Welding Resources and Tips

MIG Welding Transfer Types

Introduction

Part of what makes MIG welding what it is, is the transfer of metal, via heat, from the electrode (or welding wire) to the base metal(s) being welded. There are four different transfer types available to MIG welders, and each has its benefits, uses, and drawbacks. Each type is a result of the voltage settings and shielding gases used, so it’s crucial to be aware of how your voltage and gas selection will interact to generate the transfer type.

Short Circuit Transfer

 Short circuit transfer occurs when, as the name suggests, the welding wire touches the metal(s) being welded. Electricity from the gun courses through the wire and creates a short circuit. Within the circuit, the welding wire heats up and drips onto the base metal(s), creating a “puddle” that welds the joint. The welding wire heats and drips multiple times a second, and the process produces a fast crackling sound, like something frying in a very hot pan.

Short circuit transfer is achieved using a combination of low voltage and a carbon dioxide shielding gas or gas mixture. One benefit of the short circuit transfer is that the required shielding gases are less expensive. The limitation is the thickness of the base metals this type of weld can handle. It’s used on sheet metals or thin metals measuring a quarter of an inch or less - anything thicker will prevent the low-voltage weld to penetrate the joint well.

Globular Transfer

Globular transfer is similar to short circuit transfer, with the main difference being the speed and intensity of the dripping from the welding wire to the joint. With a globular transfer, the wire melts and collects in a “glob” at the end of the wire, dripping into the joint only a few times per second. Rather than sounding like a sizzle or a crackle, globular transfer pops. 

Globular transfer happens with a combination of high voltage and an argon shielding gas or gas mixture. One benefit of globular transfer is that it can handle welding thicker metals, but a drawback is that the drops aren’t always easily controlled and can lead to spatter.  

Spray Transfer

Spray transfer happens when the welding wire melts into very fine droplets and sprays, or “mists,” onto the base metals being welded together. A good spray transfer will make a hissing sound, rather than a crackle or popping sound. Another characteristic of a good spray transfer is a clean arc from the welding gun to the base metals.

Spray transfer is achieved with a combination of high voltage and an argon shielding gas or gas mixture, though if carbon dioxide is more than about 15% of the gas mixture, the electrode will never make the transition from globular to spray, no matter how high the voltage goes. This type of transfer is often preferred for welding thicker metals because, when done correctly, it has no spatter. The shielding gas or gas mixture can be expensive due to the high argon content, however.

Pulsed Spray Transfer

Pulsed spray transfer, unlike the other transfer types, requires a high-end welder. The welder, when set to pulse, pulses the voltage instead of providing the usual steady flow of voltage. The pulses occur many times a second, and the result is a transfer that alternates between spray and globular transfer. 

Because the voltage is pulsed, it doesn’t have to be quite as high as with regular spray transfer. This is beneficial because it decreases the overall amount of heat being applied to the weld, allowing for a smaller, neater weld pool and joint. The smaller weld pool also allows for greater flexibility with weld positions, making it ideal for welding pipe and other difficult projects. The main drawback is the greater expense associated with welders that provide this function.

More About Transfer Types

• Mig Welding - Short Arc and Spray Transfer
• Pulse Spray Metal Transfer

Picture Source: draco_cd via Flickr

Successful Brazing – 7 Steps

The term brazing often leaves beginner welders curious and a little put off. After all, it's a strange sounding word that means something much simpler than you would think. Brazing is simply a metal joining process. Filler metal is heated above and then distributed by capillary action between two or more close-fitting parts. It is brought slightly above its melting point and is protected by a flux, or suitable atmosphere, and then it flows over the base metal (wetting) and joins the workpieces together as it is cooled. It's not as difficult to master as it may sound and there are seven steps you can take to make sure that your brazing work is successful.

Picture Credit: welding-fabrication-kent.co.uk

1. Designing and Fitting

The design is the first step to a successful and strong brazed joint. In order to assure that the joint is as strong as it can be, the joint needs to be designed with an overlap that is three or four times thicker than the thinner member. The lap joint is the easiest way to do this. A scarf join can be the next best choice. Joint clearance – distance between faying surfaces – is another consideration. It's important because brazing works through capillary action and the clearance will define the capillary. Most brazing alloys in the B-Ag and B-CuP families need a clearance of between .001” and .005”. If you're using metals that are dissimilar, don't forget that the rates of thermal expansion may be different when you are deciding about joint clearance.

2. Cleaning

The metals being joined must be as clean as possible for the best capillary action. Always remove grease and oil using a chemical solvent or vapor degreasing. Abrasive cleaning should be used to remove surface oxides.

