Case Studies In TRIZ

Case Studies in TRIZ: Fretting Failure in Automotive Electrical Components Tressia Hobeika Department of Mechanical Engineering American University of Beirut, Lebanon Tomasz Liskiewicz School of Mechanical Engineering University of Leeds, UK Darrell Mann Systematic Innovation Ltd, UK

Introduction Fretting corrosion is a main cause of automotive electrical components failure and has been studied in many publications.1 2 3 Fretting corrosion is a form of accelerated atmospheric oxidation at the interface of mating materials subject to small cyclic relative motion.4 It is essentially caused by a combination of corrosion and the abrasive effects of corrosion debris, usually observed in equipment with vibrating or moving parts. 5 Tin plated contacts are one of widely used electrical contacts in the automotive industry. Their disadvantage, however, lies in the fact that tin is very sensitive to fretting corrosion and rapidly forms a thin and hard oxide layer, which easily leads to electrical failure. The major agents leading to fretting are mechanical vibrations, shocks, differential thermal expansion and contraction of the contacting metals, and junction heating as power is turned on and off. Many parameters enter into play when evaluating fretting corrosion, including corrosive environment, amplitude and frequency of load fluctuation, load cycles, temperature and humidity. 6 This article summarises a short study programme applying TRIZ methodology and tools to the problem of fretting corrosion failure in automotive electrical contacts. 7 TRIZ is the Russian acronym for the “Theory of Inventive Problem Solving”, a systematic problem-solving toolkit developed in 1946 by Genrich Altschuller and centred on the process of solving physical and technical contradictions.8 Altshuller identified three premises of TRIZ: 1) ideality – the basic design is a goal, 2) contradictions – help solve problems, and 3) systems approach – the 1

See, for example, Y. Park, T. Sankara Narayanan and K. Lee, Effect of fretting corrosion of tin plated contacts: evaluation of surface characteristics, Tribilogy International 2007; 40: 548-549. 2 J. McBride, Electrical contact and connectors in automotive systems. Connectors on vehicles, IEE Colloquium, 1993. 3 Kang Yong Lee, Dae Ki Jeong, and Jae Hyung Kim, Simulational study of electrical contact degradation under fretting corrosion, Tribology International 2011; 44: 1651–1658 4 E. M. Bock and J. H. Whitley, Fretting Corrosion in Electric Contacts, Paper Prepared for Presentation at the Twentieth Annual Holm Seminar on Electrical Contacts, October 29-31, 1974. 5 A. Kowal and S. Strzelecki, Analysis of fretting corrosion in machine elements, Tribotest 2007; 13: 51–66 6 Ibid. 7 The article is based on the method and tools developed by Darrell Mann (2007), Hands on Systematic Innovation, Clevedon, IFR Press. 8 G. Altshuller, On The Theory of Solving Inventive Problems, Design Methods and Theories, 1990; 24: 12161222. 1

innovative process can be structured systematically.9 10 TRIZ methodology implies a systematic approach for solving inventive problems, whereby problem solving is a four-step process, including a problem definition or “define”, followed by a “select tool”, then “generate solution” and finally, “evaluate” the potential solutions.11 TRIZ is a comprehensive problem solving toolkit, which can complement other toolkits by filling the gap on how to come up with innovative concepts to solve problems, including Total Quality Management, Quality Function Deployment, Lean Six Sigma or Value Engineering. 12 It has been applied in numerous domains. Cavallucci and Weill (2001) integrated Altshuller’s development laws for technical systems into the design process.13 Wu (2006) employed both TRIZ theory and Taguchi in automotive muffler optimisation design.14 Butdee and Vignat (2008) applied TRIZ to assist a lightweight bus body structure design, which has been then accepted and used for manufacturing. 15 TRIZ was also applied in other fields, such as in crowd management. Pin et. al (2010) found the contradictions that arise in the context of crowd management and identified potential solutions based on a selection from the 40 inventive principles and the 76 standard inventive solutions developed by Altshuller.16 TRIZ is indeed a scientific methodology for technical innovations, but recent studies have proven that its principles and process can also be applied to domains like business and management.17 TRIZ has been selected as a reference methodology to better understand fretting corrosion in automotive electrical contacts. The study is therefore centred around the contradictory requirements of electrical contacts: the need for sliding action for an easy installation and connection, on the one hand, and the fact that this sliding action is also the origin of fretting corrosion and destruction of the mating surfaces, on the other. Two classic connectors are used nowadays in the automotive industry. The most used one is a connector with a tin (Sn) top layer, which is worn out after long-time operation leading to electrical and mechanical problems in cars. As for the other connector, it is mainly coated by Gold (Au), a noble material who has been found to be more durable and more reliable than tin but at the same time, has become more and more expensive for automotive use. There is therefore a stronger economic motivation to reduce or eliminate both the use of Gold and fretting corrosion in nonnoble materials such as tin, which in return offer significant economic advantage.

