How Strong Is 3D Printed Plastic: A Comprehensive Guide

3D printing technology has rapidly evolved in recent years, allowing designers, engineers, and hobbyists to create a wide array of prototypes, models, and functional end-use parts using a variety of different materials. Today, 3D printed plastics are the most commonly used materials due to their versatility and cost-effectiveness. However, as the demand for 3D printed plastic parts increases, so does the need to understand the strength and durability of these parts. This comprehensive guide will delve into the world of 3D printed plastic to answer the question ‘how strong is 3D printed plastic?’, exploring the different types of plastics used, factors that affect their strength, techniques to improve their strength, and a comparison to traditional manufacturing methods. By the end of this article, you will have a deep understanding of the strength of 3D printed plastics and how to make the most of this innovative technology.

Types of Plastic Used in 3D Printing

Today, there are many plastic materials adapted for 3D printing technologies, each with its unique set of properties and applications. To understand the strength of 3D printed plastic, it is essential to familiarize yourself with the various types of plastics commonly used in the industry. This section will discuss three widely-used plastics: PLA, ABS, and PETG, providing insights into their properties, common applications, and how their strength and durability compare.

PLA (Polylactic Acid)

Polylactic acid, or PLA, is a biodegradable thermoplastic derived from renewable resources such as corn starch, sugarcane, or tapioca. It is one of the most popular materials for 3D printing due to its ease of use, low cost, and environmental friendliness. PLA exhibits a low melting point, typically around 200-220°C, which makes it suitable for printing on most consumer-grade 3D printers without requiring a heated bed.

In terms of strength and durability, PLA is considered a relatively strong material, but it has some limitations. While it can be stiff and strong, with a tensile strength of 50 MPa, it is also more brittle than other materials such as ABS or PETG.[1] This brittleness can lead to parts breaking under stress or impact, which may not be suitable for applications requiring high mechanical strength or resistance to impact. 

Common uses for PLA in 3D printing include prototypes, decorative objects, and low-stress functional parts. Its biodegradability makes it an excellent choice for environmentally-conscious projects, but it should be noted that its degradation can be slow and may require industrial composting facilities to break down efficiently. When considering the strength of PLA, it's essential to weigh its advantages and limitations against the requirements of the specific application for which it is being used.

Recommended reading: PLA bed temperature & print temperature settings

ABS (Acrylonitrile Butadiene Styrene)

Acrylonitrile Butadiene Styrene, or ABS, is a widely-used thermoplastic in both traditional manufacturing and 3D printing. It is known for its durability, high impact resistance, and overall strength, making it a popular choice for functional parts and prototypes. ABS is a petroleum-based plastic, that requires a high temperature for printing (typically between 220-250°C). ABS also often requires a heated bed (between 95–110 °C) when 3D printing to prevent warping and improve layer adhesion.

One of the significant advantages of ABS over PLA is its improved flexibility and impact resistance. The material has a superior elongation at break than PLA as well as higher flexural strength, meaning it can better withstand bending forces.[2] These properties make ABS more suitable for applications that require mechanical strength and resilience, such as automotive components, enclosures, and toys. ABS also has better heat resistance and chemical resistance, making it an ideal choice for applications that might be exposed to chemicals or harsh environments.

However, ABS is not without its drawbacks. Its higher printing temperature and the need for a heated bed can make it more challenging to print, particularly for hobbyists. Additionally, ABS produces fumes during printing, so it is prudent to use the material in spaces with proper ventilation and to use an enclosed printer with a filtration system. Overall, ABS offers a robust and durable option for 3D printed plastic, but careful consideration should be given to its printing requirements and potential drawbacks.

Recommended reading: ABS print temperature considerations: Nozzle, bed, enclosure

The material properties of each type of filament will give users an indication of the tensile strength of final printed parts

PETG (Polyethylene Terephthalate Glycol)

Polyethylene Terephthalate Glycol, or PETG, is a thermoplastic that combines the best qualities of both PLA and ABS, making it an increasingly popular choice for 3D printing. PETG is a glycol-modified version of PET, which is commonly used to make plastic bottles and food packaging. The glycol modification results in improved flexibility, shock resistance, and temperature resistance compared to standard PET.

PETG offers a balanced combination of strength, flexibility, and ease of printing. Its printing temperature typically falls between 220-260°C, similar to ABS, but it does not produce unpleasant fumes during the printing process. PETG also demonstrates excellent layer adhesion and reduced warping, making it easier to print large or complex parts.

The strength and durability of PETG make it suitable for a wide range of applications, from prototypes to functional parts. It is particularly well-suited for applications that require a combination of strength and flexibility, such as snap-fit joints, hinges, and enclosures. 

PETG provides a versatile and robust option for 3D printed plastic parts, offering a balance between the desirable properties of both PLA and ABS. Its growing popularity, particularly in the packaging and manufacturing segments, is a testament to its ability to cater to various applications requiring strength, durability, and flexibility.

