Written By: Tony Varela
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One of the most adaptable building materials in the manufacturing industry, sheet metal has rightfully found its place as one of the most important materials in the industrial age. Steel, aluminum, brass, copper, tin, nickel, titanium, or other precious metals are traditionally used to make sheet metal. Thicknesses vary but are mostly broken into two distinctions; thin gauge and heavy plate. Many different industries rely on the versatility and durability of sheet metal including aerospace, appliance manufacturing, consumer electronics, industrial furniture, machinery, transportation and many more.
Sheet metal offers plenty of advantages as compared to both non-metal alternatives and other metal fabrication processes, as well. When compared to machining, sheet metal is much less expensive in both processing and material costs. It does not have the extremely high tooling costs of injection molding, which makes sense at high volumes.
As found in machining, rather than starting with an expensive block of material, much of which is wasted in the milling process of removing unneeded material, sheet metal lets you buy what you need and use what you need with relatively low material waste. The unused sheet can then be used for another project, while the shavings produced in machining, need to be discarded and recycled.
With the advancement of technology used in modern fabrication, automation and new CAD (computer aid design) programs make designing in sheet metal easier and easier. CAD programs now have the ability to design in the same material you intend to fabricate with and will allow programming of the parts to come straight from the CAD model itself. No longer is there a need to create a separate set of shop drawings to interpret the design. Perhaps most significant, in a world of mass production, sheet metal has the ability to scale rapidly. The greatest cost for sheet metal fabrication is in the first piece. This is because the cost is all in the setup. Once the setup is complete, and the costs are spread out across the larger volume of pieces being fabricated, the price drops significantly, greater so than most subtractive processes like machining.
Sheet metal can be cut, stamped, formed, punched, sheared, bent, welded, rolled, riveted, drilled, tapped, machined. Hardware can then be inserted to fix electronic components, metal brackets or other pieces of sheet metal. To finish sheet metal, it can be brushed, plated, anodized, powder-coated, liquid painted, silkscreen, laser-etched, and pad printed. And of course, parts can be welded riveted into complex assemblies.
Just like any other technology, the processing of precision sheet metal is constantly evolving. Materials, processes, tooling, and equipment are becoming highly specialized which is improving the time involved to make common sheet metal parts and speeding up the design process as well. To fully leverage all the technological advantages, it is important that you select the right supplier and know the differentiation between metal fabricators; architectural sheet metal (HVAC and ductwork), heavy plate fabricators (staircases, fences, heavy structures) precision fabricators (thin gauge sheet metal, enclosures, brackets etc').
Along these lines, this white paper will explore key components of the precision sheet metal fabricator, precision sheet metal fabrication. This paper will focus on:
By definition, sheet metal starts out flat, but before this, it comes from large cast ingot and the rolled into a long ribbon in the desired thicknesses. These rolled coils are then flattened and sent as large sheets cut to different lengths to accommodate the manufacturing shop's needs. While this paper focuses on bending sheet metal along a single axis, there are processes out there, hot and cold forming techniques that include bending and forming sheet metal along multi-axis points in one process such as deep drawing, hydroforming, spinning and stamping. These processes are most commonly found in the manufacturing of products like automobile panels, aluminum cans, and complex formed consumer appliances. Another similar process is progressive stamping which moves a ribbon along a series of stamping which forms and punches different stages. At the end of these progressive stages, you are left with a finished part.
Cold forming will be the focus of this paper. Examples of cold-forming processes are as follows
Cutting
Hemming ' The edges of the sheet metal are folded over itself or folded over another piece of sheet metal in this forming operation to achieve a tight fit or a stronger, rounded edge. Hemming is a technique to join parts together, improve the appearance, or increase the strength and reinforce the edge of the part. Two standard hemming processes include roll hemming and conventional die hemming. Roll hemming is carried out incrementally with a hemming roller. An industrial robot guides the hemming roller and forms the flange. Conventional die hemming is suitable for mass production. With die hemming, the flange is folded over the entire length with a hemming tool.
Bending ' Most sheet metal bending operations involve a punch and die type setup when forming along one axis. Punch and dies come in all sorts of geometries to achieve varied different shapes. From long gently curves to tight angles at, below, or above 90-degree angles bending metal can achieve many different shapes. Press brakes are generally needed when a sharp angle is desired. Rolling and forming methods are used when a long continuous radius is desired in one direction, or along one axis.
