What are the characteristics of the lathe cutting process?
Turning is a method of cutting a workpiece on a lathe using a workpiece relative to the tool rotation. Turning is the most basic and common cutting method. Most workpieces with a rotating surface can be turned, such as inner and outer cylindrical surfaces, inner and outer conical surfaces, end faces, grooves, threads and rotary forming surfaces. Common lathes can be divided into horizontal lathes, floor lathes, vertical lathes, turret lathes, and profiling lathes, most of which are horizontal lathes. Due to the development of modern science and technology, various high-strength and high-hardness engineering materials are increasingly used. Traditional turning technology is difficult or impossible to achieve certain high-strength, high-hardness materials, and modern hard turning Technology makes it possible and achieves significant benefits. Here is a brief introduction to the characteristics of turning:
一. The characteristics of the turning process
(1) High turning efficiency
Turning has higher efficiency than grinding. Turning often uses large depth of cut, high workpiece speed, and the metal removal rate is usually several times that of grinding. A variety of surfaces can be completed in one setup during turning, while grinding requires multiple installations, so the auxiliary time is short and the positional accuracy between the surfaces is high.
(2) Low equipment investment
When the required amount is the same, the lathe investment is obviously better than the grinding machine, and the auxiliary system is also low. For small batches, no special equipment is required for turning, and large-volume high-precision parts require CNC machines with good rigidity, positioning accuracy and high repeatability.
(3) Suitable for small batch flexibility requirements
The lathe itself is a wide range of flexible methods. The lathe is easy to handle and the turning clamp is fast. Hard turning is better suited to the flexibility requirements than grinding.
(4) Hard turning can achieve good overall accuracy of parts
Most of the heat in hard turning is carried away by the cutting oil, which does not cause surface burns and cracks like grinding. It has excellent surface quality and precise roundness, which ensures high positional accuracy between the surfaces.
二. The cutting tool materials and their selection
(1) Coated carbide tool
Coated cemented carbide tools are coated with one or more layers of good wear resistance on hard tough carbide tools. The coating usually plays the following two roles: on the one hand, it has a specific tool The much lower heat transfer coefficient of the substrate and the workpiece material weakens the thermal action of the tool base; on the other hand, it can effectively improve the friction and adhesion of the cutting process and reduce the generation of cutting heat. Compared with cemented carbide tools, coated carbide tools offer significant improvements in strength, hardness and wear resistance.
(2) Ceramic material cutter
Ceramic knives have the characteristics of high hardness, high strength, good wear resistance, good chemical stability, good anti-blocking performance and low friction coefficient. When used normally, it is extremely durable and can be several times faster than cemented carbide.
(3) Cubic boron nitride cutter
The hardness and wear resistance of cubic boron nitride is second only to diamond, and it has excellent high temperature hardness. Compared with ceramic tools, its heat resistance and chemical stability are slightly worse, but impact strength and crush resistance are better. It is widely used in the cutting process of hardened steel, pearlitic gray cast iron, chilled cast iron and superalloy, and its cutting speed can be increased by an order of magnitude compared with cemented carbide tools.
三. The selection of cutting oil
(1) Tool steel cutters have poor heat resistance and lose hardness at high temperatures. Therefore, it is required to use cutting oil with good cooling performance and low viscosity.
(2) When high-speed steel cutting tools are used for high-speed rough cutting, the cutting amount is large and a large amount of cutting heat is generated, and a cooling oil with good cooling properties should be used. If high-speed steel tools are used for medium and low speed processes, low-viscosity cutting oils are generally used to reduce the frictional bond between the tool and the workpiece, suppress the formation of the cutting tumor, and improve the accuracy.
(3) Cemented carbide tools have higher melting point and hardness, better chemical and thermal stability, and better cutting and wear resistance than high speed steel tools. Active sulfur cutting oil can be used in general processes. If it is heavy cutting, the cutting temperature is very high, and it is easy to wear the tool very quickly. At this time, the inactive vulcanized cutting oil should be selected and the flow rate of the cutting oil should be increased to ensure sufficient cooling lubrication.
(4) Ceramic tools, diamond tools and cubic boron nitride tools have high hardness and wear resistance. Low-viscosity inactive vulcanized cutting oil is generally used for cutting to ensure the surface finish of the workpiece.
The above is the characteristics of the turning process. Precautions for the selection of tools and cutting oil can significantly improve the quality of the workpiece.