TRIBOLOGY RELIABILITY

Transcription

1 TRIBOLOGY RELIABILITY \

2 AGENDA Introduction 5 minutes Webinar 45 minutes Q&A 10 minutes

3 Who Are We? Ops A La Carte HQ in Santa Clara, CA

4 Ops A La Carte Founded in 2001 Named top 10 fastest growing, privately-held companies in the Silicon Valley in 2006 and 2009 by the San Jose Business Journal. Over 1450 projects completed in 10 years Over 500 Customers in over 30 countries Over 100 different industries, 6 main verticals CleanTech, MedTech, Telecom, Defense, Oil/Gas, Consumer We run FREE monthly webinars.

5 Ops Solutions Ops provides end-to-end solutions that target the corporate product reliability objectives Ops Individual A La Carte Consulting Ops identifies and solves the missing key ingredients needed for a fully integrated reliable product Ops Training Ops highly specialized leaders and experts in the industry train others in both standard and customized training seminars Ops Testing Ops state-of-the-art provides comprehensive testing services

6 Ops Mechanical ReliabilityProjects Touchscreens ALT to determine the life of the screen. Pumps ALT to determine life of pumps. Robotics ALT to determine the repeatability and robustness Valves ALT to determine life of valves. Gaskets ALT to determine degradation pattern. Fans/Blowers ALT to determine life of fan. Drills ALT to determine wear pattern of drilling equipment.

7 Upcoming Events we are at International Reliability Innovations Symposium (IRIS) March 16, 2012, San Jose, CA and webinar Ops A La Carte helped organize the conference and we were on the paper review committee. SMTA Solar Conference March 21-23, 2012, Webinar Ops A La Carte's Mike Silverman will be giving a presentation at this conference on "Reliability Risks in the Solar Industry."

8 Upcoming Events we are at IPC Conference on Test & Inspection May 15-17, 2012, Costa Mesa, CA. Ops A La Carte will be giving a presentation at this conference on "New Techniques for More Effective ESS". SMTA Conference on Soldering and Reliability May 15-18, 2012, Toronto. Ops A La Carte's Peter Arrowsmith will be giving a presentation at this conference on "Improving Product Reliability Using Accelerated Stress Testing".

9 MD&M East Upcoming Events we are at May 22-24, 2012, Philadelphia, PA Ops A La Carte's Mike Silverman will be giving a 3 hour class on "Medical Reliability Testing - Identifying Testing Requirements Early." Applied Reliability Symposium June 13-15, 2012, New Orleans, LA Ops A La Carte's Mike Silverman will be giving a presentation on "Calculating ROI When Implementing a Design for Reliability Program".

10 Other Reliability Events Certified Quality Engineer Preparation Class Date(s): April 17 to May 29, 2012 Time: 6pm-10pm one night a week, 7 weeks Location: San Jose, CA and Webinar

11 Annual Reliability Symposium May 7-11, 2012 in Santa Clara, California and via webinar TRACK ONE - DFX TOOLS Design for Reliability (DfR): May 7-8 Design for 6 Sigma (DfSS): May 9 Design for Mechanical Reliability (DfMR): May 10 Design for Warranty (DfW): May 11 morning Design for Software Reliability (DfS): May 11 afternoon TRACK TWO - REL TOOLS: ALT/DOE/RCA Design of Experiments (DOE): May 7-8 Best Accelerated Reliability Tests (BART): May 9-10 Root Cause Analysis (RCA): May 11

12 Upcoming Reliability Webinars Design for Robustness Date: April 4, 2012, 8:30am Location: Webinar This is our next webinar in our free webinar series See link from our website

13 Webinar Stats This is our 20 th Webinar (see Ops site for past webinar topics/content) We run these webinars once a month We partner with other companies We partner with societies (IEEE, ASQ, and others for broader reach)

14 Webinar Stats Some of the past topics Solar Reliability Medical Reliability Root Cause Analysis Green Reliability Soft Errors Software Reliability Prognostics Best Reliability Testing Lead Free and Reliability Simulation and Reliability Design of Experiments

15 Webinar Stats Future Topics FMEA/TS16949 Accelerated Reliability Tests, Different Options for Return on Investment for Design for Reliability Software Reliability What would you like to see? Let us know at

16 Registration Demographics For this webinar we have signed up 100 Registrants 10 Countries

17 Registration Questions 1. Do you have portions of your product that can wear due to mechanical wear? 2. Do you know how to characterize the life of all your wearout mechanisms?

