3D Printing vs. CNC vs. Vacuum Casting: the Ultimate Comparison
This article will compare and contrast three common manufacturing methods: 3D printing, CNC machining, and vacuum casting.
Introduction
3D printing, CNC machining, and vacuum casting have all emerged as viable production options, but each has distinct material capabilities and suitability for different volume needs.
For companies developing prototypes or producing goods, the choice of manufacturing technology is crucial. Selecting the right method can mean the difference between an on-time project and missed deadlines, or a costs that meets versus exceeds budgets. As manufacturing requirements become more advanced, it is imperative that professionals understand the strengths and limitations of these technologies.
This guide provides an in-depth comparison of 3D printing, CNC, and vacuum casting from an industrial perspective. We'll discuss factors like production volumes, material options, workflows, tolerances, surface finishes, and of course costs. By reading this article, manufacturing and product development professionals will be equipped to evaluate which process best fulfills their specific technical and budgetary requirements.
Quick Overview: How 3D Printing, CNC, and Vacuum Casting Differ
3D printing, CNC machining, and vacuum casting are three widely used manufacturing methods, each with distinct principles, advantages, and ideal use cases. Understanding how they differ can help you choose the right approach for your project, whether you’re prototyping a single part or producing hundreds of units.
3D Printing (Additive Manufacturing)
3D printing builds objects layer by layer from a digital model, making it incredibly versatile. It excels at producing complex geometries, customized components, and one-off parts that would be difficult or impossible to make with traditional methods.
CNC Machining (Subtractive Manufacturing)
CNC machining removes material from a solid block to create a finished part. Known for its precision, it is ideal for producing parts with tight tolerances, high accuracy, and smooth surfaces, especially when working with metals and engineering-grade plastics.
Vacuum Casting (Replication Molding)
Vacuum casting first creates a prototype and then uses a silicone mold to cast parts under vacuum. This method is great for elevating net-shape prototyping, producing small batches of parts with excellent surface finish and fine detail, closely resembling the final product.
3D Printing: the Versatility of Additive Manufacturing
3D printing is revolutionizing manufacturing by allowing designers to turn digital concepts into physical objects quickly and efficiently. Its unmatched versatility enables the creation of complex, customized parts that would be difficult or impossible with traditional methods.
3D Printing Process: How it Works
Source: custompartnet.com
3D printing (also known as additive manufacturing or AM) involves building three-dimensional objects from a digital file through successive layers of material.
To better understand this process, let's break it down step by step from design to the finished part:
● Create a 3D Model
Design the part using CAD software.
Export the model into a 3D-printable format.
● Slice the Model
The 3D model is divided into thin cross-sectional layers.
The sliced file is sent to the 3D printer.
● Start the Printing Process
The printer builds the part layer by layer.
Materials such as plastic, metal, or ceramic are selectively deposited or solidified depending on the technology.
● Complete the Physical Object
Layers stack up to form the final 3D structure.
The part is removed from the build area once printing is done.
Main 3D Printing Technologies: FDM, SLA, SLS and SLM
The main 3D printing technologies include:
Fused Deposition Modeling (FDM) – Extrudes thermoplastic filaments layer by layer; cost-effective and versatile, commonly used for prototypes and larger parts.
Stereolithography (SLA) – Offers high resolution and smooth surface finish, ideal for detailed prototypes.
Selective Laser Sintering (SLS) – Uses a laser to fuse powdered materials, suitable for durable, functional parts.
Selective Laser Melting (SLM) – Fully melts metal powders for industrial-grade, end-use metal parts.
FDM provides a low-cost, accessible solution, SLA delivers high detail and smooth surfaces, while SLS and SLM can process industrial-grade or functional materials suitable for various applications.
If you want to learn more, this article provides a detailed comparison of SLA, SLS and SLM.
3D Printing Materials
Common materials used in 3D printing include plastics like ABS and PLA, metals including stainless steel and titanium. Powder-based systems like SLS and SLM can 3D print using nylon, plastic and polymer powders as well as metal and ceramic powders.
Pros and Cons of 3D Printing
3D printing has rapidly transformed the way products are designed and manufactured. Like any technology, it comes with its own set of advantages and limitations.
Pros:
High Customization and Design Flexibility – Easily create parts with complex shapes or tailored specifications.
Rapid Prototyping – Quickly turn digital designs into physical prototypes, speeding up the design process.
Cost-Effective for Low-Volume Runs – Small production runs are often cheaper than traditional manufacturing.
Lower Material Waste (Eco-Friendly) – Layer-by-layer manufacturing minimizes scrap.