Recommended reading: PETG temperature considerations: Nozzle temperature, heated bed & cooling

Factors Affecting the Strength of 3D Printed Plastic

While the type of plastic material used in 3D printing plays a crucial role in determining the strength of the final product, several other factors also influence the overall strength and durability of 3D printed parts. Understanding these factors is essential for optimizing the printing process to create parts with the desired mechanical properties. In this section, we will discuss three primary factors that affect the strength of 3D printed plastic: printing temperature, print orientation, and infill patterns.

Printing Temperature

The choice of printing temperature can greatly affect the strength of 3D printed plastic parts. The optimal temperature varies depending on the type of plastic being used, and finding the right settings is essential for achieving strong layer adhesion and minimizing print defects.

If the printing temperature is too low, the plastic filament will not melt sufficiently to form a strong bond between layers. Low temperatures can result in weak parts that are prone to delamination or breakage under stress. If the print temperature is too high, the plastic will melt too quickly, resulting in oozing and stringing out of the hot end. The deposited filament will also take longer to cool, which can lead to deformed prints.

To find the optimal printing temperature for a specific material, consult the instructions provided by the brand of filament you are using. Another way to determine the best print temperature is to perform a temperature tower test. This test involves printing a vertical tower, with each segment printed at a different temperature. This experiment allows you to observe the differences in layer adhesion, surface quality, and overall strength. By comparing the results, you can determine the ideal printing temperature for your filament, which will help ensure the maximum strength and durability of your 3D printed parts.

Layer Height and Line Width

Layer height and line width can also impact the strength of 3D printed plastic parts. Layer height, also known as layer thickness, refers to the vertical distance between each printed layer. This setting, which is chosen in slicer software, has a direct impact on the overall strength of the printed part, as well as its surface quality and print time.

A smaller layer height typically results in a smoother surface finish and more detailed parts, but it also increases print time. A larger layer height allows for faster printing, because the nozzle has to deposit fewer layers total. However, a larger layer height can produce a rougher surface finish is less suitable for printing small features or details. 

In terms of strength, parts printed with smaller layer heights generally exhibit better layer adhesion, leading to stronger and more durable parts. In general, it’s advisable to choose a layer height that corresponds to between 25% and 75% of the 3D printer nozzle diameter.

Line width, which is related to the nozzle diameter size, can also influence the strength of 3D printed parts. Thicker lines (>nozzle diameter) can provide stronger parts due to the fact that there is more plastic for each layer to bond to. On the flip side, a bigger line width will also result in less definition. A thinner line width may produce more detailed parts with greater dimensional accuracy, but may not provide the same level of strength. For the best print results in terms of strength, it is key to strike a balance between layer height, line thickness, and print time that best suits your specific application.

Infill Pattern and Density

Another important consideration when talking about the strength of 3D printed plastic parts is infill pattern and infill density. Typically, 3D printed components are not fully solid to save on material and minimize part weight. Infill refers to the internal structure of the printed part, which can consist of a repeating lattice-like pattern. Generally speaking, the infill provides support and strength to the part’s external shell. The infill pattern and density can be adjusted in a slicer software to control the part's weight, strength, and material usage.

There are several different infill patterns to choose from, each with its unique characteristics. Common patterns include grid, honeycomb, and cross, among others Some patterns, such as the honeycomb or gyroid, provide greater strength and resistance to deformation due to their more complex geometries. However, these more intricate patterns may also take longer to print and use more material compared to simpler patterns like grid.

The choice of infill pattern and infill density will have a direct impact on part strength

Infill density refers to the percentage of the part's internal volume filled with material. A hollow part, for example, would have an infill density of 0%, while a solid part would have an infill density of 100%. A higher infill density results in a heavier and stronger part, but it also increases material usage and print time. Conversely, a lower infill density reduces material usage and print time but may produce a weaker part that is more susceptible to breakage or deformation. Infill density can also influence a print’s modulus and elongation. [3]

To achieve the desired strength and durability for your 3D printed plastic parts, it is crucial to carefully consider the infill pattern and density. By selecting the appropriate pattern and density for your specific application, you can optimize the strength, weight, and material usage of your printed parts.

Recommended reading: Cura infill patterns: What are they and when to use them

Techniques to Improve the Strength of 3D Printed Plastic

While the inherent properties of different polymers play a significant role in determining the strength of 3D printed parts, there are additional techniques that can be employed to enhance the mechanical properties of these parts. These methods can help overcome the limitations of 3D printing processes and produce parts with improved strength, durability, and stress resistance. In this section, we will explore techniques that can be used to improve the strength of 3D printed plastic parts: annealing, coatings, and fiber reinforcement.

