Quality can be broadly defined as meeting customer needs and expectations with a product. Therefore the starting point is to understand these needs and expectations with voice of the customer research.
There are two types of needs or requirements from customers: stated needs where a customer is able to state or describe what they want in a product and unstated needs. Unstated needs are needs or requirements that the customer takes for granted and needs that they don’t realize they have or think about.
By understanding the unstated or latent needs, the developer can provide capabilities in the product to respond to these needs and provide excitement opportunities or an enhanced value proposition. One of the ways to identify these unstated or latent needs is by observing the customer use the product and through other voice of the customer techniques.
Another unstated need that a customer takes for granted is that the product will reliably perform in the environment that they operate in and the manner in which they would normally use their product. One of the challenges with product development is that across all of a product’s customers, the customer’s use environment can vary significantly, the level or frequency of use of a product can vary significantly, and the way the product is stored and cared for can vary significantly. It is a challenge then for the manufacturer to understand this use environment and consider this as part of the product development effort. The best way to accomplish this is to get out in the field and explore and observe customer’s use environment. Then typically, the product developer will define the extreme conditions of the use environment as the basis for the product requirements (e.g., upper and lower temperature range, upper and lower humidity level, maximum duty cycle, etc.)
This knowledge of the customer needs or requirements along with any regulatory requirements and manufacturer objectives for the product should be captured in a customer or market requirements document. These customer needs or requirements are then translated into product requirements or specifications. A customer need for a “car with good acceleration” might be translated into product specifications such as total weight, horsepower, foot-pounds or torque, 0-60 acceleration time, etc. A customer need for a “reliable, durable car” would be translated into the planned life of the car, the mean time between failures, average service cost over 100,000 miles, etc. To support this specification, it would also be necessary to define the environmental conditions that the car would be subjected to and still meet the performance requirements.
One of the keys to good product requirements or specifications is to define measurable and objective requirements of specifications. It is only when a specification is measureable that one can determine whether that specification has been satisfied when verification of the product design is performed. The process of defining product requirements or specifications is critical because there are often trade-offs that must be made. A car with good acceleration and a powerful engine to haul loads is not going to be as fuel efficient. In a structure, there is often a trade-off between the weight of the structure and its strength.
Quality function deployment (QFD) is a good methodology for planning a product and translating customer needs into technical characteristics of the product or product requirements. Depending on the organization and the terminology, the customer needs, market needs or customer requirements along with the product requirements or specifications are referred to as “design inputs”.
These product requirements or design inputs should be the subject of a formal requirements review to 1) gain internal agreement within the manufacturer that the requirements represent the best mix of characteristics (and tradeoffs) to meet customer needs, and 2) confirm that the list of requirements is complete, e.g., it considers unstated customer needs, the use environment of the product, etc. These requirements or design inputs should later become the basis for a verification plan – a plan to define the analysis and tests that should be performed to assure that the defined requirements or design inputs have been met with the product design.
Once the requirements have been defined, design engineers should start by developing a high-level or conceptual design of the product. They should use a decomposition approach to define and design lower and lower levels within the product architecture next moving to subsystems, modules/sub-assemblies and then the components that will be required for this product to achieve the desired function and requirements. The design engineers should then consider the materials to be used to make up these components. Potential suppliers of materials and components should be consulted to understand the characteristics of their materials and components. The design engineers should perform analysis, use simulation tools, and build and test engineering prototypes to check that the resulting design should meet requirements. Design of experiments can be used to help optimize product and process design parameters. Based on this feedback, they should then make adjustments to the design. This process is highly iterative. Based on the product design, the manufacturing process should be developed and suppliers should be selected.
The result of the product design activity should be various documents and files that describe the product design and how it will be manufactured (process design). These documents or files could include drawings, computer-aided design (CAD) models, parts lists or bill of materials (BOM), part or material specifications, manufacturing work instructions, quality control plans which define manufacturing inspection or test steps, etc. These documents or files are referred to as “design outputs”. A formal verification and validation plan should be prepared to define the analysis and testing that should be done to determine that the product will meet requirements (“design inputs”).
During development, analysis and developmental testing should be conducted to assure that the design approach will meet requirements. Some of the common verification techniques are computer-aided engineering analysis, mathematical calculations, and failure modes and effects analysis.
One or more design reviews should be conducted during the development process. The design reviews should involve senior technical people as well as senior people from other functional disciplines that will be involved in producing this product. The objective of the design review is to review the design, identify any potential issues based on the collective knowledge of this senior group of reviewers, satisfy the organization that the design is mature and will meet requirements, and satisfy the organization that all development process steps have been followed and all necessary documentation and information has been produced.
