5 Must-Have Features in a Custom Sheet Metal Fabrication Services

5 Factors For Choosing Sheet Metal Fabrication

­ Written By: Tony Varela

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Introduction:

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.

Why Choose Sheet Metal?

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.

1. How is Sheet Metal Being Used?

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:

• Fabrication techniques
• Common Materials
• Design considerations
• Finishing options

2. Sheet Metal Fabrication Techniques

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

• Shearing was one of the longest standing means to cut sheet metal but has since been replaced by faster, more precise methods.
• Punch Press use tools called punch and dies, which punches holes and shapes to make any number of patterns.  Particularly effective for cutting simple patterns that are more economical than cutting on a laser cutter or a water jet. Punch presses can operate at hundreds of strokes per minute making this a suitable center for processing parts quickly.
• Laser Cutting works with a combination of oxygen, nitrogen, helium, or carbon dioxide to burn away material and produce a clean edge.  This form of cutting can hold very tight tolerances.
• Photochemical Machining is a process of controlling the etching using CAD-generated stencils to leave a pattern that is chemically activated to remove unwanted material.

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.

3. Common Types of Sheet Metals

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:

• Austenitic stainless is a non-magnetic – any of the 300 series steel – that contains high levels of chromium and nickel and low levels of carbon. Known for their formability and resistance to corrosion, these are the most widely used grade of stainless steel.
• Ferritic – Stainless steels that are magnetic, non-heat-treatable steels that contain 11-30% chromium but with little or no nickel. Typically employed for non-structural uses where either good corrosion resistance is needed such as with seawater applications or decorative applications where aesthetics are the main concern.  These metals are most commonly found in the 400 series stainless steel.
• Martensitic – A group of chromium steels ordinarily containing no nickel developed to provide steel grades that are both corrosion resistant and hardenable via heat-treating to a wide range of hardness and strength levels.

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.

4. Design Considerations for Sheet Metal Fabrication

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:

• Sheet metal fabrication is most cost-effective when standard tool sizes are used as opposed to costly custom tools that need to be made specifically for the job. If a single part becomes too complex, consider welding or riveting parts together that can be made using standard, or universal tools.
• Because bends will stretch material, features such as holes, cut-outs, inserted hardware should be located well enough away from bends to prevent distortion of the hole. To help with this rule, remember “4T” which means located features four times the material thickness away from any bends.
• Press brakes create bends by pressing sheet metal into a die with a linear punch, so the design does not allow the creation of closed geometry.
• Sheet metal tolerances are far more generous than machining or 3D tolerances. Factors affecting tolerances include material thickness, machines used, and the number of steps in the fabrication process.  Suppliers generally will provide detailed tolerance specifications as it related to their shop and machines.
• A uniform bend radius such as 0.030 in. (industry standard) should be used on every bend of a part to reduce multiple setups and accelerate production.
• Welding thin materials can lead to cracking or warping. Consider other joining methods when working with thin materials.
• Consider material thickness and manufacturers’ minimum requirements when installing PEM hardware.

5. Finishing Sheet Metal

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:

Furui Product Page

• Brushing is used to deburr and remove surface defects from sheet metal parts.  The surface pattern created is a uniform parallel grain resulting from the brush moving against the metal surface in one direction.
• Plating is a process of coating a layer of metal to an object of different types of metal.  This process is done, commonly, for aesthetic purposes or more practical reasons such as corrosion resistance and protection from wear and tear.
• Polishing sheet metal as a means of finishing is where a layer of oxidation and also a thin layer of the material itself is ground off.   In doing so it smooths out the metal, removing imperfections, and making it gleam once more.  Generally, start with a coarse grit of sandpaper, like a 40 to 80 grit and then work towards a finer grit to finish off the polish effect.
• Powder Coating creates a hard finish that is tougher than conventional paint.  Powder coating comes in any color and therefore makes a great custom finish method when both durability and aesthetics are desirable finishes.
• Abrasive Sand Blasting, more commonly known as sandblasting or media blasting, is the operation of forcibly propelling a stream of abrasive material against a surface under high pressure to smooth a rough surface, roughen a smooth surface, shape a surface or remove surface contaminants.

Concluding Thoughts

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.

Source:

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

Unlocking access to quick turn prototype sheet metal assemblies is the key to keeping your project on time and within budget. While Protolabs sheet metal has a fantastic team of applications engineers ready to walk you through your design, the key to rapid quoting and manufacturing is keeping a few important assembly design tips in mind.

Mating Components: Mind the Gap!

Sheet metal tolerances are significantly looser than those for standard machined parts, which have a tolerance of +/-0.005 in. (+/-0.127mm). In fact, if you are crossing multiple bends with your dimension the tolerance could be as loose as +/-0.030 in. (+/-0.762mm). 

