Machining Technology of Precision Stainless Steel Nozzle Parts

The lathe and composite machining of many high-precision, multi-batch, and complex-shaped small precision composite parts are a major challenge facing the machinery manufacturing industry. With the rapid development of aerospace, hydraulics, communications, microelectronics, medical equipment and other industries. Traditional CNC machining methods and processes have been unable to meet the diversified and personalized needs of profile machining. The manufacturing industry is developing rapidly in the direction of high efficiency, high precision and integration.

In view of the characteristics of such parts and components, most domestic enterprises are adopting methods of designing new machining techniques to improve equipment performance and increase production efficiency to meet machining needs. This article takes a typical composite nozzle assembly as an example, using the characteristics and advantages of the B0326-II precision automatic lathe. Detailed machining technology research has been carried out from the aspects of tool selection, machining technology development, main machining route design, trial machining problem analysis and so on. It solves the problems of large batches, low efficiency, and difficult machining of such parts.

Part machining technology analysis of technical requirements of parts

The monthly output is 20,000 pieces, made of stainless steel 1Cr18Ni9Ti. This is a difficult material. The machining elements of this part include outer circle and screw rotation, plane milling and so on. Drilling center holes and bottom holes, boring holes, self-tapping screws, etc. In addition, the dimensional accuracy and surface roughness of the parts are required, and the coaxiality of the holes at both ends is 0.02mm.
Based on the above analysis, the difficulty of parts machining: to ensure the dimensional accuracy of the outer hole and the inner hole, the two inner holes are coaxially required, and mass production.

Machining Nozzle

B0326-II precision automatic lathe is mainly used for turning. We also have drills, engraving, slot milling, tooth milling, tapping and reaming. The multi-process multi-task precision machine tool has C-axis and Y-axis indexing functions, and can perform processes such as radial plane milling, drilling and tapping. The dual-spindle control system provides automatic positioning and feeding of the rear axis after the spindle side is processed, effectively solving the problem of low efficiency and accuracy caused by the rotation of the workpiece.
As shown in Figure 2, according to the characteristics of the machine tool, the machining route for the outer contour of the part is designed as follows: spindle side → rotating end face → rotating the outer circle to 39 mm. → Rotate the outer circle to 65.1mm from the end of the rear axle.

The key step in the design process, the left hole

Drilling

The left hole is machined on the T31-T35 5-hole tool post on the spindle side. The 5-hole tool holder has a compact layout, which reduces the time for the tool to pass through the tool, and the machining efficiency is high.

The precision of drilling Φ7 is higher, and the drilling process is adopted. The 38mm hole depth is a deep hole drill. The problem lies in the cooling and chip removal of the cutting area of the drill bit when drilling. High-pressure oil cooling and G83 pecking drill can effectively prevent chip breaking and chip entanglement.

Specific procedures

First, drill a center hole about 2mm with a Φ6 center drill. Don’t make it too shallow. Otherwise, the chamfer of the hole will produce burrs. Then use a Φ5.8 drill bit to drill, leaving a machining allowance of about 0.5mm on one side. Due to the high hardness of the component materials, most of the remaining amount must be removed during machining and high-pressure oil cooling must be turned on. Finally, the hole size is ensured by boring, and the cutting method is fast and low feed. Choose S25.0G-SVNR12SN boring bar, insert model VNBR0620-01, spindle speed 3000r/min, cutting depth ap=0.25mm, feed rate f=0.02mm/r.

Turning 39mm outer circle

This step is the outer contour machining, and the focus is on how to improve the machining efficiency and ensure the surface quality. Consider the structure and material properties of the part. Figure 3 shows the route design of the tool. This step “LL” and “JP2” are completed in 3 times. The first two use the G90 rectangular path to remove most of the tolerances and the third finishing. The first two times I used the G90 rectangular toolpath to eliminate most of the tolerances. Finished for the third time.

When the first rectangular machining route is executed, it is processed to point A, each cutting depth is 0.5mm, feed rate is 0.05mm/r, and 3 cuts. When the second rectangular machining route is executed, each cutting depth reaches 0.3mm, the feed rate reaches 0.03mm/r, the machining reaches point B, and 4 cuts are completed. The final finishing depth is 0.1 mm, and the feed rate is 0.01 mm/revolution. This step uses Kyocera SCLCR1616H-12 cylindrical knife, blade model CCGT09T304M. The surface quality of the parts is excellent.

Due to counterclockwise

M10 screws need to be matched with other medical equipment parts, and the screw diameter needs to be controlled, and the roughness value reaches Ra0.8.

