Tips for preparing your material before welding

The welding process is a very important step in a variety of manufacturing and fabrication processes. All different types of metals are welded for many different types of fabrication. However, for any welding process to be accurate and effective the first time around, it is universally true that the parent material must be properly prepared.

Material preparation is so critical that it is often documented to ensure consistency in the procedure, regardless of the material. Removing coatings such as paint, oils, greases, and rust (oxides) ensures that the area to be welded is in the best possible condition.

When working with carbon steels, it is critical to remove any rust and other impurities such as mill scale. Oil-based coatings and acidic pickling chemicals also must be removed before welding takes place. Removing chromium oxide to produce a decorative finish on stainless steel alloys often is achieved in a direct process. But the subsequent cleaning of the welded area to remove any surface oxide (often seen as the discoloration next to a weld) allows for the re-formation of a protective layer that is very important in the stabilization of stainless steel alloys. This stabilization is known as passivation.

Nonferrous materials present their own challenges in the weld preparation process. With metals such as aluminum and titanium, there is a shorter window of time between the surface cleaning and the welding, as oxidation can form very quickly. Cleaning large areas too early before welding often leads to the need for rework.

Tips for Manual, Mechanical Cleaning

When you are using a stainless or nonferrous power brush for weld cleaning, run it at a very slow speed, between 1,250 and 4,250 surface feet per minute (SFPM).

Stringer bead wheels, including variants with a reversible twin-nut feature or those containing an alternating-twist knot construction, will provide effective, even cleaning and excellent operator control for cleaning carbon steel fillets between welding passes (see Figure 1).

You can control surface marks with bonded and coated abrasive products. Thin cutoff wheels, ranging from 0.030 to 0.045 in. thick, are available in special bond and grain types specifically for use on aluminum, stainless steel, and carbon steel. They can offer fast cutting, long life, low friction, and minimal residual burrs on the material being cut. Specially designed flap wheels that incorporate a top-sizing in the coated material reduce heat buildup on poor heat-conducting materials like stainless steel and provide extremely aggressive stock removal rates.

Operating speed is another critical component of proper weld preparation and cleaning. A good rule of thumb to remember when preparing a surface for welding is “slower is often faster.” Using slow speeds to control friction helps to reduce surface and weld area contamination. High surface contact speeds can generate excess vibration, causing the abrasive material or brush tips to skip over surfaces, allowing impurities to remain. Fast operating speeds also can reduce your ability to control the tool.

Lowering the speed by as little as 10 percent can yield more efficient surface preparation and increase your consumable’s life, making the weld prep process more cost-effective. A variable-speed power tool can help fine-tune your operating speed. While these power tools tend to require a bit more of an upfront investment, they usually end up paying for themselves when you consider operator fatigue and consumable performance.

With nonferrous materials, using nonwoven abrasive products, such as surface conditioning or surface finishing discs, can be problematic, as these products are typically constructed with a loose nylon filament impregnated with abrasive grain and are prone to melting and “smearing” when run at high speeds. Not only can this affect the efficiency of the abrasive by leaving an uneven surface finish, it can leave a nylon residue on the workpiece. This residue interferes with the integrity of the weld and will require rework.

To avoid other types of surface contamination and loading or clogging of the abrasive, only use products specified for use on aluminum and other nonferrous materials.

When working in tight areas, hand brushes can be your best tool. Specially designed brushes, such as a V-groove scratch brush, which has three rows of wire angled into an extremely narrow brush face, allow you to focus and reach into those tight areas (see Figure 2). An added benefit to this full-sized brush is it gives you better control when wearing gloves.

General Best Practices

For best overall performance of any product used to prepare a weld surface, it’s important to calculate and control both the speed and the friction applied to the surface. Your best bet is to consult the manufacturer’s recommendations for maximum RPM for safe use of the consumable based on material and disc size.

Avoid removing too much of the parent material or creating deep scratches around the weld area. Removing too much material, also known as undercutting, may result in inclusions or poor arc control during the weld process. This is a serious concern if you are working with stock that has been preworked with plasma or torch cutting. Typically, excess plasma dross or slag is removed with a chisel or ground off with a very coarse abrasive product. This can leave deep marks in the workpiece and drive surface impurities deep into the material to be welded, increasing the likelihood of weld porosity or poor coating adhesion at a later stage in the fabrication process. Any of these errors could result in costly rework.

Also, avoid cross-contamination by using a new, clean abrasive product. Contamination can occur directly or indirectly. Direct contamination, such as from using a steel wire brush on an aluminum part, is preventable as long as you keep your consumables for ferrous and nonferrous materials separated and organized.

The real challenge is preventing indirect contamination, which can be caused by airborne dust from other manufacturing processes in the same facility. Using any abrasive product will create dust, which can spread easily throughout the shop. One economical and effective solution is storing new abrasive products in clear plastic bags to keep them both visible and protected from dust. You should also change out soft materials, such as cardboard, on your work surface (beware of the potential fire hazard). Or, you could place a thin sheet of stainless steel on the top of a steel workspace to help reduce the potential of contamination.

Establishing a daily cleaning regimen, both on your work area and on other surfaces such as lamp tops, toolboxes, and cabinets, will pay off by lowering your contamination risk.

John Thompson is national technical sales manager at PFERD, 262-255-3200, www.pferd.com.

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