Annealing

Annealing is a heat treatment process commonly used in traditional manufacturing to improve the mechanical properties of materials, including plastics.[4] In the context of 3D printing, annealing involves heating the printed part to around its glass transition temperature (which is lower than its melting temperature). At this temperature, the material is not yet melting or losing its structure, but is softened, allowing for the material's internal structure to reorganize, relieving residual stresses and improving its strength, stiffness, and dimensional stability.

Here are the steps to perform annealing on a 3D printed plastic part:

1. Place the part in a temperature-controlled oven or chamber.

2. Set the temperature to a value between the material's glass transition temperature and its melting point. The specific temperature and duration will depend on the type of plastic used.

3. Allow the part to heat for between half an hour to an hour, then gradually cool it back to room temperature.

Annealing can cause some dimensional changes in the part, so it may be necessary to account for these changes in the design process. Using 100% infill can help to maintain the part’s dimensional accuracy. Additionally, different plastic materials will have different annealing requirements, so it is important to research the specific material you are using to determine the optimal annealing conditions.

Coatings

Applying coatings to a 3D print can also improve the strength of final plastic parts. This process involves applying a protective shell or coating to the printed part’s surface, effectively shielding it from external stresses and increasing its overall durability.

There are various materials that can be used to coat 3D prints, including epoxy resins, polyurethane coatings, and thermoplastic films. The choice of coating material will depend on the specific application and desired properties. In general, the coating process involves the following steps:

1. Prepare the coating according to the manufacturer's instructions.

2. Apply the material to the surface of the 3D printed part, ensuring complete and even coverage. This can be done through methods such as brushing, spraying, or dipping.

3. Allow the encapsulation material to cure or harden, following the manufacturer's recommended cure times and conditions.

Applying a coating can not only enhance the strength of the 3D printed part, but can also provide other benefits, such as improved chemical resistance, enhanced UV protection, and better resistance to wear and abrasion. Before applying a coating to your 3D print, ensure that the coating material is compatible with the 3D print material. 

Fiber Reinforcement

Fiber reinforcement is not so much a technique, but a type of 3D printing material that integrates high-strength fibers, such as carbon or glass, into a polymer matrix to enhance the mechanical properties of the printed part. The addition of these fibers results in a composite material that has superior part strength, stiffness, and durability. Ultimately, fiber reinforced materials can make parts suitable for demanding applications.

There are two primary ways to benefit from fiber reinforcement when it comes to FDM 3D printing:

1. Composite Filaments: These are specially engineered filaments that are made up of a plastic matrix reinforced with fibers, such as carbon fibers or fiberglass. When used in the printing process, these filaments produce parts with improved mechanical properties compared to those made from standard (aka neat) plastic filaments. Popular composite filaments include carbon fiber-reinforced PLA, ABS, and PETG, among others.

2. Continuous Fiber Reinforcement: This method involves embedding continuous fibers directly into the printed part during the printing process. There are specialized 3D printers designed to handle continuous fibers, laying them down alongside the plastic filament to create parts with exceptional strength and stiffness. This technique is more complex and requires dedicated equipment, but it can produce parts with mechanical properties that rival those of traditional manufacturing methods.

Fiber reinforcement is an effective method for improving the strength and durability of 3D printed plastic parts. Not all desktop 3D printers can process fiber reinforced 3D printing filament, and those that can require a hardened steel nozzle to withstand the extra abrasion of the filled materials.

The right print settings, materials, and post-processing techniques can all improve how strong a final component is.

Strength Comparison: 3D Printed Plastic vs. Traditional Manufacturing Methods

There’s no question that 3D printing offers several advantages compared to traditional manufacturing processes in terms of design freedom and rapid prototyping. But how do 3D prints compare to traditionally made part in terms of strength? In this section, we’ll provide an overview of the strength of 3D printed plastic parts compared to that of components made using injection molding and CNC machining. Understanding the differences in strength between these methods can help you make informed decisions when selecting the most appropriate manufacturing technique for your specific application.

Injection Molding

Injection molding is a manufacturing process used to mass produce plastic parts. In this process, molten plastic is injected into a mold cavity, which is then cooled until it is solid. The part is then removed and finished using various post-processing methods if required. Injection molding is known for producing parts with high strength, tight tolerances, and excellent surface finishes.

Compared to 3D printed plastic parts, those produced through injection molding tend to exhibit higher strength and better mechanical properties. This difference is primarily due to the continuous nature of the material in injection-molded parts, which minimizes the presence of layer lines and weak points. Additionally, the injection molding process subjects the material to high pressure, promoting better adhesion between the plastic molecules and resulting in a more homogeneous structure.

That said, it is important to note that advancements in 3D printing technology and the techniques mentioned earlier, such as annealing, coatings, and fiber reinforcement, have significantly narrowed the strength gap between 3D printed and injection-molded parts. While injection molding may still offer superior strength in many cases, 3D printing can produce parts with adequate strength for a wide range of applications, especially when these techniques are used. 3D printing can also be a more cost efficient process for producing smaller batches of parts. 

