Designing for Sheet Metal Fabrication

DESIGNING FOR SHEET METAL FABRICATION An exploration of materials, manufacturing processes, design considerations, and finishing options for sheet metal prototypes and low-volume production parts Designing for Sheet Metal Fabrication

Contents Sheet metal is one of the most versatile materials in the manufacturing industry. It’s made from steel, aluminum, brass, copper, tin, nickel, titanium, or precious metals. It ranges in thickness from wispy leaf through light foil to 2 Why Sheet Metal? heavy plate. It takes a variety of forms: plain flat sheets, embossed, etched, ribbed, corrugated, and perforated. And its uses expand across many different 2 How is Sheet Metal Being Used? industries including transportation, aerospace, appliance manufacturing, consumer electronics, industrial furniture, machinery, and more. 3 What Types of Sheet Metal are There?

4 What Technologies and Techniques are Used to Shape Parts?

5 Design Considerations

6 How to Finish Parts

7 Final Thoughts on Choosing Sheet Metal Fabrication

ON THE COVER: Sheet metal can be cut, stamped, punched, sheared, formed, bent, welded, rolled, riveted, drilled, tapped, and machined. Sheet metal has been used for millennia, and sheet metal fabrication today continues to be popular, with an industry worth tens of billions of dollars.

A BRIEF HISTORY WHY SHEET METAL? HOW IS SHEET METAL Depending on the application, sheet metal BEING USED? OF SHEET METAL offers advantages, not just over non- Sheet metal is cut, stamped, punched, metal alternatives but over other types Sheet metal has been used for millennia, having sheared, formed, bent, welded, rolled, of metal fabrication as well. Compared to reportedly shown up in ancient Egyptian jewelry. riveted, drilled, tapped, and machined. machining, it generally has a significantly It was a mainstay of medieval armor when metal Hardware can be inserted into sheet metal lower material cost. Rather than starting fabrication was still a costly manual process. There components. The components can be with a block of material, much of which will was an explosion of sheet metal work beginning brushed, plated, anodized, powder coated, at the time of the Industrial Revolution. Today it is be machined away, sheet metal lets you buy spray painted, silk screened, or otherwise in our cars and appliances, can be found in almost what you need and use what you need. The marked. And, of course, parts can be riveted, any room in the home or office, it encases computer remainder of a metal sheet is still usable, hardware, and is travelling around the world in screwed, or welded into complex assemblies. while swarf—the shavings removed in aircraft and through space in rockets and satellites. machining—must be recycled. Like most other technologies today, sheet After centuries of hammer-forming, the first rolling As with many modern fabrication metal fabrication is evolving. Materials, mills appeared in the 16th century to produce sheet metal stock, in at least one case using a techniques, sheet metal manufacturing equipment, and tooling have become more design originated by Leonardo da Vinci. The 17th can be automated and parts produced specialized than ever before. To take full century saw the industrialization of sheet metal directly from CAD models. The technology advantage of sheet metal, it is critical manufacturing culminating in the creation of the first uses a variety of materials and a range of that you leverage the correct supplier and cold rolling plant in England. The Industrial Revolution processes for shaping finished components method of manufacturing for your parts of the 18th century saw the advent of assembly line and products. Perhaps most important, in and their application. Along these lines, this production, press brakes, and the hydraulic press. a world of mass production, sheet metal In the 19th century, aluminum was introduced, the white paper explores key components of Bessemer converter allowed mass production of fabrication is highly scalable. While setup sheet metal fabrication: steel, and the steam hammer was also introduced. for the first piece can be costly, the price per Developments affecting sheet metal production and piece drops quickly as the volume increases. • Materials use have continued at an This is, of course, true of many processes, • Manufacturing processes ever-growing rate into the but cost-per-piece for sheet metal generally 20th and 21st centuries drops more steeply than for a subtractive • Design considerations making sheet metal today an industry worth tens of process like machining. • Finishing options billions of dollars.

An early model of a power press brake.

