By Earnell Kelly
Editor's Note: Stability of composition usually refers to a change of the materials, not change of volume. It is noteworthy, however, that even an incorrect answer can lead to innovative solutions.
In an industry where "if it ain't broke, don't fix it" is the mantra that dominates culture, this case study should help to demonstrate what an effective tool The Theory of Inventive Problem Solving (TRIZ) can be with real world problem solving and real world design solutions. Some engineers/designers view this methodology as theoretical or great for ideal cases. They have a hard time accepting it as a solution to real world problems, especially when the material written on the subject refers to ambiguous processes and scenarios that rarely correlate to actual problems.
It is easy to be a bit skeptical of its practicality when all there is to read are articles and case studies written by doctors and highly renowned scholars with years of experience and accolades. There is nothing from average, run-of-the-mill engineers or designers working on real world problems that are faced everyday in the workplace.
The focus of this tutorial is to prove that ordinary engineers can generate ideal solutions to real world design problems by applying basic level TRIZ. It will also explore how TRIZ can be used to verify the accuracy of design solutions that have already been conceived.
An automotive customer requested the development of a diesel fuel filter capable of withstanding high pressure applications (up to 95 pounds per square inch or psi; 6.6 bar). The current filter model series can only withstand a maximum pressure of 60 psi (4.1 bar) before permanent deformation to the filter element case occurs; particularly at the top cap of the filter element. The deformation (outward bulging) of the top cap causes the plastisol in the cap to break away from the grommet seal located in the top (shown in Figure 1). The shearing of the plastisol seal causes a fuel leak at the interface. The objective is to conceive a solution that allows the filter to withstand the required pressure without causing a leak at the seal interface. This must be achieved within the following constraints:
This must be achieved with minimal changes or complications that could be introduced into the system.
The first step in using TRIZ is to clearly identify the problem statement. In order to accomplish this implement the 5-why's tool to identify the root cause. Figure 2 includes details on how this is accomplished.
The 5-why's tool allows for isolating the cause of the leakage to the insufficiency in the strength of the top cap of the filter assembly. It is this parameter that must be improved while satisfying the conflicting parameter and constraints.
The technical contradiction is defined as two parameters in opposition. One is improving while the other is worsening. In this case, as system pressure is improved, deflection of the top cap is worsened.
The technical contradiction is formed by the following statements:
If the fluid pressure increases to the maximum level, then the system requirement is met, but the top cap of the filter deflects, which causes the plasitol to leak at the grommet seal.
If the fluid pressure does not reach the maximum level, then the top cap does not deflect and there is no leak in the filter; but the system requirement is not met.
The conflict statement is desired to achieve increased system pressure without causing increased deflection to the top cap of the filter with minimal changes or complications introduced into the system.
The two parameters that most closely correlate to the conflicting parameters in the TRIZ matrix include:
Parameter 13 refers to a change in the stability of a material's composition. In this case, stability is referring to mechanical, not chemical composition. The material's rigidity is what must change. This will affect its stability, which can refer to mechanical as well as chemical properties. The contradiction of these two parameters yields the following (suggested) inventive principles:
The suggested inventive principles are then analyzed in the order listed with the TRIZ matrix.
A Change an object's physical state (e.g. to a gas, liquid or solid).
B Change the concentration or consistency.
C Change the degree of flexibility.
D Change the temperature.
E Change the pressure.
Make objects interact with a given object of the same material (or a material with identical properties).
Separate an interfering part or property from an object or single out the only necessary part (or property) of an object.
A Change the shape or properties of an object from symmetrical to asymmetrical.
B Change the shape of an object to suit external asymmetries (e.g.ergonomic features).
C If an object is asymmetrical, increase its degree of asymmetry.
Considering the scope of the problem, item "C" under principle 35 best satisfies the contradiction in the application. The deflection of the top cap directly correlates to the degree of flexibility. It is this parameter that must be limited or minimized in order to overcome the contradiction in the system.
The most widely used method to minimize flexibility is to increase the stiffness of an object. In this case that object would be the top cap. Increasing stiffness is most commonly achieved by increasing the thickness of the material. This is represented by the following formula:
D = Et3/ 12 (1 v2)
In which "E" is Young's modulus, "v" is Poisson's ratio of the top cap material and "t" is the thickness of the cap. By increasing the thickness of the entire top cap this prevents the current manufacturing tool from producing the embossments in the side of the cap. This would directly conflict with one of the parameters and cannot be fully implemented.
