Log in with Facebook Log in with Google. Remember me on this computer. Enter the email address you signed up with and we'll email you a reset link. Need an account? Click here to sign up. Download Free PDF. Adamantios Mettas. A short summary of this paper. International Journal of Performability Engineering Vol. Received on Aug. What is DFR? What are the ingredients for designing for reliability, and what is involved in implementing DFR?
In this paper, we will try to answer these questions and, at the same time, we will propose a general DFR process that can be adopted and deployed with a few modifications across different industries in a way that will fit well into the overall Product Development Process.
Keywords: Design for reliability DFR , reliability management, reliability planning. In fact, for many, these analysis techniques have become almost synonymous with reliability. The reality, though, is that although life data analysis is an important piece of the pie, performing just this type of analysis is not enough to achieve reliable products.
Rather, there are a variety of activities involved in an effective reliability program and in arriving at reliable products. Design for Reliability, however, is more specific than these general ideas.
It is actually a process. Specifically, DFR describes the entire set of tools that support product and process design typically from early in the concept stage all the way through to product obsolescence to ensure that customer expectations for reliability are fully met throughout the life of the product with low overall life-cycle costs. In other words, DFR is a systematic, streamlined, concurrent engineering program in which reliability engineering is weaved into the total development cycle.
It relies on an array of reliability engineering tools along with a proper understanding of when and how and to use these tools throughout the design cycle. This process encompasses a variety of tools and practices and describes the overall order of deployment that an organization needs to follow in order to design reliability into its products. Why is DFR Important? Why should a company commit resources for deploying a DFR process? The answer to this question is quite simple Field failures are very costly.
Three important statements summarize the best practice reliability philosophy of successful companies: 1 Reliability must be designed into products and processes using the best available science-based methods. Understanding when, what and where to use the wide variety of reliability engineering tools available will help to achieve the reliability mission of an organization.
And this is becoming more and more important with the increasing complexity of systems as well as the complexity of the methods available for determining their reliability. System interactions, interfaces, complex usage and stress profiles need to be addressed and accounted for. With such increasing complexity in all aspects of product development, it becomes a necessity to have a well defined process for incorporating reliability activities into the design cycle.
Without such a process, trying to implement all of the different reliability activities involved in product development can become a chaotic situation, where different reliability tools are deployed too late, randomly, or not at all, resulting in the waste of time and resources as well as the occurrence of problems in the field.
Managers and engineers have come to this realization and a push for a more structured process has been seen in recent years. It is thus only natural for organizations to look to these existing processes and sometimes even try to include reliability into them. However, although Six Sigma and DFSS have been quite successful in achieving higher quality, reducing variation and cutting down the number of non-conforming products, the methodologies are primarily focused on product quality and many organizations are starting to realize that they do not adequately support the achievement of high reliability.
Therefore, these organizations are starting to put more emphasis on the separate, although often complementary, techniques of Design for Reliability. Since the distinctions between reliability and quality, and consequently between DFR and DFSS, are often still poorly understood, it is worthwhile to address this topic briefly in the next few sections before presenting the overall process and the specific techniques that comprise DFR. Traditional quality control assures that the product will work after assembly and as designed.
Whereas reliability provides the probability that an item will perform its intended function for a designated period of time without failure under specified conditions. In other words, reliability looks at how long the product will work as designed, which is a very different objective than that of traditional quality control.
Therefore, different tools and models apply to reliability that do not necessarily apply to quality and vice versa. The primary goal of DFSS is to achieve a significant reduction in the number of nonconforming units and production variation. It starts from an understanding of the customer expectations, needs and Critical to Quality issues CTQs before a design can be completed. DFSS rarely looks at the long-term after manufacturing issues that might arise in the product.
On the other hand, Design for Reliability is a process specifically geared toward achieving high long-term reliability. This process attempts to identify and prevent design issues early in the development phase, instead of having these issues found in the hands of the customer. As mentioned previously, a variety of tools are used in order to accomplish this objective.
These tools are different than those used in DFSS, even though there is some overlap. As you can see from this graphic, the types of tools used in DFR are based on modeling the life of the product, understanding the operating stresses and the physics of failure.
Of course, there are also many natural affinities between the two disciplines and it is understandable that many organizations have traditionally combined both quality and reliability under the same umbrella. In some cases, when the organization clearly understands the distinction between quality and reliability and applies the appropriate tools for both objectives, this combination can be appropriate and effective. However, when there is not a clear understanding of the essential differences in the tools involved, this can lead to very poor outcomes resulting from the improper use of tools and data.
The DFR Process The Stress-Strength Interference principle states that a product fails when the stress experienced by the product exceeds its strength as shown in Figure 2. In order to reduce the failure probability and thus increase the reliability, we must reduce the interference between stress and strength.
A structured process, such as the DFR process presented in this article, is needed in order to achieve this. The proposed process can be used as guide to the sequence of deploying the different tools and methods involved in a program to ensure high reliability. In addition, the sequence of the activities within the DFR process will vary based on the nature of the product and the amount of information available.
Figure 3 presents a summary of the full process and the ways in which techniques may interact. In order to make this DFR process general enough, and applicable to different industries, we decided to break the process down into six key activities, which are: 1 Define, 2 Identify, 3 Analyze and Assess, 4 Quantify and Improve, 5 Validate and 6 Monitor and Control.
By dividing the process into these activities, we can identify and group the different tools, and provide a roadmap that can easily be followed, as well as easily mapped into a Product Development Process Concept, Design, Assurance, Manufacturing and Launch.
These can be at the system level, assembly level, component level or even down to the failure mode level. Determining the usage and environmental conditions is an important early step of a DFR program. Companies need to know what it is that they are designing for and what types of stresses their products are supposed to withstand. The conditions can be determined based on customer surveys, environmental measurement and sampling.
Requirements can be based on contracts, benchmarks, competitive analysis, customer expectations, cost, safety, best practices, etc. Some of the tools worth mentioning that help in quantifying the "voice of the customer" include KANO models, affinity diagrams and pair-wise comparisons.
The system reliability requirement goal can be allocated to the assembly level, component level or even down to the failure mode level. Once the requirements have been defined, they must be translated into design requirements and then into manufacturing requirements.
Quality Assurance: Meaning and Steps Industry. We use cookies We use cookies to personalise content and ads, to provide social media features and to analyse our traffic. You consent to our cookies if you continue to use our website.
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