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Research on CNC machining methods of thin-walled aluminum alloy shell parts

Based on specific CNC machining examples, a thin-walled aluminum alloy shell processing scheme is introduced. Through reasonable process arrangements and the design of special tooling fixtures, the problems of vibration and deformation during part processing are perfectly solved, and it has strong operability and It is instructive and provides a reference for the CNC machining cof similar parts.


1 Preface

Thin-walled aluminum alloy shell parts are widely used in the mechanical field. However, such parts have special structures and shapes. Due to their poor rigidity and weak strength during the cutting process, they are prone to vibration and deformation [1], making it difficult to ensure that the parts are The processing quality of thin-walled aluminum alloy shell parts has always been a difficult problem in the field of mechanical processing. This article takes the processing of a drum-shaped thin-walled aluminum alloy shell as an example. Through the determination of the process plan, the design and application of tooling fixtures, a processing method for solving special-shaped thin-walled shell parts is introduced.

2 Part structure analysis

The drum-shaped thin-walled aluminum alloy shell is shown in Figure 1. The material is aluminum alloy 2A12. The blank is a φ500mm×520mm cylindrical solid body in solid solution T4 state. The middle part structure is a drum-shaped curved surface and the end face flange structures at both ends. The maximum outer diameter of the part is 480mm. The two end parts have φ296mm and φ314mm stops respectively. There are holes evenly distributed on the end faces. The wall thickness of the drum-shaped part in the middle is only 2mm. The size of the part requires IT6 level accuracy, the outline is 0.1mm, and the surface Roughness value Ra = 1.6 μm. Analyze the processing difficulties: ① The large amount of blank removal can easily cause stress deformation in the workpiece. ② The wall thickness of the workpiece is only 2mm, and the overall structure has poor rigidity and strength. It is easy to cause vibration and deformation during the cutting process. ③The workpiece has a special-shaped structure, the thickness of the flanges at both ends is only 18mm, and the strength of the middle part is poor. Applying clamping force in the axial or radial direction of the workpiece will cause deformation of the part, so how to clamp it is a problem. [2] Based on the above analysis, the focus of processing this part is to fully consider stress relief in the process plan, avoid clamping deformation in the clamping method, and strengthen the rigidity of the workpiece.


a)Three-dimensional data model

b)Two-dimensional data model
Figure 1: Drum-shaped thin-walled aluminum alloy shell

3 Processing plan determined

3.1 Develop a CNC machining technology plan

The specific processing plan [3] formulated is as follows.​

1) Processing is divided into three stages: roughing, semi-finishing and finishing. In the rough machining stage, most of the margin is removed while ensuring that the shell has sufficient strength; in the semi-finishing stage, the flanges at both ends and the inner shape are basically formed with a small margin, and the end holes are processed; the finishing process is divided into The key parts are processed in two steps, the first step is to process the flanges at both ends and the inner shape to the process size, and the second step is to process the entire outer shape to the process size.

2) Arrange stress relief and aging treatment after rough machining, semi-finishing and before finishing to remove the internal stress generated during part processing and reduce stress deformation to ensure dimensional and geometric accuracy.

3.2 Fixture design

The design of the fixture is the focus of the processing of this part. In order to ensure the dimensional and geometric requirements of the part and enhance the rigidity of the part, the fixture must have the functions of clamping, positioning and supporting at the same time. The designed fixture is shown in Figure 2. The fixture includes a cylinder ( The inner diameter is 210mm), A support plate, B support plate, adjustable support column, rubber protective cap, open wedge ring, compression nut and other components [4,5]. One end of the cylinder is provided with a clamping end, the middle cylindrical array has cross-set threaded holes, and the other end is provided with sliding parts and threads; the inner stop of the A support plate matches the clamping end of the cylinder with a small gap and is fixed with screws; Install the locking nut on the adjustable support column and place it together in the threaded hole on the middle cylinder of the cylinder. Put the rubber protective cap into the other end of the adjustable support column; the inner tapered hole of the B support plate and the outer end of the open wedge ring The cone surface fits and is inserted into the sliding part of the cylinder at the same time; a station for clamping parts is formed between the A support plate and the B support plate; the compression nut is placed on the thread of the cylinder and the open wedge ring is pressed to wedge it It is inserted between the B support plate and the sliding part of the cylinder, so that the B support plate and the sliding part of the cylinder are closely connected; the rubber protective cap can not only play a supporting role, but also play a role in reducing vibration and protecting the surface of the workpiece.

