SME Member: Share Your Story (Sample)

SME Member: Share Your Story (Sample)

YOUR INFORMATION:  (to submit your story go to:  http://www.sme.org/member-story/

First Name *    Dave
Last Name * Davidson
Job Title  Retired Consultant
Company  Deburring Solutions
Phone * 509 230 6821
Email *  dryfinish@gmail.com

hat is ONE word that can describe your membership experience? *

X  Connections
Helpful
Resourceful
Other

How has being an SME member impacted your personal life and/or professional career? *

The networking, mentoring and connectivity that SME afforded me had a profound effect on my subsequent career.  Although my SME profile indicates that I have been a member since 2004, I have actually been a member and involved in SME activities since the 1980’s.  At that time I was involved in a family business that manufactured wooden shoe pegs that at the time were a popular materiel for tumble polishing plastic items such as eyeglass frames, dental acrylics, buttons, jewelry and the like.  This family business was over 100 years old at the time and used steam era machinery to produce its product. [SEE: http://www.slideshare.net/dryfinish/kearsarge-history-2011rev  ] The company lacked understanding of the technology and I became a member of SME’s Burr, Edge and Surface Technology (BEST) division.  Involvement with this group led to my acquaintance with John Kittredge, LaRoux Gillespie, Larry Rhoades, Bernard Hignett, Sam Thompson and others, some of whom were to become SME mentors and who coached me into contributing written technical material on mass finishing processes.  [SEE: http://www.slideshare.net/dryfinish/sme-mr-85-hardwood-media-dry-process-applucations  and   http://www.slideshare.net/dryfinish/almost-buffed  ]  With the help of these SME mentors I established a working process laboratory from which I developed a new line of abrasive and polishing products and also developed new mass finishing processes for barrel, vibratory and centrifugal finishing systems to find the solution to customer finishing problems.  Later additional SME mentors such as Jack Clark and Rodney Grover helped me with the product launch of Dr. Michael Massarsky’s Turbo-Abrasive Machining technology in North America [SEE:  http://www.slideshare.net/dryfinish/october-2013-f2-deburring-1  ]  and as a consultant and advisor to industry on high energy edge and surface finishing processes  [SEE:  http://www.slideshare.net/dryfinish/november-2012-f4-deburring-1-final  ]

How long have you been in manufacturing and how did you first get involved in the industry?

I have been involved in manufacturing since 1975, worked my way up as a millwright and production manager.  Among my early duties was operating an 1878 Portland Marine and Locomotive stationary steam engine that was the power plant for the shoe peg manufacturing plant that belonged to the family business.  As time went by I became more actively engaged in process and product development activities.

If you’re a new member, how did you hear about SME?

 I am not a new member, I am an old member.  I became an SME member because a mentor figure, Sam Thompson all but dragged me down to the SME booth at an SME trade show in Hartford CT back in 1983 and made me sign my name to an SME application.

Have more to share about your manufacturing experience or the industry?

 SME was an early adopter of mass finishing technology education programming.  Through its BEST division it sponsored conferences and symposiums and published technical papers and articles on the subject.  However this an area of industry that is still often neglected by the mainstream manufacturing community, and most engineers graduating from school have little understanding of its importance and how critical it can be to overall part and component functionality and performance.

 

 

 

 

Isotropic Mass Finishing for Surface Integrity and Part Performance : Products Finishing

The costs of neglecting to consider deburring and surface conditioning in production planning and engineering can be substantial. Frequently overlooked, however, are the potentially serious problems that can develop from the ad hoc and interim solutions that are selected to deal with what now has become—in some instances—a manufacturing crisis.

by Jack Clark, Surface Analytics, jclark@surfaceanalytics.com
and Dave Davidson, SME Deburr/Finish Technical Group

When presented with edge and surface finishing problems, many manufacturers continue to reach for solutions that rely on out-of-date, time-consuming and labor-intensive methods. It is still not unusual to see precision parts and critical hardware being manually handled, and edge and surface finishing operations being performed with abrasive hand tools or manually controlled power tools that use coated abrasives or abrasive filaments.

This situation often arises from insufficient planning and a lack of understanding of what will be required to render the manufactured part or component acceptable for the end user. At the root of the problem is a manufacturing and design engineering culture that considers its work done when the part comes off the machining center or the fabricating machine. Too often, part edge and surface condition is simply someone else’s problem.

This is a situation that deserves and is getting an increasing amount of scrutiny. It is a subject repeatedly discussed at the “Deburring, Edge-Finish, and Surface Conditioning Technical Group” sponsored by SME Manufacturing’s Machining/Material Removal Technical Community in Dearborn, Michigan.

The costs of neglecting to consider deburring and surface conditioning in production planning and engineering can be substantial. Frequently overlooked, however, are the potentially serious problems that can develop from the ad hoc and interim solutions that are selected to deal with what now has become—in some instances—a manufacturing crisis.

Hidden Costs

The manufacturers who resort to hand or manual finishing do not do so because of its cost on a per piece basis (it is by far the most costly method of handling the problem) but, often, it is the most obvious solution and the easiest and the quickest to implement. The reason this problem persists is that there is an imperfect understanding of the serious hidden cost this manual and uncontrolled approach imposes. This is not to say that some deburring and finishing problems don’t require some manual intervention; some do. In many cases, however, manual methods are selected because they are an easy and quick fix.

