Search results1 – 4 of 4
For geometries exhibiting overhanging surfaces, support structures are needed to dissipate process heat and to minimize geometrical distortions attributed to internal…
For geometries exhibiting overhanging surfaces, support structures are needed to dissipate process heat and to minimize geometrical distortions attributed to internal stresses. The use of support structures is often time- and cost-consuming. For this reason, this study aims to propose an approach which minimizes the use of such structures.
For minimizing the use of support structures, process parameters in combination with a contour-like exposure strategy are developed to realize support-less overhanging structures of less than 35°. These parameters are implemented in a shell-core strategy, which follows the idea of applying different processing strategies to the critical (overhanging) shell and the uncritical core of the part. Thereby, the core is processed with standard parameters, aiming a dense material. On the critical shell, optimized processing parameters are applied, reaching good results in terms of surface quality, especially at extreme overhang situations.
The results show that the selective laser melting (SLM) technology is able to realize support-less overhanging surfaces by choosing suitable scan strategies and process parameters. Particularly good results are always obtained when the exposure direction of the shell is parallel to the contour of the sample.
The validity of the results is demonstrated through the successful reproduction of the build strategy on two commercial SLM machines, reaching support-free builds of surfaces with an angle to the horizontal of less than or equal to 30°.
To ensure the reliable monitoring of machining operations, e.g. by lathes, the forces generated during the metal removal process must be detected with the utmost…
To ensure the reliable monitoring of machining operations, e.g. by lathes, the forces generated during the metal removal process must be detected with the utmost precision. Almost every type of lathe can be straightforwardly monitored for these factors with a force sensor which not only measures forces in three directions but which also incorporates the necessary electronics to amplify the output signals.
Anthropologists have long discussed the ways in which their discipline has been entangled, consciously and unconsciously, with the colonized populations they study. A…
Anthropologists have long discussed the ways in which their discipline has been entangled, consciously and unconsciously, with the colonized populations they study. A foundational text in this regard was Michel Leiris' Phantom Africa (L'Afrique fantôme; Leiris, 1934), which described an African ethnographic expedition led by Marcel Griaule as a form of colonial plunder. Leiris criticized anthropologists' focus on the most isolated, rural, and traditional cultures, which could more easily be described as untouched by European influences, and he saw this as a way of disavowing the very existence of colonialism. In 1950, Leiris challenged Europeans' ability even to understand the colonized, writing that “ethnography is closely linked to the colonial fact, whether ethnographers like it or not. In general they work in the colonial or semi-colonial territories dependent on their country of origin, and even if they receive no direct support from the local representatives of their government, they are tolerated by them and more or less identified, by the people they study, as agents of the administration” (Leiris, 1950, p. 358). Similar ideas were discussed by French social scientists throughout the 1950s. Maxime Rodinson argued in the Année sociologique that “colonial conditions make even the most technically sophisticated sociological research singularly unsatisfying, from the standpoint of the desiderata of a scientific sociology” (Rodinson, 1955, p. 373). In a rejoinder to Leiris, Pierre Bourdieu acknowledged in Work and Workers in Algeria (Travail et travailleurs en Algérie) that “no behavior, attitude or ideology can be explained objectively without reference to the existential situation of the colonized as it is determined by the action of economic and social forces characteristic of the colonial system,” but he insisted that the “problems of science” needed to be separated from “the anxieties of conscience” (2003, pp. 13–14). Since Bourdieu had been involved in a study of an incredibly violent redistribution of Algerians by the French colonial army at the height of the anticolonial revolutionary war, he had good reason to be sensitive to Leiris' criticisms (Bourdieu & Sayad, 1964). Rodinson called Bourdieu's critique of Leiris' thesis “excellent’ (1965, p. 360), but Bourdieu later revised his views, noting that the works that had been available to him at the time of his research in Algeria tended “to justify the colonial order” (1990, p. 3). At the 1974 colloquium that gave rise to a book on the connections between anthropology and colonialism, Le mal de voir, Bourdieu called for an analysis of the relatively autonomous field of colonial science (1993a, p. 51). A parallel discussion took place in American anthropology somewhat later, during the 1960s. At the 1965 meetings of the American Anthropological Association, Marshall Sahlins criticized the “enlistment of scholars” in “cold war projects such as Camelot” as “servants of power in a gendarmerie relationship to the Third World.” This constituted a “sycophantic relation to the state unbefitting science or citizenship” (Sahlins, 1967, pp. 72, 76). Sahlins underscored the connections between “scientific functionalism and the natural interest of a leading world power in the status quo” and called attention to the language of contagion and disease in the documents of “Project Camelot,” adding that “waiting on call is the doctor, the US Army, fully prepared for its self-appointed ‘important mission in the positive and constructive aspects of nation-building’” a mission accompanied by “insurgency prophylaxis” (1967, pp. 77–78). At the end of the decade, Current Anthropology published a series of articles on anthropologists’ “social responsibilities,” and Human Organization published a symposium entitled “Decolonizing Applied Social Sciences.” British anthropologists followed suit, as evidenced by Talal Asad's 1973 collection Anthropology and the Colonial Encounter. During the 1980s, authors such as Gothsch (1983) began to address the question of German anthropology's involvement in colonialism. The most recent revival of this discussion was in response to the Pentagon's deployment of “embedded anthropologists” in Afghanistan and elsewhere in the Middle East. The “Network of Concerned Anthropologists” in the AAA asked “researchers to sign an online pledge not to work with the military,” arguing that they “are not all necessarily opposed to other forms of anthropological consulting for the state, or for the military, especially when such cooperation contributes to generally accepted humanitarian objectives … However, work that is covert, work that breaches relations of openness and trust with studied populations, and work that enables the occupation of one country by another violates professional standards” (“Embedded Anthropologists” 2007).3 Other disciplines, notably geography, economics, area studies, and political science, have also started to examine the involvement of their fields with empire.4