▌ Process AnalysisAccording to the technical requirements provided by the drawings, the aluminum workpiece is processed with seamless steel pipes. The surface roughness of the inner hole and outer wall is Ra1.6μm, which can be achieved by turning, but the cylindricity of the inner hole is 0.03mm. For thin-walled parts Higher requirements. In mass production, the process route is roughly: blanking – heat treatment – car end face – car outer circle – car inner hole – quality inspection. The “inner hole machining” process is the key to quality control. It is difficult to guarantee a cylinder of 0.03mm when we cut the inner hole apart from the outer circle and thin-walled casing.
▌ The Key Technology Of Car HoleThe key technology of turning is to solve the problem of rigidity and chip removal of the inner turning tool. To increase the rigidity of the inner hole turning tool, take the following measures:
- Try to increase the cross-sectional area of the tool handle. Usually, the tip of the inner hole turning tool is located on the top of the tool handle, so that the cross-sectional area of the tool handle is less than 1/4 of the cross-sectional area of the hole, as shown in the left figure below. . If the tool tip of the inner hole turning tool is located on the center line of the tool holder, the cross-sectional area of the tool holder in the hole can be greatly increased, as shown in the right figure below.
- The extension length of the tool shank should be as long as 5-8mm as long as the length of the workpiece to be processed, so as to increase the rigidity of the turning tool shank and reduce the vibration during the cutting process.
▌ Solve The Chip Removal ProblemIt mainly controls the cutting outflow direction. The rough turning tool requires the chips to flow to the surface to be machined (front chip removal). For this purpose, an inner hole turning tool with a positive edge inclination is used, as shown in the figure below. When fine turning, it is required that the chips flow to the centripetal incline for chip removal (hole core chip removal), so when sharpening the tool, pay attention to the grinding direction of the cutting edge, and the method of chip removal by tilting the arc to the front, as shown in the following figure. The knife alloy uses YA6, the current M type, which has better bending strength, wear resistance, impact toughness, and resistance to steel and temperature. When sharpening, the rake angle is ground with a circular arc-shaped angle of 10-15°, and the back angle is 0.5-0.8mm away from the wall according to the machining arc (the bottom line of the tool is along the arc), and the c-cutting edge angle in the k direction is §0.5-1. The wiper edge at point B of the chip edge is R1-1.5, and the secondary clearance angle is ground to 7-8°.
▌ Machining Method
- A shaft guard must be done before machining. The main purpose of protecting the shaft: to cover the inner hole of the thin-walled sleeve with the original size, and fix it with the front and rear tops so that the outer circle can be processed without deformation, and the quality and accuracy of the outer circle machining can be maintained. Therefore, the machining of the shaft guard is a key link in the process of machining the thin-walled casing.45﹟ carbon structure round steel is used for aluminum cnc turning the shaft guard blank; the end face of the car, the B-shaped top hole at both ends, and the outer circle of the car is rough, leaving a margin of 1mm. After heat treatment, it is quenched and tempered, and then finished with a 0.2mm margin for grinding. The surface of the broken fire is re-heat treated, the hardness is HRC50, and then it is ground by a cylindrical grinder as shown in the figure below.
- In order to complete the machining of the aluminum workpiece at one time, the blank remains in the clamping position and cutting allowance.
- Heat treatment and tempering to set the rough embryo first, and the hardness is HRC28-30 (hardness within the machinable range).
- The turning tool adopts C620. First, put the front center into the taper position of the spindle to fix it. In order to prevent the deformation of the workpiece when the thin-walled sleeve is clamped, an open-loop thick sleeve is added. In order to maintain mass production, one end of the outer circle of the thin-walled casing is processed into a uniform size d, and the ruler of t is the axial clamping position, and each thin-walled casing is pressed to improve the quality of the inner hole of the car and maintain the size. Considering the generation of cutting heat, the expansion size of the workpiece is difficult to grasp. It is necessary to pour sufficient cutting fluid to reduce the thermal deformation of the workpiece.
- Clamp the workpiece firmly with the self-centering three-jaw chuck, turn the end face, and rough the inner circle of the turning. Leave a margin of 0.1-0.2mm for fine turning, and replace the fine turning tool to process the cutting allowance until the shaft guard meets the requirements of excessive fit and roughness. Remove the inner hole turning tool, insert the guard shaft to the front top, clamp it with the tip of the tailstock according to the length requirements, change the outer turning tool to rough turn the outer circle, and then finish the turning to meet the drawing requirements. After passing the inspection, use a cutting knife to cut it according to the required length. In order to make the incision smooth when the workpiece is disconnected, the blade edge should be obliquely ground to make the end face of the workpiece flat; the small section of the shaft guard is ground to leave a gap for cutting. The shaft guard is to reduce the deformation of the workpiece, prevent vibration, and cut Falling and bruising.
▌ ConclusionThe above method for machining thin-walled casing solves the problem of deformation or dimensional errors and shape errors that fail to meet the requirements. Practice has proved that the machining efficiency is high, easy to operate, and suitable for machining long thin-walled parts, and the size is easy to grasp. One-time completion, mass production is also more practical.
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