Rapid prototyping methods
Rapid prototyping processes have been around for several decades, but they are still relevant in engineering and many other fields. CNC machining, 3D printing, Fused Deposition Modeling (FDM), Laminated Object Manufacturing (LOM), and related specific techniques help manufacturers enjoy valuable advantages.
For instance, the product development cycle is shortened, manufacturing costs are minimized, and designs are tested. Rapid prototyping also helps engineers and designers make product development a team effort through enhanced engagement.
Rapid prototyping methods are the go-to solution for any business looking to get products to market faster, enhance inventory intelligence, and close business deals faster.
This article explores the different methods in rapid prototyping, discusses their basics, and highlights tips for choosing the most suitable one.
What Is A Prototype? What Is Rapid Prototyping?
A prototype can be considered to be the first tangible segment of the product development process between ideation and manufacturing. While it is a model of the envisaged product, a prototype carries the main features and is thus usable for testing purposes before full-scale manufacturing. A good example is the prototype car below.
A prototype car
Manufacturers use the prototype concept to uncover design and manufacturing flaws and are therefore able to save time and resources over time.
Rapid prototyping is the fast and repetitive process of generating tangible parts from digital designs. Usually, these parts are made within a few days, not the weeks’ timeline for standard prototyping. With such a prompt production of the parts, manufacturers or designers can test and improve the products in time for mass production.
Under normal circumstances, the gap between idea creation and manufacturing is large, but this changes with rapid prototyping processes. As will be realized in the sections below, several methods help in rapid prototyping, with CNC machining being one of them.
History Of Rapid Prototyping
The earliest concept of rapid prototyping is widely attributed to the efforts of Charles Hull and Hideo Kodama in the 1980s, alongside 3D printing. That was after Bayer from Germany had developed the reaction injection moulding technique in 1969.
Since then, the technology has advanced, as evidenced by unique techniques like Selective Laser Sintering (SLS) and Fused Deposition Modeling (FDM), but also its seamless integration with industrial manufacturing and tooling processes.
Rapid Prototyping vs Traditional Prototyping
In many ways, rapid prototyping methods are an upgrade of traditional rapid prototyping. Aspects that support this argument are material compatibility, scaled 3D manufacturing, machining precision, and speed control.
What Is Traditional Prototyping?
Traditional prototyping is a form of prototyping that significantly uses human effort and traditional machines such as molds, mills, and lathes. Machinists have used traditional prototyping for decades to manufacture functional prototypes.
A conventional lathe
The main features of traditional prototyping are;
- Longer duration – Weeks, months
- Limited design versatility – design modifications can be extremely difficult and expensive
- Suits large-scale manufacturing – Traditional prototypes are perfect for rough testing or even mass production
The differences are clearer with the outline of rapid prototyping features below.
What Are Three Key Characteristics Of A Rapid Prototype?
The core value of a rapid prototype is based on three main characteristics, namely cost-effectiveness, speed, and iteration.
Speed
The time taken from the design stage to production of a tangible part can be as short as hours, but some can take longer, say, months.
Cost Effectiveness
A rapid prototype is manufactured using low-cost tools and materials.
Iteration
A good rapid prototype is easy to modify and can be produced in multiples for analysis and testing.
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What Are the Different Types Of Rapid Prototyping?
Rapid prototyping processes come in different styles to suit the varying industrial needs – Metal-based rapid prototyping, plastic-based rapid prototyping, and composite & other material prototyping.
For a better understanding of where the types of prototyping apply, below is a detailed discussion.
What Is The Rapid Prototype Method For Metals?
Metal-based rapid prototyping is an ideal option for rapid prototyping parts that meet requirements for precision and strength. These prototypes are likely to be subjected to heat or mechanical stress, particularly in areas like heavy machinery and aerospace.
Metal casting, sheet metal fabrication, 3D printing, and CNC machining headline the approaches manufacturers use to create metal prototypes. As seen below, each has a special place in the prototyping industry.
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Metal Casting Prototypes
Metal casting prototypes are preferable for complex shapes that may be difficult to produce with 3D printing or CNC machining, especially if the machinability of the material is lacking. Since the molten metal is poured into a mold, it is easy to create almost any complex geometry.
Benefits
- Strong and durable
- Cost-effective
- Versatile – many metal alloys
- Suits complex internal geometries
Limitations
- High initial investment cost
- Material waste
- High expertise required
Cast metal prototype
The surface finish may not be the best, but it can be refined with supplemental processes such as painting and coating.
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Sheet Metal Prototypes
Sheet metal for prototyping is a method of creating parts made of thin metal sheets (normally less than 6mm). This cold-working procedure involves bending, stamping, welding, punching, and cutting.