The first casualty of this manual approach is the investment the manufacturer has made, often in the millions, for precise and computer controlled manufacturing equipment. The idea behind this investment was to have the ability to produce parts that are uniformly and carefully manufactured to exacting specifications and tolerances. At this point, in too many cases, the parts are then handed off to manual deburring and finishing procedures that will guarantee no two parts will ever be alike.

Figure 1 and 2: It is axiomatic that almost all surfaces produced by common machining and fabrication methods are positively skewed.  These positively skewed surfaces have an undesirable effect on the bearing load of surfaces, negatively impacting the performance of parts involved in applications where there is substantial surface-to-surface contact.  Specialized high energy finishing procedures can truncate these surface profile peaks and achieve negatively skewed surfaces (Fig 2.) that are plateaued, presenting a much higher surface bearing contact area. (Photo Courtesy of Jack Clark, Surface Analytics).

Moreover, the increased complexity and precision requirements of mechanical products have reinforced the need for accurately producing and controlling the edge and surface finish of manufactured parts. Variations in the surface texture can influence a variety of performance characteristics. The surface finish can affect the ability of the part to resist wear and fatigue; to assist or destroy effective lubrication; to increase or decrease friction and/or abrasion with cooperating parts; and to resist corrosion. As these characteristics become critical under certain operating conditions, the surface finish can dictate the performance, integrity and service life of the component.

The role of mass finishing processes (barrel, vibratory and centrifugal finishing) as a method for removal of burrs, developing edge contour and smoothing and polishing parts has been well established and documented for many years. These processes have been used in a wide variety of part applications to promote safer part handling (by attenuation of sharp part edges) improve the fit and function of parts when assembled, and produce smooth, even micro-finished surfaces to meet either functional or aesthetic criteria or specifications. Processes for developing specific edge and/or surface profile conditions on parts in bulk are used in industries as diverse as the jewelry, dental and medical implant industries on up through the automotive and aerospace industries.

Less well known and less clearly understood is the role specialized variants of these types of processes can play in extending the service life and performance of critical support components or tools in demanding manufacturing or operational applications.

Improved Technology

Industry has always been looking to improve surface condition to enhance part performance, and this technology has become much better understood in recent years. Processes are routinely used to improve the life of parts and tools subject to failure from fatigue, and to improve their performance. These improvements are mainly achieved by enhancing part surface texture in a number of different, and sometimes complimentary, ways.

To understand how micro-surface topography improvement can impact part performance, some understanding of how part surfaces developed from common machining, grinding and other methods can negatively influence part function over time. A number of factors are involved:

Positive vs. Negative Surface Skewness. The skew of surface profile symmetry can be an important surface attribute. Surfaces are typically characterized as being either negatively or positively skewed. This surface characteristic is referred to as 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 (a positive skew). It is axiomatic that almost all surfaces produced by common machining and fabrication methods are positively skewed. These positively skewed surfaces have an undesirable effect on the bearing ratio of surfaces, negatively impacting the performance of parts involved in applications where there is substantial surface-to-surface contact. Specialized high energy finishing procedures can truncate these surface profile peaks and achieve negatively skewed surfaces that are plateaued or “planarized,” presenting a much higher surface bearing contact area. Evidence confirms that surface finishing procedures tailored to develop specific surface conditions with this in mind can have a dramatic impact on part life. In one example, the life of tooling used in aluminum can stamping operations was extended 1,000%, or more, by improved surface textures produced by high-energy mechanical surface treatment

Directionalized vs. Random (Isotropic) Surface Texture Patterns. Somewhat related to surface texture skewness is the directional nature of surface textures developed by typical machining and grinding methods. These machined surfaces are characterized by tool marks or grinding patterns that are aligned and directional in nature. It has been established that tool or part life and performance can be substantially enhanced if these types of surface textures can be altered into one that is more random in nature. Post-machining processes that use free or loose abrasive materials in a high energy context can alter the machined surface texture substantially, not only reducing surface peaks, but generating a surface in which the positioning (or lay) of the peaks and valleys has been altered appreciably. These “isotropic” surface effects have been demonstrated to improve part wear and fracture resistance, bearing ratio and improve fatigue resistance. These performance related effects are even more pronounced with high energy finishing methods such as centrifugal barrel finishing and spindle finishing. See Figures 3 and 4.

Figure 3: (Photo Courtesy of Jack Clark, Surface Analytics).

Figure 4: (Photo Courtesy of Jack Clark, Surface Analytics).

Residual Tensile Stress vs. Residual Compressive Stress. Many machining and grinding processes tend to develop residual tensile stresses in the surface area of parts. These residual tensile stresses make parts susceptible to premature fracture and failure when repeatedly stressed. Certain high-energy mass finishing processes can be implemented to modify this surface stress condition, and replace it with uniform residual compressive stresses. Many manufacturers have discovered that as mass finishing processes have been adopted and put into service, the parts involved have developed a working track record with unanticipated developments (their parts are better) and not just in the sense that they no longer have burrs or sharp edges, or that they have smoother surfaces. Depending on the application, they last longer in service, are less prone to metal fatigue failure, exhibit better tribological properties (translation: less friction and better wear resistance) and, from a quality assurance perspective, are much more consistent and uniform.

