5 essential factors to consider when designing for optimal sheet metal manufacture
Unless you’ve been socially distancing in an underground bunker since the 1970s, you’ll have heard of the term Design for Manufacture (DFM). It sounds like a fairly grand phrase but is really a very simple concept. It’s about streamlining the design of parts so they can be made as cost-effectively as possible.
Wherever you wander around the engineering world, you’ll find DFM in every discipline. Some companies have adapted it to DFSS, which sounds like a government department but actually stands for Design for Six Sigma. However, the principles are always the same. Reduce cost by considering the manufacturing method at the design stage.
DFM doesn’t only remove cost from the manufacturing process. It reduces the design time by a considerable margin. Statistics show that significant amounts of design time are spent on amending drawings for parts which are difficult to manufacture. If you’re a design engineer, you’ll have probably had calls from manufacturing companies asking for concessions to ease manufacture. Amending the drawing, reissuing and making sure the correct revision is being used all takes time.
There are three general principles of DFM that apply across all sectors:
- Minimise quantities of parts – Basically, don’t make a component in five parts when you could do it in three. The more pieces you have in production, the more chance there is of compound errors creeping into the finished assembly. More parts are harder to control and require more significant production planning time. And that’s the main point; more parts means more time which means more cost.
- Design for known manufacturing processes – Understanding the standard tooling used is vital for optimal designs. New tooling is expensive, and manufacturers have to pass those tooling costs on to the customer. Designing around existing capabilities can have a massive impact on the total cost of a part.
- Consider the final assembly – Whether your final assembly has tens, hundreds, or thousands of components, you should consider how they’re all going to fit together at the end. If parts can only fit together one way, there is no chance of them being incorrectly assembled. Building in Poka-Yoke techniques, such as using tabs and slots for location, speeds up the final assembly and reduces the chance of errors.
These three principles alone will reduce your overall cost of manufacture and increase the quality of your parts. However, suppose you really want to get the most out of your sheet metal fabrications. In that case, you should also consider some specifics.
When manufacturing out of sheet metal, we’re always starting with a flat sheet. We either punch or laser cut parts out of that sheet, then bend, weld, and finish. Understanding the particular quirks of each of these processes will supercharge your designs.
Here are our top five factors to consider when designing for sheet metal manufacture:
Hole sizes – One of the most common issues is holes that are too small for us to punch. As a general rule of thumb, the diameter of the hole must be no less than the gauge of material. For example, the smallest hole you can punch in 3mm thick steel is 3mm diameter. For small holes, punching is definitely the better option than laser cutting as it creates an accurate, round hole. Also, give some thought to any secondary operations. For example, if the hole needs threading, then laser cutting may not be the right application. Laser cutting can leave an oxide layer on the internal bore of the cut hole which is very difficult to tap.
Hole Location – If you need holes close together, punching may be a better choice than laser cutting. When you have holes closer together than two material thicknesses, the heat from the laser can distort them. Another factor to consider with hole location is how close it is to a bend. Whether it’s laser cut or punched, if a hole is too close to a bend, it will distort. Our usual recommendation is to keep holes a minimum of 1.5 sheet thicknesses away from a bend.
Sheet Squareness – Although we use the highest quality materials for all our fabrications, the raw material sheets we buy aren’t always perfectly square. This is never a problem as we usually cut parts out of the sheet. However, with large fabrications, it may be tempting to use the outside edges of the bought-in sheets for the edges of your parts. Resist that temptation! Always aim to cut material out of the sheet.
Bent Edges (Flanges) – When we bend a flange, there is a minimum width of edge that we can produce. It’s impossible to bend very short flanges using standard tooling. Imagine a four-sided tray. The minimum flange height of the four sides depends on the type of material and gauge required and the bending tooling we use. When you’re designing a very short bent edge, it’s best to ask us what minimum length we can produce. As a rule of thumb, the minimum bend height should be twice the material thickness plus the bend radius.
Bend Relief – If you need a tight bend near the edge of the material, it’s best to use a bend relief to avoid the material tearing or cracking when being bent. A bend relief is, basically, a small notch at either end of the bend.
As you can see from these points, sheet metal fabrication is a complex topic with many more factors to consider when creating your designs.
At Pegasus Precision, our clients value our input into their design process. If you’d like to save costs and improve the quality of your fabricated components, contact us now on 01233 801649.