Figure 2 Fixture
1. 3—M12 screws 2—A support plate 4—cylinder body 5—rubber protective cap 6—adjustable support column
7—B support plate 8—M6 screw 9—Split wedge ring 10—Compression nut

4 Specific implementation methods

1) First rough machine the workpiece blank to ensure that the shape is similar to the part, leaving a 3mm margin for each size, and the wall thickness after processing is 8mm.

2) Perform an aging heat treatment to fully release the internal stress of the workpiece.

3) Semi-finishing, the flanges at both ends and the inner shape are basically formed with a 1mm margin, and the end holes are processed.

4) Perform another aging heat treatment to fully release the internal stress of the workpiece.

5) Finish the inner shape and both ends of the workpiece to the process size requirements. The wall thickness of the workpiece is 5mm when the processing is completed.

6) Use the designed tooling fixture to process the entire shape of the part. First, install the part on the fixture, as shown in Figure 3. Insert the A support plate into the cylinder so that its inner stop is clamped with the end of the cylinder. Match and fix with M12 screws (see Figure 4 for the connection between the pressure plate at the left end of the fixture and the workpiece). Install a locking nut on the adjustable support column and place it in the threaded hole on the middle cylinder of the barrel. In the initial state, all the adjustable support columns must be retracted. The inner cavity of the cylinder ensures that the workpiece can be loaded smoothly. Put the rubber protective cap into the other end of the adjustable support column. Load the workpiece from the right end of the cylinder so that the flange surface stop at the small end is in line with the stop on the A support plate. Fit and connect through M6 screws 3; install the B support plate from the right end of the cylinder, so that the stop on the B support plate matches the stop on the big end flange of the part.Connect through M6 screws 10 and install the split wedge ring so that the outer conical surface of the split wedge ring contacts the inner taper hole of the B support plate. Install the compression nut to compress the split wedge ring so that the split wedge ring is wedged into the B support plate. and the cylinder, ensure that the B support plate is tightly connected to the sliding part of the cylinder (see Figure 5 for the connection between the pressure plate at the right end of the fixture and the workpiece), and adjust the adjustable support column from the inner cavity of the cylinder (insert the cylindrical wrench into the hole of the adjustable support column (Turn clockwise), adjust the adjustable support columns one by one from the inside to the outside until the rubber protective cap is against the inner wall of the workpiece. The tightening force should be uniform and reliable. It is necessary to ensure that the rubber protective cap has support for the inner wall of the workpiece. And the workpiece cannot be deformed (if you cannot control the strength well, you can observe the pressure gauge when adjusting the support column). After the adjustable support column is adjusted, lock it with a lock nut. Install the left end of the fixture with the workpiece on the machine tool chuck, and the machine tool tailstock top plate against the right end of the fixture, and process the part to the final size.

Figure 3: Parts mounted on fixture
1—Cylinder 2—A support plate 3. 10—M6 screws 4—M12 screws 5—Workpiece 6—Rubber protective cap
7—Adjustable support column 8—Locking nut 9—B support plate 11—Open wedge ring 12—Compression nut

Figure 4: Connection between the pressure plate at the left end of the fixture and the workpiece

Figure 5: Connection between the pressure plate at the right end of the fixture and the workpiece

5 Conclusion

This article introduces a thin-walled aluminum alloy shell processing scheme based on specific processing examples, focusing on a tooling fixture design method that can simultaneously achieve clamping, positioning and supporting functions, which perfectly solves the problem of vibration and vibration during part processing. To solve the problem of deformation, this processing plan ensures the size, shape, surface and other process requirements of the processed parts. It has strong operability and guidance. It also provides solutions and processing experience for the processing of similar parts.