Introduction
In the current manufacturing, complicated designs are turned into tangible objects by the use of various materials and various processes. Of these, the two most common techniques are additive manufacturing and subtractive manufacturing. Of course, you may not use these two terms in your everyday conversation, but I am sure you know the processes related to these terms, 3D printing, laser cutting, plasma cutting and CNC all fall under one of these two terms.
While both methods are designed to produce the final product, the working mechanism is quite the opposite. This article will compare and contrast additive manufacturing and subtractive manufacturing in terms of their differences, uses in industries, and how to decide between the two.
What is Additive Manufacturing
AM or 3D printing is a process of creating objects in layers by depositing material on the object’s surface. This method usually starts with a digital model, which can be made using a computer aided design or CAD. The CAD model is then divided into many thin layers in the form of cross-sectional layers. The additive manufacturing machine then takes these digital blueprints, and lays down successive layers of material or solidifies them in a layer by layer fashion according to the cross-sectional layers of the object to be produced, and builds up the final object with intricate geometries.
Additive manufacturing encompasses a variety of technologies, such as:
- Fused Deposition Modeling (FDM)
- Stereolithography (SLA)
- Selective Laser Sintering (SLS)
- Direct Metal Laser Sintering (DMLS),
- Binder Jetting (BJ)
- Directed Energy Deposition (DED)
- Sheet Lamination (SL)
- Laminated Object Manufacturing (LOM)
- Selective Deposition Lamination (SDL)
- Digital Light Processing (DLP)
- Continuous Liquid Interface Production (CLIP)
All of these techniques use different methods of depositing material and solidifying it but the concept of adding layer by layer is the same. Additive manufacturing has the capability to produce intricate structures directly from the design without the use of tools and molds, which has created new opportunities in design and production, particularly for small parts.
What is Subtractive Manufacturing
Subtractive manufacturing (SM) is a conventional manufacturing process whereby material is progressively removed from a solid block of material or workpiece to achieve the required shape. This is normally done through various processes of machining. Subtractive manufacturing is also generally based on a digital model, which is converted into instructions for computer-controlled machines such as CNC mills and lathes. These machines employ the use of cutting tools to cut out material from the workpiece until the final product is produced.
Common subtractive manufacturing techniques include:
- Milling
- Turning
- Drilling
- Grinding
- Cutting
- Electrical Discharge Machining (EDM)
- Waterjet Cutting
- Laser Cutting
- Plasma Cutting
It is a well-established and widely used method for producing parts with high accuracy and good smooth finish across a broad range of materials.
Key Differences: Additive Vs Subtractive Manufacturing
Although both processes start with raw materials or digital blueprints and aim to produce completed parts, additive and subtractive manufacturing differ greatly in their manufacturing methods and features. Knowing these differences is important to choose the right approach for a particular application.
| Characteristic/Aspect | Additive Manufacturing | Subtractive Manufacturing |
| Material Waste | Lower | Higher |
| Material Selection | Relatively Limited | Broader/Wider(e.g., Aluminum, Steel) |
| Design Complexity | Well-suited for complex geometries and internal features | Complex internal features may be limited |
| Production Volume | Suitable for low to medium volumes, prototypes | Suitable for medium to high volumes |
| Manufacturing Speed | Fast for complex part prototypes, slower for volume production | Fast for volume production of simple parts |
| Accuracy and Tolerance | Generally Lower | Generally Higher |
| Surface Finish | Usually requires post-processing | Better initial surface finish |
| Cost | Potentially more economical for low volumes and complex parts | Potentially more economical for high volume production |
Material waste
Subtractive manufacturing begins with a large piece of material and the process of cutting and removing material to get the desired shape of the product, means that a large amount of material is wasted in the form of chips, shavings or cut-offs. Although some of this waste can be recycled, it still means that in many cases, raw materials are used in a less efficient manner.
On the other hand, additive manufacturing is relatively less wasteful of material in the manufacturing process. Since material is added only where required, the amount of wastage of material is also less in this method. This often creates the impression that it is a more environmentally friendly process and while this may be true, it is necessary to look at the details of each process to determine if it is the best for the application.
Material selection
Subtractive manufacturing typically offers a broader range of material options compared to additive manufacturing. Almost any material that can be machined, including various metals (steel, aluminum, stainless steel, copper, brass, etc) , plastics, wood, composites, and ceramics, can be processed using traditional subtractive manufacturing methods, including laser beam cutting techniques.
Although additive manufacturing is steadily broadening its material applicability, it is still quite limited in terms of the wide range of materials that can be used efficiently. The choice of materials for specific additive manufacturing processes may be limited and some of them may need special equipment or conditions for processing. However, additive manufacturing is particularly useful in making parts with different materials in a single build, which may not be feasible using the conventional methods of material removal.
