Ensuring Powder Quality for Additive Manufacturing: A Look Inside Croom Medical’s Materials Lab

Croom Medical has been a pioneer in the development of metallic additive manufacturing within the SME orthopedic sector since 2010. Additive manufacturing (AM) has revolutionized the production of orthopedic implants, offering numerous advantages such as design freedom, reduced material waste, and improved customization capabilities. Laser Powder Bed Fusion (LPBF) is a popular AM technique for producing orthopedic joint replacement implants. However, the quality of the end product is highly dependent on the quality of the metal powders used in the process. In this blog post, we delve into Croom Medical’s materials lab to explore how we ensure powder quality for the LPBF process, discussing material selection, process parameter optimization, post-processing, quality control, and cost considerations.

Section 1: Material Selection and Properties

Selecting the right material for orthopedic implants is crucial to ensure the desired mechanical, chemical, and biological properties. The most common materials used in LPBF for orthopedic joint replacement implants are:

1. Titanium and its alloys (e.g., Ti-6Al-4V)
2. Stainless steels (e.g., 316L)
3. Cobalt-chromium alloys (e.g., CoCrMo)
4. Tantalum (e.g., Ta) Stay tuned to our blog post series for more information on this topic!

These materials offer a combination of biocompatibility, strength, corrosion resistance, and wear resistance, making them suitable for orthopedic applications.

To ensure the highest quality powders, it is essential to understand and control various material properties, including:

1. Optical properties
2. Rheological properties
3. Mechanical properties
4. Chemical properties
5. Metallurgical properties
6. Thermal properties
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Section 2: Powder Quality Evaluation and Control

In Croom Medical’s materials lab, we utilize various techniques to evaluate and control powder quality, including:

1. Particle size distribution analysis (e.g., using laser diffraction)
2. Particle morphology assessment (e.g., using scanning electron microscopy)
3. Powder flowability assessment (e.g., using the Hall flowmeter funnel)
4. Powder density measurements (e.g., using gas pycnometry)
5. Chemical composition analysis (e.g., using energy-dispersive X-ray spectroscopy)
6. Powder bed density assessment (e.g., using computed tomography)
7. Contamination analysis (e.g., using inductively coupled plasma mass spectrometry)
8. These evaluations help us identify any potential issues with the powder and ensure that the material properties are within the desired range for successful LPBF.
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Section 3: Powder Quality Monitoring at Croom Medical

In this section, we’ll discuss the key methods and instruments we employ to measure powder quality for the LPBF process at Croom Medical.

Particle Size Distribution:

The particle size distribution of the metal powder directly influences the LPBF process’s efficiency and the final part’s properties (Sames et al., 2016). At Croom Medical’s materials lab, we use laser diffraction particle size analyzers to accurately measure the size distribution of the powder (ISO 13320:2009). This method provides a rapid and reliable assessment of particle size and helps us ensure that the powder meets the specified requirements (FDA, 2021).

Particle Shape and Morphology:

The shape and morphology of the powder particles can impact the powder’s flowability and packing density (Gupta et al., 2017). We use scanning electron microscopy (SEM) to analyze the particle shape and surface features at high magnification (ASTM E3-11). This allows us to identify any irregularities, such as satellites or agglomerates, and ensure that the powder has the desired morphology for the LPBF process (FDA, 2021).

Chemical Composition:

Ensuring the correct chemical composition and purity of the metal powder is crucial for the final part’s performance and biocompatibility (Sames et al., 2016)[. We employ techniques like X-ray fluorescence (XRF) and inductively coupled plasma-optical emission spectroscopy (ICP-OES) to analyze the elemental composition of the powder (ASTM E1621-13). These methods help us detect any impurities or contaminants and confirm that the powder meets the required composition standards (FDA, 2021).

Flowability:

The flowability of the powder is essential for achieving consistent and uniform powder layers during the LPBF process (Gupta et al., 2017). In our materials lab, we use methods like the Hall flowmeter test and angle of repose measurement to evaluate the powder’s flowability (ASTM B213-17). These tests help us identify any issues related to poor flowability and ensure that the powder is suitable for the LPBF process (FDA, 2021).

Apparent and Tap Density:

The apparent and tap densities of the powder influence the packing density and porosity of the final part (Gibson, Rosen & Stucker, 2015). We use standardized methods, such as the gas pycnometer for apparent density (ASTM D5550-14) and the tap density tester for tap density (ASTM B527-18), to measure these properties. By monitoring the density values, we can ensure that the powder has the appropriate packing characteristics for the LPBF process (FDA, 2021).

