^ Large Market Share of Arc Welding (Source: http://www.transparencymarketresearch.com/pressrelease/welding-products-market.htm)
The Strategic Importance of Arc Welding
Wind-Power, automotive, and building-construction will continue to create demand for the welding equipment market. Transparency Research Market expects the global welding equipment market to grow to $23.78billion by 2020. Global Research and Data Services forecasts the growth of this market at 4% p.a. in 2014-18.
Arc Welding makes up 40% of the global welding-product market on account of its simplicity, versatility, flexibility, and cost-effectiveness. It is indispensable for building ships, power plants, automobiles, and steel-frame buildings. As a fabricator, you just cannot do without knowing best arc welding practices.
For Top-Class Stick Welding
Although Shielded Metal Arc Welding (SMAW) welding is the most tolerant to dirt and rust, don’t take this for granted for unclean materials can cause porosity, cracks, inclusions, and fusions.
Select a comfortable position from where you can maneuver the electrode while having a full view of the puddle. Keeping your head at the side, away from smoke provides an excellent view. Warm up the rod on scrap material before you start.
CLAMS or current setting, length of arc, angle of electrode, manipulation of electrode, and speed of travel are the five techniques for best stick welding:
- Current Setting: the electrode/rod determines the current setting: AC, DC-negative, or DC-positive. The type and diameter of electrode and the welding position determine the amperage
Most SMAW procedures need machines of 200amperes or less. For material over 3/8-inch thick, employ multiple passes with the same machine. Select current levels that generate 15% less heat for overhead welds vis-à-vis flat welds
High currents make the arc louder, char the electrode rapidly, and produce extremely fluid puddles. Low amperages extinguish and stutter the arc and sticl the rod to the workpiece
Straight polarity DC-negative better welds thinner metals. DC-positive offers around 10% more penetration than AC at same currents. Change amperage in steps of 5-10amperes
- Length of Arc: select a length equal to or less than the core of the electrode. Long arcs generate porosity, spatter, and undercuts. Short arcs extinguish faster creating weld beads with high crowns
- Angle of Electrode: is important because the electric arc generates an electrical force called arc force. This force controls the puddle that may lag or lead the pool
A 5-150 angle in the direction of travel is acceptable for flat, overhead, and horizontal positions as also for welding thin and heat-sensitive metals
In-direction inclination directs heat away from the puddle during overhead welding and prevents the downward fall of molten material. It however gives shallower penetration
For vertical-upward welding, choose a 0-150 opposite to the direction of the travel. Opposite inclination is called dragging the electrode. It provides maximum penetration
- Manipulation of Electrode: is welder-specific. The longer an arc stays in the middle of the puddle, the longer it takes for heat to be transferred to the base material
Weaving i.e. moving the electrode from side-to-side along the joint saves welding time and is used for wider weld-gaps. The alternative is stringer beads produced in a single pass of the rod
Stringer beads are useful for narrow weld-gaps. Using multiple stringer bead passes for wide gaps impairs placement and bead profiles. Improperly executed weaving causes fusion-underneath
You don’t need weaving for material of or under ¼-inch thickness. Restrict the weaving width to 2.5 times the electrode-core diameter. Undertake multiple weaving passes for thicker joints
Weaving for overhead welds is the toughest. Keep the electrode inside the molten puddle while weaving. Outside the puddle, electrical resistance decreases suddenly creating a current surge that showers sparks and gives out a loud pop
For vertical-upward welding, slowly move the electrode from the middle to the side and pause momentarily at the sides. This prevents the puddle from lagging the rod, ensures strong bonding with the sides, and prevents undercut edges
For positions other than vertical-upwards, weave fast when at the center of the puddle to prevent high crowns i.e. central bulges. Common weave types:
- triangular weaves efficiently fill steep pockets
- semi-circular weaves with the stroke crossing the front of the puddle prevent puddle overheating
- pulling crescent or semi-circular weaves back through the puddle generates greater heat
- Speed of Travel: must maintain the arc in the leading one-third part of the pool but not exceed the rate at which the arc melts the base metal
Effect of Travel Speed on Weld Quality
Very fast travel produces shallow penetration, underfills, and undercuts. Slow travel creates shallow penetration and cold-lapping i.e. the weld appears to sit on the surface
Stickout or Electrode Extension is the distance between the arc and the contact tube measured along the length of the wire. Smaller stickout boosts weld heat and penetration while checking heat-buildup in the electrode.
- Shield your eyes and skin from UV light and spatter with overalls, gloves, and helmets with dark visors. Spatter are the molten material droplets that fly around
- Ensure ventilation to maintain welding fume levels below 5mg per cubic meter of clean air
- Cleanse the welding area of inflammable materials as spatter can ignite them. With a helmet, you may not notice a fire. Always have a fire extinguisher ready
- Prevent electric shocks by having wires with good insulation and wearing dry gloves. Note: sweat dampens gloves and lowers their shock-proofing ability
- Cooling welds throw off tiny slag particles. Don’t look at them for the slag may end up in your eyes
- The electrode is always live. Insulate it from the ground when not in use
Executing SMAW is more of an art than rocket science. And it is among the toughest welding processes to master. Rookies will do well to practice and practice hard. Good Luck!