Tips For Properly Prepping Metal For Welding
November 07, 2024Welding is a complex procedure of joining two metal pieces with an everlasting bond that compiles several steps. Although welding is straightforward, what comes before and after the procedure matters.
Metal preparation is a critical step in creating perfect conditions for your following welds. The more time you spend cutting, cleaning, and preparing the pieces, the better overall welding results you'll get. In addition, you will spend less time in post-weld cleaning and rework.
In this article, we present the essential tips for properly prepping metal for welding, including planning, cutting, cleaning, and more.
Source: https://www.youtube.com/watch?v=mh-rcTCEwfE
Why Is Metal Preparation Crucial in Welding?
Metal preparation and weld preparation, in general, are essential steps in the welding procedure. Properly cutting, cleaning, and fitting up the pieces before welding them will greatly impact the final results.
Simply put, the more time you spend preparing and cleaning the pieces, the better results you'll get. Squeaky clean surfaces and good fit-up will produce the highest quality, clean welds that all welders desire.
Besides the weld appearance, clean welds also mean there is no contamination on weld defects that can affect the structural integrity of the weldment. In addition, you will spend less time in the post-weld cleanup and rework. Lowering the welding time significantly reduces the overall welding costs, which is crucial in industrial applications.
Therefore, properly preparing metal before the welding will produce clean, high-quality welds with little to no need for post-cleanup. The paramount steps in metal preparation are:
- Planning the prep
- Cutting, fitting, and beveling
- Cleaning the pieces
- Choosing the right abrasive
- Choosing the right profile
- Considering preheating
So, let's further explain each.
Tip 1: Plan ahead of metal preparation
Before you even start metal preparation, you should first plan the entire preparation. The planning will include several considerations regarding the following:
- Welding process selection
- Type of metal you are welding
- Desired finish
Therefore, before prepping, ask yourself a few questions.
Welding Processes and Metal Preparation
The first question is: What welding process will I be using?
Welding processes react differently to surface contamination and poor fit-up. For example, Shielded Metal Arc Welding (SMAW) or Stick welding is known for its performance on thin layers of rust, paint, or dirt. If you need to get the job done quickly, you can weld through the light contamination, but at the price of somewhat more spatter. The same rules apply to Flux-cored arc welding, where higher penetration and self-shielded wire can cut through some contaminants.
However, Gas Metal Arc Welding (GMAW) or MIG welding and Gas Tungsten Arc Welding (GTAW) or TIG welding require clean surfaces. TIG welding is the cleanest method but requires squeaky clean surfaces to work. MIG welding is somewhere in between, but when in doubt, it is always better to clean the surface to avoid porosity, cracks, inclusion, and spatter.
Types of Metal and Metal Preparation
The next question is: What metal type will I be welding?
Each metal shows different metallurgical, chemical, and physical properties. While you may know each metal type welds differently, the same rules apply to metal preparation.
For example, aluminum has an aluminum-oxide surface layer that you must remove before welding for consistent results. Both aluminum and stainless steel are corrosion-resistant, so you need a dedicated stainless steel brush to avoid surface contamination.
Some materials, such as hot-rolled steel, have a heavy mill scale on the surface that you must remove completely before welding. Hard metals such as INCONEL require high-performance abrasives. Meanwhile, soft, non-ferrous metals require special abrasives that prevent wheel loading or clogging.
Desired Finish And Metal Preparation
The final question is: What kind of surface finish do I need?
Metal surfaces can have a different finish depending on the weld specifications or your wishes. The finish requirements will dictate your abrasive choice.
The primary surface appearance is a matte finish. This is the mill finish that has not been processed further. Although it doesn't require further processing, the matte finish has a dull appearance and is not ideal for aesthetic end-uses.
A brushed finish produces a distinctive look with a muted luster and a pattern of fine parallel lines. Creating this finish requires a 120-180 grit belt, followed by softening with an 80-120 grit medium non-woven belt.
The mirror finish is highly reflective and created by polishing. Polishing involves using a series of progressively finer abrasives, that create shiny, mirror-like metal surfaces. This finish is often used in stainless steel.
Tip 2: Proper cutting, beveling, and fit-up
Once you planned the metal preparation and answered the questions, it is time to cut, and/or bevel and fit up the pieces.
Cutting is an indispensable part of metal fabrication, and your welding performance can depend on the first cut you've made. The more care and preparation you put into the initial cut the less the amount of cleaning and further preparation.
