How Strong Are 3D Printed Parts? A Comprehensive Analysis

Introduction

3D printing has emerged as a transformative technology, creating a new paradigm in the manufacturing and design industry. The strength of 3D printed parts is a key consideration in determining the suitability of this technology for various applications. It's essential to explore how strong these components are and what factors contribute to their robustness. This exploration reveals insights that can guide the optimization of 3d printing materials and parameters to enhance the durability of the printed parts. Ultimately, understanding the strength of 3D printed parts is critical to harnessing the full potential of this technology.

Understanding 3D Printing

3D printing, also known as additive manufacturing, has drastically transformed the manufacturing landscape. Unlike traditional manufacturing processes, which involve subtracting or carving out material from a larger block, 3D printing builds objects from the ground up, layer by layer, adding material where needed. This shift in methodology allows for unparalleled design freedom and complex geometries, opening the door to myriad applications, from rapid prototyping to customized products and even large-scale manufacturing.

What is 3D Printing?

At its core, 3D printing is a process where a digital 3D model is turned into a physical object. The digital model is first created using Computer-Aided Design (CAD) software or through a 3D scanner in the case of recreating an existing object. Once the 3D model is ready, it's then sliced into hundreds or even thousands of horizontal layers through specialized software. These layers are then fed to a 3D printer, which reads them and prints the object layer by layer, using a variety of materials such as plastics (ABS, PLA, PETG, etc), resins, metals, or even ceramics, depending on the type of 3D printer used.

Complex geometries can be manufactured easily with 3D Printing

A range of 3D printing technologies exist, with the most common being Fused Deposition Modeling (FDM), Stereolithography (SLA), and Selective Laser Sintering (SLS). FDM printers work by extruding a thin filament of thermoplastic material layer by layer. In contrast, SLA printers use a light source to solidify a photopolymer resin layer by layer. SLS printers, on the other hand, use a laser to sinter powdered material, binding it together to form a solid structure. Each of these technologies has its advantages, limitations, and ideal use cases, with strength characteristics varying across the different methods and materials.

The Growth of 3D Printing

The growth of the 3D printing industry has been exponential over the past decade. According to Statista, the global market for 3D printed products and services is expected to surpass $40 billion by 2024, up from $12 billion in 2020. This rapid growth can be attributed to advancements in 3D printing technologies, the increasing availability of diverse printing materials, and falling costs of 3D printers and materials.

As 3D printing technology continues to evolve, it's being embraced across a broad range of industries, from aerospace and automotive to healthcare and construction. In the aerospace industry, for instance, 3D printing has been instrumental in manufacturing lightweight components that can withstand extreme conditions. Airbus, for example, reported using over 1,000 3D printed parts in their A350 XWB aircraft, contributing to significant fuel savings.

Similarly, the automotive industry has been leveraging 3D printing to manufacture complex parts and prototypes rapidly. Companies like BMW and Ford have integrated 3D printers into their production processes, reducing development time and cost. In the healthcare sector, 3D printing has opened up new possibilities, such as creating customized prosthetics, dental implants, and even bioprinting tissues and organs for transplants.

Furthermore, 3D printing has empowered individuals and small businesses by enabling them to manufacture customized products and prototypes at relatively low costs, effectively democratizing manufacturing. The proliferation of online platforms that provide 3D printing services has made this technology accessible to virtually anyone, anywhere. These platforms allow users to upload their designs, select the material of their choice, and have the printed object shipped to them.

This wide-ranging application and growth of 3D printing have invariably increased the focus on the quality of 3D printed parts, particularly their strength, given that these parts are now being used in critical applications where failure is not an option. As such, understanding how strong 3D printed parts are and what factors influence their strength has become even more crucial than ever.

Recommended Reading: Types of 3D Printing Techniques 

Components of 3D Printed Parts

The strength and durability of 3D printed parts are determined by a combination of factors. These factors include the type of material used, its melting point and tensile strength, the printing technology, the design of the part, and the print settings. Each of these aspects contributes to the overall strength and robustness of the final printed part, making it vital to understand each of them when discussing the strength of 3D printed parts.

Types of Materials Used in 3D Printing

Material choice significantly influences the strength of a 3D printed part. Several materials can be used in 3D printing, each having distinct properties that can affect the strength and durability of printed parts.

