An Engineers' Guide to Sheet Metal Bending

Table of Contents

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What is Sheet Metal Bending?

CNC sheet metal bending is one of the most underrated processes available for sheet metal part production. With bending, it&#;s possible to produce a wide variety of part geometries without tooling, at fast lead times, with high levels of repeatability and through automated processes. Bending is especially useful for low and medium volume production, where the reduced quantities (such as, several hundred to several thousand per lot) don&#;t justify the creation of costly, difficult to maintain stamping tools, or where production costs for other methods are otherwise high for the volume of production required.

Bending techniques are a key tool in the arsenal of product developers, engineers and business owners who are looking to manufacture metal parts. Often, bending is paired with laser cutting as a series of processes to handle low to medium volume production.

It&#;s good to understand the possibilities with sheet metal bending at the design phase. Bending is a tool that gives engineers the ability to create a wide variety of shapes and designs. In many cases, bending also allows a part to be created from one piece of material. This can have benefits over producing parts from multiple pieces joined together with hardware or welding. These include reducing cost and allowing for improved strength, simplified assembly and little-to-no tooling.

This Komaspec guide provides an overview of the main sheet metal bending processes, the advantages and disadvantages of each, basic design considerations with sheet metal bending and material selection information. This guide, along with our other articles exploring sheet metal fabrication will help you gain a grounding in sheet metal fabrication. The overall aim is to provide you with the information you need to understand how sheet metal parts are manufactured. With this information, you can better discuss the fabrication of your products with sheet metal manufacturers such as ourselves.

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Types of Sheet Metal Bending

There are multiple ways in which sheet metal parts can be bent during fabrication. However, the two main basic methods are:

• Brake press bending
• Rolling

The exact process followed with each method will depend on the material being bent as well as the part being produced. Less commonly used methods are employed when bends can&#;t be achieved through simpler means.

Brake Press

A brake press is a tool that has been in use for many years in traditional fabrication shops all over the world. In its simplest form, a work piece is formed between two dies, as seen in the image below.

Figure 1: CNC Sheet Metal Brake Press (Bystronic Inc.)

Brake presses can be used for a very wide range of sheet and plate materials. Material thicknesses from 0.5mm up to 20mm can be accommodated due to the flexibility of the tooling and the high power levels of hydraulic machinery.

Brake presses are specified by two general parameters: Tonnage and width. The capacity or &#;tonnage&#; of a brake press refers to the maximum amount of force it can exert. The material thickness, type and bend radius dictate how many tons of force are needed when fabricating a part. Width refers to the maximum bend length the press can achieve. A typical brake press, for example, could be 100T x 3m (&#;press brakes&#;).

Brake press bending processes are categorized into two main types: Air bending and bottom bending.

Air Bending

The most commonly used brake press bending method is air bending. This involves using a brake press with a bottom tool that is a v-shape and a top punching tool of narrow shape with a rounded point. To create a bend, the press pushes the top tool downwards a set distance, bending the material inwards into the the v-shaped bottom tool. Air bending is called air bending because a gap is left between the sheet metal being bent and the bottom tool when the sheet metal is at its full bend depth.

Bottom Bending

Bottom bending also uses a punch and bottom v-shaped die in a brake press. The difference is that the punching tool pushes the sheet metal fully into the die to form a bend that is the shape of the die. The specified bend angle determines the specific die to be used, and so it is necessary to select the correct die for each bend being performed.

Bottom bending generates less springback and creates more accurate angles. However, each bend radius will require a different bottom die, and the process requires more machine pressure. With air bending, many different bend angles can be produced with the same die, less pressure is needed, and the process is faster.

For a full insight into both methods, check out our guide here: Bottom Bending Vs Air Bending.

Figure 2: - Air and Bottom Bending (Skill-Lync)

Rolling

When a cylinder or curved part is required, sheet metal or plate can be rolled to the required curvature. This is achieved with a machine called a roller. Rollers range in size from around 3 feet/1 meter wide to over 5 meters. The thickness of material being bent can range from 1mm to 50mm+.

Figure 3: Bending Rollers (Barnshaws)

The most common rolling machines have 3 rolls, arranged as seen below in figure 4. The middle or top roll is moved closer to the bottom rolls (in some cases vice versa), and the material is then moved through the rollers as they spin. The material deforms as it moves through the rollers, obtaining a curved shape.

As with all bending processes, some springback will occur with rolling. As such, sheet metal parts are generally rolled to a slightly tighter radius than required to compensate for this.

Figure 4: Bending Rollers (Barnshaws)

Once the rolling process is complete, the bottom roller can be adjusted downwards to release the bent section of sheet metal. Otherwise, most rolling machines also have the provision to open the top end yoke as seen below.

One disadvantage, when using rolling to produce a cylinder, is that a pre-bend operation may be required to ensure each end of the cylinder meets after rolling is complete.

Figure 5: End Yoke Removal (&#;A Rundown on Rolling Machines&#;)

When to Use Sheet Metal Bending in Fabrication

Sheet metal bending offers a great deal of flexibility in terms of the type and thickness of metals that can be bent. Complex parts can also be produced. Bending processes can be used to create sheet metal parts and assemblies in every industry, including automotive, transport, domestic appliances, furniture, industrial equipment and more.

A wide range of metal types can be bent, including common metals such as steel and aluminum, as well as less common metals, such as copper and titanium. Thick materials can also be bent as well as thin materials. Note that the term &#;sheet metal&#; is typically used to refer to materials that are under 3mm in thickness. Sheet metal bending processes, however, can be used on materials that are as thick as 20mm.

In many cases, and with the advent of modern CNC machines that can do both cutting and bending, complete parts can be produced from one piece of sheet metal. Previously, welding or other joining techniques were required where they are now unnecessary. Being able to produce whole parts from one piece of sheet metal can cut costs and production times.

Where it&#;s not possible to produce a complete part from one piece of material, sheet metal bending can often be combined with other value-adding operations without difficulty. Other fabrication processes, on the other hand, can present issues at this stage.

