Search Results for process selection

There are many reasons why plastic materials should not be considered for an application. It is the responsibility of the design/materials engineer to recognize when the expected demands are outside of what the plastic can provide during the expected life-time of the product. This article reviews the numerous considerations that are equally important to help ensure that part failure does not occur. It provides a quick review of thermoplastic and thermoset plastics. The article focuses primarily on thermoset materials that at room temperature are below their glass transition temperature. It describes the motivation for material selection and the goal of the material selection process. The use of material datasheets for material selection as well as the processes involved in plastic material selection and post material selection is also covered.

Manufacturing process selection is a critical step in plastic product design. The article provides an overview of the functional requirements that a part must fulfil before process selection is attempted. A brief discussion on the effects of individual thermoplastic and thermosetting processes on plastic parts and the material properties is presented. The article presents process effects on molecular orientation. It also illustrates the thinking that goes into the selection of processes for size, shape, and design factors. Finally, the article describes how various processes handle reinforcement.

This article presents the benefits of selecting plastics for products to be manufactured. It discusses the four key considerations for plastic part design: material, process, tooling, and design. The article provides a detailed discussion of the development sequence for plastic parts. The basis for the development sequence is twofold: first, to create the best solution for the application, and second, to minimize potential project risks through careful and thoughtful work habits.

Materials selection is closely related to the objectives of failure analysis and prevention. This article briefly reviews the general aspects of materials selection as a concern in both proactive failure prevention during design and as a possible root cause of failed parts. Coverage is more conceptual, with general discussions on the following topics: design and failure prevention, materials selection in design, materials selection for failure prevention, and materials selection and failure analysis. Because materials selection is just one part of the design process, the overall concept of design is discussed. The article also describes the role of the materials engineer in the design and materials selection process. It provides information on the significance of materials selection in both the prevention and analysis of failures.

Materials selection is an important engineering function in both the design and failure analysis of components. This article briefly reviews the general aspects of materials selection as a concern in proactive failure prevention during design and as a possible root cause of failed parts. It discusses the overall concept of design and describes the role of the materials engineer in the design and materials selection process. The article highlights the significance of materials selection in both the prevention and analysis of failures.

A plastic bracket exhibited relatively brittle material properties, which ultimately led to catastrophic failure. The part had been injection molded from a medium-viscosity polycarbonate resin and had been in service for a short duration prior to the failure. Investigation (visual inspection and analysis using micro-FTIR in the ATR mode) revealed the spectrum showed changes in the relative intensities of several bands, as compared to the results representing the base material. A spectral subtraction was performed, and the results produced a good match with diphenyl carbonate, which is a common breakdown product produced during the decomposition of polycarbonate. The conclusion was that the most likely cause of the molecular degradation was improper drying and/or exposure to excessive heat during the injection molding process that in turn caused the material degradation.

A broken aircraft crankshaft and a severely damaged main brass bearing were examined to determine whether engine failure was initiated in the bearing or in the crankshaft. The steel crankshaft failure was a classical fatigue fracture. The bearing had been subjected to extremely high temperatures, as indicated by melting in the brass components and the extreme distortion in the rollers. Microscopic examination on the crankshaft material showed it to be a good quality steel. On the other hand, the chromium plate was thick, porous, and cracked in many places, including the point of the main fatigue crack. It was concluded that the over-all failure was initiated in the crankshaft, and the failure of the bearing resulted from that failure.

The fracture cause had to be determined in a three-cylinder crankshaft made of chrome steel 34Cr4 (Material No. 1.7033) according to DIN 17200. The fracture occurred after only 150 h of operation. The fracture was of the bend fatigue type which originated in the fillet of the main bearing and ran across the jaw almost to the opposite fillet of the adjoining connecting rod bearing. The fillet was well rounded and smoothly machined. Thus, no reason for the fracture of the crankshaft could be found externally. No material defects were discernible in the origin or anywhere else. No cause for the crank fracture could be established from material testing. Probably the load was too high for the strength of the crank. Tensile strength could have been increased for the same material by tempering at lower temperature. Additionally, the resistance against high bend fatigue stresses or torsion fatigue stresses could have been increased substantially by including the fillet in the case hardening process.

This article focuses primarily on what an analyst should know about applying X-ray diffraction (XRD) residual stress measurement techniques to failure analysis. Discussions are extended to the description of ways in which XRD can be applied to the characterization of residual stresses in a component or assembly. The article describes the steps required to calibrate instrumentation and to validate stress measurement results. It presents a practical approach to sample selection and specimen preparation, measurement location selection, and measurement depth selection, as well as an outline on measurement validation. The article also provides information on stress-corrosion cracking and corrosion fatigue. The importance of residual stress in fatigue is described with examples. The article explains the effects of heat treatment and manufacturing processes on residual stress. It concludes with a section on the XRD stress measurements in multiphase materials and composites and in locations of stress concentration.

One of the two AISI 4340 steel pitch horn bolts from the main rotor hub assembly failed while in service. Optical microscope revealed evidence of corrosion pitting in regions adjacent to the fracture. Fractographic examination utilizing a scanning electron microscope revealed multiple crack origins which assumed a “thumbnail” shape and displayed surface morphologies which resulted from intergranular decohesion. Many of the crack sites initiated from corrosion pits. Energy dispersive spectroscope performed on areas within the crack initiation site showed the presence of chlorides. The failure was attributed to stress-corrosion cracking. Short- and long-term recommendations to prevent future failures are given.

