The devil is in the details

At least when it comes to planning development of mechanical products. Many mechanical products can seem simple and straightforward at first glance. But the fact is that there is usually a lot of work behind the simplest solutions. For best results, it is important to work out the manufacturing method, material choice, design, etc., and preferably as early as possible in the project.

In my experience, spending a lot of time on development at the beginning of a project has proven to pay off later. In this blog post, I thought I'd suggest how you can best prepare for your upcoming development project and thus avoid any mistakes that may arise along the course of the project. Because all of us who work with product development know that it is rarely complication-free.

The design and the importance of size

The first step in developing a mechanical component (¹) should be to prepare a rough outline of the design. As early as this stage, you have to start thinking about things that can affect the design. There may be requirements for the product regarding material, environmental impact, weight, appearance or, for example, series size. These requirements can affect the manufacturing method and may even exclude certain methods right from the start.

The series size can have a major impact on the manufacturing method used. For products that are to be manufactured in small runs or even as single components, tool-bound methods are not usually suitable. This is based on the fact that tools for casting or injection molding, for example, can cost a lot, and the manufacture of just a few components entails a high cost per item. So, when manufacturing only a few components, you usually try to use machining processes such as milling or turning, 3D printing perhaps and other tool-free fabrication methods that have now become commonplace. However, there may also be times when machining processes are used in the production of larger series due to precision requirements or other factors. You can also combine manufacturing methods by first, for example, casting a component to produce a rough geometry that is then machined to meet requirements such as for flatness, roundness, parallelism and so forth.
The devil is in the details

Once you have readied a concept, you can start with detailed fabrication. This is done in CAD programs where you first draw the product in 3D. You can prepare incredibly detailed and complex drawings of components in the programs, but they may not always be possible to manufacture. This is why you have to keep practical matters in mind when preparing your drawings. An example is that a hole cannot be as deep as might be shown on your drawing because there are no infinitely long drill bits for drilling the hole. The component must also installable – you must be able to access all screws and other fastening elements with the tools to be used, for example.
It pays to be liberal

Once a 3D model is finished, you proceed with 2D drawings of the component, even though you could continue with only the 3D model. These 2D drawings contain information about the material, surface treatment, weight, volume, standards to be followed during manufacture and other necessary information. Most often you specify a standard, such as "ISO 2768-mK". This standard has tables that set out different tolerances (2) depending on the dimensions specified in the drawing or 3D model. As an example, a length measurement that is nominally 40 mm long can vary +/- 0.15 mm and still be within tolerance according to ISO 2768-mK. When defining tolerances for a component, it is important to keep in mind that the stricter the requirements, the more expensive the component. It is important to set as liberal tolerances as possible, but that are still good enough for the component to work as intended.
From start to finish

The last step in the chain is to get the product made. One or more prototypes are usually developed to ensure that the product works and meets the requirements placed on it. For larger series, you usually move on to a 0-series where you manufacture a small number of components with a final manufacturing method. When manufacturing a 0-series, you get a very good picture of how the final product will be, while at the same time, you get the opportunity to adjust machinery and tools to achieve the desired results.

These are some of the things that I usually keep in mind when starting a new development project. Do you have any pieces of good advice? Sharing is caring!

// Parham Barati, mechanical engineering consultant, Prevas AB

1) What in some disciplines is called "a part" is often called a component in mechanical engineering. A product usually consists of a number of components.

2) A tolerance is a range of deviation from the nominal value. A dimension that deviates from the nominal value but is still within the given tolerance values is an approved dimension.