Mechanical fasteners, such as bolts or more permanent fixings such as rivets or welding, can be used to join bent parts to other parts, for example. Parts of different thicknesses can also be attached to one another as well as parts of the same thickness. Other processes, such as threading, chamfering, countersinking or boring, can also further increase the flexibility and versatility of sheet metal components.

Our article about &#;Value Added Operations for Sheet Metal Components&#; provides more information.

Figure 6: Sheet Metal Parts (&#;Precision Sheet Metal Fabrication and Assembly in China&#;)

Advantages

Speed of Manufacture - Once designed and programmed, due to the lack of tooling required and the high levels of automation available (many shops are able to run 24/7 with a handful of personnel monitoring production), sheet metal parts can be produced very quickly.

Accuracy - If the considerations that need to be made in the design phase are made adequately, sheet metal parts can be manufactured to a high level of accuracy. Advancements in fabrication techniques and equipment have made it possible to achieve accuracy levels of ±0.05 mm in some cases. As well as bending being accurate in the first place, accuracy can also be repeated consistently. This is particularly true with CNC bending machines with modern software and equipment.

Reduced Post-Processing &#; Other fabrication processes require post processing before a part is complete. Heat used in welding, for example, can cause dimensional distortion in a sheet metal part. Straightening may be required to correct this. Alternatively, with welding, weld spatter may need to be removed through time-consuming and labor-intensive grinding and polishing. Issues such as these usually aren&#;t present with bending. Bent sheet metal parts are often ready to go, straight from production.

Less Weight &#; With sheet metal bending techniques, stiffness and strength can often be achieved in parts without using additional material during manufacture. This reduces part weight and can be beneficial to in-use part performance. This can also help to reduce issues associated with the transport of parts after production.

Low Cost, and Little-to-No Tooling - Due to the advances in technology, using CNC bending processes often cuts down the manual labor required to produce sheet metal parts. As well as less labor being needed, work can also often be performed by unskilled workers rather than more expensive specialist workers.

Because most manufacturers carry a line of common tools (such as punches and dies) that can produce most standard bends, using sheet metal bending processes often eliminates the need for specialized tooling. This means no tooling investment and significantly shorter lead times, as there is no need to wait for complex tooling to be produced, tested or adjusted.

Reduction in Part Complexity &#; With bending, it&#;s often possible to create relatively complex components from one piece of material instead of from multiple parts with joints. This reduces time, the potential for errors, failure points and procurement complexity.

Disadvantages

As with all fabrication processes, there are some downsides to using sheet metal bending, as detailed below.

Thickness Limitations &#; A rule of thumb in sheet metal bending is that thicker materials have higher bend radiuses (&#;Designing Sheet Metal Components Using Laser Cutting and CNC Sheet Bending&#;). As a result, tight bends are usually better performed on thinner sections of sheet metal rather than thicker ones.

This can mean that some complex parts can become limited to relatively lightweight materials, suitable for low-load or no-load applications. Bending excessively thick material can also result in the material &#;bulging&#; outward post bend (&#;How Material Properties Impact Air Bending Precision and Tolerances&#;), the material to crack if it is too rigid, or the need to move to a higher tonnage (and more expensive) press.

Need for Consistent Thickness &#; Because it&#;s optimal to produce parts from one piece of material instead of by joining different pieces, it&#;s better if the thickness of separate flanges on a part does not change. This means that it may be necessary to design a part to have the same thickness throughout.

Cost of Manufacturing - Sheet metal bending is most competitively priced at low to medium volumes. Part volumes from the 100s to 1,000s are usually best. When volumes increase further, stamping is generally considered to be more cost effective, although this can depend on part geometry and other design specifications. This is because CNC bending requires components to be processed one bend at a time, while multiple bends can be produced at the same time through progressive stamping. Even roboticized bending (generally used for volumes of parts in the thousands) cannot compete with high-volume stamping costs.

While labor costs are usually reduced with machine assisted bending processes, in some cases they can be labor intensive. When this is the case, costs will be increased. Some specialist bending projects may also require custom tooling, which while significantly lower than custom stamping tooling, can still be a capital expense.

Production Issues &#; In some cases, bending will cause indentations or scratches to occur on products during processing, due to the pressure exerted on the part through the narrow bending tool &#; these types of bending marks are often visible depending on placement in the part. Fractures may also occur if hard metals are bent parallel to the direction sheet metal has been rolled in during production. Holes, slots and other features close to bends can also become distorted during bending. Finally, bends need to be in a position on the sheet metal where there is enough material for it to fit into the equipment without slipping during bending. These issues may all arise during production.

Sheet Metal Bending Compared to Other Fabrication Processes

 

 Process Best used for Process Precision Level Thickness (mm) Custom tooling required Minimum order quantity Lead Time from CAD to 1st production Laser cutting Small to large parts with every geometry possible ± 0.10mm 0.5mm to 20.0mm No 1 to 10,000 units Less than 1 hour CNC sheet bending Small to large parts with straight anglegeometry, multiple bend possible ± 0.18mm 0.5mm to 20.0mm No 1 to 10,000 units Less than 1 hour CNC Punching Small to large parts with most geometry available, good for parts with multiple holes and embossed ± 0.12mm 0.5mm to 4.0mm* No unless special form required 1 to 10,000 units Less than 1 hour Stamping  High volume production with tight tolerances, restricted geometry ± 0.05 to 0.10mm 0.5mm to 4.0mm* Yes from 250 USD to 100,000 USD+ &#;5,000 units 25 days to 40 days Shearing Thin material with simple geometry straight lines and low tolerances requirements ± 0.50mm 0.5mm to 4.0mm* No 1 to 10,000 units Less than 1 hour

Table 2: Sheet Metal Bending Compared to Other Fabrication Processes (&#;Sheet Metal Fabrication&#;)

Materials Suitable for Bending

Almost all engineering materials are available in sheet form, and thus can be bent to some degree. There are, however, different processing limitations with different materials because of their different inherent properties.

Sheet metal is available in a selection of sizes, which are commonly referred to as gauges. These range from gauge 50 (or 0.03mm), to gauge 1 (7.62mm). Bending with a brake press can be performed with all these thickness gauges and higher (&#;Sheet Metal Gauge Conversion Chart&#;).