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T. Schweizer, Problem Solving with TRIZ: Historical Perspectives and Understanding Ideality, Methodology, 1998. 10 J. Terninko, A. Zusman, and B. Zlotin (1998), Systematic Innovation: An Introduction to TRIZ. Boca Raton: CRC Press. 11 Darrell Mann (2007), Hands on Systematic Innovation, Clevedon: IFR Press. 12 Kareb Gadd (2011), TRIZ for Engineers: Enabling Inventive Problem Solving, Hoboken: Wiley. 13 D. Cavallucci and D. Weill, Integrating Altshuller’s development laws for technical systems into the design process, CIRP Annals – Manufacturing Technology, 2001; 50: 115-120. 14 T.D. Wu, The study of problem solving by Triz and Taguchi methodology in automobile muffler designation, TRIZ Conference, Taipei, 2004. 15 S. Butdee and F. Vignat, TRIZ method for light weight bus body structure design, Journal of Achievements in Materials and Manufacturing Engineering, 2008; 31. 16 Soo Chin Pin, Applying TRIZ principles in crowd management, Safety Science, 2011; 49: 286-291. 17 Darrell Mann (2004), Hands on Systematic Innovation: For business and Management, Clevedon: IFR Press. 2

Problem Definition – 1) Problem Explorer This part of the problem definition process is frequently the most critical stage to identify the problem in question and lead to the selection of the suitable solving tools for the electrical contacts problem. It consists of three parts: problem hierarchy explorer, identification of resources and sore point analysis. We will explain illustrate each case. Problem Hierarchy Explorer Here, we shed light on the space surrounding the originally stated problem leading to a list of definitions which broaden and narrow the problem (Figure 1). Broader Problem

electrical system integrity fretting corrosion leads to the destruction of the electrical integrity of the automotive electrical contacts, especially next to the engine.

Why do I want to solve this problem? Why else?

Original Problem(start here)

fretting corrosion of automotive electrical contacts.

Narrower Problem

What’s stopping me solving this problem? What else? -external conditions  vibrations, shocks, junction heating. -internal conditions  oxidation, wear. -cost of noble materials  gold.

-High contact electrical resistance. -inadequate coating. Narrower Problem

need for assembly/ dis-assembly

permanent AND removable assembly

Figure 1. Problem Hierarchy Explorer

Identification of Resources The following tool, also called “system operator analysis”, confirms that the system should be studied on time and scale levels thus pushing the problem solver to see the problem from different perspectives. Recall that a resource is “anything in or around the system that is not being used to its maximum potential”. The ‘9-Window’ tool will be used to demonstrate this stage of the problem definition (Figure 2).

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Packaging, instore presentation.

Engine, weight, load, frequency, user, cycle rate, electricity.

Mechanical vibration, differential thermal expansion and contraction of the contacting materials, shock…

Manufacturing of the electrical contact.

Electrical contacts: connectors, relays, switches.

Failure, destruction of electrical integrity.

Selection of materials and coating.

Two mating parts of the contact, coating, interface between components.

Oxidation, friction, wear, coating wearing away.

