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Several common processes for machining mechanical parts

January 6, 2023

I. Material removal manufacturing process ((10) m <0)

 

The material removal manufacturing process is to remove excess material from the workpiece in a certain way to get the desired shape and size of the part. This type of process requires sufficient excess material on the surface of the workpiece. During the material removal process, the workpiece gradually approximates the shape and size of the desired 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 machining process. Sometimes the volume of material lost even exceeds the volume of the part itself.

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Although the material removal process has a low material utilization rate, it is still the main means of improving the quality of parts and also has a strong processing adaptability, making it the most widely used processing method in machine manufacturing. The material removal process combined with the material forming process can significantly reduce the consumption of raw materials. With the development of less cutting-free processing technology (precision casting, fine forging, etc.), the utilization rate of materials can be further improved. When production quantities are small, it is also economically reasonable to use material removal processes alone in order to reduce investment in material forming processes

 

Material removal processes come in many forms of machining, including traditional cutting and special machining.

 

Cutting machining is a process of removing excess metal from a workpiece (blank) on a machine tool with a metal cutting 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 mounted on the machine tool and driven by the machine tool to achieve a certain regular relative motion. During the relative motion of the tool and the workpiece, the excess metal is removed and the machined surface of the workpiece is formed. Common metal cutting processing methods are turning, milling, planing, broaching, grinding, etc. There are force, heat, deformation, vibration, wear and other phenomena in the metal cutting process. The machining process, the processing quality are certain impact on the freezing H ÒÒ to select the processing method, processing machine tools, tools, fixtures and cutting parameters, improve the quality of processing, improve the processing efficiency will be the focus of this book to tell the content.

 

Special machining is a processing method that uses electrical energy, light energy, etc. to remove material from a workpiece. There are EDM, electrolytic machining, laser machining, etc. EDM uses the pulse discharge phenomenon between the tool electrode and the electrode to remove the workpiece material for processing purposes. When processing, there is a certain discharge gap between the workpiece electrode and the tool electrode, and there is no direct contact, so there is no force in the processing, and any mechanical properties of conductive materials can be processed. Its main advantage in the process is that it can process the inner contour surface of complex shapes and transform its processing difficulty into the processing of the outer contour (woof of the workpiece), so it has a special role in mold manufacturing. Due to the low metal removal rate of EDM, it is generally not used for the shape processing of products. Laser processing, ion beam processing is mostly used for fine processing.

 

With the progress of science and technology, in the field of aerospace and computer, some parts with particularly high processing accuracy and surface roughness requirements require precision machining and ultra-precision machining. Precision and ultra-precision machining to achieve dimensional accuracy can reach sub-micron or even nanometer level. These machining methods are ultra-precision turning, ultra-precision grinding, etc.

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Second, the material forming manufacturing process ((10) m = 0)

 

Material forming manufacturing process mostly uses models to make raw materials form parts or blanks. Material forming process, the shape, size, organization state of the raw material, and even the bonding state will be changed. Since the forming accuracy is generally not high, the material forming manufacturing process is often used to make blanks. It can also be used to manufacture parts with complex shapes but less demanding precision. The productivity of material forming process is high. Commonly used forming processes are casting, forging, powder metallurgy, etc.

 

(A) casting

 

Casting is the liquid metal is poured into the cavity of the mold with the shape and size of the part, after cooling and solidification to obtain the blank or parts of the process. The basic process is modeling, melting, pouring, cleaning, etc.. Due to the alloy casting filling capacity, shrinkage and other factors, the casting may have uneven organization, shrinkage, thermal stress, deformation fishy arthritis so that the accuracy of the casting, surface quality, mechanical properties are not high. Nevertheless, due to the adaptability and low production cost, casting processing is still very widely used. Complex shape, especially with complex internal cavity parts of the blank is often used casting.

 

At present, the common casting methods used in production are ordinary sand casting, fusion casting, metal casting, pressure casting, careful casting, centrifugal casting and so on. Among them, ordinary sand casting is the most widely used.