There are many different metals and alloys that come in sheet form and are ultimately used in the fabrication of manufactured parts. The choice of which material depends largely on the final application of the fabricated parts, things to consider include formability, weldability, corrosion resistance, strength, weight, and cost. Most common materials found in precision sheet metal fabrication include:
Stainless Steel ' There are a number of grades to choose from, for the purpose of this white paper we will focus on the top three found in precision sheet metal fabrication:
Cold Rolled Steel ' A process in which hot rolled steel is further processed to smooth the finish and hold tighter tolerances when forming. CRS comes in and alloys.
Pre-Plated Steel ' Sheet metal material that is either hot-dipped galvanized steel or galvanealed steel, which is galvanized then annealed. Galvanization is the process of applying a protective zinc coating to steel in order to prevent rust and corrosion. Annealing is a heat treatment process that alters the microstructure of a material to change its mechanical or electrical properties, typically reducing the hardness and increasing the ductility for easier fabrication.
Aluminum ' An outstanding strength to weight ratio and natural corrosion resistance, aluminum sheet metal is a popular choice in manufacturing sectors meeting many application requirements. Grade offers excellent corrosion resistance, excellent workability, as well as high thermal and electrical conductivity. Often found in transmission or power grid lines. Grade is a popular alloy for general purposes because of its moderate strength and good
workability. Used in heat exchanges and cooking utensils. Grade and are commonly found in metal fabrication. Grade is the most widely used alloy best known for being among the stronger alloys while still formable, weldable, and corrosion-resistant. Grade is a solid structural alloy most commonly used in extrusions or high strength parts such as truck and marine frames.
Copper/Brass ' With a lower zinc content brasses can be easily cold worked, welded and brazed. A high copper content allows the metal to form a protective oxide later (patina) on its surface that protects it from further corrosion. This patina creates an often highly desirable aesthetic look found in architectural or other consumer-facing products.
Engineers designing sheet metal enclosures and assemblies often end up redesigning them so they can be manufactured. Research suggests that manufacturers spend 30-50% of their time and 24% of the errors are due to manufacturability. The reason behind these preventable engineering errors is usually the wide gap between how sheet metal parts are designed in CAD programs and how they are actually fabricated on a shop floor. In an ideal scenario, the designing engineer would be familiar with the typical tools that will be used to fabricate the sheet metal parts while also taking advantage of designing within the CAD programs available sheet metal settings.
The more that is known about the fabrication process during the design phase the more successful the manufacturability of the part will be. However, if there are issues with the way certain features were designed, then a good manufacturing supplier should be able to point those out and suggest good alternatives to address them. In some cases, the suggestions may
same time and unneeded costs. Here are some considerations while designing sheet metal for fabrication:
There are several different methods and reasons to finish sheet metal parts. Depending on the material chosen, some finishing techniques protect the material from corrosion or rust while other finishing materials are done for aesthetic reasons. In some cases, finishing can achieve both purposes. There are finishing processes that include simple alterations to the surfaces of the materials. Other finishing processes consist of applying a separate material or process to the metal. Standard finishing techniques include:
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Selecting a material, in this case, sheet metal is the first step in any design process. The process begins with the function of the part you are intending to design. The function of the part will help determine the needed design. Choosing a material and gauge are critical steps that involve balancing factors like strength, weight, and cost. This is not a simple process but can be streamlined by using CAD models with the above design considerations found in this white paper. The next real test, however, is prototyping.
While today's engineering tools are powerful, it is only when you can see and handle a part that it becomes known whether the design will meet expectations. Is it strong enough? Light enough? Does it look, feel, and balance the way it should? Does it sacrifice other components? Even relatively simple components benefit from real-world try out before committing to hundreds or thousands of parts. In some cases, it may take several prototype iterations to get the sheet metal part right. With a good manufacturing supplier, this process
can be kept at a minimal impact on the overall project but getting it right earlier in the prototype process.
It is tempting for larger enterprises to outsource design to engineering service providers so they can focus on core activities. However, selecting the right partner helps avoid further widening the gap between the ideal design and fabrication process and the all too common real-world scenario of poor designs making to the fabrication floor without resolution of design flaws. Working with partners willing to collaborate, interested in knowing more about the manufacturing process, and involved in developing sheet metal products. When selecting fabrication suppliers, look for companies with a proven track record in producing parts and who bring a vast wealth of fabrication knowledge to ensure fewer hiccups in the design to the fabrication process and product is brought to market faster.