Figure 2. 9-Window Tool

Sore Point The sore point of a system is the “element which prevents it from delivering the required benefits”. Therefore, to ameliorate the functioning of the electrical contacts, we have to treat or eliminate this sore point. The following scheme clarifies the idea explained above (Figure 3).

Reliability of electrical contacts, durability, material selection.

Interface between the two mating parts of an electrical contact, external factors, cost of noble materials, and fretting failure of non-noble materials. Figure 3. Sore Point Analysis

Problem Definition – 2) Function and Attribute Analysis This element of the problem definition process clarifies the functioning of a system. Moreover, it will guide the selection of the solving tools. Conducting a function and attribute analysis means constructing the related diagram, which will systematically define the problem in question. We will also examine how time can affect the system (figure 4.1-2-3-4). 4

Types of interactions Effective Missing Insufficient Excessive Harmful Symbols Mechanical vibrations, shock, differential thermal expansion and contraction of the contacting materials, junction heating as power is turned ON and OFF (M) MUF: Main Useful Function Simple system

Mating part 2

Mating part 1

Figure 4.1. Simple Two-Component Manufacture System

Past slides (M)

Mating part 1

Mating part 2 holds (M)

Figure 4.2. During Installation and Before Operation

Present

External Agent moves

moves Thermal expansion or contraction Conducts (M)

Mating part 1

Mating part 2 holds (M) Slides

Figure 4.3. During Operation

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Future External Agent moves

moves Thermal expansion or contraction holds (M)

Mating part 1

holds (M)

Nonconductive film

Mating part 2

slides conducts (M) Figure 4.4. After Long-Time Operation

Problem Definition – 3) Ideal Final Result The notion of an ‘Ideal Final Result’ is one of the cornerstones of TRIZ. The ideal system is one that requires no materials to build, consumes no energy, and does not need space and time to operate: the required function is fully performed. A useful definition of ideality can be represented using the following equation: Ideality 

( Perceived ) Benefits Cost  Harm

Which means that if we want to increase ideality in a certain system as an evolutionary direction, we have to either increase benefits (perceived by the customer) and/or decrease cost and harm. We will further develop this equation in the “S-Curve Analysis” section. The Ideal Final Result concept (IFR) can help guide our problem definition thinking through a simple questionnaire: 1. What is the final aim of the system? A life lasting durability of electrical contacts. 2. What is the Ideal Final Result outcome? Electrical contacts that behave as a single part. 3. What is stopping you from achieving this IFR? The fact that I have two mating parts instead of one. 4. Why is it stopping you? I need the two parts for the installation process yet the interface between them is the source of fretting problems. 6

5. How could you make the thing(s) stopping you disappear? If the mating parts could solder themselves 6. What resources are available to help create these circumstances? Coating, electricity, atmosphere, user, heat, vibrations. After the above IFR definition, we notice that it has identified future options. Therefore, we take steps back along the IFR definition space (figure 5). How might you work back from the IFR to a practical solution?

IFR Electrical contacts that have a smart interface between the mating parts, that can adapt to the environment

Electrical contacts’ mating parts solder to eliminate the interface, thus a behavior as a single part

Electrical contacts that behave as a single part

Figure 5. IFR Definition Space

As a matter of fact, having mapped the steps back from the IFR to the nearest present generates indeed some useful ideas that might lead to the solution of our problem.

Problem Definition – 4) S-Curve Analysis The characteristic manner of the S-curve describes the evolution and the ‘goodness’ of systems in function of time. The ideality of a system is examined using the S-curve which consequently determines if there is potential for further improvement of the system or whether a new approach is required. Figure 6 shows the significant positions of the S-curve.

Figure 6. Generic S-Curve Characteristic

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Moreover, as we will see in the coming sections, the S-curve analysis leads to the selection of the problem solving tools and helps prioritize which problems to deal with, thus bridging the gap between the experimental/technical solutions and market requirements. In this section, we will tackle two quantitative properties of the system proposed by Altshuller, which translates into the performance of the system in the S-curve and analyze the ideality equation presented in the previous section. Number of inventions or patents over time Correlating between the S-curve position and the number of inventions over time is a powerful way to help establish where a system stands on its s-curve. This is best done by analyzing patents related to the system. Finding the number of inventions over time in this case was performed using a combination of online patent databases with the keywords: “Automotive electrical contact” from 1960 until 2008. The below graphs compare between a generic Scurve and the curve related to the number of inventions (figure 7).