The question that comes up is why do commonly used mass media finishing techniques produce this effect? There are several reasons. The methods typically are non-selective in nature. Edge and surface features of the part are processed identically and simultaneously. These methods also produce isotropic surfaces with negative or neutral surface profile skews. Additionally, they consistently develop beneficial compressive stress equilibrium. These alterations in surface characteristics often improve part performance, service life and functionality in ways not clearly understood when the processes were adopted. In many applications, the uniformity and equilibrium of the edge and surface effects obtained have produced quality and performance advantages for critical parts that can far outweigh the substantial cost-reduction benefits that were the driving force behind the initial process implementation.

Vibratory Finishing and Burnishing

The assertion above has been affirmed by both practical production experience and validation by experiment in laboratory settings. David Gane and his colleagues at Boeing studied the effects of using a combination of fixtured-part vibratory deburring and vibratory burnishing (referred to by them as Vibro-peening or Vibro-strengthening) processes to produce (1) sophisticated edge and surface finish values and (2) beneficial compressive stress to enhance metal fatigue resistance. In life cycle fatigue testing on titanium test coupons, it was determined that the vibro-deburring/burnishing method produced metal fatigue resistance that was comparable to high intensity peening that measured 17A with Almen strip measurements. The striking difference between the two methods, however, is that the vibratory burnishing method produced the effect while retaining an overall surface roughness average of 1 μm (Ra), while surface finish values on the test coupon that had been processed with the 17A high intensity peening had climbed to values between 5-7 μm (Ra). The conclusion the authors reached was that the practicality and economic feasibility of the vibro-deburring and burnishing method increased with part size and complexity.

Dr. Michael Massarsky of the Turbo-Finish Corp. was able to supply comparative measurements on parts processed by his method for edge and surface finish improvement. Using 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

High Energy Centrifugal Finishing is widely used in the manufacture of medical, surgical and dental devices to develop very highly refined surfaces. Shown here is a dental device made up both of acrylic and cast chrome alloy materials that have been machine polished. (Photo courtesy of Mass Finishing Inc.)

Mass media finishing techniques (barrel, vibratory, and especially high energy centrifugal and spindle finish) can be used to 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 with 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 finish processing needs to be better understood and deserves closer study and documentation. Industry and public needs would be well served by a research consortium of partners at the industry, university and governmental agency levels to better understand the role surface textures and stress equilibrium play in enhanced component life and performance.

The authors wish to acknowledge the technical assistance of the following: Dr. Michael Massarsky, Turbo-Finish Corp., Barre, Massachusetts; Thomas Mathisen, Mass Finishing Inc., Howard Lake, Minnesota, and Katie MacKay at MacKay Manufacturing, Spokane, Washington.

Dave Davidson is with SME Manufacturing and an adviser to the Machining/Material Removal Technical Community; he can be reached at dryfinish@gmail.com. Jack Clark, also an SME member, is with the Colorado State University’s Department of Mechanical Engineering and with Surface Analytics, LLC; he can be reached at jclark@surfaceanalytics.com.

DRY MECHANICAL EDGE AND SURFACE FINISHING FOR ROTATING AEROSPACE COMPONENTS

[See the process, SEE THE VIDEO: Turbo-Abrasive Machining Video ]

DRY MECHANICAL EDGE AND SURFACE FINISHING FOR ROTATING AEROSPACE COMPONENTS

(New York, NY — July 24, 2014) Turbo-Abrasive Machining (TAM) is a new process for deburring and surface conditioning sophisticated multi-axis machined parts. Many parts, because of size and shape factors, can not be finished by a mass media technique but need manual intervention for final abrasive finishing. Apart from safety and production line/time considerations, a significant disadvantage of manual deburring is its impact on quality control and assurance procedures, which have often been computerized at great cost. The TAM process addresses these problems by automating the final machining and finishing production steps.

In TAM, fluidized bed technology is utilized to suspend abrasive or even peening materials in a specially designed chamber: Part surfaces are exposed to and interact with the fluidized bed materials on a continuous basis by high speed rotational or oscillational motion in an entirely dry environment.

The combination of abrasive envelopment and high speed rotating contact can produce important functional metal surface conditioning effects and deburring and radius formation very rapidly. Because abrasive operations are performed on all parts of rotating components simultaneously, the part and feature uniformities achieved are very hard to duplicate by other methods. In addition, sophisticated computer control technologies can be applied to create processes tailored for particular parts.

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 multi-directional and rolling nature of abrasive particle or peening particle contact with part surfaces. 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 micrto-textured random abrasive pattern is a highly attractive substrate for subsequent coating operations. In addition to the foregoing, the process has additional advantage, in that it develops significant beneficial compressive stress and stress equilibrium in parts as well as edge and surface finish conditions that are isotropic, plateaued or planarized surface characteristics and have negatively or neutrally skewed low micro-inch surface profiles.