Gauge is a traditional term still widely used, despite many materials, such as steel and stainless steel, being specified directly in their millimeter thicknesses. This is especially the case in Europe. One exception is aluminum, which is often still defined in all three dimensions by imperial measurements, i.e. feet and inches, and gauge for thickness.

For the best information on the materials available, refer to our standard materials page.

Fig 7. Sheet Metal Parts (&#;Sheet Metal Surface Finishing Standard Options&#;)

Each metal has its own unique characteristics, and the following table outlines some of the factors you should consider when making your choice of materials.

MATERIAL SURFACE FINISH YIELD (MPA) TENSILE (MPA) HARDNESS GB STANDARD Powder Coating E-Coating Zinc Plating Darcomet Anodized Passivation Cold Rolled Steel (CSR)                     SPCC             &#;210 &#;350 HB 65 - 80 JIS G- SAPH440             &#;305  &#;440 HB 80 ± 30 Q/BQB 310- Hot Rolled Steel                     Q235             &#;235 375 - 500 HB 120 ± 40 GB/T 700- Q345             &#;345 GB/T 490 - 675 HB 120 ± 40 - Spring Steel                     65Mn             &#;785 &#;980 HB 190-340 GT/T - Aluminum                     AL             &#;35 &#;75 HB 26 ± 5 GB/T - AL T6             &#;276 &#;260 HV 15 &#; 18 GB/T - AL T5             &#;170 &#;250 HB 25 ± 5 GB/T - AL H32             &#;70 210-260 HB 11 ± 2 GB/T - Stainless Steel                     SS301             &#;205 &#;520 HB 76 &#; 187 GB/T - SS304             &#;205 &#;520 HB 76 &#; 187 GB/T - SS316             &#;205 &#;520 HB 76 &#; 187 GB/T - Cold Galvanized Steel                     SGCC             &#;200 &#;380 HB 60 - 65 JIS-G

Table 3. Sheet metal materials (&#;Sheet Metal Standard Options in China&#;)

Mild Steel - This is available in both hot and cold rolled variants. Both offer excellent cold working performance, with high ductility. Also known as low carbon steel, mild steel is the most commonly used material in the world (&#;5 Most Popular Types of Metals and Their Uses&#;).

The largest downside to mild steel is the requirement for coating, which is needed to prevent rust from forming in the presence of moisture. Galvanized steel is available to counter this issue. This comes with a hard wearing pre-applied zinc coating that prevents rust.

Aluminum - First used for aircraft production, various aluminum alloys are available, with a very wide range of applications. Because aluminum alloys with other elements so successfully, an incredibly wide range of types of aluminum alloy can be sourced. These come with a range of different properties.

The most used aluminum alloys for sheet metal applications are the series alloys, particularly aluminum. This alloy is widely used due to its high workability and low weight. The series is also widely used in sheet metal bending. The high level of workability in these metals allows the material to be bent to tight radii without cracking, specifically, and this is often vital for complex parts (&#;Aluminium / Aluminium Alloy&#;).

For general guidelines to material suitability for CNC bending, see the table below:

MATERIAL MALLEABILITY Aluminum Difficult to bend and often cracks. Cold bending will weaken the metal. Annealing improves malleability. Aluminum Very malleable and a good choice when using aluminum. Cracking is rare unless a part is reworked. Annealed Alloy Steel Varies based on the alloy. has good malleability. Annealing helps prevent cracking. Brass Zinc content is important. Higher zinc levels make it less malleable. Good for simple bends but complex parts may require heat. Bronze More difficult to bend and may require heat to avoid cracking. Copper Very malleable. Cold Rolled Steel Less malleable than hot rolled steel. Hot Rolled Steel More malleable than cold rolled steel. Mild Steel Very malleable. Heat not required. Spring Steel Malleable when annealed. Once work hardened, it requires heat to bend again. Stainless Steel Stainless steels like 304 and 430 are easier to form than 410, which can be brittle. Different grades will perform differently although stainless steel is prone to work hardening. Titanium Strong material, so best to design with a large internal bend radius. Overbending required because of springback.

Table 4: Material Properties (&#;How Material Properties Impact Air Bending Precision and Tolerances&#;)

Stainless Steel - Commonly used in the food and medical industries, stainless steel is an alloy of mild steel. To be stainless steel, steel must contain over 10.5% chromium. This gives the material corrosion resistance, with some grades excelling at resistance to acids, alkalis and other chemicals.

Commonly used grades of stainless steel are 301, 304 and 316, with the latter having higher strength and corrosion resistance, 301 having superior flexibility and &#;spring&#; and 304 being a good middle of the road material for general use (Burnett).

Design Considerations for Sheet Metal Bending

Parts that are to be processed using bending equipment should be designed from the outset with the characteristics and limitations of the bending process in mind (&#;Designing Sheet Metal Components Using Laser Cutting and CNC Sheet Bending&#;).

We will discuss the main considerations that need to be made below. For even more information, however, you can refer to our sheet metal design guide.

Bend Radius - When a material is formed into a bend, the outer surface is stretched, and the inner surface is compressed. The result is that the part has a rounded corner at the bent edge on both the inside and outside.

The bend radius is a measurement of the curvature of the inside bend edge. The bend radius that is possible with a section of sheet metal will differ depending on the material being bent as well as the tooling geometry and material condition.

It&#;s good practice to ensure that all bends on a particular part are equal in radius because this greatly simplifies tooling set up, reducing cost.

Bend Length - Another critical pressing variable is bend length. The bend length required will usually depend on the design specifications of a sheet metal part. Bending machines, however, all have maximum widths according to their physical size and configuration. It&#;s best to seek guidance if your parts are above 2 m as this is a standard sheet and press brake size.

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Bend to Bend Distance - When making bends, a physical limit on how close bends can be together is enforced by the size and shape of the tooling being used in the bending machine. Bends on the same side of a metal sheet that are too close will interfere with the tooling, and bends on opposing sides will often be impossible to reach because of the bottom tool.

Common instances of this occurring are where &#;U&#; sections are required with the legs or upright flanges being longer than the horizontal section. In some cases, extra deep tooling can be used.