Product Design Complexity
Additive manufacturing excels when it comes to the creation of complex and intricate shapes that cannot be created by the traditional methods of material removal. Complex geometries like internal lattices, complex curves and fine details can be easily manufactured through additive processes without the need for special tools or multiple setups.
Subtractive manufacturing is a very accurate method of manufacturing parts but it has the drawback of reach of cutting tools and fixturing. Internal features or undercuts that are intricate may need several tooling and setting up, which makes the process longer and expensive.
Production volume
Subtractive manufacturing, is typically more productive and economical for mass production of components with simple shapes in various machine shops. After the tooling and setup are done, the time taken to produce each part is less than that of additive manufacturing.
Additive manufacturing is most suitable for low volume production, prototyping and production of parts that are unique where the cost of setting up for the subtractive manufacturing would be very expensive. Still, the improvements in the technology of additive manufacturing are steadily making it possible for the medium volume production as well.
Manufacturing Speed
The rate at which additive and subtractive techniques can be produced can be greatly influenced by the complexity of the part and the number of pieces to be produced. In the case of prototypes and small series of intricate parts, additive manufacturing can be faster because it does not require tooling and complex setups.
However, for large quantities of relatively uncomplicated components, the well-developed and efficient processes of the subtractive manufacturing can provide much shorter total production time.
Build time in additive manufacturing depends on the size and complexity of the part since each layer has to be deposited and solidified. In subtractive manufacturing, the machining time is a function of the amount of material that has to be cut and the type of operations to be performed.
Accuracy and tolerance
Subtractive manufacturing especially precision machining processes are capable of delivering high levels of accuracy and small tolerances. CNC machines can move and cut with high accuracy and this makes it possible to produce parts with tolerances of a few micrometers.
Additive manufacturing, while improving in accuracy, generally has wider tolerances compared to subtractive methods. The precision of the parts produced by additive manufacturing depends on the type of material used, the type of technology used in the manufacturing process and the settings of the machine.
In cases where the dimensions of the product need to be very accurate and the tolerances very small, then the subtractive manufacturing is the most suitable.
Surface finish
Subtractive manufacturing processes, such as machining and grinding, can produce very smooth and high-quality surfaces. These cutting tools can generate surfaces with low roughness, which means that a subsequent finishing operation may not be required.
AM parts are normally built in layers and therefore the surface finish of the parts is not as smooth as that of the parts made through the subtractive manufacturing process. Although, techniques like sanding, polishing, and coating can be applied to enhance the surface finish of the additively manufactured parts, these extra processes add to the time and cost of production.
In some cases, where the surface finish is an important factor, then it is more appropriate to use the subtractive manufacturing.
Additive vs Subtractive Manufacturing: Industry Applications
Both additive and subtractive manufacturing have found widespread applications across various industries, each leveraging the unique strengths of the respective processes.
Applications of Additive Manufacturing
Additive manufacturing has revolutionized several industries with its ability to create complex and customized parts. Key industry applications include:
Aerospace
Aerospace applications such as fabrication of lightweight structures for aircrafts and space shuttles, prototyping and tooling. AM’s capability to produce intricate structures with minimal material is vital in cutting down the weight and enhancing the fuel economy in aerospace applications. It also enables fast cycling in the design and testing stages of the development process.
Medical
Creation of implants, prosthetics, dental restorations, or even surgical guides tailored for each individual patient. With AM, the level of customization reaches astonishing levels which yield well-fitting, and thus, more efficient medical devices for the patients. The technology also allows for the development of complex internally structured and porous tissues that enhance the growth of beneficial materials.
Automotive
Rapid prototyping, tooling, manufacturing of special products and elements, spare parts. AM enables rapid prototyping and the generation of intricate designs without the need for costly molds and dies. It also makes it possible to manufacture small quantities of specialized components and spare parts when needed, thus minimizing inventory expenses.
Architecture
Production of detailed architectural models and prototypes. AM can help architects to produce more accurate and detailed physical models of their designs, which will help them to explain their ideas and visualize the structures that they are going to build.
Applications of Subtractive Manufacturing
Subtractive manufacturing is still widely used in many industries because it allows for high accuracy, good surface finish, and low cost for large production. Key industry applications include:
Automotive
Subtractive manufacturing is widely used in the automotive industry for creating a vast number of essential parts. This includes engine parts such as cylinder heads and engine blocks, chassis and suspension parts that need to be very accurate and strong. Subtractive manufacturing is ideal for mass production since it is efficient in providing high quantities of products that are uniform in quality and performance to suit the automotive industry’s needs for millions of vehicles.
Aerospace
Subtractive manufacturing is widely used in aerospace industry to produce intricate and high-strength structural parts for aircrafts and space vehicles. Components such as aluminum, titanium, and other specific alloys are cut and shaped to the necessary specifications for weight and strength. These methods help to achieve the required accuracy of the details and the quality of the material, which is crucial for the safety of aerospace vehicles used in severe conditions.
