What is efficiency in welding & welding efficiency for SMAW, GMAW,TIG, FCAW and SAW?

Efficiency in Welding

In Welding a number of efficiency factors are involved and the most common are:

  1. Arc Efficiency or thermal efficiency
  2. Welding process Efficiency,
  3. Deposition Efficiency and,
  4. Welding operator or welder Efficiency

What is Welding Arc Efficiency?

The proportion of the energy that is available to melt the electrode/filler metal and the workpiece is termed the arc Efficiency. Arc efficiency takes into account the fraction of the arc energy that goes into the workpiece and is not
lost to the surrounding atmosphere. Submerged arc welding process has the highest arc efficiency and gas tungsten the smallest.
The arc efficiency for some of the commonly used arc welding processes varies between 20% and 90%. For a given process, factors like welding in a deep groove, arc length, etc. also influence the arc efficiency. Higher arc efficiency usually means that for a given arc energy, a greater amount of weld metal is deposited and the workpiece cools at a comparatively slower rate. The efficiency value for various processes are given in below table as specified in EN 1011-1.

The welding arc provides the intense heat needed to locally melt the workpiece and the filler metal. In fact, all the electrical energy supplied by the power source is converted into heat (current x voltage). Some energy is lost in the electrical leads, and therefore the energy available for welding is the product of the current (I) and voltage drop between the electrode where the current enters it and the weld pool (V). For example, with 400 A current and 25 V drop from the contact tip to the weld pool, the arc energy is 10,000 Joules/second. This arc energy is partly used up in heating the electrode, melting the consumable electrode or the separately added filler metal in a non-consumable electrode process, and heating and locally melting the workpiece. The rest of the heat is lost by conduction, convection, radiation, spatter, etc.

What is Deposition Efficiency?

Welding processes are classified based on Manual or Semi-automatic or Automatic as well as on type of wire such as cored wire or solid wire. Each factors in these classifications affects the overall weld deposition in the welding process.

Here, the deposition Efficiency or Welding Efficiency refers to the ratio of the weight of filler metal deposited in the weld metal to the weight of the filler metal melted, expressed as a percentage. In simple word, the total amount of filler wire that is deposited into the weld metal compare to what is being supplied. As some metal lost in weld spatters and evaporation etc. Deposition efficiency for various process is given in below table.

Reference: AWS Handbook, Volume 1

What is Welding Efficiency?

Welding efficiency and the deposition efficiency are two different terms. Welding efficiency means how fast a welding process can deposit the weld metal while the deposition efficiency means the actual weld deposit vs. filler wire melted irrespective of the time.

Shielded Metal Arc Welding or Stick Welding Efficiency: 60%

Flux cored Arc Welding-Gas Shielded (FCAW-G) Efficiency: 80- 85%

Flux cored Arc Welding-Self Shielded (FCAW-G) Efficiency: 75- 80%

Gas Metal Arc Welding (GMAW-MIG/MAG) Efficiency: 93- 98%

Submerged Arc Welding (SAW) Efficiency: 99%

Metal Cored Arc Welding (MCAW) : 95- 98%

Gas Tungsten Arc Welding (GTAW or TIG) Efficiency : 93-98%

SMAW process yields a deposition efficiency of less than 60% based on a comparison of the weight of electrodes purchased to the weld deposit weight achieved. FCAW process efficiency is lower than that in gas metal arc welding (GMAW) due to slag ingredients that aid in protection from the atmosphere but do not become weld metal.

What is Welder/Operator Work Efficiency Factor (Dw)

This is a factor for the average arc time per welder manhour while the welder works on welding and welding related functions. In other words, this is the total number of minutes out of an hour during which welding is actually taking place. This is an important factor, which is often difficult to establish. It will have a significant influence on the weld cost estimate so one should make a careful decision on selecting Dw. The Dw factor is weld-shop specific, influenced by shop supervision, shop layout, and the welder’s ability to work efficiently.

The following are examples of typical Operating Factors for the most common welding processes. They should be used as a baseline from which to start, and compared against the experiences of the shop.

a) SMAW Process
– Dw could typically be 10% – 20%. This will provide 6 to 12 minutes arc time per hour.

b) FCAW Process
– This is a continuous wire feed process so the efficiency factor will be higher than for SMAW.
– Using semi-automatic welding on continuous weld joints, the welder will stop every two to three minutes to change weld position. When applied to short welds, the stops will be more frequent.
– Assume the welder stops each minute for ½ minute, and takes 5 minute breaks each hour.
– Dw could typically be 20% – 40%. This will provide 12 to 24 minutes arc time per hour.

c) GMAW Process
This process is similar to the FCAW, with the exception that there is no slag covering the weld.
– Dw could typically be 20% – 40%. This will provide 12 to 24 minutes arc time per hour.

d) SAW Process
SAW process is usually employed on long weld runs, and often on a production basis. If the weld length is longer or welding thick joints, the material handling will be less and higher operating factors will result. For these reasons, the range of operating factor is very wide.
– Dw Could typically be 30% – 70%.

Note: The above Dw factors are approximations. The estimator can correlate welds of similar type and welding process, then choose a Dw factor that is suited to the specific shop operation.

Recent Posts