Do-it-yourself spot welding: how to make resistance welding yourself

Resistance welding has long been used in all industries. This technology is no less popular among home craftsmen. It is quite difficult to assemble a spot welding machine with your own hands, but this approach helps reduce the cost of purchasing equipment.

Where is resistance spot welding used?

The technology involves connecting workpieces or welding individual parts to metal structures without creating an electric arc.

The method is applied under the following conditions:

At manufacturing plants. Spot welding is used in the manufacture and repair of cars, aircraft, and complex technical equipment. The method helps to create strong, durable connections that have no signs of deformation or other defects.
At home. A self-made machine is suitable for performing simple welding operations. It will help you weld elements of a fence or pipeline, or repair a car or motorcycle.

Equipment

Ready-made machines for spot welding are either stationary or portable; they are convenient to use when carrying out repair work. Automatic welding machines are used in industry. There are portable lever welding devices called tongs.

Welding equipment is expensive, and you rarely need to use it. Craftsmen found a rational way out of the situation.

It is quite possible to make a spot welding device for batteries and a body yourself. It can be used to repair household appliances and create decorative metal products.

Device design and necessary parts

Any contact type welding unit consists of 2 units:

power supply (transformer);
clamping pliers.

To obtain a powerful electrical discharge at a minimum voltage, an induction transformer is used.
The correct ratio of windings allows you to generate a current that is strong enough to melt the metal. The design of the pliers includes graphite or copper contacts installed on different levers that fix the mechanism.

The following types of clamps exist:

Mechanical. Includes a powerful spring and lever. The welder's muscle force is used to compress metals. Clamps of this type are installed in household devices used for simple operations.
Pneumatic. Installed in portable hand-held devices. Adjustable by changing the pressure in the air channel. The disadvantage is considered to be low productivity and the inability to adjust operating parameters during welding.
Hydraulic. The clamps also have a low operating speed, but their range of settings is wider than the previous type.
Electromagnetic. They are distinguished by the highest productivity and are installed in both manual and stationary units. Electromagnetic clamps allow you to adjust the compression force of parts during welding. This reduces the likelihood of lack of fusion and metal leaks.

Sometimes the design is complicated by adding liquid cooling systems, control of current parameters, and automatic movement of electrodes.

When assembling a homemade spot welding machine, the master will need the following parts and materials:

a modified transformer from an old microwave oven or car battery;
thick copper wire or cable harness of small cross-section;
levers used to assemble clamps;
base for installing unit blocks;
clamps;
wires;
insulating materials;
copper electrodes necessary for welding;
control key.

We recommend reading Description of resistance spot welding technology

Safety precautions

To ensure their own safety, the worker must know and comply with the safety instructions for spot welding:

To prevent electric shock, ground the unit;
Before starting work, be sure to check its serviceability;
use personal protective equipment for hands, eyes and body;
exclude high voltage supply to the device controls
use only wires of the specified cross-section in the device;
carry out work in a room with well-equipped ventilation or use special masks to protect the respiratory system.
locks and toggle switches (buttons) for turning on or off must be in working order, clearly visible and easily accessible;
During work, the area of the clamping mechanisms must be covered with a shield.

Compliance with these safety measures will ensure the health of the employee and others and will allow the required amount of work to be completed accurately and on time.

General operating principles

The algorithm for assembling the welding unit includes the following steps:

Removing the transformer. The part is taken from an old microwave oven. It is not completely needed; to manufacture the device, a primary winding and a magnetic circuit will be required. The remaining parts are carefully removed as unnecessary.
Formation of a new secondary winding. To do this, use a copper cable with a cross-section of at least 100 mm². Durable rubber insulation is replaced with textile insulation. To create a powerful welding machine, 2 transformers with a common winding are used.
Installation of a control unit that ensures uninterrupted flow of the contact welding process.
Manufacturing and connection of electrodes, the type and diameter of which are selected taking into account the properties of the metals being welded.
Housing assembly. The main units of the device must be reliably protected from external influences. At this stage, you can use the housing from an old microwave oven or assemble the structure yourself from sheets of metal.