Sheet metal prototyping
The best sheet metal fabrication service providers can develop any sheet metal prototype according to client requirements for tolerances, surface finish, volumes, and so on.
Benefits
- Fast turnaround
- Cost-effective thin-walled rapid prototyping parts
- Many types of metals
Limitations
- Thickness limitation
- Issues such as springback
- Not ideal for complex bends
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CNC Machining Metal Prototypes
The CNC machining process is an equally exciting option for rapid prototyping with its high speed, low cost, and excellent surface finish. Compared to an additive manufacturing option like 3D printing, subtractive CNC machining is capable of producing superior surface finishes.
CNC machining
The process comes in different https://proleantech.com/multi-axis-cnc-machining/ configurations, prompting comparisons like 3 axis vs 5 axis CNC.
Benefits
- Tight tolerances and dimensional accuracy
- Can produce undercuts and other complex geometries
- Superior surface finish
- A broad array of metal grades is machinable
Limitations
- High material waste
- Time-consuming, especially for complex parts
- Costly for complex parts
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3D Printing Metal Prototypes
Where conventional metal fabrication techniques cannot produce prototypes, manufacturers can use direct metal laser sintering (DMLS), selective laser melting (SLM), and other metal 3D printing methods. Materials that cannot be successfully processed through other methods can be printed layer by layer to produce complex rapid prototyping parts.
Metal 3D printing
Benefits
- Fixturing and tooling are not necessary
- Minimal material wastage
- Simultaneous production of multiple parts is possible
- Can produce complex internal geometries
Limitations
- Post-processing often necessary
- High equipment and raw material costs
- Takes longer for larger parts
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Metal Injection Molding (MIM)
The process entails four main steps: Feedstock preparation, injection molding, binding removal, and sintering. Metal injection molding is an effective rapid prototyping method for complex metal parts.
MIM is cost-effective for prototyping small intricate parts in large volumes. Mobile phone plugs and watch casings are produced using this technique.
Benefits
- Suitable for thin-walled parts (smaller than 100 micrometers)
- Low environmental impact
- Fast process
- Cost-effective for small parts
Limitations
- Limited to production of small parts. Large parts are too costly.
Plastic-Based Rapid Prototyping
When cost-efficiency and speed are the top rapid prototyping priorities, plastic parts are often the best choice. Manufacturers of consumer, medical, and electronic products usually build their functional prototypes using plastics.
Depending on the level of detailing, surface finish, or strength needed for the prototype, the options include PolyJet 3D Printing, Fused Deposition Modeling (FDM), Selective Laser Sintering (SLS), and Stereolithography (SLA).
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Rapid Injection Molding
Rapid injection molding injects uses high pressure to force thermoplastic resins into a mold. It is a fast proces that follows these steps:
- Designing using CAD software
- Mold production
- Selecting the resin material
- Injection molding
- Cooling
- Post-processing
Benefits
- Speed and efficiency
- Cost-effective (for low to medium volumes)
- Material versatility
- Fast response to the market
Limitations
- High initial cost
- Pricey design modifications
- Lead time initially long
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PolyJet 3D Printing
This technology entails spraying layers of thin photopolymer resin of high resolution. The resin is held by a special gel matrix, which is removed after the completion of the process.
The PolyJet 3D printing process diagram
PolyJet is used for thin-walled intricate parts and comes in different colors. Its limitation is low strength and inappropriateness for functional testing.
Benefits
- Superior surface finish
- Multi-color and multi-material
- Minimal post-processing
Limitations
- Poor mechanical properties
- Parts may degrade faster
- Not suitable for functional parts
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Fused Deposition Modeling (FDM)
Fused deposit modeling
In simple terms, FDM involves creating a 3D part from many layers of thermoplastic material. This rapid prototyping method is open to various materials and is relatively affordable. Its challenge is related to poor surface finish and limited z-axis strength.
Benefits
- Numerous thermoplastic material options
- Minimal post-processing
- Large volumes
Limitations
- Visible layer lines
- Need for support structures
- Shrinkage and warping issues
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Selective Laser Sintering (SLS)
Part made by the SLS method
The SLS method uses an aggregation or sintering process using the power of a laser on polymer powder. It is an effective technique for manufacturing prototypes of complex geometry. The resulting parts are accurate and durable, although the structure may be brittle and the surface gritty.
Benefits
- Support structures are not necessary
- Superior mechanical properties
- Complex geometries
Limitations
- Expensive to set up
- Poor surface finish
- Cools slowly
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Stereolithography (SLA)
SLA is a process where a laser is directed at liquid resins and produces a part. The rapid prototypes of this nature have an excellent surface finish and precise geometry. Engineers and designers also prefer SLA prototypes because they are cost-effective, albeit with relatively lower strength.
