Get better welds during plant maintenance
The ability to make good welds is vital to plant maintenance. However, for many plant engineers, welding is only a part of their jobs and a skill that is practiced as needed. Following are some tips to help you keep welding skills sharp and make high quality welds consistently. We’ll focus on MIG and stick processes, since they’re most commonly used for repairs.
Read the operator’s manual for the equipment. It includes important safety information and instructions for getting the most from the welding equipment.
Even quick welds require the use of proper safety equipment: welding gloves, non-flammable pants and shoes, welding jacket, beanie or hat and proper welding helmet. Be sure to cover all exposed skin to avoid the effects of arc rays.
Breathing welding fumes can be hazardous to health. Keep out of the fumes and take precautions to not breathe them in. Use proper ventilation techniques such as forced ventilation at the arc to keep fumes and gases away from the breathing zone and the general area.
To make the process easier and increase weld quality, use an industrial-grade, auto-darkening welding helmet. Auto-darkening helmets help eliminate weld defects because they allow welders to position the gun or electrode with the helmet down.
Before you weld
While stick welding is more forgiving than MIG welding on dirty or rusty metal, all welding is best done on clean material. For best weld quality, clean off rust, paint and oil.
For stick welding, most will usually use a 3/32-inch-diameter rod for material 1/8 inch and thinner and a 1/8-inch-diameter rod for thicker material. Common electrodes used for general work include 6010, 6011, 6013, 7018 and 7024. For better bead appearance and work on higher strength steels, use a 7018 rod. Note that 7018 rods are notoriously difficult to restart if the edge of the flux on the end of the rod is not broken off first. Most welding distributors can help select rods to meet specific needs.
Many plant engineers use just one wire for MIG welding. The one that will give the most flexibility is 0.035 inch wire, in combination with a 75/25 Argon/CO2 gas mixture. Be sure to match the contact tube, the gun liner and the drive rolls to the wire size being used. Clean the gun liner and drive rolls occasionally, and keep the gun nozzle clean of spatter. Replace the contact tip if blocked or feeding poorly.
Creating a good weld
Proper position is important. Find a comfortable position that allows use of both hands to steady the gun during the weld. For longer welds especially, rehearse the weld beforehand to make sure you can maintain a steady travel speed, arc length and electrode angle.
Your position should provide a clear view of the puddle and the arc. This makes it easier to read the puddle, maintain an optimal arc length and keep the electrode or wire on the leading edge of the puddle, which is important in creating sound welds. Staying on the edge of the puddle helps ensure proper penetration. If the electrode or wire is hitting the middle of the puddle, the puddle becomes an insulator and the weld no longer penetrates as deeply.
To create a solid, cosmetically appealing weld, it is important to maintain a constant travel speed. Dwelling on a specific spot of the weld too long creates an uneven bead profile. Judge whether you’re going too fast or too slow by watching the width of the bead. If you’re going too slowly, the arc will strike the puddle, which will absorb the arc force. The arc will not penetrate to the base metal, leaving a wide weld bead with poor fusion. If you’re going too quickly, there will not be as much heat input into the weld, reducing the melting of the base metal. This leads to a thin weld bead and insufficient penetration. The best travel speed is usually one that puts the arc at the puddle’s leading edge once the bead width is established.
In the flat position, the ‘back stepping’ technique helps achieve the ‘stacked dimes’ look. In this technique, the welder positions the arc so it strikes at the leading edge of the puddle, ensuring good penetration. Then they back up to the middle of the puddle to fill and move out again to the leading edge, advancing each time.
Stickout and arc length
In MIG welding, it’s important to maintain the proper stick-out: the length of the electrode extending from the tip of the contact tube. In short-circuit MIG, the optimal stickout is from 1/4 to 3/8 inch. If it’s longer than that, the extra length of wire acts as a large resistor. Arc amperage and penetration will decrease, resulting in lack of fusion and poor starting, and the electrode may no longer be covered by the shielding gas, leading to porosity in the weld.
Note that when starting a weld, a short stickout helps ensure a good, hot start; a longer stickout %%MDASSML%% once you’ve established the arc %%MDASSML%% can help bridge a gap when encountering poor fit-up. If the distance is too short, you risk an excessive amount of spatter coming back into the nozzle, which could lead to wire feeding problems.
