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It has been observed that post weld heat treatrents designed to reduce or remove residual welding stresses, may cause weld metal eTnbrittlen. ent. In this investigation, the effects of post weld heat treatment on three high strength submerged are weld metals were examined in terms of changes in'mechanical properties, principally fracture toughness. Metallographic work was carried out to determine the cause of ezbrittlement. Post weld heat treatment was performed in the 450 to 650 0C temperature range for times up to 50 hours and embrittlement was meatured in terms of Charpy, COD and J contour integral tests. It was found that each weld metal could be enbrittled and that two distinct forms of embrittlement occurred. The first was due to alloy carbide precipitation which promoted trans-granular cleavage. Vanadium at 0.12% could cause severe embrittlement while molybdenum, at up to 0.6% did not. The second forn of embrittle-ment was classical temper embrittlement which caused low energy decohesion along prior austenite grain boundaries. This was caused by the migration of phosphorus to these boundaries during heat treatment and bulk phosphorus concentraticrs of 0.011% could cause severe erbrittlement. Embrittlement occurred in the 450 to 550 0C temperature range and increased with time and decreasing cooling rate. Marten-sitic microstructures were more susceptible than acicular ferrite. Defect tolcrance calculations based on COD-and J determinations showed that defect tolerance could increase after heat treatment despite-embrittlement although the final defect tolerance was strongly dependent on residual stress levels remaining, after heat treatment. Heat treatment procedures for the three weld metals examined were suggested, along with general guidelines for the post weld heat treatment of other high strength weld metals.

The mechanism of "Helical Interference" in milled slots is examined and a coherent theory for the geometry of such surfaces is presented. An examination of the relevant literature shows a fragmented approach to the problem owing to its normally destructive nature, so a complete analysis is developed for slots of constant lead, thus giving a united and exact theory for many different setting parameters and a range of cutter shapes. For the first time, a theory is developed to explain the "Interference Surface" generated in variable lead slots for cylindrical work and attention is drawn to other practical surfaces, such as cones, where variable leads are encountered. Although generally outside the scope of this work, an introductory analysis of these cases is considered in order to develop the cylindrical theory. Special emphasis is laid upon practical areas where the interference mechanism can be used constructively and its application as the rake face of a cutting tool is discussed. A theory of rake angle for such cutting tools is given for commonly used planes, and relative variations in calculated rake angle between planes is examined. Practical tests are conducted to validate both constant lead and variable lead theories and some design improvements to the conventional dividing head are suggested in order to manufacture variable lead workpieces, by use of a "superposed" rotation. A prototype machine is manufactured and its kinematic principle given for both linear and non-linearly varying superposed rotations. Practical workpieces of the former type are manufactured and compared with analytical predictions,while theoretical curves are generated for non-linear workpieces and then compared with those of linear geometry. Finally suggestions are made for the application of these principles to the manufacture of spiral bevel gears, using the "Interference Surface" along a cone as the tooth form.

This industrial based research project was undertaken for British Leyland and arose as a result of poor system efficiency on the Maxi and Marina vehicle body build lines. The major factors in the deterioration of system efficiency were identified as: a) The introduction of a 'Gateline' system of , vehicle body build. b) The degeneration of a newly introduced measured daywork payment scheme~' DJ relating the conclusions of past work onpayrnent systems to' the situation at Cowley, it ,was concluded that a combination of poor industrial relations and a lack of managerial control had' caused the measured dayworkscheme to degenerate into a straightforward payment for time at work. This eliminated the monetary incentive to achieve schedule with the consequence that both inefficiency and operating costs increased. To analyse further the cause of inefficiency, a study of Marina gateline stoppage logs was carried out. This revealed that poor system efficiency on the gateline was caused more by the nature of its design than poor reliability on individual items of plant. The consideration given to system efficiency,at the design stage was found to be negligible the main obstacles being:a) A lack of understanding pertaining to the influence of certain design factors on the efficiency of a production line. b) The absence of data and techniques to predict system efficiency at the design stage. To remedy this situation, a computer simulation study of the design factors was carried out from which relationships with system efficiency were established and empirical efficiency equations developed. Sets of tables were compiled from the equations and efficiency data relevant to vehicle body 'building established from the gateline stoppage logs~ Computer simulation, the equations and the tables when used in conjunction. with good efficiency data, are shown to be accurate methods of predicting production line system. efficiency.

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