Fractal nature in fat crystal networks

The determination of the mechanical and rheological characteristics of several plastic fats requires a detailed understanding of the microstructure of the fat crystal network aggregates. The fractal approach is useful for the characterization of this microstructure. This review begins with information on fractality and statistical self-similar structure. Estimations for fractal dimension by means of equations relating the volume fraction of solid fat to shear elastic modulus G’ in linear region are described. The influence of interesterification on fractal dimension decrease (from 2,46 to 2,15) for butterfat-canola oil blends is notable. This influence is not significant for fat blends without butterfat. The need for an increase in research concerning the relationship between fractality and rheology in plastic fats is emphasized.La determinación de las características mecánicas y reológicas de ciertas grasas plásticas requiere conocimientos detallados sobre las microestructuras de los agregados que forman la red de cristales grasos. El estudio de la naturaleza fractal de estas microestructuras resulta útil para su carac­terización. Este artículo de información se inicia con descripciones de la dimensión fractal y de la "autosimilitud estadística". A continuación se describe el cálculo de la dimensión fractal mediante ecuaciones que relacionan la fracción en volumen de grasa sólida con el módulo de recuperación (G') dentro de un comportamiento viscoelástico lineal. Se destaca la influencia que la interesterificación ejerce sobre la dimensión fractal de una mezcla de grasa láctea y aceite de canola (que pasa de 2,64 a 2,15). Esta influencia no se presenta en mezclas sin grasa láctea. Se insiste sobre la necesidad de incrementar las investi­gaciones sobre la relación entre reología y estructura fractal en grasas plásticas.Peer reviewe

New Development in Chip Control Research: Moving Towards Chip Breakability Predictions for Un-manned Manufacture

In the over-broken and effectively broken ranges, as the ratio increases, the radius of the chip also increases. However, in the region where tangled chips are produced the trend reverses itself. In this region, the chip radius decreases as the ratio increases. The results regarding the chip radius are interesting, but they do not provide much useful information for the machine operator who needs to know where to place a chip breaker to effectively control chips in a turning operation. In order to make the graph useful for this purpose, it has been broken down into three distinct regions by two vertical dashed line. The first line is located at the point where the ratio of breaker location to feed equals 13.5. To the left of this line the chips are over-broken. The second line is located at the point where the ratio is 29.5. To the right of this line the chips are all underbroken. Between these lines lies the region where effective breakage was noted. The transitions from one type of chip to another are very distinct. This indicates that the ratio of breaker location to feed is a good measure for predicting and adjusting breaker location for proper chip control when turning 4150 steel. Conclusions The data collected for this investigation indicates that it is possible to provide a practical means for a machine operator to predict where an obstruction type chip breaker should be placed for effective chip control when working with 4150 steel. The location of the breaker can be calculated using a ratio of breaker location to the feed which results in well-broken chips. Since the feed will have been set and is known to the operator, the proper breaker location can be calculated by multiplying the feed by the proper ratio. A good value of this ratio appears to be about 20, so for effective chip breaking with 4150 steel, the breaker should be located back from the primary cutting edge by a distance 20 times the feed. The beauty of this method is that the main cutting parameters need not be changed to get good chips. This means chip control is possible without decreasing the efficiency of the process significantly. These experimental results also agree with the analysis in the sense that the ratio of the feed to the location of the chip breaker is indeed the most important parameter. The optimal ratio of chip breaker location to feed may also depend on other parameters such as tool geometry and materials as these variables affect the cutting process. However, for a given tool geometry and materials, properly broken chips can be obtained over various machining conditions by maintaining the ratio at a constant value

Opportunities in abrasive water-jet machining

Machining with abrasive waterjets has many advantages over other machining technologies. The most important advantages are: no heat is generated in the workpiece, low machining forces on the workpiece, machining of a wide range of materials is possible and free contouring possibilities without the need of material or geometry specific tools. The main application is abrasive waterjet cutting (AWJC) for separation of sheet materials, although other processes as abrasive waterjet milling (AWJM) and turning (AWJT) exist. The limited use of abrasive waterjet machining up to now is due to high machine and maintenance costs, and the still somewhat unpredictable results of the machining processes. Proper modelling of the material removal process can improve that. This report describes the developments in equipment and process models which make it possible to exploit the advantages of abrasive waterjet technology completely, thereby eliminating or minimising the disadvantages. It is mainly based on several discussions held at STC- E meetings in recent years and on input provided by many CIRP-members. Abrasive waterjet machining