This article discusses failure mechanisms in tool and die materials that are very important to nearly all manufacturing processes. It is primarily devoted to failures of tool steels used in cold working and hot working applications. The processes involved in the analysis of tool and die failures are also covered. In addition, the article focuses on a number of factors that are responsible for tool and die failures, including mechanical design, grade selection, steel quality, machining processes, heat treatment operation, and tool and die setup.

Plastic product failures are directly attributed to one of the following four reasons: omission of a critical performance requirement, improper materials specification, design error, and processing/manufacturing error. Therefore, product failures can be minimized or eliminated if all of these parameters are comprehensively examined during the design process. This article focuses on all of these factors, except processing-related failures, which are outside the design and engineering domain. It is dedicated to the identification and avoidance of common problems associated with the selection and designing of plastic parts. The article provides information on the material-related design criteria that depend on the applications, environmental conditions of use, and performance requirements. It discusses physical properties of plastics based on their relevance to real-world environmental conditions. The most-common design problems related to design considerations are also covered.

This article provides background information needed by design engineers to create part designs optimized for plastics and plastic manufacturing processes. It describes the four essential elements of plastic part development, namely, material, process, tooling, and design, and provides general design rules for the plastic forming processes covered. It also discusses the steps involved in design validation and verification.

The various methods of furnace, torch, induction, resistance, dip, and laser brazing are used to produce a wide range of highly reliable brazed assemblies. However, imperfections that can lead to braze failure may result if proper attention is not paid to the physical properties of the material, joint design, prebraze cleaning, brazing procedures, postbraze cleaning, and quality control. Factors that must be considered include brazeability of the base metals; joint design and fit-up; filler-metal selection; prebraze cleaning; brazing temperature, time, atmosphere, or flux; conditions of the faying surfaces; postbraze cleaning; and service conditions. This article focuses on the advantages, limitations, sources of failure, and anomalies resulting from the brazing process. It discusses the processes involved in the testing and inspection required of the braze joint or assembly.

Examination of a damaged component involves a chain of activities that, first and foremost, requires good observation and documentation. Following receipt and documentation, the features of damage can be recorded and their cause(s) investigated, as this article briefly describes, for typical types of damage experienced for metallic components. This article discusses the processes involved in visual or macroscopic examination of damaged material; the interpretation of fracture features, corrosion, and wear damage features; and the analysis of base material composition. It covers the processes involved in the selection of metallurgical samples, the preparation and examination of metallographic specimens in failure analysis, and the analysis and interpretation of microstructures. Examination and evaluation of polymers and ceramic materials in failure analysis are also briefly discussed.

The thin plates within a type 309 stainless steel chlorinated solvent combustion preheater/heat exchanger designed to process fumes from a solvent coating process showed severe corrosion within 6 months of service. Within a year corrosion had produced holes in the plates, allowing gases to shunt across the preheater/exchanger. Metallographic examination of the plates showed that accelerated internal oxidation had been the cause of failure. Corrosion racks of candidate alloys (types 304, 309, and 316 stainless steels, Inconel 600, Inconel 625, Incoloy 800, Incoloy 825, and Inco alloy C-276) were placed directly in the hot gas stream, containing HCl and Cl2, for in situ testing. Results of this investigation showed that nickel-chromium corrosion-resistant alloys, such as Inconel 600, Inconel 625, and Inco alloy C-276, performed well in this environment. Laboratory testing of the same alloys, along with Inconel alloys 601, 617, and 690 and stainless steel type 347 was also conducted in a simulated waste incinerator nitrogen atmosphere containing 10% Co2, 9% O2, 4% HCl, 130 ppm HBr and 100 ppm SO2 at 595, 705, 815, and 925 deg C (1100, 1300,1500, and 1700 deg F). The tests confirmed the suitability of the nickel-chromium alloys for such an environment. Inconel 625 was selected for fabrication of a new preheater/exchanger.

Several surface-mount chip resistor assemblies failed during monthly thermal shock testing and in the field. The resistor exhibited a failure mode characterized by a rise in resistance out of tolerance for the system. Representative samples from each step in the manufacturing process were selected for analysis, along with additional samples representing the various resistor failures. Visual examination revealed two different types of termination failures: total delamination and partial delamination. Electron probe microanalysis confirmed that the fracture occurred at the end of the termination. Transverse sections from each of the groups were examined metallographically. Consistent interfacial separation was noted. Fourier transform infrared and EDS analyses were also performed. It was concluded that low wraparound termination strength of the resistors had caused unacceptable increases in the resistance values, resulting in circuit nonperformance at inappropriate times. The low termination strength was attributed to deficient chip design for the intended materials and manufacturing process and exacerbated by the presence of polymeric contamination at the termination interface.

This article considers the main characteristics of wear mechanisms and how they can be identified. Some identification examples are reported, with the warning that this task can be difficult because of the presence of disturbing factors such as contaminants or possible additional damage of the worn products after the tribological process. Then, the article describes some examples of wear processes, considering possible transitions and/or interactions of the mechanism of fretting wear, rolling-sliding wear, abrasive wear, and solid-particle erosion wear. The role of tribological parameters on the material response is presented using the wear map concept, which is very useful and informative in several respects. The article concludes with guidelines for the selection of suitable surface treatments to avoid wear failures.

This article describes the characteristics of tools and dies and the causes of their failures. It discusses the failure mechanisms in tool and die materials that are important to nearly all manufacturing processes, but is primarily devoted to failures of tool steels used in cold-working and hot-working applications. It reviews problems introduced during mechanical design, materials selection, machining, heat treating, finish grinding, and tool and die operation. The brittle fracture of rehardened high-speed steels is also considered. Finally, failures due to seams or laps, unconsolidated interiors, and carbide segregation and poor carbide morphology are reviewed with illustrations.