An aerospace SLA-made prototype
Benefits
- Perfect surface finish
- Excellent tolerances and dimensional accuracy
- Small and medium parts are built fast
- Numerous resin materials are usable
Limitations
- Post-processing required
- Overhangs require support
- Proper storage is required for UV light-sensitive parts
Composite And Other Material Prototyping
Sometimes, rapid prototyping is looking for parts that can withstand wear, heat, and meet other requirements not covered by either metal or plastic prototypes. Options like Ceramic 3D Printing, Laminated Object Manufacturing (LOM), and Lost Wax Casting (via 3D Printed Patterns) fill that gap.
Truth be told, these materials are not as established as the other two, but they can be better options in some circumstances. Let’s see what each of them represents.
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Ceramic 3D Printing
Ceramic 3D printed part
Ceramic prototypes can be produced by systematically building a part from ceramic powder or slurry. A binding agent and heat make sure every layer is well established before placing another one on top.
Benefits
- Chemical and temperature resistance
- Biocompatible parts
- Hardness and wear resistance
Limitations
- Post-processing is required
- High material costs
- High material shrinkage
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Laminated Object Manufacturing (LOM)
This modern additive manufacturing RP technique, which was innovated by Helisys Inc., entails the use of laminates coated with adhesive as the printing medium. When the material is layered and stuck together with the help of laser cutting, a prototype is created.
LOM process diagram
Benefits
- Uses affordable sheet material
- Fast production for simple shapes/geometries
- Suitable for visual prototypes
Limitations
- Material restrictions
- Not ideal for functional mechanical parts
- Poor surface finish
- A lot of post-processing
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Lost Wax Casting (via 3D Printed Patterns)
Lost wax has been around for centuries, and with 3D advances, the method is now applicable for composite 3D printing. A 3D model is designed, and a castable resin pattern is printed.
The pattern is embedded in a ceramic slurry to produce a mold. When molten composite is poured into the cavity and left to solidify, the result is a composite prototype.
Benefits
- Superior surface finish
- Complex geometries
- High-dimensional accuracy
Limitations
- High expertise is required
- Part size limitation
- Cost per part is high
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Comparison Table
Here’s a simplified comparison table of the different rapid prototyping methods:
| Category | Main Options | Best Used For | Top Benefits | Main limitations |
| Metal-based | CNC machining Metal 3D printing Sheet metal Casting | Precision components High-strength parts | Superior functional testing Strong components Stress resistant Heat resistant | High material cost Longer processing time Specialized expertise required |
| Plastic-Based | FDM SLA SLS PolyJet | Consumer products, Design verification | Fast production, Cost-effectiveness, Simple design modifications. Broad range of materials | Lower mechanical strength Limited heat resistance. May not suit all functional tests |
| Composite & other | Lost wax casting Ceramic 3D printing LOM | Specialized applications | Temperature resistance Chemical resistance | Higher costs Limited availability |
Note that, based on the purpose and stage of rapid prototyping in the manufacturing process, the categories are:
- Engineering Prototypes
An engineering prototype
- Low-fidelity
- High-fidelity
- Proof-of-Concept
- Looks-Like Prototypes
- Works-Like Prototypes
- Validation Testing and Manufacturing Prototypes
We will cover these in more detail in a later post.
Further reading:
Importance Of Rapid Prototyping Methods In Manufacturing
In a fast-paced world where competition is tight, nothing beats an accurate and fast production development process. Rapid prototyping allows designers and manufacturers to actualize ideas quickly and prompt them for manufacturing.
This strategy presents various advantages, including faster product development, improved product quality, higher cost savings, and early detection of design mistakes.
Showcasing Product Ideas
Designers use rapid prototyping processes to show and explain ideas to stakeholders, who could be investors, the board of directors, or other departments. The idea is to accelerate the design approval process, but this step also promotes team togetherness in the process.
Avoids Costly Design Mistakes
Another notable reason to use RP is to identify design flaws early in the product development cycle. Designers are able to prevent costly mistakes before the product goes into full manufacturing.
Can Suit Low-Volume Manufacturing
Yes, rapid prototyping is an option for low-volume manufacturing because some of its methods produce market-ready items. Vacuum casting, 3D printing, and injection molding can provide high-precision prototyping services.
Low-volume manufacturing
Accelerates Product Development
The foremost essence of rapid prototyping is to deliver test parts from the design as fast and efficiently as possible. Firms are interested in shortening the time between idea conception and translation of the same into a tangible product. That’s exactly what rapid prototyping services do.
Rapid Prototyping Applications and Use-Cases
Rapid prototyping is commonly used in modern industries, including architecture & construction, consumer electronics, healthcare & medical devices, and robotics & automation.