SEE ALSO: http://www.turbofinish.wordpress.com
FOR TECHNICAL INFORMATION CONTACT:
Dr. Michael Massarsky
michael@turbofinish.com

Turbo-effects

<div style=”margin-bottom:5px”> <strong> <a href=”//www.slideshare.net/dryfinish/aerodef-tam-isotropic-finishing-17048034″ title=”Aerodef tam isotropic finishing” target=”_blank”>Aerodef tam isotropic finishing</a> </strong> from <strong><a href=”//www.slideshare.net/dryfinish” target=”_blank”>Dave Davidson</a></strong> </div>

<div style=”margin-bottom:5px”> <strong> <a href=”//www.slideshare.net/dryfinish/october-2013-f2-deburring-1″ title=”October 2013 f2 deburring 1″ target=”_blank”>October 2013 f2 deburring 1</a> </strong> from <strong><a href=”//www.slideshare.net/dryfinish” target=”_blank”>Dave Davidson</a></strong> </div>

Centrifugal Surface Finishing for Improved Part Performance

by Dave Davidson and Jack Clark

SEE THE PROCESS IN ACTION, watch the video…

Centrifugal barrel machine for high speed and high intensity mass media finishing

Centrifugal barrel finishing (CBF) is a high-energy finishing method, which has come into widespread acceptance in the last 25–30 years. Although not nearly as universal in application as vibratory finishing, a long list of important CBF applications have been developed in the last few decades.  Similar in some respects to barrel finishing, in that a drum-type container is partially filled with media and set in motion to create a sliding action of the contents, CBF is different from other finishing methods in some significant ways. Among these are the high pressures developed in terms of media contact with parts, the unique sliding action induced by rotational and centrifugal forces, and accelerated abrading or finishing action. As is true with other high energy processes, because time cycles are much abbreviated, surface finishes can be developed in minutes, which might tie up conventional equipment for many hours.

The principle behind CBF is relatively straightforward. Opposing barrels or drums are  positioned circumferentially on a turret. (Most systems have either two or four barrels mounted on the turret; some manufacturers favor a vertical and others a horizontal orientation for the turret.) As the turret rotates at high speed, the barrels are counterrotated, creating very high G-forces or pressures, as well as considerable media sliding action within the drums.  Pressures as high as 50 Gs have been claimed for some equipment. The more standard  equipment types range in size from 1 ft3 (30 L) to 10 ft3, although much larger equipment has been built for some applications.

Centrifugal barrel principle. Four drums are mounted on the periphery of a rotating turret, the drums counter rotate creating a vigorous slide of media within the drum as well as high centrifugal pressure of the media against part surfaces.

Media used in these types of processes tend to be a great deal smaller than the common sizes chosen for barrel and vibratory processes. The smaller media, in such a high-pressure environment, are capable of performing much more work than would be the case in lower energy equipment. They also enhance access to all areas of the part and contribute to the ability of the equipment to develop very fine finishes. In addition to the ability to produce meaningful surface finish effects rapidly, and to produce fine finishes, CBF has the ability to impart compressive stress into critical parts that require extended metal fatigue resistance. Small and more delicate parts can also be processed with confidence, as the unique sliding action of the process seems to hold parts in position relative to each other, and there is generally little difficulty experienced with part impingement. Dry process media can be used in certain types of equipment and is useful for light deburring, polishing, and producing very refined superfinishes.

Practicality and questions of cost effectiveness often determine whether high-energy methods are selected over conventional barrel or vibratory processes. If acceptable surface finishes can be developed in a few hours, conventional equipment is usually the most economic alternative. CBF equipment’s strong suit is the ability to develop surface finishes that may require over-lengthy time cycles in conventional equipment and the ability to develop a wide range of special surface finishes required for demanding and critical applications.

Centrifugal Barrels can be segmented too separate parts during processing to prevent part-on-part contact. This is especially useful for larger or more delicate parts.
Centrifugal Barrels can be segmented too separate parts during processing to prevent part-on-part contact. This is especially useful for larger or more delicate parts.

Centrifugal Disk Machines

Another high-energy finishing method that has become popular in recent years is the centrifugal disk. Most equipment is in the form of a cylinder or bowl with a spinning disk at the bottom. This disk propels the media upward against the interior sidewalls of the cylinder, which act as a brake, causing the mass to turn over and return to the center of the disk, where it is set in motion again. This unique media action is said to perform abrading operations at five to 10 times the speed of conventional vibratory action. As the machine is basically an open end chamber, in-process inspection and monitoring are possible. Faster time cycles can also reduce work in progress and make the equipment a good choice for manufacturing cells.  In general, larger or lengthy parts are not good candidates for disk finishing and, at times,  higher than usual media-to-part ratios must be maintained to avert part-on-part contact.

Machined, ground and cast surfaces can be substantially changed from their initial characteristics by high energy finishing contributing to significant increases in part performance and life.
Machined, ground and cast surfaces can be substantially changed from their initial characteristics by high energy finishing contributing to significant increases in part performance and life.

Equipment size ranges from 1/2 ft3 (15 L) bench-top models to 20 ft3 (600 L) floor machines.  One critical area of attention on this equipment is the gap between the spinner disk and the ring located around the exterior of the disk. Particles or fines of media that are capable of lodging in this area may cause significant damage to certain types of equipment. Correct media maintenance and attention to water flow-through rates can be an important factor in extending the useful service life of main components. Some equipment has the ability to run either wet or dry process media. Many equipment models, however, are designed for dedicated use in either wet or dry finishing and should not be used in the other mode without extensive consultation with the manufacturer.

Spin/Spindle Finish Equipment

An abrasive mass finishing media used for “roughing” or cutting in mass finishing machine finishing operations.

