Traditional numerical control processing methods and processing techniques have been unable to meet the needs of diversified, individualized, and profiled processing. The manufacturing industry is developing rapidly in the direction of high efficiency, precision and compounding.
With the rapid development of aerospace, hydraulics, communications, microelectronics, medical equipment and other industries, the turning and milling composite processing of many high-precision, multi-batch, and complex-shaped small precision composite parts poses a great challenge to the machinery manufacturing industry. . In view of the characteristics of this type of parts, most domestic enterprises have adopted methods of improving equipment performance and designing new processing techniques to meet processing needs and increase production efficiency. This article takes a typical composite nozzle part as an example, using the characteristics and advantages of the B0326-II precision automatic lathe, starting from tool selection, processing technology formulation, key processing route design, and trial processing problem analysis, etc., to carry out in-depth processing technology Research has solved the problems of large batches, low efficiency and difficult processing of such parts.
1. Analysis of parts processing technology
Part technical requirements
Figure 1 is a nozzle part in a medical device, with a monthly output of 20,000 pieces, the material is stainless steel 1Cr18Ni9Ti, which is a difficult-to-machine material; the part has many processing elements, including turning outer circles and threads; milling flat surfaces; drilling center holes and Bottom hole; boring hole; tapping thread, etc. In addition, the dimensional accuracy and surface roughness of the parts are required to be high, and the coaxiality of the holes at both ends is required to be 0.02mm.
Based on the above analysis, the difficulty in processing this part is to ensure the dimensional accuracy of the outer circle and the inner hole, the coaxiality requirements of the two inner holes, and mass production.
Nozzle parts processing technology
B0326-II precision automatic lathe is a precision machine tool that is mainly used for turning, and also has multiple processes such as drilling, engraving, milling, milling, tapping, reaming and so on. It has C-axis and Y-axis indexing functions. Carry out radial plane milling, drilling, tapping and other processes. Its dual-spindle control system can realize the automatic positioning and receiving of the back shaft after the main shaft side machining, effectively solving the problem of low efficiency and accuracy caused by the turning of the workpiece.
As shown in Figure 2, according to the characteristics of the machine tool, design the machining route of the part outer contour: spindle side ① car end face → ② car outer circle to 39mm → ③ car outer circle to 65.1mm → back axle side car end face.
According to the above analysis, the processing technology design of nozzle parts is shown in Table 1.
2. Key process design
Left hole machining
When the left hole is processed, it is arranged on the T31-T35 five-hole tool holder on the spindle side. The five-hole tool holder has a compact layout, which can reduce the time for the tool to go empty and has a higher processing efficiency.
The hole Φ7 requires high precision, and it is processed by boring. The hole depth of 38mm belongs to deep hole processing. The difficulty lies in the cooling of the drill bit cutting area and chip removal during the bottom hole drilling process. The high pressure oil cooling and G83 pecking drilling method are used. It can effectively avoid drill bit breakage and chip entanglement.
Specific steps: first use a Φ6 center drill to drill a center hole of about 2mm, and the depth should not be too shallow, otherwise there will be burrs on the chamfer of the hole; then use a Φ5.8 drill bit to leave a machining allowance of about 0.5mm on one side. The material of the parts is harder. Most of the margin should be removed in this process, and high-pressure oil cooling should be turned on; finally, the hole size accuracy is guaranteed by boring, and the high-speed low-feed mode is used for cutting, and the S25.0G-SVNR12SN boring bar is selected , Insert model VNBR0620-01, spindle speed 3000r/min, cutting depth ap=0.25mm, feed rate f=0.02mm/r.
The outer circle of the car to 39mm
This step is the outer contour processing, focusing on how to improve the processing efficiency and ensure the surface quality. Comprehensively consider the structural characteristics and material properties of the parts. The path design of the tool is shown in Figure 3. This step 〖LL〗〖JP2〗 is processed in three times. The first two uses the G90 rectangular tool path to remove most of the margin, and the finishing is completed in the third time.
When the first rectangular processing route is executed, it is processed to point A, and the depth of cut is 0.5mm each time, and the feed speed is 0.05mm/r. It is completed in three cuts; when the second rectangular processing route is executed, it is processed to point B, and the depth of cut is every time. 0.3mm, feed speed 0.03mm/r, finished in four cuts; the cutting depth is 0.1mm in the last finishing process, and the feed speed is 0.01mm/r. This step uses Kyocera SCLCR1616H-12 cylindrical knife, the blade model is CCGT09T304M, and the surface quality of the parts is good.
Threading on the left
As the M10 thread needs to be matched with other medical equipment parts, it is required to control the pitch diameter of the thread, and the roughness value reaches Ra0.8.
