If you’ve ever wondered why some manufacturing projects use CNC machines while others opt for 3D printers, the answer often lies in the materials. These two dominant manufacturing technologies—one subtractive, one additive—handle materials in fundamentally different ways, and those differences shape everything from part strength to production costs. In this guide, we’ll break down exactly how CNC machining and 3D printing differ when it comes to materials, helping you decide which technology is right for your next project.
The Fundamental Material Philosophy: Additive vs Subtractive
Before diving into specific materials, it’s crucial to understand the core difference in how these technologies approach material usage.
3D printing is an additive process. This means it builds parts layer by layer, adding material only where it’s needed. Think of it like building a sandcastle with a squeeze bottle—you deposit material precisely according to your design. This approach minimizes waste and allows for complex geometries that would be impossible with other methods.
CNC machining, on the other hand, is subtractive. It starts with a solid block (or billet) of material and removes excess to create the desired shape. Imagine carving a statue from a block of marble—that’s essentially how CNC works. This method relies on the material’s original properties remaining intact throughout the process.
This basic distinction explains many of the material differences we’ll explore, from waste production to available options and final part properties.
Material Selection: What Each Technology Can Work With
One of the most significant differences between CNC machining and 3D printing lies in their material compatibility. Let’s take a closer look at what each technology can handle.
CNC Machining Materials: Virtually Unlimited Options
CNC machining truly shines when it comes to material versatility. Because it works by removing material from a solid block, it can handle almost any engineering material you can name. Here’s a breakdown of the most common categories:
- Metals: Aluminum, stainless steel, titanium, brass, copper, magnesium, and even exotic alloys like Inconel and Hastelloy. CNC machines can easily handle both soft and hardened metals.
- Plastics: ABS, nylon, polycarbonate (PC), PEEK, acetal (Delrin), PVC, Teflon, and many more engineering plastics.
- Wood and composites: Various hardwoods, plywood, and composite materials like carbon fiber-reinforced polymers.
- Specialty materials: Glass, stone, foam, and even some ceramics can be CNC machined with the right tools.
The key advantage here is that CNC isn’t limited by how materials need to be deposited or cured—if it comes in a solid block form, it can likely be machined. This makes CNC the go-to choice when specific material properties are non-negotiable.
3D Printing Materials: Growing but Still Limited
3D printing materials have expanded dramatically in recent years, but they’re still more limited than CNC options. Availability depends heavily on the specific 3D printing technology being used. Here are the main categories:
- Plastics and polymers: The most common 3D printing materials. PLA, ABS, PETG, nylon, TPU (flexible), and specialty filaments like carbon fiber-reinforced plastics.
- Resins: Photopolymer resins cured by UV light, available in various formulations for different properties (flexible, rigid, high-temperature).
- Metals: Titanium, stainless steel, aluminum, and precious metals like gold and silver can be 3D printed using processes like SLM (Selective Laser Melting) or binder jetting, though these require industrial-grade printers.
- Specialty materials: Ceramics, concrete, food materials, and even biological materials for medical applications, though these are niche applications.
3D printing materials must be formulated to work with specific printing processes—whether that means being extrudable through a nozzle, sinterable by a laser, or curable by light. This formulation requirement limits the available options compared to CNC machining.
| Material Type | CNC Machining Compatibility | 3D Printing Compatibility |
| Metals | All common and exotic metals | Limited to specific metals (titanium, steel, aluminum) with industrial printers |
| Plastics | All engineering plastics | Specific filaments and resins formulated for 3D printing |
| Wood | Yes | Limited (specialty wood filaments with mixed results) |
| Composites | Yes, including carbon fiber | Limited to fiber-reinforced filaments |
| Ceramics | Limited (with special tools) | Limited to specialty ceramic printers |
| Glass | Yes (with special tools) | Very limited niche applications |
Material Properties: How Processing Affects Final Part Characteristics
It’s not just about what materials each technology can use—it’s about how the processing changes those materials’ properties. This has major implications for part performance.
Strength and Structural Integrity
CNC machined parts retain the full strength of the original material. Because you’re simply removing material from a solid block, the material’s internal structure remains unaltered. A CNC-machined aluminum part has the same tensile strength, hardness, and fatigue resistance as the original aluminum billet.
3D printed parts often have reduced or anisotropic (direction-dependent) strength. This is because they’re built layer by layer, creating potential weak points between layers. For example:
- FFF (Fused Filament Fabrication) printed ABS parts may only have 10-20% of the strength of solid ABS
- SLS (Selective Laser Sintering) nylon parts can reach close to 100% of solid nylon strength, but still exhibit some anisotropy
- Metal 3D printed parts can achieve near-isotropic properties with proper post-processing, but rarely match the consistency of CNC machined metal
Density and Porosity
CNC machining produces parts with the original material’s density since no new material bonds are created. The material remains as dense as it was in its original billet form.
3D printing, depending on the process, can introduce porosity. SLA resin prints are generally dense, but FDM prints have tiny gaps between layers. Metal 3D printing often requires hot isostatic pressing (HIP) to eliminate porosity, adding time and cost to the process.
Heat Resistance and Chemical Resistance
CNC machined parts maintain the full heat and chemical resistance of the base material. A CNC-machined PEEK part, for example, retains PEEK’s excellent high-temperature performance.
3D printed parts may have reduced heat or chemical resistance due to:
- Changes in material properties during printing (like resin curing)
- Porosity that allows chemicals to penetrate
- Layer boundaries that can fail under thermal stress
No comments:
Post a Comment