Mirror turning technology for copper alloy shaped grooves


Through experimental analysis of tool selection, machining parameters and tool angles, the best solution for mirror surface machining of copper alloy shaped grooves is finally arrived at, providing a theoretical basis and research foundation for improving the surface machining quality of copper alloy parts.

With the improvement of the use performance of scientific and technological products and the growth of the use cycle, manufacturing enterprises have put forward higher requirements for the dimensional accuracy, geometric tolerance and surface roughness of product parts. In ultra-precision machining, in order to ensure the roughness of the parts, most of them use grinding processing technology. However, copper alloy is a non-ferrous metal, and the material characteristics of non-ferrous metal determine that grinding processing is not suitable, and turning processing by lathe is appropriate. By analyzing the causes of the formation of surface roughness and combining with the actual processing experience, a set of turning methods to improve the surface roughness of the parts is summarized.

Part structure analysis
A model of copper alloy material parts structure as shown in Figure 1, according to the design requirements, V-shaped groove and the inner circle coaxiality requirements φ0.01mm, surface roughness value Ra = 0.2μm. material for brass H62, the material has good mechanical properties, good plasticity, good turning performance, but there are sticky tool. The current existing machining capacity of the factory makes the surface roughness value Ra of the part reach 0.8μm, which cannot meet the design requirements. Therefore, the processing technology of V-groove needs to be studied in depth to explore a suitable processing method to meet the production requirements.

Figure 1 Copper alloy part structure

Machining solutions
3.1 Mirror machining technology turning and forming
(1) Tool The tool material currently used in the factory is mainly cemented carbide. Cemented carbide is made of tungsten-cobalt class (WC), tungsten-cobalt-titanium (WC-TiC), tungsten-titanium-tantalum (niobium) cobalt (WC-TiC-TaC) and other refractory metal carbides, which are pressed and sintered by powder metallurgical methods with metal binder Co (cobalt) or Ni (nickel). Cemented carbide has high hardness, wear resistance, better strength and toughness, heat resistance, corrosion resistance and a series of excellent properties, can be used for processing non-ferrous metals. It can be used for rough machining when processing copper alloy V-groove.
In the field of non-ferrous metal mirror processing, diamond tools are one of the more commonly used. Diamond tools have the advantages of extremely high hardness and wear resistance, low friction coefficient, high elastic modulus, high thermal conductivity and low thermal expansion coefficient, as well as low affinity with non-ferrous metals, and not easy to produce chip tumors. In addition, due to the diamond elastic modulus, cutting cutting edge sharp, edge deformation is small, the non-ferrous metal extrusion deformation of the cutting is small, can make the cutting process in a small deformation to complete, so you can improve the quality of surface processing. Diamond tools mainly have: thin film coated tools, thick film diamond welding tools, diamond sintered tools and single crystal diamond tools. The copper alloy V-groove with an angle of 60° needs to be studied for the selection of tool angle in order to avoid interference during machining. Considering the machining cost as well as the test convenience, the machine clamp tool is used. As shown in Figure 2 and Figure 3, 35° and 45° inserts were used, and two types of fixtures were tested.

Fig. 2 35° inserts Fig. 3 45° inserts

(2) Machining parameters Machining parameters directly affect the surface roughness. In mirror machining, the spindle speed will become the main factor affecting the surface roughness when the tool feed is reduced below a certain value. When the spindle speed is kept constant, the surface roughness increases rapidly when the turning depth is less than a certain value, while when it is greater than this value, the surface roughness shows an approximately linear increasing trend. The most appropriate depth of cut needs to be found for a particular material. Therefore, different process parameters need to be selected for experimental verification.
3.2 Machining of V-grooves using cloth wheel polishing technology
The current factory processing conductive ring V-shaped groove, the surface roughness value can reach Ra = 0.8μm. in order to make the surface roughness value of Ra = 0.2μm, it can be polished, with cloth wheel, plasma polishing of brass.
Cloth wheel polishing, is made of cloth into a wheel type used to polish. The hardness of the polishing wheel is determined by the distance of the suture line, the smaller the distance of the suture line, the higher the hardness of the polishing wheel. Polishing wheel can be divided into non-stitched whole cloth wheel, air-cooled cloth wheel and stitched type. Non-stitched whole cloth wheel is mostly made of fine soft cotton cloth, suitable for polishing complex shape workpiece, or for small workpiece fine polishing. Air-cooled cloth wheel with 45º angle line cutting method, is a ring-shaped fold, the middle is equipped with a metal disc, with the characteristics of ventilation and heat dissipation, suitable for polishing large workpiece. Stitching type mostly made of coarse cloth, non-woven fabric and fine flat cloth, etc., stitching line can be concentric circle type, spiral type and straight radiation form, suitable for polishing various plating and the shape of the simpler workpiece. Polishing copper alloy, commonly used cloth wheel circumferential speed of 22 ~ 30m / s, for this study of the conductive ring V-shaped groove, the specific processing parameters need to be tested.
3.3 Electrolyte plasma polishing
(1) electrolyte plasma polishing research Plasma polishing is the workpiece and polishing fluid in the energized detached metal ions adsorbed on the surface of the workpiece, the workpiece bump by the impact of current to remove the block, the current flow, the concave and convex constantly change, the surface of the part is gradually leveled. The technology can effectively improve the surface quality of the parts.
(2) Influencing factors For plasma polishing, the factors that affect the quality of surface polishing are: solution temperature, processing time, solution concentration, dive depth, solution flow rate, etc. The company currently has plasma polishing equipment, which can be tested according to the relevant influencing factors. The conductive ring V-groove size of this attack is small, need to make fixture for fixing, and in order to ensure the consistency of the entire part polishing, also need to be further modified according to the equipment, rotate the parts, so that all directions of the ring are polished in place.

