Five Factors to Consider When Designing Metal Parts

From the cars we drive and the foil we put over our leftovers to the planes we fly and the roofs over our heads, metal is everywhere. Since metal is hailed for its strong and sturdy qualities, it is a leading material used for countless projects all over the world. Today, with improved technology through computer-aided design, it's easier than ever to create your own sheet metal design and watch it come to life through fabrication. However, if you want to save time and money, you must consider a few critical things while designing for your formation process go as smoothly as possible.

What Is Sheet Metal Design?

Sheet metal design is the process of making your sheet metal ideas a reality by forming parts from the sheet metal through processes like punching, cutting, stamping or bending. The design process starts with an idea and maybe even a rough sketch, which can be transformed and upgraded using computer-aided design (CAD). These 3D CAD files are then converted into machine code which controls the machine to start the custom metal fabrication process. During fabrication, the machine will cut and form the metal sheets into your desired end product with ease and accuracy. Since sheet metal is known for its durability, the design process brings you one step closer to creating a strong backbone for your metal project.

The fabrication process starts once your design is complete, using different methods and machinery to create your design based on the results you need. The first step is typically cutting the metal into whatever shape or size is desired, often using laser cutters or shears. After the metal is cut, it can be bent into shape and then drilled, threaded and tapped with holes and any inserts through machining. Then the pieces are connected using welding techniques. Finally, after your project has been double-checked to meet all specifications, it receives a rust-resistant protective powder coat as the finishing touch.

However, before you get into the fabrication process at all, you must keep some specifics in mind. These include the overall function of your design, the method you plan to use for attachments, and both mechanical and manufacturing properties. It's vital to consider manufacturing capabilities while designing to avoid errors during the shop fabrication process. Manufacturers spend an estimated 30 to 50% of their time correcting errors, while 24% of those errors are directly correlated with manufacturability. Errors are usually the result of the gap between how sheet metal is designed in CAD systems and how they are actually fabricated in a shop and can prove to be costly. To avoid these errors, keep the manufacturer in mind by remembering some key metal design fundamentals to aid you in your design process.

Design Fundamentals for Your Custom Metal Project

Engineers who keep the manufacturer in mind could save time and money by taking a more realistic approach rather than an idealistic one. Such an approach could involve adopting a Design for Manufacturability (DFM) strategy, which considers different factors in manufacturing while bringing designs to life. A Design for Manufacturability strategy reduces errors and engineering change orders, decreases part counts and simplifies the design overall, which in turn can save you valuable time and money. This strategy eliminates the gap between CAD systems and fabrication and provides you with sheet metal part design considerations that make your project easier to manufacture. Some manufacturing things you may keep in mind include:

  1. Choosing the right metal

  2. Hole size and placement

  3. How to use hems

  4. Accounting for bend edge distortion

  5. Minimum flange length

1. Choosing the Right Metal

Before getting into some more formation specifics, you should establish your desired metal and thickness for your project by exploring different options. Considering thickness when designing your project is essential as it can affect some aspects of the custom fabrication process, such as bending or cutting. Designs must also maintain a uniform thickness throughout since parts are made from one sheet of metal. Some commonly used metals for projects include steel, stainless steel and aluminum. By learning more about each metal and their different properties, you can determine which would be the best fit for your custom metal project.

Steel

Mainly composed of iron and carbon, steel is the most popular engineering material used today. Many look to steel as the standard, likely due to its high strength. Steel can also reduce weight and tends to offer a lower thickness, which could help make your custom metal project feel less bulky. As far as pricing goes, steel is considered the most cost-effective material used in the industry, so it can help you with better affordability.

Stainless Steel

Stainless steel is used everywhere from kitchens and medical environments to buildings and transportation. As a widely-used steel subcategory, stainless steel is a good option for resisting corrosion. Since stainless steel is an alloy with chromium or nickel added to steel, it is also a hard, durable option. However, compared to other standard construction steels, stainless steel tends to be more expensive.

Aluminum

Aluminum offers a low density but also has less strength compared to steel. For example, for aluminum to be as durable as steel, it would have to increase its thickness by about one and a half times more than its steel counterpart. Therefore, aluminum has the potential to be made stronger and can maintain its low weight by increasing its thickness.

2. Hole Size and Placement

During the design process, CAD software can aid in determining size and placement for holes in your metal project. However, you must consider how they will be manufactured in the fabrication process. Messing up a hole's size or placing it too close to an edge or a bend could severely impact your project's durability, appearance, performance and function. Therefore, you need to get hole size and placement down on the first try to protect your project and avoid wasting money and time.

Hole Size

When creating a hole, it's crucial that the minimum diameter of the hole is equal to the material's thickness or 1.00 millimeter — whichever is larger. Having a hole diameter smaller than the sheet's thickness could result in higher punch loading, longer burnish in the holes and excessive burr, a defect in your sheet metal. Holes with small diameters can also cause slug-pulling when the punch is withdrawn, ultimately impacting the life of the punch and the sheet metal. Therefore, it's always better to have a hole with a diameter greater than the sheet's thickness rather than being too small.