Oxygen Content:

The oxygen content of the metal powder can affect the mechanical properties and corrosion resistance of the final part (Sames et al., 2016). We use techniques like inert gas fusion (IGF) to measure the oxygen content in the powder (ASTM E1019-18). By controlling the oxygen level, we can minimize thepotential adverse effects on the final part’s performance and ensure compliance with the relevant standards (FDA, 2021).

Metallurgical Properties:

The metallurgical properties of the metal powder, such as phase composition and microstructure, play a crucial role in determining the final part’s mechanical performance (Gibson, Rosen & Stucker, 2015). We use techniques like X-ray diffraction (XRD) to identify the phase composition (ASTM E572-18) and metallographic examination to analyze the microstructure (ASTM E3-11). These methods help us ensure that the powder has the desired metallurgical properties for the LPBF process (FDA, 2021).

Thermal Properties:

Thermal properties, such as melting point, specific heat capacity, and thermal conductivity, can impact the LPBF process’s stability and the final part’s performance (Gupta et al., 2017). We use techniques like differential scanning calorimetry (DSC) to measure the melting point and specific heat capacity (ASTM E1269-11), and laser flash analysis (LFA) to determine thermal conductivity (ASTM E1461-13). By understanding the powder’s thermal properties, we can optimize the LPBF process parameters and ensure the production of high-quality orthopedic implants (FDA, 2021).

Manufacturing Process Properties:

The manufacturing process used to produce the metal powder can also affect its quality and performance in the LPBF process (Gibson, Rosen & Stucker, 2015). We closely monitor and control the production of our powders, whether using gas atomization or water atomization, to ensure consistency and quality. This includes evaluating parameters like gas pressure, nozzle design, and cooling rates (ASTM B922-19). By optimizing the manufacturing process, we can produce high-quality powders tailored for the LPBF process (FDA, 2021).

Section 4: Process Parameter Optimization and Quality Control

Optimizing process parameters is crucial for ensuring the desired mechanical properties, surface quality, and dimensional accuracy of orthopedic implants produced using LPBF. At Croom Medical, we employ a systematic approach to optimize process parameters, including:

1. Laser power
2. Scan speed
3. Layer thickness
4. Hatch spacing
5. Gas flow rate

Optimizing these parameters helps minimize defects such as porosity, cracking, and warping, leading to higher-quality orthopedic implants. In addition, we implement robust quality control measures, such as in-process monitoring, non-destructive testing (e.g., X-ray or ultrasonic testing), and destructive testing (e.g., tensile or fatigue testing), to ensure the quality of our products [10].

Section 5: Post-Processing and Cost Considerations

Post-processing is an essential step in the production of orthopedic implants using LPBF. Common post-processing techniques include:

1. Support removal
2. Heat treatment
3. Surface finishing (e.g., polishing or blasting)
4. Sterilization

These post-processing steps help to enhance the mechanical properties, surface quality, and biocompatibility of the orthopedic implants. However, post-processing can also add significant costs to the production process. Therefore, it is crucial to optimize post-processing techniques to minimize costs while maintaining the desired product quality.

Cost considerations in LPBF include material costs, processing time, post-processing expenses, and quality control measures. By optimizing material selection, process parameters, and post-processing techniques, Croom Medical is able to produce cost-effective orthopedic implants using LPBF, while ensuring the highest quality standards.

Section 6: Quality Control and Regulatory Compliance

Quality control is a critical aspect of the production process for orthopedic implants. Croom Medical follows stringent quality control measures to ensure that the produced implants meet the required industry standards, as well as customer and regulatory requirements. Some of the key quality control measures include:

1. Powder quality control: As discussed earlier, Croom Medical uses a range of techniques to evaluate and ensure the quality of the metal powders used in the LPBF process.
2. In-process monitoring: During the LPBF process, Croom Medical employs in-process monitoring techniques to ensure that the process parameters are maintained within the specified range, and any deviations are promptly addressed.
3. Post-processing quality control: After the LPBF process, Croom Medical performs a series of inspections and tests on the produced implants to ensure that they meet the required specifications, including dimensional accuracy, surface finish, and mechanical properties.
4. Documentation and traceability: Croom Medical maintains detailed records of the production process, including material lot numbers, process parameters, and quality control data. This ensures traceability and facilitates compliance with regulatory requirements.

Croom Medical is also committed to complying with regulatory requirements, including those set by the FDA and other international regulatory bodies. To achieve this, the company follows the guidance provided by these regulatory bodies, including the FDA’s “Technical Considerations for Additive Manufactured Medical Devices” .

