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An examination of material, manufacturing process, design considerations, and finishing options for sheet metal prototypes and low-volume production parts
In the manufacturing industry, sheet metal is one of the most versatile materials. The metal can be steel, aluminum, brass, copper, tin, nickel, titanium, or even precious metals. Sheet thickness varies from thin foil to heavy plate to wispy leaf.
The sheets come in a variety of forms: plain, embossed, etched, ribbed, corrugated, or perforated. Applications include transportation, aerospace, appliance manufacturing, consumer electronics, industrial furniture, machinery, and many more.
Sheet metal allows the manufacturer to purchase as needed rather than starting with a block of material for machining away. So as long as there is no welding or machining, the remaining metal sheet is still usable; the swarf, however, must be recycled.
A wide variety of sheet metal applications offer advantages over alternative non-metal materials and other types of fabrication methods as well. This process generally has a significantly lower material cost than machining.
Furthermore, sheet metal fabrication is highly scalable. Although the setup for the first piece can be costly, the price per piece decreases rapidly as the volume grows. While many processes have the tendency to drop in cost per piece over time, in a subtractive process such as machining, sheet manufacturing costs usually drop comparatively faster.
The various sheet metal operations include cutting, stamping, punching, shearing, forming, bending, welding, rolling, riveting, drilling, tapping, and machining. Sheet metal components can be inserted with hardware. Depending on the application, components may be brushed, plated, anodized, powder-coated, spray-painted, silk-screened, or otherwise marked. Parts can be riveted, screwed, or welded together to make complete assemblies.
Today, sheet metal fabrication is evolving just like most other technologies. In the past decade, materials, equipment, and tooling have become increasingly specialised. It is imperative to select the right supplier and manufacturing method for your sheet metal components.
The following are some key components of sheet metal fabrication explored in this white paper:
By definition, sheet metal starts out flat but can be shaped in a wide variety of ways to meet a variety of needs. In this paper, we discuss materials that are shaped through the bend of a single axis. However, there are numerous ways to mold the material into forms that are not flat or shaped through bending alone.
Metal fabrication techniques such as deep drawing, hydroforming, spinning, and stamping are examples of methods that can be used hot or cold. Processes like these are used to make the body panels for modern vehicles, complex formed objects like metal sinks, and aluminum beverage cans. These techniques can often be iterative, repeating a process several times to progressively alter the shape and size of the metal.
3. A CNC laser cutting process burns away metal with jets of oxygen, nitrogen, helium, or carbon dioxide. Depending on the thickness of the metal, the speed of this process varies, and the cuts can be quite complex, with tolerances of +/- 0.005 in. or better. Additionally, laser tooling doesn’t wear out as much as a mechanical cutter since there is no contact. Lasers are used in sheet metal fabrication in two different ways. The fiber-optic laser can perform precise cutting on thinner and more reflective materials. In order to accommodate thicker gauges, multi-gas or CO2 lasers are more powerful.
4. Photochemical machining involves using CAD stencils to leave a pattern that will be chemically activated to take away unwanted metal.
Metals can generally be bent along straight axes using various presses. Depending on their shape, bends can range from gentle curves, such as those along the vertical axis of a steel can, to sharp corners at 90-degree angles. Generally, these sharp bends are created by press brakes. Continuous bending can be achieved using rolling and forming methods to produce open and closed single-axis curves.
By rolling a metal shape, you can create a smoother, stronger edge. In open hems, an air space is left between the folded metal, while in closed hems, the folded metal is pressed into tight quarters. When a piece of metal is curled, it produces a rounded edge, also known as a barrel hem. Alternatively, it can serve a specific function, for example to hold a pin within a door hinge, eliminating the sharp edges.
Forming metal sheets and fabricating sheet metal parts can be done from a number of metals and metal alloys. The choice of material is determined by the application requirements, and factors like formability, welding, corrosion resistance, weight, and cost are taken into account. Materials commonly used for sheet metal include:
In sheet metal fabrication, stainless steel is categorized into two types: standard and spring-like.
• Any 300 series steel can be non-magnetic, and this is the type of stainless most commonly used. As far as manufacturing is concerned, no heat or other stress relief is required. The stainless steel grade 316 has the highest corrosion resistance and maintains its strength even at elevated temperatures. While grade 304 is somewhat less corrosion-resistant, it is highly formable and weldable.
• Magnetized stainless steel 400 series is the most commonly used type in sheet metal fabrication. Although grade 410 has lower corrosion resistance, it is heat treatable. A brush-finished appliance surface made from grade 430 stainless steel is an inexpensive alternative to other stainless steel types. Due to their elastic rather than plastic deformation characteristics, these materials must be over bent in order to achieve their final form.
• When forming spring-like steels, heat is needed to relieve stresses, since the steel hardens quickly. Grades include 301, 17-4, 1095, and 1075. Stainless steel springs typically require specialized equipment and processes as well as a significant amount of over bending to achieve the final shape.
During cold rolling of steel, the finish is smoothed and the tolerance is tightened when forming. A wide range of alloys are available for CRS. 1018 and 1008 are the most common.
Galvanized steel or galvanealled steel is used for these sheets, which is galvanized and then annealed.
Aluminum is a moderately priced material that has a range of properties across a range of grades to meet specific application requirements. In Grade 1100, strength can be somewhat low, but it is chemical and weather resistant, weldable, and ductile, which allows deep drawing.
The 3003 grade is strong and formable, weldable, corrosion-resistant, and affordable. The 5052 grade is significantly stronger while still being formingable, weldable, and corrosion-resistant. The alloy grade 6061 is corrosion-resistant and strong, but cannot be shaped. It is weldable, though it sacrifices some strength when welded.
For engineers and designers looking for a red metal, they typically select electrolytically tough pitch copper (ETP), such as C110 or C101. As an alternative, cartridge brass is sometimes used in less frequent cases.
Sheet metal can be finished in several ways and for different reasons. There are finishes that protect vulnerable materials from rust or corrosion and others that are applied for simple aesthetic reasons. In some cases, finishing serves both purposes. Some treatments are simply alterations to the metal surface itself; others consist of another material or process that is applied to the metal. Finishing treatments include:
It consists of shooting jets of abrasive material at the metal to roughen and clean the surface. Sandblasting is typically used on stainless and carbon steel and is often used as a preliminary step before painting to remove impurities and improve adhesion.
It is similar to sandblasting in function, but uses abrasive brushes to clean and score the metal surface. It can serve as a final finish on materials like aluminum and stainless steel and is commonly used as an appliance finish.
Polishing yields a glossy surface and is used on metals like stainless steel, aluminum, and copper. It can serve as the final finish or as preparation for other finishing processes such as plating. It is generally unsuitable for metals that are to be painted because it does not enhance adhesion.
Powder coating electrostatically applies a dry powder—typically a thermoplastic or thermoset polymer—to the metal surface and then cures it with heat. The process results in surface that is more durable than conventional paint but may not have paint’s aesthetic qualities.
Plating can be done electrolytically or electroless for various purposes. It can inhibit corrosion, improve solderability, harden a surface, prevent wear, reduce friction, or aid paint adhesion. Plating processes for sheet metal include:
It is still possible to turn small quantities of prototypes into low-volume, end-use production parts once a design is developed, prototyped, and tested. Several different methods can be used to produce the same part, resulting in differing costs. It would be easy to choose if all metal shops provided the same range of services. Due to this, multiple quotations are necessary, as each will have distinct expertise and capabilities.
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