5 Things to Know Before Buying precision sheet metal fabrication

There’s nothing worse than submitting an RFQ for a precision sheet metal fabrication project and getting back no-quote after no-quote. 

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Many shops will no-quote projects that pose manufacturing challenges, which adds pressure on engineers to ensure their designs are easily manufacturable. 

At All Metals Fabricating, we’re happy to offer Design for Manufacturability (DFM) advice that consistently yields functional designs optimized for manufacturing. 

9 Design for Manufacturing Considerations for Sheet Metal Fabrication

When engineers understand DFM best practices, they set themselves up for success by ensuring that manufacturing can occur as seamlessly as possible. Designs that are easily manufacturable are associated with shorter lead times and lower prices. If you like the sound of that, check out these DFM tips for sheet metal fabrication: 

1. Be smart about hole diameter

In general, a hole’s diameter should be no smaller than the material’s thickness. This rule is especially important for thicker materials. 

While it’s technically possible to cut holes smaller than the material’s thickness, the approach often involves using a CNC mill, which will significantly increase the cost. 

Adding another operation and setup drives up cost and lead time, so we recommend thinking critically about your hole diameter in conjunction with your material thickness. 

2. Consider bend location and radii

Bends can impact the functionality and aesthetics of cutout features throughout your part. For example, if a hole is located too close to a bend, it could pull, potentially interfering with hardware insertion or affecting the aesthetics of the feature. Generally, it’s best to keep bend lines an entire hole diameter distance away from the cutout feature. 

To ensure efficient manufacturing, we recommend consistently using the same bend radii and angles throughout the part to prevent the need for multiple setups. If possible, note that your sheet metal shop may use their discretion regarding bend radii. Often, shops default to the tightest radius possible to enhance a part’s aesthetic appearance. 

What happens when you don’t indicate that the bend radius is up to our discretion? We’ll contact you to obtain approval on our chosen radius. That back-and-forth creates inefficiency in the manufacturing process, so it’s best to avoid it. 

3. Understand your material needs

When designing your part, it’s important to consider how it will fit onto a standard-sized sheet. Our standard sheet sizes are 48” x 120” or 60” x 120” and require an edge buffer of .125” on the exterior of the sheet and between nested parts. With these parameters in mind, you can achieve optimal sheet utilization and prevent waste. 

For optimized sheet metal fabrication, we recommend keeping material thicknesses the same when possible to improve dynamic nesting and using the same material type for all parts in an order. 

4. Call out aesthetic requirements 

We put in the effort to protect your parts from scratches and other imperfections that can occur during the manufacturing process. But the precautions we take can drive up costs and lead times. 

If you don’t mind a few surface imperfections on your part, let us know up front, and we can likely provide a lower cost estimate. It is best to have a standard for different surface requirements that clearly outlines what kind and how many imperfections are allowed per a defined space. 

5. Indicate design asymmetry

One major issue we want to prevent is forming your parts backward. When parts appear symmetrical but aren’t, they could get bent in the wrong direction. 

To avoid this mistake, we recommend adding a small feature on your part, like a hole, so brake operators can identify the asymmetry and distinguish the directions of the bends. If adding a distinguishing feature isn’t an option, then you can also clearly notate it on the print to help draw attention to the brake operator. 

6. Clarify precise hardware needs

Even something as small as a fastener can have a significant impact on the manufacturability of your design. Sometimes, customers will indicate a random name for a piece of hardware without specifying the length, leaving us unsure of what they need. 

Instead, we recommend using the same PEM brand hardware when possible and indicating the PEM part number in the bill of materials. If your PEM hardware has its own internal part number that you created, be sure to specify it. It’s also helpful for us to get the PEM CAD file when you send us the model of your part, so we’re all on the same page about what you need.  

Want to optimize the manufacturing process even further? Select hardware sizes 10-32 for greater ease of assembly. And if your part has press-in hardware, make sure your non-hardware holes are a different size to ensure the hardware always goes into the correct hole. 

7. Be flexible with finishing requirements 

Finishing is often necessary for parts, but certain finishing specifications could lead to inefficiencies and added costs. Here are a few helpful dos and don’ts: 

• DON’T indicate plating as a paint prep process. Zinc plating before powder coating can cause bubbles that hinder the powder coating process, often requiring us to re-apply powder coating. If you need zinc plating, we recommend using yellow zinc instead of clear zinc because yellow zinc is less prone to bubbling. 

• DO allow for multiple marking options. When we have the opportunity to use a metal stamp, inkjet, or laser mark to mark parts, we can choose the most efficient marking option that will require the fewest setups. 

• DON’T require chem film on powder coated parts. Many engineers will indicate that a part needs chem film as a preparation for powder coating, but our powder coat preparation process uses a phosphate cleaning that is sufficient. This process is already built into the powder coating price, so by including chem film prior to powder coat you are unnecessarily adding cost and lead time. 

• DON’T use multi-colored silk screens. Each color silk screen adds a setup and drives up the cost. When possible, use one color to save time and money. 

8. Provide clear welding instructions 

Including clear welding instructions prevents back and forth, but many engineers may not know the exact welding method their part needs. We recommend calling our sheet metal shop to discuss welding options from the beginning so we can all be on the same page. 

One quick welding tip: use the tab and slot method—which focuses on the orientation of parts rather than the fixture—when designing your weldments to reduce setup time and ensure parts fit together correctly. 

9. Call out critical dimensions

The more dimensions a part has, the more we need to measure during inspection—which adds to your project’s lead time. It’s important to find the sweet spot of giving us the information we need to make a functional, precise part without going overboard. 

We advise customers to indicate every dimension our operators need to know when fabricating a part and using a bubble or triangle to signify the critical dimensions we should focus on during inspection. 

At All Metals Fabricating, we want to help you create the best precision sheet metal fabrication designs possible. Request a quote today, and we’ll help you take your design to the next level.

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5 Factors For Choosing Sheet Metal Fabrication

­ Written By: Tony Varela

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.

For more information, please visit High-quality Sheet Metal Fabrication.

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:

• 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