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Seeing Into The Future Of Computed Tomography

Jesse Garant Metrology Center is a specialized part inspection company located in North America with a focus, since 2009, on providing Industrial CT Scanning Services. Metrology.News recently sat down with company founder and president Jesse Garant, a mechanical engineer with 20 years of management and practical manufacturing experience, to get his overview and vision on how the role of CT metrology could change in coming years.

What are the main technology challenges with Industrial CT Scanning and what is holding Industrial CT back from offering mainstream metrology to manufacturers?

When the technology went fully digital and started to become mainstream with the latest generation of industrial CT systems in 2005, we have only seen incremental improvements to mechanical technology challenges.  Most of the technology challenges over the last 15 years have been software related.  These would include manipulation methods, acquisition methods, and advanced voxel-based software solutions.  At this point in time the major setbacks from CT going mainstream is the supply chains and major OEM’s not having requirements and standards in place that allow confidence in the technology and final results.

What is the difference between Nano CT, Micro/Macro CT, and High Energy CT?

The differences between the main types of system classification relate to how the spot sizes of the X-Ray sources are classified.  The main differences are;

  1. Nano CT are systems with spot sizes measured nanometers
  2. Micro/Macro CT are systems with spot sizes measured in microns
  3. High Energy CT are systems with spot sizes measured in millimeters.

The smaller the spot size the greater the detail recognition, the greater the effective spot size the greater the latitude of penetration.

What are the system resolution and size limitations of each?

Any system’s voxel dimension can be determined by understanding the achievable geometric magnification and detector’s pixel pitch (Voxel Size = Detector Pixel Pitch/Magnification). This means the minimum voxel size of any system has hardware limitations and all projects have size limitations that affect the level of magnification possible.  System limitations are determined by their scan envelope and operating power. These factors are evaluated against object size, density, geometry, and client objective.

As a quick reference for a simple scan on a Industrial CT system that fits into the detectors field of view;

  1. Nano CT systems would have a scan resolution under 1 micron and a maximum scan envelope under 5mm.
  2. Micro/Macro CT systems would have a scan resolution under 400 micron and a maximum scan envelop under 275mm
  3. High Energy CT systems would have a scan resolution over 400 micron and a scan envelop over 275mm

*As a note the scan envelope can be drastically increased on customized systems to include offset scanning and helical scanning.  However, these scanning methods can have a drastic change to the overall scan time and image quality.

You manufacture your own CT machines. What drove you down this path?

We use a mixture of both purchased systems and systems modified / manufactured by our company for services.  As we have a highly talented staff that operates close to the system manufacturer level, it was a logical choice to leverage our internal skill-sets.  Integration of our own systems with the acquisition of reputable and proven components has allowed our team to be get ahead of our client curve. This allows our team to reduce system and project limitations quickly. Being able to adjust system hardware to meet a client’s specific objective is a key factor in our businesses success. This increases our scanning repertoire without having to purchase an additional system.

In fact, we just completed a large-scale project in which we manufactured a “new” highly customized system from components in a single month. These system alterations removed the critical project limitation allowing successful completion of the time critical inspection for several hundred thousand parts to be completed in a period of months as opposed to years.  Specifically related to our accelerator services, we manufacture our own large format high energy industrial CT scanning systems with proprietary technology we have developed internally.  We use this proprietary technology to feasibly qualify mid-size parts in 1.5 hour scans.  As a service lab we provide this service for manufacturers and OEM’s primarily in the aerospace, defense, oil & gas, and automotive industries.

How do you overcome inherence CT issues associated with Artifacts and Partial Volume?

Computed tomography imaging is based on simulated projections and similar to many imaging techniques this can result in artifacts. As you mentioned one of the most common artifacts is a partial volume effect or a Feldkamp effect. Skilled operators can overcome this and many other potential issues by understanding the cause of the effect and altering the scan approach to mitigate their influence. As an example the Partial volume effect is caused when then area of a object is parallel to the x-ray source resulting in the parallel surface becoming blurry. An operator could take a few different approaches to remove the presence of this artifact.  Fixturing the sample at an angle removing the parallelism would one of the best options. Operator skill and their understanding of potential artifacts is key when trying to complete a quality service in a timely manner.

The ISO10360-11 standard for CT machine performance, when used for dimensional inspection, is still under development. In the absence of the standard how do CT users currently know that the reported CT data is accurate and to what level of uncertainty?

Without a CT specific standard to adhere to, the onus falls on the lab scanning and providing the results to supply sufficient documentation for the end customer to trust the process.  Our company is taking two approaches to overcome this hurdle. We have added a Quality Management System that is recognized by third party registrars. These ISO 9001:2015 and AS9100D certificates show our clients we are customer focused, committed to continued improvement, and we have records that back up our process outputs.

The second approach is sharing these records with our clients and revising them into unique data cards. These data cards are typically approved by our clients when accuracy, process metrics, and competency are required above our default record keeping processes.  As a service lab have successfully completed several of these documents for repeat qualification and measurement of critical aerospace and oil & gas products.

Do you see the traditional CMM role being challenged by CT CMMs over the next ten years and for what applications?

For large and dense parts I do not see the CMM role being challenged by CT in the foreseeable future.  However, for complex small to medium parts being manufactured, CT Metrology can measure certain dimensions in different ways than a traditional CMM. I think this will alter the design and GD&T tolerancing before it will directly challenge traditional measurement.  CT scanning will be one of the measurement tools in a manufacturer’s tool kit. Thinking about measurement in this fashion will allow products that fit with CT technology to be dimensioned in easier to interpret and measurement ways.

One example would be using 3D surface profiles and wall thickness call outs in place of traditional measurements for non-critical features.  Utilizing this approach would allow the number of dimensional part print points to be drastically reduced while keeping in place dimensions for fit and function.  A second example will be more utilization of coaxality to measure and tolerance features than concentricity due to how much more robust a cylinder can be in comparison to multiple circles. Another example could be coaxaility used to tolerate two coaxial cylindrical features in replacement of true position. The reconciliation of this approach would allow faster interpretation of measurement outputs.

What current CT technology limitations must be addressed for CT to adopt a main stream metrology role in coming years?

I think very little has to change on the technological side, most of the change will occur at the level of understanding and design implementation. In my opinion for CT to adopt a main stream metrology role in the coming years the following needs to occur;

  • CT needs to be properly understood from the standpoint of its benefit to qualify low to medium density products ranging from small to midsize components.
  • Manufactures need to accept the realization that CT wont easily save quantifiable costs. CT allows manufactures to qualify parts with less risk and saves qualification time, which in turn saves costs in the long run.
  • First article inspection layouts should utilize 3D tolerancing in the latest manufacturer designs to drastically reduce programming times and qualification times.
  • Manufactures need to trust the process being used by the lab scanning and releasing the results.

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