In order to meet the requirements, the thread turning is carried out in three steps: the first step is to turn the large diameter by 0.2mm with the external tool; the second step is to turn the external tool along the thread surface to remove the top burr after the first completion of the thread turning. When the burr is pressed toward the bottom of the tooth; in the third step, the thread cutter is used to turn the last two passes of the thread turning to remove the burr that is pressed toward the bottom of the tooth in the second step.
Plane milling mainly uses the spindle C-axis indexing function of the B0326-II precision automatic lathe to effectively solve the problem of secondary clamping. The total thickness of the milling layer of this step is 2.3mm, and an end mill with a large diameter can be used to improve the processing efficiency.
According to the analysis, select the diameter Φ10 end mill. After the spindle is braked, the milling is divided into three times. The first milling depth is 0.65mm, the second milling depth is 0.65mm, the third milling depth is 0.35mm, and the feed rate of each milling is 50mm/ min, one side of the C axis is indexed 180° and the other side is milled after processing. After plane milling is finished, the outer end of the plane will have burrs turned outwards. At this time, it is advisable to use an external circular knife to deburr along the Φ13 external circle.
The outer circle of the car to 65.1mm
The difficulty of external turning here is that the C area is groove-shaped, which limits the angle of the tool and is not easy to cut. Turning with conventional external tools is easy to interfere and chip, and the surface quality of the groove is poor.
Therefore, the turning is carried out in three times. The path of the tool is shown in Figure 4. For the first time, a grooving tool with a tool width of 3mm is selected to cut to the bottom of the groove with a finishing allowance of 0.1mm, and the tool feeds along path 1. Provide cutting space for the next turning; for the second time, select the conventional 90° external turning tool, feed along route 2, and process according to the G90 rectangular route. This time, a total of 6.4mm margin is removed; for the third time, the post-sweeping tool is selected For finishing along route 3, due to the small space at the groove, the cutting edge of the 90° external circular cutter is easy to interfere. The use of a back sweep tool can effectively solve this problem and ensure the roughness value of the groove bottom.
Back shaft receiving material drilling
As shown in Figure 5, after all the processing on the spindle side is completed, position the cutting knife to the cutting position, align the back shaft with the spindle, and clamp the back shaft T9900 along the spindle direction BB, and the main and back shafts rotate at the same time, which greatly increases 了rigidity. Cut the material of the back shaft, and use the T35, T36, T37 tools on the back shaft side for turning and drilling. The back shaft is automatically positioned to be clamped in a concentric position with the main shaft, avoiding the coaxiality error caused by re-clamping, ensuring the coaxiality requirements of the holes Φ7 and Φ4, and solving the problem of coaxiality processing of the part.
3. Trial processing problem analysis
After the machining process was drafted, the program was compiled. After repeated simulation and verification, the first trial machining of the part showed problems such as burr upturning at the bottom of the Φ7 hole, no 60° chamfer at the Φ4 hole, and depth deviation of the Φ7 hole.
The Φ7 hole in this part has high dimensional accuracy and surface quality. When the Φ5 drill bit is drilled to the bottom of the hole, the chips cannot be discharged in time due to extrusion, which causes the burr at the bottom of the hole to turn up, which affects the quality of the part. After repeated tests, make the following adjustments: When the drill bit is drilled to the bottom of the hole, the drill bit will not directly withdraw, but lift it up by 0.1mm along the hole, then delay 0.2s (that is, G04U0.2) and then leave the bottom of the hole to remove the upturn burr .
As shown in Figure 6, the Φ4 hole chamfer is processed by a Φ6 center drill. If the hole is not chamfered, it is judged that the center hole has been drilled too deep, which has exceeded the 60° cone surface at the bottom of the center drill, and the T36 wears on the back shaft side. Compensation +0.5 can solve this problem.
When the first product was inspected, it was found that the depth of the Φ7 hole was 37.8mm, which was 0.2mm smaller than the actual size. The main reason for the analysis was the deviation of the T23 boring tool on the spindle side during tool setting. Re-calibrate the T23 boring tool accurately on the spindle side, and input +0.2 in T23 wear compensation. After repeated debugging, the nozzle parts meet the acceptance requirements. The actual processing is shown in Figure 7.
After the nozzle parts are successfully debugged, the machine tool is equipped with an automatic feeder, which fully automates the feeding, processing, receiving and discharging, and realizes the processing demand of 20,000 pieces per month, which solves the miniaturization, multi-variety, and large-scale production in the modern manufacturing process. The problem of batch and high precision.
By studying the processing technology of the small composite shaft parts of the B0326-II precision automatic lathe, it provides a technical basis for the promotion of the new turning-milling composite processing technology, and also provides a reference and reference for processing similar parts.