Spindle finishing is performed by fixturing parts at the end of a (stationary, rotating, planetary, or oscillating) spindle, and arranging for the part to be immersed in a mass of fine media, which may be vibrating, stationary, or directed at the workpiece by a spinner arrangement or rotation of the entire media chamber. As all parts must be fixtured, impingement from part-on-part contact is nonexistent. Time cycles can be very short, ranging from a few seconds to a few minutes. Equipment from various manufacturers may feature single or multifixture capabilities. Types of operations vary from heavy abrasive operations for deburring and stock removal, to the use of very fine dry polishing media in some equipment to develop color-buff-type finishes. One recent development in spindle finishing is the turbofinish method, which involves the high-speed rotation of components in a fluidized bed of fine abrasive or polishing material.

MASS FINISHING MEDIA

Media can be generally defined as the loose material contained in the work area of a mass finishing machine, which, when in motion, performs the work desired on part surfaces. Media may be natural or synthetic, abrasive or nonabrasive, random or preformed in shape. Much of the versatility inherent to mass finishing processes can be traced to the wide array of media types, sizes, and shapes available to industry. What follows is a rundown of the more commonly used media types.

Parts of all sizes, shapes and compositions have been deburred, edge-finished, surface conditioned and even polished using mass finishing methods such as centrifugal barrel finishing.  These parts exhibit isotropic surface conditions that can extend service life and improve function.
Parts of all sizes, shapes and compositions have been deburred, edge-finished, surface conditioned and even polished using mass finishing methods such as centrifugal barrel finishing. These parts exhibit isotropic surface conditions that can extend service life and improve function.

Natural/Mineral Media

Crushed and graded stone was once the predominant source for tumbling abrasives in the early days on barrel finishing. Raw source material included both limestone and granite. Some naturally sourced materials still find some barrel finishing applications today, such as corundum and novaculite. As a general rule, problems with fracturing, rapid wear and attrition rates, lodging, and disposal of the high amount of solid or sludge waste material created mitigates against crushed and graded mineral materials being an effective media for most applications.

Agricultural Media

Larger capacity CBF machine designed for superfinishing and polishing of cam and crankshafts, is said to accomodate 42 inch shafts.
Larger capacity CBF machine designed for superfinishing and polishing of cam and crankshafts, is said to accomodate 42 inch shafts.

A variety of granular media such as ground corn cob, walnut shell, pecan shell, sawdust, and wooden pegs are used in all of the equipment discussed. These dry process media are used in conjunction with various fine abrasive compounds similar to compounds that might be used in buffing applications. These media are often used in secondary cycles, after initial cutting and smoothing, to produce very fine reflective finishes. Attractive decorative finishes can be produced for jewelry and other consumer articles and, by extension, very low Ra finishes can be produced for precision industrial components.

Preformed Media

These media have largely replaced the crushed and graded mineral materials mentioned above. Media preforms are made from either extruded ceramic/abrasive shapes, which are fired, or resin-bonded, or which have been molded. The preform concept was an important one for the finishing industry. Unlike the more random shaped mineral media, size and shape preform selection could prevent media lodging and promote access to complex part shapes. The uniformity and predictable wear rates of the media also made it possible to prevent both lodging and separation problems caused by undersized, worn media. A wide variety of shapes have been developed by various manufacturers over the years to accommodate these requirements, including cones, triangles, angle-cut cylinders, wedges, diamonds, tristars, pyramids, arrowheads, and others.  Ceramic media are generally harder and more abrasive and are customarily used for more aggressive applications. Plastic media, as a rule, are somewhat softer and capable of producing finer finishes.

Burnishing Media

Steel burnishing media, is used in some systems to improve surfaces after initial abrasive cutting operations, unlike polishing, burnishing produces its effects by a compressive alteration of surface peaks and asperities, it also has a tendency produce substantial work-hardening of surfaces.
Steel burnishing media, is used in some systems to improve surfaces after initial abrasive cutting operations, unlike polishing, burnishing produces its effects by a compressive alteration of surface peaks and asperities, it also has a tendency produce substantial work-hardening of surfaces.

Media made from case hardened steel, stainless steel, and other formulations are used widely in barrel and vibratory equipment to produce burnished surfaces. These media are very heavy (300 lb/ft3 versus 100 lb/ft3 for ceramic media) when compared with other media types and are nonabrasive in nature. It should be noted that not all vibratory equipment can turn or roll steel media. Because of the weight, enhanced or heavier duty equipment may be necessary. The media performs by peening or compressive action; surface material is not removed, as is the case with abrasive media. Burnishing processes with steel media can be used either to develop reflective decorative finishes or provide functional finishes. One attribute of burnishing processes is that part surfaces are often work-hardened, which can extend the service life of components in moving assemblies. Steel media can be extremely long lasting, if care is taken to prevent corrosion of surfaces while in use and/or storage.  Nonabrasive porcelain media are also used for some burnishing procedures and are prevalent in some centrifugal applications.

