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.
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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 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 should a company commit resources for deploying a DFR process? The answer to this question is quite simple Field failures are very costly. One case in point is the recently publicized Xbox issue, which has cost Microsoft more than a billion dollars in warranties aside from loss of business and market share. Three important statements summarize the best practice reliability philosophy of successful companies:.
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 in 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. First, let us start with some basic clarifications. Traditional quality control assures that the product will work after assembly and as designed.
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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.
How to Ensure Your Reliability Journey Is Successful
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.
As the previous sections demonstrate, there is a clear distinction between the goals and tools employed to assure quality versus those employed to analyze and improve reliability. 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 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: 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.
Illustration of Stress-Strength Interference. 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. Without excess discussions of the complex related mathematics, he creates principles that enable readers to identify problems before product release into the market.
These novel concepts and methodology can reduce product troubles by establishing test specifications that produce quantified outcomes that constitute conclusive judgment data. In addition, it explains basic, fresh new methods for maximizing customer satisfaction and securing a competitive edge in performance. We provide complimentary e-inspection copies of primary textbooks to instructors considering our books for course adoption. Learn More about VitalSource Bookshelf. CPD consists of any educational activity which helps to maintain and develop knowledge, problem-solving, and technical skills with the aim to provide better health care through higher standards.
It could be through conference attendance, group discussion or directed reading to name just a few examples. We provide a free online form to document your learning and a certificate for your records. Already read this title? Please accept our apologies for any inconvenience this may cause. Today's manufacturing plants are a mosaic of many moving parts.
In some cases, the same part is used to do different things. In one application, failure of the part may only be a small consequence, while in a different application, the failure may cause a major catastrophe, resulting in considerable loss of time and product. As each plant is different, with its own unique set of potential problems and mitigating tasks, the identification and mitigation of high-consequence failures requires conscious effort, experience and knowledge.
A strong focus on reliability is vital to maintaining first-pass, first-quality production. It is important to remember that reliability is not a characteristic but rather a continuous journey. One of the most important objectives of this journey is to identify and eliminate defects that can compromise systems and equipment. Where reliability is concerned, a defect is anything that is not perfect, whether that condition is related to a single piece of equipment or an entire operation.
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A defect can be as simple as a broken gear tooth or as complex as an entire production line that cannot handle the demands being placed upon it. What is most important is to track the defects back to their sources and address the issues to prevent the defect's return. Defects are caused by a variety of sources, including normal degradation of items in their environment, design deficiencies, improper manufacture or use of the item, exposure to contaminants, improper repairs, collateral damage from other failures or inadequate preventive maintenance.
A defect condition may lie dormant for years, only to be revealed when the defective item is stressed in an abnormal way. While the principles of defects and their sources can be described broadly, specific failures are defined in terms of their causes and their consequences. A pump impeller failure will have different causes from a motor bearing failure.
Depending on the location of a part within a system, a failure could cause anything from a reduction in product quality to a complete line shutdown. Fundamental to understanding how to improve reliability of a manufacturing facility is the understanding of how the items can fail and, once they fail, understanding the effect of those failures.
How to Ensure Your Reliability Journey Is Successful
Once you understand the effect of the items, you can then design an appropriate mitigating task. Mitigating tasks are all around us, and they protect us in many different ways. Some common mitigating tasks include applying sunscreen to prevent sunburn, using a speedometer to avoid getting a speeding ticket or washing your hands to avoid getting sick.
In other words, mitigating tasks are the things you do to prevent or minimize harmful consequences. Mitigating tasks do not happen automatically, nor are they free. They are part of a reasoned analysis done by an expert. The expert makes a recommendation for mitigating tasks based on a cost-benefit analysis of the consequences. Furthermore, once these high-consequence items are identified, systems must be designed to reduce the consequence. Once the systems are in place, they must stay active to protect against future failure events. The effort needs to be ongoing so that as things change, the analysis is repeated to ensure the systems are still adequate.
The old saying goes, "The journey of a thousand miles begins with a single step. But what is the first step?
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