Figure 7. Number of Automotive Electrical Contact Inventions

The analysis of generic “Number of Inventions” graphs states that the first jump of the curve followed by a relatively small decline, as we can see in the graph above, determines the position of the system along its S-curve. According to Figure 7 we might begin to conclude that we currently have a system between infancy and growth stage or youth and maturity. Level of inventiveness over time Another way to identify where a system stands on its current S-curve is to analyze the ‘technical focus of inventions’. Figure 8 identifies a number of generic steps in the types of patents being granted for a given system over the course of its evolutionary life:

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MINIMIZE COST MAXIMIZE RELIABILITY Ideality

MAXIMIZE EFFICIENCY

MAXIMIZE PERFORMANCE MAKE IT WORK PROPERLY MAKE IT WORK Time

Figure 8. Correlation between S-Curve Position and Invention Focus

In fact, by tracking this evolution, we obtain a reliable estimate of the system maturity which is, in this case, standing between maximize performance and efficiency. Indeed, we should work more to improve the efficiency of the electrical contacts, which confirms our goal to improve durability and adaptability of the contacts. Ideality Equation As we have seen in a previous section, the definition of ideality was represented by an equation called the ‘ideality equation’: ( Perceived ) Benefits Ideality  Cost  Harm As stated before, the most used electrical contact is coated by tin (Sn) which is worn out after long-time operation leading to electrical and mechanical problems in cars. On the other side, other contacts are coated by Gold (Au), a noble material who has been found to be more durable and more reliable than tin but at the same time, has become more and more expensive for automotive use. The following graphs (figures 9-10) illustrate the evolution of Gold and Tin prices over time.

Figure 9. Tin Prices in USD$/Kg over time

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Figure 10. Gold Prices in USD$/troy ounce over time

Indeed, the price of Gold is much higher than the price of Tin and we notice from the above graph that the most common market anomaly is a sudden increase in the dominance of the cost element in the ideality equation. Which means that, using Tin for the coating of electrical contacts, the cost is low but the benefits are also low due to a limited durability of the tincoated contacts. Consequently, to increase ideality, boosting the benefits would be necessary.

Problem Solving Tools It is known that one of the most essential problems faced by new users of TRIZ is knowing how to find the most relevant solving tools to the problem. Many methods help determining many solving tools. In our case, we will start by examining the position of the system on its current S-curve (figure 7): in fact, the system seems to be reaching the end of the first half of its evolution. According to the Hands-On Systematic Innovation select solving tool method, it means that the system contains contradictions. Next, from the FAA model (figure 4), we identify the contradictions from the existence of components which have positive and negative interactions with other components. In fact, the mating parts both slide and hold/conduct. This means that the ‘Physical Contradiction separated in Time’, followed by the ‘Technical Contradiction’ are the most important tools for our problem. From the same model, we also notice the existence of excessive actions; this leads us to use the ‘Knowledge/Effects’ tool followed by ‘Trends of Evolution’. We also have missing action (hold/conduct) which leads to the use of ‘S-Field Analysis’. Contradictions The first tool problem solving tool offered by TRIZ is the recognition that an invention comes as the result of the resolution or elimination of a ‘contradiction’. In TRIZ terminology, the contradiction toolkit has two main forms: technical and physical. A technical contradiction or two-parametrical contradiction occurs when there are two parameters in conflict with each other (ex. High strength and Low weight), or when all the following conditions are fulfilled: (i) there is a desired function in a system, (ii) there is a conventional mean to realize this function and, (iii) the realization is opposed by harmful factors (figure 11). 10

Desired Function

Contradiction

Harmful Factor Figure 11. Definition of a technical contradiction

In graphical terms, the conflict between the two parameters can be illustrated as a hyperbolic curve which gets shifted towards the origin of the graph when trying to eliminate a contradiction (figure 12).

