“Computed Radiology In The Casting Industry” By: Stuart Kleven Alloyweld Inspection Company, Inc. 796 Maple Lane Bensenville, IL 60106 (630) 595-2145 (630) 595-2128 Fax E-mail: skleven@alloyweldinspection.com Introduction: Radiography has served as a valuable tool for the casting industry for over 50 years. It is employed in a variety of ways to the cast products. It may be specified on a sampling basis, and if rejections are noted, one hundred percent inspection may be required. Other contracts or specifications may require one hundred percent inspection of the casting lot. Location of cores and placement of chills and repair welding require the use of radiographic techniques also. Regardless of its use, either as a quality control tool or as an order requirement, radiography has, in some instances, become an obstacle to production and a cost factor. The use of polyester based film with an emulsion and interspersed silver halide crystals has long been the standard method of imaging and/or recording the results of examinations of raw materials and various product forms. Recent innovations have come with regard to the development of radiographic films with specific speeds which have been produced to address the needs of the casting industry. Other methods for acquiring and displaying the image have also been used with some success. These include use of fluoroscopic screens, real time imaging, and exposure on paper based films. Several factors have affected the use of radiography as an inspection tool over the last few years. The cost of film has been a factor that has to be considered when testing parts. The inspection of lower cost injection molded castings has been limited due to the amount of parts that could be placed on a film, the number of exposures required to obtain acceptable densities, and the cost of the film and chemistry required to develop the film. At times it has been more cost effective to scrap and entire lot of parts than to 100% inspect them. The use of real time imaging systems has found a niche in the die-casting market since there are no film costs. To accomplish full coverage of the entire casting, each part requires either rotation or reorientation within the radiation field. This can be tedious, labor intensive and time consuming, especially on large runs. At times customer specifications demand a specific radiographic technique and quality level. This may include the use of longer source to film distances to achieve code unsharpness requirements and/or magnification to achieve sensitivity levels such as 2-2T. With magnification comes longer interpretation times to view the entire part.

“Computed Radiology – A Useful Tool for the Casting Industry” Page 2 The sand and investment casting industry also uses a significant amount of film radiography. Usually parts are examined on a sampling basis. If rejects are found in the sample, then increased inspection, usually 100%, is required. Many foundries also use radiography as a quality control tool to verify the casting quality, placement of chills, and cores, and to ensure proper gating and risers. Casting repair welding is still another area where a large volume of film is utilized. After initial radiographic exposures, castings are marked up for grinding out of discontinuities or excavating by some other method to prepare them for repair welding. With thicker castings defect removal is, at times, verified by radiography prior to applying anyweld filler metal. This ensures that if the discontinuity was not removed during grind out, excessive time and money will not be wasted due to complete weld removal and further excavation. After repair welding, the casting is again re-examined to verify the acceptability of the repair in accordance with the initial quality requirements. Use of Computed Radiography: Since the development of the phosphor imaging plate, computed radiology is replacing film radiography in a number of applications. This new technology is the ability to digitize the image and store the information in a computer format. The generation of the image follows standard radiographic practice, but an imaging plate is used instead of film. An imaging plate is similar to a piece of film in that it is flexible. It has a polyester type base and then phosphors bonded on to the base. There is a clear layer over the phosphor to protect it. The imaging plate is placed in a standard cassette with lead screens, in a rigid plate cassette, or in a plastic packet. The plate is exposed and processed through the plate reader. The exposed barium fluorohalide, europium doped phosphor plates contain electrons that have been excited into a conduction band. These trapped electrons form a latent image on the plate. The plate is then exposed to a helium-neon laser in the plate reader, which releases the trapped electrons. The recombining of the electrons into their former lower orbit shells causes energy in the form of light to be emitted. This phenomenon is known as PSL or photo-stimulable luminescence. The resultant light energy is collected by a light guide and is quantified by assigning gray scales to the various intensities emitted and is then converted to an electrical signal. The information is then processed by the reader and transferred to a digital format in the computer. The resultant data can then be viewed on a high resolution monitor, stored on the hard drive, on optical disk, on a CD, DVD, imaged on laser film similar to a radiographic image, or printed on paper.

