Precision processing technology for elastic sheet parts

1 Introduction

Many easy-to-deform elastic sheet parts are encountered in production, such as common washers, friction plates, disc springs, thin plates, flying sheets, etc., which are poor in rigidity, difficult to dissipate heat, and tend to cause deformation during clamping, which may occur during processing. The music seriously affects the machining accuracy of the parts. The heat treatment technology of such parts and the precision clamping technology during processing are studied to reduce the heat treatment deformation and clamping deformation of the workpiece, and reduce the influence of the deformed workpiece on the final precision of the parts, so as to ensure the processing precision of the elastic sheet parts. Crucial significance.

In the production, most of the easily deformable elastic sheet parts were in-situ inspection, and found that the machining accuracy can fully meet the design requirements, but after taking off, it was found that the size and shape tolerances changed greatly, and some even exceeded Design license range. The reason is that the rigidity of the easily deformable elastic sheet part is weak, and the precision of the workpiece reference surface is not high, the flatness is poor, and the workpiece is attracted by the atmospheric pressure or is pressed by the pressing force. The workpiece is deformed and deformed in the deformed state. Although the size and shape tolerance of the workpiece are found to meet the design requirements, the workpiece deformation is restored after the removal, and the dimensional and geometric tolerances of the workpiece change greatly. So that it exceeds the design requirements.

When inspecting another part of the easily deformable elastic sheet part, it is found that the size and shape tolerance of the workpiece are far from the normal machining accuracy of the machine. This is because the cutting force causes the workpiece to deform when the workpiece is cut, and the deformed part after the cutting edge leaves. Recovery caused.

Therefore, improving the precision of the parts before finishing and reducing the deformation of the parts and reducing the cutting force are important measures to improve the machining accuracy of the easily deformable elastic sheet parts.

2 Technical approach to improve the processing accuracy of elastic sheet parts

2.1 Reduce heat treatment deformation and improve the dimensional accuracy of the workpiece before finishing

For workpieces with high mechanical properties, heat treatment is generally required to improve the overall mechanical properties of the workpiece. However, due to the expansion of the austenite when it is transformed into martensite during quenching, a large amount of structural stress is generated, and the thermal stress caused by the rapid cooling forms a large internal stress, which causes deformation and even cracking when the workpiece is quenched. For the easily deformable elastic sheet parts, the deformation is greater due to the weaker stiffness. To improve the machining accuracy of parts, heat treatment deformation must be reduced.

Design to reduce heat treatment deformation

Design heat treatment type tooling

When designing the part, it should be closely combined with the process, pay attention to the limitation of the process conditions, and reduce the heat treatment deformation from the part structure as much as possible.

When selecting parts, the material should be selected with steel with high carbon content or high alloying elements, because the higher the carbon content and the higher the alloying element, the lower the final temperature of austenite transformation to martensite. The more retained austenite after quenching, the smaller the tissue stress during quenching, and the smaller the deformation. And the alloy steel has good hardenability, generally adopts oil quenching, the workpiece is cooled in oil, the cooling speed is slow, and the thermal stress is relatively small, so the deformation cracking tendency is small.

When designing the workpiece, if there is no other influence, increase the end flange as much as possible to increase the rigidity of the part.

After the workpiece is quenched, it must be tempered immediately, that is, the quenched parts are reheated to a critical temperature lower than the austenite transformation, and after being kept for a while, cooled to room temperature. Design the school-type tooling, put the quenched workpiece into the calibration tooling and fix it in the shape, and then put it into the furnace to temper and shape it together with the workpiece, which can correct the deformation of the workpiece after quenching. It has been confirmed by experiments that the elastic profile parts with outer diameter of Ø350mm and thickness of 3mm are used in the heat treatment, and the deformation amount is 0.20mm. If the calibration tool is not used, the deformation will be more than 1mm.

2.2 Selection of clamping methods

When finishing parts, the clamping method should be considered, and the parts should be in the same state as the free state when they are in the processing state, that is, the clamping deformation should be avoided or reduced, and the clamping or clamping, topping, pressing, etc. should not be used as much as possible. form.

