TURBOFINISH® Process Report: Edge-Contour and Isotropic Surface Finish on Turbine Disk Features
TURBO-FINISH EDGE CONTOUR EFFECTS
This area was masked during TAM processing preserving the original nonisotropic ground surface These edge-area and tooth flat surfaces have been given isotropic surfaces with a two step method with TurboFinish and Turbo-Polish NOTE: edge contour shown here was achieved without a chamfer machining process
High Speed Precision Edge and Surface Finishing for Rotating Components INDEX TERMS: Deburring Edge Contour Isotropic surfacing Non-traditional Grinding Non-traditional Machining Super-Polishing Surface Finishing Loose Abrasive Edge Finishing Super-Finishing Turbo-Abrasive T U R BO - F I N I S H CORPORATION
25 Williamsville Road Barre MA 01005 Dr. Michael Massarsky President Phone: 978-355-9070 Fax: 978-355-2917 Email: Michael@turbofinish.com
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BEFORE TURBO-FINISH
This close up photo shows details on disk features and geometries prior to TAM Process-
NOTE: Original sharp edge condition (this edge not modified by chamfer machining)
NOTE: prior to TurboFinish processing surfaces exhibit positive skew and nonisotropic surface characteristics
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TURBO[TURBOTURBO-FINISH [TURBO-ABRASIVE MACHINING] is a loose abrasive machining method that can deburr and produce edge contour effects very rapidly. The method is especially useful for the final machining and finishing of larger complex rotating components. These types of parts often are not good candidates for other mass media finishing techniques and until now have required very tedious and expensive manual deburring. The Turbo-Abrasive Machining process can automate much of this work, not only reducing labor and costs, but improving the uniformity and consistency of edge and surface effects in a way not possible to duplicate with single-point-of-contact machining methods. This uniformity and the isotropic nature of the edges and surfaces that are developed can also markedly improve the surface integrity and fatigue resistance of many types of critical components. TURBOTURBO-FINISH PROCESS PARAMETERS There a number of processing parameter that will contribute to the results on a given part. These parameters are controllable and repeatable with programmable TURBO-FINISH PLC process control technology . These parameters include: ■ ■ ■ ■ ■ ■ Part Rotational Speed Part Positioning (including distance from or depth of fluidized bed envelopment) Time cycle of Rotation and Counter-rotation Abrasive Grain Velocity within Fluidized Bed Abrasive Grain Size Abrasive Grain Composition and Pre-treatment
________________________________________________ Pictured to the right is a Turbo-Finish Model TF-522 TurboAbrasive Machining Center. This machine is capable of producing Turbo-Finish results on 250-500mm diameter Turbine disks
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Not processed, non-isotropic surface TAM Isotropic Surface Raw machine chamfered edge
TAM process radiuses chamfered edge BEFORE: This photo detail shows the edge and surface condition of the disk prior to Turbo-Abrasive Machining with the TF-500 TurboFinish machine. AFTER: Shown here is the removal of secondary burrs produced by the chamfer machining process early in the TAM abrasive edge-contour and smoothing process. Ground and TAM (isotropic) surfaces also contrasted.
TAM technology has several advantages in comparison with other mechanical finishing processes. Some of these advantages are: • A High flow of free abrasive grain allows for penetration of abrasive media particles into difficult to access part areas that require edge and surface finish improvement. • Low energy consumption; especially in contrast to pressure blast surface finishing. Very simple tooling, processing, and maintenance requirements • Combination of rapid deburring and high rates of metal removal with significant improvements in the physical and mechanical properties of metal surfaces that can enhance surface integrity. These changes include developing: residual compressive stress, surface isotropicization, surface profile The above graph shows a detail of a typical radius produced on a tur- skewness correction, contact rigidity and load bearbine disk feature by Turbo-Abrasive Machining utilizing a combination ing ratio improvements. of edge contact with loose abrasive granules in a fluidized bed and controlled rotational velocity of the spindle mounted component.
