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About the author : Richard Webster

Are you designing cost into your sheet metal fabrications?

Metal fabrication is a process that has been around for thousands of years and isn’t likely to disappear soon. The demand for metal fabrications will always be there, regardless of other types of materials and their applications.

Carbon fibre is lightweight and strong, and plastics are easier to use for complex shapes (as long as a large quantity is required). But there are countless occasions where metals are needed.

However, the world is a more competitive place than ever, and there’s a continuous drive towards cost reduction in every industry. As a result, the whole manufacturing industry is used to finding more efficient and productive ways to make their products, and it’s no surprise that it’s where the term “continuous improvement” originated.

Using lean manufacturing tools or six sigma approaches to quality, manufacturers are experts in making their processes more efficient in order to provide a lower-cost product or service.

But if the original design isn’t optimised for manufacture, companies may be building unnecessary costs into their fabrications. So, here are a few thoughts to consider to help your fabricator provide the lowest cost part without compromising quality.

Material Sizes

All sheet metal fabrications begin life as a flat sheet of material. To create the finished fabrication, those flat sheets are then manipulated by a series of processes, including cutting, bending, welding, and finishing.

Materials comprise a significant part of the overall cost of the part. Therefore, utilising as much of the material sheets as possible is critical to keeping the associated costs as low as possible.

For mild and stainless steels, there are three standard sheet sizes available:

  • 3000mm x 1500mm
  • 2500mm x 1250mm
  • 2000 mm x 1000mm

From the design drawings of the parts, the first job for the fabricator is to “unfold” them to understand their flat dimensions. Historically, this was done manually by sketching out the flat-form part or scribing it onto a sheet of material. Nowadays, it’s all done through CAD/CAM software specifically designed for sheet metal fabrications.

Using another piece of software, the part will be nested onto a sheet of material so the total number of parts per sheet can be calculated. Depending on the order quantity, the fabricator will decide which material sheet size is the most appropriate.

With small fabrications, it’s a relatively simple case of nesting on the different sizes of sheets until finding the optimum size. However, with larger fabrications, the flat-form dimensions are critical.

For example, if the developed (unfolded) part measured 2400 x 1300, the fabricator would have to use a full 3000×1500 sheet but not utilise an efficient percentage of the material. Tweaking the design to bring the width less than 1250 means they can use a high percentage of a 2500×1250 sheet.

Bear in mind that this can be complicated further if using polished stainless steel material. The grain direction will affect the part’s orientation on the sheet, which can have a knock-on effect on the utilisation.

Material Gauges

The gauge (thickness) of material also has a tremendous effect on the part price. Steel is priced per kg, and a seemingly small difference in gauge can have a significant impact.

For example, a 2000x1000x1.5mm thick mild steel sheet weighs 23.55kg. However, the same size sheet, 2mm thick, is 31.40kg. So, even though it’s only 0.5mm thicker, it’s 30% heavier and therefore more expensive.

Designers should carefully consider the gauge of material used and reduce it while still maintaining the required mechanical properties of the finished fabrication.

Welding

Outside of an automotive-style, high-speed, robotic production facility, the welding of sheet metal fabrications is a manual process. It takes time and skill to create the perfect welded joint and additional time in dressing or polishing the weld afterwards. As such, anything that reduces welding time should be considered.

One of the simplest ways to reduce or remove welding is to bend the material instead. For example, a bent edge takes seconds on a CNC press brake but would take hours of welding. However, caution should be exercised as an overly complex bend sequence on a small batch of parts could add the saved welding time onto setting up the press brake. Like all things, there’s a balance to be had.

Finishing

Painting or powder coating finished parts is another process in the production sequence that carries a setup and processing time. Usually, a secondary process like painting or plating is needed to protect mild steel parts from corrosion. But it may be worth considering using stainless steel, depending on the size and quantity of parts required. Although stainless steel is more expensive than mild steel, it doesn’t need any surface protection applied afterwards and could prove to be a cheaper option when you consider the total cost of the parts.

Summary

When designing for sheet metal fabrication, there are many factors to combine when aiming for cost-efficiency. At Pegasus Precision, our engineers have decades of combined experience to share with your designers.

Before putting pen to paper (or mouse to screen) on your design, talk to us about your requirements. Then, we’ll help you create the most cost-effective parts without compromising on quality.