Figure 12. Graphical Representation of a Technical Contradiction

As for the physical or one-parametrical contradiction, it occurs in occurs in a situation of conflicting values of one parameter (ex. High weight and Low weight), where we desire different properties of a certain parameter. Tackling our problem, in other words, solving the contradictions can be achieved by a three-step systematic process, whether technical or physical: Step 1: Identify the contradiction. Step 2: Determine the generic inventive principles successfully used in the past to resolve contradictions. Step 3: Apply the generic principles to our specific problem. As proposed by the analysis in the Select Solving Tool section, we will start by analyzing the physical contradiction present in our system then head towards the technical contradiction and interactions between technical and physical contradictions. Physical contradiction Step 1: Identification of the physical contradiction. One of the contradictions present in the electrical contacts case is a physical contradiction because the electrical contact is needed to SLIDE during installation and NOT SLIDE during 11

operation for the prevention of fretting corrosion at the interface between the two mating parts. Indeed, the conflict SLIDE/NOT SLIDE generates our physical contradiction based on conflicting values of one parameter, which is the sliding action. Step 2: Determination of the generic inventive principles. One important result of Altshuller’s comprehensive patent analysis is the 40 inventive principles. In fact, his major discovery was based on the fact that a large number of inventions were only related to a small number of generic principles. Three basic methods of separating physical contradictions are generally used: (i) In space (where?) (ii) In time (when?) (iii) On condition (if?) The where, when and if questions can be used to establish which of the three strategies is most likely to resolve the SLIDE and NO SLIDE contact requirements: a) Where do I want the mating part to slide? - On the other mating part. Where do I want the mating part not to slide? - On the other mating part. In this case, the answer both times is the same which means that the problem is not amenable to solution by separation in space. b) When do I want the mating part to slide? – During installation. When do I want the mating part not to slide? – During operation. In this case, we get two different answers which mean that the contradiction is amenable to elimination by separation of time. c) I want the mating part to slide if? – I am installing the system. I don’t want the mating part to slide if? – The system is operating. As is often the case, here we also get the differing answers seen in (b), which means that we can also examine the separate on condition strategies to resolve the problem. Table A.1, which can be found in the Appendix, represents an important TRIZ tool: it lists the Inventive Principles for each separation category in order of descending frequency of use by other problem solvers. As a matter of fact, the separation in time and condition strategies contained in table A.2 gives us a host of inventive principles: Time & Condition – 11, 16, 19, 20, 23 Time – 9, 10, 18, 21 Condition – 6, 8, 12, 33, 38, 39 The most productive solutions generated using these triggers headed in the direction of adding additional actions to the system. Given that the electrical contact is intended to be a fundamentally simple component, costing, in most cases, a few cents, it was felt that, whilst these solution directions shouldn’t be eliminated, it would be preferable to look at possibly stronger directions. In general terms, this means looking at the Inventive Principles that don’t relate to any of the separation strategies. Looking again at Appendix A1, this means Principles: 2, 3, 4, 5, 13, 22, 24, 25, 32, 35, 36 12

Rather than exploring these Principles directly, at this point it was decided to examine the contradiction story in more detail through the technical contradiction route. Recently, there have been many debates about the importance of the physical versus the technical contradiction, especially that both tools generated high numbers of ideas. The emerging standard template for examining both physical and technical contradictions together is the template shown in Figure 13. This template represents a modified version of the “Evaporating Cloud” worldview described in the Theory of Constraints:

Figure 13. The Modified Evaporating Cloud Scheme

In fact, “evaporating the cloud” or solving the problem necessitates at least one of the links between adjacent ovals to be broken or “evaporated”. The parameters A and –A represent the physical contradiction whereas the Conflict Parameters 1 and 2, the technical contradiction. We now apply the scheme to our system (Figure 14).