If your bends do need to be close together, it may be possible to find workaround solutions. Alternatively, it may be possible to implement supplementary processes, such as welding or bolting to get to the correct geometry.

Hole to Edge Distance - When bends are produced, the material is stretched. This causes internal stresses that are evenly distributed across the part. If a hole or slot is made too close to a bend, these stresses will be focused on this hole, and this could cause deformation.

Springback - Metals have elasticity and will tend to return towards their original position to a small degree after bending. This effect is called &#;springback&#;. The exact process is related to metal&#;s compressive and tensile strength. After bending, sheet metal is compressed on the inside, where the press is applied, and stretched on the outside. Because the material has a higher compressive strength than tensile strength, it springs back towards its original shape.

In practice, springback generally only amounts to 1-2°. This can often be sufficiently compensated for in brake press control because many sheet metal parts don&#;t need a high level of accuracy. The latest CNC bending machines even incorporate built-in sensors and control to automatically compensate for material variability and other factors to ensure consistent performance.

Where a high level of accuracy is needed, springback can be a challenge because it can be difficult to accurately calculate how much there will be.

Several factors affect springback:

• Materials with higher tensile strength have more springback.
• A sharp bend radius usually has less springback.
• Wider die openings result in more springback.
• The larger the bend radius relative to the material thickness, the more the springback.

Fabricators often use the K-factor to calculate springback and better understand how to compensate and achieve tighter tolerances where accuracy is needed.

Processing Tolerances - As with any fabrication process, there are tolerances on dimensional accuracy. These often arise due to variations in sheet metal composition, thickness and processing. Variation should be considered when designing parts, and each process should be utilized to its strengths according to the material being used and part specifications.

CNC control has reduced variation in recent years, and most tolerances can be achieved with modern press brake machines. It can, however, still be a pertinent issue, particularly when designing complex or precision parts.

Here are some rules of thumb:

• You can&#;t typically achieve a true 90° corner.
• Corners will have a radius.
• Bend angles have a standard tolerance of ± 1°.
• Bend length tolerances are typically ±0.20 mm per bend (0.010&#;).

Consulting with an experienced sheet metal fabricator can help you better understand tolerances in sheet metal bending processes.

Tonnage - Factors such as bend radius, material properties, material type and bend length all contribute to how much pressure is required to make a particular bend. As mentioned, presses have a maximum tonnage capacity, and it may be worth checking that it will be possible to perform the bends you need. Check with your manufacturer before committing to a design you are unsure of.

Heat Affected Zones (HAZ) - Processes such as laser and plasma cutting create heat affected zones in metal. These can sometimes cause issues during bending, such as inconsistent bending near holes and edges. Another issue sometimes seen is cracking due to the increased surface hardness from cutting. If your parts will need other processes that create heat, these issues may need to be taken into consideration.

Sheet Bending Linear Bend Angle Standard High Precision Standard High Precision ±0.1mm ±0.05mm ±1˚ ±0.5˚

Table 5: CNC Sheet Metal Bending - Process Tolerances and Techniques

Feature Type Minimum Distance Guidelines*  Between a curl and an internal bend ±6 times the curl's radius + material thickness Between a curl and an external bend ±9 times the curl's radius + material thickness Between a hem and an external bend ±8 times the sheet thickness Between a hem and an internal bend ±5 times the sheet thickness Between a counterbore and a bend ±4 times the sheet thickness + bend radius Between a countersink and a bend ±3 times the sheet thickness Between hole and a bend ±2.5 times the material length + bend radius Between a slot and a bend ±4 times the sheet thickness + bend radius Between an extruded hole and a bend ±3 times the sheet thickness + bend radius Between semi-pierced hole and a bend ±3 times the sheet thickness + bend radius Between a notch and a bend in a perpendicular plane ±3 times the sheet thickness + bend radius Between a notch and a bend in a parallel plane ±8 times the sheet thickness + bend radius Between a dimple and a bend ±2 times the sheet thickness + inside radius of the dimple + bend radius Between rib to a bend perpendicular to the rib ±2 times sheet thickness + radius of the rib + bend radius

Table 6: Minimum Distance Guidelines for Features Relative to Bends

In Summary

Sheet metal bending has distinct advantages over alternative sheet metal fabrication processes, including higher output, lower cost and high flexibility in design. It also removes many difficulties associated with assembly techniques such as welding or riveting. With careful consideration during the design process, and with the aid of modern technology, sheet metal parts can be made stronger, lighter and more quickly through bending than through traditional fabrication methods.

The sheet metal specialist at Komaspec are happy to work to review your product design together and to help you select the fabrication process that best suits your product design and application needs.

Sheet metal fabrication is a crucial process in the manufacturing industry, with numerous applications in construction, automotive, aerospace, and other fields. The versatility of sheet metal and its ability to be formed into various shapes and sizes make it a popular choice for creating complex and intricate designs.

However, to ensure the success of any sheet metal fabrication project, it is essential to have a solid understanding of the design principles and best practices. In this article, we will provide a comprehensive guide to sheet metal fabrication design, including tips for material selection, geometric constraints, and cost-effective design strategies.

Whether you&#;re a seasoned engineer or a novice designer, this guide will help you create high-quality sheet metal parts that meet your project&#;s requirements and specifications.

Overview of Sheet Metal Fabrication

For manufacturing purposes, sheet metal is classified as anything thinner than 0.25 inches. All sheet metal parts come with the requirement of having consistent width, which limits some of its applications. But ensures that the resulting part is able to fulfill the requirements of durability and longevity.

Generally, sheet metal parts are common in applications like automobile chassis and other areas where the strength-to-weight ratio is important. Sheet metal has a lower thickness and parts made of it are generally hollow. This means that they&#;ll weigh less but will have the same capacity to sustain greater loads.

There is no point in opting for precision processes for simple applications. However, avoiding precision sheet metal fabrication for high-value applications is also not feasible. Because it may cause damage to sensitive equipment due to wear and tear.

The Working Principle

The working principle behind sheet metal fabrication is quite simple. It depends on the elasticity of the metal and the fact that cold-rolled metal performs better in terms of durability. Sheet metal fabrication consists of two methods, cutting and forming.

