hardness is sometimes scarified in or/ mushrooming.

Projection welding is a resistance process by which the current and heating during welding are localized at a predetermined point by the design of the parts being welded. This is usually accomplished by a projection, or embossment, on one or both of the work pieces.

It can readily be seen that the size of the electrode tip has no bearing in projection welding and that the current density may be considerably reduced, permitting the use of harder and tougher electrode material.

A projection may be embossed in a sheet of metal, it may be produced on a solid piece of metal by machining, or produced on the edge in a punch press in any of several ways. The height may be anywhere from a few thousandths of an inch to 0.125-in or more depending on the thickness of the material to be welded. The purpose of projections is to concentrate the current and force at predetermined points. In this modification of the spot welding process the concentration of the welding current is determined by the preparation of the workpiece rather than by the size or shape of the electrode.

There are several advantages to be gained by the use of projection, namely:

  • Ease of obtaining satisfactory heat balance for welding difficult combinations.
  • More uniform results in many applications.
  • Increased output per machine because of making several welds simultaneously.
  • Longer electrode life
  • Welds may be placed more closely together.
  • Parts are more easily welded in a assembly fixture.
  • Finish, or surface appearance, is often improved.
  • Parts may be projection welded that could not be otherwise resistance welded.

 

The advantages will be discussed as numbered:

  1. The major portions of the heat tends to develop in the part bearing the projections during the welding operation. Weldments composed of thickness ratios of 4 (or more) to 1 are sometimes difficult to spot weld. The flexibility of selecting the projection size and its location allow ratios of 6 (or more) to 1 to be readily projection welded. For this reason the projections should be produced on the heavier of the two pieces of the same metal or, if possible, on the piece of higher conductivity if dissimilar metals are being joined. The reverse can, however, be used under some conditions.
  2. Uniform projections may be readily obtained on a punch press. The effect of variables such as contact area between the parts and electrode mushrooming are reduced. The surface condition of the parts has less effect than in spot welding. If a part requires several welds, they can be made simultaneously, thus avoiding difficulties due the shunt currents. Both the location and strength of the resulting welds are more reliable.
  3. The only limits to the number of welds that can be simultaneously made seems to be the ability to control force and current so they are equally divided between the welds, and the capacity if the equipment. It is much easier to achieve the proper division of force and current with projections than with flat surfaces. When several welds, approximately six or eight are needed, they are usually made simultaneously.
  4. In many cases, the areas to be joined are flat except for the projections. In such cases the electrodes are flat and large enough to contact a large area. In other cases, when the surface to be contacted is irregular in shape, the electrode is fitted to the surface so that a night force may be applied without distortion the part. A large current may be introduced without damaging the surface. Electrodes with large contact surface show little wear and consequently require less attention or maintained.
  5. If two spot welds are located too closely together, current from the second weld is shunted though the preceding weld. Since projection welds are made simultaneously, there is less trouble due to shunting. However, if they are placed to closely together irregularities in forming the projections may lead to poor distribution of the current. The only limitations on the arrangement or spacing of projections are the ease of equalizing the distribution of force and current and the size of the machine. If, however, more than three projections are welded simultaneously, the height of the projections must be uniform within close limits, to avoid having some of the projections fused before other have made contact. Multiple-impulse welding or the use of upslope may be help in this case.

 

For more information, you can contact us directly to our email or check AWS Resistance Welding Manual

 

 

Projection Welding Mexico

 

In normal soldering foil-laminated, We saw how the size and shape of the electrodes ripple were of great importance to determine the size, resistance and weld quality. It was also observed that all the welding current is concentrated on the electrode tip. This current is on the order of thousands of amperes per square inch.

Thus, the strength or hardness of the electrode is sometimes deformed or scarifying.

Projection welding is a resistance process by which the current and heating during welding is located at a predetermined point by designing parts that are welded. This is usually accomplished by a projection, or embossment, in one or both parts.

It can easily see that the size of the electrode tip has no mark on the projection welding and the current density can be considerably reduced, allowing the use of electrode material harder as copper Class 2, or cases to increase duration copper tungsten is used.

A projection may be labeled embossed on a metal sheet, It can be produced from a solid piece of metal by machining, or produced on the edge in a punch of any of several ways. The height can range from a few thousandths of an inch to 0.125 inches or more, depending on the thickness of the material to be welded. The purpose of the projections is to concentrate the power and strength at predetermined points. In this modification of the welding process, the concentration of the welding current is determined by the preparation of the workpiece rather than the size or shape of the electrode.

Several advantages are obtainable using the screening, namely:

1- Ease of obtaining satisfactory balance heat for welding difficult combinations.

2- More uniform results in many applications.

3- Increased production machine because several welds are performed simultaneously.

4- Longer life of the electrode.

5- Welds can be placed closer together.

6- The pieces are more easily welded to a fitting.

7- finishing, or surface appearance, often improves.

8- The pieces may be welded by projection which otherwise could not be welded by resistance.

 

The advantages will be discussed as numbered:

  1. The main parts of heat tend to develop in the part carrying the projections during the welding operation. Welds composed thickness ratios 4 (or more) a 1 sometimes they are hard to tap. The flexibility to select the projection size and location allow relations 6 (or more) a 1 You are easily welded by projection. For this reason, projections should occur in the heavier of the two pieces of the same metal or, if possible, in the part of higher conductivity if they are joining different metals. The reverse can, but nevertheless, It is used under certain conditions.

 

  1. Uniform projections can be easily obtained in a punch. The effect of variables such as the contact area between the parts and the electrodes are reduced proliferation. The surface condition of the parts has less effect on the welding. If a piece requires multiple welds, They can be made simultaneously, thus avoiding difficulties due to shunt currents. Both the location and strength of the resulting welds are more reliable.
  2. The only limits the number of welds that can be performed simultaneously seem to be the ability to control the strength and power to be split equally between the welds and equipment capacity. It is much easier to achieve proper division of power and current projections with flat surfaces. When multiple welds are needed, about six or eight, generally they are simultaneously.
  3. In many cases, areas to be joined are flat except for the projections. In such cases, the electrodes are flat and large enough to contact a large area. In other cases, when the contact surface has an irregular shape, the electrode conforms to the surface so that it can apply a force night without distorting the part. You can enter a large current without damaging the surface. Electrodes with large contact surface show little wear and, Therefore, require less attention or maintenance.
  4. If two spot welds are located too close, current of the second welding is diverted through the previous welding. Since projection welds are made simultaneously, there are fewer problems because of the derivation. But nevertheless, if placed too close irregularities forming projections, This can lead to poor current distribution. The only limitations on the arrangement or spacing of the projections are easy to equalize the distribution of force and current and the size of the machine. But nevertheless, if more than three projections are welded simultaneously, the height of the projections should be uniform within close limits, to prevent some of the projections merge before others have made contact. Multipulse welding or using upslope may be helpful in this case.

 

For more information, You can contact us directly to our email or check the resistance welding Manual AWS