In order to implement it first conceive a way to allow the top cap to be thin enough to deform during the embossment process yet thick enough to prevent the cap from deflecting during the maximum pressure event. It is here when a physical contradiction is identified to allow for better focus on the ideal solution.
The physical contradiction is formed by creating a logic statement. The logic statement identifies the characteristic that must meet both opposing requirements by defining it in terms of time (T) for the contradiction:
In terms of this problem, the physical contradiction implies that the physical characteristic of the top cap must be thin (before T1) for the maximum pressure event (the embossment process) and thick during T2 for the maximum pressure event. The logic statement would be:
"To achieve the desired function of the filter, the thickness of the top cap must be low during T1 and high during T2."
Physical contradictions are best solved by using the separation principals. The parameter for the contradiction is analyzed in four different states:
When a parameter must exist in two conditions (at different times) use the separation in time and separation in condition to conceive the solution.
This condition separates the requirement by assigning the parameter to the system at different time intervals.
With this principal first conceive a solution where the top cap is thin before the pressure event occurs (for embossment) and thick during the pressure event. To achieve this, the top cap would need to have the embossments produced and then have an additional layer of material welded or bonded to stiffen the cap. The stiffness can also be increased by hardening the material as opposed to thickening it. This could be achieved by initiating an annealing process after the embossments are produced. While both of these options could solve the contradiction, both entail introducing an additional step to the manufacturing process, which in turn adds unwanted complications to the product.
This condition separates the requirement by assigning the parameter to the system at different conditions.
With this principle the solution must allow the top cap to be thin during the embossment process (condition) and thick during the maximum pressure event (condition). To achieve this, without adding an additional step to the manufacturing process, the top cap needs to accommodate both of these conditions simultaneously. A solution could be to construct the top cap of a composite design. This would be capable of satisfying both conditions. It can be achieved by using the current (thinner) material in the location of the embossments and a thicker material in the location of the grommet seal where the cap is deflecting under pressure. Figure 4 shows an example of this construction.
This solution requires only a small change to the construction of the top cap without introducing any change to the manufacturing process, thus satisfying all of the constraints. The only drawback to this solution is that the center tube and grommet would have to be redesigned to accommodate the thicker wall of the cap. This is a good opportunity to also enhance the design by adding a radial feature around the grommet/cap interface. This would improve the sealing capability between the two components, thus making the design much more robust.
A similar design was conceived by the applications engineer working on this project, which consists of welding a cut-off portion of an identical cap to the top for reinforcement (shown in Figure 5). This concept allows for use of the current grommet and requires minimal changes to the part.
Another way to reinforce the top cap is to add some support ribs to the top portion of the cap for rigidity (shown in Figure 6). This also satisfies both conditions. Both concepts shown in Figures 5 and 6 are currently under testing to confirm adequacy of the design.
After conversing with the applications engineer, it was revealed that he too conceived the same solution (stiffening the top cap by locally reinforcing the cap near the grommet seal) through traditional brainstorming. The primary difference between the two methods is that the applications engineer arrived at his conclusion after approximately three weeks. While the same conclusion was reached using TRIZ methodology within two hours.
By virtue of its systematic progression, TRIZ provides a means to streamline the design/problem solving process by eliminating the ambiguity from conceptualization.
Often times TRIZ is perceived as a theoretical methodology that lacks real world application. The findings of this case study have helped to verify two things:
In this case, although the engineer had already conceived the ideal solution, TRIZ was able to confirm this, allowing the design efforts to progress with a greater assurance of certainty.
It also confirms that by using a more structured and directed method of concept generation, TRIZ can reduce the innovation timeline dramatically, allowing design and product solutions to be integrated at a much faster pace. This reduces the time to market, which increases the profitability of a new product endeavor. In the case of initiating a design improvement, it reduces the time it takes to implement an effective solution, thus increasing customer satisfaction and confidence in the company's ingenuity to solve problems. All of this further verifies that in a technology-driven market a company cannot afford to be on the heels of its competition. Use every advantage to be one step ahead of the pack.
Earnell Kelly is a Project Engineer for Stanadyne Corporation, a manufacturer of diesel fuel injection and filtration systems. He coordinates development and application activities for some of their top customers. Earnell graduated from the University of Central Florida with a double major in Design Engineering Technology and Operations Engineering Technology. He also received a Certificate of Completion in Basic TRIZ from BMG International in 2008. Contact Earnell Kelly at ekelly (at) stanadyne.com.