In stick welding, the correct arc length varies by the diameter of the electrode. In general, for 1/16 and 3/32 inch, use an arc length of 1/16 inch. For 1/8 and 5/32 inch, use an arc length of 1/8 inch.
Gun and electrode angles
In MIG welding, there are three common gun angles in relation to the direction of travel (Fig. 1): perpendicular (where the wire is fed straight into the puddle), push (where the gun is tipped away 10 degrees from the direction of travel) and drag (when the gun is tipped 10 degrees with the direction of travel). Pushing gives a flatter, wider bead with less penetration. This technique is commonly used to prevent burn-through on light-gauge material. The dragging technique, used on thicker material, provides deeper penetration with a narrower bead and more buildup. In stick welding, hold the electrode at a 5 to 15-degree angle, and always drag it.
Welding in the flat position
In the flat position, the work angle %%MDASSML%% the angle perpendicular to the direction of travel %%MDASSML%% on a flat weld, such as a butt joint, should be 90 degrees to the workpiece, directing the filler metal straight into the joint. A weaving pattern %%MDASSML%% a back and forth motion perpendicular to the direction of travel %%MDASSML%% can help fill a large gap or can be used when making multiple passes.
On a fillet weld, maintain a 45-degree work angle or equal distances from each piece. When making multiple weld passes, change the work angle slightly to avoid uneven weld beads and undercut.
Welding out of position
Ideally, all welding would be done in a flat position. In out-of-position welding %%MDASSML%% horizontal, vertical and overhead %%MDASSML%% gravity is working against you, pulling the puddle down. In out-of-position MIG welding, using slightly less voltage and wirefeed speed helps lead to a smaller puddle and better control.
In the horizontal position, a push or drag technique can still be used, but work angle is usually dropped 0 to 15 degrees to counteract the effects of gravity. Traveling too slowly or with too large of a wire will put more metal into the puddle, causing it to sag.
Use a back and forth weave bead on thicker metal when making multiple-pass welds, or to bridge a slight gap where fit-up is poor. A slight hesitation at the top toe of the weld helps prevent undercut and ensure proper tie-in of the weld to the base metal.
The vertical down position is usually used on 3/16-inch and lighter, cold-rolled steel because the arc penetrates less and helps eliminate burn-through. In this position, the puddle can easily get ahead of the arc, which means the arc is no longer on the leading edge and no longer hitting the base metal. Then the puddle becomes an insulator and penetration is lost. Welders will have to travel fast to stay on the leading edge.
Use a vertical-up technique on hot-rolled steel and cold-rolled steel 3/16 inch and thicker to get deeper penetration.
When creating a fillet or groove-weld using the vertical up position, a side-to-side weave technique can be used. Manipulating the arc from the right, to the center, to the left, in the form of a triangle, lets the corners of the triangle cool so the puddle isn’t too molten and allows a good foundation for the next pass. Pausing briefly at each side of the joint provides good fusion.
For overhead welding, you may have to turn down the heat, move quickly and keep the weave narrow so the puddle remains small and the metal will not fall out of the joint. Keep out from underneath of the weld puddle and make sure you wear the proper safety gear, your jacket is completely closed and you wear a welding beanie.
Keeping these tips in mind will facilitate consistently good weld results. However, the proper choice of equipment can make it even easier. If you haven’t updated your welding equipment in the last few years, take the time to see what’s available. Inverter technology puts a very high quality arc into lighter weight packages for increased portability, better puddle control, easier setup and decreased likelihood of weld defects.
A multi-process inverter provides excellent stick, TIG, MIG, flux-cored and gouging capabilities, while an all-in-one MIG welder can weigh as little as 50 pounds and allow you to take a high-quality MIG arc to where the work is. Even some non-inverter welders have improved, taking the guesswork out of setting parameters and allowing the user to focus on proper gun technique.
|Neal Borchert is a certified welding inspector and businesses development manager with Miller Electric Manufacturing Co. In his 30 years at Miller, he’s been a welding instructor, coordinator of weld process training and product manager. He’s been involved in the training of and the introduction of new technologies to the construction trades, and he leads Miller’s training efforts with educational institutions.|
|Ken Stanzel is product manager for Miller Electric’s Small Integrated MIG Systems business unit, where he is responsible for the Millermatic 140 with Auto-Set, Millermatic 180 and Millermatic Passport all-in-one MIG systems. As product manager, Ken’s responsibilities include new product development.|