Quality itself is no longer a differentiator among manufacturers. High quality is expected and achievable. With enough time and money, any manufacturer can produce a high-quality product. The focus of manufacturing quality has shifted to a discussion about the cost of quality and how to manage it. The manufacturer that can minimize the cost of quality while producing products the fastest, is the one that will win in today’s market.
The “closed-loop” approach to quality management, which uses virtual simulations and tolerance analysis software, can link cost factors with tolerance adjustments so users have the data they need to achieve a strategic balance between quality and cost. With such an approach, users determine how to precisely meet their quality requirements by identifying and focusing on the key points that affect quality and avoiding unnecessarily tight tolerances.
The cost of quality includes four components:
1. Prevention costs involved in preparing and implementing a quality plan
2. Appraisal costs involved in testing, evaluating, and inspecting quality
3. Internal failure costs of scrap, rework, and material losses
4. External failure costs at customer site, including returns, repairs or rework, and recalls
Successful manufacturers use simulation-based dimensional engineering processes in their quality management programs to anticipate problems before they occur. Simulation-based analyses prevent problems that might not otherwise be discovered until manufacturing finds them—or worse—the end customer experiences them as quality issues. By using tolerance analysis that is linked to actual measurement results, engineers can quickly pinpoint sources of variation and perform root cause analyses to solve problems, which takes the time-consuming guesswork out of the equation.
Most complex, assembled products built today are subjected to simulation-based dimensional engineering processes, which help product design and manufacturing engineers understand dimensional fit characteristics and quality statuses. Engineers use this type of analysis before they start a product launch and continually through production.
This is not new or revolutionary. However, in a closed-loop dimensional engineering process, there are several built-in steps that enable engineers to define and refine their plans and objectives early in the process, as well as through ongoing checks and balances, to achieve the precise quality required by the customer at the least possible cost.
There are eight steps involved in a closed-loop quality management process.
1. Achieve management commitment.
Before establishing a formal closed-loop quality management process, it is essential that management not only buys into the concept, but also understands that the process should affect everyone—including design engineers, purchasing agents, quality inspectors, and manufacturing engineers. It is also critical that management drives the plan for how simulation-based tolerance analysis and dimensional engineering processes are used across the organization so they are applied in a way that allows the manufacturer to set and achieve quality goals while keeping cost to a minimum.
2. Establish build objectives.
The first step in developing any product is to establish build objectives. A cross-functional team analyzes the quality levels of competitor products to determine the appropriate levels of variation allowable for the products. The balance between build requirements and cost will vary based on the particular quality levels of the product.
3. Set build strategies.
Once build objectives are set, the product team develops and documents build strategies for how the product will be assembled, including all relevant points and operations. The build strategy defines the way parts will be located, which is also the way the parts must be held in their checking fixtures. There is always more than one way to manufacture parts and products, and the team’s goal is to find the most appropriate approaches given the quality and cost objectives associated with the product. For instance, one build strategy might lead to a high-quality product with very low tolerances, yet the associated cost does not meet the cost goals.
4. Establish geometric dimensioning and tolerancing (GD&T) requirements.
At this point, geometric dimensioning and tolerancing (GD&T) is applied to products, taking into account the build objectives and strategies. Through GD&T, best understood as the “language of dimensional engineering,” data locators are set, and all related dimensions are then measured based on their location relative to the locators.
5. Analyze tolerances.
During a development phase, the “manufacturability” of all parts must be ensured before production release. During a production phase, the possible product and process changes must be optimized before expensive tooling changes have been executed. Tolerance analysis produces neutral, realistic facts for the decision makers. Tolerance analysis is performed in parallel with the setting of build strategies and GD&T requirements.
6. Establish measurement plans.
The next step in the closed-loop quality management process is establishing a measurement plan to identify the critical quality characteristics identified through tolerance analysis. This plan documents tolerance limits for each part within the finished product. The plan is used in quality inspection labs as a road map of what critical features must be checked and monitored during production. This process provides for a coordination of measurement points from the individual detailed component, through any subassemblies, to the final product.
