Based on the application of the machine tool accessory indexing head and the hanging gear on the ordinary vertical lifting table milling machine, taking the cylinder of a marine high-power low-speed diesel engine part as an example, the piston plane cam lead surface is milled. Under the conditions of the existing machine tool equipment in the workshop, analyze the cylinder piston cam profile structure and lead parameters, combine the gear transmission ratio calculation formula and the application function of the indexing head, and analyze the machine tools, milling cutters, indexing heads and gears involved. The relevant technical parameters are calculated and carefully arranged. After machining practice and the movement function testing of the piston parts after they are installed in the diesel engine exhaust valve air cylinder, a set of stable quality and low-cost machining process solutions are summarized.
#01
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Preface
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For precision machining of flat cam profiles, the most ideal process solution is CNC machine tool milling, especially CNC machining centers with CNC rotation axes (A-axis or B-axis). High-power marine low-speed diesel engine parts are all in small batches and of various types. The capital investment in NC machining center equipment is relatively large. The input-output ratio of the new NC machine tool with multi-axis machining function for this part alone is not ideal. Ordinary vertical lifting table milling machines are standard production equipment in most traditional mechanical processing workshops. It is the process research goal of workshop technicians to fully utilize the processing functions of existing machine tool equipment and form low-cost input and high-efficiency output. The piston plane cam is the lead surface of the guide rod movement and has high precision. The milling process involves linkage processing in which the linear axis and the rotation axis are in a certain proportion. Milling on non-CNC machine tools is difficult. The lead of the piston plane cam is small, that is, in order to form a large angle of rotation in a short linear distance, it is necessary to use the functions of an ordinary vertical milling machine to develop a novel and mature linear axis and rotary axis linkage processing technology scheme [1]. Explore the processing technology of plane cam parts and gear application technology to ensure the quality of parts processing.
#02
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Application of milling machine and indexing head accompanying gear
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The application of ordinary vertical milling machine and indexing head with hanging gear processing is shown in Figure 1. As shown in Figure 1a, the X53K ordinary vertical lift table milling machine has a longitudinal feed screw pitch P=6mm. The FW250 universal indexing head has a fixed number of 40 and is equipped with a standard available gear library. The optional gear teeth z are 25, 30, 35, 40, 50, 60, 70, 80, 90 and 100[2]. The main drive gear is installed on one end of the longitudinal screw shaft of the vertical milling machine, and the driven gear is installed on the tail side of the indexing head. A gear set with a corresponding transmission ratio is hung between the main drive gear and the driven gear. The gear set is adjusted to the appropriate mesh. After the gap is cleared, fix it with the bracket locked on the indexing head and tail sides. After the installation is completed, the longitudinal screw of the vertical milling machine drives the worktable to feed longitudinally. At the same time, the main drive gear integrated with the longitudinal screw transmits the corresponding rotational motion to the indexing head through the gear set with the corresponding transmission ratio. The rotation of the indexing head clamping The parts are rotated accordingly to realize synchronous linkage processing of the linear axis and the rotating axis.
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a) X53K vertical milling machine
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b) The indexing head is equipped with a hanging gear
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c) Plane cam milling
Figure 1: Application diagram of ordinary vertical milling machine and indexing head equipped with hanging gear processing
#03
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Piston part flat cam lead surface
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The cylinder piston in the air cylinder cavity of the marine high-power low-speed diesel engine exhaust valve assembly is a precision moving part. The piston rotates up or down under the action of the cylinder pressure. The cam lead surface on the end face of the piston drives the movement of the guide rod in contact with it. The rotation of the piston The accuracy of the angle and up-and-down movement distance is critical for functions such as exhaust timing. The processing size requirements for the lead surface (0°~144.3°) of the piston flat cam are shown in Figure 2. The flat cam is in the form of an end ring boss with an inner circle of R60mm and an outer circle of R70mm. It spirals upward clockwise from 0° (expanded on the R65mm circumference, rising angle 1.75°). When it reaches 144.3°, it ends on the rear cam surface with a height of 5mm. , the surface roughness value of the cam surface Ra=3.2μm. The material of the parts is QT400.
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a) Top view of piston
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b) Cross-sectional view of the piston
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c) Lead surface expansion diagram
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d) Piston isometric drawing
Figure 2 Dimensions of the piston plane cam surface of a certain model
#04
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Machining of cam lead surface
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4.1 Process preparation
The dimensional requirements of the turning process before the piston cam surface milling process are shown in Figure 3. The turning process is not introduced in this article.
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Figure 3 Dimensional requirements for turning process before piston cam surface milling process
4.2 Calculation selection of matching gears
(1) Calculation of cam lead L: The height distance corresponding to the axial rise of the cam surface spiral 360° is the cam lead L. According to the dimensions of the lead surface expansion diagram in Figure 2c, the cam surface rises h=5mm from 0° to 144.3°, and the cam lead L is calculated based on this. From 5/L=144.3/360, we can get L=12.474 (mm).