“Computed Radiology – A Useful Tool for the Casting Industry” Page 3 Advantages of Computed Radiology: The formation of a radiographic image on film is a fairly precise process. A radiographic technique is developed that will produce a specific density and sensitivity, usually within a very narrow range of exposure conditions. Computed radiology allows for a greater range of exposure conditions and still permits an image to be formed that can be adjusted and interpreted. This range or latitude of the imaging plates is a distinct advantage. Expensive reshooting and reprocessing time is not wasted since the range of use is so wide. Since the plates are sensitive to exposure to radiation, the length of time for exposure can be reduced. Typical times for standard film radiography have been cut by one half and some shots have been as low as one third the original exposure time. In addition to the saving of time on exposures, the time involved in processing of film is reduced from a 10-12 minute cycle time in automatic film processors down to less than one minute using computed radiography since the image is available for viewing at the work station almost immediately. A secondary monitor at the plate reader gives instantaneous information on the image formation as it is being displayed. If no image is obtained due to improper technique, a second shot can be made immediately, thereby reducing the time necessary to verify technique or exposure. The plate that is read by the plate reader is automatically erased and ready for another shot within 30 to 60 seconds. The plates can be used over and over. If treated with care, they can yield thousands of shots on each plate. They are almost indestructible in a cassette. They can be bent to the shape of the part much like film. The primary artifact or problem is if the plate becomes scratched. The scratch will appear on the image, much like a film that has a scratch or artifact on it. Plates that are scratched can be used for preliminary radiography, weld grind outs or for foundry control. The scratch only becomes an issue if it conceals or covers over a discontinuity on the image on an exposure for final acceptance. The same advantages apply when working on repair welding of castings. If a repair welded casting is radiographed and does not meet the specified quality level, the interpreter can release the item to the welders for reprocessing without waiting for film processor cycle time. Grind out excavation can be monitored by reshooting until the discontinuity is removed and no film is wasted. The wide range of the imaging plates also reduces the number of exposures. When a part thickness varies significantly and a number of shots are required along with multiple loaded cassettes, several exposures are normally required. Computed radiology reduces the number of exposures required, therefore, reduces the time and ultimately the cost of the inspection process. Use of lower kV and mA values for exposure reduce the risk to personnel of exposure to radiation, reduce maintenance costs and extend the life of the equipment since the x-ray or high energy unit is not operating as long. Film and chemical costs are eliminated also since the process is filmless. Dry laser printers can be used if a hardcopy is required for layout of defects for weld repair. Waste of film due to reshots because of density variations or misalignment is eliminated as well. The final advantage is the ability to manipulate and enhance the radiologic image. The main advantage is the ability to view castings that vary in thickness and density over

“Computed Radiology – A Useful Tool for the Casting Industry” Page 4 a wide range. By clicking on preset buttons in the computer program, parts with various thicknesses can be bracketed and each thickness viewed from a single shot. The sensitivity of the exposure can be adjusted to highlight edges that are difficult to see due to scatter or undercutting of the image. The ability to measure distance and area and magnify the image can greatly assist during interpretation of the casting. Density histograms can be generated so that areas can be compared along a line, much like a small slice through the casting. Separate parts can be viewed side by side on the monitor for comparison purposes using either a reject standard or for comparison of initial versus repaired views. The critical part of the process is being able to control the image by specific reading parameters that are embedded in each image. These can be recorded on the radiographic technique so that the image can be viewed the same way each time it is accessed, rather than by allowing a wide open, infinitely variable viewing which may not necessarily provide coverage of the area specified. This provides for consistency and an auditable process. If a particular exposure is not properly being displayed, it can be re-processed at the reader station without making another exposure. Codes, Standards and Quality Control: Typical radiographic work using film for castings may be performed to a variety of standards available such as ASTM E1742, ASTM E142, ASTM E1030, ASTM E2104, ASME Section, V, AMS STD 2175, and a host of others. Computed digital radiology has been accepted into industrial documents such as ASTM E2033, Standard Practice for Computed Radiology, ASTM E2007, Standard Guide for Computed Radiology, E2445, Standard Practice for Qualification and Long-Term Stability of Computed Radiology Systems, ASTM E2446, Standard Practice for Computed Radiology Systems, and ASTM E2422, Standard Digital Reference Images for Inspection of Aluminum Castings. The development of other standard reference images is currently in progress as well for ASTM E2660, Investment Castings and ASTM E2669, Titanium Castings. ASME Section V, Article 2, including Mandatory Appendix III, IV, and VI. Calibration or verification of computed radiological systems uses several gages that are common to radiography. A line pair gage is used for determining spatial resolution. Contrast sensitivity is performed using contrast steps that change in small increments of 1%. These can be found under ASTM E1647, Standard Practice for Determining Contrast Sensitivity. Determination of image unsharpness has been defined under ASTM E2002, Standard Practice for Determining Total Image Unsharpness in Radiology. Monitors are controlled by use of SMPTE patterns on the screen or use of automated digital electronic systems such as a Dome card. Light meter readings are also taken on the monitor surface. Storage and transfer of data is vital to maintaining quality records. Digital data is stored either on hard drives, optical disks, compact disks (CD) or DVD’s. The raw data image is stored and can be retrieved for viewing and manipulation, either on the original system or as a separate software system, such as the “ImageShare” program. The consistency of the raw data is controlled by ASTM E2339, Digital Imaging and Communication in Nondestructive Evaluation

“Computed Radiology – A Useful Tool for the Casting Industry” Page 5 and ASTM E1475, Standard Guide for Data Fields for Computerized Transfer f Digital Radiological Examination Data. The information is transferred to storage disks by a means called lossless compression. In this way each copy is an original, with no data loss. DVD and CD disks have been rated for storage life from 50 to 100 years. Conclusion: Rapid advancement in digital technology is going to change the means by which casting inspection is performed. The ability to control or maintain costs will make the casting market more competitive and will provide a cost-effective tool for testing departments. Improvement in casting turnaround due to reduced inspection time will help make castings a choice selection for purchasers as well. New means of comparison to reference standards and possibly even automatic digital anomaly recognition in the future may lead to greater efficiency and productivity for the casting industry. State of the art computed digital radiology has proven to be one of these new avenues that can be easily adapted to many types of industry and yield quality added value along with significant cost savings.