Accessible to Startups and Hobbyists – Allows individuals and small businesses to prototype or produce without large facilities.
Cons:
Material Limitations – Not all engineering-grade materials are available.
Slower and Higher Costs for Large-Scale Production – Each part is printed individually, making mass production less efficient.
High Initial Investment – Industrial-grade 3D printers can be expensive.
Skill Requirements – Operating printers and preparing 3D models requires knowledge and experience.
Intellectual Property and Design Risks – Designs can be easily copied, raising IP concerns.
For a more detailed breakdown of the advantages and limitations of 3D printing, check out our dedicated article: Pros and Cons of 3D Printing.
Typical Applications of 3D Printing
Source: Unionfab
Areas where 3D printing truly excels include low-volume production of customized components, rapid prototyping to validate part functionality, creating intricate internal structures or geometries otherwise not possible, and producing specific parts for applications like medical implants or bespoke automotive components.
Overall, 3D printing technology enables new frontiers in customized, on-demand manufacturing.
CNC Machining: Unleashing Precision
Source: Unionfab
CNC (Computer Numerical Control) machining has its origins in the 1950s and has since revolutionized manufacturing through automation and high precision. By using computer-controlled machine tools, such as mills, lathes, and routers, CNC machining allows manufacturers to produce complex and highly accurate parts efficiently.
CNC Machining Process: How it Works
CNC machining is a subtractive manufacturing process where material is precisely removed from a solid block to create a finished part. To see how this process transforms a 3D design into a physical component, let's break it down step by step:
● Design the Part
Create a 3D CAD model of the component.
Prepare the model for machining using CAM (Computer-Aided Manufacturing) software.
● Generate the Toolpath
CAM software converts the 3D model into G-code instructions.
These instructions precisely control the movement and speed of cutting tools along multiple axes.
● Start the Machining Process
CNC machines perform milling, turning, drilling, and other subtractive operations.
Material is removed from solid blocks or plates to form the desired shape.
● Finish and Inspect the Part
After machining, the part may undergo deburring, polishing, or other finishing operations.
Final inspection ensures dimensions and tolerances meet specifications.
CNC Machining Options: Milling, Turning and More
CNC machining offers a variety of ways to turn raw materials into precise, functional parts. Among these, milling is a key technique. In milling, rotating cutting tools remove material from a stationary workpiece to create flat surfaces, complex shapes, or intricate features. This method is widely used for parts that require high precision and detailed geometries.
Turning, on the other hand, rotates the workpiece against a stationary cutting tool. It is particularly effective for producing cylindrical or symmetrical shapes, such as shafts, rods, or threaded components. Turning allows for very accurate diameters and smooth finishes, making it ideal for parts that need to fit together with tight tolerances.
In addition to milling and turning, CNC machining also includes other options such as drilling, grinding, and multi-axis operations. These techniques provide extra flexibility for creating parts with unique shapes or complex features.
If you want to know more about the differences between CNC milling and turning, you can check out our article here.
CNC Machining Materials
Materials that are well-suited for CNC machining include metals such as aluminum, steel, and titanium, as well as plastics, wood, and composites. Metals are commonly chosen for their strength, durability, and industrial performance, while plastics are often used for lightweight parts or components that require chemical resistance or electrical insulation.
Wood and composite materials can also be machined with precision, making CNC a practical choice for prototypes, custom parts, or specialized components.
Choosing the right material is important because it affects not only the machining process but also the final part’s performance and finish. Selecting materials carefully ensures that components meet both functional requirements and aesthetic expectations.
Pros and Cons of CNC Machining
CNC machining is widely used for producing parts that require high accuracy and detailed features. Its automated systems make it possible to manufacture complex components at scale, but like any manufacturing method, it has both strengths and limitations. Here’s a quick overview:
Pros:
High Precision – CNC machines can achieve tight tolerances down to the micron level.
Excellent Surface Finish – Parts produced have smooth surfaces suitable for demanding applications.
Automated Production – Mass production of intricate or complex parts is possible with consistent quality.
Cons:
Lengthy Setup Times – Preparing the machine and programming the toolpath can take significant time.
Material Waste – As a subtractive process, material is removed from a solid block, which generates scrap.
Typical Applications of CNC Machining
Source: Unionfab
Sectors that extensively use CNC machining are:
Die/mold making - CNC milling machines and CNC wire EDM (electronical discharge machines) create molds and dies with tightly controlled features for plastic injection and other processes.
Electronics - Tight-tolerance backplane/housing fixtures, test sockets, precision parts for small mechanical components, and enclosures are machined with CNC.
Energy - Critical parts used in oil/gas drilling and wind/solar installations require the precise sealing surfaces and tight tolerances of CNC production. Also prototypes for structural testing before mass production.
