Unit Manufacturing Processes: Issues and Opportunities in Research (1995)

Any manufacturing system can be decomposed into a series of unit processes that impart both physical shape and structure to the product. Unit processes are intimately linked to one another by the fact that the output of one process becomes the input for the next process. The quality of the final product depends not only on the capability of each unit process but also on the unit processes working together. Continuous improvement of the manufacturing system includes better integration of each process with those that precede or follow, as well as of improvements to the unit processes themselves.

This part describes opportunities for technical advancements in the five unit process families:

• mass-change processes;
• phase-change processes;
• structure-change processes;
• deformation processes; and
• consolidation processes.

The committee selected several examples of unit processes from each of the five families and developed recommendations for research opportunities by applying criteria developed in Chapter 2. These specific recommendations are representative of how priorities in unit process R&D can be established within a defined context.

Chapter 3, ''Mass-Change Processes,'' discusses unit processes that remove or add material by mechanical, electrical, or chemical means. These processes include traditional chip-making processes such as shaping, turning, milling, drilling, sawing, and grinding, as well as nontraditional processes such as laser machining, electrodischarge machining and electrochemical machining.

Chapter 4, "Phase-Change Processes," discusses processes that produce a solid part from material originally in the liquid or vapor phase. These processes include metal casting, infiltration of composites, and injection molding of polymers. They are necessarily specialized to the type of material being processed.

Chapter 5, "Structure-Change Processes," discusses processes that alter the microstructure of a workpiece. The changes are usually achieved through thermal treatments involving heating and cooling under controlled conditions, sometimes in combination with mechanical force. These processes are dependent on the type of material being processed. Surface treatment processes are included within this family, for example, applying very thin highly adherent coatings, surface alloying, and inducing compressive residual stresses.

Chapter 6, "Deformation Processes," discusses processes that alter the shape of a solid workpiece without changing its mass or composition. These processes can be further decomposed into those that are bulk forming (e.g., rolling, extrusion, forging, drawing) and those that are sheet forming (e.g., stretching, flanging, drawing, and contouring).

Chapter 7, "Consolidation Processes," discusses processes that combine materials such as particles, filaments, or solid sections to form a solid part or component. The interaction between the material and the energy that produces the consolidation is a key feature of these processes. The chapter provides an overview of powder processing, polymeric composites, and welding/joining.

Chapter 8, "Integrated Processes," discusses processes that combine more than one specific unit process into a single piece of equipment or into a group of work stations that are operated under unified control. The potential of such integration is beginning to be realized by processes such as those that use directed-beam technologies.

The opportunities for improvements to individual unit processes derive from the need to overcome specific technical limits and barriers to process performance. The resulting set of research recommendations provides the basis for identifying several key enabling technologies that support all unit process families and material classes. These enabling technologies are described in Part III.

R&D on unit processes enhance the knowledge level of unit processes and allow the production of better, more cost-effective and competitive products.¹ Over the long run, better understanding of manufacturing processes result in an improved competitive posture for U.S. industry in the global environment.

R&D activities within the enabling technology groups are typically initially focused on a particular process and material. This coupling ensures that the results can eventually be implemented to improve an actual unit process. The understanding developed by such focused activity often may be applied to other materials and processes.

Unit process R&D may involve the processing of traditional or emerging materials by either conventional or novel processes. Significant benefits may also result from the optimization and improvement of traditional processing of high-volume conventional materials. Incremental improvements in quality at reduced costs, although not dramatic, can be significant when applied to large production quantities.

Application of traditional processes to advanced or emerging materials is often cost-effective, because existing equipment and facilities are used. However, the extension of current process practices to these materials requires developing a new understanding of the process requirements specific to the new material.

Novel processes may be required for high-performance materials, such as producing affordable metal-matrix composites. Novel processes may also provide a significant benefit in the processing of traditional materials, for example, near-net-shape casting of steel into structural shapes.

Unit processes should be designed for flexibility, so that variations in starting materials, initial conditions, and so on, can be accommodated without requiring substantial additional process development to produce a quality product.