3. Flux

When the metals are cleaned, you have to protect them from oxidation while they are being heated. The oxygen in the gas flame will result in oxide formation on unprotected metals and prevent capillary action. Proper fluxing (which is a protective atmosphere) protects the filler metals and the base from oxide formation.

4. Assembly

It is very important to maintain the alignment of the base metals while the brazing process is being done so that you know you are getting capillary action that is effective. Gravity alone can often accomplish this but sometimes you need to add a little bit of weight. When parts need fixturing, design the fixtures with the smallest mass possible and with materials that are poor heat conductors. This prevents heat from being taken away from the braze while it is being heated.

5. Selecting Filler Metal

Whenever you select a filler metal for any application, a number of factors come into play. The main ones are the joint clearance, the compatibility with the metals you are joining, the heating method and brazing temperature, appearance, environment, and service temperature. Learn about the different alloys you have available and what each can do and you shouldn't have too much difficulty deciding what is the best one for the job.

6. Heat

There are many different kinds of heating methods available for brazing, with torch brazing being the most common one. The entire assembly should be brought evenly up to brazing temperature. When the parts are at the right brazing temperature (you usually will see a dull red glow) add the brazing alloy to the joint. Capillary action draws the alloy into the joint as long as you have followed the other steps (keeping it clean, etc).

7. Cleaning Post-Braze

Once the metal has been brazed, allow it to air cool and solidify. Flux is corrosive, so remove any flux left by immersing the piece in hot water and brushing it off. If left, it can attack and weaken the joint. When the flux is saturated a residue might result and if so, an acid bath will be needed to remove it. Once it is all removed, you're done and your piece is brazed and strong.

 

Electricity for Welding

All forms of arc welding use electric current to generate the intense levels of heat necessary to weld metals together. You don’t need to be an electrician to understand the process, but the greater your knowledge, the safer and better off your welding will be.

A Quick Science Lesson

Electric current is created by the flow of electrons from a high electron concentration (positive charge) to a low electron concentration (negative charge). The flow of electricity though a conductor generates heat, the level of which is based on the amount of resistance offered by the conductor.

An arc welder discharges electricity into the air (via the gap between the electrode and the metal being welded). Air offers heavy resistance to electrical conduction, and therefore generates a great deal of heat.

Units of Measure

Electricity is measure by voltage, amperage and wattage.

Voltage (Volts) measures the potential electric pressure. Voltage determines the distance an arc can travel across the gap between the electrode and the metal - the higher the voltage, the further the gap.

Amperage (Amps) is the volume of electrons flowing through a conductor, and controls the size of the arc.

Wattage (Watts) measures the amount of electrical power in the arc, and determines the depth and width of the weld

Welding Power is supplied by:

• Constant Voltage (CV) maintains the arc’s voltage, despite changes in the current flow
• Constant Current (CC) maintains the same output, despite the changes in the currents flow
•  Open Circuit Voltage determines the voltage at the tip of the electrode before the arc is activated

Welding power is sourced through the following three processes:

• A mechanical generator produces power from a gasoline or diesel fuel engine.
• A step down transformer changes high voltage alternating current into low-voltage high-amperage current.
• An inverter changes current with solid state electronics, minus the heavy weight of a transformer.

Currents used for welding include:

• Alternating Current (AC), which changes the positive-negative electron flow twice per cycle and creates an even current build-up
• Direct Current (DC), in which electrons flow one direction – a rectifier is used to convert DC current into AC current, and direct current is specified by one of two polarity options:

                o   Direct Current Electrode Negative (DCEN), in which the electrode is negative and the                      workspace is positive

                o   Direct Current Electrode Positive (DCEP), in which the electrode is positive, and the                      workspace is negative (widely considered to be the best option for arc welding purposes)

Duty Cycle is the level of continuous running time for a given power out-put of a welding machine, measured in ten minute intervals. Welding machines produce high internal heat, and require cooling time. A 60% duty cycle indicates a machine can run continuously for six minutes, and then requires a four minute cooling period.

 

Tips for Improving Stick Welding

Stick welding is technically called Shielded Metal Arc Welding. It's a very good skill to have, and one that is in high demand in many places. There are many tips out there for improving your skills with stick welding, but there are some basic tips that will really improve your work with shielded metal arc welding. These can help improve the technique of both veteran and beginning welders.

Picture Source: www.hobartbrothers.com

For all around use, a welder with AC/DC output is best. It doesn't matter if it's a gas engine driven one or a electric arc machine. For most Stick applications, you will want to use DC welding because it has many advantages over AC. Some of the advantages are fewer arc outages or sticking, easier starts, less spatter, easier overhead and vertical welding, welds that look better,  easier learning, and smoother arcs. If you choose DC straight polarity thinner metals can be welded better while the DC reverse polarity will give you around 10% more penetration.

