Material selection determines the success or failure of your design. The perfect metal will provide the strength, appearance, weight, and durability you need at a surprisingly low price. Unfortunately, the perfect metal doesn’t exist, so compromises are always needed.
This blog reviews what to consider when choosing the metal or metals to be used in your fabrication, and why.
The Top Three Factors for Your Metal Fabrication Project
Calling out every attribute needed in your design or structure could result in a long list. In most cases though, they can be grouped under these three headings:
Function refers to properties like strength, corrosion resistance, weight, and appearance. These relate to whether the fabrication will do its job, for the lifetime required.
Manufacturability in fabrication refers to characteristics like ductility, (needed for bending), and weldability. Some metals are challenging to work with, others cut, bend, and weld so easily that it’s a joy to use them.
Cost is less a desired characteristic than an outcome. A low-cost metal might need more processing. An expensive metal might satisfy an appearance requirement but lack the strength needed, so requiring more metal for the fabrication.
We’d also argue the importance of considering lifetime costs. A corrosion-resistant metal may increase the cost but if the finished fabrication has three times the life of one made from a cheaper alloy, isn’t it less expensive overall?
The point here is that there are trade-offs to be made when selecting an alloy or alloy for a metal fabrication. Weighing up those trade-offs requires some knowledge of what the application requires.
The purpose of the structure to be fabricated dictates what’s important. Properties to consider include:
- Tensile strength: Determines load-bearing capability; stainless steel is among the strongest metals used in fabrication.
- Density: Aluminum is often a good choice for minimizing the mass of fabrications used in transportation
- Corrosion resistance: Some metals, notably stainless steel and aluminum, have this property. Those that don’t may need a coating or other treatment process to slow the progression of corrosion.
The importance of corrosion resistance depends on the application. Marine uses, on boats and around docks, can be especially challenging, needing special alloys and techniques to slow the rate at which corrosion advances.
- Appearance: Unless a patina of rust is acceptable, metals with little-to-no corrosion resistance need painting or coating to provide an attractive, durable appearance. Aluminum and stainless however can be brushed or polished to a pleasing finish.
A commonly-sought trade-off in mobile/transport applications is high strength with low weight. This requires a material with high specific strength, (strength per pound of mass), which is an area where aluminum excels.
In fabrication, manufacturability has three main components:
- Formability: To what extent can the material be bent into shape? What radii can be achieved? Aluminum, other than the 7000 series generally has good ductility and is readily formed. Low-carbon steels are similar. High carbon and stainless steels can be challenging to form. Some materials harden as they are bent, limiting the extent of forming that’s possible.
- Weldability: Some alloys are easier to weld than others. Welding an alloy to itself is almost always easier than welding different grades, thicknesses, or materials.
High thermal conductivity can pose a challenge in thin materials as they need more heat input. Highly alloyed metals can suffer segregation during cooling where the various constituents solidify at different temperatures.
- Secondary processing: If the material isn’t inherently corrosion-resistant, some form of coating will almost certainly be needed. Whether powder, paint, galvanizing, or some other process, this is going to add both time and cost to the fabrication.
The least expensive material doesn’t necessarily result in the lowest-cost fabrication, especially when lifetime costs are taken into account. (Side note: “inexpensive” doesn’t mean poor quality, just that the price is lower, usually resulting from lower levels of alloying elements and less processing during casting, rolling, or extrusion.)
Inexpensive metals, like low-carbon steel, are of lower strength than those containing elements like chromium and nickel, so more may be needed to provide the load-bearing ability needed. However, they are often easier to cut, bend, and weld, possibly saving money in fabrication.
Lack of corrosion resistance is often a major limitation, necessitating coating or other surface treatment processes. While some are relatively inexpensive – galvanizing low-carbon steel for example – they alter the appearance in ways that might be undesirable.
This is a growing concern for many people, and it can have a bearing on metal fabrication work. It takes a lot of energy to produce metal in sheet, plate, or extruded form, so it’s wise to use it as efficiently as possible, (which is also a cost issue).
Offcuts and waste are however inevitable while cutting the pieces needed in a fabricated structure, so recycling is an important consideration. Just about all material used in metal fabrication can be recycled, although it’s usually necessary to separate ferrous from non-ferrous. Separating aluminum and copper is advisable too.
Aluminum recycling is an especially sustainable thing to do. Aluminum is made by smelting bauxite ore, which takes a lot of energy. Melting scrap aluminum is far more energy efficient, which makes scrap collection financially worthwhile.
A Material Selection Case Study
Consider a spiral chute of the type used in many material handling applications. This will be deployed indoors so corrosion resistance may not seem a high priority. However, the chute surface and side rails cannot be painted or coated as this will rub away, so a corrosion-resistant material is a good choice. It should also be hard-wearing and capable of being polished to a high shine, low friction finish.
Stainless steel appears the best candidate. To reduce cost though, the support structure could be fabricated from low-carbon steel. Paint or powder coat will be needed for appearance and to prevent corrosion.
A manufacturing challenge to address is joining stainless to low-carbon steel. While welding is possible, it will be difficult, (due to different metal points and the composition of the stainless steel.) A better solution may be to design two separate units – chute and support – and join them mechanically.
Although a simple example, this illustrates the role of material selection in a successful metal fabrication project.
The Future: What Might be Coming in Materials for Fabrication?
A recurring theme here is the need for corrosion prevention. This has major implications for durability and cost, so perhaps it’s not surprising scientists are working on ways of increasing corrosion resistance.
Rather than adding coatings, which just postpone the problem, a lot of effort is going into finding more corrosion-resistant alloy formulations. A new tool in this is Machine Learning (ML). ML is a specialized form of artificial intelligence that can be used to generate new solutions to existing problems. Currently, scientists in Germany are developing ML tools to find more corrosion-resistant alloys. Although in its infancy, perhaps we will one day have more options than stainless steel.
Get Expert Advice on Material Selection
When you’re designing a metal fabrication you have a lot of material options. Let the application dictate the important considerations – strength, corrosion resistance, appearance – before reviewing manufacturability. If the cost then comes out higher than you’d like, be prepared to compromise some of your requirements – for example, accept a shorter life or a different appearance.
To avoid multiple design iterations and save time, it pays to involve a metal fabrication expert early on. Over the many years we’ve been in business we’ve seen and learned a great deal. Our materials and fabrication expertise are second to none, and we work hard to delight our customers. That’s why you can rely on us for honest, trustworthy advice. Contact us to discuss all your metal fabrication needs.