Feb172019
2019 Past Events

Introduction to Metal Joining and Cutting

Prepared for the Porsche Club of America- Chesapeake Tech Session 2/9/19

By Jim Earlbeck

This document introduces the conventional, better known non-mechanical metal joining and cutting processes. The purpose is to make the reader aware of the differences and benefits of each process. More detailed information can be found by consulting other sources such as the American Welding Society’s (AWS) Welding Handbook and the American Society of Metals (ASM) volume 6 Welding Brazing and Soldering.   Those society’s websites are www.AWS.org and www.ASM.org, respectively.

ARC WELDING

The arc welding group of joining processes is widely used by industry and hobbyists. The term arc welding applies to a large and diversified group welding processes that use an electric arc as the source of heat to melt and join metals. The welding arc is struck between the workpiece and the tip of an electrode. The electrode will be either a consumable wire or rod or a nonconsumable carbon or tungsten rod which carries the current. When a nonconsumable electrode is used, filler metal can be supplied by a separate rod or wire if needed. A consumable electrode, however, will be designed not only to conduct the current that sustains the arc, but also to melt and supply filler metal to the joint. It may also produce a slag covering to protect the hot melt from oxidation. 

GAS TUNGSTEN ARC WELDING (GTAW) a.k.a. Tungsten Inert Gas (TIG) and Heli-Arc

GTAW uses a nonconsumable tungsten electrode which must be shielded with an inert gas. The arc is initiated between the of the electrode and the work to melt the metal being welded, as well as the filler metal, when used. A gas shield protects the electrode and the molten weld pool, and provides the desired arc characteristics. The shielding may, in all cases, be 100% Argon. Sometimes a mixtures of Argon and Helium are used to increase the energy density at the arc. On rare occasions 100% Helium is used on aluminum. The attributes of GTAW are as follows:

  • Suitable for all alloys
  • Aluminum and copper alloys are typically done with AC CC power sources with continuous high frequency arc initiation. The AC wave form may be sine or square. A square wave form will allow welding to be done without continuous high frequency or with lift start
  • Ferrous alloys are typically done with DC CC lift start
  • Handles a very wide range of thicknesses, but best suited for ultra thin to 1/4″
  • Suited only for clean materials
  • Generates very low levels of welding fumes and no spatter
  • Produces high degrees of distortion due to elevated amounts of heat input into the weldment
  • Very difficult to master
  • Outstanding control of weld puddle and capable of an autogenous remelt
  • The shielding gas is easily disturbed by wind 

GAS METAL ARC WELDING (GMAW) a.k.a. Metal Inert Gas (MIG)

GMAW is a semi-automatic process in which the heat for welding is generated by an arc between a consumable electrode and the work metal. The electrode can be either a bare solid wire or a cored metal wire. The electrode is continuously fed to the arc and becomes a filler metal as it is consumed. The electrode, weld puddle, arc and adjacent areas of the base metal are protected from the atmospheric contamination by a gaseous shield provided by a stream of gas, or gas mixture, that is fed though the gun. The shielding gases have a great influence over the arc characteristics, the mechanical and the corrosion properties of the weld metal. By altering the gas mixture and the energy; i.e., amps and volts supplied to the arc, various modes of metal transfer can be obtained. Short circuit transfer is best suited for material thicknesses less than 1/4″ and it can be used in all positions. Spray metal transfer is best suited for materials exceeding 1/4″. Spray transfer can only be used in the flat and horizontal positions for ferrous alloys, but can be used in all positions for aluminum. Pulsed spray most easily be described as a hybrid of short circuit and spray. It can be used on thin and thick materials in all positions. For short circuit transfer it is a generally accepted practice to use 100% Argon for non-ferrous applications such as aluminum or copper, 75% Argon / 25% CO2 for carbon steel and  90% Helium / 7.5% Argon / 2.5% CO2 for stainless. Use of 100% CO2 for steel is desirable only if increased penetration and fusion are needed on carbon steel and increased amounts of spatter can be tolerated. Spray transfer typically uses a mixture of 98% Argon/ 2% Oxygen of 92% Argon/ 8% CO2 for steel and 100% Argon for aluminum.  The attributes of GMAW include:

  • Suitable for joining a very wide range of metal thicknesses. 
  • Suitable for joining ferrous and non-ferrous alloys. Best suited for carbon steel, stainless steel and aluminum
  • The equipment is moderately complex as it involves a DC Constant Voltage (CV)  power source, a wire feeder, a gas supply 
  • Not suited for dirty, rusty or painted material
  • Generates very little weld fumes and spatter
  • Produces very little distortion due to its low heat input
  • Is almost too easy to master- in very little time one can learn to deposit an attractive weld bead, but caution must be exercised as lack of fusion or penetration may be hidden beneath that pretty bead on materials above 1/8″ in thickness
  • Good control on thin sheet metal, such as body panels or exhaust tubing
  • The shielding gas is easily disturbed by wind  
  • High travel speeds which may result in poor operator control on intricately shaped weldments

FLUX CORED ARC WELDING (FCAW)

FCAW operates similarly to GMAW and can use the same equipment. The electrode is always a cored metal wire. One variation of the process does not use an external shielding gas. This process is called gasless FCAW. Sometimes it is commonly called outershield welding which is a proprietary name of Lincoln Electric. Think of it as almost a SMAW (stick) electrode turned inside out. The attributes of gasless FCAW are similar to GMAW except that:

