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rapid prototyping

Rapid Prototyping in Custom Machining: The Ultimate Guide

Rapid Prototyping(RP) allows design teams to quickly and cost-effectively transform 3D digital designs into high-fidelity physical prototypes that match final product specifications.

By enabling the creation of multiple design iterations and prototypes, rapid prototyping optimizes concepts and accelerates the product development workflow.

This guide explores rapid prototyping fundamentals, processes, applications in custom machining, and how to select the optimal process for transforming 3D digital designs into physical prototypes that match final product specifications.

What is Rapid Prototyping?

what is rapid prototyping
What is Rapid Prototyping

Rapid prototyping is a typical early step in the product development process. It is a fast and reliable iterative approach involving the use of CNC machining or 3D computer-aided design (CAD) to fabricate a physical part or assembly. The focus of the product designer or engineering team during the rapid prototyping phase of product development is on usability testing to ensure the part fulfills the purpose of the design. This design is usually called the minimum viable product (MVP) because it comprises of the features required to conduct tests and gather feedback.ot

The Role of Rapid Prototyping in Custom Machining

3d printing prototyping
3D Printing Prototyping

Rapid prototyping is crucial in advancing products through the strict validation stages of product development towards mass production. This production process allows engineers and designers to make prototypes from digital model models generated in CAD software faster and perform efficient and continuous design modifications according to real-world testing and feedback. Rp technology allows you to make a high-fidelity prototype with a design closely matching the proposed finished part. In contrast, low-fidelity prototyping creates a prototype part with significant differences from the final product.

Unlike traditional subtractive, rapid prototyping with 3D printing technology serves unlimited form freedom in custom machining. It offers remarkable speed during this product development phase, allowing your custom products to reach the market faster. Moreover, RP technology reduces the costs of custom machining since product teams do not necessarily have to invest in tooling or manufacturing equipment required for a production run of parts.

Moreover, small-scale and more affordable manufacturing processes, including injection molding with aluminum tooling, CNC machining, or 3D printing, can meet the manufacturing demands of rapid prototyping at considerably lower costs. 

Advantages of the Rapid Prototyping Processes

advantages of rapid prototyping
Advantages of Rapid Prototyping

Rapid prototyping offers extensive benefits in creating and introducing new products to the ever-growing consumer market. Below are their common advantages:

Effective Idea Communication

Physical models encourage product designers and engineers to discuss their concepts with collaborators, clients, and customers, conveying ideas in ways not achievable by visualizing screen designs. Rapid prototyping helps product developers gather clear and actionable user feedback to fully understand user needs and optimize their design to meet expectations.

Cost and Time-Saving

3D printing technology doesn’t require expensive tooling and setup. It can use the same equipment to produce different geometries. More so, in-house rapid prototyping prevents the high costs and lead time involved in outsourcing

Design Iteration and Instant Incorporation of Changes

Generally, design is an iterative process that requires countless rounds of testing, evaluation, and improvement before achieving a finished product. Rapid prototyping with 3D printing guarantees the flexibility necessary for faster production of more realistic prototypes and instant change implementation. Thereby elevating this critical trial-and-error process.

Easy Concepts Realization and Exploration

Rapid prototyping promotes initial design ideas to low-risk concept explorations that are very similar to real products in no time. It helps designers transcend beyond virtual visualization by facilitating an easy understanding of how the design looks and feels and comparing the concepts.

Thorough Testing and Design Flaw Mitigation

Early detection and correction of design flaws can help you avoid costly design revisions and tooling changes in product design and manufacturing in the long run. Product engineers can thoroughly test prototypes that look and function like the final products using rapid prototyping processes. Hence, this mitigates the risks of usability and manufacturability challenges before transitioning to production.

Comparing Prototyping Processes

rapid prototyping process
Rapid Prototyping Process

Engineers and product designers rely on various rapid manufacturing processes in the design process. These processes use varying prototyping tools to provide desired results. Here are the commonly applied processes:

Selective Laser Sintering (SLS)

This automated process involves using a computer-controlled C02 laser to draw on a hotbed of nylon-based powder from the bottom, where it fuses the powder into a solid. A roller lays a new layer of powder on the bad after each layer, repeating the cycle.

SLS uses either elastomeric TPU powders or rigid nylon like actual engineering thermoplastics. Hence, products made with SLS are accurate and exhibit greater toughness. However, they often bear rough surfaces and lack fine detail. SLS is suitable for handling high-volume production and durable parts with intricate geometries.

The SLS process creates durable and more accurate prototypes and production-quality parts than SLA. It can make complex parts suitable for functional testing. However, this process has restricted resin choice, and its parts often bear grainy or sandy texture.

