What is 3D Printing? Its Features, Classifications, and Differences from Machining

2024-09-02

3D printing is a novel manufacturing technology capable of creating various shapes, and it has seen increasing applications in recent years. However, it has its drawbacks and may not be suitable for every manufacturing scenario. When is 3D printing most effective, and when is traditional machining a better choice? Below is an overview of the characteristics of 3D printing and its differences from machining.

What is 3D Printing?

Fused Deposition Modeling (FDM): This method extrudes thermoplastic material from a nozzle and deposits it layer by layer. It is available in a wide range of products, from affordable models for personal use to more advanced systems for commercial applications. The primary materials used are resins, although metal-based materials are also available for certain products. For example, some thermoplastic products can be printed using the same materials used in actual injection molding.
Stereolithography (SLA): In this method, ultraviolet light is projected onto a liquid resin to harden it, forming layers of material. UV projectors or lasers are typically used for this process, which is primarily limited to resin materials. The materials used in this process are specialized and require specific handling.
Selective Laser Sintering (SLS): This method involves using a laser or similar device to heat and sinter thin layers of powdered material. A new layer of powder is spread over the previous one, and the process is repeated to build the object. The materials used are usually a mixture of base materials and additives, where the additive facilitates the binding of the material upon heating. Like SLA, this method also requires specialized materials.

Classification Based on Material

Resin Materials
Metal Materials

3D printers can process both resin and metal materials, but the specific materials that can be used vary depending on the machine. Therefore, different equipment must be selected based on the intended application.

3D printing often gives the impression that it can easily produce any shape, but achieving high-quality results requires experience and a proper approach. Not everything can be produced as desired, and post-processing is sometimes necessary to remove support structures or other elements used to stabilize the model. Many companies offer specialized services for this purpose, and these should be considered for optimal results.

Differences Between 3D Printing and Machining

The most significant difference between 3D printing and machining lies in their manufacturing methods, but there are also several other key distinctions:

Manufacturing Method:
- 3D Printing: Builds up material to achieve the desired shape through additive manufacturing.
- Machining: Removes unwanted material from a block or other raw form to shape the desired part.
Shape Capabilities:
- 3D Printing: Can create hollow structures, overhangs, and curved internal channels. However, it is less suitable for producing thick, solid parts due to the large amount of material required.
- Machining: Cannot easily create hollow structures or curved internal channels. Overhangs and lateral holes require multiple clamping steps during machining, reducing design flexibility. However, machining is ideal for creating thick-walled features.
Data Requirements:
- 3D Printing: Requires not only 3D design data but also specific 3D printing data. Depending on the shape, support structures may also need to be designed, requiring specialized software. Data in formats such as STL, STEP, or IGS may be needed, and creating this data can be time-consuming.
- Machining: Can work from 2D drawings, with NC (Numerical Control) "automated machining" becoming increasingly common. CAM (Computer-Aided Manufacturing) applications are widely used to automatically generate NC programs. Data in formats like DXF for 2D or STEP and IGS for 3D can be easily converted into NC programs, facilitating machining.
Material Options:
- 3D Printing: Typically requires specialized materials, which can be more expensive and offer limited choices compared to conventional materials.
- Machining: Can process a wide range of materials, including metals and plastics.

Scenarios Where 3D Printing is More Suitable than Machining

Each manufacturing method has its advantages and disadvantages. Here are some examples where 3D printing is more suitable than machining:

• Design Concept Validation: During the product planning phase, 3D printing can be effectively used to verify the appearance of a product. It provides a tangible model that is easier to evaluate than a specification sheet, drawing, or illustration.

• Hollow Structures and Curved Internal Channels: If you need to create a hollow structure to reduce weight or want to design a complex internal curved channel, 3D printing is ideal. Machining would require drilling from both directions to create a straight hole with a radius, whereas 3D printing can easily produce intricate curves and channels.

• Prototype Production: Especially for plastic products, prototype molds are typically required for machining. However, 3D printing allows for low-cost prototyping without the need for molds. Another approach is to print molds for injection molding or stamping rather than the prototypes themselves.

• Architectural Models: 3D printing excels at producing complex curved surfaces and hollow shapes, making it suitable for architectural models. Hollow shapes are difficult to achieve with machining, which would require multiple parts to be manufactured and assembled. Abroad, there is a growing trend of using 3D printing to construct entire buildings, though challenges remain with material costs and the precision of assembled parts.

• Low-Volume, High-Mix Production: The flexibility of 3D printing lies in its ability to produce without molds, making it ideal for low-volume, high-mix production, such as prosthetics, reproductions of discontinued products, and jigs used in production lines. It can also cater to customized products like automotive parts. Moreover, once the data is available, identical parts can be produced on demand, minimizing the risk of unsold or excess inventory.

Effective Use of 3D Printing and Machining

The biggest challenge with 3D printing is its lower precision. Post-processing is essential to ensure parts fit with other components, making it unsuitable for precise features like threads. Additionally, 3D printing is slower and more expensive to operate, including material costs, making it less suitable for mass production. Therefore, except for specialized cases of low-volume, high-mix production, 3D printing is generally used for prototypes or molds during the early stages of development. While industries like automotive and aerospace have started using 3D-printed parts directly in final products, the technology is not yet ready to replace traditional manufacturing methods completely.

For best results, 3D printing should be reserved for specific applications like prototyping, while precision and mass production should continue to rely on machining. Moreover, when it is necessary to evaluate parts under the same conditions as mass-produced items, 3D printers may not use the same materials as those used in production. In such cases, machining remains the preferred choice.

Basic Knowledge, Applications, and Characteristics of CNC (Computer Numerical Control)

What is "General Tolerance"? How Does It Differ from Other Tolerances?