18 Registration Questions 1. Do you have portions of your product that can wear due to mechanical wear? Yes 83% No 17%

19 Registration Questions 2. Do you know how to characterize the life of all your wearout mechanisms? Yes 21% No 79%

20 Agenda Introduction to Tribology Stribeck Curve-Rolling element bearing Hertzian Contact Mechanics Wear and Wear Mechanisms

21 Tribology Tribology is the science and engineering of interacting surfaces in relative motion. Includes the study and application of the principles of friction, lubrication and wear. Annual cost of friction and wear-related energy and material losses is over $700 billion -- 5% to 7% of the United States $14 trillion gross national product (DOE, 2010) Every aspect of tribology impacts product reliability Tribology is a branch of mechanical engineering, but

22 Tribology Gets Complicated

23 Key Aspects of Tribology Friction and Wear, Fluid Film Lubrication, Elastohydrodynamic Lubrication, Surface Properties and Characterization, Contact Mechanics, Magnetic Recordings, Tribological Systems, Seals, Bearing Design and Technology, Gears, Metalworking, MEMs, Lubricants, and Artificial Joints

24 Friction Regimes Friction regimes for sliding lubricated surfaces have been broadly categorized based on film thickness (h) versus the average distance between asperity contacts (R) : Solid/boundary friction Boundary Lubrication, h=0 Fluid friction Elastohydrodynamic and Mixed, h~r Mixed friction Hydrodynamic Lubrication, h>r Stribeck curve -Basic curve clearly show the minimum value of friction as the demarcation between full fluid-film lubrication and some solid asperity interactions.

25 Stribeck et al Stribeck and others systematically studied the variation of friction between two liquid lubricated surfaces (5 Dec 1905) Journal Bearings used in the research easy to recreate results Curve is friction against function of a dimensionless lubrication parameter ηn/p, where η is the dynamic viscosity, N the speed (e.g. revolutions per minute of a bearing) and P the load projected on to the geometrical surface. [STLE] Leads to understanding of wear behavior based on regime

26 Stribeck Curve f versus ηn/p, the latter called Sommerfeld no.

27 Reliability of Surfaces in Contact Reliability of mechanical elements is a tribological phenomenon based on wear characteristics Each regime leads to different failure modes and Weibull curve can be used to model elastohydrodynamic and hydrodynamic lubrication Application to mechanical elements is advanced since industry is established well ahead of electrical and electronic industries e.g. mechanical roller bearings

28 Rolling Element Reliability Seemingly identical rolling bearings operated under identical conditions may not last the same amount of time Impractical to test a statistically significant number of bearings, so engineers rely on standardized bearing-life calculations to select and size bearings for a particular application. Calculations continue to evolve and become more accurate over time, reflecting the collective experience of the bearing industry, including recent advances in manufacturing, tribology, materials, end-user condition monitoring, and computation.

29 Bearing Life Equations RATING LIFE EQUATIONS The equation from ISO 281, 2007 or the American Bearing Manufacturers Association (ABMA) Standards 9 and 11 figures basic, non adjusted rating life by: L 10 = (C / P) p in millions of revolutions where C = basic dynamic load rating, lb; P = equivalent dynamic bearing load, lb; p = life-equation exponent ( p = 3 for ball bearings; and p = 10/3 for roller bearings)

30 Tribology of A Roller Bearing

31 Bearing Life Definitions Basic life or L 10 as defined in ISO and ABMA standards is the life that 90% of a sufficiently large group of apparently identical bearings can be expected to reach or exceed. Median or average life, sometimes called Mean Time Between Failure (MTBF), is about five times the calculated basic rating life. Service life is the life of a bearing under actual operating conditions before it fails or needs to be replaced for whatever reason. Specification life is generally a requisite L 10 basic rating life based on experience in similar applications by manufacturer.

32 Roller Bearing Example Roller bearing is to be selected to withstand a radial load of 4kN and have an L 10 life of 1200h at a speed of 600 rpm. The rated life is 3000 hours and nominal speed of 500 rpm. C R =F*[(L D /L R )(N D /N R ] 1/a where C R is rated load L D /L R ratio of actual life to rated life N D /N R ratio of actual speed to rated speed F is the load a is the bearing exponent (3 ball and 10/3 roller bearings )

33 Sample Solution C R =F*[(L D /L R )(N D /N R ] 1/a C R =4[(1200/3000)(600/500) 3/10 C R =3.21kN Engineer looks through bearing journals with rated load for the roller bearing with the right dimensions for application In reality, bearing manufacturer s do all this for you and have complete databases of rated life for applicable loads for bearings specific to the application

34 Tribology Poll Question 1 Does your company use mechanical or electromechanical components in their products? a) all the time b) some times c) rarely d) never

