Tips for CNC turning thin-walled parts
During the cutting process, the thin wall is subjected to the cutting force and is prone to deformation, resulting in an ellipse or a small "waist" phenomenon in the middle. In addition, the thin-walled casing is prone to thermal deformation due to poor heat dissipation during processing, and it is difficult to ensure the processing quality of the parts. The parts in the figure below are not only inconvenient to set up, but also the processing parts are difficult to process. It is necessary to design a special thin-walled casing and shaft.
First, process analysis
According to the technical requirements provided by the drawings, the workpiece is machined with seamless steel tubes. The surface roughness of the inner and outer walls is Ra1.6μm, which can be achieved by turning, but the cylindricity of the inner hole is 0.03mm, which is required for thin-walled parts. Higher. In mass production, the process route is roughly as follows: blanking - heat treatment - car end face - outer circle - interior hole - quality inspection.
The “inner hole machining” process is the key to quality control. We can't guarantee a 0.03mm cylinder by cutting the outer hole and thin-walled casing.
Second, the key technology of the car hole
The key technology of the hole is to solve the rigidity and chip removal problem of the hole cutter. Increase the rigidity of the hole turning tool and take the following measures:
1.Try to increase the cross-sectional area of the shank. Usually, the tip of the boring tool is located above the shank, so that the cross-sectional area of the shank is less, and it is less than 1/4 of the cross-sectional area of the hole, as shown in the left figure below. If the tip of the hole cutter is located on the center line of the shank, the cross-sectional area of the shank in the hole can be greatly increased, as shown in the right figure below.
2.The length of the shank can be 5-8mm longer than the length of the workpiece to increase the rigidity of the shank and reduce the vibration during the cutting process.
Third, solve the problem of chip removal
The main control of the cutting outflow direction, the roughing tool requires the chip to flow to the surface to be machined (front chipping), for which the inner hole turning tool with the positive edge inclination is used, as shown in the following figure.
When finishing the car, the chip is required to flow toward the center of the centripet (chip hole chip removal), so pay attention to the grinding direction of the cutting edge when grinding the knife, and the method of chip removal for the forward arc, as shown in the following figure Knife alloy uses YA6, the current M type, its bending strength, wear resistance, impact toughness and anti-stick and temperature with steel are better.
When sharpening, the front angle grinds a circle with an arc angle of 10-15°, the back angle is 0.5-0.8mm from the machining arc according to the machining arc (the lower curve of the tool bottom line), and the cutting edge angle k of the c is §0.5-1. The cutting edge of the chip B point is R1-1.5, the secondary back angle is ground to 7-8°, and the AA point of the E inner edge is ground into a circular outward chip.
Fourth, processing methods
1. A shaft must be made before processing. The main purpose of the shaft protection is to cover the inner hole of the thin wall sleeve of the car in the original size, and fix it with the front and rear tip to make it process the outer circle without deformation, and maintain the quality and precision of the outer circle. Want to learn UG CNC programming, in the 373600976 group can help you, so the processing of the shaft is the key to the process of processing thin-walled casing.
45# carbon structure round steel for processing the shaft blank; the end face of the car, open the B-type top hole at both ends, the outer circle of the rough car, leaving a margin of 1mm. After heat treatment, quenching and tempering, and refining the car to leave a 0.2mm remaining amount. Reheat the surface of the broken fire, the hardness is HRC50, and then grind into the following figure through the external grinding machine. The accuracy is up to the requirement and will be used after completion.
2. In order to enable the workpiece to be processed in one time, the blank is left in place and cut off.
3. The hair embryo is first heat-treated and shaped, and the hardness is HRC28-30 (hardness of the processable range).
4. The turning tool adopts C620. Firstly, the front tip is placed in the spindle cone position. To prevent deformation of the workpiece when the thin wall sleeve is clamped, add an open-loop thick sleeve, as shown in the figure below.
In order to maintain mass production, one end of the outer circumference of the thin-walled casing is machined to a uniform size d, the ruler of the t-axis is the axial clamping position, and the thin-walled casing is pressed tightly to improve the quality of the inner hole of the vehicle and maintain the size. Considering the heat generated by the cutting, the expansion dimension of the workpiece is difficult to grasp. It is necessary to cast sufficient cutting fluid to reduce the thermal deformation of the workpiece.
5. Use the automatic centering three-jaw chuck to clamp the workpiece, the end face of the car, and the inner circle of the rough car. The remaining amount is 0.1-0.2mm, and the precision turning tool is used to process the cutting allowance to the full complement and roughness of the shaft. Remove the inner hole turning tool, insert the retaining shaft to the front tip, clamp with the tip of the tailstock according to the length requirement, change the outer circle of the outer turning tool roughing, and then refine the car to meet the drawing requirements. After passing the inspection, cut it with the cutting knife according to the required length. In order to make the cutting of the workpiece smooth, the cutting edge should be inclined to make the end surface of the workpiece flat; the small part of the shaft is ground to cut off the gap, and the shaft is designed to reduce the deformation of the workpiece, prevent vibration, and cut off. Dropped the cause of the injury.
The above method processes the thin-walled casing, solves the problem of deformation or dimensional error and shape error, and fails to meet the requirements. The practice proves that the processing efficiency is high, the operation is easy, and it is suitable for processing long thin-walled parts, and the size is easy to grasp. Sub-finished, mass production is also more practical.