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TURBO-FINISH: Notes on Edge/Surface Finishing and Surface Integrity Issues and TURBO-FINISH:
This technology has been demonstrated to successfully impart compressive stresses into parts in a fashion that is in some ways superior to shot peening. 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 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 and the creation of an overall stress equilibrium in parts with a complex feature set. To elaborate: (1) The linear characteristics of ground or machined surface patterns can be modified into one in which surface tracks developed by abrasive action have a random (isotropic) non-linear nature, minimizing potential crack propagation points. (2) The basic character of the surface profile can also be changed from one having a positive skew in which surface peaks were the predominant surface feature to a neutral or negatively skewed surface. These types of plateaued surfaces have much higher bearing load ratios than their positively skewed counterparts, and can increase the service life of components or tools in high wear situations dramatically. This characteristic along with surface isotropicity can improve contact rigidity of mating surfaces, improving seal contact and broadening the surface area of mating surfaces generally. These types of surfaces often display improved lubricant retention properties as well. Almost all common machining and manual finishing methods produce uneven stress hot-spots in machined parts. This occurs because of the rapid rise and fall of temperature on metal surfaces at the tool or wheel point of contact. TAM not only produces beneficial compressive stresses, but also in many cases, where all surfaces and features are effected identically and simultaneously, can promote a stress equilibrium or uniformity through out the entire part. Thus TAM could be looked at as a corrective after process for critical parts that suffer from these machining related surface integrity issues. The synergy involved in developing these kinds of effects can add a potential value to service life, performance and functionality of parts that far exceeds the value of the improvements to fit, function and aesthetics commonly associated with other mechanical or mass finishing processes. The technology is currently used in the United States to deburr and contour the edges of complex parts, and to create isotropic surface finishes essential in finishing many complex parts. Unlike single-point-ofcontact machining technologies the technology is relatively simple to control once process parameters for a given part have been developed, and thus enjoys the attributes of reliability and repeatability of simpler mechanical (vs. digital feedback) technologies. However, It accomplishes uniform results on very complex parts that often cannot be achieved reliably by other much more complex, processes. The technology involves developing a fluidized bed of media in which the part to be processed is partially immersed while being rotated. A wide variety of differing results may be achieved by varying the process parameters (media, process time, rotational speed etc.). Process results can be closely controlled and are programmable, and are totally repeatable, providing unequaled process quality control. The process is dry, and involves no chemicals or environmentally unfriendly materials.
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TAM Process Elements. Turbo Abrasive Machining (TAM) technology depends on utilizing relatively small free abrasive grains to access intricate part shapes. Unlike blasting or other impact metal finishing methods, the mechanism behind TAM processes utilize a combination of kinematic forces to produce unique and distinctive edge and surface finishes on complex and intricate parts which can not be processed with other automated deburring or finishing methods, and usually are processed with manual deburring techniques. These two forces act synergistically and are mutually dependent. They consist of (1) envelopment of the part with abrasive grain suspended in a fluidized bed and (2) interfacing part edges and surfaces with abrasive grain by rotational motion of the part. Although the abrasive materials used for TAM processing are in some ways similar to grinding and blasting materials, the surface condition produced is unique. One reason for this is the multidirectional and rolling nature of abrasive particle contact with part surfaces. These surfaces are characterized by a homogenous, finely blended abrasive pattern developed by the non-perpendicular nature of abrasive attack. There is no perceptible temperature shift in the contact area and the finely textured random (isotropic) abrasive pattern is a highly attractive substrate for subsequent coating operations.
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Machining marks evident on disk face prior to TAM processing
TurboTurbo-Finish Processes and Component Service Life Improvement. Although Turbo-Finis is primarily utilized as automated method for deburring and developing edge-contour, as the chart above shows, very important service life attributes can also be achieved. By utilizing this spindle oriented deburr and finish method it is possible to produce compressive stresses in the MPa = 300 - 600 range that formed to a surface layer of metal to a depth of 20 - 40 µm. Spin pit tests on turbine disk components processed with the method showed an improved cycle life of 13090 ± 450 cycles when compared to the test results for conventionally hand deburred disks of 5685 ± 335 cycles, a potential service life increase of 2 – 2.25 times, while reducing the dispersion range of cycles at which actual failure occurred. Vibratory tests on steel test coupons were also performed to determine improvements in metal fatigue resistance. The plate specimens were tested with vibratory amplitude of 0.52 mm, and load stress of 90 MPa. The destruction of specimens that had surface finishes developed by the Turbo-Finish method took place after: (3 - 3.75)*104 cycles a significant improvement over tests performed on conventionally ground plates that started to fail after: (1.1 - 1.5)*104 cycles.
