1 Preface
Carbon fiber reinforced PEEK material effectively improves the wear resistance and mechanical properties of the material after adding carbon fiber. This is a special engineering plastic with excellent performance. Among them, the high wear resistance and outstanding mechanical properties of PEEK5600CF30 material make it widely used in air sealing and support positioning parts. Major problems were also encountered when turning PEEK5600CF30 materials, such as rapid tool wear and low processing efficiency. When processing high-precision dimensions, the tool compensation value changes significantly, and the processing accuracy is not easy to guarantee. PCD (polycrystalline diamond) tool material has the advantages of tight particle combination, difficult to break and high wear resistance. As a turning tool, the front and rear angles can reach a large value, and the cutting force is small. process non-metallic materials.[1-3]。
2 Structural characteristics and part processing issues
The anti-friction ring of the ejection hook processed by the author’s unit is made of carbon fiber reinforced engineering plastic PEEK5600CF30. The wall thickness of the part is 1 mm. The surface roughness value of the inner hole and outer circle is 1.6 μm. The diameter of the circle is 30 to 55 mm. The length is 1 to 10 mm. The part structure and three-dimensional view are shown in Figure 1 and Figure 2.
Figure 1 Structure of the anti-friction ring
Figure 2 Three-dimensional view of the anti-friction ring
There are currently three major problems facing the processing of PEEK special engineering plastics: firstly, the use of carbide tools for processing, the tool life is extremely low, secondly, the dimensional accuracy and the Surface roughness of parts cannot be effectively guaranteed during processing; , and the quality stability is poor; third, the turning processing efficiency is low and the cutting parameters need to be optimized.[4，5]。
3 solutions
3.1 PCD cutting tools
A general PCD tool consists of three parts: a metal tool, a PCD patch and an adhesive layer. Figure 3 is a schematic diagram of a typical PCD blade structure. The cemented carbide metal matrix and the PCD patch are connected by an adhesive layer.
Figure 3 PCD Tool
The quality of PCD tools is mainly determined by the grinding quality of PCD patches and the material quality of PCD patches. At present, domestic major PCD tool manufacturers have succeeded in accurately locating and processing PCD materials. Therefore, the price of domestic PCD cutting tools has risen from unattainable in the 1990s to almost the same price as high-quality carbide. However, compared with imported PCD tools, domestic PCD tools still have some disadvantages, such as unstable quality and short service life. Some domestic PCD cutting tools use imported materials. Due to domestic processing levels, their edge processing technology always lags behind foreign countries. Depending on the size of the diamond particles that make up the material, commonly used PCD materials are divided into 20, 30 and 30M grades. The larger the particle size, the higher the quality of the material. Similar to the grain size of cemented carbide, larger particles have better wear resistance and are suitable for processing harder materials.
3.2 Tool selection
Taking the processing of the ejector hook anti-wear ring of a typical PEEK5600CF30 part as the test object, carbide tools and PCD tools were respectively used for processing. The difference in wear and wear value change between the two was observed, as well as the difference in wear. the treatment parameters of the two were compared. The blade material, processing equipment and number of processed parts are shown in Table 1.
Table 1 Blade material, processing equipment and number of parts processed
During the machining process of cemented carbide inserts, crater wear, flank wear and groove wear on the cutting face are likely to occur. At the initial stage of tool wear, the cutting edge is prone to cracking due to extrusion of carbon fiber; the coating of the rake surface is quickly damaged under the friction of the carbon fiber material, and the blade matrix is worn quickly, resulting in edge resistance. to further reduce and intensify damage to the cutting edge; In the severe wear stage, the surface of the tool flank is seriously worn and the arc shape of the tool tip is damaged (see Figure 4), resulting in reduced machining. the precision of the parts, serious clamping and burrs, as well as the quality of the surface cannot be guaranteed.
Figure 4 Tool tip arc shape is damaged
The value of the arc radius of the blade tool tip shown in Figure 4, measured using an OLYMPUS high-power electron microscope, is 0.34 mm, and the tip radius of unused blade is 0.4mm. The difference shows that the deviation from the theoretical position of the tool tip. is -0.06 mm. When processing according to the tool tip position measured when processing the first workpiece, it means that the contour error of the workpiece processing is +0.06mm. Comparison of wall thickness tolerances of anti-friction ring parts
mm, this tolerance is sufficient to cause the part to be scrapped.