COMPOUNDS

Prepared aluminum oxide or sintered bauxite nugget media is used in high energy machinery to produce burnishing and cold hardening effects on many parts.  Part surfaces usually must often be prepared with an abrasive operation prior to this burnishing step, which produces substantial cosmetic and aesthetic improvement in addition to the functional surface changes.
Prepared aluminum oxide or sintered bauxite nugget media is used in high energy machinery to produce burnishing and cold hardening effects on many parts. Part surfaces usually must often be prepared with an abrasive operation prior to this burnishing step, which produces substantial cosmetic and aesthetic improvement in addition to the functional surface changes.

Many abrasive and burnishing applications use water with specially formulated compound additives. The proper selection and dosage of these additives (in either liquid or dry powder form) can have a critical effect on the viability of the process. These compounds perform an assortment of functions including water conditioning or softening, pH control, oil/soil and metallic and abrasive fine suspension to prevent redeposition on part surfaces, rust inhibition, cleaning, foam development or control, as well as media lubricity control. Some special compounds are used to chemically accelerate finishing cycle times; some of these may be intensely caustic or corrosive and may require some special handling.

Below is excerpted from SME Technical Paper MR79-569 by J. Bernard Hignett

[ed. note: Harperizer and Harperized are trade names that refer to a specific OEM’s brand of centrifugal barrel finishing equipment]

Metal fatigue is the most common cause of fracture in metal components. It is usually caused by numerous repeated applications of low stress—stress much lower than that needed for fracture in a single application. The higher the stress, however, the fewer applications are needed to cause failure.    It follows that fatigue failure will be most cannon in components that are highly stressed and subject to repeated applications of stress in their functioning. A fatigue crack usually starts because the tensile componentof stress at the surface of the material is too high. It is thus beneficial to impart compressive stress of components to oppose any tensile stress towhich the component may be subjected in service.

Edge and surface finishing improvement can reduce the risk of fatigue failure. Surface imperfections can act as stress raisers and removal of these will invariably improve performance of any highly stressed part. For critical components it is desirable to achieve very high surface finishes to facilitate inspection for stress raises. Removal of burrs and uniform radiusing of all sharp edges and corners will similarly improve performance.

As has already been discussed, the CBF process can simultaneously deburr, edge radius and surface finish an immense range of components. It can also impart very high compressive stresses uniformly to the parts while edge .land surface finishing so offering unique capability of improving the resistance to fatigue failure of many highly stressed parts. The capability to improve resistance to fatigue failure is demonstrated by the results of some tests made by a manufacturer of stainless steel coil springs which were taken from a standard production run, Half of the components had the conventional finishing process of barreling, followed by shot peening, and the other half were processed in a centrifugal barrel machine for 20 minutes. The springs were tested to failure by compressing them from 1.104″ length to .730″, corresponding to a stress change from 9 to about 50,000 psi.   The results were that all springs finished by the conventional method failed at between 160,000 and 360,000 cycles. The springs that had been Harperized failed at between 360,000 and 520,000 cycles, an average performance improvement of 60%.

This photo shows bearing surface as seen by 2D and 3D scanning measurement.  The surface peaks and asperities are typical of machined or ground surfaces.
This photo shows bearing surface as seen by 2D and 3D scanning measurement. The surface peaks and asperities are typical of machined or ground surfaces. Photo courtesy of Jack Clark, Surface Analytics and Colorado State University Mech Eng Dept.

The tests indicated a benefit potentially greater than mere improvement of resistance to fatigue failure. It was noted that some of the parts that were processed in centrifugal barrel equipment had clearly visible surface defects or inclusions. Such defects were not visible in the parts that had been barreled and peened. It was the parts with the visible defects which were always those that failed below 400,000 cycles so that if in inspection department were instructed ot to accept parts with such defects, then performance of the springs put into service would be of consistently much higher quality.

Even more striking results were observed during a series of tests in another set of production springs of a somewhat different type. The springs which were not processed in CBF equipment all failed life tests before 600,000 cycles. None of the springs which were Harperized had failed at 800,000 cycles, the limit of the test.

After high energy centrifugal finishing the surfaces are far more functional for the bearing application.  More isotropic, more plateaued, more negatively skewed and have imparted a beneficial compressive stress.  All of these attributes improving the load bearing and tribological properties of the part.  Photo courtesy of Jack Clark, Surface Analytics.
After high energy centrifugal finishing the surfaces are far more functional for the bearing application. More isotropic, more plateaued, more negatively skewed and have imparted a beneficial compressive stress. All of these attributes improving the load bearing and tribological properties of the part. Photo courtesy of Jack Clark, Surface Analytics. and Colorado State University Mech Eng Dept.

Using CBF markedly to improve resistance to fatigue failure by a combination of edge and surface finishing, together with imparted very high compressive stresses, is cheaper than finishing by conventional means and then shot peening. There are opportunities to improve the ultimate resistance to fatigue failure of many parts, and, of prime importance, enable much better quality control by facilitating inspection. There is no longer need for components to be designed to allow a proportion of parts to fail prematurely due to surface defects. Of course, the technique has wide use for spring components, for instrument parts, for bearings and throughout the aerospace industry. There are also many opportunities to utilize improved and more consistent performance to design some of the cost out of many more mundane components within the metalworking industry, in particular, some automotive parts.

