How to complete the machining of parts on the lath

2022-08-06
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How to complete the machining accuracy requirements of parts that can only be achieved by grinding machine on the lathe

through the careful study of the drawings of high-precision titanium alloy parts, the machining scheme and process parameters are determined, and the machining of parts is finally successfully completed by using the existing ordinary lathe equipment, realizing the machining accuracy requirements that can only be achieved by grinding machine on the lathe

1. Analysis of processing difficulties

there are a number of production tasks from an optical and Mechanical Institute. This task is a new challenge in terms of processing materials and processing accuracy. Among them, there are the following problems in the processing of the convex lens rotating shaft (see Figure 1):

(1) the convex lens rotating shaft is made of titanium alloy. Due to its high strength and hardness, it is easy to produce a surface hardening layer during processing, and the material has small thermal conductivity and small elastic modulus, During cutting, the springback of the machined surface is very large, resulting in severe friction, adhesion and bonding wear of the tool flank

take the sensor of S-type experimental machine as an example (2) while ensuring the shape machining accuracy, the coaxiality at both ends of the part is required to be 0.006mm, which is almost difficult to achieve for the existing machine tools. Since the spindle runout of the existing machine tool has been 0.01mm after startup, it is conceivable that it is difficult to complete the processing task on such a machine tool

(3) the dimensional accuracy requirements of part shape and hole are very high, which are 0.005mm and 0.01mm respectively. The surface roughness value ra=0.8 is required μ m。 Under normal circumstances, it is necessary to process on the grinder to meet the requirements of the drawing. Since there is no grinder equipment for precision machining in the branch, the task must be completed by the lathe. Before processing, the drawings were carefully studied and various processing schemes were analyzed. Finally, the following methods were adopted for processing

2. Selection of process parameters

according to the characteristics of titanium alloy materials, cutting tool materials with high strength, good wear resistance and brand YW series are selected for processing

(1) tool parameters: select one positive and negative cylindrical deflection tool and one horizontal groove turning tool with a main deflection angle of 90 °. While ensuring the cutting strength of the tool, in order to reduce the cutting resistance and prevent the material from overheating and deformation in the cutting process, the tool rake angle shall be 20 ° - 25 °. In order to avoid sharp friction and adhesion between the flank of the tool and the surface of the part during cutting, the flank angle of the tool is selected as 5 ° - 8 °

(2) cutting parameters: due to the low thermal conductivity and small elastic modulus of titanium alloy, it is easy to produce bonding during processing, so it is not easy to set the cutting parameter value too large during processing. In his opinion, the spindle speed should be 350-500 r/min, which should not be too high. The feed rate and feed rate shall be larger for rough turning and smaller for fine turning

3. Machining process method

(1) rough turning: first, rough turn the shape of both ends of the part with a transverse groove turning tool (see Figure 2), with a margin of 0.5mm left on one side. Due to the small resistance and easy chip breaking in the cutting process of the horizontal groove turning tool, the rough turning effect of the figure 1 at both ends is better when using the horizontal groove turning tool. However, titanium alloy is very easy to be deformed during machining, so cutting fluid must be used for full cooling during cutting

(2) semi finish turning: after the parts are completely cooled, use the 90 ° excircle deflection cutter to turn out the reference excircle of the parts, clamp the part shape through the soft claw, and use the micron lever table to correct the part shape (see Figure 3), so that the circular runout is within 0.005mm. Process one end of the parts, which cannot be processed in place at one time, and leave a margin of 0.1-0.2mm on one side

(3) finish turning: ① after the shape allowance of the part is removed, drill and bore the hole to ensure the size and accuracy requirements. The part shape shall be corrected again to ensure that the dimensional accuracy is within 0.005mm, and 0.05mm shall be reserved for the finish turning shape. As the double top is positioned based on the inner holes at both ends, and the shape allowance before the final finishing turning of the parts is small (0.05mm), the drilling, boring and finishing contour door Jisa 4702 (1) 996 are completed in one clamping and centering, and the hole chamfering is done to prepare for the next double top process. ② On the top of the machine tool, pass the part through the double top method, and use the positive and negative deviation cutter to finish the shape of the two ends (see Figure 4). Polish the part shape to reach the surface roughness value ra=0.8 μ M

4. So as to improve the product quality and service life of the device. Through inspection, the dimensional accuracy and form and position tolerance of the parts meet the requirements of the design drawings

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