Assembly represents a significant fraction of overall manufacturing time and total manufacturing cost in the automotive industry. With increasing product complexity and variety, humans remain a cost effective solution to meet the needs of flexible manufacturing systems. This element necessitates a better understanding of the human role in manufacturing complexity. Presented herein is a framework for enumerating assembly variables correlated with the potential for quality defects, presented in the design, process, and human factors domain. A case study is offered that illustrates a method to identify variables and their effect on assembly quality for a manual assembly process.
Despite their increasing use in leading industries, manufacture of alloys with superior mechanical properties have been a big challenge in the recent years. Researchers have been working on using assisted or augmented processes to overcome this challenge, with methods such as ultrasonically assisted, thermally assisted, vibration-assisted, magnetic field-assisted, and laser-assisted machining. Utilizing electrical assistance in manufacturing has not caught much attention due to its difficult-to-apply nature. However, it is possible to increase the ductility and machinability (through reduced flow stress) of certain metallic materials through the use of electricity. In this method, the electrical current resistively heats the material while aiding in deforming the material through the electroplastic effect. The limited amount of work in this topic is mainly focused on exploring the forming characteristics of relatively softer materials. Application of this augmentation to alloys with superior mechanical properties at elevated temperatures, on the other hand, has not been explored. This study aims to fill in that void through an investigation of applying different currents through the tool concentrated on the tool-workpiece contact zone. Both the titanium alloy Ti-6Al-4V and the nickel-based superalloy IN-738 were investigated, and the results showed that for both materials, there are two separate thresholds that need to be considered in any analysis. The first threshold is where the material starts to get deformed, below which no significant divergence from the baseline (no current) tests was observed. After exceeding this value, machining forces start decreasing with increasing current up to a certain point (second threshold) where the effect of electric current is reversed. If the second threshold is surpassed, the machining forces increase rapidly. Findings of this study can be used in assisting the machining of such materials.
Fuel economy standards are getting increasingly stringent over the period of time. Automotive OEMs are required to pay penalties to the government if their vehicles fail to meet the Corporate Average Fuel Economy (CAFE) standards. One of the techniques to improve fuel economy is vehicle lightweighting. Hence, OEMs demand their suppliers to individual materials with increased strength to weight ratios. Advanced high strength steels (AHSS) may serve this purpose, but they have poor formability and high springback characteristics. Advanced high strength steels such as TRIP exhibit good formability but their high alloying content adversely affects their weldability and high cost of production makes it infeasible for these materials to be put to use on a large scale. Electrically assisted forming has been proposed as a means of reducing cold stamping tonnage, improved ductility and eliminating springback. The increasing maturity of research on electrically assisted forming has developed to a point where it can be introduced onto a manufacturing scale. The objective of this project is to study various parameters related to electrically assisted forming and translate a research level idea into a production level process. This will allow introduction of AHSS like Dual Phase steels into the automobile industry and help contribute to overall lightweighting of a vehicle, which, in turn, improves sustainability. Abram Pleta, Harshal Date, Dr. Laine Mears, Dr. Durul Ulutan Clemson University ICAR apleta@clemson.edu, hdate@clemson.edu, mears@clemson.edu, dulutan@clemson.edu, CONCLUSION AND FUTURE SCOPE: The results of wiping die test will help us further improvise on electrical assistance in forming, which, in turn will contribute toward vehicle lightweighting. Also, with optimized process parameters based on results, total energy consumption can be reduced and hence the cost of manufacturing, if put to use on a wide scale. This research can be extended to components other than seating assembly and will eventually contribute towards better sustainability in the industry. ACKNOWLEDGEMENTS: I would like to thank Gary Lee Mathis for fabrication of the die and would also extend my thanks to Ionic Technologies for performing heat treatment of steel. The results of springback and load characteristics for air bending on DP 780 steels are as shown below. Wiping die design and test: Wiping die test will allow us to investigate effects of varying electrical flow paths and path lengths in addition to the parameters already investigated in the above tests. This will allow for improvement in existing EA models and can potentially establish new models which will depend also on length of plastic deformation zone and thickness The test will be conducted on two DP 980 sheets 1 mm and 1.2 mm thick respectively. The figures alongside show the wiping die design and experimental plan; and the table shows an initial calculation of load reduction (non experimental) The table right below shows die force calculations based on the wiping die force formula by Kalpakjian Fmax = k UTS Lt2
This paper presents the use of subassembly models instead of the entire assembly model to predict assembly quality defects at an automotive original equipment manufacturer (OEM). Specifically, artificial neural networks (ANNs) were used to predict assembly time and market value from assembly models. These models were converted into bipartite graphs from which 29 graph complexity metrics were extracted to train 18,900 ANN prediction models. The size of the training set, order of the bipartite graph, selection of training set, and defect type were experimentally studied. With a training size of 28 parts, an interpolation focused training set selection with a second-order graph seeding ensured that 70% of all predictions were within 100% of the target value. The study shows that with an increase in training size and careful selection of training sets, assembly defects can be predicted reliably from subassemblies' complexity data.
