1. Material removal manufacturing process (⑽m <0)
The material removal manufacturing process is to remove excess material from the workpiece in a certain way to obtain parts of the desired shape and size. Such processes require sufficient excess material on the workpiece surface. During material removal, the workpiece gradually approaches the shape and size of the ideal part. The greater the difference between the shape and size of the raw material or blank and the zero h, the more material is removed, the greater the material loss, and the more energy is consumed in the cnc machining process. Sometimes the volume of material lost even exceeds the volume of the part itself.
Although the material utilization rate of the material removal process is low, it is still the main means to improve the quality of parts, and it also has strong machining adaptability, which is the most widely used manufacturing method in machine manufacturing. The material removal process combined with the material forming process can greatly reduce the consumption of raw materials. With the development of less cutting and machining technology (precision metal casting, precision forging, etc.), the utilization rate of materials can be further improved. When the production quantity is small, in order to reduce the investment in the material forming process, it is also economical and reasonable to simply use the material removal process.
Material removal processes come in many forms, including traditional machining and specialty machining.
Cutting is a process in which metal cutting tools are used to remove excess metal on the workpiece (blank) on the machine tool, so that the shape, size and surface quality of the workpiece meet the design requirements. During the cutting process, the tool and the workpiece are installed on the machine tool, and are driven by the machine tool to achieve a certain regular relative movement. During the relative movement of the tool to the workpiece, excess metal is removed, forming the machined surface of the workpiece. Common metal cutting methods include turning, milling, planing, broaching, and grinding. In the process of metal cutting, there are phenomena such as force, heat, deformation, vibration, and wear. There is a certain influence on the cnc machining process and aluminum cnc machining quality. It is important to choose the processing method, processing machine tool, tool, fixture and cutting parameters to improve the processing quality and improve the processing efficiency. This will be the focus of this book.
Special processing refers to a cnc machining method that uses electrical energy, light energy, etc. to remove material from a workpiece. There are EDM, electrolytic machining, laser machining, etc. EDM is to use the pulse discharge phenomenon generated between the tool electrode and the electrode to erode the workpiece material to achieve the purpose of machining. During machining, there is a certain discharge gap between the workpiece electrode and the tool electrode without direct contact. There is no force during machining, and conductive materials with any mechanical properties can be machined. In terms of technology, its main advantage is that it can process the inner contour surface of complex shapes, and convert its processing difficulty into the processing of the outer contour (gongjie), so it has a special role in mold manufacturing. Due to the low metal removal rate of EDM, it is generally not used for shape processing of products. Laser processing and ion beam cnc machining are mostly used for fine processing.
With the advancement of science and technology, in the aerospace and computer fields, some parts with particularly high machining accuracy and surface roughness require precision machining and ultra-finishing. The dimensional accuracy achieved by precision and ultra-precision machining can reach sub-micron or even nano-scale. These cnc machining methods include ultra-precision turning, ultra-precision grinding, etc.
2. Material forming manufacturing process (⑽m = 0)
The material forming manufacturing process mostly uses a model to make raw materials into parts or blanks. In the process of material crumb, the shape, size, organization state, and even combination state of raw materials will change. Since the forming accuracy is generally not high, the material forming manufacturing process is often used to manufacture blanks. It can also be used to manufacture parts with complex shapes but less precision requirements. The production efficiency of the material forming process is high. Commonly used forming processes include casting, forging, powder metallurgy, etc.
Casting is a process in which liquid metal is poured into a mold cavity suitable for the shape and size of the part, and a blank or part is obtained after cooling and solidification. The basic process is modeling, smelting, pouring, cleaning and so on. Due to the influence of mold filling ability, shrinkage and other factors during alloy casting, castings may have uneven structure, shrinkage cavities, thermal stress, and deformation, resulting in poor accuracy, surface quality, and mechanical properties of castings. Nevertheless, casting cnc machining is still widely used due to its strong adaptability and low production costs. Casting is often used for blanks with complex shapes, especially parts with complex inner cavities.
At present, the commonly used casting methods in production include ordinary sand casting, investment casting, metal casting, die casting, centrifugal casting, etc. Among them, ordinary sand casting is the most widely used.