7. Generate dimensional data reports.
As the product enters preproduction and initial runs begin, quality inspection data are collected and dimensional data reports are generated. This ensures that measurement plans are being followed and that the end products achieve the tolerances expected based on the results of all prior steps in the process.
8. Conduct root cause analyses.
The final stage of the closed-loop quality management process involves reviewing dimensional data reports and root cause analyses of any quality issues. As has been the case at most other stages, if the end products are not achieving the tolerances expected, engineers can loop back to find out where problems originated and either resolve any issues or adjust build objectives, build strategies, or tolerances as needed.
The closed-loop approach is referred to as such because it closes the loop on product and manufacturing. It enables engineers to use comprehensive virtual simulation to analyze variation and tolerances in product design, from initial product development through production, ensuring that the value of the analyses is maintained across the full product life cycle.
Through this process, dimensional quality data reports are generated as the product enters preproduction and initial runs begin. Engineers refer to the reports and check key points to ensure that measurement plans are being followed, and that end products achieve quality targets. If the end products are not achieving quality targets, engineers can loop back to see where problems originated and fix them.
Through the eight-step closed-loop dimensional engineering system, data reports are generated as the product enters preproduction and initial runs begin. Engineers refer to the reports and check key points to ensure that measurement plans for the detailed parts are being followed and that end products achieve the quality targets expected based on the results of all prior steps in the process.
Technology tools allow manufacturers to thoroughly appraise design and manufacturing robustness by quickly evaluating GD&T, assembly tooling, and build sequencing—all well ahead of production release. Tolerance simulation identifies areas of concern, potential failure rates, and statistical results for each measurement, such as percent out of specification. A sensitivity analysis then looks at each tolerance as it relates to each measurement, and it identifies the percentage contribution or affect on each measurement.
Such tools rely on these critical measurements to create measurement plans and generate measurement reports, steps six and seven of the closed-loop process. The plans and reports define which critical-to-quality characteristics are to be inspected for dimensional variability and the results of the inspections.
By relying on virtual simulations throughout this process and feeding measurement inspection data back into the tolerance model, engineers can quickly pinpoint issues and perform corrective actions—avoiding the need to chase problems through their build processes by trial and error. This saves direct and indirect costs required to achieve quality goals.
The closed-loop dimensional engineering process and the tolerance analysis tools that support such a process comprise a technology-driven approach that drives forms of waste (e.g., scrap and rework), out of design and manufacturing to minimize the overall cost of quality.
A major tier-one supplier to automotive and aerospace manufacturers is one of many real-life examples of organizations that can attest to the success of the closed-loop process. Its engineers and quality professionals stated during a tolerance analysis workshop that a closed-loop quality management process is one of the most effective methods they have found to reduce product life cycle costs. They noted that if they did not apply a thorough tolerance analysis process across their vast number of programs, their product life cycle costs could easily increase to 10 times the cost of following such a process.
A closed-loop process enables the manufacturing enterprise to avoid unnecessary costs involved in achieving quality. Users of such a process automatically gain control over all four components of cost of quality highlighted earlier:
Prevention costs. Costs of preparing and implementing a quality plan. A closed-loop dimensional engineering process includes the development of quality plans for each product and program enhancement using tools and processes that are well-established, speedy, and efficient.
Appraisal costs. Costs of testing, evaluating, and inspecting quality. Testing, evaluation, and inspection of quality are included as critical components of a closed-loop process—again, through a highly effective, resource-efficient process.
Internal failure costs. Costs of scrap, rework, and material losses. With the capability for users to loop back and make process, measurement, and design corrections and adjustments during the “as-built” phase of a product’s life cycle, the closed-loop approach minimizes internal costs associated with scrap, rework, and material losses.
External failure costs. Costs of failure at customer site, including returns, repairs and recalls. A closed-loop quality management process, with its many checks and balances, minimizes the number of quality defects or issues that may slip through to the customer, thereby minimizing the costs associated with returns, repairs, and recalls.
In short, using a closed-loop dimensional engineering process, including tolerance simulation tools and techniques, enables engineers to control all of the areas of waste that feed into an organization’s total cost of quality. Users of such a process are able to minimize their overall cost of quality, giving them an edge against their competition.