35 (Hertzian) Contact Mechanics Study of deformation of solids in contact where deformation can be elastic, viscoelastic and plastic. Hertz formulated the concept of local elastic deformation of two bodies in contact such as a sphere on a plain (1886) Adhesion at the contact first considered by JKR theory (Johnson, Kendall, Roberts 1970) more than elastic forces Bradley provided the model for Van der Waals forces between two spherical bodies in contact A more involved theory (the DMT theory) also considers Van der Waals interactions outside the elastic contact regime

36 Hertzian Contacts All contacts assume elastic deformation based on the geometry and configuration of the contact. Contact areas define the surface and subsurface stress state: 1. Point Contact Cone on plane 2. Circular Contact - sphere on a plane, sphere on sphere 3. Line Contact cylinder on a plane 4. Elliptical Contact sphere on a cylinder, cylinder on cylinder

37 Real Surfaces In Contact Every surface is rough at a microscopic level asperities are visible, sometimes referred to as micro asperities or micro roughness

38 Micro Asperities Under Load Asperities deform under load and behave elastically as defined by material limits Flattening occurs as shown right

39 Tribology Poll Question 2 Does your company experience unanticipated wear failures of mechanical or electromechanical components? a) all the time b) some times c) rarely d) never

40 Wear And Wear Mechanisms Most Important Mechanism in Tribology Least Understood

41 Wear - General Classification Wear is classified by mechanism: adhesive (mild and severe), abrasive, fatigue, corrosive and delamination wear Major problem with wear is that the mechanism of wear alters as the process goes on transition presents difficulties Clear picture of wear, but the theory for the particular types is lacking-theory is wear and application specific Main weapon against wear is to design using hard materials, choosing suitable lubricants, and having a perfect and maintainable filtration system.

42 Adhesive Wear Most prominent type of wear occurs when asperities touch and weld together resulting in subsurface tearing Most common with inadequate lubricating film (h<r); metal oxide film on the surface is worn away allowing micro weld Adhesion of junction is stronger than cohesion of base metal

43 Abrasive Wear Relatively harder material cuts into a softer counter surface Micro-cutting can be a useful tool in industrial processes such as grinding, diamond or carborrundum powder polishing, and as most households know, sanding

44 When there is cyclic surface contact, opposing asperities elastically deform and recover, but ultimately fatigue off In fatigue wear, the harder the material, the greater its resistance to asperity failure higher modulus effective Micro cracking Surface phenomenon Normal stress, E Subsurface phenomenon Shear stress, G Fatigue Wear

45 Fatigue Wear Illustration of the facets of fatigue, including crack propagation, spheric particles and larger fatigue spall particles. SEM Photograph showing asperity wear including spheric and larger fatigue spall particles

46 Fatigue Wear

47 Corrosive Wear Oxygen, moisture or other active chemicals in the lubricating film form a layer which prevents surfaces adhering together This formative layer is rubbed off during the contact and has to be reformed before the next contact comes round i.e. this amount of material is worn away The art of choosing the right additive is to find one just active enough to replace the worn layer e.g. e.p. additives Extreme pressure (e.p.) additives protect by creating a surface boundary layer increase load carrying capability

48 Corrosive Wear Theory Actual

49 Delamination Wear Most common in rolling element bearings where stresses are cyclical resulting in larger metallic flakes delamination Originally proposed that dislocations pile up at or near the surface due to stress cycles and Hertzian stresses Postulated that the thickness of the flakes was related to the depth below the surface of Hertzian shear stresses

50 Tribology Poll Question 3 What follow-up Tribology topics do you have interest in? a. Wear and Wear Mechanism Modeling b. Elastohydrodynamic Lubrication c. Wear and Reliability Modeling d. Wear and Accelerated Life Testing e. Other f. None

51 Q&A

52 Contact Information Ops A La Carte, LLC Mike Silverman Managing Partner (408) mikes@opsalacarte.com

53 Special offer for webinar participants: Free 1 hour Reliability Consultation Offer expires on 3/31/12

54 Our Next FREE Webinar will be on April 4 th on Design for Robustness

55 POLLING QUESTION 4 Are there any aspects of Design for Robustness you are most interested in? a. How Design for Robustness relates to Design for Reliability b. Unique differences between Design for Robustness and Design for Reliability c. Both d. Other e. I m not interested in Design for Robustness and probably will not attend

56 After signing off the webinar, you will be asked to take a quick 3 minute survey If you fill out survey, you will receive a link to the slides and to the broadcast.

57 Contact Information Ops A La Carte, LLC Mike Silverman Managing Partner (408) mikes@opsalacarte.com