Micro CT

Micro CT is a computed tomography system that utilizes a micro-focus X-ray tube as the source and typically uses a flat panel detector array. The combination can render an image with resolution as low as 0.5 microns to 50 microns. diondo CT components and manipulator are capable of the needed accuracy  to meet imaging specifications. This is why diondo uses a solid granite frame construction. The main micro CT advantage is the ability to magnify a component to acquire a volumetric 3D image showing material structures, bonding and micro defects. 

Metrology and Granite

It has long been recognized by master machinists that granite provides the best surface for metrology. Granite is an igneous rock formed by volcanic eruptions. By comparison, marble is metamorphosed limestone.  For metrology use, the granite selected meets specific requirements outlined in Federal Specification GGG-P-463c, Part 3.1 3.1 . Granite should be a fine to medium-grained texture and gray in color. Young’s Modulus of Elasticity is used to express the flexibility or indication of the hardness of the stone.  Gray granite averages 5-7 points. Making it soft enough not to chip easily for every day use.  

Quality Assurance

One might ask "Why we spend so much time and money to encapsulate the micro CT system in granite?" Quality testing requires absolute repeatability and proven accuracy. It is evident that multiple axis movements on a less rigid structure will cause deviations in the measured accuracy of the CT machine. This is especially true with steel framed structures. To assure the accuracy and quality of our calibrations over time, it is necessary to use the best materials and positioners available. The diondo micro CT system uses granite to maintain an accuracy of movement to +/- 1 micron.

According to Asia Pacific Metal working Equipment News: 

"Rock Solid Foundations: Granite For High Accuracy Measurement 

The use of granite in 3D coordinate metrology has already proven itself for many years. No other material fits with its natural properties as well as granite to the requirements of metrology.

The requirements of measuring systems regarding temperature stability and durability are high. They have to be used in a production-related environment and be robust. Long-term downtimes caused by maintenance and repair would significantly impair production.

For many years now, manufacturers of coordinate measuring machines trust in the quality of granite. It is the ideal material for all components of industrial metrology which demand high precision. 

Granites favorable Characteristics

The following properties demonstrate the advantages of granite:

  • High long-term stability: Thanks to the development process which lasts many thousand years, granite is free of internal material tensions and thus extremely durable.

  • High temperature stability: Granite has a low thermal expansion coefficient. This describes the thermal expansion at the temperature changing and is only half that of steel and only a quarter of aluminum.

  • Good damping properties: Granite has optimal damping properties and thus can keep vibrations to a minimum.

  • Wear-free: Granite can be prepared so that a nearly level, pore-free surface arises. This is the perfect base for air bearing guides and a technology which guarantees the wear-free operation of the measuring system.

Manual Labor As Predicate

Based on the favorable characteristics above, the base plate, rails, beams and sleeve of Wenzel measuring machines are also made of granite. And because they are made of the same material, a homogeneous thermal behavior is provided.

In order for the qualities of granite to apply fully when operating a coordinate measuring machine, precision is imperative when processing of the granite components are carried out. The final processing step is the hand lapping of the granite. The evenness of the lapped granite is inspected minutely with a digital inclinometer.

The flatness of the surface can be determined sub-µm-precisely and be displayed as a tilt model graphic. Only when the defined limit values are followed and the smooth, wear-free operation can be guaranteed, the granite component can be installed.

Robust Measuring Systems

In today’s production processes the measuring objects have to be brought as fast and uncomplicated as possible to the measuring systems, irrespective of whether the measuring object is a large and heavy component or a small part.

It is therefore of great importance that the measuring machine can be installed close to production. The usage of granite components supports this installation site as its uniform thermal behavior shows clear benefits to the use of molding, steel and aluminum.

A one meter long aluminum component expands by 23 µm when temperature changes by 1 deg C. A granite component with the same mass however expands itself for only six µm. For additional safety in the operational process, bellow covers protect machine components from oil and dust.

Precision And Durability

Reliability is a decisive criterion for metrological systems. The usage of granite in the machine construction guarantees that the measuring system is stable and precise in the long term. As granite is a material which has to grow for thousands of years, it does not have any internal tensions and thus the long term stability of the machine base and its geometry can be ensured. Accuracy starts with a sollid platform and the ability to manipulate the object, X-rat Tube and detector without error.

Variable FDD

The focal spot to detector distance (FDD) is an important factor in the quality of your CT image because it provides you with enough space to get the highest magnification factor possible. With micro CT the focal spots can be as small as 2 microns. There is not allot of radiation because Power [W] = Resolution [µm]. Having FDD continuously variable from 1200mm to 400mm will allow one to increase the dose to the detector and thus shorten scan time. Let's say engineering is testing a process for butt welds and has 40 samples that they need scanned at a resolution of 50 microns. If scanning at a mag factor of 2.68X, you are able to set your integration time to 2000ms per projection at a distance of 1200mm FDD. Each scan is about 60 minutes. However, because of the inverse square law, set the FDD closer to 600mm the same 50 micron resolution can be attained in about 500 milliseconds per projection and the total scan time is now 15 minutes. The total project scan time goes from 40 hours down to 10 hours. This makes a great deal of difference in the material sciences because so many samples require CT. For quality testing we should come away with the points as follows:

Micro CT Systems Need Maximum Flexibility

  1. Highest dose rates for fast CT scans at small FDD

  2. Higher resolution due to large FDD

  3. Higher resolution due to flexible FOD and FDD

  4. Larger 3D scan field due to large FDD

  5. Stability of the Frame from vibration and changes in environment

  6. Accurate and repeatable location feedback is required

  7. Small focal spot for higher resolution

  8. Efficient and small pixel size

  9. Large format imaging detector

The micro CT system is used to analyze multiple materials such as composites and new alloys developed in conjunction with additive manufacturing processes. The micro CT has become invaluable to the quality lab as a tool to look for flaws in materials. When used in conjunction with metrology testing such as tensile testing and environmental chambers, a volumetric record can be kept of crack migration and characteristics of material weakness. Composite materials especially rely on accurate quality test equipment using micro CT scanners because the quality tester will show minute mathematical  differences between stressed material and non-stressed material providing insight into real internal structure and defect behavior. Micro CT in conjunction with a tensile tester can provide examination of  crack crawl in composites and other materials. The best way to examine the development of a weakness in a material is to examine it under load and have a high enough resolution to provide nominal actual comparisons. Micro-focus computed tomography can also help the quality engineer to identify product processes that reengineer the concept of quality by providing repeatable tests and identification of allowable anomalies

Magnification

 
 
 

Magnification of the X-ray image gives the radiographer the advantage to see much more detail than if the image was a direct transfer of size. Micro CT's advantage is that the 2 micron sized point source allows the magnification to increase without the image blurring. That is, the micro focus X-ray tube creates a small focal spot so that magnification is possible. In conventional X-ray before digital imaging, the radiographer would put the object close to the film so that there was minimal scatter radiation to blur the image and detail that existed in the object. An eye loop or magnifying glass was used to magnify the image by taking advantage of a convex lens to increase the region of interest. With Micro CT we can capture an image with the object much closer to the source of the X-ray. The digital image can also be manipulated to increase the magnification. However, without the micro CT small focal spot, the resolution would not be high enough to discern the required features of todays additive manufacturing components.

With additive manufacturing (AM), engineers are able to use computer aided design software to increase strength of a component in highly stressed areas by adding support or material only where it is needed. In the past a casting was poured into a mold. The component or casting was then machined. If possible machining was done to decrease weight. With the weight reduction and increase in productive use of materials in a design using AM, the complexity of a component increases tremendously. By using Micro CT, which is the utilization of a micro focus X-ray tube and the computing power of a CT machine, one can image the ever increasingly complex components developed by AM. Not only can one image such components but also due to the exact pixel size of flat panel technology for imaging detectors, one can provide metrology, actual and nominal comparisons with CAD data, set acceptable porosity measurements as well as wall thickness measurements. The micro CT system increases the productivity of gathering absolute values in components infinitely. 

 
 

CT Batch Mode

Having a CT system that works for you is important. I know that my own personal experiences scanning object samples can be very time consuming. As we go forward in exploring Micro-CT it is important to remember that thorough analysis of several different processes that may change the makeup of the materials and objects we examine with CT can bring us to the reality that we need a scanner in which automates the imaging processes to create and analyze 3D X-ray imaged. Well indeed the systems that diondo incorporated designs are based on first hand knowledge from CT scanning customer materials and components for the CT services industry. We found that many applications do not require the investment in capitol equipment,  training or experience to learn how to program a robot to pick up a part and put it in a CT scanner. In review of the application especially in additive manufacturing to develop new materials it is necessary to take a volumetric 3D X-ray scan of thousands of small test objects. To achieve a productive process we developed a multiple parts changer that can pick up stacked trays full of parts vertically and CT scan them in batch mode. The automatic component changer has been designed for feeding parts in the d2 system. After they have been loaded manually, up to 6 test objects can be measured without interruption, resulting in an increase in machine running time. The component changer is secured to the manipulator frame. The automatic component changer is equipped with 6 small (or 3 large) rotary plates, each offering a maximum bearing capacity of 55 kg. The rotary plates have been designed as self-centering units. When the measurement progresses automatically, a loaded rotary plate is picked up, moved to the measuring position and returned to its original position after the measurement has been taken. The corresponding manipulator axes are locked during loading and unloading. The automatic component changer is controlled using the di control software. The component changer has been fully integrated into the control system; a press of the EMERGENCY STOP button will also shut down the corresponding axis. Error messages will be displayed on the PC.

 

What makes the best Micro CT System?

With the diondo compact Micro CT system, we leave nothing to be desired with regard to accuracy, speed, ease of use and flexibility. The micro computed tomography systems d1, d2, and d5 not only optimally meets the stringent requirements of metrology, but also the high demands of non-destructive material testing with great precision.


diondo consciously focuses on premium component parts. Instead of the metal manipulator commonly used in this market sector, the system rests on a solid granite base. Its inherent stiffness and temperature stability guarantee perfect results even after many
years of intensive use. Furthermore, the axes are equipped with glass scales, a feature that is otherwise only provided in CT systems at higher price brackets. The concept works: the highest accuracy according to the VDI / VDE guideline 2630 is consistently achieved. Another highlight of the diondo micro CT systems are the high-contrast 3K detector. The combination of a narrow pixel grid and a particularly large active area offers the user several advantages: on the one hand, it allows an extremely high resolution
when examining small objects; on the other hand, it offers the imaging of large test pieces „in one shot,“ without having to capture them in multiple partial scans, which is time-consuming.

Due to customer requirements the Micro-CT system can be equipped with a transmission and / or reflection tube. By choosing the optimal tube parameters (max. voltage, target-power and resolution) for the transmission and reflection target, diondo ensures the ideal combination of final resolution and material penetration. 

 

diondo has the highest precision even for large inspection parts without restrictions in the inspection scope compared to traditional compact CT systems. diondo d5 is designed for the installation in a walk-in radiation protection cabinet or spacious radiation protection room. The final size of the system is designed as agreed upon with the customer. Therefore even bulky and voluminous inspection-parts can be scanned with the typical accuracy of a high-resolution micro-CT system.

 

diondo Incorporated copywrite 2019 Last modified December 18, 2020

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