For example, when you are designing components that will be riveted together, it's important to think about this tolerance range and afford design accommodations, preventing components that can't mate because of interfering tolerances once fabricated. This mindful design philosophy will make the assemblers job quicker and easier with fewer opportunities for quality failures and non-conforming product. 

A good rule of thumb is to allow for 0.005-0.010 in. (0.127-0.254mm) between your components. Also keep in mind that powder coating adds 0.002-0.005 in. (0.051-0.127mm) to your material thickness. So, if your parts are powder-coated, lead towards the large end of the gap range. 

If that baseline separation between components is present, our programming department will do their best to adjust the geometry and maintain your original design. Lastly, following gap guidelines will reduce potential design-for-manufacturing (DFM) issues identified by our automation software, preventing additional processing time for your quote as well as when we get started on your order. 

Design for Tooling and Hardware Access

Tooling and equipment such as welding torches, hardware installation tools, and spot welders need to have access to the areas of that part where the feature is being added. We have a variety of tools available to work through complex situations, but by going just a bit further to ensure the assembly is easy, simple, and straightforward, you can save on cost and time. 

PEM hardware is installed with tooling on both sides of the hardware. that means we need direct access up and down from the hardware. If you must design a return flange over a piece of installed hardware, add a 0.75 in. (19.05mm) hole to accommodate hardware tooling. Asking yourself, "How would I install this hardware?" will take you far in designing a manufacturing-ready assembly that is easy to quote and produce. 

MIG/TIG torches and pop riveting machines both need substantial room to operate. To simplify manufacturing and quoting, design your assembly to utilize welds and rivets installed from the exterior of the part. This will allow us to grind your welds to a nice finish, substantially reducing setup and run time and ensuring your project can be assembled quickly without creating unnecessary quality concerns. 

Spot welders, just like PEM hardware, need access to both sides of the weld location for proper functionality. This means that your assembly must be designed in such a way that provides easy access to each component that will be spot-welded and should have a minimum flange length of 0.625 in. (15.875mm) to accept the spot welt tips that come together to fuse your parts. 

Hand/assembly tool access It is easy to lose sight of the size and accessibility of fasteners and components during assembly after manufacture. Think about how you will install your loose hardware and components when designing your assembly after manufacture. Think about how you will install your loose hardware and components when designing your assembly. This foresight could save you the cost and time associated with numerous revision cycles during which these details are overlooked. There's nothing worse than going to assemble a project for which you spend thousands of dollars, as well as development and manufacturing time, only to get stuck with a fastener you can't fit into its hole. 

Consistency and Flexibility with Punch-form Tools

If your project requires multiple punch-form features, such as embosses, ribs, louvers, or others, try to use the same features throughout your assembly. This will reduce quoting time substantially and positively affect the setup and run time on the punch. 

When you are designing your features, be as flexible as possible. Our sheet metal team has an immense library of on-hand tools/features. If you can allow us to use one of our on-hand tools, and keep that tool consistent throughout your assembly, you will save thousands of dollars on custom tooling and close to a week of lead time waiting for those tools to come in. This compounds with the existing lead time because punch-form tools must be in hand before manufacturing begins. 

Avoid Thin Materials when MIG/TIG Welding 

It may be tempting to save on weight by using thin material for your welded assembly. This can be a pitfall because decreasing material thickness in a welded assembly increases risk of heat-related deformation, in particular. If you must create a welded assembly with material thickness of less than 0.063 in. (1.6mm), consider spot- or plug-welding (or rivets, ideally) first. 

If that is not an option, choose the least amount of welding that will be effective for your needs. This could mean opting for 1 in. (25.4mm) of weld every 6 in. (152.4mm) rather than a fully welded seam or joint. That nice, welded corner you are looking for won't be so nice when heat causes the sheet to oil can. Oil canning, in this case, is when deformation is introduced to the sheet because of the immense heat from the welding operation. 

Don't Submit Models with Non-Fabricated Components

This tip is applied during the quoting process. It may be tempting to drop your complete assembly model into our digital quoting platform but that will cause the estimating process to grind to a halt. Our automated systems are unable to process non-sheet metal components or loose hardware, so when a model is received with wire and cable harnesses, printed circuit boards, and EFI gaskets, the automated support in our system stops and the assembly must be processed 100% by a human estimator. 

If you feel it is critical that we understand the design intent of your assembly as it pertains to your non-fabricated components, submit that information in a print and provide a 3D model of the fabricated components and permanently installed fasteners (PEM and rivets) only. We want to be the first one to deliver your quote and execute your project, sending us only the relevant 3D data is the best way to work with our systems and secure an actionable quote and lead time quickly. 

Following these design tips will help you design a project that is ready for manufacture, can be quoted rapidly, and synchronizes with our strengths and capabilities. We know your project is important and timelines are never generous, but we're here to be your partner in rapid innovation. Engineering your assembly with manufacturability in mind form the beginning will help set up a smooth transition into production. 

The company is the world’s best Custom Sheet Metal Fabrication Services supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.