As its name suggests, cutting requires removing a part of the sheet to obtain the desired shape. On the other hand, forming is a bit difficult method consisting of three different processes. They mostly work together to create the form of the object you need. The process requires careful consideration of the design and manufacturability to minimize any waste and ensure perfection.      

In most cases, manufacturers rely on CAD files in either the DXF or DWG model to ensure compliance with the available design. In most projects, the cutting and forming processes work in tandem as it allows for quicker results. Moreover, sheet metal fabrication generally requires no post-processing but may need some finishing and joining depending on the application.

The 4 Main Sheet Metal Fabrication Techniques

The sheet metal fabrication process consists of two main processes; forming and cutting. These two techniques work together to create the final form of any product. While cutting is a simple process, forming has further classifications, namely stamping, bending, and punching.

Here are the basic details related to the main techniques for creating sheet metal parts:

1 &#; Cutting

The cutting process removes the excess sheet metal in a particular shape to obtain the final form. There are 3 main approaches when it comes to cutting sheet metal:

2 &#; Bending

The bending process simply applies a great force on the sheet metal at a specific point to obtain the required shape. In some cases, the area under the bend might need some preparation. For instance, bend notches not only show the technician the location of the bend but can also facilitate the process itself.

3 &#; Stamping

To create a complex part in a limited time, manufacturers often select the stamping process, which is a complex form of form. The process uses a combination of different techniques using shearing, bending, and stretching to create new shapes out of sheet metal. 

4 &#; Punching

To create a complex part in a limited time, manufacturers often select the stamping process, which is a complex form of form. The process uses a combination of different techniques using shearing, bending, and stretching to create new shapes out of sheet metal. Furthermore, some stamping processes even go as far as joining multiple pieces using different techniques as well. 

The Main Advantages and Limitations of Using Sheet Metal for Fabrication

Sheet metal parts designs are quite popular in many industries because of their perceived advantages. However, there are multiple limitations to the process as well. These advantages and limitations are among the most important design considerations for manufacturers as they determine the correct applications of the metal.

AdvantagesDisadvantagesQuick turnaround when compared to other manufacturing methods.Difficult to make complex designs with intricate details, which can limit the range of shapes and forms that can be produced.High-quality parts for both production and prototyping. Requires significant investment for tooling and other equipment, which can be a barrier to small-scale production. Versatile enough to work with several metals, such as steel, aluminum, and copper. Have longer lead times compared to other fabrication methods due to the multiple stages involved in the process, such as cutting, forming, and finishing.Delivers a high strength-to-weight ratio because of the hollow design. Requires skilled labor, which can be expensive Needs no post-processing in most cases.  

Guidelines for Sheet Metal Fabrication Design

As stated before, the design for sheet metal fabrication needs attention to some design requirements. Most of those requirements depend on the overall design of the product. For instance, a simple product would not have many requirements but an intricate geometry would naturally need more processes to be market-ready.

Generally, sheet metal fabrication requires a series of best practices that can ensure perfection and deliver the best quality in the shortest time. The general guidelines for sheet metals include the following 5 categories.

1 &#; Tolerances

Tolerance is one of the most important parameters for a variety of applications. The general rule of thumb states that more precision requires more resources and has additional costs. So, the tolerances should be according to the application.

The perfect example of this can be the automobile industry.

The precision required for the door or any other part of the body would obviously be lower than the requirement for the chassis or some other integral part. Generally, tolerance requirements depend on the project requirements but that approach can have a lot of inconsistencies in the product.

Many manufacturers and industries prefer set quality standards to avoid those inconsistencies. While these standards are not a one-size-fits-all solution, they are an excellent tool for maintaining consistency and performance. Furthermore, compliance with industry standards also makes it easier to fulfill industrial requirements and build consumers&#; trust in the brand.

For sheet metal fabrication, the prevalent standard is ISO . This covers the tolerance requirements for multiple industries while maintaining the perfect balance between costs and processing capabilities.

General Tolerances

For sheet metal fabrication, there are a few general tolerances that the industry uses everywhere. They are in compliance with international standards. However, there will be several exceptions to them in the case of sensitive applications like aerospace and automobile where precision is critical for performance.

General Tolerances of Sheet Metal FabricationFeaturePrevalent Tolerance RangeAdditional NotesWall thickness0.9mm to 20mm Offsets0.3mm to 0.7mm Curls>2x material thicknessAnything less than the recommended curl dimension would make the sheet brittle.Bends0.9mm &#; 1.2mm1.8mm &#; 2.4mm3.8mm &#; 5.0mm7.5mm &#; 10mm15mm &#; 20mmA +/- degree deviation is expected on all bends. Moreover, any other specifications will add to your costs.HemsInside dia = material thickness with return length to be 4x the thickness CountersinksMajor dia = +/- 0,254 mmMinor dia > 2/3 thickness Holes and slotsDia > material thicknessA diameter less than the material thickness would cause cracks in the sheet.Notches and tabsNotch width > 1.5x thickness
Length > 5x thickness 

Forming Basics

In this process, a flat sheet of metal is bent into a predetermined form by applying pressure. The process requirements and details change according to the type of bending process. While there are numerous ways, the following three methods of sheet metal bending are the most common.

• Brake pressing: Manual process uses a clamping bar and a plate to form the metal sheet. The process is only suitable for prototyping and small-scale productions.
• Roll bending: The same fundamentals, but the result would be in the form of cylinders, cones, or other arcs. 
• Press brake bending: The most advanced bending process that uses hydraulic machines with a punch and dies. This is suitable for metal sheets up to the thickness of 6mm and can easily produce precise features. 

Integral Parameters for Sheet Metal Bending

When it comes to the bending process, there are multiple parameters that manufacturers and designers must consider. These design requirements are what fundamentally characterize any sheet metal bend and it&#;s advisable to adhere to their standards to ensure excellent results.

Here are the 6 most important parameters for any sheet metal bending operation.

