Welding Dissimilar Metals Guide

Many welding methods metals are available to sear joints and ridges together, but not all metals are made equal. As a result, some welding methods are better suited for different kinds of metals. This situation is made slightly more difficult when a job calls for welding two different kinds of metals together. Various options to combine these metals exist, but, again, different methods are better suited for different metals. There are also situations where welds can benefit from transition welding.

Deciding what kind of weld is necessary for a particular job is the first step in any welding process, and can depend on a wide variety of factors. Additional preparation requires purchasing transition metals (if necessary) and weld materials and equipment.

Materials and Metals

Often, a decision to use dissimilar metals in a weld is one of financial reasons. Certain kinds of steels can be priced up or down depending on the current raw materials market as well as the relative purity—and therefore strength—of the steel. In order to achieve financial savings without jeopardizing structural integrity, welders will often employ lower grades of steel in joints in a staggered fashion, welding stronger, higher grade types of steel with lower grade steels as spacers of transition pieces. Additionally, not all parts of a structure are susceptible to the same kinds of corrosive elements or pressure requirements. As a result, many welders use less expensive metals where these considerations are not required, and weld these metals to more durable pieces, like stainless steel, where needed.

However, depending on the weld, this staggered welding can be a difficult process. Different grades of steel and different kinds of metals have varying melting points and molten metals do not always join easily. To join two dissimilar metals, they must have mutual solubility. This means they melt at similar temperatures into molten forms that are relatively equal. Additionally, the welded forms of these metals must have intermetallic chemistries that do not easily corrode, crack or wear.

Nickel for Metallurgical Transition

The problem with welding seemingly similar metals is that the potential for corrosion and wear is often evident only at the microstructural level. For instance, welding stainless steel with a low grade steel might seem like a decent match, but there are chemical considerations that aren’t so apparent. The carbon in the steel might react poorly if the weld is performed at two high a temperature, which could result in a metal known as chromium carbide. While chromium carbide is very hard, it has low ductility, which makes the welding process extremely difficult. Many such dissimilar welds can pose these kinds of unforeseen consequences.

The solution is the introduction of transitional metals. This means the welder interposes a third metal into the weld that will counteract the negative effects of welding dissimilar metals based on its own reaction to the weld. Research and trial and error have resulted in nickel being the metal of choice for transition needs. When welded, nickel dilutes the carbon, chromium, and other chemicals that form tough, hard and inductile metals, making the metal that much easier to bend and shape.

Cladding

Another solution for welding dissimilar metals is by using clads. Clads are pieces of dissimilar metals that have been bonded, usually through extruding, pressing or rolling. The resulting metal form consists of an interior of one type of metal with a coating of another type.

When using clads, the metal on the outside surface of the piece is usually the metal that is intended to make the welding process more appropriate for welding. The interior metal is intended for longer lasting situations, the life of the piece; for instance, a stainless steel piece clad with some other type of alloy, perhaps nickel. The weld is performed on the clad side, which then can be removed through a carbon gouging process, resulting in a weld of stainless steel and another type of metal.

High Temperatures to Prevent Problems

One final method for establishing dissimilar welds is the use of high temperatures. With a transition or filler piece of nickel, using high temperatures can make an austenitic weld. An austenitic weld means the iron of the steel undergoes a phase transition to an austenite form, which results in a face-centered cubic configuration of the iron. This cubic configuration provides extra ductility and flexibility for the weld, which is much easier for a welder to shape and form, but when it sets it will be incredibly strong.

Factory Mezzanine Considerations

The addition of a mezzanine level, a secondary floor, in a factory can be a cost-effective alternative to plant expansion, offering both increased floor space and increased storage. There are an array of mezzanine structures that may be appropriate for a given plant depending on the specific factory parameters and operations, but regardless of the type of plant there are several considerations that should be examined before implementing a mezzanine structure. Technical Considerations In thinking about mezzanines, it’s important to examine the physical parameters of the space within which you intend to erect a mezzanine. The ceiling should be at least 14 feet high, and the intended mezzanine floor load should not be more than 150 lbs per square foot. The elevation of any machines or processes should be gauged and the mezzanine should provide an appropriate level of clearance and headroom. In addition to mezzanine floor load, the factory floor should also be examined for necessary strength and integrity. Poor flooring will not be able to withstand the addition of a mezzanine with substantial weight. Additionally, ensuring that a dual sprinkler system can be implemented on both the factory floor and the upper mezzanine is a key safety precaution. Making sure that the space meets all necessary requirements in terms of support spacing, design, and security will help in the mezzanine selection process by ruling out certain structures. No mezzanine should occupy more than one-third of the total building footprint, or this could require that the building be made compliant with multiple-floor structure codes. Therefore, it’s important to understand exactly how much space and weight are involved in the addition of a mezzanine before moving forward with installation. Layout Considerations In addition to technical considerations regarding space and weight, access to power, lighting, heat, and ventilation also play essential roles, and are contingent upon the number of mezzanine levels. With the addition of one mezzanine, usually the same power supply can be used to run additional second-level machinery. It is also possible to add more than one level, although care should be taken in regards to additional power, lighting, and especially weight. With rack-supported mezzanines, the addition of a second level in spaces with high clearances is relatively common, especially for materials handling and storage operations. Mezzanine Floor Material Considerations Depending on the intended use of the mezzanine, various materials may be more appropriate than others. The main consideration when selecting a material is that it be strong enough to support the necessary weight, and durable enough to withstand factory floor traffic. Of course, material selection hinges heavily upon the specific application. In general, the mezzanine deck is supported by steel or steel roof decking (16 gauge steel). Additional support is added in the form of extra support legs if the anticipated mezzanine load is above that which steel is designed to support), which can be placed strategically under the location of heavy machines to enhance the strength of the structure. The surface of the mezzanine floor can vary. Solid materials, such as plywood and plywood combined with various coatings, Masonite, tile, or metal plating, are common floor surfaces. Other semi-open materials, such as grating and perforated metal, can also be used as a surface material Uncoated plywood can be a cost-effective floor surface, but tends to wear down faster than other alternatives. When used with certain overlays, such as Masonite or tile, the plywood becomes easier to clean and more wear-resistant. In order to decide which material combination is best for a particular mezzanine, consulting with a professional or specialist can be productive.

Manufacturing Group Pushes for Bill Reform to Support Tooling

Sunday, October 25, 2009

I’m not sure the concept necessarily puts my mind at ease if this is what it takes to buoy our manufacturing base. However, the world we live in is full of nuts, such as those in Afghanistan, North Korea and Iran.

A new bill has passed through the Senate and if all goes well could be signed by president Obama soon. A group of tooling stakeholders is pushing the U.S. House of Representatives for reforms to the Defense Production Act (DPA).

“The DPA is a 60-year-old program that gives the President broad power a) to require businesses to sign contracts or fulfill orders deemed necessary for national defense; b) to establish and enforce means of allocating materials, services, and facilities for national defense; and c) to control the civilian economy so that scarce and/or critical materials are available for national defense purpose.”

Our friends over at Kinetic Die Casting have a post with further details about the Defense Production Act.

Die casting video review (courtesy of SME)