Stereolithography (SLA)

stereolithography sla prototyping
Stereolithography (SLA) Prototyping

SLA is a common prototyping technique that uses a computer-controlled laser to create products in a pool of UV-curable photopolymer resin. The laser traces out and cures a cross-section of the product’s design on the surface of the liquid resin. Then, the hardened layer is lowered below the liquid resin’s surface as the process is repeated.

Each newly formed and cured layer joins the layer below it. This process continues the cycle till the part has been completed. This process is widely embraced across industries due to its material versatility, high resolution, and precision.

Unlike other technologies used in prototyping, SLA is best suited for making parts with intricate features and excellent surface finish for complex designs, cosmetic prototypes, and concept models. Moreover, the technology is available from several sources and offers competitive costs.

However, prototype parts made using the SLA process may not be as strong as those from engineering-grade resins. Hence, SLA-produced parts have limited use for functional testing. Similarly, parts made using SLA are compatible with minimal UV and humidity to prevent degradation even though parts undergo a UV cycle to harden the outer surface.

Fused Deposition Modeling

This rapid prototyping technique creates finished prototypes with an extrusion method that sublimes and re-solidifies thermoplastic resin in layers. Polycarbonate, ABS, and ABS/polycarbonate thermoplastic resins are typical materials used in FDM. FDM prototypes are usually stronger than binder jetting because they use real thermoplastic resins. Hence, its use for functional testing may be limited.

Parts produced with FDM have moderate prices and are relatively strong, making them suitable for functional testing. The FDM process creates products with complex geometries. FDM parts possess a poor finish with a noticeable rippled effect. Unlike SLA or SLS, FDM is a slower additive process with limited suitability for functional testing.

Injection Molding

rapid injection molding
Rapid Injection Molding

Rapid injection molding involves injecting thermoplastic resins into a mold. However, the process is rapid due to the technology used to create the mold. Unlike the traditional steel employed in production molds, molds used in rapid injection molding are usually made from aluminum.

Molded items are usually strong and possess excellent finishes. As the industry standard production process for plastic products, it offers inherent benefits to prototyping in the same process. This process is compatible with almost any engineering-grade plastic or liquid silicone rubber. Hence, material limitations of the prototyping process do not limit the product designers’ capabilities.

Molded items can be produced from a broad range of engineering-grade resins. These parts often bear an excellent surface finish. However, rapid injection molding involves upfront tooling costs that do not apply to other prototyping processes or CNC machining. Hence, conducting one or more rounds of rapid prototypes to confirm the fit and function before adopting injection molding would be best.

Direct Metal Laser Sintering

Direct metal laser sintering is another additive manufacturing technology suitable for rapid prototyping. Manufacturing experts use this process to create metal prototypes and functional finished parts. It uses a laser system that draws on the surface of atomized metal powder, welding the metal powder into a solid structure. A blade spreads a new layer of powder after each layer and repeats the procedure.

DMLS is compatible with most alloys. Hence, it allows prototypes to be full-strength functional hardware created from the same raw material as production components. With manufacturability in mind, DMLS has the potential to transition into injection molding if there is a need to increase

DMLS produces strong prototypes from different metals suitable for functional testing. Besides, it is possible to design internal features and passages that are challenging to cast since the process builds the components layer by layer.

On the downside, the cost of producing DMLS parts can increase if you make more than a few parts. The surfaces of DMLS parts are slightly rough because of the powdered metal origin of the process. Moreover, the process is time-consuming and requires expensive post-processing.

Binder Jetting

Binder jetting is a fast fabrication technique that allows you to produce one or more parts simultaneously. However, parts made with this process are not as strong as SLS parts. Binder jetting works like SLS, using a powder bed to layer the prototypes. The method uses an industrial printhead to selectively deposit a liquid binding agent onto a thin layer of powder particles to build unique parts and tooling.

This powder-based prototyping process is popular for its relatively high speed, lower costs of producing complex geometries, and high-volumetric output. It is compatible with powder materials like sand, metals, ceramics, and composites.

This prototyping technology makes use of economical materials. Its fast production time ensures a low cost per part. Hence, it is perfect for precise and scalable large build volumes of small, accurate parts. However, most parts created with the binder jetting process require post-processing steps, affecting production times. The process offers relatively lower resolution than other additive manufacturing processes.

Selecting the Right Rapid Prototyping Process

metal cnc machining
Metal CNC Machining Rapid Prototyping

Choosing the right rapid prototyping process is essential to develop a product successfully. Moreover, rapid prototyping processes offer varying benefits and constraints. Hence, the choice of the right approach depends on certain factors, including:

Complexity of the Prototype

Examining the complexity of the prototype design is a crucial consideration in choosing the right prototyping process. Some rapid prototyping processes, like SLA and SLS, are perfect for handling intricate geometries, while others are best suited for handling simpler designs or features. Similarly, pick a process that accurately imitates your prototype’s design details.

