Search Results for production steps

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.

Randomly selected dictating-machine drive mechanisms, which contained small ball bearings, were found to exhibit unacceptable fluctuations in drive output during the early stages of production. It was indicated that the bearing raceways were being true brinelled before or during installation of the bearings. The preinstallation practices and the procedures for installing the bearings were carefully studied. It was revealed that during one preinstallation step, the lubricant applied by the bearing manufacturer was removed and the bearing was relubricated with another type of lubricant prior to which the bearings were ultrasonically cleaned in trichloroethylene to ensure extreme cleanness. Equally spaced indentations resembling true brinelling were revealed by careful examination of the bearing raceways. It was concluded that the ultrasonic energy transmitted to the balls brinelled the raceways enough to cause fluctuations in machine output. Solvent-vapor cleaning was employed as a corrective technique for removing bearing lubricant.

During the inspection of a boiler containing cracks at the superheater header connection, cracking also was detected within the main steam drum. This was fabricated from a Mn-Mo-V low-alloy steel. It operated with water and saturated steam at approximately 335 deg C. Cracking was detected at the nozzles connecting the tubes for the entry of steam and hot water to the drum, at the downcomers, and at the connection to the safety valve. All cracks had a similar morphology, running in a longitudinal direction along the drum from the cutouts in the shell. All the cracks had developed under the influence of the hoop stress and were associated with the locally increased stress levels relating to the cutouts at nozzle and pipe connections. At their ends the cracks were filled with corrosion products, and their surfaces were seen to be very irregular. The process of crack growth was not due to fatigue only but can most probably be attributed to corrosion fatigue. The boiler steam drum design should be reviewed to reduce the local level of stress at the shell-nozzle connections.

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.

Failure analysis is the process used to determine the cause of a failure. There is no definitive method for performing a failure analysis, and the method chosen is dependent upon the type of failure, the availability of background information, the tools available to perform the analysis, and the skills of the analyst. The information outlined in this article focuses on the general methodology while allowing for case-specific techniques to be utilized along the way. It covers the causes of failure, why a failure analysis is performed, the failure analysis process, the planning of failure analysis investigation, recommendations to prevent the need for a failure analysis, the implementation of product reviews, and forensic standards.

A type 304 austenitic stainless steel tube (0.008 max C, 18.00 to 20.00 Cr, 2.00 max Mn, 8.00 to 10.50 Ni) was found to be corroded. The tube was part of a piping system, not yet placed in service, that was exposed to an outdoor marine environment containing chlorides. As part of the assembly, a fabric bag containing palladium oxide was taped to the tube. The palladium served as a “getter.” Investigation (visual inspection and EDS analysis of corrosion debris) supported the conclusion that chlorides and palladium both contributed to corrosion in the crevice created by the tape on the tube, which was periodically exposed to water. Recommendations included taking steps to prevent water from entering and being trapped in this area of the assembly.

This article discusses technologies focused on processing plastic materials or producing direct tools used in plastics processing. The article focuses on extrusion and injection molding, covering applications, materials and their properties, equipment, processing details, part design guidelines, and special processes. It also covers the functions of the extruder, webline handling, mixing and compounding operations, and process troubleshooting. Thermoforming and mold design are covered. Various other technologies for polymer processing covered in this article are blow molding, rotational molding, compression molding, transfer molding, hand lay-up process, casting, and additive manufacturing.

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.

Failure analysis of a fishhook that broke during retrieval is described. Although the broken hook was discarded, several companion hooks were analyzed (chemistry, microhardness, metallographic cross section, and tensile properties) as were comparable products made by other hook manufacturers. Tensile test data indicated that the companion hooks were significantly different from hooks made by other manufacturers. The hooks broke into several pieces and failed with little or no plastic deformation, while hooks made by other manufacturers plastically deformed and did not break during testing.

