CNC machining and 3D printing are common processing methods in industrial manufacturing. The two processing methods are different and have their own characteristics, which can bring great help to industrial production. Therefore, before choosing a manufacturing method, something must be carefully considered, including the size of the production, the development history of the product, the working time, and the overall budget.
What is subtractive manufacturing?
Subtractive manufacturing refers to the reduction of materials to achieve the purpose of processing in the process of CNC processing and production. The most common method of subtractive manufacturing is computer numerical control processing (CNC processing and manufacturing). The history of subtractive manufacturing dates back to the 1940s. Engineer John T. Parsons developed the first numerically controlled machine in order to achieve a production design with high complexity, high repeatability, and high precision.
In the process of subtractive manufacturing, metal, plastic, wood and other raw materials are gradually removed through cutting, drilling, grinding etc. to complete the processing and manufacturing. Although these processes can be completed by manual processing, processing and measurement by humans will inevitably lead to errors. In addition, the time cost and labor cost required for production are relatively high, so in industrial manufacturing, CNC machining is often relied on for production. Other common subtractive manufacturing methods include laser cutting, water jet cutting, electrical discharge machining, and plasma cutting, which are mostly used in planar processing.
In CNC machining, the production process is numerically controlled by a computer, including designing products with CAD software, and controlling CNC machining machines with CAM software to produce geometric shapes.
CNC machining has been developed for more than 80 years. With the change of technology, CNC machining is applicable to a wide range of fields. In the process of machining, raw materials must be reduced to complete product production. In the past ten years, processing methods have been innovated, and many new processing and manufacturing methods have been developed in industrial manufacturing, but subtractive manufacturing is still the most common and widely used processing method.
What is Additive Manufacturing?
Additive manufacturing refers to the process of adding materials—usually layer by layer—to complete the fabrication process. Additive manufacturing was first invented in 1981 by Hideo Kotama of Nagoya City Industrial Research Institute, and began to develop in the 1980s. With more than 40 years of development, the technology has gradually become mature and reliable, and has gradually expanded its scope of use to various fields, including machinery and medical-related manufacturing.
Additive manufacturing includes 3D printing, layered manufacturing, and direct numerical production. The most common additive manufacturing method is 3D printing. The 3D printer first melts the raw materials and deposits them layer by layer until the finished product is completed. The raw materials used in additive manufacturing are still dominated by plastic polymers, but there will also be opportunities for a large number of metal processing in the future.
The production process of additive manufacturing is similar to that of subtractive manufacturing. To perform 3D printing, the first step is to design the product on CAD software, and then export/download the STL file related to the product for subsequent 3D printing. The third step is to select the material. Common 3D printing materials are ABS, PLA, PETG, nylon, TPU, PVA, HIPS, or other plastic polymers. Then, after setting the function and transferring the G code, you can start 3D printing.
Usage of subtractive manufacturing
There are various types of materials suitable for subtractive manufacturing, including metals, plastics and their composites, wood, leather, etc. Subtractive manufacturing can handle almost any shape, including planes, holes, cylinders, threads, grooves, etc., and can be produced with a tolerance less than 0.025mm, with high precision, and achieve a smooth finished product surface.
Since subtractive manufacturing is processing by reducing raw materials, material waste is bound to occur during the processing process. Even if it can be recycled, these materials still cannot be of practical value. Compared to additive manufacturing, subtractive manufacturing takes more time to produce parts.
Even with industrial-grade machines, additive manufacturing such as 3D printing technology cannot avoid uneven product strength and quality at this stage. In contrast, the quality of CNC-processed products is relatively stable and can withstand stricter engineering requirements. Therefore, most highly sophisticated industries, such as the aerospace industry, still use CNC machining technology for manufacturing.
Uses of Additive Manufacturing
The market estimates that in 2026, the additive manufacturing market will expand to 14.4%, and the total market value is expected to reach 2 trillion US dollars. More and more companies are investing money to accelerate the development of the additive manufacturing industry.
Common materials used in additive manufacturing are plastic materials, such as PLA, ABS, PETG, nylon, TPE, and PC. They can also be made of carbon fiber, metal, ceramics and other materials, but the cost is higher than that of plastic materials ( For the introduction of some materials, please refer to Chapter 3). The part of the tolerance is usually below ±0.2mm or ±0.1mm.
Since additive manufacturing is produced by the superposition of materials, it can effectively reduce the amount of waste compared with subtractive manufacturing. However, since it is made by superposition, after injection, polishing procedures are required to ensure the finished products are smooth.
In general, the entire production process will also be faster than subtractive manufacturing. Production is highly automated and requires less manpower.
Subtractive manufacturing is suitable for the production of plastic processing for weight reduction, or hollow objects, as well as small quantities and highly specialized products, such as small engines or parts.
Comparison of features and usages
The maturity of additive manufacturing has made the manufacture of small parts more productive. In addition to coping with more complex geometries, it can even achieve some production that cannot be handled by injection molding.
Although additive manufacturing is already a mature technology, and a lot of money has been invested in research and development in the past few decades, there are still practical limitations at this stage.
For example, the types of materials suitable for additive manufacturing are more limited than subtractive manufacturing. Engineers should take these constraints into account in the design to ensure the quality of the finished product. In terms of strength, thermal resistance, and smoothness, additive manufacturing cannot achieve the product quality of subtractive manufacturing.
In addition, if metal processing is to be done with additive manufacturing, the cost is much higher than with subtractive manufacturing. It is generally believed that the status of subtractive manufacturing will not be replaced. The traditional subtractive manufacturing can handle more mature processing types and suitable materials.
Although additive manufacturing can now handle metal processing, subtractive manufacturing can retain more material properties and the finished product is stronger than additive manufacturing.
Both are now used in sample manufacturing, usually larger samples are preferably produced by subtractive manufacturing; small parts can be produced by additive manufacturing.
Conclusion
Although subtractive and additive manufacturing overlap in many uses, there are differences in the timing and scope of their use. Subtractive manufacturing is better at handling metal processing, and the error value of the finished product is small; additive manufacturing can effectively reduce the loss of materials and is suitable for the production of light-weight plastic processing.
At present, subtractive manufacturing still has a large scale, and handles a variety of production modes. Although additive manufacturing is not a mature industry, it still attracts considerable investment and attention, so there are bound to be more breakthrough results in the future.
Read More: What is CNC machining? ── CNC machining 101
Reference:
https://www.fastradius.com/resources/additive-subtractive-manufacturing/
https://blog.spatial.com/additive-vs-subtractive-manufacturing
https://marketbusinessnews.com/financial-glossary/subtractive-manufacturing/
https://xometry.eu/en/subtractive-manufacturing-vs-additive-manufacturing/
https://www.bcn3d.com/the-beginners-guide-to-3d-printing-6-steps/