One of the most common analytical techniques for verification is Failure Modes and Effects Analysis (FMEA). FMEA is a procedure in which each potential failure mode in every component or material in a product is analyzed to determine potential failure modes and their effect on the required function of the item. It is used to identify potential failure modes and their associated causes/mechanisms, consider risks of these failure modes, and identify mitigating actions to reduce the probability or impact of the failure.
Another similar verification technique is Hazard Analysis. Hazard Analysis is the detailed examination of a product from the user perspective to detect potential design flaws (possibilities of failure that could cause harm) and to enable manufacturers to correct them before a product is released for use. The result of a hazard analysis is the identification of unacceptable risks and the selection of means of controlling or eliminating them. This method is used in industries providing safety-critical products including avionics, commercial aerospace, chemical processing, the food industry, and medical devices.
Fault Tree Analysis (FTA) is another verification technique. It is a top-down, hierarchical analysis of faults to identify the various fault mechanisms and their cause. It uses Boolean logic to graphically describe the cause and effect relationships that result in major failures. The fault or major failure being analyzed is identified as the “top event.” All of the possible causes of the top event are identified in a tree using “or” nodes for independent causes and “and” nodes for multiple causes that must exist concurrently for a failure to occur. FTA is used with many safety critical products.
Next, the product developer should produce and test product prototypes. This is the most critical validation step. This validation should be based on a verification and validation plan or test plan that addresses the specific test procedures steps to be taken to meet all defined requirements (design inputs). While the initial focus of verification and validation is on whether the product performs as intended, verification and validation also needs to address whether the product will perform over its intended life in its use environment. This is accomplished with life testing where the product is exposed to environmental conditions representing its use environment. Since life testing of the product could take a long period of time with a long-life product, this can be addressed by accelerated life testing where the product is exposed to more extreme environmental conditions and continuous usage modes. There are several common approaches taken to validate and monitor that the product will meet the expected life requirements.
HALT is used during development to find ways that product will fail over its planned life. This is done by exposing the product to extreme environmental conditions until a product fails. The cause of the failure is then determined and the design is refined to make it more robust with respect to the environmental conditions. In other words, HALT is focused on testing a product to failure in order to identify its weak points and, thereby, make it more robust.
ALT exposes the product to more extreme environmental conditions than the operating environment to reduce the amount of time test how the product will perform when exposed to less extreme conditions (the operating environment) over a longer period of time (the product’s expected life). ALT is oriented to testing a product to determine the reliability or durability of a product and to determine the dominant failure modes.
On-going reliability testing (ORT) supplements the initial HALT and ALT verification, by testing the product over longer periods of time when exposed to environmental use conditions. This is done by either using samples of the product, exposing them to varied environmental conditions, and then testing them or by pulling in used vests from the field that have been exposed to a variety of conditions and testing them. ORT should be planned in advance, well-structured and proceduralized, and regularly conducted.
Some more subjective product requirements such as appearance, style, and usability can be verified by having typical users try prototype products and obtaining their feedback.
Once a product is verified and validated, it can then be launched and put into production. Final specifications for raw materials and components should be provided to suppliers. Quality control procedures should be established by the product developer and manufacturer. Purchase orders should be issued to suppliers which include or incorporate the defined specifications and/or designs for the raw materials or components. The purchase orders also should reference the quality requirements and procedural requirements. As necessary, suppliers should be qualified to produce the materials or parts that go into the product. Internally, the manufacturing process should be set up, operators should be trained, quality controls should be established, and the process should be verified.
The manufacturer should define the specifications that that the supplier must meet. The supplier is responsible for delivering the raw material or components to this agreed upon specification. The manufacturer is responsible for verifying that the raw materials or components meet its defined specifications.
It is in supplier’s interest to establish quality procedures that meet or exceed their customer’s quality requirements. The supplier will typically perform some level of inspection or testing of their product in conformance with the supplier’s internal procedures or the external requirements from their customers. The supplier may be required to certify that the product meets the requirements or specifications that have been imposed on them by their customer, but such requirements or specifications must be explicitly stated.
In addition to the supplier’s quality control steps, the manufacturer should perform its own procedural steps to insure that they are receiving a quality product that meets its requirements. At the minimum, the product manufacturer should perform a visual inspection of the raw materials and components for damage or obvious discrepancies and a review of any test results or certification paperwork provided by the supplier to see that the raw materials and components conform to the specifications required of the supplier. Beyond these basic steps, the product manufacturer may perform its own inspection and test steps as defined in its quality plan. This could range from a selected subset of inspection and test steps on a sample on raw material or component parts to 100% inspection and more comprehensive testing for a larger number of specification attributes.
If any discrepant material is found, the product manufacturer should segregate the discrepant material, notify the supplier of the problem, and generally require corrective action be taken to prevent or minimize the reoccurrence of discrepant materials or components be provided in the future.
Once product and process designs have been validated, the manufacturer should define factory acceptance test or inspection procedures to insure that production of the product will continue to meet the customer’s requirements.