Automotive - CNC create low-volume body molds for specialty vehicles, prototypes. High-precision transmission/suspension parts in hardened alloys like chromium-molybdenum are also made with CNC machining, plus jigs, fixtures for component testing/validation.
Vacuum Casting: Elevating Net-Shape Prototyping
Vacuum casting is a manufacturing process that uses vacuum-assisted injection to fill a precisely-crafted mold. This method allows complex geometries to be replicated in high resolution with minimal air pockets or defects.
Vacuum Casting Process: How it Works
Source: Marmax Design
Vacuum casting, also known as replication molding, is a method for producing precise parts by first creating a prototype and then using a silicone mold to cast materials under vacuum. Here’s how it works step by step:
● Prepare the Mold
A master pattern or 3D printed prototype is used to create a multi-piece silicone mold.
● Inject the Material
Liquid polymers, resins, or other materials are poured or injected into the mold.
The vacuum removes trapped air, ensuring the material reaches all corners of the mold.
● Set and Cure
The material is allowed to set and cure inside the mold.
● Demold the Part
Once cured, the finished part is carefully removed from the mold.
If you want to learn more about vacuum casting, please read this article.
Vacuum Casting Materials
Vacuum casting can be used with a variety of materials, making it a flexible choice for producing prototypes, low-volume parts, and complex components. Common materials include epoxy resins, polyurethane resins, and silicones, each offering unique properties depending on the application.
Epoxy resins are known for their excellent strength, chemical resistance, and ability to produce detailed, high-resolution parts. They are often used when durability and dimensional stability are required.
Polyurethane resins are versatile and can mimic the properties of many production plastics. They are commonly used for functional prototypes, small batches, and parts that need to be tough, flexible, or wear-resistant.
Silicones are highly elastic and heat-resistant, making them ideal for parts that require flexibility, cushioning, or the ability to withstand repeated use. Silicone molds themselves are also a critical component of the vacuum casting process.
Pros and Cons of Vacuum Casting
Pros:
Vacuum casting can produce accurate and detailed casting replications of intricate master models/molds, capturing subtle surface textures and complex geometries well.
Achieves smooth, void-free surfaces thanks to vacuum assistance drawing out air.
Produces net or near-net shapes requiring little post-processing machining or finishing.
Cons:
High setup costs for molds that are only offset by multiple castings. This makes it less economical for very low (≤ 5 parts) production volumes.
Material options are limited to those suitable for vacuum forming techniques like thermosets.
Molds degrade with use and must be replaced (typically after 15 - 50 casts), adding recurring costs versus reuse of injection molds for example.
Not as dimensionally precise as CNC milling or other high-tolerance techniques. The dimensional accuracy achievable through vacuum casting is dependent on the accuracy and surface finish of the master mold used. In general, the dimensional tolerance of vacuum cast parts will be within ±0.2mm of the original master mold dimensions.
Typical Applications of Vacuum Casting
Source: Unionfab
The combination of smooth finishes, low order quantity requirement, and material properties close to injection molding materials make vacuum casting a first choice in many creative and low-volume application areas:
Prototyping and Product Development - Vacuum casting is commonly used for rapid prototyping to create functional prototypes that closely mimic the final product’s appearance and performance. This is especially valuable in product development and design validation.
Consumer Electronics - Vacuum casting is employed to create casings, bezels, and custom electronic components, especially for low to medium volume production of niche electronic devices.
Automotive - In the automotive sector, vacuum casting is used to produce concept car models, customized automotive parts, and interior components for design testing.
Factors Influencing Vacuum Casting
Several factors can influence the precision and quality consistency of vacuum cast parts:
Mold/Pattern Quality: Imperfections get duplicated, degrading over time, affecting tolerances.
Mold degradation - Over time and with repeated use (about 15~50 casts), molds may slowly deteriorate or warp, resulting in slightly less accurate replications.
Vacuum Leaks: Incomplete evacuation leads to air pockets reducing fidelity and strength.
Thermal Effects: Curing shrinkage/warping varies by materials and temperature control methods.
Material Properties: Viscosity changes during pouring/curing can induce variances batch to batch.
Curing Processes: Precise timing, environmental monitoring required to reliably replicate curing cycles.
In-Depth Comparison: 3D Printing vs. CNC Machining vs. Vacuum Casting
Let’s explore how 3D printing, CNC machining, and vacuum casting stack up against each other. We’ll compare them in terms of cost and efficiency, material options, precision, surface finish, strength, and product size limits to help you figure out which method is right for your project.