Plastics are the most common materials used in 3D printing, particularly in Fused Deposition Modeling (FDM). The most commonly used plastics include ABS (Acrylonitrile Butadiene Styrene) and PLA (Polylactic Acid). ABS is known for its high strength, flexibility, and temperature resistance, making it suitable for creating durable parts that can withstand physical stress. PLA, on the other hand, is more rigid and brittle but is popular due to its lower melting point which makes it easy to print Additionally, PLA has lower warping tendencies, and is also biodegradable.

Plastic Filaments for 3D Printer

Polymers and Resins are typically used in Stereolithography (SLA) and Digital Light Processing (DLP) 3D printing. These materials are known for their high detail resolution and smooth surface finish. Polymers are frequently used in 3D printing because of their cost-effectiveness, convenience of use, and design versatility. However, they tend to be more brittle than plastics used in FDM. Generally speaking, a polymer's chemical makeup, polymer structures, and degree of curing all affect its mechanical, physical, and chemical characteristics.

Metals are used in more advanced 3D printing methods such as Direct Metal Laser Sintering (DMLS) and Selective Laser Melting (SLM). Metal 3D printing can produce parts with strength and durability comparable to traditionally manufactured metal parts. However, due to such rigid and durable parameters, 3d printers require specialized hardened steel extruder nozzles and the temperature between 190 °C and 220 °C to print with metal filaments.  Commonly used metals include stainless steel, titanium, and aluminum, each with their distinct properties. 3D printing with metal has several applications in industries such as aerospace, engineering, medical, etc.

3D Metal Printing using DMLS Technique

Ceramics are used less frequently due to their challenging printing process, but they offer unique properties like heat resistance and hardness.

The material used significantly influences the strength of the final part, but it's only one piece of the puzzle. The printing technology, design, and print settings also play crucial roles in determining how strong 3D printed parts are.

Understanding the Strength of 3D Printed Parts

The strength of 3D printed parts is a complex subject, influenced by numerous factors. It's not solely reliant on the materials used but is also determined by the printing process, the design of the part, and post-processing treatments. Before diving into the specifics, it's essential to note that the strength of a 3D printed part refers to its ability to withstand forces or stress without breaking or deforming. Now let's consider the factors that influence the strength of a 3D Print:

Material Selection

 As discussed earlier, the material used in 3D printing significantly influences the final part's strength. Different materials have different mechanical properties, such as tensile strength, flexibility, and hardness, which define how they behave under stress. For example, PLA material can reach up to the yield strength of 66 MPa, while the structural stiffness of titanium alloy printed parts can go up to 659 MPa.

Printing Parameters 

Parameters like layer height, infill density, print speed, and temperature have a substantial effect on the part's strength. For instance, higher infill densities can increase the part's strength, but they also increase the print time and material usage. 

• The layer height plays a crucial role in determining the strength of the printed part. Generally, lower layer heights result in stronger parts because the layers have better adhesion to each other, creating a more solid and unified structure. However, lower layer heights also increase the print time and can lead to more noticeable printing errors if the printer isn't properly calibrated.

Recommended Reading: Nozzle Diameter and Layer Height Explained 

• Infill density and pattern are critical aspects to consider. The infill density refers to the percentage of the interior volume of the print that is filled with material. Higher infill densities result in stronger, but also heavier and more material-intensive parts. The infill pattern, or the geometrical shape that the infill takes, also impacts the strength. Patterns like grid, triangle, or honeycomb can offer more strength than others.

Recommended Reading: What are Infill Percentages in 3D Printing 

• The print speed also influences the strength of 3D printed parts. Printing too fast can result in poor layer adhesion, leading to weaker parts. On the other hand, printing too slowly can cause overheating, which may deform the part and reduce its strength.
• Temperature settings can significantly impact the quality and strength of the printed part. The ideal temperature settings can vary depending on the type of material used. For instance, ABS generally requires a higher temperature around 240°C - 270°C compared to PLA which can be printed at a temperature around 210 °C. Proper temperature ensures good flow and adhesion of the material, which is essential for creating strong parts.

It's clear that the strength of 3D printed parts is a multifaceted issue. Careful selection and adjustment of printing parameters can greatly enhance the strength and durability of the final product. 