<div style=”margin-bottom:5px”> <strong> <a href=”//www.slideshare.net/dryfinish/covert-machined-surfaces-to-plateaued-surf” title=”Convert machined surfaces to plateaued surf” target=”_blank”>Convert machined surfaces to plateaued surf</a> </strong> from <strong><a href=”//www.slideshare.net/dryfinish” target=”_blank”>Dave Davidson</a></strong> </div>

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<div style=”margin-bottom:5px”> <strong> <a href=”//www.slideshare.net/dryfinish/greem-finishdavidson” title=”Greem finish-davidson” target=”_blank”>Greem finish-davidson</a> </strong> from <strong><a href=”//www.slideshare.net/dryfinish” target=”_blank”>Dave Davidson</a></strong> </div>

37 things you can do with Mass Media Finishing (Centrifugal Barrel or Vibratory Finishing) Equipment

by Dave Davidson, SME MMR Tech Community, dryfinish@gmail.com

The applications list shown below was compiled by a major OEM (Original Equipment Manufacturer) of finishing equipment. As you can see by examining some of the commercial applications listed, a lot more goes on here than just simple deburring. These applications say as much about the ingenuity of the people who developed them as it does about the versatility of the processes themselves.

1.  Deburring and radiusing of machined steel components.

2.  Deflashing zinc, aluminum or magnesium die castings.

3.  Deburring and edge-contour of powdered (sintered) metal parts

4.  Deburring of any punched, sheared, or formed (bent) metal

Machining and milling marks apparent on the front medical device have been completely removed by centrifugal barrel finishing
Machining and milling marks apparent on the front medical device have been completely removed by centrifugal barrel finishing

5.  Washing oil off of screw machine parts.  or  dry processing of screw machine parts for oil adsorption, smoothing and polishing especially in high pressure centrifugal machines (to reduce or eliminate effluent from conventional aqueous finishing)

6.   Deflashing plastic parts, also radiusing abrasively or producing dry process polishing effects.

7.   Pre-plate finishing items such as golf clubs, hand tools, small components,  costume jewelry and many other items.

8.  Improving surface finish on 3 ft. (900mm) – 4 ft. ( 1200mm) cermatel coated jet-engine stators from 55 micro-inch Ra to 19 micro-inch Ra

Even parts with extraordinary size and shape considerations are now candidates for mass finishing processes, as this machined titanium bulkhead for a fighter jet demonstrates.
Even parts with extraordinary size and shape considerations are now candidates for mass finishing processes, as this machined titanium bulkhead for a fighter jet demonstrates.

9.  Improving surface finish on turbine blades and vane clusters. In sequential multiple processing as low as 5 micro-inch Ra

10.  Improving surface finish and polishing surgical instruments and biomedical implants and devices.

11.  Polishing brass and copper torch tip components for plasma M.I.B. welding torches.

12.  Cleaning/degreasing automotive used alternator and starter housings.

13.  Cleaning/degreasing brass power line clamps and aluminum cable terminals.

14.  Prepaint finish on plastic telephones.

15.  Burnishing (polishing) of pewterware and pewter figurines, jewelry etc.

16.  Two-step deburring and cob drying and polishing of kitchen cutlery, pruning shears, industrial/commercial scissors and putty knife blades.

17.  Deburring and weld discoloration blending on components used in the manufacture of exercise machines, stair climbers, etc.

This photo shows two round bowl vibratory systems being used in series.  An automated part feeder meters in parts.  After processing in an initial operation, parts can be separated and then transferred to either a secondary finishing operation or dried.  Photo courtesy of Giant Finishing Inc.
This photo shows two round bowl vibratory systems being used in series. An automated part feeder meters in parts. After processing in an initial operation, parts can be separated and then transferred to either a secondary finishing operation or dried. Photo courtesy of Giant Finishing Inc.

18.  Degreasing of jumbo jet landing gear (entire brake housing, torque tube case and stator plates)

19.  Improve surface finish to under 10 micro-inch Ra on titanium, brass and stainless ball valves from 3 inches (75mm) to 2 feet (600mm in diameter

20.  Deburring sintered metal clutch plates, gears and hubs for automotive engines.

21  Degreasing fasteners (nuts, bolts, etc) used in the assembly of aircraft brakes.

22.  Deburring sawcut endmill blanks prior to fluting and sharpening

23.  Coloring pure sterling silver grain to casting grade in a part-on-part (no media with special compound)

24.  Deburring and blending clear plastic kidney dialysis pump bodies.

25. Smooth and burnish brass, bronze and stainless steel boat propellers (replacing most hand grinding and buffing operations)

26.  Deburr and dry stainless steel cooking stove coil supports

27.  Deburr and smooth machined cast iron manifolds for C.A.T. tractors.

28.  Descale screwdriver blades, worm gears and other parts with heat treat scale

29.  Separating floor tile that sticks together, and scrub firing sand from surfaces utilizing a vibratory finishing operation with dry performed media.

30.  Burnishing zinc belt buckles.  Mass Finished Parts

32. Separating unwanted scrap “knockouts” from fineblanked parts utilizing a vibratory screen separator

33. Burnishing 303 stainless steel food service stainless steel food service ketchup pump cylinders using 5/16 x 3/4 inch angle cut cylinder media in a vibratoryt process

34.  Pre-paint finish of golf balls us using a large and small media combination in a vibratory process.  Larger media drives drives smaller media points into dimpled areas of the part.  The method left a much smoother and uniform surface finish than the blasting method which had been utilized previously.