How to make electrodes

When manufacturing these elements, the following points are taken into account:

The diameter of the electrode must correspond to the cross-section of the wire to which it is connected. Copper rods can be used as rods. Electrodes for low-power welding units are made from soldering iron tips.
During the welding process, the electrodes wear out quickly. To restore their operating parameters, the ends are sharpened. Over time, the electrodes are replaced with new ones.
The wire for connecting the welding rod should be short. Otherwise, part of the device's power will be lost. The current strength also decreases if there are a large number of connections in the electrode-transformer circuit.
It is recommended to solder copper tips onto the wires to which the rods are connected. This increases the efficiency of the equipment. Since the electrodes are removable, the connection points with the tips are not soldered.

Best models

According to many people who work closely with welding equipment, the following models should be noted.

Name	Description	Price	Advantages	Flaws
Caliber SVA-1.5 AK	The best price/power option, but not for “garage use”	13890 rub.	The welding process goes smoothly No machining required Powerful return spring	The overhead console is overheating Heavy Heavily loads the 220V network
FoxWeld KTP-8 3098	Popular when working with large metal structures	15560 rub.	Large carrying handle Small-sized Increased current power when welding	Backlash Loads the network Heavy Unregulated power
Spotter FUBAG TS 2600 38 666	Suitable for car body repair	32620 rub.	Overheat warning Four different operating modes	Heavy Expensive Unregulated current
Spotter RedHotDot HAMMER IT 275116	Notable for the presence of numerical control. Suitable for use in garage conditions.	RUR 30,168	Does not load the home network Small-sized Large melting and welding depth	High price Heavy - weighs more than 16 kg
FoxWeld MTP-25 3373	An excellent option for production conditions.	67900 rub.	Easy to operate Durable The pliers are compressed using a pedal Read also: What is a spotter? Purpose, characteristics, types and choice	Very expensive Special installation required Constant sharpening of electrodes is required
WIEDER KRAFT WDK-6000	An acceptable option for auto repair shops.	65273 rub.	Availability of trolley Powered by 220V Increased reliability Can weld in eight different modes Microprocessor control	Very expensive No fan or cooling mechanism Overall (60x50x95 cm)

Assembling a device from a microwave oven

The device manufactured in this way allows welding with alternating current with unregulated force.

List of required tools

To create a homemade device from a microwave oven, you will need the following equipment:

Screwdriver Set;
sandpaper;
copper rods;
hammer;
chisel;
knife.

Conversion of microwave parts

After removing the transformer from the furnace, perform the following steps:

Remove the secondary winding using a hacksaw or chisel. Dismantling is carried out carefully, trying not to damage the underlying layer. It is advisable to fill the space between the windings with corrugated cardboard.
Remove the metal shunts that limit the current.
A secondary winding is formed. At this stage, you will need a KG 1x35 wire. It can withstand prolonged exposure to high voltage and current up to 1200 A. The outer rubber insulation is removed from the cable.
The core is covered with tape, which facilitates the sliding of the wire during winding. The cable is laid in 3 tight turns. For winding, the use of stranded soft wire is allowed. The total diameter of the cores must be at least 1 cm.

We recommend reading: How to make a welding machine from a microwave

After the alteration, the transformer must have an open circuit voltage of no more than 3V and a current of at least 800 A.

Homemade device diagram

Creating an electrical circuit for a welding machine is not difficult. The electrode is connected with a soft cable to the secondary winding of the transformer. The circuit includes thyristors and rectifier bridges. One end of the pressure gun is connected to the secondary winding, the other is securely fixed to the device.

The operating principle of the electrical circuit of the unit is as follows:

Single-phase or three-phase current is supplied to the clamping mechanism.
When the button on the gun handle is pressed, the thyristor opens.
The capacitor is charged from the transformer. The thyristor closes, the clamping mechanism is activated. The latter operates until the capacitor discharges. Pressing the button again will generate a new impulse. The time for maintaining the charge of the capacitor is set by a variable resistor.

