Impact Of Iso 25178 Updates On Additive Manufacturing Surface Measurement

The world of additive manufacturing (AM), also known as 3D printing, is rapidly evolving, pushing the boundaries of what’s possible in design and production. As AM technologies advance, so too must our ability to accurately and reliably characterize the surfaces they produce. This is where ISO 25178, the international standard for areal (surface) texture, comes into play. The recent updates to ISO 25178 have a significant impact on how we measure and interpret surface data in AM, leading to improved quality control, process optimization, and ultimately, better AM products. This article explores the crucial role of ISO 25178 and its updates in the context of additive manufacturing surface measurement.

Understanding the Importance of Surface Measurement in Additive Manufacturing

Additive manufacturing distinguishes itself through its layer-by-layer construction process. This inherent characteristic directly influences the surface texture of the final product. Unlike traditional manufacturing methods that rely on subtractive processes like machining or grinding, AM builds parts from the ground up, often resulting in unique surface features.

These surface features are not merely cosmetic; they significantly impact a part's functionality and performance. Consider these critical aspects:

• Mechanical Properties: Surface roughness can influence fatigue life, wear resistance, and friction. Rougher surfaces may lead to stress concentrations and premature failure.
• Adhesion and Coating Performance: The surface texture affects the ability of coatings and adhesives to bond effectively. Controlled surface roughness can enhance adhesion.
• Fluid Flow: In applications involving fluid dynamics, surface texture can affect flow rates, pressure drop, and even heat transfer.
• Optical Properties: Surface finish influences reflectivity, scattering, and overall appearance, which is crucial for optical components.
• Biocompatibility: For medical implants, surface texture plays a critical role in cellular adhesion and tissue integration.

Therefore, precise surface measurement is paramount in AM to:

• Ensure part quality and consistency: By quantifying surface characteristics, manufacturers can establish tighter control over the AM process and produce parts that meet specific requirements.
• Optimize manufacturing parameters: Surface data can be used to fine-tune AM parameters like layer thickness, laser power, and scan speed to achieve desired surface finishes.
• Predict performance: Surface measurements provide valuable insights into how a part will perform in its intended application.
• Facilitate communication and standardization: Using standardized measurement techniques allows for clear communication of surface requirements between designers, manufacturers, and end-users.

Evolution of ISO 25178: A Brief Overview

ISO 25178 is a comprehensive set of standards that define terms, parameters, and procedures for characterizing areal surface texture. It represents a significant advancement over previous standards that primarily focused on profile-based (2D) measurements. Areal measurements, as defined by ISO 25178, capture the entire surface, providing a more complete and accurate representation of its characteristics.

The ISO 25178 standard is comprised of several parts, each addressing specific aspects of surface texture measurement. Some key parts include:

• ISO 25178-1: Specifies general terms, definitions, and surface texture parameters. It lays the foundation for understanding and applying the standard.
• ISO 25178-2: Provides guidance on terms, concepts and parameters for measuring surface texture on areal surfaces.
• ISO 25178-3: Deals with the specification operators, including filtering techniques, that are essential for separating different components of the surface texture (roughness, waviness, and form).
• ISO 25178-6: Focuses on the classification of methods for measuring surface texture. This includes stylus-based instruments, optical instruments, and other techniques.
• ISO 25178-7: Describes the software measurement standards
• ISO 25178-600: Provides guidance on the metrological characterization of areal surface textures.

The recent updates to ISO 25178 reflect the evolving needs of industries like additive manufacturing. These updates incorporate new measurement techniques, address limitations in previous versions, and provide more specific guidance for complex surface textures.

Key Updates in ISO 25178 and Their Impact on AM

Several key updates in ISO 25178 are particularly relevant to additive manufacturing surface measurement. These updates address the unique challenges posed by AM surfaces and offer improved tools for their characterization.

