Process analysis and CNC machining of eccentric sleeves (2)

2. CNC machining

(1) Selection of processing origin and setting of zero offset

The principle of selection of the machining origin should be: easy to find in the workpiece; it is conducive to simplify the programming; when processing symmetrical graphics, the symmetry center of the symmetrical graphic should be selected as much as possible. According to this principle, the machining origin of the eccentric sleeve is selected at the symmetrical center of the 5.5 mm wide groove. Since there are many tools used, a plurality of zero offsets are set for the convenience of processing.

(2) Selection of tools for CNC machining

In the selection of tools for CNC machining, many people think that CNC machining must use CNC tools, coated blades, etc., in fact, it is not entirely possible, you can also choose high-speed steel, carbide tools. Although the cutting speed of CNC tools is very high and has high processing efficiency, it only has obvious advantages in mass production, and it seems that the processing cost is high in small batch or single piece production. Therefore, when selecting a tool, the tool to be used should be selected according to the existing production cycle, production conditions, and number of parts. The eccentric sleeve is small in size and small in quantity, and only requires its processing precision, shape consistency and interchangeability between parts. The material of the eccentric sleeve is 45 steel, so the tool of high speed steel can be selected. The milling method during machining has a great influence on the surface roughness of the tool and the workpiece. There are two types of milling: up-cut and down-cut. When the direction of rotation of the milling cutter is opposite to the direction of feed of the workpiece, it is called up milling, and the same is called down milling. In the case of up-cut milling, the cutting thickness gradually increases from zero. The edge of the milling cutter has a blunt radius Rn, which causes the rake angle to be negative when starting the cutting. The teeth are pressed and slid on the transition surface, which causes a severe chill layer on the surface of the workpiece and exacerbates the tooth wear. In addition, when the instantaneous contact angle is greater than a certain value, fn is upward, there is a tendency to lift the workpiece; when milling, the cutting thickness of the cutter starts from the maximum, avoiding the phenomenon of extrusion and sliding, and fn is always pressed against the table, Conducive to workpiece clamping, can improve the life of the milling cutter. If there is a gap between the screw and the nut pair, the feed force will gradually increase. When the friction of the table exceeds the friction of the table, the table will drive the screw to the left, causing uneven feeding. The milling cutter is chipped. During the up-cut milling, due to the feed force, the screw and the nut transmission surface are always tightly attached, so the milling process is smooth and the surface quality is high. Up-cut milling is often used during machining. The number of revolutions of the tool and its feed should be calculated or given at the same time as the tool is selected. According to the formula:

Usually, fz should be selected according to the specific processing conditions and then vf should be calculated. The machine should be adjusted according to vf. Therefore, according to the processing flow and the existing production status, the tools are selected as follows:

(3) Preparation of CNC machining program

The difficulty and focus of the eccentric sleeve NC machining program is the programming of the 3×M5 threaded bottom hole and the three 5.5mm long grooves. The eccentric sleeve CNC machining program is manually programmed. The principle of manual programming is to simplify the calculation as much as possible and to simplify the length of the program. Because the process is long and the shape is complicated, the eccentric sleeve is relatively long. However, according to this principle, some programming techniques, including drilling cycles, programmable rotation, subroutines, and subroutine calls, are used in the compilation process to make the program simple and clear.

1 tool compensation

The radius compensation of the tool must be used when machining due to complex shapes and dimensional accuracy requirements. In the machining of the eccentric bushing, the tool radius is set to the right compensation G42 due to the use of up-cut M03.

2 tips in the eccentric program

Drilling cycle, programmable rotation, subroutine, subroutine call. Drilling cycle: In the processing of the eccentric sleeve, there are 3 M5 threads to be made into holes, and 3 holes are on the same circumference. Continuous drilling must be performed. Therefore, the modal drilling cycle MCALLCYCLE81 ​​(RTP, RFP, SDIS, DP, DPR) and hole position HOLES2 (0, 0, 39.5, 0, 120, 3). The MCALL cancels the modal drilling cycle after the modal drilling cycle is called. Mill the center hole N170 ~ N270, and then drill N280 ~ N400. The specific procedures are as follows:

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