Subtractive vs. additive manufacturing
The two manufacturing methods in comparison
In the industrial environment there are largely two fundamentally different manufacturing options: additive and subtractive manufacturing. In this article we give you an overview of the differences between the two methods. We also go into their process, function, typical applications as well as advantages and disadvantages.
How subtractive manufacturing works
Subtractive manufacturing is considered to be the classic or conventional method for manufacturing components. The starting point is usually cuboid or round blocks made of metal or plastic, from which a molded body is produced through the controlled removal of material. This is done through machining processes such as turning, milling, grinding or drilling, which are carried out either by hand or by a numerical control (Computer Numerical Control, CNC).
For the CNC processing, CAD data of a 3D model designed on the computer are first required. This data has to be converted into a code that the machine can read. It specifies in which order and with which tools the material must be processed. After the data has been processed, the system can be set up. This means that the material blank is inserted and clamped. In addition, necessary cutting tools, such as milling cutters and drills, must be provided and the manufacturing data must be played onto the system.
Since subtractive manufacturing involves machining the component from a solid material, a lot of unused material is usually left behind. Most of this can be reused in the field of metal cutting. In plastics machining, however, the share that has to be disposed of is much higher. Here it depends on what kind of plastic it is and whether it is recyclable or not.
How additive manufacturing works
The starting point in additive manufacturing is similar to that in CNC machining. Here, too, 3D data form the basis, which must also be prepared for production. With 3D printing, this is done using a so-called "slicer", which automatically divides the component into individual levels. Each level represents a 2D model or the contour of the component at a specified height. With these individual models, a 3D printer can now build up the component layer by layer and connect them to one another. The sum of all solidified individual layers then results in the final component. To start production after slicing, a push of a button is usually sufficient, as no major set-up processes have to be carried out.
The printing process itself can vary greatly depending on the technology. With powder-based processes such as With selective laser sintering , the finest plastic powder is fused with a laser beam. In the case of the HP Multi Jet Fusion process, this is done using an infrared heat source. In the classic FDM process , on the other hand, a strand of material is melted and applied to a plate in the desired shape. You can find out more about our 3D printing technologies on our website.
Unlike the subtractive approach, additive manufacturing largely uses only the material that is also required for the part itself. The only exceptions here are so-called support structures in FDM and overstressed material in powder bed-based processes. Overall, this means that less input material is required and less waste is generated in the process, which can lead to a beneficial environmental balance.
Hybrid approaches
Even if the two processes differ fundamentally, additive and subtractive manufacturing do not have to be mutually exclusive. There are enough use cases where both methods are used and complement each other perfectly. For example, metal 3D printing components are very often subjected to machining reworking in order to obtain the known accuracies or surface qualities of conventional processes.
Often, 3D printing also plays a major role in the development of a component. Since a 3D printer usually gets by without long set-up times and does not require any molds or the like, a new component can be created within a very short time. Many engineers take advantage of this because they can go through the development time of optimization and iteration cycles much faster than with conventional manufacturing methods. After the final component shape has been found, the market response can be tested with a 3D printing small series and the associated low risk. But it is also possible to switch to conventional manufacturing methods.
Comparison of additive vs. subtractive manufacturing
Depending on the component volume and geometry, a component can take a few minutes to several days to manufacture. Accordingly, it is important to know the advantages and disadvantages of different types of manufacturing, and how they affect the price, quality and properties. More information about the pricing of 3DBAVARIA can be found in our article "How are 3D printed parts calculated". We have summarized an overview of the main differences for you below:
Subtractive
Additive
Basic principle
The starting material is removed piece by piece in order to obtain the desired component.
Basic principle
Individual layers of material are put together to form the desired component. Depending on the technology, the starting material is either plastic powder or a plastic strand.
Equipment
In CNC machining, computers are used to create a 3D model. The machining is also prepared by this and can be supported by robots, for example.
Equipment
Computers are used to create a 3D model and prepare it for printing. The production takes place with 3D printing systems.
Advantages and disadvantages
Advantages and disadvantages
- All solid materials regardless of their melting point can be processed.
- Much more isotropic material properties.
- A wide variety of surfaces can be realized, from rough to smooth.
- Complex geometries can be easily produced and therefore allow great design freedom.
- Due to the very little effort between the 3D model and the start of printing, highly individualized products can be created without higher preparation costs.
- Overall very cheap process, especially for small quantities.
- Hardly any unused material.
- Little waste.
- Very quickly, especially with prototypes, as no set-up process or time-consuming programming of various tools is necessary. However, the manufacture of large components is time-consuming.
- The different manufacturing processes allow less design freedom.
- Generally much more expensive than additive manufacturing because more manual work is involved.
- Waste products such as chips and coolant occur in large quantities.
- The preparation time - especially for individual, small components - slows down production. The actual manufacture can be viewed as very quick.
- Only materials with a low melting point, such as plastics, can currently be processed cost-effectively. Metal 3D printing is possible, but more costly.
- The layered structure usually results in a rough surface, which can only be refined by post-processing steps.
- Depending on the technology, the final component can have anisotropic material properties.
Applications
- Components to which tight tolerances or component geometries must be adhered to.
- Metal components that have to withstand high loads.
- Large components with comparatively simple geometries.
Applications
- Unbeatable thanks to its speed in rapid prototyping.
- Small series which do not justify the use of injection molding or which cannot be reproduced cost-effectively due to the component geometry using subtractive manufacturing.
- Complex geometries with, for example, undercuts, lines, etc.
Conclusion
Both types of production have influenced and even revolutionized the manufacture of products in their own way. In summary, it must be noted that for each product / component it should be carefully assessed which method is the most suitable. In order to discuss the most economical approach, it is advisable to include all influences such as quantities, requirements and costs. Particularly with components with complex geometry, it should also be noted that the subtractive manufacturing processes reach their limits much more quickly.