Various casting knowledge

Die casting (note that die casting is not the abbreviation of pressure casting) is a metal casting process, which is characterized by using a mold cavity to apply high pressure to the molten metal. The mold is usually made of a stronger alloy, and the process is somewhat similar to injection molding.

Sand mold casting is to make molds with sand. Sand casting requires placing the finished part model or wooden model (pattern) in the sand, and then filling the sand at the weekend of the model. After unpacking the model, the sand forms the casting mold. In order to take out the model before casting the metal, the casting mold should be made into two or more parts; during the casting process, the hole for casting metal into the casting mold and the vent hole must be left to synthesize the casting system. After pouring the metal liquid in the casting mold, it is maintained for an appropriate time until the metal solidifies. After the parts are taken out, the casting mold is destroyed, so a new casting mold must be made for each casting.

Investment casting, also known as lost wax casting, includes the steps of wax pressing, wax repairing, tree formation, dip slurry, melting wax, casting molten metal, and post-treatment. Lost wax casting is to use wax to make the wax mold of the parts to be cast, and then apply wax to the wax mold, which is the mud mold. After the clay mold is dried, it is baked into a ceramic mold. Once roasted, the wax mold is completely melted and lost, leaving only the pottery mold. Generally, the pouring gate is left when the mud mold is made, and then the molten metal is poured from the pouring gate. After cooling, the required parts are made.
Die forging is a forging method that uses a die to shape a blank on a special die forging device to obtain a forged part. According to different equipment, die forging is divided into hammer forging, crank press forging, flat forging machine forging, friction press forging, etc. Roll forging is a plastic forming process in which a material undergoes plastic deformation under the action of a pair of counter-rotating dies to obtain the required forging or billet. It is a special form of forming rolling (longitudinal rolling).

Forging is one of the two major components of forging (forging and stamping). It is a processing method that uses forging machinery to apply pressure to metal blanks to cause plastic deformation to obtain forgings with certain mechanical properties, certain shapes and sizes. Through forging can eliminate defects such as loose metal in the casting process during smelting and optimize the microstructure. At the same time, due to the preservation of complete metal flow lines, the mechanical properties of forgings are generally better than those of the same materials. In the related machinery, the important parts with high load and severe working conditions are mostly forged parts except for rolled plates, profiles or welded parts with relatively simple shapes.
Rolling, also known as calendering, refers to the process of shaping a metal ingot through a pair of rollers. If the temperature of the metal exceeds its recrystallization temperature, the process is called «hot rolling», otherwise it is called «cold rolling». Rolling is the most commonly used method in metal processing.

The essence of pressure casting is the method of making liquid or semi-liquid metal fill the cavity of a die casting mold (die casting mold) at a high speed under high pressure, and form and solidify under pressure to obtain a casting.

Low-pressure casting A casting method in which liquid metal fills the mold and solidifies into a casting under the action of low-pressure gas. Low-pressure casting was primarily used for the production of aluminum alloy castings, and it was further expanded to produce copper castings, iron castings, and steel castings with high melting points.
Centrifugal casting is a technique and method that injects liquid metal into a mold that rotates at high speed, so that the liquid metal fills the mold and forms a casting under the action of centrifugal force. The mold used for centrifugal casting can be non-metallic (such as sand, shell or investment shell), metal, or coated with a coating layer or resin sand layer according to the shape, size and production batch of the casting. Of the mold.

Lost foam casting is the combination of paraffin or foam model similar to the size and shape of the casting to form a model cluster. After being coated with refractory paint and dried, it is buried in dry quartz sand and vibrated. It is poured under negative pressure to gasify the model , Liquid metal occupies the position of the model, a new casting method that forms the casting after solidification and cooling. Lost foam casting is a new process with almost no margin and accurate forming. This process does not need to take a mold, no parting surface, and no sand core, so the casting has no flash, burrs and draft slope, and reduces the core due to Dimensional error caused by combination.

Squeeze casting, also known as liquid die forging, is to inject molten metal or semi-solid alloy directly into the open mold, and then close the mold to produce a filling flow to reach the external shape of the part, and then apply high pressure to make the solidified The metal (shell) is plastically deformed, the unsolidified metal is subjected to isostatic pressure, and high-pressure solidification occurs at the same time, and the final method for obtaining a part or blank is direct squeeze casting; The solid alloy is injected into the closed mold cavity through a punch, and is subjected to high pressure, so that it is crystallized and solidified under pressure, and finally a method of obtaining a workpiece or a blank.