Part Design

 The design of the part itself plays a crucial role in its strength. Elements such as the part's geometry, orientation during printing, and the inclusion of specific design features can all affect the printed part's ability to withstand stress. Inclusion of ribs and redundant topological areas increase the factor of safety of the part. It is generally recommended to conduct an CAE Analysis on the part or assembly to understand the forces and deformations a part may undergo when subject to the stresses of its intended application.

Post-Processing

Post-processing treatments, such as heat treating or chemical smoothing, can enhance the strength of 3D printed parts. Some post-processing techniques can increase the overall tensile strength by a maximum of 56%. However, these processes should be used judiciously as they can also introduce stresses or alter the part's dimensions if not correctly applied.

Recommended Reading: Post Processing 3D Prints 

Post Processing of a 3D Printed Model

In conclusion, maximizing the strength of the 3D printed parts is not just a matter of choosing the right material but also involves optimizing the printing parameters, designing the part effectively, and potentially applying post-processing treatments.

Comparing Strength of 3D Printed Parts with Traditional Manufacturing

The strength of 3D printed parts, as compared to traditionally manufactured parts, tends to be a topic of interest in manufacturing circles. In comparison to traditional manufacturing methods such as injection molding or CNC machining, 3D printing exhibits some unique strengths and weaknesses.

Starting with materials, in traditional manufacturing methods, the material properties are consistent and isotropic, meaning they're identical in all directions. In contrast, the strength of 3D printed parts can be anisotropic, primarily due to the layer-by-layer printing process. This anisotropy means that a 3D printed part's strength may vary based on the direction of the applied force relative to the printed layers.

For instance, parts printed using Fused Deposition Modelling (FDM) tend to be weaker along the Z-axis (the build direction) due to the layer adhesion process. In contrast, parts made using injection molding have uniform strength in all directions, as the material is formed in a single process under high pressure. However, there still seems to be some disparities in overall strength parameters, for example, traditional manufacturing technique using titanium alloy tends to outperform with a compressive strength of 1070 MPa against 3d printed procedure yielding only 659 MPa of strength. 

One area where 3D printing often surpasses traditional manufacturing in strength is when complex, optimized structures are required. Advanced techniques such as generative design allow for the creation of structures that are not only lighter but also stronger than their traditionally manufactured counterparts. These structures, often inspired by natural forms, are impossible to manufacture using conventional methods.

In terms of materials used, traditional manufacturing can often access a broader range of high-strength materials, such as high-grade steels or exotic alloys. However, the spectrum of materials available for 3D printing is continually expanding, with high-performance plastics, metals, and even composites now being printable.

Lastly, post-processing methods can have a significant impact on the strength of a part. Heat treatments, for instance, are commonly used in both traditional manufacturing and 3D printing to enhance part strength. However, each method may have specific treatments that are unique to it, such as chemical smoothing for 3D printed parts, which can cause an increase of about 50% in strength by reducing surface flaws and irregularities.

In conclusion, while traditionally manufactured parts often have a higher baseline for strength, 3D printing offers unique advantages that can lead to stronger parts in specific scenarios. The nuanced understanding of these factors allows engineers to select the best manufacturing method for their specific requirements.

Testing the Strength of 3D Printed Parts

Methods of Testing

Assessing the strength of 3D printed parts involves applying various testing methods, each providing different insights into the mechanical properties of the material. Different types of testing methods provide a comprehensive understanding of how the part might behave under real-world conditions.

One of the most common methods is the tensile test. In this method, a sample is subjected to an increasing uniaxial force until it breaks. The resulting stress-strain curve provides critical data, including yield strength, tensile strength, and elongation at break. For 3D printed parts, this test can be particularly informative when performed in different directions relative to the print layers to assess anisotropic strength properties.

Tensile Testing Apparatus

Another common method is the compression test, which applies a compressive force to the sample. This test provides similar data to the tensile test but in compression rather than tension. It's particularly useful for materials and designs expected to experience compressive loads in their application.

Impact tests, like the Izod or Charpy tests, measure the material's toughness, its ability to absorb energy during fracture. These tests involve swinging a pendulum to strike a notched sample and measuring the energy absorbed in breaking the sample. The toughness of 3D printed parts can depend heavily on the print parameters, especially layer height and print orientation.

