Mechanical processing methods
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1: Turning – In turning, the workpiece rotates, which constitutes the main cutting motion. When the cutting tool moves along a parallel rotational axis, inner and outer cylindrical surfaces are formed. When the tool moves along a slant line that intersects the axis, a conical surface is formed. On a profiling lathe or a CNC lathe, it is possible to control the tool’s feed along a curve, thereby creating a specific rotational surface. By using a shaping end mill and performing transverse feeding, rotational surfaces can also be machined. Turning can also be used to machine threaded surfaces, end faces, and eccentric shafts, among others. The turning precision is generally IT8–IT7, with a surface roughness of 6.3–1.6 μm. During finish turning, it can achieve IT6–IT5, with a roughness of 0.4–0.1 μm. Turning offers high productivity, a relatively smooth cutting process, and simpler tools. II: Milling The main cutting motion is the rotation of the tool. During horizontal milling, the formation of the plane is accomplished by the cutting edges on the outer circular surface of the mill cutter. During end milling, the plane is formed by the end face cutting edge of the mill cutter. Increasing the rotational speed of the milling cutter allows for a higher cutting speed, thereby resulting in higher productivity. However, due to the cutting in and out of the milling cutter teeth, shocks are generated, and vibrations easily occur during the cutting process, thereby limiting the improvement of surface quality. Such impact also exacerbates the wear and damage of the cutting tool, often leading to the fragmentation of the cemented carbide blade. During the normal time for cutting the workpiece, a certain degree of cooling is achieved, resulting in good heat dissipation conditions. Depending on whether the direction of the main motion speed during milling is the same as or opposite to the direction of workpiece feed, it is further divided into forward milling and backward milling. In clockwise milling, the horizontal component of the cutting force is in the same direction as the feed direction of the workpiece. There is generally a gap between the feed screw of the workpiece table and the fixed nut; as a result, the cutting force can cause the workpiece and the table to move forward together, leading to an abrupt increase in the feed rate and thus tool collision. When milling workpieces with a hard surface such as castings or forgings, the cutting edges of the mill first make contact with the hard layer on the workpiece, which accelerates the wear of the mill. Back milling can prevent the shifting that occurs during forward milling. During back milling, the cutting thickness increases gradually from zero; as a result, the cutting edge goes through a phase of sliding under compression on the hardened machined surface, which accelerates tool wear. At the same time, during back milling, the cutting force lifts the workpiece, which can easily cause vibration; this is a disadvantage of back milling. The machining precision of milling generally reaches IT8–IT7, with a surface roughness of 6.3–1.6 μm. Ordinary milling can generally only machine flat surfaces, while shaped end mills can also be used to create fixed curved surfaces. A CNC milling machine can use software to control several axes through the CNC system, enabling them to move in relation to each other in order to mill complex surfaces; in such cases, ball-nosed end mills are generally used. CNC milling machines are of particular importance for machining workpieces with complex shapes, such as blades for turbomachinery and core and cavity components of molds.
