Due to the poor rigidity of large-diameter thin-walled sleeve, it is difficult to control the clamping force in grinding, which affects the machining quality. In view of this situation, several improvement schemes are adopted to ensure the machining accuracy requirements and product quality.

1. Preface

When grinding the inner and outer surfaces of the sleeve with large diameter and thin wall thickness (not more than 2mm), due to poor rigidity and difficult control of the clamping force during actual processing, the workpiece is often deformed due to excessive axial clamping force, which affects the machining accuracy or the workpiece is thrown out of the chuck due to poor clamping. To overcome these problems, the key is to control the clamping force. To this end, we can adopt the following methods to improve.

2. Internal and external surface grinding device with conical surface to adjust clamping force

Figure 1 thin wall sleeve machined parts drawing
In order to improve the grinding quality of the inner and outer surfaces of the large-diameter thin-walled sleeve as shown in Figure 1, the key is to make the workpiece well positioned during machining, so that the stress on the workpiece can be well controlled, so as to ensure that the workpiece is not deformed. Therefore, we can adjust the clamping force on the workpiece by contacting the conical surface. The device is divided into two types for grinding inner hole and outer circle, which are introduced as follows:

2.1 Cylindrical grinding fixture

The structure of the cylindrical grinding fixture is shown in Figure 2. Its main working process is as follows: mill three 2mm wide grooves in the cone part of the clamp 5 in advance. During assembly, clamp the clamp 5 on the grinder chuck 6, adjust the center, and then set the workpiece 3 on the fixture. Next, install the spring 4 and the tensioning sleeve 2 with a 1:10 conical surface on the clamping bolt 1, and install the device into the fixture with the same conical surface, and then adjust the clamping bolt to expand the clamp to clamp the workpiece firmly, which can be processed.

rawing of cylindrical grinding fixture

Figure 2 drawing of cylindrical grinding fixture
1 – screw 2 – tension sleeve 3 – workpiece 4 – spring 5 – clamp 6 – jaw
Because the fixture is clamped through expansion, the workpiece has small deformation and good positioning, so the machining accuracy is improved.

2.2 Fixture for grinding inner hole

After grinding the excircle to the size given in the drawing, locate the excircle, clamp the workpiece on the fixture as shown in Figure 3, and grind the inner hole and end face. The working principle of the fixture is as follows: firstly, mill 3 segments evenly from the specific conical part of the clamp, connect the press sleeve with 1:10 conical surface to the clamp with the same taper through threads, and adjust the press sleeve to make each segment shrink inward evenly to clamp the workpiece. Pay attention that the tightening force of the pressing sleeve should not be too large, and the workpiece cannot be taken out by hand after clamping.

fixture for grinding inner hole

Figure 3 fixture for grinding inner hole
1 – clamp details 2 – pressing sleeve 3 – workpiece
This set of fixture for grinding inner and outer circles has the characteristics of simple structure, convenient clamping and improving workpiece accuracy.

3. Use tension fixture to grind the excircle

In order to reduce the parallelism error at both ends of the workpiece, the roundness error of the hole and prevent the deformation at the action point of the clamping force, we can use the tension clamp to fix the workpiece.

Before using the device, six evenly distributed process screw holes shall be machined on both ends of the workpiece to be machined to fix the workpiece. The structure of the device is shown in Figure 4. Its working principle is as follows: firstly, the workpiece is sleeved on the main positioning plate 1 and fixed with 6 screws, then the adapter plate 2 is installed on the right end of the main positioning plate, and the adapter plate is connected with the workpiece with 6 screws, so that the workpiece can be processed when it is in tension.

drawing of tension clamp

Figure 4 drawing of tension clamp
1 – main positioning shaft 2, 5 – screw 3 – workpiece 4 – disc 6 – key
Using this method to fix the workpiece, the roundness error at both ends is reduced, and the overall and local deformation of the workpiece is avoided, so as to better ensure the quality.
Practice has proved that through the improvement of the grinding method of thin-walled sleeve, the problem of workpiece deformation caused by difficult control of clamping force in the grinding process of thin-walled sleeve is well solved, the machining quality of workpiece is improved, and the product quality and production efficiency are also improved.

Author: Chen zhaolian


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