Hole Placement

When it comes to hole placement, a good general guideline to follow is ensuring spacing between holes is at least two times the sheet's thickness, if not more. If you create holes that are extremely close together, they're more likely to weaken the space between them and ultimately become one bigger, deformed hole. Maintaining this minimum distance ensures the metal stays strong and the holes keep their original shape during any bending or forming processes.

Similarly, a hole could become deformed if placed near a bend or an edge. If a hole is near a bend, it runs the risk of alteration and additional time and money. To prevent this, make sure the distance between holes and a bend is, at minimum, two times the material's thickness plus the bend radius. If holes must be placed close to a bend, they should be created following the bending process with a secondary drilling operation. When it comes to holes near edges, the results can be equally as damaging and even weaken your metal. To figure out how far to place a hole from an edge, you must look at the size and shape of the hole as well as the material's thickness, as they are directly proportional. Typically, the distance between a hole and an edge should be equal to about one and a half times the material thickness.

3. How to Use Hems

When it comes to sheet metal manufacturing, hemming is a term to describe metal folding back on itself. Hems can create folds in the sheet metal to transform sharp, raw edges and make them smooth and safe to touch. They can also stiffen the sheet metal and create a thicker appearance without adding much weight to the material. Hems are single, 180-degree bends that could be an open "U" shape, a closed hem, or a teardrop hem.

Many avoid using closed hems as they usually fracture at the bend and may cause solutions to be trapped inside during the finishing process. For open hems, the minimum diameter should be equal to the material's thickness and have a return flange height equal to or greater than four times the material thickness. If the inside diameter of an open hem is larger than the material's thickness, the hem can lose its U shape. Teardrop hems should have a minimum diameter equal to the material's thickness and a return flange height that is more than or equal to four times the material thickness. These hems should also have an opening of at least one-fourth of the material's thickness.

When looking at the minimum distance from a hem to a hole, it should equal two times the material thickness plus the hem's radius. The minimum distance between a hem and an internal bend should equal five times the material's thickness, while the distance from an external bend should be eight times the material's thickness.

Hems can help make sharp edges safer, hide imperfections and re-enforce the metal, but they come at a cost. Typically, hems are created during manufacturing using multiple bending strokes or machine cycles, which add expenses and time to your project. Hems sometimes even require different specific tooling setups that could add to costs. If you're thinking about using hems for your metal project, you must weigh your options and determine if it's significantly beneficial. You could also get in contact with the shop carrying out your fabrication process to find out what hem tooling they already have and how it could add to your project.

4. Accounting for Bend Edge Distortion

To form the sheet metal and transform its shape, it must undergo a bending process. It is crucial to design with the metal bending process in mind so you can avoid any torn or misshapen metal. As a general rule, bends on the same plane should be going toward the same direction as to prevent reorientation and save you time and money. The bend radius should also be consistent for parts to stay affordable. Typically, the smaller the radius, the better, but the minimum radius inside of a bend should equal the material's thickness. To take appropriate precautions against tearing or deformation during the bending process, you must also understand bend relief.

Bend relief creates a space between bent and unbent surfaces to make the edge of the sheet metal perpendicular to the bend by creating an incision down the sides of a planned bend. With the space created using bend relief, it creates a gap between the bend and the material around it. This allows the sheet metal to be easily and cleanly shaped in the press brake come fabrication time. Bend reliefs are not necessary for every design. However, they are vital when it comes to any material you want to protect on either side of a bend that would otherwise tear.

As a general rule, bend relief length should exceed the radius of the bend, and the width of the bend relief should at least equal the material's thickness. The bigger the bend relief, the easier it typically is to line it up over tooling in the formation process, reducing costs and minimizing set-up time. This process also helps eliminate all cracking and tearing and can be shaped according to your design.

5. Minimum Flange Length

During the bending process, metal can be formed into flanges, which can help speed up and simplify your design's fabrication process. The shop's press brake machine can limit the size of the flange to be bent. To determine the minimum length of a bent flange, you must look at the material's thickness, bend radius and length of the bend as they're all related. Typically, though, flange width can never be less than four times the thickness of the sheet metal. If those requirements aren't met, it could leave a mark on the material's surface during manufacturing.

Contact APX York Sheet Metal for Custom Design and Fabrication Services

From the early stages design to completing custom fabrication, designing metal parts can be a long and complicated process. With our specialized software and tools to support the design and manufacturing processes, APX York Sheet Metal can create accurate metal fabrication designs that are both efficient and functional. With more than 70 years of experience in the industry, we welcome both the broadest and the most intricate metal fabrication design jobs for various industries across Pennsylvania and Northern Maryland. Contact us today for a free quote or call us at 717-767-2704 to get started.