Forging and sheet metal stamping are collectively referred to as forging. Forging is the use of forging equipment to apply external force to the heated metal to plastically deform to form a part blank with certain shape, size and microstructure. The internal structure of the forged blank is dense and uniform. The distribution of metal streamlines is reasonable, which improves the strength of the parts. Therefore, forging is often used to manufacture blanks for parts with high comprehensive mechanical properties.
Forging can be divided into free forging, model forging and die forging.
Free forging is to place the metal between the upper and lower irons for plastic deformation of the metal. The use of free-flowing aluminum alloy has low vortex rate and low precision. It is generally used to produce forgings with small batches and simple shapes.
Model forging is to deform the metal in the die cavity of the forging die. The plastic flow of the metal is restricted by the die cavity. The forming efficiency is high, the precision is high, and the metal streamline distribution is more reasonable. However, due to the high cost of mold manufacturing, it is usually used for mass production. The forging force required for forging with the free-slightly Yujiu-Ci model is large, and it cannot be used for the forging of large-scale forgings.
Die forging is to forge metal using die forging on free forging equipment. The tire mold is simple to manufacture, low cost and convenient to form, but the forming accuracy is not high, and it is often used to produce small forgings with low precision requirements.
On the sheet metal stamping machine, the die is used to stamp the sheet into various shapes and sizes. Stamping has extremely high productivity and high speed cnc machining accuracy, and its processing forms include blanking, bending, deep drawing, and forming. Blanking is the process of punching sheet metal into various flat parts. Forming processes such as bending and deep drawing punch the sheet into various three-dimensional parts. Sheet metal stamping has a long way to go in electrical products, light industrial products, and automobile manufacturing.
(3) Powder metallurgy
Powder metallurgy uses metal powder or a mixture of metal and non-metal powder as raw materials, and processes such as mold pressing and sintering to manufacture certain metal products or metal materials. It can produce both special metal materials and metal parts with less machining. The utilization rate of powder smelting wheel can reach 95%, which can greatly reduce the input of cutting and reduce the production cost, so it has been widely used in machinery manufacturing. Due to the high price of powder raw materials used in powder metallurgy, the fluidity of the powder during forming is poor, and the shape and size of the parts are limited to a certain extent. There are a certain amount of tiny pores inside powder metallurgy parts, and their strength is about 20% to 30% lower than that of castings or forgings, and their plasticity and toughness are also poor.
The process flow of powder metallurgy production includes powder preparation, compounding, pressing, sintering, shaping, etc. The preparation and compounding process of the powder is usually completed by the manufacturer that provides the powder.
3. Material accumulation manufacturing process (⑽m>0)
The material accumulation manufacturing process is to gradually accumulate and grow parts in the form of micro-element superposition. In the manufacturing process, the three-dimensional solid model data of the part is processed by the computer to control the accumulation process of the material to form the desired part. The advantage of this type of process is that parts of any complex shape can be formed without the need for production preparation activities such as tools and fixtures.
Manufactured prototypes are available for design evaluation, bids or prototype presentations. Therefore, this process is also called rapid prototyping technology. Rapid prototyping technology is used in the manufacture of product samples, mold manufacturing and a small number of parts. It has become an effective technology to accelerate the development of new products and realize concurrent engineering, so that the products of enterprises can quickly respond to the market and improve the competitiveness of enterprises.
The development of rapid prototyping technology is very rapid, and now several methods have entered the application stage, mainly including light curing method (SL: Stereolidog-rapy), laminated manufacturing method (LO M: Laminated Object Manufacturing), laser selective sintering method (SLS: Selec) -tive Laser Sintering), Fused Deposition Modeling (FD M: Fused Deposition Modeling), of which the light curing method is the earliest rapid prototyping technology put into commercial application.
The light-curing method uses photosensitive resin as raw material, and the computer-controlled ultraviolet laser scans the liquid resin point by point according to the predetermined layered section of the part, so that the thin resin layer in the scanned area produces a photopolymerization reaction, thereby forming a thin layer section of the part. When one layer is cured, the tray is lowered by a thin layer height. Apply a new layer of liquid resin on the surface of the previously cured resin for the next scan to cure. The newly cured layer is firmly bonded to the previous layer, and this repeats until the entire part prototype is fabricated.
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