Material Requirements

Identifying the required material for the final product is crucial to choosing a prototyping process compatible with such materials. SLA has a broad range of material compatibility, followed by SLS and CNC machining. Hence, you should ensure the compatibility of the chosen material with the required properties of the prototype since some processes are limited to certain materials.

Prototyping Speed

Prototyping processes exhibit varying speeds, some offering faster lead times than others. It would help to evaluate the speed at which the prototypes are to be ready to choose the right process. Examine the project timelines to determine the appropriate rapid prototyping process that fits your schedule.

Available Equipment and Expertise

Consider the required expertise and availability of the equipment in your establishment or from manufacturing partners during prototype process selection. Ensure you pick a prototyping process that matches your organization’s expertise and resources to ensure optimal implementation.

Post-Processing Requirements

Identify any additional processing procedures that the prototypes may require. Some rapid prototyping processes may need secondary processes like curing, painting, or polishing to get the preferred results.  Also, it would be best to consider the required time and resources for the post-processing steps.

Rapid Prototyping for Various Applications

high accuracy cnc aluminum prototype

Rapid prototyping is core to product development stages in different industries. Manufacturers in architecture, archeology, modeling, aerospace, and medical care industries use rapid prototyping for different purposes due to its versatility. Here are the typical applications of rapid prototyping across sectors:

Prototype Concept Models

Fast and economical prototype concept models are ideal for providing ideas or concepts to workmates. These prototypes enable product designers to validate their ideas and assumptions by exploring the initial concept and showing its validity to clients or investors. It helps to understand and approve a product’s development while creating communication around it.

Functional and Working Prototypes

Fully functional prototypes are pivotal to achieving quality prototypes that meet your design requirements and can imitate the functionality and performance of your final parts. These prototypes help save cost and time. Moreover, rapid prototyping proves that a functional prototype is economically feasible.

Visual Presentation Prototypes

Visual presentation prototypes often serve as ideal samples for exhibitions. These prototypes feel like the actual physical product. Hence, product designers and engineers use them to seize market opportunities, obtaining large orders and equivalent investment capital.

Low Volume Production

Rapid prototyping enables the quick production of parts between one and several thousand. Rapid prototyping processes, including 3D printing, low-volume injection molding, CNC prototyping, and rapid tooling, help meet the demands of low-volume production runs.

Design and Engineering Verification

Concept models and functional prototypes are perfect for your design and engineering verification. You can create prototypes with the intended material, color, finish, size, strength, and durability as the intended product. The appropriate design prototyping method with key manufacturability, functionality, and viability elements is crucial in rapid prototyping.

Challenges and Solutions in Rapid Prototyping

at machining rapid prototype
AT-Machining Rapid Prototype

Rapid prototyping, a critical process in product development, comes with challenges and limitations. We will explore some of the common rapid prototyping challenges and remedies below:

Material Selection

One of the challenges of rapid prototyping is choosing the ideal material that represents the final part. However, to overcome this, you have to use materials that closely imitate the final production material’s properties. Moreover, advances in 3D printing offer various materials with several thermal, mechanical, and optical properties.

Accuracy and Resolution

Manufacturing experts sometimes encounter difficulty achieving accuracy and resolution in prototypes, especially when handling complex geometries. However, advanced 3D printing technologies like SLA or SLS offer high resolution compared to traditional techniques such as FDM. As a result, it would be best to consistently calibrate and maintain the printing tools to ensure optimal accuracy.

Prototyping Speed

Most times, it might be difficult or nearly impossible to align the speed of creating prototypes with the project timeline. This may be a result of design complications or downtime. It would be best to use a rapid prototyping process like 3D printing, injection molding, or CNC machining to meet the project’s timeline and requirements.

Costs of Prototyping

Using high-end raw materials or advanced technologies can increase the cost of the rapid prototyping process. However, with practical cost consideration, you can balance material quality and precision requirements in rapid prototyping. It would help to examine alternative materials that match your project’s needs and optimize your product design for cost-effective manufacturing processes.

Quality Control

Ensuring the prototype’s quality and reliability can be challenging when using any of the different rapid prototyping techniques. Hence, strict quality control measures such as inspections, testing, and validation would be best. Also, consistently review and refine the quality control processes based on feedback and gathered insights.


Rapid prototyping technology is amongst the fastest-growing manufacturing technologies in recent times. It allows the product development team to assess the complexities of design ideas not easily seen on engineering drawings and validate their concept ideas. This prototyping technology is efficient in the early stage of product development since it helps build a conceptual model or modify the details before transitioning to mass production. This article has discussed everything you need to understand about rapid prototyping to get the best from your project.

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