 

(B) forging and pressing

 

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 for plastic deformation, the formation of a certain shape, size and organizational properties of the part blank. After forging of the blank its internal organization is dense and uniform. The metal flow line distribution is reasonable, which improves the strength of the part. Therefore, forging is often used in the manufacture of comprehensive mechanical properties required for the parts of the blank.

Forging can be divided into free forging, model forging and die forging.

 

Free forging is to place the metal between the upper and lower offset iron for metal plastic deformation, the use of free-flowing couples Sha Shang Wei 3 Shang vortex rate is low, low precision. It is generally used to produce forgings with small batches and simple shapes.

Model forging is to place the metal in the die chamber of the forging die for deformation, the plastic flow of metal is restricted by the die chamber, high forming efficiency, high precision, and more reasonable metal flow distribution. However, due to the high cost of die manufacturing, it is usually used for mass production. The forging force required in free forging is large and cannot be used for forging large forgings.

 

Tire die forging is the forging of metal using a tire die on the equipment of free forging. The tire die 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 accuracy requirements.

Sheet metal stamping is the process of stamping sheet metal into various shapes and sizes on a press. The stamping process has high productivity and high processing accuracy, and its processing forms include punching, bending, deep drawing and forming. Punching is the process of stamping sheet material into various flat parts. Bending, deep-drawing and other forming processes are used to stamp the sheet into various three-dimensional parts. Sheet metal stamping has a road stop in electrical products, light industrial products, automobile manufacturing

 

(C) Powder Metallurgy

 

Powder metallurgy is a process of using metal powder or a mixture of metal and non-metal powder as raw materials to manufacture certain metal products or metal materials through the process of mold pressing and sintering. It can produce both special metal materials and metal parts with less cutting process. Powder metallurgy can reach 95%, which can greatly reduce the input of cutting process and reduce production costs, so it is increasingly widely used in machinery manufacturing. Due to the high price of raw materials used in powder metallurgy and the poor flowability of the powder when forming, the shape and size of the parts are somewhat restricted. Powder metallurgy parts have a certain amount of internal microporosity, its strength is about 20% to 30% lower than castings or forgings, and plasticity, toughness is also poor.

 

The process of powder metallurgy production includes powder preparation, mixing, pressing and forming, sintering, shaping and so on. Among them, the powder preparation and mixing process is usually done by the manufacturer who provides the powder.

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Third. Material accumulation manufacturing process ((10m > 0)

 

The material accumulation manufacturing process is a gradual accumulation of parts grown in a micro-element superposition. In the manufacturing process, the three-dimensional solid model data of the part is processed by computer to control the accumulation process of the material to form the desired part. The advantage of this process is that it is possible to form parts of any complex shape without the need for production preparation activities such as tools and fixtures.

 

Prototypes are produced for design evaluation, bidding or prototype demonstration. Therefore, this process is also known as rapid prototyping. Rapid prototyping technology is used in the manufacturing of product prototypes, mold manufacturing and manufacturing of a small number of parts, becoming an effective technology for accelerating new product development and achieving parallel engineering, enabling companies to respond quickly to the market and improve their competitiveness.

 

The development of rapid forming technology is very rapid, and now there are several methods have entered the application stage, mainly light curing method (SL: Stereolithog -raphy), laminated manufacturing method (LO M: LaminatedObject Manufacturing), laser selection sintering method (SLS: Selec -The photocuring method is the first rapid prototyping technology to be commercially applied.

 

The photocuring method uses photosensitive resin as raw material, and a computer-controlled ultraviolet laser scans the liquid resin point by point according to the predetermined part layering cross-section, causing the thin layer of resin in the scanned area to produce a photopolymerization reaction, thus forming a thin layer cross-section of the part. When one layer is cured, the pallet is lowered one thin layer height. A new layer of liquid resin is applied to the surface of the previously cured resin for the next scan. The newly cured layer is firmly bonded to the previous layer and so on until the entire part is prototyped.