Thin-walled workpieces are special workpieces, and there are certain differences between the turning process and the general workpiece turning. When turning thin-walled workpieces, due to the poor rigidity of thin-walled workpieces, some problems may arise in the process of turning. Below, we will introduce the turning process of thin-walled workpieces so that everyone can understand some problems when turning thin-walled workpieces.
Machining characteristics of 1. thin-walled workpieces
1. Due to the thin wall of the workpiece, it is easy to deform under the action of clamping force. Thus affecting the dimensional accuracy and shape accuracy of the workpiece. Under the action of the clamping force, it will slightly become a three-sided shape, but what is obtained after the car control is a cylindrical hole. When the claw is released and the workpiece is removed, the outer circle returns to a cylindrical shape due to elastic recovery, while the inner hole becomes an arc-shaped three-sided shape. If the diameter is equal in all directions when measured with an inner micrometer, but the deformation is not the inner cylindrical surface, it is called equal diameter deformation.
2, because the workpiece is thin, cutting heat will cause thermal deformation of the workpiece, so that the workpiece size is difficult to control. For metal thin-walled workpieces with large linear expansion coefficient, if semi-finishing turning and finishing turning are continuously completed in one installation, the thermal deformation of the workpiece caused by cutting heat will greatly affect its dimensional accuracy, and sometimes even make the workpiece stuck on the fixture.
3. Under the action of cutting force, especially radial cutting force, vibration and deformation are easy to occur, which affects the dimensional accuracy, shape, position accuracy and surface roughness of the workpiece.
Processing Technology of 2. Thin-walled Workpiece
1. The workpiece is divided into coarse and finishing stages
When fine turning, due to the large cutting allowance, the clamping force is slightly larger, and the deformation is correspondingly larger; when fine turning, the clamping force can be slightly smaller, on the one hand, the clamping deformation is small, on the other hand, it can also eliminate the deformation caused by excessive cutting force when rough turning.
2. Reasonable selection of set parameters of props
When finishing turning thin-walled workpieces, the rigidity of the tool handle is required to be high, and the smooth cutting edge of the turning tool is not easy to be too long. Generally, it is 0.2-0.3mm, and the cutting edge should be sharp.
3. Increase the clamping contact surface
Slit sleeve or some special soft jaw. The contact surface is increased, so that the clamping force is evenly distributed on the workpiece, so that the workpiece is not easy to produce deformation when clamping.
4. Axial clamping fixture shall be adopted
When the car thin-walled workpiece, the workpiece by the axial clamping sleeve (threaded sleeve) of the end face to achieve axial clamping, due to the clamping force along the workpiece axial distribution, and the workpiece axial stiffness, not easy to produce clamping deformation.
5. Added process ribs
Some thin-walled workpieces have several special process ribs in their clamping parts to enhance the rigidity here, so that the clamping force acts on the process ribs to reduce the deformation of the workpiece. After processing, the process ribs are removed.
6. Fully pouring cutting fluid
By fully pouring the cutting fluid, the cutting temperature is reduced and the thermal deformation of the workpiece is reduced.
Definition of 1. Drilling
Chinese name: Drilling
English name: drilling
Other name: Drilling
Definition: the drilling tool and the workpiece for relative motion and axial feed motion, in the workpiece on the processing of holes.
Drilling is one of the most basic hole processing methods. Drilling is often done on drilling machines and lathes, but also on boring and milling machines. Commonly used drilling machine has bench drilling machine, vertical drilling machine and radial drilling machine.
Features of 2. drilling:
Drilling and turning of the outer circle, the drill work is much more difficult to work locally in the working conditions of the machined surface, thus causing some special problems. For example, the stiffness and strength of the drill bit, chip holding and chip removal, guiding and cooling, moistening and relief, etc., can be summarized as follows:
1. The bit is easy to deflect
Deviation: refers to the expansion of the hole diameter, the non-round hole or the skew of the axis of the hole caused by the bending of the drill bit during processing, as shown in Figure 2-6.
Reason: Due to the inaccurate centering of the chisel edge of the drill bit, the rigidity and guiding effect of the drill bit are poor, and the drill bit is easy to offset and bend when cutting in.
2. Chip removal is difficult
The chip of drilling is wide, the size of the chip groove is limited, and the surface of the hole wall is violently rubs when it flows out, and the hole is forced to roll into a spiral shape. The chip and the hole wall have a greater friction, extrusion, pulling and scratching the surface has been processed, reducing the surface quality. Even the chips will be blocked in the chip holding groove, stuck or broken drill bit, tool wear fast.
In order to improve the chip removal conditions, a chip separation groove can be ground on the drill bit to divide the wide chips into narrow strips to facilitate chip removal. When drilling deep holes, suitable deep hole drills shall be used for machining.
3. High cutting temperature
Since drilling is a semi-closed cutting, the main cutting edge near the drill core and the chisel edge have a large negative rake angle, the heat generated during drilling is absorbed by the workpiece, a large number of high temperature chips can not be discharged in time, cutting fluid is difficult to inject into the cutting zone, cutting heat is not easy to spread. The friction between the chip, the tool and the workpiece is very large, so the cutting temperature is high, the tool wear is large, and the drilling amount and productivity are limited.
4. Low accuracy
The accuracy of drilling is low, the surface is rough, the general processing accuracy is below IT10, the surface roughness Ra value is greater than 12.5mm, and the production efficiency is also low. Therefore, drilling is mainly used for roughing or pre-machining operations.
Structure Diagram of Vertical Drilling Machine and Radial Drilling Machine
Application of 3. Drilling
In single-piece and small-batch production, small holes (D<13mm) on small and medium-sized workpieces are commonly processed by bench drilling machines, and larger holes (D<50mm) are commonly processed by vertical drilling machines;
The holes on the large and medium-sized workpieces should be processed by radial drilling machines, and the holes on the rotating workpieces should be processed on the lathe.
In batch and mass production, in order to ensure the processing accuracy, improve production efficiency and reduce processing costs, widely used drilling, multi-axis drilling or combination of machine tools for hole processing.
High precision, small roughness of small and medium diameter holes (D<50mm), after drilling, often need to use expansion and reaming for semi-finishing and finishing.