A hardness test, such as the Rockwell or Brinell hardness tests, measures the resistance of the material to localized plastic deformation. For 3D printed parts, hardness can provide insight into how the part might resist wear or scratching in service.

Conducting the Brinell Hardness Test 

Lastly, fatigue tests are essential for parts expected to undergo repeated loading over their service life. These tests subject the sample to cyclic loading at various stress levels until failure occurs. The number of cycles to failure at each stress level is used to construct an S-N curve (Stress vs Number of cycles), providing crucial data for predicting the part's lifetime.

Each testing method has specific requirements for the sample's shape and size, and standards organizations such as ASTM and ISO provide detailed guidelines for preparing and conducting these tests. Proper application of these testing methods can ensure the 3D printed parts will perform as expected in their intended application.

Interpreting the Test Results

Interpreting the results of strength testing of 3D printed parts requires a solid understanding of the underlying principles of materials science and mechanical engineering, along with the specifics of 3D printing technology.

Tensile Test Results

In a tensile test, the stress-strain curve generated will typically exhibit an elastic region where the material deforms linearly with applied stress, and a plastic region where permanent deformation occurs. The point at which the material transitions from elastic to plastic deformation is known as the yield strength. This value is crucial as it signifies the stress level beyond which a part will be permanently deformed.

Beyond the yield strength, the material continues to deform plastically until it eventually breaks. The maximum stress achieved on the stress-strain curve is the tensile strength, indicating the maximum stress that the material can withstand before breaking. 

Compression Test Results

Compression test results are interpreted similarly to tensile tests, but they provide information about the material's behavior under compressive stress. Some materials exhibit different properties under tensile and compressive loads, and this can also be true for 3D printed parts due to their anisotropic nature.

Impact Test Results

Impact tests provide a measure of toughness, the energy absorbed by the material before breaking. A high toughness indicates that a material can absorb more energy before failure, making it better suited to applications involving impact or shock loading.

Other Test Results

Hardness tests measure the resistance of the material to localized deformation. A higher hardness implies greater resistance to wear and scratching. For 3D printed parts, the hardness can be influenced by factors such as the print temperature and the layer height.

Fatigue test results are typically presented as an S-N curve, plotting the stress amplitude against the number of cycles to failure. This curve allows engineers to estimate the lifespan of a part under cyclic loading.

Each of these tests provides a piece of the overall picture of a 3D printed part's mechanical performance. Interpreting the results requires not only understanding these mechanical properties but also considering how the 3D printing process influences these properties. The layer orientation, print temperature, layer height, and other printing parameters can significantly affect the strength of the printed part.

Improving the Strength of 3D Printed Parts

Strategies for Increasing Strength

Increasing the strength of 3D printed parts is an area of active research and development, as improved strength can enhance the functional capabilities of these parts in various applications. Several strategies are often employed in the pursuit of this goal, many of which are deeply intertwined with the unique characteristics of 3D printing technology. Some of these strategies are listed below:

• A primary strategy involves the careful selection and manipulation of printing materials. For instance, manufacturers might select filaments made from high-strength plastics such as polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), or polycarbonate (PC). Researchers have also been exploring the use of composite materials, which blend plastic with materials such as carbon fiber, glass fiber, or metal particles, resulting in significant enhancements in strength.

• The optimization of printing parameters is another powerful strategy for improving strength. Key parameters include the extrusion temperature, print speed, layer height, and infill density. For instance, the extrusion temperature must be precisely controlled to ensure optimal layer adhesion, with too low a temperature leading to poor bonding between layers and too high a temperature causing the material to degrade. A balance must be struck to achieve the best results. 

• Orientation of the part during printing can also play a critical role in determining its strength. Given the layer-by-layer nature of 3D printing, parts are often weaker along the build direction due to the presence of interlayer boundaries. Therefore, orienting the part such that the loads are applied perpendicular to these boundaries can enhance strength.

• Another strategy is the use of design for additive manufacturing (DfAM) techniques. These methods involve designing parts specifically for 3D printing, leveraging the unique capabilities of the technology such as complex geometry creation and topology optimization. Topology optimization involves designing the part's structure to distribute stresses effectively, thereby improving strength.

