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2022.12.28
Machine tool casting is a type of large-sized casting, what materials are often used to make machine castings and which casting process is better?
The machine tool castings like lathe bed casting are made of fine gray cast iron, and 45% steel is used for smelting to improve the rigidity of machine tool castings. There are also customers who require ductile iron. The rigidity of ductile iron is better than that of gray iron, but the damping effect is far from that of gray iron, and the casting cost is much higher than that of gray iron. Nodular cast iron is not suitable for making the main components of machine tools, and is more suitable for making machine tool worktable castings.
Advantages of Gray Cast Iron for Machine Tool Casting:
1) The cost of gray iron machine tool castings is low, and gray iron has good casting performance, which is convenient for casting various complex structures.
2) Cast iron material has good shock absorption performance, which is more conducive to avoiding vibration and reducing noise when the machine tool is running.
3) Although the tensile strength of cast iron is lower than that of steel, its compressive strength is close to that of steel. Most machine tool beds have low requirements for tensile strength, which can meet the performance requirements;
4) The machine tool bed castings made of gray iron have good lubrication performance, because the micro holes in the atomic structure of gray iron can hold more lubricating oil, and the carbon element contained in it has self lubrication effect.
5) Cast iron has better corrosion resistance than steel, which is convenient to maintain the accuracy of machine tool guide. The casting of machine tool bed has good dimensional stability, and it is not suitable for deformation when used to make machine tool bed, which is conducive to maintaining the precision of machine tool casting for a long time.
Sand casting is preferred because of its low cost, simple production process and short production cycle compared with other casting methods.
1) When the wet sand mold cannot meet the requirements, the clay sand surface dry sand mold, dry sand mold or other sand molds shall be considered. The casting weight of clay green sand casting can be from several kilograms to tens of kilograms, while the casting weight of clay dry mold production can be up to tens of tons.
2) The casting method should adapt to the production batch. Low pressure casting, die casting, centrifugal casting and other casting methods are only suitable for batch production because of the high price of equipment and molds.
3) The molding method should be suitable for the factory conditions. For example, the same method is used to produce castings such as large machine tool bed. Generally, the core assembly molding method is used. The pattern and sand box are not made, and the core is assembled in the pit; In other factories, sand box molding method is used to make patterns; Different enterprises have different production conditions (including equipment, site, staff quality, etc.), production habits, and accumulated experience. We should consider what products are suitable for doing and what products are not suitable (or not) for doing according to these conditions.
4) The quality of machine tool castings mainly includes appearance quality, internal quality and use quality.
Criteria for casting of machine tool:
1) Machine tool casting cleaning. The cleaning is to improve the surface quality of the casting. For small parts, the hexagonal cylinder shall be used for primary rough cleaning, and then the rotary table for shot blasting shall be used for secondary fine treatment, and then the grinder with its own dust removal equipment shall be used for finishing, and the qualified parts shall be painted with antirust paint before warehousing. For medium and large pieces, first use a vibrating shaker to coat large sand balls, then send them to the shot blasting room for shot blasting, and then manually use a portable grinder for finishing. If qualified, brush antirust paint for warehousing.
2) The influence of molten iron quality during smelting and pouring of cast iron on the surface quality of castings is mainly shown in two aspects: one is the content of impurities in molten iron, especially the content of iron oxide, which is easy to produce slag inclusion or slag porosity on the surface of castings; The other is the gas content in molten iron. High gas content easily causes blowholes on the surface or under the skin of castings. The main measures we have taken are to increase the temperature of molten iron, establish a perfect cupola detection system, and ensure that the cupola is in a normal state.
3) High temperature standing and low temperature pouring are the control criteria for pouring to reduce the porosity, shrinkage cavity and surface sand adhering defects of castings. Improve casting technology level and surface quality of machine tool castings for export
4) Reasonably determine the parting surface to reduce the parting surface as much as possible to reduce the casting surface defects such as flash, surface concavity and convex formed by the parting surface; Improve the integrity of the clay core, reduce the number of joints between the clay cores, and reduce the fit gap between the clay cores or between the clay cores and the mold, so as to improve the surface concavity and convexity of large castings and the contour clarity.
5) The selection of process parameters has great influence on the dimensional accuracy and contour definition of castings. After many process tests, each process parameter is carefully selected.
6) The widely used casting process results can improve the casting process level to reduce casting defects, especially the surface defects of machine tool castings.