How to MIG weld Square Tube

A Square tube is a hollow structure metallic tube with a square geometry and has a widespread applications in the world. The tube is also available in other shapes like circular and rectangular. Unlike pipe the square tube has four sides with curved profile corners and are available in wide range of material grades and dimensions. Hollow square tubes can be applied to manufacture a variety of products with innovative designs and welding is the foremost technique to join them. Below is the brief description on the welding procedure of square tubing.

Joint Configuration
Square tubing can be done with different joint configuration in different fashions. Most common way is to weld perpendicular pieces like shown in the figure mainly applied in construction, framing etc. Placing one piece upright to the other, we come across three types of joint configurations; one butt joint, one fillet weld and two flare bevels. All of you are quite familiar with these types of joints. On the outer side of the frame one side of open end square tube piece is making butt joint with the wall of second tube piece. Similarly on the inner side of frame, we get wall to wall fillet joint of square tubes. Close study on the remaining other sides shows that curved edges of lower tube are making a junction with side walls of upper tube which is the flare bevel.

Joint Assembly
Once the pieces are in contact having the specific joints, firm tie-in is required so that pieces may not displace from their exact positions during welding. For this, tack weld are laid in order to fix the pieces firmly. Tacking is primarily followed by suitable clamping.

Clamping
Slight pressure on the pieces to avoid any disposition. In order to keep the joint assembly intact, suitable clamping tools are available in market. Sometimes manual clamping is endorsed by welders by making temporary supports. Tolerable pressure on the work piece allows good tacking.

Tack Weld
Before welding to commence, tack welds are applied for ease of joining. Two ways are exercised to weld tacks. Some like to tack at the center of joint sides and some tack at the corners. In former case, misalignment of joint may occur if not clamped properly. It is a usual practice to make next tack opposite to the first one to avoid any distortion. Once the tacks are applied, the joint is ready for the complete welding.

Welding Pattern
In square tubing, welding variables like travel speed, heat input matters a lot in attaining best results. In worst case, complexities may arise which are difficult to deal with later on. Your job is to ensure the complete penetration with suitable speed. If you go with too slower travel, your tubes might be getting burnt. After filling flare bevels move ahead for the fillet weld.  Fill the weld with weaving bead pattern. Side to side motion along the joint regulating the desired heat level. Apply flat weld position on the butt joint. Here you have to deal with thin edges of open end tube which could be burnt so adjust the travel speed accordingly. Grind the weld curves if you want to see the tubes as a whole piece.

Applications
  • Square tubes are commonly used in automotive industry.
  • In construction of buildings, bridges, framing, railing, poles.
  • Office, supermarket, school, residential and home items, furniture, doors, windows, frames.
  • Security and safety apparatus.
  • They are applied in the manufacturing of transport containers.
  • Production of equipment in large industries like mining, agriculture, transport, oil fields.
  • Now a days commonly using in production of towers for telecommunications industry. 

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