How to Get Your Product Made, Part II – Fabrication Processes

In a previous post I discussed where to start when you have an idea for a product but have no idea how to get it made. This was only a high-level overview and there are many, many details and ‘gotchas’ which can make or break the success of your product. In this post I will get into some more detail of the specific processes you can choose and how they affect various attributes of your product. We’ll start with the most common and work our way into the world of the exotic (and expensive).

Machining

This is the most straightforward option to get something made quickly and accurately. Machining is any process in which a cutting tool is spinning relative to your part, slowly removing material from a solid block. The process is well understood and widely available so it’s not hard to find someone to make your parts.

Machining can also create your parts in a very wide range of materials. Metals are the most common, but plastics and foams can also be machined with relative ease. And if we loosen the definition to include grinding, it’s also possible to machine parts from brittle materials like glass and ceramic.

Of course, there are some design limitations. In order to make your part, the spinning tool needs to be able to reach the material you want to remove so features like internal cavities are not possible with standard milling. Some undercuts can be made with the use of clever tooling like T-cutters, but if the tool can’t reach the material, it can’t cut it.

3D Printing (Additive Manufacturing)

Yes, 3D printing has come a long way from its humble beginnings around a decade ago. Now typically branded as ‘additive manufacturing’, at its core this technology is the opposite of machining. Instead of removing material from a solid monolith, here we are depositing small amounts of a given material one layer at a time to build your part from the bottom up. Years ago this could only be done using plastics with low melting temperatures but the technology has advanced rapidly and it is now possible to print parts in a range of materials, including metal alloys, with properties approaching those of solid billet. Like almost everyone else, I believe that in the near future we will be able to print production-level parts directly and will rely much less on casting, molding, and machining for high-volume manufacturing.

3D printing is not just an alternative to machining, it has its own advantages. The most useful is that with printing you can create internal cavities and negative spaces which can’t be done in a bulk removal process like machining. This ability greatly expands the envelope of possible designs and allows for some real innovation. One example is that hollow parts can be fabricated in a single piece whereas with machining or molding (casting), the same design might need to be fabricated as two pieces and then fastened together. Removing fasteners makes your part cheaper and lighter and may actually be a net gain in strength.

The list of drawbacks to additive manufacturing is shrinking all the time, but there are still a few important tradeoffs to know about. For one, additive processes are still dimensionally less accurate than other methods. This may not matter if your part has loose(ish) tolerances, but if you need features in the sub-1mm range then 3D printing is going to have a hard time meeting your needs.

The second drawback is material strength. Because of how the material is processed, printed parts tend to have voids and non-homogenous material interfaces which can act as sites for fracture initiation, giving them overall less yield strength than cast billets of the same material. However, this is changing all the time as the technology improves and the current capabilities may be sufficient for your application. My friends in the AM world will be sending me counterarguments if they read this so just know that if yield strength is critical to you parts, make sure you know what you’re getting if you choose a 3D printing process.

Sheet Cutting

This category could include all of the processes that can cut flat sheets of material such as laser cutting, water jet, plasma cutting, flat stamping, numerically-controlled turrets, routers, etc. For simplicity sake I will keep it to laser and water-jet cutting which are the most common for simple parts on common materials.

These two processes can cut almost any non-brittle material and even some brittle ones. They are limited to flat parts of a constant thickness but once the parts are cut, they can be bent, welded, seamed, or joined with fasteners. If your project can be composed of flat shapes then this is the way to go.

Casting

Injection Molding