A common question that we are asked is: what is the resolution of a CT scan for determining gaps or voids or true surface locations? We are also asked: How can you measure a gap between two parts that may be closer than 1 voxel in size? The answer lies in sub-voxel surface determination and in the number of voxels that are involved and continuous surfaces as detailed below.
Modern Additive Manufacturing (AM) methods often employ subtractive machining to achieve precise dimensional and surface finish characteristics. This is due to current AM limitations in build precision and surface quality. These hybrid AM / subtractive components also demand a hybrid approach to measurement. Internal features on AM parts are difficult or impossible to non-destructively measure using solely traditional metrology methods and so industrial computed tomography (CT) must also be employed. CT scanning not only allows for precise measurements using metrology CT, but allows for detection of internal defects that are not otherwise able to be seen. However, well machined portions are best served through other measurement methods due to precision requirements and data characteristics. This can necessitate a hybrid measurement approach. However, traditional CT scanning and service providers are not trained as metrologists and do not follow particular standards related to metrology – especially ISO17025. Also complicating measurement is the design and datum reference frames used for additive parts that typically follow a traditional machined component print layout. A layout method following best practices from the casting industry is suggested here. This article explores the methods (GD&T), issues, limitations and current solutions associated with good metrology practices for AM and hybrid AM components.
3D Engineering Solutions has expertise in inspection and reverse engineering for many different applications. We combine the best available equipment and a well trained staff to deliver correct results in a rapid manner.
For PCB’s, we use the Nikon X-Tek 160kV Industrial CT Scanner which is designed to meet every need related to the inspection of PCB’s. It provides up to 160kV and 20W power, a 1µm X-ray focal spot size, and a magnification range of 2x-600x. The detector can also tilt to a max angle of 75° which provides extra flexibility in examining multi-layer boards.
Radiographic testing is a widely accepted method for finding voids and defects in materials. Makers of castings and solder connections on printed circuit boards have used radiographic testing to detect voids in 2D images and Computed Tomography (CT) in 3D images with excellent results that are well documented. As CT scanning continues to evolve and emerge as the inspection method of choice new challenges arise. Many times customers are unaware of the difference and apply old specifications on their drawings that may no longer apply. Or they do not know the full capabilities of the newer technologies or have not yet defined the specifications for their application.
Industrial CT scanning has gained prominence in dimensional data collection technologies with the advent and continual development of additive manufacturing. Now, CT scanning processes are being added to ISO17025 scopes of accreditation and the emergence of Metrology based CT is gaining recognition and acceptance across many industries.
Many measurement and reverse engineering requirements require more than simple caliper or micrometer measurements. Whether you are conducting a First Article Inspection (FAI), troubleshooting a manufacturing issue or reverse engineering a legacy part for improvements, one or multiple of the modern data collection methods may work – but what is best and what are you compromising on by using any particular method? Do you do this work yourself or hire out an experienced service provider?
Non-contact or touchless dimensional measurement devices are the modern new comer to an array of contact devices that have been traditionally used. Contact devices are discussed in this link on Common Contact Measurement Devices. All of the non-contact devices generate a point cloud or voxel data set as their most raw form of data. The exception is the optical comparator which has been around since the late 1920s. It does not expressly produce digital data, but some of the variant equipment that evolved from this equipment does.
Industrial CT scanning continues to gain popularity for use in measurements. The real question to be asked is: Is the data extracted from CT scans accurate? Since its inception, CT scanning has been used to visualize internal structures from people to industrial items. It is unparalleled in its ability to see those things that are hidden inside an assembly. It is also important for measuring the effects of an assembly in its assembled state. Using CT data to provide accurate measurements has always been around but there was no universally agreed upon ways to ensure the validity of the measurements.
Every day, we in industry find ourselves in need of verifying the parts we have designed and built. Part of this verification comes in the forms of physical testing, as well as measurement and analysis. Whether you are looking at a prototype component or have a need to create an inspection plan for a production component, you will need someone who is proven capable in the science of measurement, otherwise known as the field of metrology. A simple Google search will reveal that there seems to be no lack of companies offering the services of metrology.
Since shortly after X-Rays were discovered in 1895 they have been widely used in many diverse applications. The medical field was an early adopter of this technology, using X-Rays throughout the world within the first year. As it developed in medicine other uses emerged on the industrial side.