• Bend Line: The bend line is a straight line on the sheet&#;s surface that marks the beginning to the end on both sides of the bend. The industry standard for bend lines is to keep the distance of 5x the sheet thickness between the inside edge and outside of the bend.
• Bend Radius: The bend radius refers to the distance from the bend axis to the inner surface of a material between two bend lines. It is generally advisable to use a bend radius that is at least as large as the thickness of the material. A larger bend radius is even better, but using a smaller radius than the material thickness can reduce the load-bearing capacity of the part.
• Bend Angle: The angle created by the bend with the imaginary perpendicular line coming from the axis. Rather than a specific number, the industry practice for bend angles is to ensure that the flange length must be 4 times the thickness. It&#;s also good practice to keep all bend angles the same.  
• Neutral Axis: The neutral axis is the portion of a sheet that remains at its original length because it is neither stretched nor compressed. It is an independent parameter, and there is no legal limit or guideline for its location. However, the accuracy of other factors such as bend radius and angle play a crucial role in determining the performance of the final product. Therefore, the more precise these factors are, the better the product is likely to perform.
• The K-Factor: The K-factor of a material is a measure of its location, determined by dividing the distance between the material and its thickness (t) by its T. The K-factor is subject to a range of factors, including the material type, bending process, bend angle, and others. To ensure optimal results, the K-factor should fall within the range of 0.25 to 0.50. The K metric can be calculated by the formula K = T/t.
• Bend Allowance: To make accurate and consistent bent parts, it&#;s important to carefully measure and account for the arc length and the distance between the neutral axis and the bend lines. You should also use accurate bend allowances that are appropriate for the material and thickness to bend, as well as the type of bending process being used (e.g., air bending, bottom bending, or coining).

Cutting Basics

Another important process in sheet metal fabrication is cutting. In many cases, it&#;s an easier alternative that delivers fast results with acceptable precision. During the design phase, sheet metal design guidelines focus on the following 5 parameters.

Material Selection

During the process, the material characteristics play an important role in determining the suitable process for the specific material. Consider the example of Aluminum and Steel to understand this better. Naturally, cutting Aluminum would be simpler than dealing with steel because of steel&#;s relative strength and durability.

For material selection, the best practice is to consider manufacturability as well. For instance, if both steel and aluminum can sustain loads of a particular operation, it&#;s not always smarter to go for the stronger alternative (steel) without considering the manufacturing capabilities.   

Hole Diameter

When designing a product that involves drilling holes in a sheet, it is important to consider the thickness of the sheet and the diameter of the hole. A general rule of thumb is to ensure the diameter of the hole is at least equal to the overall thickness of the sheet.

If the diameter of the hole is too small in comparison to the thickness of the sheet, it can result in the formation of cracks and brittle areas around the hole. These cracks can propagate over time and lead to durability issues that can negatively impact the overall performance of the product.

Therefore, it is important to make sure the diameter of the hole is appropriate for the thickness of the sheet in order to maintain the structural integrity and long-term durability of the product.

Localized Hardening

When materials are cut, the process can generate significant amounts of heat, which can have an impact on their properties. Specifically, the region surrounding the cut may become overheated, leading to localized hardening. To prevent this problem, it is recommended to slow down the cutting speed overall and to use coolants to regulate the temperature in the affected area. By doing so, the risk of localized hardening can be minimized.

Distortion

Distortion in sheet metal fabrication refers to the warping, bending, twisting, or buckling of the metal sheet during the manufacturing process. This issue can occur due to a variety of factors, such as changes in temperature, stress, or pressure during the fabrication process. Distortion can cause significant problems in the final product, such as dimensional inaccuracies, poor fitment, and reduced strength.

Kerf

The kerf is directly related to the width of the cutting tool used and the thickness of the material being cut. Essentially, it represents the width of the material that is removed by the cutting tool, and it determines how much material is wasted in the cutting process.

For example, if a laser beam has a kerf of 0.1mm, and a cut is made through a sheet of metal that is 1mm thick, then the total width of material removed from the sheet will be 0.2mm (0.1mm from each side of the cut). The kerf width may vary depending on the type of cutting process, the type of material being cut, and the thickness of the material.

It&#;s important to consider the kerf when designing parts for sheet metal fabrication, as it can affect the final dimensions of the part. If precise dimensions are required, then the designer should take the kerf into account and adjust the design accordingly. Additionally, the kerf can also impact the cost of the fabrication process, as more material may be wasted with a wider kerf.

Common Features in Sheet Metal Parts

The sheet metal design deals with multiple features that allow these parts to fulfill the requirements of the industry. Here are the 6 main common features that sheet metal parts will often have.

