What do access panels, cabinets, drip rails, and toolboxes have in common? Well, the answer we were looking for is that they are all fabricated from sheet metal.
As metal fabricators, we do a lot of work with sheet metal, but we’ve noticed that sometimes people don’t understand what is and is not possible with this material. Sometimes we’re shown designs that would benefit from greater use of sheet metal, while on other occasions it’s used inappropriately.
We believe a better understanding of sheet metal fabrication will help our customers design better products. It will support weight reduction goals, improve appearance and durability, and perhaps of greatest importance, it could save some money too.
Cutting, Bending, Joining and Finishing: An Overview of Sheet Metal Fabrication
Metal sheets are made by rolling billets into long, flat strips of a set thickness or gauge. This rolling process gives the strip a grain, which becomes important during cutting and bending. For some applications, these strips are coiled, and for others, they’re cut into standard sizes, the largest of which is 48” x 144”.
Fabricating anything from sheet metal starts by cutting out the shape needed. This blank is then bent to a particular geometry. Bending is complicated because metal will spring back towards its original shape, and if the job isn’t planned properly, it can crack.
Once individual metal parts have been formed they usually need joining in some way. Welding creates permanent joins but for some applications fasteners of various types might be more appropriate.
Lastly, unless made from metal that doesn’t corrode, fabrications need some kind of protective coating.
Materials Used in Sheet Metal Fabrication
A wide range of materials are available in sheet form and are suitable for fabrication. Those we work with most often are:
- Mild (low carbon) steel
- Stainless steel
- Galvanized steel
All come in thicknesses (gauge) ranging from around 1/64” up to 3/16”. Notice that alloy or high-carbon steel is absent from this list. That’s because, being very hard, it tends to crack when bent.
We have a range of equipment for cutting shapes from sheets. Simple, straight cuts are made with CNC shears but for complex shapes, we have several options.
Laser cutting is good for many lower-quantity orders. We have both CO2 and fiber lasers and these can be programmed to follow complex paths. Heat-affected zone (HAZ) is something to watch for on edges, but our new 8kW laser cuts so fast this isn’t much of a problem.
Higher quantity work can run on a CNC turret punch. This has a set of tools that are powered up and down while the sheet is moved underneath. It’s fast, although perhaps not as fast as the most powerful laser.
Another option is waterjet cutting. This cuts with abrasive grit transported in a very thin jet of water moving at supersonic speed. Its strength is thinner sheet and non-metallic materials, and it has the advantage of not leaving a HAZ.
A secondary cutting process that comes in useful sometimes is notching. When a blank will be folded up into a box shape it’s often useful to notch out corners to improve the way the sides meet.
Most sheet metal bending is done on press brakes. These are a type of wide press with an upper and lower tool. The lower piece has a vee-shape which the upper tool pushes the sheet into to create a bend.
When planning bending work the sequence of operations is very important. Get this wrong and it won’t be possible to put the last bend in because of how the metal has been bent.
It’s also important to consider grain direction. Generally, you want to bend across the grain. Bending in the direction of the grain can result in cracking. This has to be considered when planning how to cut the blank from the sheet.
Edges can also be bent on a folder. As the name suggests, this folds the metal over to create an attractive, and safe, edge.
Joining Sheet Metal
If a structure or assembly might need to come apart in the future we use fasteners. Screws and bolts are most often used, although riveting is an option. For permanent joins, we weld.
Welding involves using heat to melt a small region of the two pieces being joined. This “weld pool” may be moved along to create a continuous weld or could form local “tack” welds like staples.
Our welding options are MIG, TIG, and resistance welding. MIG and TIG are both forms of gas metal arc welding: an electric arc creates the heat and filler metal is added into the weld pool. TIG is often preferred for sheet metal work because it’s a more precise process.
Resistance welding involves clamping two pieces of sheet between copper electrodes. Current flows through this assembly, with electrical resistance generating enough heat to form a small weld “nugget”.
Low-carbon steel loves to corrode, so it always needs either painting or powder coating. Painting is best done by the e-coat process, which uses an electrical charge to draw paint onto every edge and crevice.
Stainless, aluminum, and other non-ferrous metals don’t corrode but they do oxidize. They can be polished to a bright shine, (see our fire truck bumpers for an example), but in the case of copper, a clear coating is advisable to prevent an unsightly green oxide layer from forming.
CAD/CAM in Fabrication
Cutting and forming processes are tough to plan, especially in terms of maximizing sheet utilization. We deal with this by using special-purpose CAD/CAM software. It helps with nesting (to fit as many pieces as possible on a sheet), and planning the bend operations sequence.
Sustainability in Sheet Metal Fabrication
Like all engineers, we have a deep-seated dislike of waste. That’s why we try to maximize material utilization and avoid scrap-producing mistakes, (although there is a limit to how many offcuts we keep around “just in case” we need that particular gauge of alloy in the future.)
Fortunately, just about all sheet metal is recyclable, especially aluminum and copper. Consequently, we try to recover scrap and offcuts to sell back to the producers for remelting.
Applications for Sheet Metal Fabrications
Putting bends into sheets creates very stiff structures, making it a good way to minimize weight. Look around and you’ll see sheet metal fabrications almost everywhere. It’s used for boxes and containers, covers, guards, shields, access panels, cabinets, drip rails and toolboxes.
It’s hard to think of an industry or sector where sheet metal isn’t used. Truck trailers use a lot of it, as do RVs. A lot of agricultural equipment is fabricated from sheets and it’s used in manufacturing companies and utility vehicles. Even the aerospace sector uses sheet metal, although titanium might be their preferred material.
Choosing a Sheet Metal Fabrication Partner
If you’re looking for a supplier to make fabrications you’ll know there are a lot around. We suggest using three criteria to identify the best:
- Do they have a wide range of equipment, or will they need to change your design to suit what they have? (Another way to look at this is, can they use the best equipment on your job to keep costs down and maximize quality?)
- Do they have a Quality Management System that ensures they take the time to understand what you need and keep their processes under control? (We could also add, are their welders certified?)
- Do they have a culture of genuine customer care and respect for every employee?
At Wiley, we check all these boxes. If you’d like to learn more about what we can do for you, please contact us today.