Ball joints made from carburized En 353 (BS970:815A16) steel failed after several hours of being fitted into vehicles. The parts were forged, machined, and thread rolled. The threads were copper plated to prevent carburization. The heat treatment consisted of carburizing in a cyanide bath for 12 hours at 930 deg C. After tempering for 2 h at 170 to 175 deg C, the copper plate was removed by immersing in an acid bath for 45 min. The investigations found the microstructure, hardness, and chemistry all met the specification. The case depth was approximately 0.75 mm to 1.0 mm. The SEM studies showed that it was a brittle fracture and completely intergranular to a depth of about 2.5 mm. It was concluded that the failure was due to hydrogen embrittlement for the following reasons: (i) failure did not occur immediately after loading, (ii) the fracture was intergranular to a depth of two to three times the case depth, (iii) secondary cracks were observed at the surface. The hydrogen was introduced during copper plate removal by acid dipping. If the tempering operation was performed after the acid dip operation, the hydrogen would have been driven out.

Electroless nickel plating separation from copper alloy CDA175 retaining clips used on printed circuit boards was caused by a copper oxide layer that reduced adhesion of the nickel plating on the clips. Stresses that developed during module insertion caused flaking to occur at the oxidized copper surface. Electroless nickel plating separation from OFHC copper leads was caused by improper handling rather than a plating anomaly per se. Tin plating separation from copper underplating on a hybrid package lid occurred because of a four-week delay between the copper plating and tin plating steps. It was recommended that tin plating should follow the copper underplating within 24 h and a cleaning step of bright dipping after copper plating be performed.

This article reviews the most common reasons for failures and the purpose of a failure investigation. It discusses the nine steps for the organization of a good failure investigation. The three basic tools that are helpful in any failure investigation, namely, a fault tree, a failure mode assessment chart, and a technical plan for resolution chart, are reviewed. The article briefly describes failure investigation pitfalls and concludes with information on the other common tools used for failure investigation and root cause determination.

A service water pump in a nuclear reactor failed when its shaft gave way. The fracture originated in the threaded portion of the sleeve nut on the drive-end side of the shaft. Results of the failure analysis showed that the cracking initiated at the thread root as a result of corrosion fatigue. Crack propagation occurred either by corrosion or mechanical fatigue. Evidence was found indicating high rotary bending stresses on the shaft during operation. The nonstandard composition of the En 8 steel used in the shaft and irregular maintenance reduced the life of the shaft. Recommendations included use of a case-hardened En 8 steel with the correct composition and regular maintenance of the pump.

New aircraft wing panels extruded from 7075-T6 aluminum exhibited an unusual pattern of circular black interrupted lines, which could not be removed by scouring or light sanding. The panels, subsequent to profiling and machining, were required to be penetrated inspected, shot peened, H2SO4 anodized, and coated with MIL-C-27725 integral fuel tank coating on the rib side. Scanning electron microscopy and microprobe analysis (both conventional energy-dispersive and Auger analyzers) showed that the anodic coating was applied over an improperly cleaned and contaminated surface. The expanding corrosion product had cracked and, in some places, had flaked away the anodized coating. The corrodent had penetrated the base aluminum in the form of subsurface intergranular attack to a depth of 0.035 mm (0.0014 in.). It was recommended that a vapor degreaser be used during cleaning prior to anodizing. A hot inhibited alkaline cleaner was also recommended during cleaning prior to anodizing. The panels should be dichromate sealed after anodizing. The use of deionized water was also recommended during the dichromate sealing operation. In addition, the use of an epoxy primer prior to shipment of the panels was endorsed. Most importantly, surveillance of the anodizing process itself was emphasized.

This article provides an overview of metal additive manufacturing (AM) processes and describes sources of failures in metal AM parts. It focuses on metal AM product failures and potential solutions related to design considerations, metallurgical characteristics, production considerations, and quality assurance. The emphasis is on the design and metallurgical aspects for the two main types of metal AM processes: powder-bed fusion (PBF) and directed-energy deposition (DED). The article also describes the processes involved in binder jet sintering, provides information on the design and fabrication sources of failure, addresses the key factors in production and quality control, and explains failure analysis of AM parts.

Failure analysis is a process that is performed to determine the causes or factors that have led to an undesired loss of functionality. This article describes some of the factors and conditions that might be considered when approaching a failure analysis problem. It focuses on the key principles, objectives, practices, and procedures of failure analysis. The article provides guidelines on the preparation of a protocol for a failure analysis. It also demonstrates the proper approaches to failure analysis.