Architecture & Construction
Architects and engineers can use 1:1 scale prototypes in construction projects to get effective user feedback. This can help them promptly know if the proposed design needs adjustments or not.
Consumer Electronics
Consumer electronics manufacturers use rapid prototyping tools and techniques to build iterations that advance manufacturing effectively. Popular rapid prototyping methods for the industry are CNC machining, 3D printing, and vacuum casting.
For instance, aluminum enclosures are CNC-milled, and internal brackets are CNC-milled.
Electronic prototype
Healthcare & Medical Devices
The healthcare & medical industry perpetually demands innovative products that meet the regulatory standards. With rapid prototyping solutions, designers can turn their ideas into physical prototypes in hours.
Techniques mostly used for diagnostic, surgical, and other devices include investment casting, CNC machining, and 3D printing.
Robotics & Automation
Rapid prototyping is useful in many areas of this industry, from actuators and sensors to biomedical engineering and nanosystems.
Bridging Prototyping And Production
Switching from rapid prototyping to full–scale manufacturing can be challenging, unless a few strategies are implemented. Experience shows that starting with 3D printing for prototypes and scaling as demand increases is an effective strategy.
The specific steps to follow are;
Step 1: Develop a digital prototype model
Step 2: Conduct thorough market research and test the product/prototype
Step 3: Switch to low-volume manufacturing
Considerations For Choosing A Rapid Prototyping Method
Speed isn’t the only consideration for a good rapid prototyping method – the functionality, project goals, type of material, and such angles also apply. The ideal method may eventually be based on surface finish, tolerance, or even part complexity, but that does not rule out turnaround time either.
In general, here are three must-consider elements:
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Properties Of The Material
Manufacturers choose the prototype material to suit the application and desired characteristics. If the budget allows, metal prototypes are ideal for functional testing because they are strong and durable. Thermoplastics can also be used for functional prototyping.
However, resin-based parts may not be good for functional testing, although they have superior resolution.
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Prototype Design Complexity
Complex metal part
Building highly complex prototypes requires an RP method that can accommodate intricate parts and also support functional tests, if required. CNC machining can attain ±0.005mm precision, hence it stands out and finds relevance in aerospace, automotive, and other industries where safety cannot be overlooked.
For more on the capabilities of this technique, check the guide:
CNC Machining Explained: Process, Techniques & Costs
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Prototyping Cost
It is also crucial to determine the budget, which should not exceed 20% of the total project budget, according to experts. Balancing between project expectations and budget is always tricky, but there are always expert hands to help in this and other stages.
Cost considerations to make include the type of rapid prototyping method, type of material, number of prototypes (Economies of scale accompany more prototypes), labor costs, and overhead costs.
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Decision Framework/Questions
Since the list of rapid prototyping methods is long, use the following approach for easier decision-making.
Need functional testing under stress? → Metal-based methods
Need fast, cost-effective iterations? → Plastic-based methods
Need specialized properties (heat/chemical resistance)? → Composite methods
The Merger Of Software And Rapid Prototyping Methods
The combination of rapid prototyping methods and software solutions is powerful. Software products, whether for design or simulation, enhance the effectiveness of the rapid prototyping process.
Examples of Computer-Aided Design (CAD) software popularly used in this process include AutoCAD, Fusion 360, Autodesk Inventor, and SolidWorks.
Fusion 360
Simulation software, which is essential in virtual analysis and testing, includes ANSYS and SolidWorks Simulation.
Popular CAM (Computer-Aided Manufacturing) software options are
Fusion 360 and Mastercam.
The list of software products to consider is long because even specific rapid prototyping techniques can come with dedicated solutions. Examples are Materialise Magics used with SLS and Insight paired with FDM.
The Common Mistakes To Avoid In Rapid Prototyping
Rapid prototyping, as part of the product development process, encompasses and, as such, should be done carefully. One mistake can render years of hard work useless.
Common mistakes teams should avoid in the process are;
- Working with unclear prototyping objectives
- Overlooking user feedback about a prototype
- Ignoring the functionality performance of a prototype
- Not factoring in the manufacturing process and raw material requirements early on
- Not embracing continuous improvement, holding on to a particular prototype instead
Conclusion
The modern manufacturing environment is epitomized by flexibility, precision, and versatility, elements that rapid prototyping enhances in many ways. The way rapid prototyping helps manufacturers steer away from risks, respond promptly to market dynamics, and accelerate innovation is perfect for competitive advantage.
If quality rapid prototyping and manufacturing mean something for your business, ProleanTech is here to help. Our CNC machining services for rapid prototyping and full manufacturing stand out for their superiority throughout the production process.
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