More and more industrial companies are attracted by the advantages of additive manufacturing and are integrating it into their production cycle. However, it is still a complementary tool to conventional production methods. So what are the differences between additive manufacturing and subtractive manufacturing? Is there one process more interesting than another? What are the advantages and limits presented by each technique?
The main subtractive manufacturing methods
These methods represent all the manufacturing processes that rely on transforming a block of solid material into the desired shape. The material is progressively removed or deformed, bit by bit, to model the final part. Among these processes we find several techniques, such as:
- Injection moulding (or plastic injection)
- Assembly (welding, gluing)
Today, the majority of industrial companies use CNC machining. This is a process in which a computer-controlled machine removes the necessary material to obtain the desired part. This technique makes it possible to achieve great precision, but it is fairly limited in terms of geometric complexity. CNC machining is used mainly to fabricate functional prototypes and engine parts. This method is quite important for the aeronautics and automobile sectors.
Injection moulding is used to produce fine parts in large production runs. In fact, the start-up costs are particularly high.
Additive manufacturing, a more viable method?
Just like subtractive manufacturing, 3D printing includes different processes known in the form of technologies:
- Fused deposition modelling
- Powder sintering
- Powder binding
Each technology has its own advantages and limits (precision, speed, materials available, printing quality, etc.)
3D printing is increasingly used in production cycles. However, most frequently it represents a complementary tool to conventional methods. We often see industrial companies that combine machining and additive manufacturing, so reducing their costs by increasing efficiency. It may be wondered if the two really are opposing methods. A few criteria are essential to decide.
Shape of the parts desired
When complex parts are manufactured, additive manufacturing will offer greater freedom. It is possible to model easily without needing to produce a complicated and costly mould. So if you are looking for geometric complexity, 3D printing will be a better response than conventional manufacturing processes. However, there remains the matter of knowing the size of your part. 3D printers don’t all have a large printing volume. But remember you can print in several stages! Assembly is often the best solution.
Additive manufacturing is also a better option for customising parts. 3D modelling will enable you to create custom parts. What’s more, you can replicate parts as many times as you like.
Quantity of parts expected
Even if additive manufacturing reduces production lead times, it is not suitable for large production runs. It is still too slow to produce hundreds of parts at a time, limited by the size of the 3D printer’s printing platform. For this reason, subtractive manufacturing techniques will be better suited to large production runs.
This criterion implies another: the manufacturing lead times available to you. With subtractive manufacturing processes, you generally have to create moulds and install fairly heavy production machines. This is a constraint that takes a lot of time and will considerably extend your manufacturing cycle. Conversely, a 3D printer can be installed quite quickly, depending on the technology chosen. In addition, it will be able to manufacture the first part in a few hours (depending on its size and complexity), without special tooling.
A wide range of materials is compatible with both manufacturing methods, particularly plastics and metals. However, this choice is more limited in additive manufacturing. In fact, depending on the 3D printer owned, you will be restricted to using this or that material. In addition, an FDM printer will reduce you to using plastics, while an SLA machine is only compatible with a UV-sensitive resin.
Finally, it would appear that additive manufacturing is better suited to creating geometrically complex parts or those requiring customisation. However, subtractive methods are used more to produce parts with fairly basic shapes in large production runs. We are beginning to see hybrid machines on the manufacturing market, meaning that in certain situations there is no need to make precisely this choice. However, we are only at the early stages of these developments, with industrial companies preferring to invest in two different and complementary machines.