How to Choose the Right 3D Printing Process and Materials for Your Application
The progression of 3D printing over the last few decades is a testament to the technology’s incredible benefits.
3D printing, also referred to as additive manufacturing (AM), has made significant impacts across industries. Since the 1980s and 1990s, when 3D printing first emerged onto the scene, this novel technology offered a promising future. In the mid-2000s, desktop printers hit the market, and industrial AM systems reached initial commercial maturity, thrusting the idea of 3D printed production parts into the minds of many. Now, 3D printing is utilized as a powerful technology capable of being used throughout the value chain. Applied alone or as a complement to traditional manufacturing methods, AM has proven to be a valuable solution, sure to give rise to future innovation.
The progression of 3D printing over the last few decades is a testament to the technology’s incredible benefits to consumers, designers, engineers and manufacturers. While traditional production methods have limitations in manufacturability, 3D printing provides unparalleled design freedom due to the additive method of building parts layer by layer. Because AM doesn’t require tooling, it’s a very fast production method, able to turn around parts within hours or days.
There are some limitations to the cutting-edge technology, however. Even the largest industrial AM systems on the market have build volumes that are relatively small compared to what can be accomplished with conventional manufacturing methods. Depending on application and budget, most high-volume projects will not lend themselves to 3D printing for full production runs. These challenges are being met every day by new advancements in the AM industry, but at present, these technologies are recommended as a key fabrication method within early product development stages for smaller, custom products, or low volume production.
Most significantly, 3D printing has established itself as a key part of the production revolution—an Industry 4.0 where smart, digital production ecosystems communicate, interpret, evaluate and augment behaviors to drive improved manufacturing. AM will act as the physical manufacturing component of the digital thread as a part of the industrial “Internet of Things,” or the inter-network of physical devices and buildings with the objects that collect data. The shortened supply chain and increased production efficiency are why so many businesses from startups to Fortune 500 companies have adopted it into their workflows.
On the way to adoption, however, questions can arise about various AM systems, their inherent qualities, the materials associated, and the cost of operating in-house versus outsourcing to a contract manufacturer. In the following, we break down common types of additive manufacturing, associated processes and systems, and how to identify which AM solution is best for your project.
Material jetting technology seen on a PolyJet printer.
Types of 3D Printing Technologies
There are four primary types of 3D printing, with newer processes frequently emerging. Each type of AM process utilizes different materials and produces components with unique properties that lend themselves well to particular applications.
Vat polymerization, in which liquid photopolymers are cured by light-activated polymerization, is one of the first additive manufacturing processes ever developed. A precise UV laser cures and solidifies thin layers of photo-reactive resin layer by layer. This method, widely known as stereolithography (SL, SLA), was commercialized in the mid-80s. Considered the original 3D printing technology, SL parts are utilized in applications such as investment casting patterns, prototypes, and concept models. Another notable vat polymerization technology is digital light processing (DLP).
This additive manufacturing type dispenses material through a heated nozzle or extruder head. After a layer is laid down, the build platform will lower, or the extrusion head will move up, and the next layer is printed onto the previous layer. The raw material is typically a thermoplastic filament coiled onto a spool that is melted as it is extruded. Common technologies that utilize this method include fused filament fabrication (FFF) and fused deposition modeling (FDM), the first commercially-available system developed in 1991. Due to the ability to build with common thermoplastic materials, this type of AM is useful for fabricating production parts, manufacturing tooling, and functional prototypes.
Powder Bed Fusion
Commercialized around the same time as material extrusion, powder bed fusion employs thermal energy to fuse cross-sectional regions of powdered material. The thermal energy melts powdered materials, which solidifies as it cools. Typically, a chamber of powder will drop as each layer is processed, forming a final “powder cake” of unused material from which the solidified part must be excavated. For polymers, the unused powder surrounding the part serves to hold it in place, so typically no additional supports are needed. For metal parts, anchors are typically required to attached parts to a build plate and support down-facing structures. Laser sintering (aka selective laser sintering) was commercialized in 1992, followed by high-speed sintering technologies, and more recently, multi jet fusion (MJF). For metal manufacturing, direct metal laser sintering (DMLS) and electron beam melting (EBM) are popular industrial systems.
