Process capability concepts

One approach that QA would use to assure itself that a given process (step) is under control is the effort associated with the concept of process capability. Ekvall and Juran [15] defined the concept as the measured inherent reproducibility of the product turned out by the process. The statistical definition of process capability is that all the measured values fall within a 6-sigma range (i.e., range of the minimum to maximum limits). The information is used to show that the process is under control over a period of time as well as determine whether there is any drifting or abnormal behavior from time to time. Process validation is a QA tool in this case because its data will be used as the origin for the data curve developed for the process capability concept. 

It is recommended at this stage of the text that the reader unfamiliar with the basic concepts of variation and process capability refer to Appendix I for an introductory treatise on statistics, and Appendix II for a discussion of process capability studies. 

In the next chapter, we introduce the concepts of component manufacturing capability and the relationships between tolerance, variability and cost. The Component Manufacturing Variability Risks Analysis is then introduced, the first stage of the CA methodology, from which process capability estimates can be determined at the design stage. The development of the knowledge and indices used in the analysis... 

Figure 11.11 A graphical illustration of the concept of process capability (from CHTF Guidance Quality Management Systems-Process Validation).

Arguably, the most important aspects of quality management for PAT are the concepts of quantitative process performance characterization using process capability indices as universal descriptors, which form the basis of the measure and analyze portions of the DMAIC model. Process capability indices consider simultaneously both process variability and process specifications to determine whether... 

Nash, R.A. Understanding the process capability index concept. J. Valid. Technol. 1998, 4 (3), 202-204. 

FIGURE 19.15 (Step 2) (a) The bio-nanocomponents will be used to fabricate complex biorobotic systems. A vision of a nano organism carbon nanotubes form the main body peptide limbs can be used for locomotion and object manipulation and the biomolecular motor located at the head can propel the device in various environments, (b) Modular organization concept for the bio-nanorobots. Spatial arrangements of the various modules of the robots are shown. A single bio-nanorobot will have actuation, sensory, and information processing capabilities. 

For both types of required flexibility, a common process description based on the product-process-resource concept (Pfrommer et al. 2013) is desirable. This description requires expressing in semantically well-defined and comparable ways, the concepts and relationships of (a) the needs for capabilities of production system components and devices (b) the component/device use conditions (access path and control) and (c) product-related processing requirements. 

The expansion of dispersed media ATRP to microemulsion provided the critical step required for development of a process for addition of pure monomer to the system to increase the percent solids in the final latex. This procedure was initially employed to prepare a forced gradient copolymer in a heterogeneous controlled copolymerization since the added pure monomer could diffuse to the latex partides containing all components required for an ATRP. An extension of the concept resulted in the development of an ab initio emulsion polymerization process, capable of directly preparing a stable latex containing block copolymers. The critical requirement for this advance in dispersed media ATRP was the ability to encapsulate all agents required for an ATRP in the initially formed micelles. This allowed pure monomer to be added to the reaction medium. The added monomer was then able to diffuse to the active micelles, allowing an increase in micelle size and concomitant increase in the percent solids and decrease in percent surfactants in the system. 

In Chapter 4, R.D. Rauh introduces the relatively new subject of photoelectrochemical processing. The injection of photon energy at an electrochemical interface adds an extra dimension to the processing capability, be it for selective etching, patterned electrodeposition, or the fabrication of optical elements. These concepts offer intriguing possibilities for the future of both electronic and opto-electronic technologies. 

---