CONTRACT FINISHING and FREE SAMPLE PART PROCESSING for Centrifugal Isotropic Finishing and Polishing

If you have parts that need edge or surface finishing and would like to have FREE sample part processing and a quotation developed for finishing the parts please contact Dave Davidson at dryfinish@gmail.com    I can also be reached at 509.230.6821

HZ60-fixed

Model HZ-60 Centrifugal Barrel Machine typically used for high energy processing for deburring, edge-contour, finishing and polishing metal and plastic parts from the aerospace, automotive, medical, dental, electronic, jewelry and other industries.

Some typical parts finished are shown in the application slide gallery shown below. [click on the image to enlarge it].

 

Super-finishing High Performance Automotive Components [Connecting Rods]

Centrifugal Super-Finishing of High Performance Automotive Components

 

Simiular processing on pistons…

Step 1 is a smoothing operation, Step 2 utilizes dry process finishing media to develop the final polished superfinish…

 

For more information contact Dave Davidson:  http://en.gravatar.com/dryfinish 

 

 

Understanding Surface Finishing’s Role in Part Performance Improvement

Mass finishing processes have been widely adopted throughout industry as the optimum methodology for producing advanced edge and surface finish effects on many types of machined and fabricated components. America industry has long been in the forefront in aggressively deploying these methods to improve edge and surface finishing operations.
All too often, situations still exist where archaic, even primitive hand or manual finishing methods are used to produce edge and surface finishing effects.  This is not to say that some industrial part applications are not going to require a manual deburring approach – some do.  In many cases, however, hand or manual methods are still being utilized because more automated or mechanized methods have not been considered or adequately investigated.
An often observed dichotomy in precision manufacturing operations, is a situation that is still all too common.  This is that many manufacturers, after spending vast sums on CNC machining equipment to produce parts to very precise tolerances and specifications consistently, in the end, hand off these expensive parts to a deburring and finishing department that utilizes hand methods, with all the inconsistency, non-uniformity, rework and worker injury potential that implies.  Even when manual methods cannot be completely eliminated, mass media finish techniques can and should be used to produce an edge and surface finish uniformity that simply cannot be duplicated with manual or single-point-of-contact methods.  Developing an overall edge and surface finish continuity and equilibrium can have a significant effect on performance and service life of critical components.

CBF - Milling mark elimination
High intensity mass finishing methods can eliminate positively skewed machined surfaces and replace them with plateaued negatively skewed surface profiles
In recent years, mass media finishing processes have gained widespread acceptance in many industries primarily as a technology for reducing the costs of producing edge and surface finishes. The economics are especially striking when manual deburring and finishing procedures are minimized or eliminated.

TAM Isotropic Edge-Contour
The first casualty of over reliance on a manual deburring and finishing approaches 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 that no two parts will ever be alike.
Moreover, the increased complexity and precision requirements of mechanical products have reinforced the need for accurately producing and controlling the 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
 CBF - Gear before and after
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. 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.
To understand how edge and 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:
(1) 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, presenting a much higher surface bearing contact area.  Anecdotal 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 1000% or more by improved surface textures produced by mechanical surface treatment.
Unfinished Bearing
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 by Jack Clark, Surface Analytics 

 

Finished bearing surfaces
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.
(2) Directionalized vs. Random (Isotropic) Surface Texture Patterns.  Somewhat related to surface texture skewness in importance 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 utilize 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 of the peaks has been altered appreciably.  These “isotropic” surface effects have been demonstrated to improve part wear and fracture resistance, bearing ratio and improve fatigue resistance.
Bearing Picture 6
Magnified view of bearing surface after surface peaks have been removed (top series of diagrams). This high intensity  CBF method is an economical way of blending in machining or grinding lines to develop isotrropic surfaces. Optical Interferometry by Jack Clark at Surface Analytics
(3) 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.   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, put into service, and the parts involved have developed a working track record, an unanticipated development has taken place.  Their parts are better—and not just in the sense that they no longer have burrs, 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 predictably consistent and uniform.
image014
Centrifugal barrel machines such as these can produce exceptional edge and surface finishes in very short cycle times. Accelerated process effects can be developed because of the high speed interaction between abrasive media and part surfaces, and because media interaction with parts are characterized by high pressure by virtue of the high centrifugal forces developed in the processes. Smaller turbine blades can be processed in the 5 x 8 inch compartments in the 12-liter capacity machine shown to the right. Larger centrifugal machines such as the 220 liter or 330 liter capacity machine shown to the left can handle much larger parts as the barrel compartments are as much as 42 inches in length. Larger parts processed in this type of machinery can be processed one at a time within the barrel compartment suspended within the media mass or be fixtured. Barrel compartments can be divided into processing segments to accommodate more than one part.
SUMMARY:
Mass media finishing techniques (barrel, vibratory, 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 to manual procedures is well known and documented, their ability to dramatically effect part performance and service life are not.

Dry super-finishing processes and cutting tool edge improvement

For many decades there has been an awareness of cutting tool edge condition and tool surface finish and the effect it has on piece part quality and tool life. There have been many independent studies, tests, and implementations of edge conditioning methods to create extended life in turning, drilling, and milling cutter tooling – some published but most kept “secret” as a manufacturing advantage.

finishing0300jpg_00000000778

  • For many decades there has been an awareness of cutting tool edge condition and tool surface finish and the effect it has on piece part quality and tool life. There have been many independent studies, tests, and implementations of edge conditioning methods to create extended life in turning, drilling, and milling cutter tooling – some published but most kept “secret” as a manufacturing advantage.  — Jack Clark, Surface Analytics LLC and Colorado State University

    The “Deburr/Finish Tech Group” of the SME has tasked itself to manage the project and use it’s member resource pool to provide tooling, applications, and the necessary documentation and reporting to objectively test cutting tool edge radius improvement on tool life and piece part consistency. This is a proposed outline on how to organize and conduct such a test.  It is the intention of the participants to publish a document, possibly an SME Technical paper or article, at the conclusion of the study.
  • To see an example of some superfinishing equipment being used for the research project see:  https://www.youtube.com/watch?v=w5pyX9ix2Sw 

    GOALS: Confirm that edge and finish conditioning improves tooling life and potentially also improves performance values in tool speed, feed speed and substrate surface finish and helps prevent part surface finish deterioration from tool wear over extended periods of time.

  • CBF - Carbide tool surface treatment

CHANGE OF SURFACE STRESS (tensile vs. compressive) WITH MASS FINISHING METHODS

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 component of 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.

HZ60-fixed

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. The machine pictured above is capable of deburring and producing surface finishes in rapd time cycles.  

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.

Below are some further examples of surface finishes that can be developed with Centrifugal Isotropic Finishing.

 

 

Tube Interior Micro-Finishing

Tube Interior Micro-Finishing
By David Davidson posted Sat, Feb 21, 2015 06:35 PM
Modified centrifugal barrel finishing equipment is now being utilized to develop precision micro finishes on the interior of tubes and cavities for demanding applications such as particle accelerators. See the video as an example of one such application:

This breakthrough process utilizes specially modified variants of the equipments and materials discussed in the SME MMR and SME-Spokane video shown below

SEE also:  https://lnkd.in/eUKdSTF

Dave Davidson
SME Manufacturing
Advisor: Machining/Material Removal Technical Community
7609 N Hughes Dr.
Spokane WA 99208 USA
Email: dryfinish@gmail.com
Blog: dryfinish.wordpress.com
Phone: 509.230-6821