ParametersDescriptionRecommendationsCorner FilletsCorner fillets are rounded edges or corners on sheet metal parts that are created to avoid sharp edges, which can be dangerous and can also cause stress concentration in the metal, leading to failure.&#; Size: The size of the fillet should be at least equal to the thickness of the sheet metal. In other words, a 2mm fillet should be used for sheet metal that is 2mm thick or less. 
&#; Symmetry: The fillets on a part should be symmetrical. This means that the fillets on opposing corners should be the same size.
&#; Uniformity: The fillets should be uniform in size throughout the part. This means that the fillets on all corners should be the same size. 
&#; Placement: Fillets should be placed in areas where stress concentrations are likely to occur. This includes areas where the sheet metal is bent or where there is a change in shape or direction. 
&#; Radius: The radius of the fillet should be as large as possible. This helps to distribute stress more evenly and reduces the likelihood of stress concentrations. 
&#; Design: The design of the part should be such that fillets can be easily added without compromising the integrity of the part.RibsRaised features that are typically perpendicular to the surface of the sheet metal part. They are used to add strength and stiffness to the part without adding much weight.&#; Keep the rib thickness to no more than 60% of the sheet metal thickness to avoid creating stress concentrations. 
&#; Use fillets to smooth the transition between the rib and the surrounding material, which will help to distribute stresses more evenly. 
&#; Avoid placing ribs too close together or too close to bends, as this can create weak spots in the material. 
&#; Consider using tapered or variable-height ribs to distribute stresses more evenly. EmbossmentRecessed features that are typically parallel to the surface of the sheet metal part. They are used to add depth or texture to the part, or to create a space for another component to fit into.&#; Keep the depth of the embossment to no more than 50% of the sheet metal thickness to avoid creating stress concentrations. 
&#; Use fillets to smooth the transition between the embossment and the surrounding material, which will help to distribute stresses more evenly.
&#; Avoid placing embossments too close together or too close to bends, as this can create weak spots in the material.
&#; Consider the impact of the embossment on the overall appearance of the part, and make sure it is aligned with any branding or design requirements. Round BossA raised circular feature in sheet metal fabrication that is used to add strength and rigidity to a part. It is typically created by punching or forming a circular depression in the sheet metal, which causes the metal around the perimeter of the depression to bulge out and form a raised circular feature.&#; Choose the right size and location: carefully consider the placement and size of the boss to ensure that it will provide the necessary support and strength without interfering with other components or creating manufacturing challenges. 
&#; Use the right tooling: Creating a round boss requires specialized tooling, such as a punch and die set or a forming tool. It&#;s important to use the right tooling for the job to ensure that the boss is formed correctly and that the sheet metal is not damaged in the process. 
&#; Consider material thickness: The thickness of the sheet metal will affect the size and shape of the round boss that can be formed. Thicker materials may require larger or deeper bosses to provide the necessary strength and rigidity. Dimple FeatureDimples are often used for a variety of reasons, including: To improve the stiffness and strength of a sheet metal part by adding reinforcement. To create a smooth and flush surface for fasteners or other components to be attached. To provide clearance for other parts or components. &#; Consider the size and location of the dimple carefully. Dimples should be placed in areas where they will provide the most benefit, and their size should be appropriate for the application.
&#; Overly large or deep dimples can weaken the material, while too small or shallow dimples may not provide sufficient reinforcement. 
&#; Choose the right tool for the job. There are a variety of tools that can be used to create dimples, including punches, dies, and form tools. The tool you choose will depend on the size and shape of the dimple, as well as the type of material being used. 
&#; Take into account the thickness and material of the sheet metal. Different types of sheet metal may require different techniques or tools for creating dimples, and thicker materials may require more force or a larger tool. 
&#; Be aware of any limitations or restrictions in the design. Dimples can be useful features, but they may not be appropriate for every application. Make sure that the design takes into account any potential issues or challenges that may arise from adding dimples. Louver FeatureThe primary purpose of louvers is to improve the airflow and ventilation in the enclosure or panel that they are installed on. Louvers can be designed to fit a specific purpose, such as directing air in a particular direction, reducing noise, or providing protection against dust, dirt, or moisture.&#; Size: The size of the louvers should be carefully chosen based on the required airflow and the amount of space available for installation. Louvers that are too small may not provide enough ventilation, while those that are too large may compromise the structural integrity of the panel. 
&#; Orientation: The orientation of the louvers should be chosen based on the direction of airflow and the location of any potential obstructions or obstacles that could affect the flow of air. 
&#; Shape: The shape of the louvers can have an impact on the efficiency of the ventilation system. Louvers that are designed with a streamlined, aerodynamic shape can improve airflow and reduce turbulence. 
&#; Material: The material used for the louvers should be selected based on the intended application, as well as the environmental conditions the panel will be exposed to. For example, stainless steel or aluminum may be better suited for outdoor applications where exposure to the elements is a concern. 
&#; Manufacturing method: The manufacturing method used to create the louvers should be selected based on the desired precision, consistency, and cost-effectiveness of the fabrication process. Round KnockoutRound knockouts can be used to create holes of various sizes, depending on the size of the punch and die used. They are commonly used in sheet metal fabrication for applications such as electrical boxes, HVAC systems, and enclosures.&#; Choose the right size: Make sure to use the correct size punch and die for the size of hole you need. Using the wrong size can result in a hole that is either too small or too large. 
&#; Use the right material: Round knockouts are typically designed to work with specific types of sheet metal, so make sure to use the appropriate knockout tool for the material you are working with. 
&#; Keep the punch and die sharp: Over time, the punch and die can become dull and start to deform, which can result in poor-quality holes. Keep them sharp and in good condition for best results. 
&#; Consider the thickness of the material: Round knockouts are best suited for thinner materials. If you need to create holes in thicker sheet metal, you may need to use a different tool or technique. 
&#; Be mindful of burrs: When using round knockouts, there is a risk of creating burrs around the edge of the hole. Make sure to remove any burrs with a deburring tool or sandpaper for a clean finish.

Material Thickness

The recommended thickness for sheet metal depends on the specific application and the material being used. Generally, thicker metals provide greater strength and durability, while thinner metals are more flexible and lightweight. Common thicknesses for sheet metal range from 0.5 mm to 6 mm, but can vary based on the material and intended use. Here is a chart showing the recommended material thickness for some common metals used in sheet metal fabrication.

MetalGaugeMillimetersInchesSteel/Stainless Steel/Aluminum220.80.031Steel/Stainless Steel/Aluminum201.00.039Steel/Stainless Steel/Aluminum181.20.047Steel/Stainless Steel/Aluminum161.60.063Steel/Stainless Steel/Aluminum142.00.079Steel/Stainless Steel/Aluminum122.50.098Steel/Stainless Steel/Aluminum103.20.126

Note: This chart provides general guidelines and the appropriate material thickness for a given application may depend on additional factors.

Common Sheet Metal Design Mistakes to Avoid

Sheet metal fabrication is a complex process that involves designing, cutting, bending, and assembling sheet metal into a final product. However, even the most skilled designers can make mistakes that can lead to costly rework or scrapped parts. To avoid these costly errors, it&#;s important to be aware of the most common design mistakes and take steps to avoid them.

Mistake 1: A CAD File with No Bends

One common mistake to avoid is providing a CAD file with no bends. A sheet metal part without bends cannot be fabricated as a single piece and may require additional parts and labor to join multiple pieces together. It is important to include bends in the design and specify the bend angles and radii to ensure the part can be manufactured correctly.     

Mistake 2: Features Too Close to a Bend

Another similar mistake includes accidentally placing features such as holes, tabs, etc. too close to a bend. What happens if you keep the features too close? You&#;ll end up with a deformed metal part that just wastes your money and time.  To avoid making this mistake, you can just implement the 4T rule in all your CAD designs. The 4T rule dictates that all features should be 4x material thickness away from any bend line at least.