(2) Calculation of transmission ratio i The transmission ratio calculation formula [2] is
i＝40t/L (1)
In the formula, i is the transmission ratio; 40 is the fixed number of the indexing head; t is the longitudinal screw pitch of the machine tool (mm), and t of the X53K vertical milling machine is generally 6mm; L is the cam lead (mm).
According to formula (1), the calculation shows that i=40×6/12.474≈19.24.
(3) The number of gear teeth is calculated based on the number of optional gear teeth equipped with the FW250 indexing head and the transmission ratio requirements. According to the conventional 2 sets (one set of main and driven gears related to direct transmission) 4 gear configurations Unable to meet the requirement of transmission ratio 19.24. According to the installation space and bracket fixing conditions, 3 groups of 6 gears are selected and configured. The gear transmission ratio calculation formula [3] is
I＝z1z3z5/(z2z4z6) (2)
In the formula, I is the gear transmission ratio; z1, z3, and z5 are the teeth of each active hanging gear respectively, and priority is given to selecting from the standard gear teeth of the indexing head; z2, z4, and z6 are respectively the number of teeth of each driven hanging gear, and priority is given to selecting from The indexing head comes standard with the number of gear teeth to choose from.
According to formula (2), a transmission with 3 groups of 6 gear teeth distribution can be obtained
The ratio I=90×80×70/(35×30×25)=19.2, which is close to the transmission ratio i (19.24) calculated from the cam lead.
4.3 Error verification
The transmission ratio I=19.2 is designed based on the selection of gear tooth number conditions. The assumed lead L=40×6/19.2=12.5 (m m) is calculated using equation (1). Then according to the part cam lead surface angle of 144.3°, inversely It is assumed that the height h=144.3×12.5/360=5.01 (mm) towards the calculated cam lead surface, and the error of 5mm from the size required in the drawing is 0.01mm, which meets the allowable requirements of part size tolerance.
4.4 Practical application
When the piston plane cam milling is clamped on the indexing head, the indexing head clamps the process spindle with a self-centering chuck and adjusts the spindle rotation concentricity error to ≤0.01mm. Position the piston with the piston inner hole and the process spindle, and use Use tie rod bolts and pressure plate washers to clamp and tighten the piston in the threaded hole at the end of the process mandrel, and use a dial indicator to check the rotational runout of the piston. The piston cam surface milling gear is shown in Figure 4. The main drive gears Z1 and Z2 are installed on the longitudinal screw end of the machine tool on the fixed bracket. Z2 is the driven gear of Z1. Z3 and Z2 are coaxial synchronous gears. Z3 drives Z4 and Z2. Z5 and Z4 are coaxial synchronous gears. Z5 drives the Z6 gear that is hung on the tail side of the indexing head (that is, drives the indexing head hanging wheel shaft), which ultimately forms the guide for the rotational motion of the parts held by the indexing head and the longitudinal feed motion of the machine tool. The relationship between stroke ratio is that the longitudinal movement distance of the machine tool is 12.5mm, and the piston rotates 360° synchronously; the longitudinal movement distance of the machine tool is 5.01mm, and the piston rotates synchronously 144.3°.
The milling tool is a φ20mm high-speed steel end mill. The cutting parameters are cutting speed vc=23.55m/min, spindle speed n=375r/min, and feed f=0.1mm/r. Align the axis line of the end mill to coincide with the center line of the piston. Use the side edge of the end mill to be at the bottom of the cam lead surface (-5mm), and turn the longitudinal feed rod of the machine tool to the right, that is, start the piston plane cam. The linear axis and rotary axis of milling are processed simultaneously. The process is divided into rough machining, semi-finishing and finishing. The starting point of the end mill cutter is 0° in the radial direction of the lead surface, and the axial position of the lead surface is planned to be -3.5mm (leaving a margin of 1.5mm), -4.8 mm (leave a margin of 0.2mm) and -5mm, a total of 3 steps of milling processing. After the milling of each work step is completed, the milling cutter is axially retracted to a safe position, and the longitudinal feed of the machine tool is reversed back to the starting position of the previous work step. Considering the reverse error of the gear clearance, each reverse return exceeds the starting position. After about 1 turn of the starting position, return to the starting position in the forward direction and pull out the indexing head rocker pin (the rotating movement of the indexing head breaks away from the constraints of the matching gear, that is, it breaks away from the longitudinal feed of the machine tool table. Linkage constraint), after the machine tool is hand-cranked longitudinally to feed the corresponding cutting amount, the pin linkage constraint gear is inserted. After the tool is lowered to the appropriate position, the linkage processing process of the previous step is repeated until the cam lead surface is processed to the finished size.
#05
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Conclusion
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The processing application of ordinary vertical lifting table milling machine and indexing head equipped with hanging gear milling piston cam surface has successfully solved the processing problem of MAN ES patented main engine such as 420mm, 460mm and other bore diameter marine low-speed high-power diesel engine exhaust valve cylinder piston plane cam , making full use of the processing capabilities of existing ordinary machine tools in the workshop, reducing the cost of production equipment, increasing the flexibility of the workshop's production organization, and achieving good product quality and high output efficiency, while using ordinary milling machines for similar parts It provides a reference for fast processing with hanging gears.