operational flexibility durable operation

AND

sliding

AND

long life

no sliding

Figure 14. The Modified Evaporating Cloud Scheme with contradictions 13

2, 3, 4 5, 13, 22 24, 25, 35 32, 36

One of the outcomes of the Figure 14 analysis is that some of the Inventive Principles emerged as frequently used for most or all six of the conflict pairs identified from the template. These were, in decreasing frequency order: 3, 13, 35, 1, 4, 17 Ideating around these Principles – and especially 3, 1, 4 and 17 – gave a fairly clear steer towards the use of non-smooth surfaces. For example, incorporating (asymmetric) grooves, ridges, dips and protrusions. As is often the case, Principle 35 offers a very broad-ranging set of possible solution directions. Looking at all of the material attributes present in the mating surfaces of the electrical contacts, and more specifically looking for step-changes in those attributes revealed two intriguing directions, the first involving a possible change of state, and the second looking at substantial changes in hardness of the material. Coupled with Principle 13, emerged the clue of moving in the counter-to-common-sense direction of decreasing rather than increasing hardness. Knowledge/Effects At this point in the proceedings, it was decided that a check on the potential validity of these solution directions was needed. Consequently, a search of the patent databases of the world was made using the state change, hardness change and surface profile change clues obtained from the contradiction analysis. Essentially what we are doing here is using keywords from the Principles to guide a search of the literature along the lines indicated by Figure 15: contact, mate, conduct

CONTEXT Words

electrical contact conductor corrosion fretting

SOLUTION DIRECTION Words

melt, hardness, rib, groove, roughen, asymmetry Figure 15. Principle-Guided Patent Search Strategy 14

Of the ‘melting’ searches, by far the most intriguing solution was US patent application 20040241403, published on December 2, 2004: ‘Composite material for producing an electric contact surface, in addition a method for creating a lubricated, corrosion-free electric contact surface’, the abstract of which describes: A modification of frictional state and surface condition of an electrical contact surface to reduce the insertion forces for establishment of an electrical plug connection and also to achieve protection from oxidation and fretting corrosion is provided. By controlled melting of a contact surface that is applied onto a support material, a lubricant film applied onto the contact surface is diffused, by using a laser, substantially without modification into the liquefied contact surface and re-solidified together with the latter, so that the lubricant film is incorporated into the contact surface.

Figure 16. US20040241403

Regarding the ribs/grooves/roughening searches, the most interesting solution seemed to be one from Palo Alto Research. US6,966,784, ‘Flexible Cable Interconnect Assembly’ was granted in November 2005. Although intended for a somewhat more sophisticated application than the electrical contact under consideration here, the solution derived by the inventors appears to have some relevance to our problem. Here’s what the invention disclosure has to say about the fretting corrosion issue: FIG. 17 is a simplified cross-sectional side view showing a connector apparatus 150S incorporating micromachined alignment structures according to another embodiment of the present invention. The highdensity interface arrangements described above depend on accurate alignment and securing between the flexible cables extending from the associated mating boards. A general alignment structure is described above for positioning the respective cables to facilitate a successful coupling procedure. As indicated in FIG. 27, further x-y alignment accuracy may be obtained by providing micromachined alignment structures 2710 and 2712 on contact structure 153S, and complementary micromachined alignment structures 2720 and 2740 on cables 120S and 140S, respectively. Such micromachined alignment structures can be fabricated during the spring formation process, thereby minimizing additional cost. Note such micromachined alignment structures can also provide accurate alignment in z-axis film-based structures because they can be produced to provide stops, which are important for controlling overdrive and insuring uniform compression, and thus wear of the contacts. In addition, current pressure contacts fretting experiments suggest that multiple touchdowns in the same scrub helps to clear debris and insure glitchfree performance. Precision alignment mechanisms that repeatedly hit the same scrub area would be necessary to make this scrub/tip cleaning technique possible.

