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In today’s competitive landscape where safety is a priority, manufacturers of precision components in such industries as aerospace, automotive and medical devices are continually challenged to improve and monitor product quality while also improving efficiency. Small defects can dramatically compromise the integrity and performance of components, leading to part rejections, costly rework and repairs, and loss of market share.

The diverse requirements and critical parameters of interest that are controlled for precision components vary greatly. Unfortunately, there is no single system that can effectively address all measurement challenges taking into consideration resolutions, accuracy requirements, surface reflectivity, measurement range, operating environment, and user skill level. In addition, throughput is another critical element in meeting cost and efficiency demands, operations need to weigh current manual practices against higher efficiency, robotic approaches.

The aerospace industry is one example of where the marrying of automation and metrology is being adopted to elevate product quality and operational excellence. The aviation industry prioritizes safety and is driving a heightened emphasis for stringent quality control and efficient labor management amid the ongoing post-pandemic labor shortages and recent highly publicized component failures.

Components in this industry have increasingly tight tolerances on defects, radii, chamfers, and blend geometries. Rapid and precise quantification of these features in production is essential to ensuring the highest quality levels efficiency and rework velocities.

Traditional Measurement Methods

To date, quantification of defects and features on precision-machined components has relied on traditional and manual measurement methods that are prone to be subjective and inaccurate but have been used for decades.

Visual Inspection

Currently, visual inspection of defects and features of engines and many other precision machined parts is the standard quality control practice. Done by eye, or with the aid of an optical comparator, manual inspection is slow and subjective. One of the most common inspection methods for assessing feature heights is to visually compare a defect to features of known quality on a coupon; a method that is neither precise nor repeatable. Inspectors err on the side of caution, and these conservative assessments often result in unnecessarily high rates of rework and rejection.

Many measurement locations cannot be measured by eye or are in hard to reach, requiring inspectors to generate replicas of the feature of interest, or even disassemble parts, and then brought to off-line measurement techniques such as optical comparators with templates (shadowgraphs), incurring higher labor costs, increasing the inspection time, and can still be subjective.

In addition, when considering the hundreds of callouts that can be needed on a single component, cycle time can take hours to days to measure – an extremely labor-intensive process.

2D Profilers

Higher resolution stylus-based measurement systems are another method widely used for quantifying feature heights, profiles and roughness. For short scan lengths, a stylus can be relatively fast, however, a stylus is a 2D technique that provides a single line of data across a feature, often not even crossing the deepest or widest portion of a defect. They are also susceptible to positional variations given their sensitivity to measurement position of the single scan. Some profilers can be programmed to do multiple scans for an area measurement; however, this greatly increases the inspection time for a single location, and exponentially for multiple locations. These systems can be difficult to set up, and susceptible to environmental factors, making them less suitable for shop floor applications. Additionally, as a contact-based method there is a higher risk of damage to the component and instrument.

3D Optical Profilers

3D optical profilers are non-contact systems known for having extremely fast, nm-resolution capability to identify surface roughness, features and defects; however, they are highly vibration-sensitive and require extremely quiet environments to be able to measure accurately and repeatably. In addition, due to their large form factors they have limited reach and are typically not considered a viable option for measuring on a shop floor.

Portable, 3D Optical Gages

Optical gages are small, portable systems that provide non-contact, 3D measurement of features and defects. One specific optical gauge technology, polarized structured light (PSL), has been successfully measuring defects and features in aerospace and precision machining applications for nearly a decade, measuring defects such as pits, scratches and corrosion and features such as edge break, radius, and chamfers from 2.0µm to 9mm in height. The surface gage is similar to PSL optical gage but its technology is significantly faster and has demonstrated to reduce rework rates by up to 30% on critical engine components with its ability to correctly quantify defects. The underlying technology is vibration-immune, making it uniquely capable of using non-contact, three-dimensional optical metrology for measuring in extreme environments, including production and shop floors. These handheld systems measure in < 1 second—hundreds of times faster than manual inspection.

Automating Optical Metrology

In industries such as aircraft engines and automotive, where hundreds of different categories of features and locations require quick, precise inspection, automated metrology is emerging as a transformative approach.

Automated inspection makes it possible to quickly measure hundreds of features and defects per part.
Automated inspection makes it possible to quickly measure hundreds of features and defects per part.

Automation significantly increases throughput with higher sampling rates, and accuracy with the robotics’ precision. For one of our customers, they were able to measure 400 typical engine callouts in under 30 minutes. It can even open up capabilities for design and specification optimization when combined with computer aided design (CAD) comparison, digital twinning, and advanced predictive analytics.

With the additional skilled workforce challenges, robotic metrology solutions are an attractive option to efficiently quantify critical callouts across many part locations with minimal operator involvement, enabling manufacturers to reallocate labor to other critical tasks.

While the upfront costs of automation may be viewed as a barrier to adoption, taking a deeper look into the return on investment (ROI) and cost savings can justify the adoption of automated optical metrology.

Table 1 below shows an example from a typical aircraft engine facility, using conservative values provided by various engine manufacturers after implementing automated 3D PSL optical gage measurements. Assuming an automated system might cost as much as $500,000, the breakeven point is a mere three months and ROI on the investment over the 5-year capital cycle would be about 20X. For a given operation, each case will need its own justification, but this provides a quick look at potential savings with an automated 3D PSL system.

Table 1: Example table showing potential cost savings associated with automated 3D measurement solution for aircraft engine components.
Table 1: Example table showing potential cost savings associated with automated 3D measurement solution for aircraft engine components.

The integration of robotics with optical polarized structured light gages is enabling new possibilities in precision manufacturing, offering improved precision, throughput and labor utilization to companies who are adopting it, and providing a competitive advantage for the future,