Increasingly strict fuel efficiency standards have driven the aerospace and automotive industries to improve the fuel economy of their fleets. A key method for feasibly improving the fuel economy is by decreasing the weight, which requires the introduction of materials with high strength to weight ratios into airplane and vehicle designs. Many of these materials are not as formable or machinable as conventional low carbon steels, making production difficult when using traditional forming and machining strategies and capital. Electrical augmentation offers a potential solution to this dilemma through enhancing process capabilities and allowing for continued use of existing equipment. The use of electricity to aid in deformation of metallic materials is termed as electrically assisted manufacturing (EAM). The direct effect of electricity on the deformation of metallic materials is termed as electroplastic effect. This paper presents a summary of the current state-of-the-art in using electric current to augment existing manufacturing processes for processing of higher-strength materials. Advantages of this process include flow stress and forming force reduction, increased formability, decreased elastic recovery, fracture mode transformation from brittle to ductile, decreased overall process energy, and decreased cutting forces in machining. There is currently a lack of agreement as to the underlying mechanisms of the electroplastic effect. Therefore, this paper presents the four main existing theories and the experimental understanding of these theories, along with modeling approaches for understanding and predicting the electroplastic effect.
Abstract Single point incremental forming (SPIF) is a dieless forming process which uses local deformations to form complex geometries. This is achieved through the use of a typically hemispherical tipped forming tool. Several variations of SPIF have been developed to improve the performance of this process. This includes the use of a partial die which is placed on the back-side of the material. The forming tool is then able to press the material into this partial die. Another method is to utilize a clamping fixture with a periphery that closely matches that of the desired geometry. While both of these methods improve the performance of SPIF, they also require dedicated fixturing. While these modifications still present an advantage over traditional stamping, it is desirable to avoid the use of any geometry-specific equipment. Springback is a significant issue when performing traditional SPIF. Springback can occur in two different ways: local and global. Local springback results from the elastic deformations created outside the region located directly beneath the forming tool. This causes poor accuracy as a result. Compensation methods have been developed to overcome this type of springback but are faced with certain limitations. Global springback refers to the springback experienced once the material is removed from its clamping fixture. This springback is a result of all residual stresses produced during forming. This springback is much more difficult to reduce and often requires annealing the workpiece subsequent to forming. A toolpath approach is explored herein as a method to reduce springback without the use of geometry-specific equipment. The toolpath developed begins at the edge of the clamping fixture, regardless of the geometry shape, and forms the flashing material prior to the desired geometry. By starting the toolpath along the edge of the fixture, elastic deformations are minimized. Additionally, the work hardening produced during this forming acts as a stiffener for the desired geometry, which behaves as a frame which matches the periphery of the desired geometry. This method was experimentally tested for its accuracy improvements when forming a truncated pyramid from 5052 aluminum. The angle of this stiffener, the step size of the stiffener, and the size of the desired geometry were varied. The fixture dimensions were held constant. This method was found to reduce the overall springback of the part and increase the accuracy of the resulting geometry. Furthermore, it was found that a large step size can be used to form the stiffener section of the part. By using a large step size, the time it takes to form this sacrificial region is minimized.
Nickel-based superalloys are designed for use in extreme environments and are getting progressively better for these environments, therefore much harder to machine. They play a crucial role in elevated temperature applications where high strength, high resistance to corrosion and creep resistance are required. Machinability suffers as a result of these properties and harsh machining conditions occur, resulting in high cutting forces and tool wear. To combat the difficulties in the machining of nickel-based superalloys, such as poor thermal diffusivity and high levels of abrasive wear, trochoidal milling was introduced as an alternative method of milling. This method of milling combines linear motion with uniform circular motion, reducing chip load in exchange for increased machining time. Industry is averse to its widespread adoption due to increasing cycle times when compared to conventional milling methods, however it has been shown that overall productivity can be improved due to less tool wear with a more predictable behavior. This work characterizes the effects of trochoidal milling and provides a comparison of trochoidal milling with a traditional milling technique, end milling, for the machining of Inconel 738. In order to compare the trochoidal and conventional machining approaches directly, metrics of productivity normalized to tool wear are introduced. The normalized metrics introduced in this study aim to provide a more representative comparison of productivity and efficiency characteristics: volumetric material removal per unit tool wear (MR/VB) and the material removal rate per unit tool wear (MRR/VB). It was found that significantly higher volumetric material removal is possible using trochoidal milling, and fewer tools are needed; material removal rates that competitive with end milling can be achieved. When the amount of time spent on tool change for the same volume of material removal is considered, material removal rate of trochoidal milling can even be higher than end milling, indicating that better productivity and efficiency of the process is possible at reduced tooling costs.
Often today's designers are relegated to degrade their own output to realize mass production on existing manufacturing capital equipment. These considerations are typically encoded in the design process through "Design for Manufacturing" where constraints on the production processes available and limits to each manufacturing approach are ideally considered early in design. This Design for Manufacturing guise inhibits true designer creativity and the possibility to realize truly revolutionary products. In this paper, the authors formalize their previous introduction of the concept of Manufacturing for Design (MFD), a framework whereby product design creativity is used instead as a motive force of innovation to rethink manufacturing process approaches and assist in facilitating real innovation in manufacturing. This is not proposed as a replacement for DFM, but an extension that can help "question" the manufacturing-based requirements during the development process. It is clear that existing machines cannot be abandoned, but one can instead consider an intermediate augmentation step to feasibly enhance existing capital, to realize new designs in new materials, or to achieve new functional requirements and desires. The blending of MFD and DFM strategies (a proposed MFD|DFM approach) can lead to feasible evolution of manufacturing, and ultimately disruptive process innovation, defined as a rethinking of manufacturing rather than just improvement on existing solutions. Herein is reported the integration of the MFD|DFM concept to two separate education programs, one undergraduate and one graduate. These programs are independent but share resources together with those of an Advanced Manufacturing technical college program to educate students across disciplines and curricula in the dichotomy of Design and Manufacturing, and how the concepts can be properly considered together.
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