Product processing flow chart
Casting process flow 1) production process preparation: according to the part drawing, production batch and delivery date to be produced, the production process plan and process documents are formulated, and the casting process drawing is drawn;
2) Production preparation, including preparation of materials for smelting, materials and patterns for molding and core making, core boxes, sand boxes and other process equipment;
3) modeling and core making;
4) melting and pouring;
5) Main processes such as sand falling cleaning and casting inspection.
Forming principle
Casting production is a metal forming method in which metal is heated and melted to make it have fluidity, and then poured into a mold cavity with a certain shape and filled with gravity or external force (pressure, centrifugal force, electromagnetic force, etc.). ), cooled and solidified into castings (or parts).
Castings are generally cut into parts as blanks. However, there are many castings that can meet the design accuracy and surface roughness requirements of parts without cutting, and can be directly used as parts.
Properties and composition of molding sand
1, properties of molding sand
The main performance requirements of molding sand (including core sand) are strength, permeability, fire resistance, concession, fluidity, compactness and collapsibility.
2. Composition of molding sand
Molding sand consists of raw sand, binder and additives. Raw sand for casting requires small mud content, uniform particles and circular and polygonal shapes in sea sand, river sand or mountain sand. Binders for casting include clay (common clay and bentonite), sodium silicate sand, resin, synthetic oil and vegetable oil, which are called clay sand, sodium silicate sand, resin sand, synthetic oil sand and vegetable oil sand respectively. In order to further improve some properties of mold (core) sand, it is often necessary to add some additives to mold (core) sand, such as coal powder, sawdust, paper pulp and so on. The structure of molding sand is shown in Figure 2.
technical characteristics
Casting is one of the main methods to produce parts blanks, especially for parts blanks made of brittle metals or alloy materials (such as various iron castings and non-ferrous alloy castings), casting is almost the only processing method. Compared with other processing methods, the casting process has the following characteristics:
1) castings are not limited by metal materials, size and weight. The casting materials can be various cast iron, cast steel, aluminum alloy, copper alloy, magnesium alloy, titanium alloy, zinc alloy and various special alloy materials; Castings can be as small as a few grams and as large as hundreds of tons; The wall thickness of the casting can be from 0.5 mm to about 65438 0 m; The casting length can be from a few millimeters to more than ten meters.
2) Casting can produce all kinds of blanks with complex shapes, especially suitable for producing parts blanks with complex cavities, such as various boxes, cylinders, blades and impellers.
3) The shape and size of the casting can be very close to the parts, which saves both metal materials and cutting time.
4) The raw materials commonly used for casting are widely available, and the casting cost is low.
5) The casting process is flexible, and the productivity is high, and it can be produced manually or mechanically.
Manual modeling of castings
Main methods of manual modeling
Sand casting is divided into manual modeling (core making) and machine modeling (core making). Manual modeling means that the main work of modeling and core making is done by hand; Machine modeling refers to the main modeling work, including sand filling, compaction, mold lifting and box closing, which is completed by the molding machine. Botou foundry workers and measuring tools friends introduce the main methods of manual modeling;
Manual modeling has the advantages of flexible operation, strong adaptability, simple process equipment and no need for modeling equipment, and is widely used in single piece and small batch production. However, manual modeling has low productivity and high labor intensity. There are many methods of manual modeling, and the following methods are commonly used:
1. Integral mold modeling
For castings with simple shape, flat ends and the largest cross section, integral modeling should be adopted. The whole mold modeling operation is simple, and the whole modeling is put in the sand box during modeling, so there will be no box dislocation defect. The whole mold modeling is suitable for castings with simple shape and the largest end section, such as gear blanks, bearing seats, covers and shells.
Integral mold modeling
2. Typing modeling
When the maximum cross section of the casting is not at the end of casting, the model should be divided into two halves or several parts in order to facilitate modeling and demoulding. This kind of modeling is called parting modeling. When the largest section of the casting is in the middle of the casting, two boxes should be used for parting molding (Figure 3), and the pattern is divided into two halves from the largest section (located by pins). During modeling, the patterns are put into the upper and lower sand boxes respectively, and the parting surface (the joint surface between patterns) coincides with the parting surface (the joint surface between sand molds). Two-box parting molding is widely used to produce castings with complex shapes, such as porous castings such as water pipes, shaft sleeves and valve bodies.
Parting of Shell and Two-box Molding Technology
The casting shape is big at both ends and small in the middle, such as pulley, sheave, lathe square tool rest, etc. In order to ensure the smooth demoulding, three-box parting molding should be adopted. At this time, the parting surface should be selected at the smallest section of the pattern, while the parting surfaces at both ends of the casting are still selected at the largest section. Because the three-box molding has two parting surfaces, the dimensional accuracy in the height direction of the casting is reduced, and the workload of cleaning flash burrs on the parting surfaces is increased. The operation is complicated, the productivity is low, and it is not suitable for machine molding. Therefore, three-box molding is only used to produce castings with complex shapes, and two-box molding cannot be used.
3. Movable block mold modeling
Parts (such as bosses, ribs, etc.). ) and the movable block is detachably connected with the die main body through a pin or a dovetail structure. The modeling method of taking out the pattern body first, leaving the movable block mold in the mold, and then taking out the movable block from the side after taking out the mold is called movable block mold modeling. Movable block mold modeling is mainly used for castings with protruding parts that hinder mold lifting, single piece and small batch, and manual modeling. If this kind of casting is in large quantities and needs machine modeling, sand cores can be used to form contours that hinder drawing.
4. Sand excavation modeling
When the outer contour of the casting is curved (such as handwheel) and its maximum cross section is not at the end, and the pattern is not suitable to be divided into two halves, the pattern should be made into a whole, and the molding sand that prevents the pattern from being taken out should be dug out during modeling. This modeling method is called dredging modeling. The parting surface of sand digging modeling is a curved surface. In order to ensure the smooth demoulding, the sand must be dug to the maximum cross section of the pattern (Figure 6). Because it is hand-dug sand, it has high technical requirements and low production efficiency, and is only suitable for single piece and small batch production.
Manual core making
The core is used to form the inner cavity or local shape of the casting. Because the core surface is surrounded by high-temperature molten metal, it is buoyed and baked by high-temperature molten metal for a long time; When the casting is cooled and solidified, the sand core often hinders the free shrinkage of the casting; Sand core cleaning is also very difficult. Therefore, core sand for core making has higher strength, air permeability, high temperature resistance, yielding and collapsibility than molding sand.
Manual core-making is widely used because it does not need core-making equipment and the process equipment is simple. According to the size and complexity of sand cores, the core boxes made by hand include integral core boxes, split core boxes and detachable core boxes.
Relationship among Parts, Models, Core Boxes and Castings