I. Design theme
Design the punching mechanism, feeding mechanism and transmission system of the punching machine for punching thin-walled parts. As shown in Figure 5- 1a), the technological action of the punching machine is that the upper die approaches the blank at a high speed, and then the drawing work is carried out at a uniform speed, and then the upper die continues to descend to push the finished product out of the cavity and finally returns quickly. After the upper die exits the lower die, the feeding mechanism sends the blank to the position to be processed from the side to complete a working cycle.
(a) (b) (c)
Figure 5- 1 Machining Action, Upper Die Movement and Force of Punch Machine
According to the above movement requirements, it is required to design the stamping mechanism that can make the upper die process parts, the feeding mechanism that pushes the blank to the top of the lower die from the side, and the transmission system of the punch, and draw the assembly diagram of the reducer.
Second, the original data and design requirements
1. The power source is motor, the lower die is fixed, and the upper die moves up and down in a straight line. Its general movement law is shown in Figure b), which has the characteristics of rapid sinking, constant feed and rapid return.
2. The mechanism should have good force transmission performance, especially the pressure angle of the working section should be as small as possible; The transmission angle γ is greater than or equal to the allowable transmission angle [γ] = 40o;
3. Before the upper die reaches the working section, the feeding mechanism has sent the blank to the position to be processed (above the lower die);
4. The productivity is about 70 pieces per minute;
5. The length of the upper die working section l=30~ 100mm, corresponding to the crank angle? 0=( 1/3~ 1/2)π; The total stroke length of the upper die must be more than twice the length of the working section;
6. As shown in figure c), the stress of the upper die in a movement cycle, the resistance F0 of the working section is 5000 N, and the resistance at other stages is f1= 50 N;
7. The driving speed ratio coefficient k ≥1.5;
8. Feed distance h = 60 ~ 250mm；;
9. The uneven coefficient δ of machine operation should not exceed 0.05.
For convenience, if the motion and dynamics of the mechanism are analyzed, it is suggested that the required parameter values should be selected as follows:
1) It is assumed that all members of the linkage mechanism are homogeneous rods with equal cross section, the center of mass is at the midpoint of the rod length, and the center of mass of the crank coincides with the rotation axis;
2) Let the mass of each component be calculated as 40kg per meter and the moment of inertia around the center of mass be calculated as 2km2 per meter.
3) Ignoring the mass and moment of inertia of the rotating slider, the mass of the moving slider is set to 36kg；;
6) The equivalent inertia moment of the transmission device (with the crank as the equivalent component) is set to 30k g·m2；; ;
7) The uneven coefficient δ of machine operation shall not exceed 0.05.
Third, the transmission system scheme design
The transmission system of the punching machine is shown in Figure 5-2. Reduce the speed of the motor through belt transmission and gear transmission, and drive the main shaft of the machine to run. The prime mover is a three-phase AC asynchronous motor, and its synchronous speed is selected as 1500r/min. You can choose the following models:
Motor model rated power (kw) rated speed (r/min)
Y 100L2—4 3.0 1420
y 1 12M—4 4.0 1440
Y 132S—4 5.5 1440
According to the productivity, the spindle speed is about 70r/min. If the motor is tentatively set as Y 1 12m-4, the total transmission ratio of the transmission system is about. If the transmission ratio of belt drive is ib=2, the transmission ratio of gear reducer is ig= 10.285, so two-stage gear reducer can be selected.
Figure 5-2 Punch Drive System
Fourthly, the design and discussion of the motion scheme of the actuator.
The punching machine includes two driving mechanisms, namely, a punching mechanism and a feeding mechanism. The driving part of the stamping mechanism is the crank, and the driven part (executive part) is the slider (upper die). There is a uniform motion section (called working section) in the stroke, which has the characteristics of quick return. The mechanism should also have good dynamic characteristics. To meet these requirements, it is difficult to use a single basic mechanism, such as an offset crank-slider mechanism. Therefore, to meet the above requirements, several basic institutions need to be properly combined. Feeding mechanism requires intermittent feeding, which is relatively simple. There are many kinds of mechanism combination schemes that can meet the above requirements. Here are some reasonable plans.
1. Gear connecting rod punching mechanism and cam connecting rod feeding mechanism
As shown in Figure 5-3, the stamping mechanism adopts a double crank seven-bar mechanism with two degrees of freedom, which is closed by a gear pair as one degree of freedom. Proper selection of trajectory of point C and determination of component size can ensure that the mechanism has the characteristics of fast return motion and nearly uniform working section, and make the pressure angle as small as possible.