In order to meet the requirements, the thread is rotated in three steps.

In the first step, the external circular knife rotates the large diameter by 0.2 mm.

In the second step, after the first thread rotation is completed, the external circular knife is called again and rotates along the thread surface to remove the upper burr, but the burr is pushed to the bottom of the tooth. complete.

In the third step, use the thread cutter to rotate the last two knives along the line, and then rotate again, and in the second step, move the burr to the bottom of the tooth.

Milling 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 in this step is 2.3 mm. You can choose a large diameter end mill to improve machining efficiency.
The analysis showed that an end mill with a diameter of 10 was selected. When the spindle is braked, it is divided into three milling machines.

The first cut depth is 0.65 mm.

The second time, the cutting depth was 0.65 mm.

For the third time, the cutting depth was 0.35 mm.

Each time the cutting feed rate reaches 50mm/min, the C-axis index is 180°, and the surface is processed. After plane milling is completed, burrs will form on the outer edge of the plane. At this time, it is best to use an outer circular knife to deburr along the outer circle of Φ13, and the effect is better.

Position the outer circle to 65.1 mm here outside the lathe

The difficulty is that the groove C area limits the angle of the tool, making it difficult to cut the knife. Traditional circular cutters are prone to interference and collapse, and the quality of the groove surface is poor.

Therefore, 3 turnings were performed.

For the first time, a 3mm wide grooving knife is selected and cut to the bottom of the groove with a finishing allowance of 0.1mm. The tool is fed along route 1 to provide cutting space for the next turning.

For the second time, the traditional 90° external turning tool was selected, and the tool was fed along route 2 and processed according to the G90 rectangular route, with a total removal of 6.4mm.

For the third time, use the post sweep tool to complete along route 3. The small space in the groove makes it easier for the cutting edge of the 90° external tool to interfere. The rear sweeping knife can effectively solve the problem and ensure the roughness value of the groove bottom.

After drilling the axle receiving hole

After all the machining on the main shaft side is completed, place the cutter at the cutting position, place the rear shaft at the center of the main shaft, and clamp the rear shaft T9900 along the main shaft direction BB. In addition, since the main rear axle rotates at the same time, the rigidity is greatly improved. After cutting off the shaft to take the material, after using the T35, T36, T37 tools for end face machining and drilling. The rear axle is automatically positioned and concentrically clamped on the main shaft to avoid coaxiality errors caused by re-clamping, to ensure the coaxiality requirements of Φ7 and Φ4 holes, and to solve the problem of coaxial machining of parts. ..

Analysis of trial machining problems

After the machining technology is drawn up, it is programmed. After repeated simulation and verification, the first trial production process of the part showed that the burr at the bottom of the Φ7 hole increased. The Φ4 port has no 60° chamfer. Φ7 hole depth deviation and other issues.

The Φ7 hole of this part has high dimensional accuracy and surface quality. When the Φ5 bit drills into the bottom of the hole, the tip cannot be ejected in time due to squeezing, and the burr at the bottom of the hole will bend and affect the quality of the part. After repeated attempts, the following adjustments are made: if the drill bit is drilled at the bottom of the hole, the drill bit will be delayed by 0.1 mm, 0.2 seconds (that is, G04U0.2), directly exit, follow the hole, and then remove the reverse burr. Do not leave the bottom.
Φ4 hole chamfer is processed by Φ6 center drill. Since the hole in the center was drilled very deep, it was judged that the hole was not chamfered. In addition, if the bottom cone of the center bore exceeds 60°, the T36 wear compensation on the rear axle side +0.5 can be solved.

When we tested the first product, we found that the Φ7 hole is 37.8mm deep, which is 0.2mm smaller than the actual size. The main reason for the analysis is that the T23 boring tool on the spindle side has a deviation in the tool setting. On the spindle side, the T23 boring tool accurately readjusts the tool, generating a T23 wear compensation input of +0.2. After repeated debugging, the nozzle parts meet the acceptance requirements.

Summary

After the nozzle parts test run, the machine tool will be equipped with an automatic feeder. The feeding, machining, receiving and unloading are fully automated, and the monthly machining demand is 20,000 pieces. It solves the problems of miniaturization, multi-variety, mass production and high precision in the latest manufacturing process.
Research on machining technology of small composite shaft parts based on B0326-II precision automatic lathe. To provide a technical basis for promoting the development of new turning-milling composite technology, and to provide references and references for machining similar parts.

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