• Post-processing methods can also be employed to improve strength. These may include thermal treatments, such as annealing, which reduces internal stresses and increases layer adhesion. Chemical treatments can also be used, including solvent vapor smoothing, which can increase the strength of ABS parts by enhancing the surface bonding between layers.

All of these strategies highlight the depth of the knowledge and the range of skills required to harness the full potential of 3D printing technology in creating parts with high strength. They underscore the importance of understanding the interplay between materials, processing parameters, part design, and post-processing in determining the mechanical performance of 3D printed parts.

Case Studies of Strength Improvement

One notable case study comes from the automotive industry. The Italian supercar manufacturer Bugatti employed 3D printing to fabricate the brake caliper for their Chiron vehicle. The caliper, made from a titanium alloy, represents the world’s largest functional component produced from 3D-printed titanium. Through the use of 3D printing, Bugatti successfully reduced the weight of the component by 40% compared to its traditionally manufactured counterpart, while also increasing its strength. The titanium alloy's tensile strength stands at around 1250 MPa, significantly higher than the standard cast aluminum, typically 170-200 MPa.

Another case study comes from the realm of aerospace engineering. NASA has used 3D printing to manufacture components for rocket engines, which are subjected to extreme temperatures and pressures. In one project, NASA fabricated a copper alloy combustion chamber liner and nickel super-alloy jacket separately using 3D printing. These parts were then seamlessly joined together using a technique called hot isostatic pressing. The completed part displayed exceptional thermal and structural performance under engine testing conditions. NASA’s use of 3D printing allowed them to achieve a significant increase in strength and durability while also reducing production lead times and costs.

A further example can be seen in medical implant manufacturing. An orthopedic implant manufacturer, Amplify Additive, uses Electron Beam Melting (EBM) technology to 3D print acetabular cups for hip replacements. The porous structure of the implants, impossible to achieve with traditional manufacturing, promotes bone in-growth, leading to stronger, long-lasting implants. The EBM technology also allows for the use of high-strength titanium alloys with a yield strength of 795 MPa, much stronger than the commonly used stainless steel, typically 205 MPa.

The diversity of these case studies – spanning the automotive, aerospace, and medical industries – underscores the broad potential of 3D printing to improve the strength of components. By leveraging the inherent advantages of the technology, these organizations have achieved significant gains in part strength, enabling new levels of performance and functionality.

Conclusion

3D printing has emerged as a significant player in the manufacturing sector, offering the potential to produce parts with enhanced strength characteristics compared to traditional methods. The technology presents unique avenues for optimizing design and material selection, which can lead to more durable, lighter, and more effective parts. While challenges persist, innovative strategies and continual advancements in technology and materials promise to further improve the strength of 3D printed components. The potential of 3D printing to reshape how we create and innovate in the manufacturing world is vast and quite promising.

FAQs

1. What materials can be used for 3D printing to enhance part strength?
   
    Various materials can enhance part strength when used in 3D printing. These include but are not limited to: carbon fiber-reinforced materials, stainless steel, titanium, and high-performance thermoplastics like PEEK and ULTEM. The choice of material often depends on the specific application and the functional requirements of the part.
   
   

2. What are the common methods of testing the strength of 3D printed parts?
   
    Several methods are commonly used to test the strength of 3D printed parts. These include tensile testing, compressive testing, flexural testing, and fatigue testing. These tests provide essential information about how a part will behave under different types of loads and over time.
   
   

3. How can the strength of 3D printed parts be improved?
   
    There are several strategies to increase the strength of 3D printed parts. These include optimizing the print orientation, adjusting print parameters like infill density and pattern, utilizing post-processing techniques like annealing and hot isostatic pressing, and choosing a suitable material for the part's application.
   
   

4. How does the strength of 3D printed parts compare to traditionally manufactured parts?
   
    The strength of 3D printed parts can be comparable to, or in some cases greater than, that of traditionally manufactured parts. This largely depends on factors like the 3D printing technology used, the material chosen, and the design of the part. Certain characteristics of 3D printing, like the ability to create complex geometries and internal structures, can lead to improved part performance.
   
   

5. Can 3D printed parts be used in high-stress applications?
   
   Yes, 3D printed parts can be used in high-stress applications. Examples include components in aerospace, automotive, and medical industries. However, it's critical to ensure that the parts are designed, printed, and post-processed correctly to meet the demands of these high-stress environments.
   
   

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