Cost and Efficiency Comparisons
Source: Unionfab
1. Very Low Volume Production: 5-100 parts
(Note: For quantities of fewer than 5 parts, 3D printing excels in both cost-effectiveness and efficiency.)
Most cost-effective choice: Vacuum Casting
Vacuum Casting
Once the master mold is created, vacuum casting can be cost-effective for very low volume production because it allows you to create multiple copies from a single mold. The setup cost for creating molds can make it less efficient for extremely low quantities.
3D Printing
3D printing is generally efficient for very low volume production as it doesn’t require tooling or molds. However, it can be relatively more expensive per part compared to other methods.
CNC Machining
CNC machining can be expensive and less efficient for very low volume production due to setup costs and machining time for each part.
2. Low Volume Production: 100-500 parts
Most cost-effective choice: 3D Printing/CNC Machining
Vacuum Casting
Vacuum casting may become less cost-effective and less efficient for high volume production due to the time and cost involved in making multiple molds (each for 15~50 casts).
3D Printing
3D printing is still suitable for low volume production.
CNC Machining
CNC machining becomes more cost-effective on a per-unit basis as volume increases but may still have higher upfront costs.
3. Low to Medium Volume Production: 500 - 1,000 parts
Most cost-effective choice: Injection Molding/CNC Machining/3D Printing
Vacuum Casting
Volume beyond 500 is not suitable for vacuum casting.
Injection Molding
Injection molding is often the most cost-effective choice for producing parts in this volume range. The initial tooling or mold setup costs can be relatively high but are spread across the entire production run, making it economical for larger quantities.
CNC Machining
CNC machining becomes a valuable choice when the part’s design, complexity, or tight tolerances cannot be adequately met by injection molding.
3D Printing
In many cases, 3D printing can be cost-effective for low to medium volume production, especially when considering design flexibility, quick turnaround times, and minimal tooling costs. When the design geometries or materials needed for the part cannot be satisfied by CNC machining, 3D printing becomes a viable alternative.
4. Medium to High Volume Production: 1,000 - 10,000 + parts
Most cost-effective choice: Injection Molding/CNC Machining
Injection Molding
Injection molding remains the most cost-effective and widely used choice for medium to high volume production. It’s optimized for mass production because it can efficiently produce large quantities of identical parts from a single mold or tool.
CNC Machining
CNC machining can be highly cost-effective and efficient for high volume production, especially when producing a large quantity of identical parts requiring precision.
Want to see exactly how much your project could cost with 3D printing, CNC machining, or vacuum casting? Use our free cost calculator to get an instant estimate and plan your production smarter!
Material Comparison
CNC Machining
Metals (steel, aluminum, titanium alloys, etc.)
Plastics/composites (fiberglass, carbon fiber, etc.)
Wood, stone, foam for non-metallics
3D Printing
Plastics like PLA (biodegradable), ABS (strong and durable), PETG (flexible), and nylon (high strength)
Photopolymer resins for SLA/DLP
Metals powders like stainless steel, aluminum, titanium, etc.
Composites like carbon fiber with MJF (multi-jet fusion)
Vacuum Casting
Thermoset & thermoplastic resins (epoxy, polyurethane, acrylic, etc.)
In conclusion, CNC machining offers a broad material selection, predominantly working with rigid, machinable materials like metals/composites but also soft materials. 3D printing is versatile with plastics, metal powders, ceramics, and composites, with ongoing material innovation. Vacuum casting primarily uses thermosets.
Precision, Surface Finish, Strength & Toughness
Precision Comparison
CNC machining offers higher precision than vacuum casting and other formative/net-shape processes which rely more on the accuracy of molds/tooling and controlling material deformation. Dimensions can vary more with these techniques.
Additive methods like 3D printing have improved but many still lag CNC in obtainable tolerances and surface finish quality, especially for demanding applications.
Surface Finish Comparison
Source: Unionfab
Source: Unionfab
CNC machining produces a part with an “as-machined” or “as-milled” finish (surface roughness of 125 μin) as soon as the manufacturing process is completed.
In contrast, 3D printing techniques rely on discrete layers that leave visible step patterns even with SLA’s fine resolution.
Vacuum casting can match or come very close to CNC-level surfaces in many applications thanks to its tight mold tolerances and vacuum encapsulation process. It produce net-shaping parts with minimal or no additional machining or post-processing requirement.
However, porosity or mold imperfections in the vacuum casting process could potentially lead to rougher regions on some vacuum cast parts where CNC excels in maintaining consistent finishes.
Strength and Toughness Comparisons
CNC parts have higher density and are closer to the theoretical density of the substrate material.
