Precision casting processing on the mold requirements
Compared with clay sand, the appearance quality of resin sand casting depends on the quality of mold, so resin sand requires higher quality of mold.Mold technology to make it better adapt to the needs of resin sand molding, mainly in the following aspects:
Machining allowance: the hardened resin sand casting has better rigidity and higher dimensional accuracy, and is not easy to be deformed. Therefore, when selecting technological parameters, a smaller machining allowance can be selected to reduce the consumption of metal solution and the cost of machining, so as to improve the dimensional accuracy of the casting.
Draft Angle: resin sand in the mold has a certain hardening strength, small retreat, greater friction, if the use of percussion method of mold, easy to damage the mold, at the same time resin sand patching poor, when the mold, if damaged, it is difficult to repair.Using resin sand molding, should be based on actual production increase the draft Angle of the mold and product structure, to draw, get the quality as the market the requirement of appearance quality of casting products is increasing, resin sand casting on the quality of advantage, will increasingly be taken seriously, the resin sand casting production process, also will get rapid development and popularization.
Surface roughness of mold: the surface roughness of mold plays a decisive role in the surface roughness of resin sand castings, so reducing the surface roughness of mold as much as possible is an important measure to obtain high-quality castings.
1. Good rigidity of resin sand mold and high strength of sand mold at the initial casting stage, which makes it possible to use graphitization expansion during the solidification process of cast iron to effectively eliminate shrinkage cavity and porosity defects, and realize casting of gray cast iron and nodular cast iron with few or no risers.
2. In the production of solid casting, polystyrene foam pattern is adopted and we-nan resin self-hardening sand molding is applied.When the metal liquid is poured into the casting mold, the shape of the foam plastic rapidly gasifies and burns under the action of the highly diffuse metal liquid, and the metal liquid replaces the position occupied by the original foam plastic and cools and solidifies into a solid casting with the same shape and shape.
3, relatively speaking, epc for single piece or small batch production of automotive covering parts, machine tool bed and other large mold robe of traditional sand mold has a big advantage, it not only saves expensive wood type, is easy to operate, and shorten the production cycle, improve the production efficiency, has high dimensional precision, small machining allowance, good surface quality and other advantages.
Large resin sand castings are made by resin sand and epc solid casting, with a single piece reaching over 40 tons and an annual production of about 8,500 tons.Including the bed, work table, column, gantry top, connecting beam.The material is fine and fine gray cast iron ht200-ht300, precise ratio, higher tensile and bending strength, so that you buy without worries.The international popular heat treatment technology can reduce the stress and deformation of castings to the minimum.Long-term use is more stable.Our professional undertake large ultra-long machining, milling and boring can be.For example, a set of 2*8 meters longmen milling, planer bed (bed overall length of 16 meters), casting into two sections to cast, rough processing can also be divided into two times, but when finishing, they can be connected together, the use of the plant 3.2*16 meters of gantry planer overall processing, to ensure the overall straightness of 16 meters bed and the final machining accuracy of the machine.
What are the characteristics of resin sand casting materials: machine tool base body casting larger size, up to several meters long;The mass can reach above 10t, and the wall thickness is 15 ~ 30mm.The requirements are: good precision stability and shock absorption, high modulus of elasticity, suitable compressive strength, moderate hardness and excellent wear resistance;In the process requires good casting performance, with high deformation resistance, and easy to cut processing, and requires lower production costs, such as the use of cupola smelting, using a small amount of alloy elements.To meet the above requirements, the microstructure should be pearlite structure, plus A type A graphite with A length less than 250tim and uniform distribution, and A certain amount of binary phosphorus eutectic is required.HT250 and HT300 inoculated cast iron are generally used as the material for machine tool castings in China.In order to improve the service life of machine tools, various alloy cast iron is widely used, such as p-cu-ti cast iron, cr-mo-cu cast iron and v-ti cast iron.In order to improve the abrasion resistance and reliability of the machine tool, its material is developed in the direction of high strength and high stiffness.(1) in the higher carbon equivalent, such as more than 3.5%, by improving the proportion of scrap, such as up to so%;Improve the overheating temperature of molten iron, such as 1500 ℃;Adopting multiple compound inoculant, such as ferrosilicon containing Ca, Mn and Bi, the grade of cast iron can reach HT350.(2) adjust the ratio of Si to c and Mn to Si in the composition of cast iron, when the carbon equivalent is 3.4% ~ 3.8%, Si/ c from o.4 ~ o.5 goes up to o.7 ~ o.8;Mn/Si from o.5 ~ o.6 goes up to 1.O ~ 1 appropriately add a small amount of stable pearlite elements such as Cr, Cu, Sb, Sn, etc.
Cast iron foaming mold is the most important and direct factor to determine the quality of the pattern.At the same time, the mold manufacturing cost, the degree of operation, the efficiency of pattern production and the cost of casting also play a very important role.
1.Basic requirements for molds
(1) the dimensional accuracy of the mold must make the castings produced within the precision required by the pattern, and the surface roughness of the working surface of the mold should be controlled within R.6.3 below m.
(2) in order to make the shape of heating and cooling uniform, fast, the thermal conductivity of mold materials should be good, with cavity is generally made into a thin shell with the structure of machine tool casting.
(3) the setting of the injection nozzle in the mold shall ensure the smooth feeding, so that the pre-hair beads can be smooth: all parts of the full shape.
(4) correctly set the position of the exhaust valve and determine the size of the exhaust area, so that the shape of the tight sinus heating and cooling evenly.
(5) reliable connection between mold and molding machine, accurate installation and positioning.
(6) the mold should have sufficient strength and stiffness, good corrosion resistance to water, steam and other media, and long service life.