October 2013 f2 deburring 1


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Mass media finishing techniques improve part performance and service life, and these processes can be tailored or modified to amplify this effect. Although the ability of these processes to drive down deburring and surface finishing costs when compared to manual procedures is well known and documented, their ability to dramatically effect part performance and service life are not. This facet of edge and surface finishing deserves closer scrutiny and this is also true of larger and more complex parts – only more so

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October 2013 f2 deburring 1

  1. 1. October 2013 | ManufacturingEngineeringMedia.com 1 T urbo-Abrasive Machining (also referred to as TAM or Turbo-Finish) is a mechanical deburring and finishing method originally developed to automate edge finishing procedures on complex rotationally oriented and symmetrical aerospace engine compo- nents. Aerospace parts such as turbine and compressor disks, fan disks and impellers pose serious edge finishing problems. Manual methods used in edge finishing for these parts were costly and time-consuming. What’s more, human intervention, no matter how skillful at this final stage of manufacturing, was bound to introduce some measure of non-uniformity in both effects and stresses in critical areas of certain features on the part. Free Abrasives Flow for Automated Finishing Exploring new methods of surface finishing that go beyond deburring to specific isotropic surface finishes that can increase service life Dr. Michael L. Massarsky Turbo-Finish Corporation David A. Davidson SME Manufacturing Deburring/Finishing Tech Group Deburring & Finishing In Turbo-Abrasive Machining, a broad, low-speed airstream is used to impart motion to powdered or granular material within a chamber.The material, typically small aluminum oxide grains, takes on the properties of and behaves like a fluid. In this example, the fluidized bed partially envelops a rotating workpiece, creating a specific abrasive environment for a certain level of deburring and finishing.
  2. 2. Since its inception, turbo-abrasive machining, a method that utilizes fluidized abrasive materials, has facilitated signifi- cant reductions in the amount of manual intervention required to deburr large components. Additionally, the process has also proved to be useful in edge and surface finishing a wide vari- ety of other nonrotational components by incorporating these components into fixturing systems. The advantages of this method go beyond the simple removal or attenuation of burrs. The method is also capable of producing surface conditions at these critical edge areas that contribute to increased service life and functionality of parts that are severely stressed in service. Among these advantages are (1) the creation of isotropic surfaces, (2) the replacement of positively skewed surface profiles with negative or neutral skews and (3) the development of beneficial compressive stress. Deburring, Finishing, Part Performance and Productivity Deburring and surface conditioning of complex machined parts is one of the most troublesome problems faced by the metalworking industry. In many cases, parts with complex geometric forms that are machined, or manufactured with very sophisticated computer-controlled equipment, are then deburred, edge finished, and surface conditioned with manual or hand-held power tools. This labor-intensive manual han- dling often has a considerable negative impact on manufac- turing process flow, productivity, and uniformity of features as well as part-to-part and lot-to-lot uniformity. The workflow interruption and production bottlenecks that can result are frequently one of the most significant headaches that manufacturing managers must confront. The total costs involved in performing manual finishing often defy quantification. As these types of processes are seldom capital intensive, they frequently escape the budget scrutiny they de- serve. Additionally, it is becoming increasingly clear that edge and surface finish effects can now be produced on parts that contribute substantially to their performance as well as wear and fatigue resistance values. TAM Advantages TAM processes were developed primarily for automating de- burring and surface conditioning procedures for complex rotat- ing components. As an automated machining/finishing process, TAM is designed to address the uniformity and productivity concerns noted above. Repetitive motion injury problems can be minimized or eliminated as manual methods are replaced with automated machining procedures. Substantial quality and uniformity improvements can be made in precision parts as the art in manual deburring is removed and replaced with the sci- ence of a controllable and repeatable machining sequence. The time and cost of having substantial work-in-progress delays, production bottlenecks, nonconforming product reviews, rework and scrap can be reduced dramatically. Manual processes consuming many hours are reduced to automated machining cycles of only a