The Aluminum Association. 'Aluminum Alloys 101,' (n.d.) Retrieved from https://www.aluminum.org/resources/industry-standards/aluminum-alloys-101
Australian Stainless Steel Development Association. 'Types of Stainless Steel' () Retrieved from https://www.assda.asn.au/stainless-steel/types-of-stainless-steel/austenitic
This is probably the most basic issue we see. Sheet metal is flat and must be bent, formed, cut, lased, and sometimes cajoled into its final shape. It's a very hands-on process. If you design your sheet metal part as a solid object, it's important that you send us a CAD file that appears folded, but shows where bends should go. Related to this, because the raw materials are single sheets of metal, the entire part must have the same material thickness throughout. For example, if you create a part that uses 0.125 in. (3.175mm) thick aluminum, your entire part will need to be that same thickness.
A quick way to create difficulties during manufacturing is to place holes, tabs, or other features too close to a bend. So, how close can you get? Just follow the 4T rule. Keep all features at least 4x material thickness away from bend lines. So, if your design tells us to use 0.050 in. (1.27mm) copper, give your feature at least 0.200 in. (5.08mm) of clearance. If you don't, the part will deform awkwardly in the press brake, and no one wants that.
When you bend sheet metal in a press brake, the resulting bend doesn't form a perfect 90-degree angle. Instead, the tool has a rounded tip that adds a radius to the bend. If you measure the length of that bent area and divide it by two, you'll get the bend radius, a figure that is defined by the tool that made it. If the size of that curve is important to you, make sure you specify it in your model.
The most common internal bend radius (and our default) is 0.030 in. (0.762mm). An important consideration to remember is that the external bend radius'the one formed on the die side of the press brake toolset'is equal to the material thickness plus the internal bend radius.
Some designers like to get fancy and create different radii for each bend in a part. Want to save some money? Use the same radius for all of the bends. When your manufacturer doesn't have to change tooling that saves you on labor costs.
Do you know of anyone who wants longer lead times? Probably not. Always remember to let your manufacturer know what kind of hardware you want to use by including the details in your top level assembly information. Whether it's a self-clinching nut like CLS-440-2, flush-head stud like FHS-M5-15, or other hardware, this guarantees that you'll get exactly what you want placed in the location you expect it. To save yourself time and trouble, download and use the PEM clinch hardware models.
Generally, finishes serve two purposes. They can protect your part or they can make it look better. Some do both. Aesthetic finishes'ones that focus on looks'don't focus on corrosion protection. Still, powder coating does offer some protection (unless a scratch reaches to the metal beneath). Silk screening, on the other hand, is used to add text and images to parts and offers no protection at all.
Chemical conversion finishes are meant to protect your parts by altering the properties of the outermost layers. For example, if you want to use steel in a corrosive environment, consider choosing galvanized or galvannealed metal, which already has a protective zinc coating. Watch out, though! We can't weld galvannealed steel due to the dangerous toxins it would give off. Instead, we can make the parts out of steel and add a zinc coating after welding.
Chromate conversion can give your part electrical connectivity and provides a primer layer to your part if you want to paint. Anodizing can add a pop of metallic color to your parts while also protecting them. Think of that colorful, small flashlight you own.
Here's a helpful summary of the most common finishes for sheet metal.
Imagine making hundreds of parts out of unfinished steel that are destined for installation in a salty, marine environment. Amazingly, we've seen quotes that request just that. Save yourself the grief of the customer complaints you'll get when your parts corrode and consider these factors when selecting the right sheet metal:
This handy chart can help.
When designing U channels, always think about the strength of the material you're using and how easily it can bend. At Protolabs, narrower doesn't work for us because of our tooling. If we had narrower tooling, we could manufacture narrower U channels. The bottom line is that it is best practice when working with us to maintain at least a 2:1 width-to-height ratio for your U channels. If you need a narrower channel, consider a welded or riveted assembly.
Have you ever tried welding a seam inside a closed box? Nope? Neither have we. Make sure that your weld requirements are realistically achievable. It's important to remember that if a welding torch can't access a seam, the weld can't happen. We strongly recommend designing so all welds are done on the outside of the part.
Metal melts under high temperature, so you need material thicknesses that can manage the extreme heat. The minimal material thickness for welding is 0.040 in. (1.016mm) to ensure that the weld doesn't end up an unholy mess of melted metal.
Finally, in your models, always indicate the need for welds using a welding function or nomenclature. Never box corners to indicate welding.
No single design tip can cover all the sheet metal mistakes we've seen, but this 'best of' collection is a start. Take a look at our sheet metal design guidelines to keep you moving in the right direction.
For additional help, feel free to contact a Protolabs applications engineer at 877-479- or [ protected]. To get your next design project started today, simply upload a 3D CAD model for an interactive quote within hours.
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