Study On Preparation And Milling Process Of The Aluminum Dihydrogen Phosphate Sand For CNC Milling

Due to manufacturing speed, low cost, high machining accuracy, less waste of materials, less pollution and other advantages, Dieless NC milling sand is especially suitable for all kinds of complex precision sand casting piece,and rapid manufacturing in small numbers. It is important for enhance the rapid response manufacturing capability and level of the key parts in many areas,such as aviation, aerospace and automobile industry etc. The sand billet used in NC Milling is still for use the commonly used formula and preparation method of original traditional sand mold /core. Because of the sand high brittleness, poor toughness, poor consistency, and the original sand particles,which is consisted of sand billet,are hard, it is easy to producing defects,such as collapse angle(edge), crack, fracture, and surface uneven and rough in milling process.In this paper, combination of the two characteristics of milling machining and casting molding, from the preparation of sand billet which is suitable for NC milling,adopts the spherical pearl sand of 70-270 mesh―angular coefficient of the original sand less than or equal to 1.10. To study the preparation, which is suitable for NC milling with hot hardness, self hardening sand aluminum billet two hydrogen phosphate. Study the original particle size, binder content, curing temperature and curing agent content etc,which influence the Strength of two hydrogen phosphate sand aluminum billet. Study hot hardness, self hardening sand slab milling process of aluminum two hydrogen phosphate. Comparing with resin coated sand billet, focus on the influence law of milling process parameters―the feeding speed, cutting width,cutting depth, spindle speed―to the three kinds of sand billet mentioned above, and establish the corresponding formula of cutting force, besides, it still further discusses fracture mechanism of two hydrogen phosphate aluminum sand in the sand molds NC milling process.The study found: in hot hardness and self hardening sand billet, the content of aluminum two hydrogen phosphate have a significant effect on the strength of thesand molds. With the content of two hydrogen phosphate solution of aluminum increasing,The strength of sand molds increases obviously. the smaller size of sand billet,the bigger tensile strength of hot hardness and self hardening sand billet. The initial strength of hot hardness and self hardening sand billet―the sand size of200/270 mesh―reach to 3.31 MPa,3.47 MPa separately. Comparing with the sand billet of 70-270 mesh, the strength increase by 67.95% and 50.87%.The hot hardness of sand, with the roasting temperature rising, the tensile strength gradually increases. The hot hardness of sand, that content of aluminum two hydrogen phosphate is 20%, the maximum intensity reach to 3.35 Mpa at 800℃. The curing agent of self hardening sand, that content of aluminum two hydrogen phosphate is 20%, add to the 20% binder. The intensity, that self hardening sand of aluminum two hydrogen phosphate, will reach a maximum in room temperature, the maximum is 1.89 Mpa. The gas evolution of phosphate sand is less than 7ml/g,it provides favorable conditions to achieve the low gas evolution of precision sand casting.The experimental results about the cutting force of three sand billet show that,the cutting force of hot hardness and self hardening sand billet is stronger than the coated sand. The cutting force of three kinds of sand present a maximum in the direction of Z axis, it is 48N、35N separately, the minimum cutting force of coated sand is 20 N, and it is far more than the force in the direction of X, Y axis. The spindle speed, feed rate and cutting depth, cutting width have obvious difference influence on sand slab milling force. Among them, when the spindle speed is less than 980(r/min),the maximum cutting force of three sand billet is stable relatively in the direction of Z axis. When the spindle speed is greater than 980(r/min), the cutting force about the coated sand blank and self setting sand billet of aluminum two hydrogen phosphate self setting sand billet decrease slightly, but the cutting force of hot hardness sand billet increase slowly. The cutting depth and feed rate have smaller influence on the cutting force of sand mold. The cutting width has the biggest influence on the cutting force of sand mold. With the cutting width increasing, the cutting force is rising sharply in a straight line. By fitting a linear regression equation, draw the empirical formula of cutting force in three sand billet cutting process, tests the formula, revises and optimizes correlation coefficient. under the same milling machining parameters,The surface roughness, that the hot hardness of aluminum two hydrogen phosphate and the milling sand of self hardening sand slab, is more smooth than milling of coated sand slab. Among them, the parameters, that the spindle speed, cutting depth,feed speed, milling width, is 1000r/min,1mm,1000mm/min,1mm separately. The Surface roughness of hot hardness sand and self hardening sand mould, is5.3μm,4.7μm separately, it is better than coated sand billet, which is 6.3μm.Observing the fracture morphology of sample milling,about coated sand, hot hardness sand, self hardening sand,it finds out, the "bonding bridge" between sand and sand in the microcosmic performance, which is fracture of adhesive in the sand surface adhesive. From the macro performance, the fracture, collapse, three sand slab milling fracture mode, are typical brittle fracture. Using the higher spindle speed, feed rate, smaller cutting depth and milling width, and set aside large machining allowance method and process when process the thinner cavity wall cavity, it can reduce the sand milling chipping, crack and fracture, improves the machining efficiency and surface quality of sand.