III: Planing. During planing, the back-and-forth linear movement of the cutting tool is the main cutting motion. Therefore, the planing speed cannot be too high, resulting in lower productivity. Planing is smoother than milling; its machining precision generally reaches IT8–IT7, with a surface roughness of Ra6.3–1.6 μm. The flatness of a precisely planed surface can reach 0.02/1000, and its surface roughness is 0.8–0.4 μm. IV: Grinding. Grinding involves processing a workpiece using an abrasive wheel or other grinding tools, with the main motion being the rotation of the abrasive wheel. The grinding process of a grinding wheel is actually the combined effect of three actions by the abrasive particles: cutting, gouging, and sliding against the surface of the workpiece. During grinding, the abrasive particles themselves also gradually become duller, which reduces the cutting efficiency and increases the cutting force. When the cutting force exceeds the strength of the adhesive, the blunt abrasive particles fall off, revealing a new layer of particles, thereby giving the grinding wheel its \"self-sharpening\" property. However, chips and broken abrasive particles can still clog the grinding wheel. Therefore, after grinding for a certain period of time, the grinding wheel needs to be trimmed using a diamond turning tool or similar. During grinding, there are many cutting edges, which ensures smooth processing and high precision. A grinding machine is a precision machining tool; its grinding accuracy can reach IT6–IT4, with a surface roughness of Ra ranging from 1.25–0.01 μm, and in some cases even as low as 0.1–0.008 μm. Another advantage of grinding is that it can be used to process hardened metal materials. Therefore, it is often used as the final processing step. During grinding, a large amount of heat is generated, so sufficient cutting fluid is required for cooling. Depending on the function, grinding can also be divided into external cylindrical grinding, internal hole grinding, surface grinding, etc. 5: Drilling and Boring. On a drilling machine, holes are drilled by rotating a drill bit; this is the most common method for hole processing. The machining precision of drilling is relatively low; it generally only reaches IT10, with a surface roughness of 12.5–6.3 μm. After drilling, reaming and honing are often used for semi-finishing and finishing operations. Reaming is carried out using a reamer, while honing is done with a hone. The turning accuracy is generally IT9–IT6, with a surface roughness of Ra1.6–0.4 μm. During reaming and broaching, the drill bit or broach generally follows the axis of the original bore, making it impossible to improve the positional accuracy of the hole. Boring can correct the position of the hole. Boring can be done on a boring machine or a lathe. When drilling holes on a boring machine, the boring tool is essentially similar to a turning tool; the difference is that the workpiece remains stationary while the boring tool rotates. The machining precision for boring is generally IT9–IT7, with a surface roughness of Ra6.3–0.8 mm. . Drilling, milling, turning
6: Tooth surface machining. The methods for machining gear tooth surfaces can be divided into two main categories: forming methods and generating methods. The machine tools used for shaping the tooth surface by this method are generally ordinary milling machines, with shaping mills as the cutting tools; two simple shaping motions are required: the rotational motion of the tool and its linear movement. Common machine tools used for generating tooth surfaces by the development method include gear hobbing machines and gear shaping machines. 7: Machining of complex surfaces – The cutting of three-dimensional surfaces is primarily carried out using profile milling and CNC milling methods, or special machining techniques (see Section 8 of this chapter). Profile milling must have a prototype as a template. During processing, the ball-shaped profiling tool remains in contact with the prototype surface under a constant pressure. The movement of the profiling head is converted into an inductance value, which controls the movement of the three axes of the milling machine to determine the trajectory followed by the cutting tool along the surface. Milling cutters often use ball-nosed milling cutters with the same radius as the profiling head. The advent of CNC technology has provided more effective methods for surface machining. When machining on a CNC milling machine or machining center, it is done by using a ball nose mill to cut at each point according to the coordinate values. The advantage of using a machining center to machine complex surfaces is that it has a tool magazine equipped with dozens of tools. For the rough and fine machining of surfaces, different tools can be used for concave surfaces with various radii of curvature, or appropriate tools can be selected as well. At the same time, various auxiliary surfaces such as holes, threads, and grooves can be machined during a single installation. This fully ensures the precision of the relative positions of the various surfaces. 8: Special Processing. Special processing methods refer to a group of techniques that differ from traditional cutting methods; they involve using chemical, physical (electrical, acoustic, optical, thermal, magnetic) or electrochemical means to process the material of the workpiece. These processing methods include: chemical machining (CHM), electrochemical machining (ECM), electrochemical-mechanical machining (ECMM), electrical discharge machining (EDM), electrical contact machining (RHM), ultrasonic machining (USM), laser beam machining (LBM), ion beam machining (IBM), electron beam machining (EBM), plasma machining (PAM), electro-hydraulic machining (EHM), abrasive flow machining (AFM), abrasive jet machining (AJM), liquid jet machining (HDM), as well as various composite machining techniques.
Great material, thanks for sharing such useful stuff; I’ll use it soon:victory:
The poster is introducing lathes, grinders, drilling machines, and milling machines
Lathes, milling machines, planers, grinders, pliers. Processing method