Source: https://www.youtube.com/watch?v=R9HeVdhuIn8&t=24s
You can cut metals using several different tools, such as a torch, plasma cutter, CNC table, shears, grinder, laser, waterjet, etc. However, as an everyday welder, you will mostly use a grinder, plasma cutter, or manual tools such as shears or cutting wheels.
Offhand cutting with an angle grinder is the cheapest way to cut the metal. However, it takes time and practice to produce clean, straight cuts, so we recommend using a plasma cutter such as YesWelder Cut-55 . Plasma cutters produce clean welds on metals up to 1/2".
Beveling the pieces
Welding metals over 1/2" or often over 1/4" requires powerful equipment, including high amperages and large filler metals. Instead of using this approach, welders prefer to bevel the sides and use multi-pass welding.
Beveling includes grinding the sides to form a 60-degree angle between pieces. The welders leave a small gap, known as root opening, and reduce it to 1/16 to 3/16 inch. These thicknesses are much more accessible to weld with hobby and home 200-250 amp welders. But, you must use multiple passes, including a root pass, fill passes, and a cap pass.
Part fit-up
You will need a clean, consistent gap between the two pieces to produce sound welds. That's where part fit-up comes into play. Ensuring a consistent and clean gap will help you weld with less filler metal, reducing costs and saving time.
However, you won't always need a gap. It is best to fit the piece tightly without the gap to weld thin pieces about 1/32" or smaller gauge.
Joint geometry is another part of fit-up, and you should adjust it to weld specifications, or your preferences. Although there are various types of weld joints, as a beginner and hobby welder, you should stick to butt welds and tee joints, as they are most manageable to work with.
Tip 3: Clean the pieces
Cleanliness is a crucial component of welding, especially methods such as TIG welding. There are various ways to clean the metal surfaces before welding, including using an old rag, wire brush, grinders, abrasives, or chemical solutions.
The amount of cleaning and the preferred method will mostly depend on the amount of contamination. For example, you can clean the oil, dust, or dirt with an old rag and some acetone. If the contamination comes off easily, you won't need special tools or more effort.
Nonetheless, as the amount of contamination increases and penetrates deeper layers, you will need bigger guns. You will need sanding paper or a wire brush to remove light surface layers of paint or rust.
You will need an abrasive product for thicker contamination, mill scale, or rust. The rule of thumb is to start with a less coarse option and increase aggression only as necessary. Flap discs are the perfect solution for this, as they are less aggressive than a grinding wheel.
If nothing helps, you will have to turn to chemical solutions. You can use pickling paste or acidic cleaners, to dissolve the oxides, scale, and discoloration from the weld surface. However, you should handle these with care, especially if you are inexperienced. Electrochemical and laser cleaning are advanced options reserved for industrial applications.
The goal of cleaning in metal preparation before welding is to remove the contamination, but to a point where you don't excessively remove the base metal. Clean the work surface thoroughly within an inch of the joint on both sides, without penetrating too deep into the metal.
Tip 4: Choose the optimal grit
The more the better is not the right approach when choosing a grit for your metal preparation and cleaning. The truth is that coarser, more aggressive abrasives will remove contamination faster, but at the price of also removing the base metal from the surface.
You want consistent material and wall thickness to achieve strong and consistent welds. Too coarse abrasive (20-50 grit) can remove excess material or damage the surface beyond the desired weld specifications. Too fine abrasive (over 150 grit) will only remove the light surface contamination.
That's why you must either start with fine abrasives and work your way up to more coarse ones, or choose the universal, medium-grit flap discs. The first approach of starting with fine and reducing the grit is always better, but it can take time. In large-scale applications, time is money, so many turn to medium-grit discs.
Medium, 60-grit-coated abrasive flap discs can provide the ideal balance between aggression and productivity. You can clean the surfaces faster compared to fine grit, but safer than coarse grit discs.
Tip 5: Consider the abrasive profile
Besides the grit, abrasive discs can have a different profile, making your metal preparation much more manageable. But, choosing the wrong profile can break your project.
Type 1 has a straight profile and a relatively small diameter. Fabricators use this profile with high-speed die grinders to grind off excess metal, so you want to avoid them in metal preparation.
Type 27 is a flat profile flap disc and, by far, the most common abrasive profile. This profile is perfect for lower grinding angles (5 to 10 degrees) and light-pressure applications like finishing and blending.