few minutes. Fluidized Bed Technology in Action TAM machines could be likened to free abrasive turning centers. They utilize fluidized bed technology to suspend abrasive materials in a specially designed chamber. Parts interface with granular abrasive material on a continuous basis by having part surfaces exposed and interacted with the fluidized abrasive bed by high-speed rotational or oscillational movement. This combination of abrasive envelopment and high-speed rotational contact can produce important func- tional surface conditioning effects and deburring and radius formation very rapidly. Unlike buff, brush, belt and polish methods or even robotic deburring, abrasive operations on rotating components are performed on all features of the part simultaneously. This produces a feature-to-feature and part-to-part uniformity that is almost impossible to duplicate by any other method. Surface finishes and effects can be generated on the entire 2 ManufacturingEngineeringMedia.com | October 2013 Deburring & Finishing This broach slot area of a turbine disk has been turbo-abra- sive machined and then turbo-polished to remove burrs and produce edge-contour with isotropic surfaces,specifi- cally at the edge-area,but generally on the disk itself. PhotocourtesyDr.MichaelMassarsky,Turbo-FinishCorporation
  3. 3. exterior of complex parts, and also fixtured nonrotational components. Various surface-finish effects can be obtained by controlling variables of the process such as rotational part speed, part positioning, cycle times, abrasive particle size and characteristics, and others. Surface-finish effects in TAM are generated by the high peripheral speed of rotating parts and the large number and in- tensity of abrasive particle-to-part surface contacts or impacts in a given unit of time (200–500 per mm²/sec). It should be noted that surface-finish effects developed from this process depart October 2013 | ManufacturingEngineeringMedia.com 3 Deburring & Finishing T his before photograph above was taken with a scanning electron microscope at 500× magnification. It shows the surface of a raw unfinished “as cast” turbine blade. The rough initial surface finish as measured by profilometer was in the 75–90 Ra (µin.) range. As is typical of most cast, ground, turned, milled, EDM and forged surfaces this surface shows a positive Rsk [Rsk –skewness–the measure of surface symmetry about the mean line of a profilometer graph. Unfinished parts usually display a heavy concentration of surface peaks above this mean line, generally considered to be an undesirable characteristic from a functional viewpoint.] This SEM photomicrograph (500× magnification) above was taken after processing the same turbine blade in a multistep procedure utilizing orbital pressure methods with both grinding and polishing free abrasive materials in sequence. The surface profile has been reduced from the original 75–90 Ra (µin.) to a 5–9 Ra (µin.) range. Additionally, there has been a plateauing of the surface and the resultant smoother surface manifests a negative skew (Rsk ) instead of a positive skew. This type of surface is considered to be very “functional” in both the fluid and aerodynamic sense. The smooth, less turbulent flow created by this type of surface is preferred in many aerodynamic applications. Another important consideration the photomicrographs indicate is that surface and subsurface fractures seem to have been removed. Observations with backscatter emission with a scanning electron microscope gave no indication of residual fractures. Surface Characterization with Optical Interferometry. Surface topographical mapping is coming into increasing use to bet- ter quantify surfaces as they relate to part service life, function and performance. The surface shown in the top row is one that has been processed to blend in parallel rows of surface peaks left behind from fine grinding operations (as shown in the bottom row of diagrams). The resultant surface is one that is more isotropic or random in nature. This type of surface can be an important surface attribute to parts that are subjected to repeated stress or strain and parts that undergo high force loading of opposing surfaces. Also contributing to the improved functional surface is the negative skew of the surface profile and beneficial compressive stress equilibrium imparted to the parts by high-energy finishing methods. Understanding Functional Surfaces Photo courtesy Jack Clark, Surface Analytics Photo courtesy Jack Clark, Surface Analytics