Continuous casting is a casting method in which liquid metal is continuously poured into one end through a continuous crystallizer and the molding material is continuously pulled out from the other end.
Drawing is a plastic processing method that uses an external force to act on the front end of the metal being pulled to pull the metal blank from the die hole smaller than the cross section of the blank to obtain a product of the corresponding shape and size. Because drawing is mostly done in a cold state, it is also called cold drawing or cold drawing.
Stamping is a forming method that uses presses and dies to apply external force to plates, strips, pipes, and profiles, etc. to cause plastic deformation or separation, thereby obtaining workpieces (pressed parts) of the desired shape and size.

Metal Injection Molding (MIM) is a new type of powder metallurgy near-net forming technology that extends from the plastic injection molding industry. It is well known that plastic injection molding technology produces various complex shaped products at low prices, but plastics The strength of the product is not high. In order to improve its performance, metal or ceramic powder can be added to the plastic to obtain a product with higher strength and good wear resistance. In recent years, this idea has evolved to maximize the content of solid particles and completely remove the binder and densify the preform during the subsequent sintering process. This new powder metallurgy forming method is called metal injection molding.

Turning processing means that lathe processing is part of mechanical processing. Lathe machining mainly uses a turning tool to turn the rotating workpiece. Lathes are mainly used for processing shafts, disks, sleeves and other workpieces with rotating surfaces. They are the most widely used machine tool processing in machinery manufacturing and repair factories. Turning is a method of cutting a workpiece by turning the workpiece relative to the tool on a lathe. The cutting energy of turning is mainly provided by the workpiece rather than the tool. Turning is the most basic and common cutting method, and it occupies a very important position in production. Turning is suitable for machining rotating surfaces. Most of the workpieces with rotating surfaces can be processed by turning methods, such as inner and outer cylindrical surfaces, inner and outer conical surfaces, end surfaces, grooves, threads and rotary forming surfaces.

Milling processing Milling is to fix the blank, and use a high-speed rotating cutter to cut the blank and cut out the desired shape and features. Traditional milling is mostly used for simple contours / features such as contours and grooves. CNC milling machines can process complex shapes and features. The milling and boring processing center can carry out three-axis or multi-axis milling and boring processing for machining, molds, inspection tools, tires, thin-walled complex curved surfaces, artificial prostheses, blades, etc. When selecting the content of CNC milling, the advantages and key roles of CNC milling machines should be fully utilized.

Planing is a cutting method that uses a planer to make a horizontal and relatively linear reciprocating motion on the workpiece. It is mainly used for the shape processing of parts. The precision of planing is IT9 ~ IT7, and the surface roughness Ra is 6.3 ~ 1.6um.

Grinding processing Grinding refers to the processing method of using abrasives and abrasive tools to cut off excess material on the workpiece. Grinding is one of the more widely used cutting methods.
Selective laser melting In a tank covered with metal powder, the computer controls a beam of high-power carbon dioxide laser to sweep across the surface of the metal powder selectively. Where the laser light reaches, the metal powder on the surface layer is completely melted and bonded together, while the place where it is not exposed still maintains the powder state. The whole process needs to be carried out in a sealed cabin filled with inert gas.

Selective laser sintering is an SLS method that uses an infrared laser as an energy source, and most of the modeling materials used are powder materials. During processing, the powder is first preheated to a temperature slightly below its melting point, and then the powder is flattened under the action of a scraping stick; the laser beam is selectively sintered according to the layered cross-section information under computer control After completion, the next layer of sintering is carried out. After all the sintering is completed, the excess powder is removed, and a sintered part can be obtained. At present, the mature process materials are wax powder and plastic powder, and the process of sintering with metal powder or ceramic powder is still under study.

Metal deposits are somewhat similar to «creamed» fused deposits, but metal powder is sprayed. While the nozzle is spraying metal powder material, it will also provide high-power laser and inert gas protection. This will not be limited by the size of the metal powder box, and can directly produce larger-volume parts, and is also very suitable for the repair of partially damaged precision parts.
Roll forming The roll forming method uses a set of continuous stands to roll stainless steel into complex shapes. The order of the rollers is designed such that the roller shape of each frame can continuously deform the metal until the desired final shape is obtained. If the shape of the component is complex, up to thirty-six racks can be used, but for simple shapes, three or four racks are sufficient.
Die forging refers to a forging method that uses a die to shape a blank on a special die forging device to obtain a forged part. The forgings produced by this method have accurate dimensions, small machining allowances, and relatively complex structures with high productivity.

Die cutting is the blanking process, positioning the film formed in the previous process on the die of the die cutting die, closing the mold to remove excess material, retaining the 3D shape of the product, and matching the mold cavity.

Die-cutting process-knife die The knife die blanking process locates the film panel or circuit on the bottom plate, fixes the die die to the template on the machine, and uses the force provided by the machine to control the blade to cut the material. The difference between him and the punching die is that the incision is smoother; at the same time, by adjusting the cutting pressure and the depth, it can punch out the indentation and half-break. At the same time, the low cost of the mold operation is more convenient, safe and fast.