WHAT TYPES OF SHEET and is used in applications where corrosion ALUMINUM resistance is not a major requirement such as A moderately METAL ARE THERE? brush-finished appliance surfaces. Because priced material, Varied metals and metal alloys can be formed these materials tend toward elastic—rather aluminum has a into sheets and used to fabricate sheet metal than plastic—deformation, they must be over range of characteristics parts. The choice of materials depends on the bent to achieve final form. across several grades to meet requirements of the application, and factors in • Spring-like steels will work-harden quickly and application requirements. Grade 1100 material selection include formability, weldability, must be heated to relieve stresses when being offers relatively low strength but is chemical corrosion resistance, strength, weight, and cost. formed. Grades include 301, 17-4, 1095, and and weather resistant, and weldable and ductile, Popular sheet metal materials include: 1075. Spring-like stainless typically requires allowing deep drawing. Grade 3003 is stronger specialized equipment and processes and must and formable, weldable, corrosion-resistant, and STAINLESS STEEL affordable. Grade 5052 is significantly stronger Two families of be significantly over bent to achieve final form. while still formable, weldable, and corrosion- stainless steel— standard and COLD ROLLED resistant. Grade 6061 is a structural alloy that is spring-like—are used in STEEL (CRS) corrosion-resistant and strong, but not formable. sheet metal fabrication: The process of It is weldable, though it sacrifices some strength cold rolling steel is when welded. • Standard stainless can be non- used to smooth the finish of magnetic—any of the 300 series steels—and hot rolled steel as well as to hold a COPPER & is the most commonly used type of stainless. It tighter tolerance when forming. BRASS does not require hot work or other stress relief CRS is available in 1008 and 1018 alloys. Designers during manufacturing. Grade 316 is the most and engineers corrosion-resistant of the stainless steel grades PRE-PLATED STEEL who want a “red” and maintains its strength at high temperatures. This sheet metal metal typically choose Grade 304 is the most widely used and, while material is either electrolytically tough pitch (ETP) it is somewhat less corrosion-resistant, offers hot-dip galvanized copper, either C110 or C101. good formability and weldability. steel or galvanealed In less frequent cases, cartridge brass is • Standard type magnetic stainless for sheet steel, which is galvanized used as an alternative. metal fabrication is the 400 series. Grade and then annealed. 410 offers less corrosion resistance but is heat treatable. Grade 430 is an inexpensive alternative to the other stainless steel options

WHAT TECHNOLOGIES Cold-forming processes addressed here are: the tool does not wear out the way a mechanical cutter does. Two types of lasers CUTTING AND TECHNIQUES ARE are used in sheet metal fabrication. Fiber-optic • Shearing was long the primary way to cut laser are used for thinner and more reflective USED TO SHAPE SHEET sheet steel but has now been replaced by materials to deliver precise cuts. Multi-gas or METAL PARTS? faster, more precise methods. CO2 lasers are more powerful and suitable for Sheet metal, by definition, starts out flat but can • A punch press can be used to punch and die thicker gauges. be shaped in many different ways to meet many sets to cut metal. This is particularly effective different requirements. While this paper focuses on • Photochemical machining is a process of for cutting relatively simpler parts than would the technologies that shape sheet metal by bending controlled etching using CAD-generated stencils be cut with a laser or waterjet. Because it it along a single axis, a variety of techniques exist to leave a pattern that is chemically activated can operate at hundreds of strokes per minute, for shaping the material into multi-axis forms to remove unwanted metal. a punch press can make suitable parts quickly. that are not made up of flat planes or bent along Punching can also be used to make holes or BENDING a single axis. These include hot and cold forming other cutouts in parts. Combining punch and Most metals can be bent along a straight axis techniques of deep drawing, hydroforming, laser cutting allows the creation of a complex using a variety of presses. The shapes of bends spinning, and stamping. These are the kind of flat pattern with size-limited stamped features. can range from gentle curves, like those along processes that create the body panels for modern the vertical axis of a steel can, to sharp corners at vehicles, complex formed objects like metal sinks, • CNC laser cutting works with jets of oxygen, angles above, below, or right at 90 degrees. Press and aluminum beverage cans. In many cases these nitrogen, helium, or carbon dioxide to burn away brakes are used to create these relatively sharp techniques are iterative, shaping the metal by metal and produce a clean, finished edge. The bends. Rolling and forming methods produce repeating the process several times to change the speed of this process differs with the thickness open or closed single-axis curves in a continuous shape of the metal in increments. of the metal, but the cut can be quite complex bending operation. and, at tolerances of +/- 0.005 in. or better, is

At left, CNC laser cutting burns away sheet metal to produce a clean, quite precise. And because there is no contact, finished edge. A punch press, center, is especially effective for cutting At right, an example of how most metals can be bent along a relatively simpler parts that would otherwise be cut with a laser or waterjet. straight axis, using varied presses.

HEMMING problematic features, a manufacturing supplier • Where possible, maintain a standard distance This involves rolling the edge of a metal shape should be able to point those out and suggest of four times the material thickness from bend to provide a smoother, stronger edge. Hems can ways of addressing them. In some cases, the to edge. This will eliminate the need to remove excess material required to make the bend. be open, leaving an air space within the bend, or supplier may even have design analysis software closed, in which the folded metal is pressed tight that can quickly highlight issues for design • Welding thin materials can lead to cracking against itself. Curling produces a rounded edge improvement. Some design consideration: or warping. Other assembly methods are to a piece of metal, also called a barrel hem. This preferable. • Sheet metal fabrication is most economical can be used to simply eliminate the sharp edge or when it uses configurations of “universal” tools • When using PEM hardware, always consider the to serve a specific operational function as in the rather than part-specific tooling. If a single minimum requirements of the manufacturer for case of a door hinge where it holds the pin around part becomes too complex, consider welding or installation locations and material thickness. which the hinge rotates. riveting together parts that can be made using universal tools. DESIGN CONSIDERATIONS • Because bends stretch the metal, features must stand away from bends to avoid distortion. FOR SHEET METAL A useful convention is 4T—four times the FABRICATION material thickness. Sheet metal fabrication is a non-additive, non- • A press brake creates a bend by pressing sheet subtractive process. It begins with flat material metal into a die with a linear punch, so design and, by definition, maintains constant material does not allow the creation of closed geometry. thickness throughout a part. In some cases, • Sheet metal tolerances are far more generous areas of a part can be selectively thickened by than machining or 3D printing tolerances. welding multiple metal sheets together, but this Factors affecting tolerances include material is a costly and uncommon practice. thickness, machines used, and number of steps in part production. Suppliers will typically Designing for sheet metal fabrication has its provide detailed information on tolerances. own criteria, which differ from those of other • A uniform bend radius such as 0.030 in. production processes. The more that’s known (industry standard) should be used across a early in the design phases about a part’s features single part to reduce the number of machine and functions, the sooner a manufacturable setups and accelerate production. Caliper measurements for bend accuracy, are part of the entire sheet metal quality control process. design will finalized. If, however a design has

