1. Graphic theory analysis
Special-shaped parts can be controlled by CNC machine tools to better control the dimensional accuracy and improve the processing efficiency.
The head of the titanium alloy spherical shell is a special-shaped part with a wall thickness of 0.8mm. The base material is a solid titanium rod with a diameter of 54mm and a length of 65mm. It is required to process one part 1 and one part 2. Although the shape is simple, there is no clamping position, the wall Thin, high precision requirements, and quality requirements after processing, the quality of a single piece is (19 ± 1.5) g, the material has high hardness, good elasticity, and the chip is difficult to fall off, which is a part that is difficult to process.
Second, the design of clamping mold
Because the part blank has no clamping position, we must first solve the clamping problem. Without damaging parts, increase the clamping force as much as possible to ensure safe and reliable processing.
According to the shape of the parts shown in the drawings, three supporting clamping molds were designed and manufactured: the first set solved the processing problem of the surface of the inner hole ball, and the outer surface of the non-through hole spherical shell was processed and formed, and then loaded into the clamping mold In the middle, the mold is fixed with threaded connection and clamps the workpiece for inner spherical surface processing. The second set is a through-hole ball shell processing and clamping mold. First, the inner spherical surface is processed, and then the parts with the inner hole are placed in the second set of clamping molds to fix and clamp, and then the outer surface is cut. The third set is to solve the problem of mass production. After inserting the blank into the fixture, the non-through-hole spherical shell is processed, and there is no need to find the correct tool; processing the inner surface of the through-hole spherical shell is also the second set of blank pieces. After the fixture is processed, there is no need to find the correct tool, which greatly improves the processing efficiency and ensures the processing accuracy.
- 1. Making jig 1
The material of the fixture 1 is 45 round steel, turned to φ60mm, one end is processed into fine-thread external threads of M60 × 1.5mm, the thread length is 19.5mm, the front end of the thread is left 3.5mm smooth, and the diameter is φ58.4mm, which is convenient for clamping and Fixture 1-2 cooperates to clamp the spherical shell without holes.
Machining the inner circle of the fixture (fixture 1-1) according to the external dimensions of the spherical shell parts SR26mm of the pattern, the surface roughness value Ra = 3.2μm.
Fixture 1-2 is a clamping nut, one end is made with a hole of φ51.4mm, and the length is 6mm; the other end is made of M60 × 1.5mm fine tooth internal thread, the length is 20mm, and the width of the relief slot is 2mm. - 2. Manufacture of jig 2
The material of the fixture 2 is 45 round steel, and the diameter is 51.4mm. The outer circle of the fixture is processed according to the inner diameter of the through-hole spherical shell parts. The front end is left 56mm to be processed into a cylinder of 12mm. (Jig 2-1).
Turning the round sleeve with outer diameter φ13.6mm, inner hole φ12mm and length 23mm (fixture 2-2). - 3. Manufacture of jig 3
Turning step opening sleeves for easy clamping of parts and positioning during batch processing.
3. Process analysis
The solution to the clamping problem enables all the processing contents of the parts to be carried out on the CNC lathe.
Special-shaped parts are difficult to process on ordinary horizontal lathes, and are easy to realize on CNC lathes. A few kinds of tools can be used to complete the processing of a series of process contents, which is conducive to program design and control of dimensional accuracy.
Because there is a special fixture as a positioning reference, the positioning problem has been considered in the design fixture.
4. the choice of processing methods
According to the different characteristics of the internal and external surface dimensional accuracy and surface roughness requirements of the parts, different processing methods are formulated for the internal and external surfaces. When machining the inner surface of the workpiece, accurate tool setting is required, and tool compensation is used to prevent over-cutting, which causes uneven wall thickness; the surface roughness of the outer surface requires high, and finishing is required during processing; the end surface processing only needs to remove the flat end surface. can.
5. Determination of processing plan
The blank is a blank connected with a closed hemispherical shell and a through-hole spherical shell. The outer surface of the closed hemispherical shell is processed first, then cut, and then clamped in the first set of fixtures for inner surface processing; while the through-hole hemispherical shell Processing is to process the inner surface first, and then clamp it in the second set of fixtures to process the outer surface.
6. Arrangement of processing order of closed spherical shell
The outer surface of the blank clamping processing:
① Put the blank into the fixture 3, and clamp it on the lathe chuck, the rough SR26mm outer spherical surface. ②Rough car inclined ladder type boss. ③ Rough car φ53mm outer round surface. ④ SR26mm outer spherical surface of fine car. ⑤Fine car inclined ladder type boss. ⑥ Fine car φ53mm outer round surface. ⑦Cut off (as far as the cutting knife allows). ⑧ Take off and cut with a sawing machine.