1. Improved Filtering Techniques

Filtering is a crucial step in surface texture analysis. It involves separating the different components of the surface (roughness, waviness, and form) to isolate the features of interest. The updated ISO 25178 standards introduce more sophisticated filtering techniques that are better suited for the complex surface textures often found in AM parts.

• Gaussian Regression Filters: These filters offer improved performance in separating long and short wavelength components, allowing for more accurate analysis of roughness and waviness.
• Robust Gaussian Filters: Designed to minimize the influence of outliers and defects on the filtering process, making them ideal for surfaces with imperfections commonly found in AM.
• Morphological Filters: These filters are based on mathematical morphology and are particularly effective for analyzing surfaces with complex geometries and sharp edges, often encountered in AM parts.

Impact on AM:

• More accurate roughness measurement: Improved filtering leads to more reliable roughness parameters (e.g., Sa, Sq, Sz), which are critical for predicting part performance.
• Better defect detection: Enhanced filtering can help identify and quantify defects such as pores, cracks, and unmelted particles, allowing for process optimization and quality control.
• Improved form removal: Accurate form removal is essential for analyzing the underlying surface texture without being influenced by the overall shape of the part.

2. New Parameters for Characterizing Functional Surfaces

The updated ISO 25178 standards introduce new parameters specifically designed to characterize the functional properties of surfaces. These parameters go beyond traditional roughness measurements and provide insights into how a surface will perform in specific applications.

• Texture Directional Parameters (Std, Sal): These parameters quantify the directionality and anisotropy of the surface texture, which are important for applications involving friction, wear, and fluid flow.
• Feature Parameters (Spd, Sfd): These parameters characterize the size, shape, and density of features on the surface, such as peaks, valleys, and pits. They are useful for analyzing surfaces used for sealing, lubrication, and adhesion.
• Material Ratio Curve Parameters (Smr, Sdc): These parameters describe the distribution of material on the surface as a function of height. They are valuable for predicting contact area, bearing ratio, and wear resistance.

Impact on AM:

• Application-specific surface design: These new parameters allow engineers to design AM surfaces with specific functional properties, optimizing performance for particular applications.
• Improved correlation with performance: By using parameters that directly relate to function, manufacturers can better predict how an AM part will perform in its intended environment.
• Enhanced process control: These parameters provide valuable feedback for optimizing AM parameters to achieve desired surface functionality.

3. Enhanced Measurement Strategies for Complex Geometries

Additive manufacturing enables the creation of parts with complex geometries, including internal channels, overhangs, and intricate lattice structures. Measuring the surface texture of these features can be challenging using traditional methods. The updated ISO 25178 standards provide guidance on how to overcome these challenges and obtain accurate measurements on complex geometries.

• Multi-scale Analysis: This approach involves measuring the surface at different magnifications to capture both large-scale form variations and fine-scale texture details.
• Advanced Measurement Techniques: Techniques such as confocal microscopy, focus variation microscopy, and optical coherence tomography (OCT) are capable of measuring surfaces with high slopes, occlusions, and transparent materials.
• Data Stitching and Registration: These techniques allow for combining multiple measurements of different areas of the surface into a single, comprehensive dataset.

Impact on AM:

• Quality control of complex parts: These enhanced measurement strategies enable manufacturers to ensure the quality and consistency of AM parts with intricate geometries.
• Design optimization for complex features: By accurately characterizing the surface texture of internal channels and lattice structures, engineers can optimize their design for improved performance.
• Process validation for challenging geometries: These techniques allow for validating the AM process for complex geometries, ensuring that the desired surface finish is achieved in all areas of the part.

4. Uncertainty Evaluation and Traceability

The updated ISO 25178 standards place a greater emphasis on uncertainty evaluation and traceability in surface texture measurement. This is crucial for ensuring the reliability and comparability of measurements across different instruments and laboratories.