Assembling the device

To create the working part of the device, perform the following steps:

Assemble the base from the bottom of the microwave oven body. One end of a metal profile or wooden beam is fixed to it. To do this, use self-tapping screws to ensure a strong fixation. A welding electrode with a cable connected to a transformer is connected to the second edge of the profile. The wire is wound around the rod, which prevents damage.
A movable part of the apparatus is installed, which looks like a lever. A long nail is used as an axis. The side posts, created from profiles or bars, are fastened with self-tapping screws. There should be no distance between them and the base of the lever. Otherwise, the accuracy of the device’s impact is reduced.

Performance test

After all installation and assembly work, the device is checked in the following ways:

The main operating parameters of the unit are measured. An oscilloscope is used for this. The current pulse strength should be about 800 A.
The assembled device is used in practice. To do this, create a test seam. After completion of work, measure the temperature of the transformer. If it is too high, the circuit is not assembled correctly. When the indicator is within the normal range, 2 more test stitches are made.

Contactor from a welding transformer

Such equipment can be turned into a full-fledged resistance welding tool. The only drawback is the inability to control the current strength.

Drawing development

The correct choice of circuit helps to produce a working welding machine. Preference is given to simple drawings that include a minimum number of parts and blocks. Such options do not allow you to create an overly powerful device, but the device is sufficient to perform minor repairs on a car, garden equipment, and fences.

We recommend reading: How to make spot welding for a 18650 battery

List of parts and consumables

To convert a welding transformer into resistance welding equipment, you will need the following elements and materials:

a transformer that converts electrical energy;
thick cable;
copper electrodes;
bolts;
tips;
breaker;
wooden blocks, plywood to create the body.

The process of creating a device

The homemade device is assembled as follows:

The welding transformer is installed in a housing made of metal sheets. The electrical board is assembled on a textolite sheet more than 1 cm thick. The part is fixed in the body of the welding machine.
A welding wire is bolted to the busbar and secondary winding. The remaining end of the cable is connected to the electrode.
The power wire is connected to the contact block located on the electrical board.

Spot Welding Operation

A master using a contact transformer apparatus must stand on a rubber mat and use protective gloves and goggles. The grounding cable is connected to the part to which another workpiece will be welded. After this, press the power key, compare the elements to be connected, and clamp with the electrode of the welding gun.

5 seconds after the start of the impact, the rod is transferred to the next point.

DIY resistance welding pliers

To make such a device yourself, follow these steps:

Form the basis. For this purpose, available materials are used - steel sheets up to 5 mm thick. Strips 2 cm wide are cut from them. The length depends on the design of the welding tongs. The strips can be replaced with metal rods. The ends of the two blanks are bent in the form of tongs.
Place the parts on top of each other and join them together. A hole is drilled in the central part where the adjusting screw will be located. A dielectric layer is placed between the plates.
A hole is drilled at one end of the rod or strip to secure the copper cable. The same actions are performed for the second workpiece. The holes should be opposite each other.
The metal elements of the pliers are covered with a rubber pad and electrical tape. The materials will protect the welder from electric shock during work.
Install the spring between the handles of the pliers. The part is necessary for fixing the elements to be welded.

Electrical circuit layout of printed circuit board

Two blue LEDs connected in series begin to glow just at a voltage of 5 V. They form a battery readiness indicator. I added a yellow electrode contact indicator. I made a circuit and laid out the board in the EasyEDA editor

Circuit based on SMD components

Using spot welding on lithium batteries

Using a battery to weld a nickel plate to the battery is the easiest way. To assemble the mini-unit you will need a battery, a charging cable, a piece of single-core wire, and electrical tape. 2 electrodes are created from the core, the ends of which are stripped and secured. The distance between elements should be 3 mm.

A charging cable connected to the terminals of the lithium-ion battery is connected to the other ends of the electrodes. Place the nickel plate on the battery and press the energized electrodes against it. As a result of a short circuit, the metal melts.