  • Suitable only for carbon and stainless alloys
  • The equipment is less complex as it does not involve a gas supply nor a power source that has the same costly stabilizers as GMAW 
  • Well suited for dirty, rusted and painted materials
  • Generates a high amount of fumes and spatter
  • Suitable for windy conditions

Gas shielded FCAW is sometimes called Dual Shield welding, which is a proprietary name of ESAB. This variation of FCAW is a hybrid of gasless FCAW and GMAW. The attributes of gas shielded FCAW include:

  • Suitable for only carbon and stainless alloys
  • Utilizes the same equipment as GMAW
  • Suited for dirty, rusted and painted materials
  • Generates a moderate amount of fumes and almost no spatter
  • Not suitable for windy conditions
  • High welding speeds
  • Very easy to master on materials above 1/4″ in thickness
  • Very high quality weld deposits

SHIELDED METAL ARC WELDING (SMAW) a.k.a. Stick Welding

SMAW is a manual process in which the heat for welding is generated by an arc established between a flux-covered consumable electrode and the work. The electrode tip, welding puddle, arc and adjacent areas of the workpiece are protected from atmospheric contamination by a gaseous shield obtained from combustion and decomposition of the flux covering due to the heat of the arc. The decomposition of the flux also results in a slag covering that helps to protect, support and insulate the molten weld pool. Attributes of SMAW include:

  • Suitable for joining metals in a wide range of thicknesses, but normally is best suited for sections of 1/8″ to 3/4″ in thickness
  • Suitable for joining ferrous and select non-ferrous alloys. Best suited for carbon and stainless steel
  • The AC or DC constant current (CC) equipment that is involved is low tech, low cost, rugged and very portable
  • Suitable for welding dirty or rusted material 
  • Generates a moderate amount of fumes and spatter

OXYFUEL WELDING (OFW)

OFW includes a group of welding processes that use the heat produced by a gas flame or flames for melting the base metal and, if used, the filler metal. The fuel gas and oxygen are mixed in the proper proportions in a chamber which is generally a part of the welding torch assembly. OFW is typically done with acetylene. Acetylene is the only fuel gas that will effectively weld carbon steel. Sometimes hydrogen is used on low melting metals, such as aluminum, in order to gain better control of the melting process. 

SOLDERING

Soldering is a group of welding processes that produces coalescence of materials by heating them to the soldering temperature and by using a filler metal having a liquidus not exceeding 450 degrees C (840 degrees F) and below the solidus of the base metal. The filler metal is distributed between closely fitted faying surfaces of the joint by capillary action.  

BRAZING

Brazing is a group of welding processes that produces coalescence of materials by heating them to the brazing temperature in the presence of a filler metal having a liquidus above 450 degrees C (840 degrees F) and below the solidus of the base metal. The filler metal is distributed between closely fitted faying surfaces of the joint by capillary action.  

CUTTING

OXYFUEL CUTTING (OFC)

OFC is a commonly used for severing or gouging metals which react chemically with oxygen. The metal is heated to its ignition temperature by a oxy-fuel mixture. At this point a high velocity stream of pure oxygen is introduced to produce a chemical reaction and to blow the molten reaction products through the thickness. The fuel gas may be acetylene, propane, propylene and natural gas. Attributes of OFC include:

  • Low cost, low tech, rugged equipment which is very portable 
  • Requires no electrical power
  • Easily learned
  • High risk- involves the use and storage of high pressure and flammable Hazardous Materials
  • Works only on materials that readily oxidize; i.e., rust. 
  • Induces distortion on thin materials
  • requires a secondary clean up operate on the cut surface

PLASMA ARC CUTTING (PAC)

PAC is accomplished with an extremely hot, electrically conductive, high velocity plasma gas jet formed by an arc and gas flowing from a small diameter orifice. Plasma is the fourth state of matter. Temperatures of the plasma jet stream are routinely measured in excess of 35,000 degrees F while the exit velocity hovers around the speed of sound. The arc energy is concentrated on a small area of the material being cut which results in the plasma jet melting the material and forcing the molten pool to exit out of the back side of the surface being cut. This is a versatile thermal cutting process. It can cut any material which is electrical conductive; i.e., it does not rely on a chemical reaction like OFC does. Attributes include:

  • Cuts any metal
  • Low operator skill requirements
  • Low distortion
  • Cuts at high speeds
  • Clean, ready to use cut surface is easily achieved
  • No Hazard Material involved in the process
  • Requires electrical power
  • High fume levels

WELDING AND CUTTING SAFETY 

Welding and cutting is a potentially hazardous activity. It involves high temperatures, high levels of ultra violet and infra red light, sparks, electricity, sharp metal objects, fumes and flying metal particles. AWS Z49.1 Safety in Welding, Cutting and Allied Processes is a free download from www.aws.org. Get it and read it before starting any welding or cutting project.   

THINGS TO CONSIDER WHEN PURCHASING WELDING EQUIPMENT

  1. Does your vendor know more about the equipment then you do and are they willing to educate you?
  2. What alloys are you welding or cutting?
  3. What thickness ranges will you be welding or cutting? What is the minimum, what is the maximum and what is the norm?
  4. What is the shape and purpose of the part that you will be working on? 
  5. What duty cycle, of the equipment, is needed to get the job done?
  6. Do you look at tools as investments or are they throw-aways?
  7. Where is the repair station and how easily is it to get replacement parts?
  8. What is the next machine that you will be buying?
  9. What is the arc quality? An amp is an amp and a volt is a volt, but how they flow through the arc will make your job harder or easier. Would you buy a car without a test drive? Is it a Porsche or a Ford? 
Category: 2019 Past Events