Mistake 3: Perfectly Perpendicular Internal Bend Radius

It&#;s always tempting to use perpendicular lines in your CAD design. However, the reality is a bit different. Bending sheet metal mostly results in a rounded tip that gives your bend a radius. Attempting to achieve a perfectly sharp corner can result in material deformation and cracking, which can compromise the integrity of the final product. To avoid this issue, it is recommended to specify a minimum bend radius appropriate for the material and thickness being used. This will allow for a smooth transition in the bend and prevent stress concentrations that could lead to failure.

For your ease, you can easily find the bend radius of your metal parts by measuring the bent area&#;s length and dividing the answer by two. While you can easily use different radii for each bent part, it&#;s far more cost effective to use the same radius for all bends.           

Mistake 4: Not Including Hardware Details in CAD File

It&#;s always best to include as many details in your CAD file as possible, including specific hardware specifications, sizes, and locations. This will ensure a smoother fabrication process and a more accurate final product.                                   

Imagine needing a specific clinching nut such as the CLS-440-2 for assembling a model but this detail wasn&#;t included in the CAD file. There&#;s nothing else to do besides waiting for other individuals to arrange the required hardware. Obviously, this delay will increase the assembly time and cost.

Mistake 5: Choose an Unsuitable Finish

Finishing is usually the last and essential step of the manufacturing process. Most people mistake finishing for only having one function, which is to make your part look better.

In reality, the type of finishing you select can also play an important part in protecting metal components against rust or corrosion. While finishing that only focuses on the aesthetics of the metal part exists, other types of finishing are designed to increase the life span of your product through their protective characteristics.

Aesthetic finishing, such as powder coating, does offer some protection. However, several finishings such as Silk Screening are only useful to add text or images to the metal parts. Chemical Conversion Finishes have the opposite function.

These finishes alter the outermost layer of your product and work as a protective coating. Besides this, you also have the Chromate Conversion finishing that gives metal parts electrical connectivity. It also provides a primer layer for painting.

It&#;s important to understand what finishing you should use and what you should avoid. The right finish depends entirely on the application of the metal part that you&#;re designing.

Mistake 6: Select the Wrong Sheet of Metal

You have to consider the application of the part you&#;re designing from start to finish. For example, you can&#;t use unfinished steel in a marine and salty environment. Doing so will leave your metal parts vulnerable to rust and corrosion.

Instead, select the right sheet metal by focusing on the flowing factors. Questions like the following are extremely important.  

• What is the daily expected wear?
• Is your metal part being used in an environment prone to corrosion and rust?
• How easily can sheet metal be manufactured?
• How important is the cosmetic appearance of your metal part?
• Does your part require conductivity?
• What mechanical properties do your metal parts need to have?

Answering these questions will allow you to understand what your technical requirements are and let you make an informed design.

Mistake 7: Not Considering Material Strength for U Channels

U channels are an important part of any product design and their strength mostly depends on the overall strength of the material. Neglecting to take the material strength into account can result in U channels that are too weak, leading to bending or breaking under stress. To avoid this mistake, it&#;s essential to select the appropriate material and thickness for the U channel. Based on the expected load and to factor in any additional stresses, such as vibrations or impacts, that the channel may experience in use.

Mistake 8: Designing Unachievable Welding Requirements

No matter how simple a design is, there are high chances that it would require some welding or other mechanical joints. Some designers make the common mistake of overestimating the welding capabilities of the unit, which in turn increases the complexity and costs.

The best way forward to avoid such issues is to implement strict design for manufacturing (DFM) practices. This ensures that all features are according to the prevalent standards.

Types of Sheet Metals

The term sheet metal is used quite widely in the industry. However, the metal used is generally one of the following.

• Stainless Steel: This is perhaps the most common and famous option because of its versatility and durability. Stainless steel is the first choice for applications where a cost-effective, durable, and strong option is needed.
• Cold Rolled Steel: An excellent option for application where material strength is the primary concern for the designers.
• Pre-Plated Steel: Similar to regular steel, but comes with a special coating to prevent corrosion.  
• Aluminum: A lightweight and practically inert option that delivers an excellent strength-to-weight ratio.
• Copper: Copper is an expensive, yet effective material. It doesn&#;t react under normal conditions and delivers long-lasting performance without any chemical or biological degradation.
• Brass: An alloy of copper and Zinc that is both corrosion-resistant and hard enough to absorb multiple impacts.

Common Finishes for Sheet Metal Parts

While sheet metal generally works well without any processing, some applications take exception to this rule. The following processes are some of the most common post-processing steps for sheet metal products.

• Anodizing
• Brushing
• Polishing
• Bead Blasting
• Powder Coating
• Plating
• Passivation
• Chrome Coating
• Custom Finishes Upon Request

RapidDirect: Your One-Stop-Shop for All Sheet Metal Fabrication Projects

The sheet metal fabrication design guide is made to introduce all the basic concepts of the process to anyone. It&#;s important for manufacturing partners to fulfill the varying requirements of the industry and comply with the ever-changing industrial standards.

RapidDirect is an experienced manufacturing partner that can help take your design from concept to production. Whether you are a startup looking to bring a new product to market or an established company seeking to streamline your manufacturing processes, our team can provide the expertise and support you need.

At RapidDirect, we understand the importance of manufacturability and how it can impact the success of your product. Our team of experts is equipped with the latest tools and technologies to provide a comprehensive design for manufacturing (DFM) analysis. We will work closely with you to optimize your design for manufacturability, identifying potential issues early on to minimize the risk of production delays or quality issues.

In addition to our sheet metal fabrication capabilities, we also specialize in CNC machining, injection molding, and 3D printing. Our manufacturing facilities are equipped with the latest equipment and technology. We can meet the needs of a variety of industries, including aerospace, automotive, medical, and consumer products.

When you partner with RapidDirect, you can trust that your products will be delivered on time, on budget, and with the highest quality standards. Contact us today to learn more about how we can help bring your design to life and accelerate your time to market.

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