In today’s article, we are going to discuss projection welding. This is a way or system of ensuring accurate heat balance in hard spot-welding applications.
It’s applicable on thick metals where the measures to be welded differ in sizes by 5:1. Weld current can be concentrated on to the small area of the projection to make heat on the required location by projection on that surface.
This method can extend electrode lifespan by growing the electric contact area. It also decreases the current density on the electrode surface. Even if the weldments are dense projection welding is useful to work with.
What Is The Difference of Spot & Projection Welding?
Spot welding is a way of joining a metal surface by the heat obtained from resistance to current. It’s also known as RSW or Resistance spot welding and subset of electric resistance welding.
Spot welding is different from projection welding. In spot welding, one or more projections are attached to one or two attached work pieces. It creates a distinct current conduction point.
All the parts are placed on top together and weld using large area electrodes. When, the current pulse under the influence of the electrode force, then it defines as large electrode areas. That is also a better option to weld several projections at the same time.
Why Need Projection Welding?
Projection welding is one kind of resistance weld where the shape or design of the part is used to make subtle point contacts to concentrate the current during welding. Mostly, in almost all applications with various small projections are molded on single parts surfaces which need to weld.
The projections might be round dimples, circular, elongated ridges or else weld nut’s prolonged corners. There are two round wires put together at 90 degrees form a point contact. And that would be the projection weld as well. The projections concentrate on the current flow once the mating parts are got together. That produces heat into these places.
When the heat is extreme, they collapse from the weld nugget forms. When the heat is reduced, you could see some nuggets are holding the part. However, on the cross wire welding, you will see single weld for each crossing position, but usually many wires or slices are welded at the similar time as in fencing.
A tight hydraulic seal could be made by a circular ring projection on the foot of the hydraulic fitting. Different parts bolted on weld nuts on the automobile. The cross wire weld is rebar or fence in a thoroughfare.
The method of projection welding is similar to spot welding, but the electrodes are not applied to focus the heat. The part arrangement or projection does this. In here several welds can be made in the same period when several projections are present. It’s quite affecting not dependent like the spot welding. Some elements must be controlled with nut welding thread protection like alignment, projection consistency, welder fellow up, etc.
Parameters for Projection Welding
Making a weld bead with accurate size, shape, and depth depend on many variables. Here is a short description of these parameters.
Usually, the amperage dictates the measurement and penetration of the weld bead when the torch is moving at the right speed. The current settings welders use comes from the welding machine; electrode manufactures or the welding procedure specifications ( WPS). There is a simple way to check the current. Take a small piece of same thickness plate to see the result.
Length of Arc
The amount of current and heat going to the joint is depending on how close to the work plates the welder holds welding electrode or the wire arc. The current and temperature will be high if you hold the work plates close. And keeping it further will produce less heat and more sprinkling.
The first rule is the length of stick welding should match the diameter of the electrode metal. Suppose, when you use 1/8 inch rod and hold it 1/8 inch from the plate; you could raise the arc length to reduce heat to the puddle or to lessen the weld metal deposition.
The wire electrode is holding far from the joint in a wire feed operation. Since the arc is more concentrated and it’s capable of burning through heavy materials. The variation between Electrode StickOut and Contact to work Distance affects the current amount going to the joint regardless of the wire speed adjustment on the machine.
Commonly two torch angles are used for welding. First and foremost, is the Work Angle; its work between the joint and torch aka rod. Welders hold it to the perpendicular of the flame to the joints or 90-degrees. But here is an exception- the T-joint. In here the work angle varies from 30-50 degrees. The second once is travel angle which uses for projection welding. It’s the relationship between the torch and line of travel. The welder tip the rod up to 10 degrees in the travel direction to see the joint and puddle. In some cases, it might go to the opposite direction of the travel.
That is means the working effort of welder when he guides the electrodes along the joints. To get the best results, it’s crucial to control the heat and penetration. Welders use different types of beads like weaver, drag, whip, and push its motions as manipulation.
The weld sizes will small if welder moves too fast. The fast movement also causes insufficient penetration. If the action becomes slow, the result will be round weld bead, and too much heat will penetrate the workpieces.
Types of Projection Welding
Advantages of Projection Welding
- The welding current intensely works on any individual parts using the profile or projection.
- Electrodes with large flat contact area can be used on the full or half identical area of the work piece.
- Even electrodes come with more lifespan. It does not make any deformation of discoloration on the project and fits well in high-volume production works.
- The method of resistant welding method is designed to allow multi-projection welding. Resulting, some electrodes or a pair of large surface electrodes is fed from a solo power source.
Disadvantages of Projection Welding
- You cannot apply this welding method on every type of materials. Metal thickness and composition is a significant matter here.
- The metal mostly used on building or engineering may not be rigid enough to support the projections. Even some coppers and brasses cannot be welded using projection welding.
- After performing projection welding, there is some additional operation to do. It’s called forming of projection.
- The projections require the same heights for precise welding.
Projection Welding Symbol
Embossment on arrow-side member of joint for projection welding
Embossment on other-side member of joint for projection welding
Strength of projection welding
Spacing of projection welds
Number of projection welds
Extent of projection welds
Contour of resistance seam welds
Welding especially, projection welding is an excellent technical method for engineering works. It uses in mass or limited production door parts, automobile industry, electrical, waterline parts compression parts and so on. Thus it’s a complicated procedure and needs expert guidance to perform.
Projection welding is especially suitable for Diamond segment welding, fan covers, auto electrics; hollow metal doors, semiconductors, etc. In the future, we are going to make a full article about different types of welding procedure and construction for our readers. To learn about more projection welding, stay with us.