HOW TO FINISH SHEET METAL PARTS COMMON Sheet metal can be finished in several ways and for APPLICATIONS OF different reasons. There are finishes that protect SHEET METAL vulnerable materials from rust or corrosion and others that are applied for aesthetic reasons. In some cases finishing serves both purposes. Some Sheet metal is one of the most versatile treatments are simply alterations to the metal materials and processes in the world Sheet metal can be finished in several ways, including powder surface itself; others consist of another material coating, as seen here, which results in a surface more durable than today. Designers and engineers develop or process that is applied to the metal. Finishing conventional paint, thought it may lack paint’s aesthetic qualities. components as small as washers and treatments include: as large as entire roofs. It appears • Powder coating electrostatically applies a dry in commodity products and in highly powder—typically a thermoplastic or thermoset • Sand blasting, which consists of shooting jets of specialized one-of-a-kind applications. polymer—to the metal surface and then cures it abrasive material at the metal to roughen and Products leveraging the possibilities of with heat. The process results in surface that clean the surface. Sandblasting is typically used sheet metal: on stainless and carbon steel and is often used is more durable than conventional paint but may • Refrigerators, freezers, as a preliminary step before painting to remove not have paint’s aesthetic qualities. and other home appliances impurities and improve adhesion. • Plating can be done electrolytically or • Automobile parts • Airplane components • Brushing is similar to sandblasting in function, but electroless for a various purposes. It can • Chassis uses abrasive brushes to clean and score the metal inhibit corrosion, improve solderability, harden • Brackets surface. It can serve as a final finish on materials a surface, prevent wear, reduce friction, or aid • Metal sinks paint adhesion. Plating processes for like aluminum and stainless steel and is commonly • Electrical enclosures sheet metal include: used as an appliance finish. • Cabinets • Busbars • Polishing yields a glossy surface and is used on - Passivation, a cleaning process that prevents • Mounts metals like stainless steel, aluminum, and copper. corrosion in stainless steels by removing free irons from the surface of the material. It can serve as the final finish or as preparation Its versatility is one of its greatest strengths, but can also be one of the for other finishing processes such as plating. It - Chromate coating, a conductive coating used challenges to its use. is generally unsuitable for metals that are to be on aluminum to protect against corrosion. painted because it does not enhance adhesion.

- Anodizing, an electrochemical process used on it is only when you can see and handle a part that aluminum and other non-ferrous metals that it’s known whether the design meets expectations. FREE provides insulation and prevents corrosion. Is it strong enough? Light enough? Does it look, feel, and balance the way it should? Does it impinge SOLIDWORKS - Zinc, a self-sacrificing anti-corrosion coating (applied by galvanizing or galvanealing) for on other components? Even relatively simple PLUG-IN steels and is often combined with a Chromate components benefit from a real-world tryout before coating over the zinc. committing to hundreds or thousands of parts. In some cases, it may take several prototype iterations The best way to start is to get a quote - Nickel, often a cosmetic coating and can serve to get the sheet metal part right, in which case the with manufacturability analysis for your as a substrate for plating processes that cannot speed with which parts are produced and tested part design. adhere to a given metal. becomes a major factor in speed to market.But Get instant sheet metal design and - Tin, a solderable, conductive coating. even once a design has been created, prototyped, costing feedback within SOLIDWORKS. and tested, there can be many options for turning Download our free SOLIDWORKS add-in, FINAL THOUGHTS small quantities of prototypes into low-volume, eRapid, to get started. end-use production parts. If you don’t have SOLIDWORKS, you ON CHOOSING can get instant sheet metal quotes SHEET METAL FABRICATION The same part can often be produced by several through our myRapid web interface at different methods at different costs. Choosing would rapidmanufacturing.com. Deciding to use—or simply consider—sheet metal be easy if all metal shops offered the same range for an application is the first step in a process. The of capabilities. Unfortunately they don’t, so it makes process begins, of course, with function, which sense to seek quotes from multiple suppliers as in turn dictates design. Choosing a material and each will bring its own expertise and capabilities. gauge are critical steps that involve balancing factors like strength, weight, and cost. This is not a simple process, but it can be streamlined with the use of CAD models and finite element analysis (FEA) tools. The real test, however, is prototyping. While today’s engineering tools are powerful,