Search Results for time proportioning

This chapter discusses the selection, use, and integration of methods to control process variables in induction heating, including control of workpiece and processing temperature and materials handling systems. The discussion of temperature control includes a review of proportional controllers and heat-regulating devices. Integration of control functions is illustrated with examples related to heating of steel slabs, surface hardening of steel parts, vacuum induction melting for casting operations, and process optimization for electric-demand control. Distributed control within larger manufacturing systems is discussed. The chapter also covers nondestructive techniques for process control and methods for process simulation.

This chapter discusses the basic principles of induction heating and related engineering considerations. It describes the design and operation of induction coils, the magnitude and distribution of magnetic fields, and the forces that generate eddy currents in metals. It explains how induced electrical current causes metal to heat in proportion to their electrical resistance and how it affects temperature dependent properties such as resistivity and specific heat and, in turn, heating rates and efficiencies. It also discusses the effect of hysteresis and explains why eddy currents tend to be confined to the outer surface of the workpiece, a phenomenon known as the skin effect. The chapter includes several data plots showing how the depth of heating varies with frequency and how heating time, power density, and thermal conduction rate correspond with hardening depth.

Critical process variables must be controlled to ensure uniform and repeatable heat-treating results. This chapter covers the subject of controlling the heat-treating process. All heat-treating equipment utilizes various sensors, timers, and other components to monitor and control the process utilizing various control methods. The chapter focuses on temperature control and measurement, including a discussion about thermocouples and devices for measuring thermal and electrical conductivity.

The tensile test provides a relatively easy, inexpensive technique for developing mechanical property data for the selection, qualification, and utilization of metals and alloys in engineering service. The tensile test requires interpretation, and interpretation requires a knowledge of the factors that influence the test results. This chapter provides a metallurgical perspective for such interpretation. The topics covered include elastic behavior, anelasticity, damping, proportional limit, yield point, ultimate strength, toughness, ductility, strain hardening, and yielding and the onset of plasticity. The chapter describes the effects of grain size on yielding, effect of cold work on hardness and strength, and effects of temperature and strain-rate on the properties of metals and alloys. It provides information on true stress-strain relationships and special tests developed to measure the effects of test/specimen conditions. Finally, the chapter covers the characterization of tensile fractures of ductile metals and alloys.

This article describes the most common, general-purpose analog design-for-test (DFT) methods, analog test buses and loopback, and shows their advantages and limitations in diagnosability and automatability. It also describes DFT and built-in self-test (BIST) techniques for the most common analog functions, namely phase-locked loop, serializer-deserializer, analog/digital converters, and radio frequency. Lastly, the challenges of creating BIST for analog functions are summarized, along with seven principles that must be exploited to meet these challenges. These principles show how the design constraints for analog BIST circuitry can be more relaxed than for the circuit under test, while delivering the required test accuracy and speed.

This chapter introduces the concepts of mechanical properties and the various underlying metallurgical mechanisms that can be used to alter the strength of materials. The mechanical properties discussed include elasticity, plasticity, creep deformation, fatigue, toughness, and hardness. The strengthening mechanisms covered are solid-solution strengthening, cold working, and dispersion strengthening. The effect of grain size on the yield strength of a material is also discussed.

The die casting process is a widely applied technique used by a variety of industries. This chapter reviews the casting design and engineering requirements for optimizing the characteristics of die castings.

This chapter is a compilation of terms and definitions related to tensile testing.

Failure analysis can sometimes involve considerations of statistics and probability. This chapter reviews some of the basic types of statistical distributions in order to understand some basic principles in their use. The main focus is on the uses of the normal distribution, which is the most commonly used statistical distribution. The chapter also includes a section discussing the reliability and probability of passing.

The temperature and atmosphere conditions must be precisely controlled in order to achieve the desired metallurgical results during heat treating operations. In order to ensure the repeatability of operation, a heat treating system must have the necessary sensors, timers, and variable (temperature, atmosphere, etc.) controllers to hold the process within prescribed or specified limits. This chapter discusses temperature and atmosphere sensors used in a heat treating system. The temperature sensors covered are contact and noncontact types. The atmosphere sensors covered are oxygen probe, dew point, and infrared. The chapter concludes with an overview of the development of integrated control systems.

This chapter addresses the issue of die failures in hot and cold forging operations. It describes failure classifications, fatigue fracture and wear mechanisms, analytical wear models, and the various factors that limit die life. It also includes several case studies in which finite-element modeling is used to predict die failure and extend die life.

This appendix is a compilation of terms, definitions, abbreviations, and symbols associated with the mechanics and mechanisms of fracture.

Diffusion is the movement of atoms through the crystalline lattice. This chapter discusses the two main types of diffusion that can occur in solids: interstitial diffusion and substitutional diffusion. It describes Fick's first and second laws of diffusion, with emphasis on several applications of the latter. The chapter also provides information on the temperature dependence of diffusion, intrinsic diffusion coefficients (Kirkendall effect), and high diffusion paths.

This chapter focuses on the design of measuring devices. The devices used to measure vibration typically consist of an electronic transducer with an interconnecting cable and an alternating current voltmeter. The working principle of each type of transducer is described in this chapter along with their important characteristics and common applications. The chapter provides general guidelines for the selection of a measuring device, and discusses vibration severity levels.

This chapter provides an overview of aluminum die casting and the equipment used. It discusses the advantages and limitations of the die casting process and the design and operation of hot- and cold-chamber die casting machines. It also discusses clamping systems and forces and the factors affecting die life, including die materials, metal injection cycles, and lubrication. A typical die casting cell layout is also provided.

This chapter addresses the question of how to deal with multiaxial stresses and strains when using the strain-range partitioning method to analyze the effects of creep fatigue. It is divided into three sections: a general discussion on the rationale used in formulating rules for treating multiaxiality, a concise listing of the rules, and an example problem in which axial creep-fatigue data is used to predict the torsional creep-fatigue life of type 304 and 316 stainless steel. The chapter also includes a brief introduction in which the authors outline the challenges presented by multiaxial loading and set practical limits on the problem they intend to treat.

The mechanical behavior of a material, in the most practical sense, is how it deforms or breaks under load; in other words, how it responds when stressed. This chapter provides a brief review of the properties associated with mechanical behavior, including stress, strain, elasticity, plastic deformation, ductility, hardness, creep, fatigue, and fracture. It also describes the primary components of a Charpy impact tester and the role they serve.