  4. 4. significantly from those obtained from air or wheel blasting. TAM processes can produce much more refined surfaces by virtue of the fact that the rotational movement of parts processed develop a very fine finish pattern and a much more level surface profile than is possible from pressure and impact methods. A very important functional aspect of TAM technology is its ability to develop needed surface finishes in a low-temper- ature operation (in contrast with conventional wheel and belt grinding methods), with no phase shift or structural changes in the surface layer of the metal. A further feature of the process is that it produces a more random pattern of surface tracks than the more linear abrasive methods such as wheel grinding or belt grinding. The nonlinear finish pattern that results often enhances the surface in such a way as to make it much more receptive as a bonding substrate for subsequent coating and even plating operations. TAM Applications TAM provides a method whereby final deburring, radius formation and blending in of machining irregularities could be performed in a single machining operation. This operation can accomplish in a few minutes what in many cases took hours to perform manually. It has become obvious that the tech- nology could address edge-finishing needs of other types of rotationally oriented components such as gears, turbocharger rotors, bearing cages, pump impellers, propellers, and many other rotational parts. Nonrotational parts can also be pro- cessed by fixturing them to the periphery of disk-like fixtures. Many larger and more complex rotationally oriented parts, which can pose a severe challenge for conventional mechani- cal finishing methods, can easily be processed. TAM as a surface-conditioning method is a blend of current machining and surface-finishing technologies. Like machining processes the energy used to remove material from the part is concentrated in the part itself, not the abrasive material interfacing with part surfaces, and like many surface- finishing processes material removal is not accomplished by a cutting tool with a single point of contact, but by complete envelopment of the exterior areas of the part with abrasive materials. As a result deburring, edge finishing, surface blend- ing and smoothing, and surface conditioning are performed on all exterior exposed surfaces, edges, and features of the part simultaneously. Many metal parts that are machined by being held in a rotational workholding device (for example: chucks, between centers, rotary tables, etc.) are potential candidates for TAM processes, and in many cases these final deburring and surface conditioning operations can be performed in minutes, if not in seconds. TAM Processing Characteristics TAM produces an entirely different and unique surface condition. One of the reasons for this is the multidirectional and rolling nature of abrasive particle contact with part sur- faces. Unlike surface effects created with pressure or impact methods such as air or wheel blasting, TAM surfaces are characterized by a homogeneous, finely blended, abrasive pattern developed by the nonperpendicular nature of abrasive attack. Unlike wheel or belt grinding, surface finishes are gen- erated without any perceptible temperature shift at the area of contact and the micro-textured random abrasive pattern is a much more attractive substrate for subsequent coating operations than linear wheel or belt grinding patterns. TAM processes have strong application on certain types of parts that have critical metal surface improvement requirements of a functional nature. Significant metal surface integrity and im- provement has been realized in processes with both abrasive and nonabrasive media. As a result of intense abrasive par- ticle contact with exposed features, it has been observed that residual compressive stresses of up to 400–600 MPa can be created in selected critical areas. Tests performed on rotating parts for the aerospace industry that were processed with this 4 ManufacturingEngineeringMedia.com | October 2013 Deburring & Finishing To see Turbo-Abrasive Machining in action, check out The Metal Shop at Manufacturing Engineering’s YouTube channel: www.tinyurl.com/mfgmetalshop This Model TF-522 Turbo- Abrasive Machining Center is designed for deburring and edge contour of rotating hardware up to 20" (+500 mm).
  5. 5. method demonstrated a 40–200% increase in metal fatigue resistance tested under working conditions, when compared with parts that had been deburred and edge finished with less sophisticated manual treatment protocols. Significant process characteristics to keep in mind include (1) very rapid cycle times; (2) a high-intensity, small media operation that allows for access into intricate part geometries; (3) a completely dry operation; (4) metal surface improvement effects: including isotropic, negatively skewed surfaces with improved bearing load ratio and contact rigidity (5) no part- on-part contact; (6) modest tooling requirements; (7) primarily an external surface preparation method some simpler interior channels can also be processed, and (8) many types of rotating components can be processed and non-rotational components can also be processed when attached to disk like fixtures. ME October 2013 | ManufacturingEngineeringMedia.com 5 Deburring & Finishing TURBO-FINISH Ph: 917-518-8205 Web site: www.turbofinish.com Want More Information? In this view,Turbo-Abrasive Machining has been performed, edge contour has been developed, and isotropic surfaces are evident in the flats visible between the slots.The previous surface condition can also be seen on the surface area closer to the center which was masked by the processing tooling.