Electronics
Subtractive manufacturing is also widely used in the manufacturing of electronic devices especially in the fabrication of casings and enclosures of different gadgets and equipment. Machining and milling are employed to cut and form metals and plastics to fit the contours of the case and protect the internal parts and enhance the appearance. Also, in the formation of heat sinks and other parts with certain thermal and electrical characteristics, the subtractive processes are used.
Medical
Subtractive manufacturing is widely used in the medical field for the production of various medical devices and instruments that require high accuracy and often use biocompatible materials. This ranges from surgical instruments, orthopedic implants, and parts of diagnostic equipment. Delicate features, as well as smooth surface finishes, are essential for the safety and efficiency of medical devices that are used to aid patients, and these are obtained through machining and grinding.
How to Choose Between Additive and Subtractive Manufacturing?
The choice between additive and subtractive manufacturing depends on several factors that are peculiar to the application and manufacturing needs. The following are some of the factors that should be taken into consideration when making the decision:
Type of Material
The type of material that you select may sometimes be a deciding factor. If you are dealing with such materials as certain steels, metals or aluminum alloys, then the subtractive manufacturing processes are more effective.
However, if the design allows for the use of materials that are easier to process or perform better through AM such as thermoplastics, then AM has a clear advantage in both the manufacturing process and the final application.
Production Volume
In the case of low production volume, especially when it comes to intricate or small-batch parts, AM can be more economical because of the low tooling costs and the capacity to create complex shapes without requiring additional tools.
However, as the volumes of production go up, the per-part cost of subtractive manufacturing becomes more favorable especially for complex geometries. Subtractive methods are generally preferred in high volume production because once the tooling is set up, the process is faster.
Sustainability
Other factors that can be taken into consideration include sustainability factors. One of the benefits of additive manufacturing is that it can help to minimize material wastage in some cases. However, the energy consumption and the recyclability of the materials used in AM should also be taken into account.
Subtractive manufacturing creates scrap, but in most of the cases, this scrap (particularly metals) can be reused. It is possible that a life cycle assessment may be needed to decide which option is more sustainable for a certain application.
Accuracy and Tolerances
If the application demands high precision and small tolerances, then subtractive manufacturing especially precision machining is the most appropriate method.
Although the accuracy of the additive manufacturing is increasing, it is still not as precise as the subtractive manufacturing for critical tolerance applications.
Strength and Durability Requirements
The mechanical properties of the parts made by the additive and subtractive manufacturing are different in terms of strength and durability depending on the material and the process used.
Subtractive manufacturing particularly when dealing with wrought metals produces parts with high strength and durability due to the continuous grain flow of the material.
AM parts may have anisotropic properties or lower overall strength based on the technology and material used in the process and may be weaker than the parts produced through subtractive manufacturing.
However, for load-bearing or high-stress applications, it is safer to use traditional materials through the subtractive manufacturing process.
Part Design
Part design intricacy greatly matters. In comparison to subtractive methods, additive manufacturing is capable of producing complex geometries, internal lattices, and intricate curves that subtractive methods are sometimes impossible or exceedingly difficult to create.
However, if the design is not very complex and can be made by cutting out material from a block, then it is more beneficial to use subtractive manufacturing.
Lead Time
Because tooling is not required for most additive manufacturing processes, rapid prototypes and short production runs can often be completed in a fraction of the time. While this is true, for high volume fabrication, the subtractive manufacturing process coupled with high process efficiency tends to yield better lead times after the initial setup is complete.
Cost
Finally, cost is a very important factor that cannot be overlooked. The costs of the material, equipment, labor, and post-processing should be compared between the additive and subtractive manufacturing processes. The cost-effective method of manufacturing will depend on the application, the number of parts to be produced, and the complexity of the part.
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Conclusion
Additive and subtractive manufacturing are two different but important methods of manufacturing in the contemporary world. All of them have their advantages and disadvantages, and they are used in various fields depending on the specific task. The decision between them depends on the assessment of the needs of the project in question.
It is clear that both additive and subtractive manufacturing technologies will remain relevant in the future as manufacturing technologies progress. It is therefore important to understand the differences between them and the factors that determine their choice in order to make the right choices and improve the manufacturing process of any project.
FAQS
Q: Is additive manufacturing more environmentally friendly than subtractive manufacturing?
A: Additive manufacturing typically reduces material waste, but it has a higher energy consumption. On the other hand, subtractive manufacturing may produce more waste but utilizes traditional manufacturing processes.
Q: Which manufacturing method is more suitable for rapid prototyping?
A: Additive manufacturing is generally more suitable for rapid prototyping because it allows for flexible design iterations and quick production of prototypes. Also, it allows for the development of intricate geometries shapes that cannot be produced using conventional techniques of production.
Q: Can subtractive manufacturing handle hard materials?
A: Yes, subtractive manufacturing is particularly suitable for processing hard materials, such as titanium alloys, hardened steel and stainless steel, which are less likely to damage the cutting tools during machining.