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Figure 17. US6966784

Trends of Technological Evolution The results of the patent searches were next used as a guide to construct a map of the relative maturity of the designs in and around the electrical contact domain. The most productive means of achieving this kind of analysis is the ‘evolutionary potential’ radar plot. Evolutionary potential is the difference between the current maturity of a system within one domain and maximum evolution achieved by others in other domains. In a typical analysis, the system under consideration is compared to each of the 38 known trends of technological evolution, taking into consideration that they are heading toward an increasing system ideality. The ‘Evolutionary Potential Radar Plot’ is then necessary to map how far along each of the TRIZ trends the current system has developed (figure 18). According to the plot, the system should evolve and exploit the remaining evolutionary potential or resources to get to the Ideal Final Result. And in so doing will resolve some or all of the problems associated with the current system – including the fretting corrosion problem under consideration here. In this regard, the Evolution Potential concept works somewhat differently from the contradiction tool analysis that preceded it: the contradiction tool starts from the definition of a problem, and takes the user through a series of steps to get to an answer, or set of answers. Conversely, the evolution potential tool highlights a series of answers (trend jumps) first and then prompts the user to identify what problems such jumps might resolve. Evolution potential analysis, in other words, works 180degrees different to the contradiction (and as it turns out all of the other TRIZ/SI) tools.

Figure 18. Composite Evolution Potential Radar Plot For Electrical Contact

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Perhaps the most striking first aspect of the radar plot is the level of untapped potential within the system. This, in fact, is not an uncommon state of affairs for a component as simple and low cost as an electrical contact. The low cost expectation, however, is also likely to be the limiting factor in terms of which trend jumps are affordable and which are not. Combining likelihood of solving the fretting problem with this affordability limitation indicated that the following trend jumps were the most likely to deliver viable solutions:  Use of ribbed and roughened surfaces (i.e. a reinforcement of the ideas generated from the contradiction analysis).  Use of composite materials or material structures – a potentially good way of separating the conflicting conduction and fretting resistance demands.  Use of curvature/v-channel shapes – i.e. geometries that cause fretting forces to be self-cancelling or self-stabilising. S-Field Analysis/Inventive Standards At this point, it could have been determined that we had sufficient solution direction clues to terminate the ideation session. However, in the spirit of completeness, it was decided that a short S-Field analysis be completed. The S-Field tool is made of 76 Inventive Standards which include rules which transform an initial technical system, thus solving specific problems. In fact, they are based on the analysis of previous inventions that found solutions to similar problems. In this section, a basic deployment strategy, suggested in “Hands on Systematic Innovation”, will be used to solve the electrical contacts problem. Function Definition We define, in simple terms, the function that the current system is supposed to deliver: “Conduct Electricity”. Substances/Fields Definition In a certain system, in order to successfully deliver the necessary function “conduct electricity”, a minimum of 2 substances (things, to be simpler) and a field (any form of energy present in the system) are required. We therefore define the substances as the mating parts 1 and 2, thus leading to 2 substances in addition to the mechanical field which dominates the thermal field, thus leading to 1 field. In order for the system to deliver the “conduct electricity” function, it must satisfy the following validity test that lies in the center of the S-field tool. Note that answering the questions is based on the Function and Attribute analysis performed in a previous section (FAA model, figure 4). a. Are the minimum 2 substances and a field present? Yes, the 2 mating parts and a field. b. Is this a measurement problem? No. c. Are there any harmful relationships in the system? Yes. So, we use the list of inventive standards especially formulated for situations containing modify/add/transition. Their sequence in the list starts with solution suggestions offering minimum disruption to the system to solutions that involve more profound changes. This will be confirmed in the following analysis.

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S-Field Diagram The transition from the FAA model to the S-field diagram is quite simple. However, some modifications to the FAA scheme need to be done: When drawing the S-field model (figure 19), we need to conduct some kind of field summation. Knowing that a field is ‘any source of energy within the system that is helping (or preventing) the delivery of the required function’, we find 2 fields: mechanical (vibrations) and thermal (expansion and contraction). In fact, adding mechanical + thermal equates to the fact that in its current state, the system has a harmful field (due to the thermal field) or an excessive field (due to the mechanical field). But which of them dominate the other? Therefore, we have a look at the general points stated in the book: - If there is only a harmful field, there can be no hope of achieving a useful solution. - In order to achieve the state whereby we do achieve a useful solution, the net sum of all fields present must equate to a single composite field acting efficiently. So, the best modification to be done on the FAA model is to join the actions of the external agent (now mechanical and thermal field) into one excessive instead of thermal, which underlies the fact that the action of the vibrations dominate the thermal expansions and contractions of the electrical contacts. Therefore, now the s-field model differs from the FAA model in that it has a mechanical field instead of an external agent but with an excessive action. The other parts of the model are left intact. As for the harmful interactions of the system, they only exist between the 2 mating parts of the electrical contact, in other terms, between the 2 substances of the S-field model. Therefore, the model enables us to see how other people have successfully tackled this generic type of “harmful effect between 2 substances model”. Mechanical Field

