Resistance Seam Welding Process | What Is Resistance Seam Welding | Seam Welding Chassis

Resistance Seam Welding:

In principle seam welding is similar to spot welding except that it uses disc shaped electrodes. A current impulse is applied through the rollers to the material in contact with them. The heat generated thus rollers to the material in the pressure from the electrodes completes the weld. If the current is put OFF and ON quickly, a continuous fusion zone made up of overlapping nuggets is obtained and the process is known as Stitch Welding Process.

01-seam welding - track seam weld - seam welding wheels

Unlike spot welding the disc shaped electrodes are not separated after each weld, but maintain continues pressure over the work pieces. The electrode current is timed to flow in pulses so that a row of welds is produced along the interface. Copper alloy electrodes are used to keep the heat at the electrode contact surface to a minimum. The motion of the electrodes and current impulses are so arranged that the weld nuggets overlap forming a gas or liquid pressure tight weld.

01-resistance seam welding Process - longitudinal seam welding

The amount of overlap depends on the ratio of current ON and OFF time. The normal overlap is generally 25 to 50 percent.

After the welding is over the electrodes and work pieces are flooded with water to dissipate the heat.

01-resistance seam welding

Types of seam welding:

Seam welding may be divided in two main categories namely:

1. Continuous motion seam welding

2. Intermittent motion seam welding

Continuous motion seam welding:

In the continuous motion method of seam welding the electrodes are rotated at a predetermined constant speed and the current impulses timed to get an overlapping weld. Alternatively the work pieces may be moved at constant speed with the electrodes idling under the welding pressure.

Intermittent motion seam welding:

In the intermittent method the work pieces move till the weld position stop for the welding to take place automatically move to the next weld position, stop again for welding and so on. This method is suitable for seam welding in thicker sheets which are too thick to be properly welded by the continuous motion method.

Resistance Seam Welding Wheel:

01-resistance seam welding Wheel

Types of seam welding joints:

The common types of seam welding joints are:

1. Lap seam weld (Common type weld)

2. Butt seam weld

01-resistance lap seam welding

01-resistance butt welding

Advantages of seam welding:

1. A continuous overlapping weld produced by the process makes it suitable for joining liquid or gas tight containers and vessels

2. Efficient energy use

3. Filler metals are not required. Hence no associated fumes or gases. This results in clean welds.

4. Roll welding simply joins two work pieces whereas stitch welding produces gas tight and liquid tight joints.

Disadvantages of seam welding:

1. Requires complex control system to regulate the ravel speed of electrodes as well as the sequence of current to provide satisfactory overlapping welds. The welding speed, spots per inch and timing schedule are all dependent on each other

2. Difficult to weld metals having thickness greater than 3mm

3. Relatively higher current is thus required for seam welding than for spot welding.

4. The work pieces to be welded are over lapped sufficiently to prevent metal flowing out from the edges of the pieces during welding under pressure.

Applications of seam welding:

1. Used to fabricate liquid or gas tight sheet metal vessels such as gasoline tanks, automobile mufflers and heat exchangers.

2. The production of seam welded pipes and tubing (Butt seam weld).

Resistance Spot Welding | Resistance Spot Welding How It Works | Resistance Spot Welding Theory

Resistance Spot Welding:

In spot welding the weld is effected by the heat produced due to resistance to the flow of current through two or more overlapping work pieces held pressed together between the electrodes. This is the simplest form of resistance welding and does not pose any problem for welding sheets ranging u to 12.5 mm in thickness. The majority of spot welding is however done with metal pieces less than 6 mm thick.

01-resistance spot welding - spot welding machine

For best results the surfaces to be welded must be free from scales and foreign matter. Spot welds should not be made too close to the end of a workpiece or to each other. When a spot weld is attempted too close to the edge of the work pieces molten metal may flow out of the weld zone. Similarly if two spot welds are made too close to each other electric current may be shunted through a parallel path provided by an adjacent weld.

01-resistance welding machine - what is resistive welding

The resulting weld nugget is typically 5 to 10 mm in diameter, with a heat affected zone extending slightly beyond the nugget into the base metal.

01-resistance spot welding process - spot welding parameters

Spot welding machines are available in three different varieties:

1. Stationary single spot welding machines

             a. Rocker arm type

             b. Direct pressure type

2. Portable single spot welding machines

3. Multiple spot welding machines

01-resistance spot welding aluminum - spot welding gun

Rocker arm type:

The rocker arm type is the simplest and cheapest but is limited to smaller sizes. It employs rocking motion of the upper arm for applying pressure and raising and lowering of the upper electrode.

Direct pressure type:

The direct pressure type employs a straight line motion of the upper electrode along the face of the machine column and can be used for larger sizes.

Electrode Tip shape:

The size and shape of the weld spot is determined by the electrode tip, the most common electrode shape being:

01-resistance spot welding - electrode tip - tip shape

1. Round (most common)

2. Hexagonal

3. Square and other shapes

Spot Gun Machines:

When the size of the work pieces to be welded increases, then spot welding machines are used on that occasion. A large number of welding guns are available for the purpose. These portable spot welders are connected to the transformers through a long cable and may be taken to the spot where welding is to be done. The electrodes used should have a contact area which gives the desired current density through the work pieces.

01-resistance spot gun machines - spot welding transformers

Welding pressure in these guns may be applied manually, pneumatically or hydraulically depending up on the size and shape of the gun.

Advantages of Resistance Spot Welding:

1. Adaptability for automation in high rate production of sheet metal assemblies

2. High speed

3. Economical

4. Dimensional accuracy

Limitations of Resistance Spot Welding:

1. Difficulty for maintenance or repair

2. Adds weight and material cost to the product, compared with a butt joint

3. Generally have higher cost than most arc welding equipment’s

4. Produces unfavourable line power demands

5. Low tensile and fatigue strength

6. The full strength of the sheet cannot prevail across a spot welded joint

7. Eccentric loading condition