A D V A N C E D M A T E R I A L S & P R O C E S S E S | J U L Y / A U G U S T 2 0 2 2 4 0 iTSSe TSS iTSSe TSS standard. Improvement plans with regular reviews can then be put in place to address any criteria below the minimum standard. In many cases, conformance to an established minimum standard can result in immediate returns in the form of reduced noncompliance. These audits are not intended to replace process specifications, Nadcap check sheets, and supplier maturity assessments. Instead, they are expected to supplement those methods and to create an environment where a cross-functional team feels ownership for the process and for ensuring that it remains under long-term control. STANDARDIZED DEFECT PREVENTION TOOLS Once a minimum standard framework is in place, the next step in the journey to zero defects focuses on defect prevention tools—ones that enable better understanding of the process, which can then be leveraged for better control. Three critical tools—the process flow diagram (PFD), the process failure modes and effects analysis (PFMEA), and the control plan—are described in SAE AS13100 and RM13004. These tools are designed to be used together by iterative interactions among them and in conjunction with other important design and manufacturing quality tools (Fig. 2). When these methods are applied and kept up to date, they become essential knowledge management tools that aid in identifying and correcting quality risks. These tools require an intimate knowledge not only of the thermal spray process, but also of the product and features to be coated. The PFD is a representation of the required process steps to apply a coating onto a component, and it includes all process steps from receipt of parts into the facility to shipment of the completed product. The PFD must also identify any inputs, resources, and controls, as well as any subcontracted process steps. It must also list the sequence of operations and a detailed description of all steps within a given operation. In turn, the PFD itself is a key input when developing a process failure modes and effects analysis (PFMEA). The PFMEA focuses on identifying those steps where potential noncompliance can jeopardize product quality. In general, each individual part number will be assigned its own PFMEA because there are typically important differences between processes among different components. The process of creating a PFMEA consists of the following steps: • Identify characteristics the process must achieve • Identify ways the coating can be applied incorrectly (failure modes) • Understand potential impact of nonconformance to the business (severity) • Determine which adverse process condition will lead to nonconformance (cause) • Identify ways to detect failure mode (controls) • Calculate a risk priority number for each potential hazard (ranking) Finally, the control plan describes feature checks and measurements to be performed at each processing step to reduce variation in the process and in its product. It summarizes all defined controls (including asset care, calibration, and maintenance) and is based on the PFMEA results. The control plan is not the same as a work instruction or process routing. Instead, it is ideally designed to work alongside such instructions to help improve long-term quality control. Once a solid foundation is in place—with the right organizational culture and reliable defect prevention tools—the benefits of digital technologies can be fully realized. DIGITALIZATION The need to understand and reduce or eliminate all possible sources of processes variation is increasingly driving development of novel sensors and improved equipment for thermal spray applications. Closed loop controllers, multi-axis robots, and in-flight particle measurement diagnostic tools are among the most successful examples embraced by the industry. One area where sensors and digital methods can bring greater process understanding is the quantification of FEATURE 6 Fig. 2 — AS13100/RM13004 scope and relationships to design and manufacturing quality tools.
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