Section 7: Material Handling in a Manufacturing Environment

Material Storage and Contamination Control

When dealing with high-quality powders for LPBF, proper material storage and contamination control are crucial to maintaining the powder’s properties. The following practices help ensure that the powder’s integrity is maintained throughout the manufacturing process:

• Store powders in airtight containers with moisture-resistant seals.
• Store containers in a temperature- and humidity-controlled environment to prevent condensation and degradation of the powder.
• Keep storage areas clean and free of contaminants such as dust, dirt, and moisture.
• Implement a traceability system to monitor powder usage and maintain quality control.
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Material Recycling and Reuse

One of the advantages of LPBF is the ability to recycle and reuse excess powder material. However, it is essential to have a robust process in place to ensure that the recycled powder maintains its quality:

• Regularly analyze the recycled powder to monitor changes in properties and particle size distribution.
• Establish a recycling protocol that defines the maximum number of recycling cycles allowed before powder quality is compromised.
• Develop a method to blend new and recycled powders in a controlled manner to ensure consistent material properties.

Stay tuned to our blog post series for more information on this topic!

Material Handling Equipment and Safety

Handling and transporting powders within the manufacturing environment requires specialized equipment and adherence to safety protocols:

• Utilize vacuum conveyance systems to minimize powder contact with oxygen, reducing the risk of contamination and oxidation.
• Use glove boxes or other controlled environments when transferring powders between containers or machines.
• Equip operators with proper personal protective equipment (PPE) such as respirators, gloves, and goggles to minimize exposure to powders.
• Implement proper training for operators to ensure they understand and follow safe handling procedures.
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Conclusion

Ensuring powder quality for additive manufacturing in the production of orthopedic implants is vital for the success of the LPBF process. By understanding and addressing the various factors that can affect powder properties, manufacturers can optimize their processes and produce high-quality, cost-effective implants. At Croom Medical, we are committed to continually improving our materials lab and manufacturing processes to meet the evolving demands of the medical industry and provide superior orthopedic solutions.

By following the guidelines and best practices outlined in this blog post, manufacturers can effectively manage powder quality for LPBF, leading to better part performance and ultimately, improved patient outcomes.

With a proven track record of excellence and innovation, Croom Medical instills confidence in its clients and partners, making them the ideal choice for those seeking to explore additive manufacturing within orthopedics. To learn more about Croom Medical’s cutting-edge solutions, do not hesitate to reach out and discover how they can revolutionize your orthopedic product offerings.

Bibliography

Gibson, I., Rosen, D., & Stucker, B. (2015). Additive Manufacturing Technologies. Springer.

Sames, W. J., List, F. A., Pannala, S., Dehoff, R. R., & Babu, S. S. (2016). The metallurgy and processing science of metal additive manufacturing. International Materials Reviews, 61(5), 315-360.

ISO 13320:2009. Particle size analysis — Laser diffraction methods.

U.S. Food and Drug Administration (FDA). (2021). Technical Considerations for Additive Manufactured Medical Devices – Guidance for Industry and Food and Drug Administration Staff.

Gupta, A., Harrison, R. J., Wagner, G. J., & Voice, W. E. (2017). Powder Characterization Techniques and Effects of Powder Characteristics on Part Properties in Powder-Bed Fusion Processes. JOM, 69(3), 479-484.

ASTM E3-11. Standard Guide for Preparation of Metallographic Specimens.

ASTM E1621-13. Standard Guide for Elemental Analysis by Wavelength Dispersive X-Ray Fluorescence Spectrometry.

ASTM B213-17. Standard Test Methods for Flow Rate ofMetal Powders Using the Hall Flowmeter Funnel.

ASTM D5550-14. Standard Test Method for Specific Gravity of Soil Solids by Gas Pycnometer.

ASTM B527-18. Standard Test Method for Determination of Tap Density of Metallic Powders and Compounds.

ASTM E1019-18. Standard Test Methods for Determination of Carbon, Sulfur, Nitrogen, and Oxygen in Steel, Iron, Nickel, and Cobalt Alloys by Various Combustion and Inert Gas Fusion Techniques.

ASTM E572-18. Standard Test Method for Analysis of Stainless and Alloy Steels by Wavelength Dispersive X-Ray Fluorescence Spectrometry.

ASTM E1269-11. Standard Test Method for Determining Specific Heat Capacity by Differential Scanning Calorimetry.

ASTM E1461-13. Standard Test Method for Thermal Diffusivity by the Flash Method.

ASTM B922-19. Standard Test Method for Metal Powder Specific Surface Area by Physical Adsorption.

FDA. (2017) Technical Considerations for Additive Manufactured Medical Devices – Guidance for Industry and Food and Drug Administration Staff. U.S. Department of Health and Human Services Food and Drug Administration, Center for Devices and Radiological Health. https://www.fda.gov/media/97633/download