AC output does have its advantages. For example, you may need to weld material that has become magnetized from friction. This can happen when hay, water, or feed rubs against a steel part continuously. If you use DC output, it won't work. The magnetic field causes "arc blow" which is where the molten filler metal is blown out of the weld puddle. AC output will allow you to weld things that have become magnetized because it alternates polarities.

You might be surprised at the size of machine that you actually need. The average person will never encounter Stick welding jobs that need a lot of amperage, as most jobs need 200 amps or less. This means that a machine that is 225 to 300 amps will be more than adequate for the average welder. If you do run into material to weld that is thicker than 3/8 inches, then you simply need to make more than one pass.

If you are new to stick welding, you might find the words "duty cycle" on the spec sheets for some products. This can confuse a lot of welders. A cycle is ten minutes, and duty cycle is the number of minutes that you can use a welding machine and the number of minutes in that cycle the machine needs to cool down. For example, some machines create 200 amp DC output and they have a duty cycle of 20 percent. This means that a welder can use the machine for 2 minutes at 200 amps, but then the machine will need to cool down for eight minutes or it will overheat.

You should remember that amperage and duty cycle are inversely proportional. The same machine that will work for 2 minutes at 200 amps, if used at just 90 amps, can be used non stop, as it will have a 100 percent duty cycle. Not all machines work this way, so be sure to read your manufacturers instructions before you try it.

While you should always use a wire brush to clean the areas that you are planning to weld, stick welding is a lot more forgiving about dirty conditions. If need be, you can weld on less than clean materials, but it is better to be as clean as possible, so that you can avoid lack of fusion, slag inclusions, and cracking.

If you are going to be hardfacing, remember that you could face abrasion or impact resistance, and in come cases, both. The type of rod that you use depends on the aggregate or soil that is in your area. Make sure that you talk to the local welding supply distributors so that you can get their opinions. If you don't know of any, you can look up the information or look up numbers to call that can give you the proper information.

Even with these tips, you can and will occasionally make mistakes. A good rule of thumb is to keep a good view of the weld puddle at all times so that you're sure you're welding where you want to be. Everyone makes mistakes, and that is how you learn, so just keep trying and you'll become a great stick welder!

Dirty Welds: Consequences & Prevention

In the course of action through your career as a welder, you will frequently find yourself in situations that require you to weld metals that are in less than pristine condition, having sustained a fair amount of wear-and-tear through many years of use.

The result of welding on dirty/rusty metal.

Image Source: www.hubpages.com

When you're called upon to make repairs out in the field, you're often presented with rusty, dirty, and greasy metals, not to mention metals that are completely covered with paint. Odds are you will find some combinations of these conditions (and sometimes all of them at the same time) on most of the jobs you're asked to perform. Even when making repairs in the shop, you’ll often be dealing with metals that are rusted, dirty and covered with paint, similar to what you might when making repairs in the field.

New metals also have their fair share of issues, given that many are covered with various coatings intended to preserve and protect the raw metal (galvanized steel being a prime example).

Preserving the integrity of your welds

Rust, dirt, grease, paint and many coating materials can compromise the integrity of your welds. These substances can contaminate the weld puddle, creating imperfection in the weld, compromising the welds overall strength. Additionally, paint and certain coating materials will be vaporized when super-heated by a welding. This vapor can be toxic and make you very sick if inhaled (the zinc coating in galvanized steel results in Fume Fever), and can also introduce air bubbles into the weld, severely compromising the overall strength of the weld. Long story short, it’s in your best interest for every welding project you work on to make sure the metal you’re working with is clean and clear of contaminates, and ready to rock!

The Cleaning process

The cleaning process depends to some degree on the type of metal you’re working with and the type of contaminant you’re trying to remove.

Let’s say you need to make some repairs to a semi-truck that’s seen quite a bit of road wear. The section you need to repair is definitely dirty, covered with some rust and grease, and to top it off, somewhere along the line the metal was painted to match the rest of the rig.

1.      Hit the whole area with a degreaser

2.      Use an angle grinder to remove the rust and paint

3.      Wipe down the weld area with acetone, using a clean shop rag

The degreaser eliminates the grease, the grinder removes the outer dirt, the rust and most of the paint, and the acetone will attack any linger elements that the first two clean methods may have missed.

Now you’re all clean and ready to weld!

*Please Note – Carburetor cleaner, and other similar automotive related cleaning chemicals are often used to clean metal before welding. You should, however, pay close attention to chemical interaction that may occur when these materials are super-heated by a welder. When vaporized, some chemicals are highly toxic and can cause stroke or death. Make sure you read all of the warning information included with these chemicals, and if you’re unsure, look it up online or just don't use it—always better off safe than sorry!