Search Results for dimensional accuracy

This article provides information on metals that can be cast in permanent molds. It describes the advantages, disadvantages, applications, and design of permanent castings. Following a discussion on the factors considered in mold design and material selection, the article details the application of mold coatings and examines the effects of major processing variables on mold life. The variables that determine mold temperature and measures for controlling it are reviewed, and the effects of short-term and long-term variables on the dimensional accuracy of permanent mold castings are explained. The article concludes with a discussion on the factors influencing the surface finish on permanent mold castings.

Forgings are classified in various ways, beginning with the general classifications open die and closed die. They are also classified according to how they are made; such as hammer upset forgings, ring-rolled forgings, and multiple-ram press forgings; and in terms of the close-to-finish factor or amount of stock that must be removed to satisfy the dimensional and detail requirements of the finished part. In addition to types and classifications, the article discusses critical design factors and ways to ensure that the resulting forgings measure up to metallurgical, mechanical property, and dimensional accuracy requirements. The responsibility for design verification is vested in material control, which depends on the proper application of drawings, specifications, manufacturing process controls, and quality assurance programs. The article addresses each of these areas as well as related topics; including stress-induced fatigue failure, tolerances, machining allowances; and the fundamentals of hammer and press forgings, hot upset forgings, and hot extrusion forgings.

This article describes the extrusion process, which converts soft, plastic material into a particular form using an extruder, or screw conveyer. It discusses the two main types of plastic extruders, twin-screw and single-screw, estimation of extruder capacity, and design and operations (heating, cooling, downstream sizing, corrugating, and crossheading) of the screw, the most important component of any extruder. It discusses the shapes produced by screw extrusion and the types of extrusion products produced by extrusion processes, including blown-film extrusion, flat-film or sheet extrusion, chill-roll film extrusion, pipe or tube extrusion, wire and cable coverings, extrusion coating, and profile extrusion, and provides some discussion on multiple-screw extruders. The article describes the dimensional accuracy of extrusion products, and lists common defects that occur frequently in the extrusion process.

This article focuses on machines that are designed, constructed, and used for drilling. It provides information on the design, materials, selection, and classification of drill. The article describes drills that are specially designed for hard steel and other specific applications. A variety of drill point styles, such as single-angle points and reduced-rake points, are described. The article discusses the factors considered to obtain expected dimensional accuracy of holes. It explains the determination of the optimum speed and feed for drilling, which depends on the workpiece material, tool material, depth of hole, design of drill, rigidity of setup, tolerance, and cutting fluid. The article illustrates the effects of operating variables on drill life of hardened steel. The advantages, limitations, design considerations, insert configurations, and applications of indexable-insert drills are discussed. The article concludes with a discussion on the requirements to drill small holes that differ from those used in conventional drilling.

Roller burnishing is a method of working a metal surface to improve its finish and dimensional accuracy and can provide some degree of work hardening. This article discusses the workpiece requirements used for roller burnishing. It illustrates the types of roller burnishing tools, such as internal tool, external tool, and tools for the roller burnishing of tapered holes and circular flat surfaces. The article contains a table that lists typical inside and outside diameter speed and feed rates for roller burnishing tools. It exemplifies typical lubrication techniques and the conditions used in the roller burnishing of magnesium alloy castings. The article reviews fillet rolling that is used to improve fatigue resistance of the materials. It concludes with a discussion on the process considerations for three basic types of bearingizing tools for the finishing of bores: bottoming, semi-bottoming, and through-hole.

Turning is a machining process for generating external surfaces of revolution by the action of a cutting tool on a rotating workpiece, usually in a lathe. This article discusses the process capabilities of turning over other machining operations and describes the classification, controlling methods, attachments, and accessories of a lathe machine. It reviews the design and various operations of single-point cutting tools in turning. In addition, the article discusses the influence of various factors on selection of equipment and machining procedure for a specific part. These include the size and configuration of the workpiece, equipment capacity, production quantity, dimensional accuracy, number of operations, and the surface finish. It presents examples that describe or compare equipment and techniques for production applications. Finally, the article provides a discussion on the classification and compatibility of cutting fluids.

The systematic study of microstructural evolution during deformation under hot working conditions is important in controlling processing variables to achieve dimensional accuracy. This article explains the microstructural features that need to be modeled and provides an outline of the principles and achievements of each of the various microstructural models, including black-box modeling, gray-box modeling, white-box modeling, and hybrid modeling.

This article discusses the principles of the press-brake forming process and its applicability with an example. It describes the types of press brakes and examines some considerations, which help in the selection of machine. The article provides information on flattening dies, gooseneck punches, wiping dies, channel dies, arbor-type punches, box-forming dies, curling dies, beading dies, and cam-driven dies, with illustrations. It discusses the tool material selection for various operations. The article explains the procedures used for producing different shapes, including simple boxlike parts, panels, flanged parts, architectural columns, fully closed parts, and semicircular parts. It examines the effect of work metal variables on results in press-brake operations. The article also reviews stock tolerances, design, and condition of machines and tools, which help in obtaining good dimensional accuracy.

This article discusses slurry molding that encompasses two distinct processes: plaster molding and ceramic molding. Plaster mold casting is a specialized casting process used to produce nonferrous castings that have greater dimensional accuracy, smoother surfaces, and more finely reproduced detail. The article describes three generally recognized plaster mold processes, namely, conventional plaster mold casting, the Antioch process, and the foamed plaster process. Ceramic molding techniques are based on processes that employ permanent patterns and fine-grained zircon and calcined, high-alumina mullite slurries for molding. The Shaw process and the proprietary Unicast processes are also discussed.

This article provides an introduction to architected cellular materials, their design, fabrication, and application domain. It discusses design decisions involving the selection, sizing, and spatial distribution of the unit cell, property-scaling relationships, and the integration of cells within an external boundary. It describes how manufacturing constraints influence achievable feature resolution, dimensional accuracy, properties, and defects. It also discusses the mechanical behavior of architected cellular materials and the role of additive manufacturing in their fabrication.

The Replicast process is developed to overcome the formation of lustrous carbon defects and carbon pickup observed in conventional evaporative pattern casting processes. This article provides a discussion on the pattern production, process capabilities, advantages, and limitations of Replicast process.

This article discusses the types of adaptive control (AC) systems for metal cutting according to the AC strategies used. These include adaptive control with optimization (ACO), adaptive control with constraints (ACC), and geometric adaptive control (GAC). The article details the milling and grinding systems based on the ACO strategy. It reviews the fundamentals of ACC systems followed by a description of a particular ACC system for a turning operation. The article also describes the basic characteristics of GAC systems and presents a particular GAC system for the turning of cylindrical parts. It examines the issues in the AC systems such as tool wear/breakage. Trends in the AC systems such as variable-gain ACC systems and integration of adaptive control into CAD/CAM/CIM systems are also discussed.