35.  Deburr and finish surgical needles 2″ (50mm) to 18″ (450mm) in length utilizing a non-abrasive media in a vibratory finishing machine.

36.  Multiple function vibratory process (burnish, degrease, chip removal, and deburring) of brass locking cylinders that are internal parts for keyed locks.  Two vibratory machines with PLC controls were utilized to adjust the wash, rinse, drain and shake out cycles which very from 30 seconds to an hour or more. Process is a part-on-part method with alkaline cleaning liquids

37.  Deflashing of plastic circuit breaker components. Process used steel media in a continuous flow-through vibratory finishing machine, and wable to proces 3000 parts per hour o a continuous basis.

CHANGE OF SURFACE STRESS (tensile vs. compressive)

Excerpted from SME Technical Paper MR79-569 by J. Bernard Hignett

[ed. note: Harperizer and Harperized are trade names that refer to a specific OEM’s brand of centrifugal barrel finishing equipment]

Metal fatigue is the most common cause of fracture in metal components. It is usually caused by numerous repeated applications of low stress—stress much lower than that needed for fracture in a single application. The higher the stress, however, the fewer applications are needed to cause failure.    It follows that fatigue failure will be most cannon in components that are highly stressed and subject to repeated applications of stress in their functioning. A fatigue crack usually starts because the tensile componentof stress at the surface of the material is too high. It is thus beneficial to impart compressive stress of components to oppose any tensile stress towhich the component may be subjected in service.

High-Energy surface finishing methods can be used to chanmge surface attributes such as compressive stress, develop isotropic surfaces and produce surface profiles that are neutral or negatively skewed.  These attributes can contribute significantly to wear resistance, metal fatigue prevention and load bearing improvement.
High-Energy surface finishing methods can be used to chanmge surface attributes such as compressive stress, develop isotropic surfaces and produce surface profiles that are neutral or negatively skewed. These attributes can contribute significantly to wear resistance, metal fatigue prevention and load bearing improvement.

Edge and surface finishing improvement can reduce the risk of fatigue failure. Surface imperfections can act as stress raisers and removal of these will invariably improve performance of any highly stressed part. For critical components it is desirable to achieve very high surface finishes to facilitate inspection for stress raises. Removal of burrs and uniform radiusing of all sharp edges and corners will similarly improve performance.

As has already been discussed, the CBF process can simultaneously deburr, edge radius and surface finish an immense range of components. It can also impart very high compressive stresses uniformly to the parts while edge .land surface finishing so offering unique capability of improving the resistance to fatigue failure of many highly stressed parts. The capability to improve resistance to fatigue failure is demonstrated by the results of some tests made by a manufacturer of stainless steel coil springs which were taken from a standard production run, Half of the components had the conventional finishing process of barreling, followed by shot peening, and the other half were processed in a centrifugal barrel machine for 20 minutes. The springs were tested to failure by compressing them from 1.104″ length to .730″, corresponding to a stress change from 9 to about 50,000 psi.   The results were that all springs finished by the conventional method failed at between 160,000 and 360,000 cycles. The springs that had been Harperized failed at between 360,000 and 520,000 cycles, an average performance improvement of 60%.

This photo shows bearing surface as seen by 2D and 3D scanning measurement.  The surface peaks and asperities are typical of machined or ground surfaces.
This photo shows bearing surface as seen by 2D and 3D scanning measurement. The surface peaks and asperities are typical of machined or ground surfaces. Photo courtesy of Jack Clark, Surface Analytics

The tests indicated a benefit potentially greater than mere improvement of resistance to fatigue failure. It was noted that some of the parts that were processed in centrifugal barrel equipment had clearly visible surfac e defects or inclusions. Such defects were not visible in the parts that had been barreled and peened. It was the parts with the visible defects which were always those that failed below 400,000 cycles so that if in inspection department were instructed ot to accept parts with such defects, then performance of the springs put into service would be of consistently much higher quality.

Even more striking results were observed during a series of tests in another set of production springs of a somewhat different type. The springs which were not processed in CBF equipment all failed life tests before 600,000 cycles. None of the springs which were Harperized had failed at 800,000 cycles, the limit of the test.

After high energy centrifugal finishing the surfaces are far more functional for the bearing application.  More isotropic, more plateaued, more negatively skewed and have imparted a beneficial compressive stress.  All of these attributes improving the load bearing and tribological properties of the part.  Photo courtesy of Jack Clark, Surface Analytics.
After high energy centrifugal finishing the surfaces are far more functional for the bearing application. More isotropic, more plateaued, more negatively skewed and have imparted a beneficial compressive stress. All of these attributes improving the load bearing and tribological properties of the part. Photo courtesy of Jack Clark, Surface Analytics.

Using CBF markedly to improve resistance to fatigue failure by a combination of edge and surface finishing, together with imparted very high compressive stresses, is cheaper than finishing by conventional means and then shot peening. There are opportunities to improve the ultimate resistance to fatigue failure of many parts, and, of prime importance, enable much better quality control by facilitating inspection. There is no longer need for components to be designed to allow a proportion of parts to fail prematurely due to surface defects. Of course, the technique has wide use for spring components, for instrument parts, for bearings and throughout the aerospace industry. There are also many opportunities to utilize improved and more consistent performance to design some of the cost out of many more mundane components within the metalworking industry, in particular, some automotive parts.