CNC Machining

CNC (Computer Numerical Control) machining is a subtractive manufacturing method used to create plastic parts with high precision and excellent surface finishes. In this process, a computer-controlled cutting tool removes material from a solid plastic block (called a blank) to create the desired part. CNC machining is often used for producing complex parts with tight tolerances and is especially suitable for low- to medium-volume production.

CNC machined parts are typically made from solid plastic blocks, which results in a continuous and homogenous material structure. This characteristic translates to higher overall strength compared to 3D printed parts, which are built layer by layer and can be more susceptible to weaknesses along the layer lines.

Similar to the comparison with injection molding, advancements in 3D printing technology have narrowed the strength gap between 3D printed and CNC machined parts. The right print parameters, materials, and post-processing can significantly improve the strength and durability of 3D printed plastic components, making them more competitive with CNC machined parts in terms of mechanical properties.

It is also worth noting that CNC machining can be more time-consuming and costly than 3D printing, especially for complex geometries and low-volume production. As a result, choosing between these manufacturing methods should be based on a comprehensive evaluation of factors such as required strength, part complexity, production volume, and cost considerations.

Conclusion

In this article, we explored the strength of 3D printed plastic parts and discussed various factors that can influence their mechanical properties. We examined the different types of plastic materials commonly used in 3D printing, such as PLA, ABS, and PETG, and highlighted their unique characteristics. We also looked into factors affecting the strength of 3D printed parts, including printing temperature, layer height, and infill pattern and density. We also discussed several techniques to improve the strength of 3D printed plastic parts, including annealing, coatings, and fiber reinforcement.

A comparison of the strength of 3D printed plastic parts to those produced using traditional manufacturing methods like injection molding and CNC machining reveals that, while there are inherent differences in strength, recent advancements in 3D printing technology have narrowed the gap. By employing the appropriate materials, settings, and techniques, it is possible to create 3D printed parts with strength comparable to those produced using conventional methods.

Ultimately, understanding the factors affecting the strength of 3D printed plastic parts and knowing how to optimize them can help you to design and print parts that meet the strength requirements of specific applications.

Frequently Asked Questions

Q: How does the strength of 3D printed plastic parts compare to those produced using traditional manufacturing methods like injection molding and CNC machining?

A: While 3D printed parts may have lower strength than injection-molded or CNC-machined components, recent advancements in 3D printing technology have significantly improved the strength of 3D printed plastic parts. By using the proper materials, settings, and post-processing, it is possible to create 3D printed parts with strength comparable to those produced using traditional methods.

Q: What factors affect the strength of 3D printed plastic parts?

A: Several factors can influence the strength of 3D printed plastic parts, including the type of plastic material used, printing temperature, layer height, infill pattern and density, and post-processing techniques.

Q: How can I improve the strength of 3D printed plastic parts?

A: Annealing, coating, and fiber reinforcement can be employed to enhance the strength of 3D printed plastic components. Additionally, using the optimal print settings, like temperature, layer height, and infill pattern, can further improve part strength.

Q: Can 3D printed plastic parts be used in load-bearing applications?

A: Depending on the material, print settings, and techniques used, 3D printed plastic parts can exhibit sufficient strength for many load-bearing applications. However, it is essential to evaluate the specific requirements of your application and consider factors like material properties, part geometry, and loading conditions to determine the suitability of 3D printed parts.

Q: Which type of plastic material should I use for my 3D printed part?

A: The choice of plastic material depends entirely on the desired mechanical properties. Common materials like PLA, ABS, and PETG offer different levels of strength, durability, and flexibility. Other materials, like engineering-grade filaments and fiber-reinforced composites can offer superior strength, but can be more challenging to print. In the end, it’s vital to evaluate your specific application requirements and select the material accordingly.

References

[1] What is PLA: Everything you need to know [Internet]. TWI Global, 2023. Available from: https://www.twi-global.com/technical-knowledge/faqs/what-is-pla 

[2] 3D printing with PLA vs. ABS: What's the difference? [Internet]. Hubs, 2023. Available from: https://www.hubs.com/knowledge-base/pla-vs-abs-whats-difference/ 

[3] Johnson GA, French JJ. Evaluation of infill effect on mechanical properties of consumer 3D printing materials. Advances in Technology Innovation. 2018 Oct 1;3(4):179. Available from: https://core.ac.uk/download/pdf/228834597.pdf 

[4] Valvez S, Silva AP, Reis PN, Berto F. Annealing effect on mechanical properties of 3D printed composites. Procedia Structural Integrity. 2022 Jan 1;37:738-45. Available from: https://doi.org/10.1016/j.prostr.2022.02.004