diamond cutting tools manufacture

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This paper introduces the design and manufacture of diamond tools and some latest achievements of diamond tools. This paper expounds the development trend of modularization and cheapness from the perspective of popularization and application, and puts forward some new ideas and methods on how to develop the key technologies of ultra-precision machining, such as modularization components, execution system, measurement control and environmental control.

With the rapid development of automotive, aviation and aerospace technology, the material performance and processing technology requirements are increasing. New materials such as carbon fiber reinforced plastics, particle reinforced metal matrix composites (PRMMC) and ceramic materials are widely used. These materials have high strength, good wear resistance, low coefficient of thermal expansion and other characteristics, which determines it in the machining tool life is very short. It is a research topic of many universities and scientific research institutes to develop new wear resistant and stable super hard cutting tools.

Diamond combines mechanics, optics, heat, acoustics, optics and many other excellent properties in one, with high hardness, small friction coefficient, high thermal conductivity, thermal expansion coefficient and low chemical inertness, is the ideal material for manufacturing tools.

Welding technology of diamond tools

At present, the application of super hard abrasive brazing tool has expanded from the past glass, stone and ceramic processing industry to silicon materials, sapphire, carbon fiber composite materials, plastics, polyester composite board, rubber, refractory materials, cast iron and other processing industry, its usage is increasing. It is worth mentioning that the use of superhard abrasive brazing tools has its unique advantages in titanium alloy, manganese steel alloy and cermet, which are difficult to process. Superhard abrasive brazing tools are characterized by sharpness, high efficiency, high cutting energy, low working temperature, strong control force of single abrasive and long service life.

There are three main methods for the manufacture of super hard abrasive brazing tools:
First, the method of heating and welding in tunnel kiln under inert atmosphere protection;
Second, induction heating welding method under inert atmosphere protection;
The third is the method of heating and welding in the furnace under vacuum protection.
, in contrast, the third method – vacuum brazing method with its oxygen, self-purification, and clean the molten alloy, melting alloy density, low melting point soldering material 50 ~ 80 ℃, to reduce the high temperature thermal damage of diamond, equipment operation process stability, repeatability and facilitate mass production characteristics, in the process of superhard abrasive tools brazing production is the most common and most useful method.

Brazing technology
In the vacuum brazing method of super hard abrasive tools, the core is the vacuum brazing technology. The whole vacuum brazing process is developed around the vacuum brazing technology. Vacuum firing technology process is mainly related to the performance of vacuum brazing furnace, soldering material in a vacuum furnace, the change characteristics of the change of the metal substrate in a vacuum furnace high temperature properties and superhard abrasive in vacuum furnace high temperature change characteristics and so on four big factors, fully understand and grasp the four factors, to do good by vacuum brazing method of superhard abrasive tools.

1.1 performance of vacuum brazing furnace
Relatively common vacuum brazing equipment – high vacuum brazing furnace. Vacuum brazing equipment is the basis of making super hard abrasive brazing tools, which involves three main technical performance points:
Is the pumping rate of the vacuum equipment fast?
Whether the ultimate vacuum value of the vacuum equipment is high
Whether the thermal field temperature uniformity of vacuum equipment is good.

The pumping rate of vacuum equipment directly affects the effective discharge of volatiles from the workpiece in the vacuum furnace. In the process of vacuum welding, three kinds of volatiles are mainly produced on the workpiece, such as oxygen element, organic matter and brazing transition element. Organic matter must be removed before 400℃, otherwise it will remain in the workpiece in the form of carbon element, affecting the welding strength of the workpiece; Oxygen elements and brazing transition elements must be removed before the brazing melting point, otherwise it will oxidize the brazing or leave residues in the workpiece, affecting the welding strength of the workpiece. The pumping rate of vacuum equipment directly affects the clean removal of volatile matter, so the pumping rate of vacuum brazing furnace should be as fast as possible.

The ultimate vacuum value of vacuum equipment can reflect two aspects.
First, it indicates whether the volatiles on the workpiece are fully discharged. The higher the ultimate vacuum value of the vacuum equipment, the cleaner the volatiles on the workpiece are eliminated.
2 it is to show that the vacuum equipment whether there is leakage phenomenon, the limit of vacuum equipment vacuum value is higher, it shows that vacuum equipment there is no leakage phenomenon, will not cause the workpiece on the substrate, superhard abrasive, soldering material and organic rubber components such as secondary oxidation, the melting temperature of soldering material would slash, and soldering material melt shape is very good. Therefore, the ultimate vacuum value of vacuum equipment must be high.

The temperature uniformity of vacuum equipment directly affects the consistency of welding quality of all workpiece in the furnace. Because the melting temperature range of brazing solder is generally around 10℃, the temperature uniformity of the vacuum equipment thermal field is poor (temperature uniformity ≥10℃), will appear in the furnace under burning welding and damaged abrasives, defective products and even waste products, so, the thermal field temperature uniformity of vacuum equipment must be very good.

1.2 variation characteristics in an empty furnace
At present, five types of brazing materials are mainly used in the brazing process to make superhard material tools: nickel-based brazing, nickel-based brazing, copper-based brazing, copper-based brazing, copper-based brazing and silver-based brazing. Under the condition of vacuum heating, there are two main changes:
The first is the evaporation of transition elements (such as phosphorus, boron, etc.) in the vacuum brazing process. For different brazing materials and transition elements, the evaporation temperature and the time required for evaporation are also different, which requires different vacuum heating processes for different brazing materials and transition elements.
Second, in the cooling phase of vacuum brazing, there are usually thermal stress changes of brazing alloy. In the heating stage of vacuum brazing process, there is no thermal stress change problem. When the brazing material is melted and the wetting of the matrix and the superhard abrasive particles is completed, the change of thermal stress of the brazing alloy usually exists in the cooling stage. In general, the change value of thermal stress of brazing material is nickel base brazing material > nickel – copper base brazing material > copper base brazing material > copper – silver base brazing material > silver base brazing material. When the change value of thermal stress of brazing alloy is greater than that of matrix, it may cause matrix deformation. When the change value of thermal stress of brazing alloy is greater than that of superhard abrasive particles, the superhard abrasive particles with poor thermal stability and fragile may be crushed by extrusion. Therefore, different cooling processes are needed for different brazing materials.

1.3 variation characteristics of metal substrate at high temperature in vacuum furnace
Usually the base material is steel or stainless steel. Under the condition of vacuum heating, two main changes occur:
One is thermal deformation. Under the influence of thermal stress, the matrix size will change to some extent. Standard steel can find a fixed thermal change law, especially through the slow heating and slow cooling of the operation process, can be controlled, the workpiece after firing, its shape geometric size in line with the user’s tolerance requirements.
The other is to change the hardness or change the rigidity. Generally, after vacuum brazing, carbon and other elements in the matrix material will be separated at the grain boundary, and the hardness of the matrix material will become soft and its rigidity will become worse. In order to ensure the user’s requirements for the hardness or rigidity of the workpiece, the hardness or rigidity of the matrix material can be improved in advance.

1.4 variation characteristics of superhard abrasives at high temperature in a vacuum furnace
Under the condition of vacuum, the properties of superhard grinding particles with good grades are not affected by the temperature in the range of brazing temperature. However, when the grade of superhard abrasive particles is poor, it is greatly affected by the temperature, which is mainly reflected in that the strength of superhard abrasive particles becomes lower due to the transformation of lattice, and there will be some thermal corrosion on the surface. For the super hard grinding particles with poor grade, the operation technology of increasing vacuum degree, reducing welding temperature, slowly heating and cooling should be adopted as far as possible to reduce the performance change.