Mating part 1

Mating part 2 Figure 19. S-Field Diagram

Inventive Standards The harmful interaction between the 2 substances should be resolved by examining the inventive standards for “harmful interactions”. Because the harmful interaction exist between the 2 substances (rather from the field), we should look first to the standards associated with modification of fields in the harmful effects section of the list. But in our case, the field cannot be modified which means that we will first look at the modification of existing substance. These standards should be then used as solution triggers to generate specific solutions to our electrical contacts problem.

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Of the possible ‘modify existing substance’ solution directions indicated by the relevant Inventive Standards, no new solution directions emerged. The Standards, however, did tend to reinforce some of the already generated ideas – i.e. profiled surfaces, composite structures.

Conclusions and Next Steps Although the main purpose of this case study was to run through the TRIZ/SI problem definition tools in order to obtain new perspectives on the fretting corrosion problem, several of the solution directions suggested through the course of the analysis have subsequently been tested in a programme of experimental testing. Figure 20, for example, shows a micrograph picture of one of the profiled-surface solutions undergoing test. A theoretical analysis of the likely benefits of this solution direction derived the thought that the valleys formed into the surface would act as a place where wear debris caused by fretting could migrate so that they then found themselves in a position where they would cause no further wear damage. The relative size and shape of the peaks and valleys need merely to be sufficient to contain the maximum volume of wear debris producible during the intended life of the component. μm 50

25

2.3 mm 1.8 mm 0

Figure 20. Micrograph of the First Tested Surface Profile Modification

Although not yet tested, another potentially interesting surface profile design direction would see the peaks and valleys oriented in directions such that relative motion between mating surfaces would cause the debris to pass along the valleys towards and ultimately beyond the edge of the contacts. Initial test results on the Figure 20 profile suggest that the first iteration surface profile (actually created very cheaply by ‘scratching’ the contact surfaces with a medium-coarse glass-paper – chosen for its low cost productionisation opportunities) would be sufficient to achieve the desired life improvement and to thus overcome the fretting corrosion problem for all but the most demanding applications.

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APPENDICES A.1: Physical Contradiction Solution Strategies SPACE

2, 3, 4 5, 13, 22 24, 25, 35 32, 36

14, 17, 26, 29

1, 28, 30 31, 40

6, 8, 12, 33 38, 39

7, 15, 27 34, 37

2, 3, 4 5, 13, 22 24, 25, 35

9, 10, 18, 21

11, 16,19 20, 23

CONDITION

TIME

A.2: Matrix 2010 Parameter List 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25.

Weight of moving object Weight of stationary object Length of moving object Length of stationary object Area of moving object Area of stationary object Volume of moving object Volume of stationary object Shape Amount of Substance Amount of Information Duration of action - moving object Duration of action - stationary object Speed Force/Torque Use of energy by moving object Use of energy by stationary object Power Stress/Pressure Strength Stability Temperature Illumination Intensity Function Efficiency Loss of Substance

26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 49. 50.

20

Loss of Time Loss of Energy Loss of Information Noise Harmful Emissions Object Generated Side Effects Adaptability/Versatility Compatibility/Connectability Ease of Operation Reliability Repairability Security Safety/Vulnerabilty Aesthetics Object affected harmful effects Manufacturability Accuracy of manufacturing Automation Productivity System Complexity Control Complexity Positive Intangibles Negative Intangibles Ability to Detect/Measure Measurement Precision