Vacuum casting
When casting metals like aluminum or zinc alloys, strengths can be on par with CNC materials if densities from the casting process are high without voids. However, porosity defects weaken parts more significantly than possible with CNC cutting a dense billet.
Thermoset polymers like epoxies and polyurethanes cast in molds have heat deflection temperatures often below 150°C/300°F. Meanwhile, many engineering-grade CNC plastics like PEEK, nylon, and composites can withstand temperatures over 150°C during machining and post-machining heat treatments, increasing durability of CNC made plastic parts.
3D printing
3D printed parts can contain voids between deposited layers. Layered microstructures in 3D printed parts introduce areas of weakness between strata that do not exist in homogenous CNC machined structures.
Metal 3D printing techniques like SLM can match densities and strengths of milled metals if parameters are optimized. But reproducibility between parts/machines is greater for CNC. Specialty composites 3D printed by SLS/SLM may see anisotropic reinforcement from grain/fiber orientations versus isotropic CNC structures.
Thermoplastics 3D printed by FDM/FFF exhibit lower elongation, impact resistance and fatigue life compared to CNC machinable plastic stock.
Product Size Limits
Vacuum Casting
Can produce parts ranging from a few centimeters up to a meter or more depending on mold/chamber size. Larger parts may require assembly.
3D Printing
Large industrial 3D printers can achieve maximum individual build volumes approaching 1-2 cubic meters. However, due to their size and slower print speeds, they typically print these largest parts using divide-and-conquer techniques like multi-part builds or multi-chamber simultaneous printing of smaller sections.
Unionfab now support large size SLA printing up to 2100700800 mm.
CNC Machining
Limited mainly by travel of largest machine axis, with gantry mills covering areas of several square meters. Routers/lathes can produce very large or extremely long parts.
Conclusion: Choosing the Right Manufacturing Method
Selecting the best manufacturing method ultimately depends on what matters most for your project—whether it’s speed, precision, cost, or the ability to create complex designs. Below is a clear breakdown of when each method is the most practical and what strengths it brings to your production workflow.
Vacuum Casting
Source: Unionfab
When to use:
Ideal for affordable prototyping and very low volume production (5–100 parts).
Strengths:
Produces prototypes with the look and feel of the final product.
Cost-effective for small quantities (5-100) with fine surface finishes.
Excels at smooth surfaces and net-shaped components that need minimal post-processing.
3D Printing
Source: Unionfab
When to use:
Perfect for rapid prototyping, iterations, and one-off or customized parts.
Strengths:
Allows quick design validation and rapid iterations.
Supports complex and intricate geometries that are difficult for traditional methods.
Enables high customization and personalized products.
CNC Machining
Source: Unionfab
When to use:
Best for high precision parts and medium to high volume production.
Strengths:
Known for tight tolerances and consistent quality.
Efficient for medium to high quantities of parts.
Compatible with a wide range of materials, including metals, plastics, and composites.
In Summary
Choosing the right manufacturing process depends on your specific project requirements:
For Affordable Prototyping and Very Low Volume (5-100) Production, consider vacuum casting for cost-effective replication of detailed parts and 3D printing for rapid iterations and customization.
For High Precision and Medium to High Volume Production, CNC machining excels in producing accurate, high-quality parts efficiently.
Complex Geometries and Customization are strengths of 3D printing, making it suitable for unique, intricate designs.
Additionally, for High-Volume Production Runs, injection molding leverages economies of scale to achieve cost-effective manufacturing.
Unionfab’s Manufacturing Expertise
If you're looking for a reliable and experienced partner to bring your designs to life, consider Unionfab's comprehensive manufacturing services.
With a focus on precision and quality, Unionfab offers a wide range of production solutions, including CNC machining, 3D printing, vacuum casting, and injection molding.
Explore Unionfab's services today to achieve your project goals with confidence! And if this is your first time using Unionfab’s services, sign up now to enjoy 10% off your first order!
FAQs
What is the difference between CNC and 3D printing?
CNC machining is a subtractive process that cuts material from a solid block, while 3D printing is an additive process that builds parts layer by layer. CNC offers higher precision and better material properties, while 3D printing provides faster prototyping and supports more complex geometries.
Is CNC harder than 3D printing?
Generally, yes. CNC machining typically requires more technical knowledge—such as toolpath programming, tool selection, and understanding cutting parameters—while 3D printing is usually more automated and beginner-friendly.
What are the disadvantages of vacuum casting?
Vacuum casting is not ideal for high-volume production since silicone molds typically last only 15–50 castings. It also requires a master pattern, has longer lead times than 3D printing, and delivers lower precision than CNC machining when tight tolerances are required.