Type 29 is a conical profile abrasive. These discs are perfect when grinding at higher angles (15 to 30 degrees). You should use them for aggressive material removal and thicker contamination.
Wire Brush Styles
Besides abrasive discs, wire brushes can also have different styles and sizes, designed for various contamination removal. Most commonly, wires differ in the gauge and knot types, and the widely used types are:
- The Stringer Bead Brush has knots twisted into a very tight and narrow profile. These brushes are ideal in tight gaps, for initial weld passes in pipeline and multipass welds. However, welders also use them in general fabrication applications.
- A Cable Twist Brush uses a knot with more wire in it and twists to the end. This design results in additional width, stiffness, and aggression. Welders find it significantly more effective for weld prep if you don't specifically need to get into a 1/8-inch gap.
- A Standard Twist Brush knot is not twisted to the edge. This design allows the tips to spread at the end to increase conformability. This type is effective for metal surfaces with many imperfections, textures, or contours. Standard twist brush covers a wide footprint and it is easy to control, making it the perfect choice for new fabricators and welders.
Tip 6: Consider preheating
Preheating is a process of raising the surface temperature shortly before welding. This process is necessary for thick sections or specific metals such as high-carbon steels, cast iron, or metals with high thermal conductivity.
A high burst of heat caused by a welding arc can cause residual stress in heat-sensitive metals such as high-carbon iron, causing them to crack. By preheating the pieces, you minimize residual stresses and improve weldability in challenging situations. However, as a hobby or DIY welder who typically welds mild steel up to 1/4", you will rarely preheat the pieces.
The need for preheating depends on material type, thickness, welding process, and welding codes or specifications. So before welding, refer to material-specific guidelines, consult experts, or follow welding procedure specifications (WPS).
Mistakes To Avoid When Prepping Metal For Welding
- Don't rush straight into preparation. Carefully plan the entire prep process based on the method you are using, the metals you are welding, and the desired finish.
- Try to produce a clean cut. The amount of the following edge and metal preparation can vary based on the cut you've made. Plasma cutters can produce the cleanest results for home applications.
- Don't ignore part fit-up. A consistent gap through the weld joint will produce sound and consistent welds. Arrange a weld joint design that works best, and can work for the given weldment.
- You don't need to single-pass weld thick pieces. Instead of tuning your machine to its peak power and producing high heat, bevel the edges and use multiple passes.
- Don't ignore surface contamination. Dirt, rust, oil, grease, paint, mill scale, or paint can affect the welding performance, appearance, or safety. Although some methods, such as Stick welding, can burn through light contamination, you will always want to clean the surfaces before welding.
- Don't weld moist pieces. If you use acetone or any solvents to clean the surface, wait until the pieces dry before welding them. Water can form an inconsistent arc, creating boiling, oxidation, spatter, or porosity in the welds.
- Be careful when cleaning aluminum. Always use a stainless steel brush when cleaning aluminum. Contamination can affect the corrosion resistance of the aluminum, and the aluminum-oxide layer can influence the weldability.
- Find the balance in grit. Too-coarse abrasives will remove contamination faster, but they can also remove more base metal than intended. Too fine abrasives will only remove light surface contamination.
- Find a suitable profile. Abrasive profiles can also be too aggressive or soft.
- Don't forget about preheating. Welding thick sections, high-carbon steels, or metal with high heat conductivity requires preheating to avoid stress, cracking, and failure.
Final Thoughts
Preparing the metal for welding is as important as welding itself. The more time you spend planning, cutting, beveling, and cleaning the pieces, the less work you'll have to put in post-weld cleaning.
Providing clean surfaces, with even edges and a consistent gap produces sound welds between metals. Producing the highest-quality welds is more than just understanding how to weld them, it is dedicating the entire procedure, including the prep, for the best results.
🧐Tips For Properly Prepping Metal For Welding FAQ
1. How to prepare metals before welding?
To prepare metals for welding, plan the process carefully by cutting, fitting, cleaning, and selecting the right abrasive, profile, and preheating as needed. These steps ensure a clean, strong weld.
2. What is the best way to clean metals before welding?
The best way to clean metals before welding depends on the level of contamination. For light contamination like oil or dust, using a rag and acetone is sufficient. For mild surface layers of rust or paint, sandpaper or a wire brush works well. For thicker contamination, an abrasive product like a flap disc is ideal. In cases of stubborn contaminants, chemical cleaners, such as pickling paste, can be effective but require careful handling.
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