- 1 Overview of Spot Welding
- 2 Choosing the Best Spot Welder: The Buying Factors
- 3 Top 5 Spot Welding Units
- 4 Conclusion
The technique of welding joins the metallic parts with the help of heat. Spot welding is a kind of welding process involving heat being generated at the interface by the joint’s electrical resistance. It joins two metal surfaces by heat fetched from the metal’s resistance to the flow of electric current, without using any arc. This is why it is also popular as a kind of resistance welding process. Usually, welds are created in around 0.2 seconds, with the help of the power boasting high current but low voltage and pressure exerted to the joint via two electrodes placed on opposite side of metal pieces. Spot welds occur at orderly intervals on a sheet metal with an overlap. This guide will help you find the best spot welder.
Overview of Spot Welding
In spot welding, two sharp copper alloy electrodes are used to cluster the welding current to a petite ‘spot’ as well as fasten the work pieces simultaneously. Inflicting a sizeable current via the two metal pieces eventually melt them a bit for welding. The best part of this procedure is that it occurs very quickly, in just 10 milliseconds and that too to a specific small spot to which the heat generated is not too much to result in warping.
The quantity of heat delivered to the welding spot is dependent upon the duration of current and resistance between the amplitude of electrodes. The heat has to be just perfect, as too little of it will not melt the metal and too much of it will melt so much that it can result in a hole rather than a weld. Spot welding does not require extra filler metals or flux.
Such a process is capable of rendering a high production rate with incessant quality control. The sophisticated equipment for such welding comes with comprehensive feedback control systems to rectify any weld that is not as per the required specifications. The strength of the joint is also great but it is dependent upon the size as well as number of the welds. Along with strength, spot welding ensures cost effectiveness and speed, which other metal -joining techniques do not surpass.
Spot welding is specifically for joining metals having a thickness of up to 3 mm (0.125 in). Due to high rate of production, a spot welder is bound to increase the productivity at a workplace as well as restore a metallic tool or vehicle to its healthy state before a mishap.
One of the major applications of such a unit is in the industry of automobiles, wherein metallic sheets are used for making the body of cars. Other applications of spot welding include in designing stuff such as batteries, nuts and bolts, metal buckets, and batteries. There are many spot welders for professionals, hobbyists, and several industrial applications.
The biggest advantages of using spot welders are high speed, dimensional accuracy, adaptability for automation in highly productive tasks, and economical range.
Choosing the Best Spot Welder: The Buying Factors
A spot welder is a versatile tool and does not need any kind of component preparation. However, the market is flooded with different spot welders and selecting the right one can be a bit confusing even for a somewhat experienced welder or metal fabricator. This is perhaps because of the price differences that are at times tough to comprehend as well as justify. The welding units are available from conventional air cooled to industrial liquid cooled ones.
Choosing a wrong spot welder can actually prove to a costly affair. With such a unit, instead of proper spot weld, you will encounter a rupture in the fused zone along with a tear of the base metal flanking the weld. Selecting the right spot welder is actually dependent upon several factors such as the enabled duty cycle by the unit, output required, extend of welding that you wish to do, and power supply. Let’s explore all such influential factors.
1. Your Major Requirements
Well, you should start by knowing your key needs without which you seriously cannot choose the right model with the required features. Following is what you need to find out or consider, even before finding about the different spot welding units.
- A list of metals that you will be spot welding. A resistance spot welder is preferred for welding metals such as galvanized steel, low carbon steel, stainless steel, titanium, and copper. Such a unit can weld clean mild cold rolled steel sheet, wire mesh, stainless steel sheet, and plates for tubing, nuts, studs, and bolts. A few models can weld any kind of metal but a few metals are welded by using a specific spot welder.
- Consideration of thickness of the metal or product that is to be welded. This is a vital factor for selecting a welder. All metals possess different level of thicknesses due to which power requirements differ due to which using a special welder might be indispensable.
- The required weld current, which depends on the type of material to be welded, its thickness, and component’s shape.
- The need of single or multiple applications of the tool, which can help you choose a more affordable spot welder in case you do not need it for a variety of applications.
In short, you should know the primary purpose for using the welder, which can be automotive, heavy production, fabrication, and farm-based. This is because each type of welder is designed for some specific use.
2. Types of Spot Welders
There are different varieties of spot welding units to consider as per the work type.