4 Determine the processing scheme
The above program one mainly studies the tool, its processing parameters can be selected through the machine tool, the process is more convenient. Program two of the cloth wheel processing, can refer to less experience, and the part V-shaped groove size is small, not easy to clamp processing. Scheme three of the plasma polishing technology is more advanced technology, the company's equipment can be fully utilized, but the scheme to ensure the consistency of the entire ring polishing, there are more difficult fixture production problems. And the need for a large number of tests on the parameters of polishing. A comprehensive analysis concluded that option one was adopted.
The main purpose of this study is to make the surface roughness value Ra of copper alloy V-groove reach 0.2μm mirror effect. In the field of mirror surface processing of non-ferrous metals, diamond tools have better characteristics. During the implementation of the project, the more advanced mirror surface turning technology in the industry was investigated, researched and analyzed together with tool manufacturers, and customized suitable tools for processing tests. The machining test was carried out mainly in terms of tool feed, spindle speed, depth of cut and programmed machining method. Combined with the part material brass H62 and the mirror machining theory, the optimal parameters were found to achieve the mirror machining effect with the surface roughness value Ra=0.2μm of the part, and the batch production was verified according to the explored parameters.
4.1 Mirror machining tool research
According to the machining scheme, the mirror machining tool is investigated. The surface roughness of the part machining is influenced by the machining parameters, the main and sub-deflection angles of the turning tool, and the material and structure of the tool is also an important influencing factor.
The cutting edge of PCD (polycrystalline diamond) material consists of many microscopic crystals, and the tool with ultra-microscopic particles helps to reduce the surface roughness value of the part during the machining process.
The V-groove angle of this attacked part is 60º. In order to avoid machining interference and to meet the test of multiple machining methods, MVVNN symmetric toolholder was selected, and machine clamping tool was used considering the machining cost as well as the test convenience.
After research and analysis, Kyocera's ultra-fine grain PCD diamond inserts were selected for the machining test. The insert model is VBMT110301NE KPD001 with a tip angle of 35º and tip R=0.1mm, as shown in Figure 4.
a) Front side of Kyocera insert b) Side side of Kyocera insert
Figure 4 Kyocera blade
Superfine PCD diamond ensures tip strength, wear resistance, chipping resistance (toughness), and sharpness for stable, long-life machining.
4.2 Machining Tests
According to the relevant machining parameters affecting the surface roughness, group tests are conducted, mainly from the programmed machining method, spindle speed, feed and depth of cut.
(1) Common machining methods for factory machining of V-groove type parts The common programming and machining methods for machining V-grooves in the workshop are the walking track type and the direct machining by forming tool. Forming knife direct machining has the characteristics of high processing efficiency, but the surface roughness of the machined parts is poor, and easy to damage the tool. Walking track machining has the characteristics of consistent surface of parts, less axial force on parts, and can effectively ensure the coaxiality of parts. Therefore, this test programming processing method uses the walking track type.
(2) group test 1 first consider the protection of the diamond tool in the initial determination of machining parameters test, first machining cylindrical surface to feel the appropriate machining parameters. Machining cylindrical surface, as shown in Figure 5, has reached the mirror effect. 2 according to the initial determination of machining parameters for the test machining of parts. In the test machining process, in the thickness of the larger cylindrical processing V-shaped groove, when the part thickness size reduced to 0.8mm, there is a knife machining trace problem, as shown in Figure 6. The preliminary analysis concluded that the vibration was caused by the thin wall thickness at the edge of the part. Therefore, the back draft and feed were gradually reduced and the speed was increased in the subsequent tests.3 After the improvements were made according to the problems that appeared above, the machined surface of the V-groove was greatly improved, but there were still spots, as shown in Figure 7.

Figure 5 Machining cylindrical surface

Fig. 6 Tool machining marks

Figure 7 Surface spots
After analyzing the machining path and parameters, and considering that the diamond tip is worn during rough machining, the carbide tool is selected for rough machining by re-calibrating the programming. Reserve 5mm machining allowance, then use diamond tool for finishing, choose spindle speed 1200r/min, feed f=0.03mm/r, for machining test. The surface of the V-groove of the part is smooth without spots, the tool marks are even, and the mirror effect is achieved (see Figure 8). The consistency of batch machining is good, and the surface roughness value reaches Ra=0.0638μm by the surface roughness instrument, as shown in Figure 9, which meets the requirements.

Figure 8 Mirror effect

Figure 9 Roughness inspection report

5 Conclusion
Through the above multiple part machining tests, the surface roughness of the part is greatly influenced by the tool and machining parameters. In the verification, the V-groove structure is continuously optimized, and the combination of tool and machining parameters is improved, and finally the surface of V-groove achieves the mirror effect. And the dimensional accuracy of the part is stable and the surface quality is consistent in batch machining, which achieves the target of the attack. By using super fine PCD diamond tools and MVVNN symmetric shanks, the mirror surface machining parameters were determined through experimental research, and the parameters and machining ideas can be extended to other parts that need to achieve the mirror surface effect to effectively improve the quality of the parts.