Pad elastic block clamping method

Three-point clamping

Workpiece bonding positioning method

The elastic clamping mechanism is used to position and clamp the parts in a free state. A layer of 0.5mm rubber with a uniform thickness is placed between the workpiece and the tool positioning surface. When the workpiece is subjected to the clamping force, the rubber is first compressed, and the elastic deformation of the workpiece is small, so that a high-precision profile can be processed. The deformation is small after loosening. This method is suitable for benchmarking with high precision requirements.

The workpiece is positioned and clamped with three points. When the workpiece is subjected to the clamping force, since the surface of the workpiece is not subjected to force, the clamping deformation will not occur, and the deformation after the workpiece is removed is small. If there is a gap between the support block and the workpiece, it should be filled and rubber if necessary. In the actual production, if the workpiece is large in size and thin in the wall, the workpiece is deformed by the cutting force when the three-point positioning is performed, and the auxiliary support can be added to solve the problem.

The workpiece is adhered to the positioning plate with an adhesive in a free state. Since the adhesive has fluidity before uncured, it can fill the gap between the workpiece and the positioning plate. When the adhesive is cured, the workpiece is bonded to the positioning plate. As a whole, it not only positions the workpiece, but also greatly enhances the rigidity of the workpiece.

For elastic sheet parts, the surface opposite to the machined surface cannot be used as the bonding surface, because most of the adhesive shrinks when solidified, and uneven shrinkage causes the workpiece to deform. Therefore, for the elastic sheet parts, the outer surface of the workpiece or the inner hole should be selected.

When selecting an adhesive, it is preferable to use a rubber type which has strong adhesion, fast curing time, and easy gel removal. Cyanoacrylate glue is a kind of glue with fast curing time (which can be processed in only 3 to 5 minutes), easy to remove glue (soaked in hot water or acetone), and strong adhesion. The use of this glue processing test, the results are satisfactory, but the use of acetone for a long time to remove the glue, affecting the processing efficiency.

Adhesives used in the bonding method should be as small as possible, so the bonding tool must be designed with a limit stop to reduce the positioning load of the adhesive. At the same time, considering that the acetone soaking time is long when the glue is removed, several holes can be designed in the relative position of the adhesive on the tooling, and the workpiece is removed by mechanically tapping the vibration through the hole. It has been confirmed by experiments that as long as the method is correct, the workpiece is hardly deformed by mechanically tapping the vibration, but the exposed adhesive should be removed with acetone before taking the workpiece.

The bonding positioning method is used for the processing test. The workpiece is Ø350×3 elastic sheet, the material is 60Si2MnA, and its positioning, the flatness of the two sides after processing can reach 0.02-0.03mm, and the parallelism can reach 0.03~0.05mm. If the large plane bonding is used, the flatness after processing will be greater than 0.20 mm.

2.3 Tool selection

Reducing the external force acting directly on the workpiece is an effective measure to reduce the deformation of the workpiece and improve the machining accuracy. Increasing the primary and secondary declination of the tool can reduce the effect of the cutting force on the normal direction of the workpiece surface, thereby effectively reducing the deformation of the workpiece.

Experiments have shown that the blade sharpness is different and the cutting force is significantly different. When the depth of cut is small, the difference is more pronounced. When the depth of cut is small enough, the unit cutting force increases sharply. This is because the cutting depth and the feed amount are small during ultra-precision cutting, and the difference in the cutting edge radius r will significantly affect the deformation. An increase in the r value will significantly increase the cutting deformation. When the depth of cut is small, the cutting deformation caused by the radius of the cutting edge accounts for a large proportion of the total deformation, and a small change in the value of r will cause a large change in the cutting deformation. Therefore, when the cutting depth is small, the cutting tool with a smaller r value should be used. #p#分页头#e#

3 Conclusion

The reason why the processing precision of the elastic sheet parts is difficult to guarantee is mainly because the deformation of the workpiece after heat treatment is large, and the workpiece is deformed under the action of the clamping force during processing. The deformation and recovery of the workpiece after processing cause a large change in the dimensional and geometrical tolerances. . The direct effect of the cutting force is also an important cause of the deformation of the workpiece. To improve the machining accuracy, the technical way is to reduce the heat treatment deformation of the workpiece. When finishing the workpiece, it is necessary to fix and clamp the workpiece in a free state to reduce the deformation of the clamping, and use sharp tools as much as possible.