Seven. Processing inner surface
Processed inner surface:
① Place the non-through hole parts into the jig 1 to drill accurately. First drill a φ12mm hole, the drilling depth is 25mm, and then expand the hole to reduce the amount of cutting and improve the processing efficiency. ② Clamp the fixture 1-1 to the lathe chuck and use a dial indicator to correct it. ③ Put the parts with no through holes into the jig 1-1 and tighten with the jig 2-1. ④In order to prevent tool interference, the rough stepped φ51.4mm inner step surface, the rough shaped special-shaped inner hole to the hemisphere depth 18mm. ⑤ Use the macro program to drive the top of the hemisphere. ⑥Inner stepped surface of fine car φ51.4mm. ⑦Inner hole surface of SR25.2mm.
8. Process arrangement for processing through-hole hemispherical shell
First clamping processing of inner hole surface:
① Put the blank of the part 2 into the fixture 3, and clamp it on the lathe chuck, and drill a φ12mm through hole. ②Ream the hole with a φ20mm drill bit first, then use a φ30mm drill bit to ream the hole, the hole depth is 25mm. ③Turning the end face to ensure that the end face is smooth and the length meets the drawing requirements. ④Rough car φ51.4mm inner step surface. ⑤Rough car SR25.2mm inner hole surface. ⑥Inner stepped surface of fine car φ51.4mm. ⑦Inner hole surface of SR25.2mm.
Second clamping process of outer surface of through-hole spherical shell:
① Clamp the fixture 2-1 to the lathe chuck and use a dial indicator to correct it. ② Put the through-hole parts of the inner hole surface of the first clamping process into the fixture 2-1, then put the fixture 2-2, and tighten with the nut. ③Rough car φ13.6mm outer surface. ④ The outer surface of rough car SR26mm. ⑤Chamfer of rough car ladder. ⑥ Rough car φ53mm outer round surface. ⑦Fine car φ13.6mm outer surface. ⑧External surface of fine car SR26mm. ⑨Chamfering of fine car ladder. ⑩Fine car φ53mm outer surface. ? Deburring the end face.
Nine, tool and machine tool selection
Special fixtures are used as clamping fixtures when parts are processed. The relative position of the origin of the part and the machine coordinate system has been determined when the first part is tooled. The origin of the program is used as the origin of the workpiece. The part belongs to a short part, so the workpiece is used The coordinate system (100, 100) is used as the tool change point, saving machining time.
1. Determination of tool path
Through-hole hemispherical shell adopts G71 longitudinal cutter when processing the outer surface. When machining the inner surface of the parts, the bore diameter of the boring tool holder and the radius of gyration are considered, and G72 horizontal cutter is adopted; when closing the hemispherical shell, the outer surface is processed using G71 longitudinal Tooling, when machining the inner surface of the part, adopt the combination of G72 horizontal tooling and macro program. When the turning tool approaches the ball top, it will interfere with the workpiece. It is necessary to program a macro program for processing to avoid tool interference. Then use G03 arc Walking knife to ensure smooth surface without connection marks.
2. Tool selection
Through comprehensive analysis of the dimensional accuracy and material of the part pattern, the CNC machine tool is used for cutting, the outer surface uses a 90 ° outer circular turning tool, the drilling uses tungsten, titanium, tantalum (niobium) alloy drill bits, and the inner hole surface processing is used The inner hole boring tool with 8 mm diameter and 107.5 ° tool tip angle is offset by 3 ° to 5 ° toward the spindle during installation to avoid tool interference as much as possible. The inserts are all carbide tips in the M series.
3. Mathematical processing in CNC programming
The nodes involved in writing the program are searched by CAD software drawing. The final tool pass of the macro program is the relative difference between the starting point of the macro program in the X direction and the part diameter.
The starting point of the last knife of the macro program in the X direction is φ35.27mm, the diameter of the part is 50.36mm, 50.36-35.27 = 15.09mm, because the finishing process leaves 0.3mm in the X direction and 0.2mm in the Z direction, the macro program independent variable control The value is -25mm (25.2mm-0.2mm), and the X-direction difference is 14.49mm (15.09mm-0.6mm).
Inspection and adjustment
Measuring the wall thickness with a modified micrometer and measuring the wall thickness with the modified height vernier caliper. The wall thickness is required to be uniform.
Weigh the mass of the part with a balance, the mass is (19 ± 1.5) g, if it is overweight, it should be put back into the fixture and reprocessed.