- Stationary Single Spot Welding Units: These units are not so portable and are of two types: Rocker Arm or Horn and Press. The horn type units features a rocking or pivoted upper electrode arm activated by pneumatic or operator’s physical power. The rocking motion of the arm applies pressure to lift the upper electrode up and down. The stationary electrode is mounted on a pivot arm, which is brought down onto the work piece via manual or pneumatic method. This type is more affordable and simpler but is limited to tasks demanding not more than 50 KiloVolt Amps (kVA). It is also ideal for metals having a high gauge (thin metals). For bigger applications requiring more than 50 kVA, the press type unit is preferable. In such a unit, the upper electrode shifts in a straight line along the machine column. The motion and pressure are given on the upper electrode by pneumatic or hydraulic means or by a motor. Such units have slide-positioned electrodes for giving you several welds in short time. Press spot welders are commonly preferred in the metal-working workplaces due to versatility, easily obtainable, typical throat depth choice, transformer capabilities, and required electrode forces.
- Portable Single Spot Welding Machines: Well, these are highly portable ones with smaller size and compact designs. They may be corded or cordless.
- Spot Gun Machines: A big number of welding guns are available to work with spot welders that are designed for working with pieces of larger sizes. These are portable spot units that are associated with transformers via a long cable and are taken where welding is done. The electrodes feature a contact area for rendering the required current density via the work pieces. In these guns, the welding pressure can be applied hydraulically, pneumatically or manually, as per the gun’s size and shape.
- Multiple Spot Welding Machines: As the name suggests, these units are ideal for several high-volume tasks, such as those in the automotive industry. They are available as press units on which separate guns hauling electrode tips are placed. To prevent all electrodes from holding the current simultaneously, welds are created sequentially. The equipment can be relatively affordable and simple even for such flexible units.
- Seam Spot Welding Machines: These units function with the help of sophisticated control technique featuring a travel speed as well as the current flow’s sequence to retain overlapping welds. The actual routine, welding tempo, and spots every centimeter are interdependent.
- Bench Spot Welding Machine: These are highly versatile units for use in production and workshop activities. They consist of top quality welded steel body that consumes a minimum bench space. While the top arm extension is combined with the frame, the secondary arm at the bottom may have some tooling.
3. Materials to be Welded
Low carbon steel is ideal for spot welding. Alloy steels and higher carbon steel result in hard welds that are prone to crack. However, tempering can bring these risks down. You can even spot weld austenitic stainless steels having the 300 series grade along with ferritic stainless sheets. However, the harder martensitic stainless steels are not apt for spot welding.
Aluminum is fine for welding through high power and neat oxide-free surface. To ensure the latter aspect, you will have to clean the surface, which just increase your cost. You cannot spot weld dissimilar stuff due to different thermal conductivity points and melting properties.
Chrome and nickel plated steels are easier to spot weld, while zinc, tin, and aluminum demand for elite preparation, which is always there in case of coating metals.
4. Electrode Material and Geometry
Electrodes are a critical factor to consider for best resistance welding process although they are the most abused ones. In fact, you need to consider their material, cooling power, tip profile, shape, and size. Technically, the shape and size of individual welds depend heavily upon the shape and size of the electrodes.
Electrodes tend to differ in terms of electrode geometry or shape and consequently in terms of function. For example, the right electrode boosts the electrical, mechanical, and thermal performance due to the increase in the cross-sectional area from the work piece.
Even the electrode contact area’s diameter has a role to play. If it is too small, it gives shorter welds with inadequate strength. Similarly, if it is too large, you get unstable as well as inconsistent welds. In short, the electrodes should conduct current to the metal piece, constrain it, and conduct heat from the piece. To ensure all these three functions, it is essential to choose the right electrode material.
The electrode material needs to maintain high loads at elevated temperatures as well as retain sufficient thermal as well as electrical conductivity. A variety of refractory- and copper-based materials are suggested, as per the application. Resistance Welding Manufacturers Association (RWMA) has prescribed materials for electrodes and has split into three groups or classes:
- Group A: Includes copper alloys and is split into two classes. Class 1 includes materials made using 1% cadmium and 99% copper and are recommended due to great electrical and thermal conductivity. These alloys are suitable for spot welding bronze, brass, magnesium allows, and aluminum alloys. Class 2 includes 0.8% chromium and 99.2% copper. These materials are general purpose ones and are suitable for production seam and spot welding of maximum metals.
- Group B: Includes refractory metals as well as metal composites.
- Group C: Includes special materials.
Conductive materials such as copper and dispersion strengthened copper (specialty material) are ideal for resistive metals such as stainless steel and nickel. These higher conductivity alloys are beneficial while welding coated steels because the ensure less heating due to low contact resistance. On the other hand resistive materials such as molybdenum are for welding conductive stuff such as copper and gold.
Described by International Organization for Standardization – ISO 5182, electrode materials can vary. Mostly, copper alloys are used for boosting hardness as well as retaining good conductivity. Some of the commonly used materials belong to Class 2, which are copper with chromium or zirconium. They are preferable for high strength and low carbon steels to be welded.
For spot welding harder sheets such as stainless steels, lower welding current but higher electrode forces are needed. Thus, they are better welded with the harder electrode materials belonging to Class 3, such as alloy of silicon, copper, and nickel.