Utilizing multi-nozzle print heads, material jetting remains one of the fastest AM methods. The AM process deposits droplets of build material layer by layer. Material jetting systems are capable of printing multi-material and graded material parts. Using different proportions of each material produces parts resulting in a variety of colors and a wide range of material properties. Generally, these systems use photopolymers, wax, and digital materials, in which multiple photopolymers are mixed and jetted simultaneously. Technologies like multi-jet modeling and PolyJet are used to create rapid prototypes, concept models, investment casting patterns, and anatomically realistic medical models.
3D Printing Materials
Unlike traditional manufacturing methods, in which there is a near limitless material catalog to choose from, 3D printing is bound to the materials that will work within each specific system and machine. Currently, most AM parts can be plastic or metal, depending on technology with some composite options available too.
Production materials need to meet certifications and mechanical properties for industry-specific requirements, such as aerospace flame ratings and medical biocompatibility. There are distinct durability, appearance and tolerance needs across industries.
Considerations for Choosing a Process
To ensure the most suitable outcome, there are several key considerations when choosing a technology for your project.
From prototypes to production-quality parts, 3D printed components can represent any point of the product life-cycle. The requirements for each application are unique and entail careful examination and planning to identify the best 3D printing process and materials to meet project needs. For example, when creating prototypes, design teams will often need fast turnarounds with cost-effective materials, while still requiring an accurate representation of the final product’s form, feel and function. On the other hand, a production part must perform as the final product, and needs to meet certain quality, testing, chemical and structural requirements. The subsequent sections dive into some considerations for determining application requirements.
Depending on the performance needs of the 3D printed part, the build style and material used will vary. If a part needs to appear cosmetically similar to the final product, or needs to hold its shape as a static model, PolyJet, with its quick turnaround and smooth, natural finish, might be the best process. Stereolithography is a good option for parts like entertainment props or large concept models that need to be lightweight with a smoother final finish. Functional prototype components that need to resist impact or high temperatures can utilize FDM for its strong, durable parts from an array of high-performance materials. If a part’s design calls for a complicated undercut for airflow or a durable living hinge, LS thermoplastics may be the ideal candidate. These considerations can be complicated, but careful deliberation of part performance requirements can help simplify selection of an appropriate 3D printing process.
Many 3D printed parts need to function in higher temperatures or humid environments. Some 3D printing processes and materials are quickly ruled out by those parameters. For example, applications that function outdoors might need a UV-stable material, but photopolymers will degrade quickly when exposed to UV light. Moisture can adversely affect some materials and cause a part to warp, curl or lose dimensional accuracy. This is due to the inherent hydroscopic nature of certain 3D printing materials. In some applications, the part could require a food-safe material. In this instance, a thermoplastic would be the most applicable.
The number of use cycles a part will go through can eliminate some processes and materials. A 3D printed jig or fixture may go through thousands of cycles and withstand a significant amount of stress, while a fit test prototype may only need to function once. Engineering-grade thermoplastics can withstand significant amounts of stress and pressure, making them ideal for functional prototypes or production parts. Photopolymer materials, on the other hand, are more effective for short-term, low-stress applications.
UV lasers cure liquid photo-reactive resin on a stereolithography machine.
Parts built using material jetting systems are smoother right off the machine and are more easily hand-finished to the desired cosmetic state. Plastic parts fabricated with material extrusion machines are more challenging to post-process due to thicker layer resolutions and require more labor and skill to achieve a smooth surface, leading to higher labor costs and increased lead time. Additive metals and alloys take even more time, effort and expertise to achieve polished product. Metal parts usually require machining to be removed from the build plate, support removal and tumbling or polishing. There are many finishing operations that service bureaus can provide such as media blasting, post-machining, painting and clear coating. Knowing your cosmetic needs and critical part characteristics will help accelerate your delivery date.
Budget, Timeline & Quality
With a tight budget, the decision may depend on cost of product. Similarly, with a fast deadline, lead time may be the deciding factor. Quality and cost can compete; quick turnarounds and a need for cosmetic finishing can be mutually exclusive. By efficiently maintaining systems and creatively finding solutions to reduce machine time, you can find the balance for making products quickly and cost-efficiently at your desired quality standard.
Ultimately, you should consider these primary factors and decide which are the most critical to your project. Oftentimes there are several competing requirements, but it is your project’s critical characteristics that should drive your decision on which is the most compatible 3D printing process and material for your application. The “one-size-fits-all” approach doesn’t apply to 3D printing. Considering the pros, cons, and nuances of each available process, material, and finishing option will help you identify the most suitable approach to your project.