• Uncertainty Budget: The standards provide guidance on how to estimate the uncertainty associated with surface texture measurements, taking into account factors such as instrument calibration, environmental conditions, and measurement procedure.
• Traceability to International Standards: Measurements should be traceable to national or international standards to ensure their accuracy and comparability.
• Proficiency Testing: Participating in proficiency testing programs can help laboratories validate their measurement capabilities and identify areas for improvement.

Impact on AM:

• Improved measurement reliability: By quantifying and minimizing uncertainty, manufacturers can have greater confidence in their surface texture measurements.
• Better decision-making: Reliable measurements enable more informed decisions regarding process control, quality assurance, and product acceptance.
• Enhanced comparability: Traceable measurements facilitate the exchange of surface texture data between different parties, promoting collaboration and innovation in AM.

Challenges and Considerations in Implementing ISO 25178 in AM

While the updated ISO 25178 standards offer significant benefits for additive manufacturing surface measurement, their implementation also presents some challenges and considerations:

• Instrument Selection: Choosing the appropriate measurement instrument for a specific AM application is crucial. Factors to consider include the surface texture characteristics, part geometry, and required measurement resolution.
• Operator Training: Proper training is essential for ensuring that operators understand the principles of surface texture measurement and can correctly operate the instruments and interpret the data.
• Data Analysis and Interpretation: Analyzing and interpreting surface texture data requires a thorough understanding of the ISO 25178 standards and the specific requirements of the application.
• Cost and Complexity: Implementing the updated ISO 25178 standards can be costly and complex, requiring investment in new equipment, training, and software.
• Standard Interpretation: It is important to note that the ISO standards are open to interpretation, and it is crucial to understand the nuances behind the standards.

Practical Examples of ISO 25178 Application in AM

To illustrate the practical applications of ISO 25178 in additive manufacturing, here are a few examples:

• Aerospace Components: An aerospace manufacturer uses AM to produce lightweight turbine blades. They use ISO 25178 parameters such as Sa and Sz to control the surface roughness of the blades, ensuring optimal aerodynamic performance and fatigue life.
• Medical Implants: A medical device company uses AM to create custom-designed hip implants. They use ISO 25178 parameters such as Spd and Sfd to control the surface texture of the implant, promoting bone ingrowth and long-term stability.
• Automotive Tooling: An automotive manufacturer uses AM to produce conformal cooling channels in injection molds. They use ISO 25178 parameters such as Std and Sal to characterize the surface texture of the channels, optimizing heat transfer and reducing cycle times.

The Future of Surface Measurement in Additive Manufacturing

The field of surface measurement in additive manufacturing is constantly evolving. As AM technologies continue to advance, we can expect to see further developments in measurement techniques, data analysis methods, and standardization efforts. Some potential future trends include:

• In-process measurement: Integrating surface measurement capabilities directly into AM machines to provide real-time feedback and control.
• Artificial intelligence (AI): Using AI algorithms to automatically analyze surface texture data, identify defects, and optimize AM parameters.
• Digital twins: Creating virtual representations of AM parts that include detailed surface texture information, enabling predictive modeling and simulation.
• Standardization of data formats: Developing standardized data formats for surface texture data to facilitate the exchange of information between different software platforms and systems.

Conclusion

The updated ISO 25178 standards represent a significant step forward in surface texture measurement for additive manufacturing. By providing improved filtering techniques, new parameters for characterizing functional surfaces, enhanced measurement strategies for complex geometries, and a greater emphasis on uncertainty evaluation and traceability, these standards enable manufacturers to achieve greater control over the quality, performance, and reliability of AM parts. While implementing these standards presents some challenges, the benefits they offer are undeniable. As additive manufacturing continues to grow and mature, the importance of accurate and reliable surface measurement will only increase. By embracing the updated ISO 25178 standards, manufacturers can unlock the full potential of AM and create innovative products that meet the demands of a wide range of applications. The key lies in understanding the intricacies of the standards, choosing the right equipment, and investing in proper training to ensure accurate data collection and interpretation. This commitment to quality will ultimately drive the advancement of additive manufacturing and its widespread adoption across industries.