Refractory materials, such as molybdenum, tungsten, and tungsten with copper, are ideal for projection welding inserts. This is because the electrode contact area is thrice of that the weld size and that the materials feature more hardness and lower conductivity than those of Class 2. However, these are not meant for spot welding because they localized heat at the contact’s tip that can invite electrode’s cracking. The only exception is for using them for high conductivity metals, where heat comes from within the electrode tip and conducted into the metals to be joined.
5. RWMA Recommendations
Following these recommendations is essential for choosing the right welder. The RWMA is committed to improving industry standards since more than 50 years. At present, it represents around 40 manufacturers selling resistance welders, components such as controls and transformers, and electrodes.
Any spot welder is rated in its thermal rating measured as KVA. The RWMA rates it by considering 50% duty cycle for standard units. Nevertheless, not all manufacturers meet these standards. So, you need to check that out.
Short-circuit current of the unit is another performance measure to check out. RWMA states this current as per the unit’s size, throat dimensions, KVA rating, and permissible duty cycle under short-circuited situations. For adhering to this standard, a spot welder should possess sufficient copper areas in the secondary loop, KVA rating as per 50% duty cycle, and sophisticated water cooling system.
You should also consider the weld force, which contributes to the overall strength of weld. Most modern welders are run with air cylinders of different diameters, which apply the force via a lever mechanism (rocker arm) or directly (press). The press-type unit’s force is calculated from the cylinder’s diameter as well as from the applied air pressure. In case of a rocker arm unit, extending the length (throat deep) of the arm affects the maximum welding force, as the latter decreases proportionately as the throat depth increases. RWMA states the maximum force to gain from both these types or from frame size of the unit.
Lastly, you also need to consider the durability and the frequency of using the welding machine. You can discuss about the same with the manufacturer who can accordingly aid you in choosing the right spot welder.
Top 5 Spot Welding Units
This unit is designed for home jobs. You can rely on it for spot welding up to 16 gauge steel, over 1 mm rails into AK47 receivers of 1 mm, and 2mm thick sheet metal. Consider it if you need a spot welder to operate from a typical 115VAC circuit within 15A. Except for power switch and insulators, all parts are metal, which indicates a fairly solid metallic build. The four copper tongs are also solid and thick and have a length through which the tips can reach around 7.5 inches into a piece. The unit has two sets of tips, which are readily available. This unit is for welding two metallic pieces each up to 1mm thick, which means it is not for 1/16″ thick sheet metal. You can consider using thinner sheets for welding, of plain, stainless, or galvanized steel or even of tin.
This one is ideal for a hobby type people and individuals performing little jobs. The unit is perfect for welding nickel terminals of high temperature to the nickel based wire. You can even use it with uncoated stainless, galvanized, or mild steel sheet. The unit is portable enough to carry it easily anywhere. It features six tongs with standard tips, locking firmly onto the work pieces.
This is a small-scale welder dedicated for making jewelry. It is not for those who have no experience in welding but for those who have can use it easily. The unit can weld alloys of precious metal such as titan, palladium, silver, gold, tungsten, platinum, and high-grade steel. It can even weld most brass alloys, tin, and aluminum with some limitations along with alloys having differing properties. You can make thousands of welds without any issues. Because it is gas-less pulse welder, avoid using it on precious stuff such as gold if you do not know about how to use the welder on them. It is easy to weld 1.6mm stainless steel with this unit. Consider it for welding for purely ascetic purpose or on less significant objects, as the chain is strong even at 1/4 weld pen. While welding 1.0mm stuff on max setting, a single weld can give you 100% weld pen.
This one is another spot welder dedicated for precision welding of batteries of laptop and mobile phones. You only need to hold the battery and raise it up to one of the welding needle butts at the right spot. Each needle applies reliable pressure, as it is regulated independently. The welding current is quite stable for offering a clean spot with smaller sparks but without blackening. There is also no moisture emission in case of lithium models. The unit comes with a single chip microcomputer that enables dual pulse welding. Further, the LED controls make it easy to set up several parameters accurately. You can use this welder for welding high-grade batteries such as lithium, nickel-hydrogen, and nickel-cadmium.
This lighter unit is dedicated to spot weld batteries as well as recharge them. The charging function is reliable, which can recharge any voltage batteries for mobile gadgets. While the instructions are no obvious, it takes no time to get used to this unit. The welder cannot be beaten in terms of price and functionality. It comes with achieved precise micro-computer, MCU start control, wider current range ability, single/double pulse soldering modes, digital battery recharge function, touch digital control, short circuit protection, and temperature display with accurate spot soldering.
It is always wise to choose a spot welder as per the RWMA standards as well as your requirements. While there will be many models and prices to tempt you, it is not recommended to get the one that does not serve as per your needs.