2021-07-26
The tungsten carbide is an alloy material made of a hard phase compound which is the refractory metal and a bonder metal through a powder metallurgy process. The alloy which is made of one or more of the carbides and the binder metal, is often referred to as a cemented carbide. It is essential for precision part machining plants.
What Is Tungsten Carbide Precision Part Machining Technology
Cutting is one of the common methods used in a tungsten carbide rod, carbide sheet and cemented carbide wire. For cutting the material of 1 mm or less, diamond ultra-thin cutting pieces are commonly used for machining.
The diamond resin matrix cutting piece, wherein the outer ring belt is a resin binding agent abrasive working layer, and the central portion is a high-strength metal, mostly for medium, large cutting slots and cutting.
During the tungsten carbide machining, the cutter tool itself must be higher than the hardness of the machined workpiece. At present, the cutting tool materials for turning tungsten carbide parts are mainly made of high-hardness high-resistant non-metallic adhesive CBN and the diamond PCD.
1. The tungsten carbide components which have a hardness of less than HRA90, select the BNK30 material CBN tool to carry out a large amount of turning and the tool is not broken. The carbide components which have a hardness greater than HRA90 generally select CDW025 Material PCD cutter tool or grinding with a diamond grinding wheel adopting a resin binding agent.
2.To process R3 groove or more of the carbide precision parts, for large machining allowance, generally adopts BNK30 CBN tool for roughing processing, then grinding with grinding wheels. For small processing margins, the grinding can be done directly with wheels , or adopting PCD tool for flush processing.
3.When the crescent groove rib of the tungsten carbide roller is processed, the CDW025 diamond carving milling cutter tool also known as rotary milling cutter is adopted.
For the milling process of carbide parts, according to customer needs, CVD diamond coating milling cutters and diamond insert milling cutter can be provided to perform tungsten carbide precision parts machining, which can replace electrolytic corrosion technology and electric spark process, improving production efficiency and product quality, such as a CVD diamond coating milling cutter to micro-milling the cemented carbide, and the surface roughness can reach 0.073 μm.
What Are The Factors Affecting The Machining Accuracy Of Tungsten Carbide Part
1. Machine tool error
The machine tool error refers to the manufacturing, installation errors and wears of machine tools. It mainly includes guide error of machine tool guide rail, machine tool spindle rotation error, transmission error.
2. Machining principle error
The machining principle error refers to an error generated by adopting the approximate blade profile or approximate transmission relationship for machining. The principle error often occurs in a thread, gear, complex surface machining.
3. Residual stress inside the workpiece
The residual stress is generated during the blank manufacturing, heat treatment process, cold strengthening and cutting processes.
4.Machining environment
The machining site often has many small chips. If there is a part locating surface or location of locating hole, which affects the processing accuracy of the parts, for high-precision processing, some small particles will affect the accuracy.
5.Manufacturing error and wear of the fixture
The error of the fixture is mainly referred to as the manufacturing error of positioning elements, tool guiding elements, an indexing mechanism. The fixture is assembled, with the relative dimensional error between the various components and worn on the working surface during use.
6.Manufacturing errors and wear of tools
The influence of tool error on machining accuracy varies according to the type of tools.
7.Thermal deformation of the processing system
During the machining process, due to the internal heat source, such as cutting heat, frictional heat or an external heat source such as temperature, heat radiation, the processing system is modified, thereby affecting the machining accuracy. In large workpieces and precision machining, the processing error caused by the thermal deformation of the processing system accounted for 40% -70% of the total processing error.
Four Preparations Must Be Done For Machining Tungsten Carbide Precision Part
There are three preparation stages when performing carbide precision parts machining.
1.Preparation stage
Before the precision machining of tungsten carbide, you need to analyze the pattern of processing parts, then determine the machining scheme, such as a process, selecting machine tool, processing cutting volume, tool, fixture, etc, and calculate the coordinate value of the tool path. It is worth spending some time for these necessary preparations, which can make your tungsten carbide parts machining are more smoothly completed.
2.Programming stage
After getting the process route and drawings, we need to write a CNC machining program language describing the processing based on the processing technology information, which can be identified by the system. Do a good job in programming, which isone of the key steps for precision parts machining.
3. Machining stage
When the program is executed, the machine tool system decodes, registers, and calculates the program, and sends a motion command to the machine servo mechanism, driving the moving parts of the machine tool automatically completing the precision parts processing.
The above three preparation stages are the indispensable steps before processing precision parts, which is a process from the drawing to the machining.
Points For Attention In Heat Treatment Of Tungsten Carbide Precision Part
In order to improve the performance of tungsten carbide precision parts, material cutting performance and eliminate the internal stress of the workpiece, some heat treatment procedures should be arranged in the machining process.
1. Preparatory heat treatment
The purpose of pre-heat treatment is to improve the cutting performance of the material, eliminate residual stress during blank manufacturing. Commonly used methods include annealing, normalizing.
2. Eliminate residual stress
Since the internal stress generated during the fabrication of the blank will cause the workpiece to deform and affect the machining quality, heat treatment must be arranged to eliminate residual stress. The best arrangement of the heat treatment for eliminating residual stress is after rough machining and before fine finishing. For parts that do not require high precision, annealing is usually performed before the blank enters the workshop to eliminate residual stress. For high-precision cemented carbide parts, such as precision screws, precision spindles, multiple heat treatments should be arranged to eliminate residual stress, and even ice-cold treatment is often used to stabilize size.
3.Final finish
The purpose of final processing is to increase the strength, surface hardness and wear resistance and is usually performed prior to grinding of tungsten carbide precision parts. Commonly used are quenching, carburizing, nitriding and carbonitride.
Therefore, in the carbide precision part machining, in order to improve the mechanical properties of the precision parts, heat treatment is essential, so that the processing quality conforms to the product requirements.
Summary
Tungsten carbide precision part machining technology is more and more widely adopted. It is essential and important in the precision part factory. The article mainly introduces useful knowledge about carbide precision part processing, such as the cutter tools, factors affecting the machining accuracy, heat treatment of the precision parts.