After using PCD polycrystalline diamond cutting tools, the tool wear was effectively improved under the same processing and cutting conditions, only the rake face of the blade has a low degree of wear, the cutting edge is basically intact and the shape of the arc. of the tool tip maintains high precision (see Figure 5), the machining precision of parts has been greatly improved.
Figure 5 Arc shape of tool tip maintains high accuracy
Figure 5 shows that the arc radius of the tool tip of the blade measured using an OLYMPUS high-power electron microscope is 0.385 mm and the tool tip radius of unused blade is 0.4mm. The difference shows that the deviation from the theoretical position of the tool tip. is -0.015mm. When processing according to the tool tip position measured when processing the first workpiece, it means that the contour error of the workpiece processing is +0.015mm. Comparison of wall thickness tolerances of anti-friction ring parts
mm, the part is still qualified at this time.
Through this test, it can be concluded that carbide inserts are not suitable for turning PEEK5600CF30 materials and PCD tools are suitable for turning PEEK5600CF30 materials. Using grade 20 PCD tools can meet the needs. The PCD cylindrical turning tool selected for actual processing is shown in Figure 6.
Figure 6 External PCD turning tool
3.3 Analysis of processing dimensional precision error
(1) The influence of tool cutting force on the processing of anti-friction rings. When processing parts, if the CNC program is compiled according to the normal part size of the anti-friction ring, it can be found that the shape of the inner hole and the outer circle after processing have a taper: along the length of 10 at 12mm, the variation of the inner hole of the workpiece is 0.04 ~ 0.05mm, and the variation of the outer circle is 0.01 ~ 0.03mm. The shape of the inner hole and outer circle is shown in Figure 7.
a) Theoretical condition of the parts after transformation b) Actual condition of the parts after transformation
Figure 7 Shape of inner hole and outer circle
The reason is analyzed by the fact that the mouth part of the workpiece has low rigidity and the tool gives way during the cutting process. After processing and debugging, the taper of the parts after processing is compensated in the CNC program to better ensure the processing accuracy. After trial machining of the parts, there is a direct relationship between the cutting quantity of the inner hole and the axial length of the parts. The axial bulk increases and the deformation of the orifice increases. After compensating the taper during the programming process, the machining accuracy of parts can be effectively improved.
(2) Impact of tool wear on the dimensional accuracy and surface quality of the parts Taking the treatment of anti-friction ring parts as an example, the situation verified on site is as follows: after the treatment of 400 parts, in due to heavy tool wear. , if it continues to be used, it is recommended to process 50 pieces each time. Adjust the compensation value of the tool and the taper once, and adjust the diameter value by 0.02mm each time. The processing conditions are as follows: use the CTX310 CNC machine tool to process PEEK5600CF30 bar stock, and the tool is a domestic PCD inner hole boring tool. Processing parameters: spindle speed 1800r/min, feed rate 0.06mm/r, finishing machining allowance 0.05mm, it is not recommended to continue to use after 700-800 parts , and the tool must be changed. The reason for this is that the cutting force increases due to tool wear, which in turn affects the dimensional accuracy and surface quality of the workpiece. The tool offset value and CNC program should be adjusted in time to ensure the qualification rate of workpiece processing. .
3.4 Cutting parameters
Table 2 shows the recommended PCD tool grades and corresponding cutting parameters. Conditions for using this parameter: The processing machine tool is a CTX310 CNC lathe, the wall thickness of the workpiece is ≥1mm, and the diameter of the processing outer circle is 30-50mm. Additionally, please note that the manufacturer of the PCD blade used above is SECO (Seco) and other brand tool parameters may be fine-tuned based on this.
Table 2 Recommended PCD tool grades and corresponding cutting parameters
4 Conclusion
After research and application on the turning performance of PEEK engineering plastics, the turning efficiency and quality of PEEK5600CF30 material have been effectively improved.
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