Frontier CNC
In the cutting process, the thin wall by the cutting force, easy to produce deformation, resulting in oval or small in the middle, the two ends of the "waist-shaped" phenomenon. In addition, thin-walled casing due to poor heat dissipation during processing, very easy to produce thermal deformation, it is not easy to ensure the quality of parts processing. The following parts are not only inconvenient to clamp, but also difficult to process parts, so it is necessary to design a special thin-walled sleeve and guard shaft.
Process analysis
According to the technical requirements provided in the drawing, the workpiece is processed by seamless steel pipe, and 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, which is a high requirement for thin-walled parts. In mass production, the process route is roughly as follows: material - heat treatment - turning end face - turning external circle - turning internal hole - quality inspection.
The "bore machining" process is the key to quality control. We put aside the outer circle, thin-walled casing on the inner hole cutting is difficult to ensure that 0.03mm of the cylinder.
Key technology of turning holes
The key technology of turning holes is to solve the problem of rigidity and chip removal of the internal hole turning tool. Increase the rigidity of the internal hole turning tool, take the following measures.
(1) Try to increase the cross-sectional area of the tool shank, usually the tip of the internal hole turning tool is located on the top of the tool shank, so that the cross-sectional area of the tool shank is less than 1/4 of the cross-sectional area of the hole, as shown in the figure on the left below. If the tip of the internal hole turning tool is located on the center line of the shank, then the cross-sectional area of the shank in the hole can be greatly increased as follows
(2) The shank extension length can be 5-8mm longer than the workpiece length to increase the rigidity of the shank and reduce the vibration in the cutting process.
Solve the problem of chip removal
Mainly control the direction of cutting outflow, coarse turning tool requires chip flow to the surface to be machined (front chip discharge), for this reason, use the positive edge inclination of the bore turning tool, as shown in the figure below.
When fine turning, the chip flow is required to centerward tilting front chip discharge (hole center chip discharge), so when grinding the tool, pay attention to the grinding direction of the cutting edge, to the front tilting arc chip discharge method, as shown in the figure below Fine turning tool alloy with YA6, the current M type, its bending strength, wear resistance, impact toughness and anti-adhesion and temperature with steel are better.
When sharpening the front angle grinding to round to arc-like angle 10-15 °, the rear angle according to the processing of the arc from the wall 0.5-0.8mm (tool bottom line along the arc), c cutting edge angle k to § 0.5-1 for along the chip edge B point trimmed edge for R1-1.5, vice rear angle grinding into 7-8 ° for the appropriate, E inner edge of the A-A point grinding into the round outward chip evacuation.
Machining method
(1) Before processing, you must do a shaft guard. The main purpose of the shaft guard: to turn the thin-walled sleeve of the inner hole to the original size of the set, with the front and rear of the top fixed so that it is not deformed in the case of processing the outer circle, to maintain the quality and accuracy of the outer circle processing. Therefore, the processing of the shaft guard is the key link to the process of processing thin-walled casing
The processing of guard shaft embryo with 45 ﹟ carbon steel; turning end face, open two B-type top hole, rough turning outer circle, leaving a margin of 1mm. by heat treatment tempering shape, and then fine turning leaving a margin of 0.2mm grinding. Re-heat treatment crushed fire surface, hardness HRC50, and then by cylindrical grinding machine into the following figure, the accuracy to meet the requirements, after completion to be used.
(2) In order to make the workpiece finished at one time, the embryo left clamping position and cut off allowance.
(3) First, the embryo is heat-treated and tempered to a hardness of HRC28-30 (the hardness of the machinable range).
(4) Turning tool using C620, first put the front center into the spindle taper position fixed, in order to prevent the workpiece deformation when clamping thin-walled sleeve, add an open ring thick sleeve, as shown in the figure below.
In order to maintain mass production, one end of the outer circle of the thin-walled sleeve is machined to a uniform size d, t the ruler is axial clamping position, a thin-walled sleeve pressed to improve the quality of the inner hole when turning, to maintain the size. Considering that there is cutting heat generated, the workpiece expansion size is difficult to grasp. Need to pour sufficient cutting fluid to reduce the thermal deformation of the workpiece.
(5) Clamp the workpiece firmly with auto-centering three-jaw chuck, turn the end face and rough turn the inner circle. Leave a margin of 0.1-0.2mm finish turning, replace the finish turning tool to cut the margin of processing to the guard shaft full over fit and roughness requirements. Remove the bore turning tool, insert the guard shaft to the front top, clamp with the tailstock top according to the length requirement, change the external turning tool to rough turn the external circle, and then finish turning to the drawing requirements. After passing the inspection, use the cutting tool to cut off the workpiece according to the required length. In order to make the workpiece disconnected when the cut is flat, the knife edge to be beveled grinding, so that the workpiece end face flat; guard shaft grinding small section is to cut off to leave a gap and grinding small, guard shaft to reduce the deformation of the workpiece, to prevent vibration, as well as cut off when falling touch the original cause.