The feeding mechanism consists of a cam mechanism and a connecting rod mechanism in series. According to the motion cycle diagram of the mechanism, the motion angle of the cam stroke and the motion law of the follower can be determined, so as to push the workpiece to the position to be machined at a predetermined time. At design time, if the log
Figure 5-3 A scheme of stamping mechanism Figure 5-4 A second scheme of stamping mechanism
2. Guide rod-rocker slider stamping mechanism and cam feeding mechanism
As shown in Figure 5-4, the stamping mechanism is composed of a rocker slider mechanism connected in series on the basis of the guide rod mechanism. The guide rod mechanism is designed according to the given stroke speed ratio coefficient, and its combination with rocker slider mechanism can meet the requirement of almost uniform working section. Proper selection of pilot position can make the pressure angle of working section smaller.
The camshaft of the feed mechanism is connected with the crankshaft through a gear mechanism. According to the motion cycle diagram of the mechanism, the motion angle of the cam stroke and the motion law of the follower can be determined, and then the mechanism can send the workpiece to the position to be processed at a predetermined time.
3. Six-link punching mechanism and cam-link feeding mechanism
As shown in Figure 5-5, the stamping mechanism is composed of a hinge four-bar mechanism and a rocker slider mechanism in series. The four-bar mechanism can be designed graphically according to the stroke speed ratio coefficient, and then the connecting rod length lEF and the guiding position can be selected, and the position of the hinge point E can be determined according to the requirement that the working section is approximately uniform. If the size is properly selected, when the actuator moves in the working section, the transmission angle γ of the mechanism can meet the requirements, and the pressure angle is small.
The camshaft of the cam feed mechanism is connected with the crankshaft through a gear mechanism. If the cam angle and the motion law of its follower are determined according to the motion cycle diagram of the mechanism, the mechanism can send the workpiece to the position to be machined at a predetermined time. When designing, do LIH
Figure 5-5 Composition of Punching Machine in the Third Scheme 5-6 Punching Mechanism in the Fourth Scheme
4. Cam connecting rod punching mechanism and gear connecting rod feeding mechanism
As shown in Figure 5-6, the stamping mechanism is a combination of cam and linkage mechanism, and the contour curve of the fixed cam is determined according to the motion requirements of the slider D.
The feeding mechanism is composed of crank rocker sector gear and rack mechanism in series. If the size of the crank-rocker mechanism is determined according to the motion cycle diagram of the mechanism, the mechanism can send the workpiece to the position to be machined at a predetermined time.
When choosing a scheme, we should focus on the following aspects:
1) Whether the selected scheme can meet the required performance index;
2) Whether the structure is simple and compact;
3) Whether the manufacturing is convenient and whether the cost can be reduced.
After analysis and demonstration, the scheme 1 is the most reasonable scheme among the four schemes, and the following is the design.
Design of verb (Verb's abbreviation) Punching Mechanism
According to the scheme 1 Figure 5-3, the stamping mechanism consists of a seven-bar mechanism and a gear mechanism. According to the design of the combined mechanism, in order to make the crank AB rotate once, the point C completes a cycle, and the tooth ratio of the two gears should be equal to 1/Z2. In this way, the design of stamping mechanism is decomposed into the design of seven-bar mechanism and gear mechanism.
Design of 1. Seven-bar Mechanism
Analytical method can be used to design seven-bar mechanism. Firstly, according to the motion characteristics and dynamic characteristics of the actuator (slider F), the length CF of the connecting rod connected with the slider is selected, and the trajectory of point C that can meet the above requirements is selected. Then, the size of five-bar ABCDE is designed according to the guiding two-bar group method.
The design of this seven-bar mechanism can also adopt experimental method, which is now explained as follows.
As shown in Figure 5-7, AB and DE are required to be cranks with the same rotational speed and opposite rotational directions. When the crank rotates within an angular range, the driven slider moves at a uniform speed within the range of l=60mm, and its stroke H =150 mm. ..
Figure 5-7 Design of Seven-bar Mechanism
1) as a straight line, as a slider guide, take a line segment with length l and divide it equally, and the score points are F 1, F2, …, Fn (take n=5).
2) Choose lCF as the radius, and make an arc with each point of Fi as the center to get K 1, K2, …, K5.
3) Choose lDE as the radius, make a circle at an appropriate position, take the arc length with the central angle on the circle, and divide it into equal parts corresponding to L, and score points D 1, D2, …, D5.
4) Choose lDC as the raDius and make an arc with di as the center. Pairs with K 1, K2, …, K5 shall be delivered to C 1, C2, …, C5.
5) With lBC as the radius and Ci as the center, L 1, L2, …, L5 are obtained.
6) Draw a proper amount of concentric circular arcs on transparent white paper. Draw five rays from the center of the circle and divide them equally (the angle between the rays is).
7) Cover the Lie curve family with transparent paper, move the transparent paper, and find out the corresponding intersection points B 1, …, B5, and get the crank length lAB and the position of the hinge center A. ..
8) Check whether there are cranks and whether the rotation directions of the two cranks are opposite. Similarly, the length of lAB can be selected first, and the position of lDE and hinge center E can be determined. You can also choose the positions of lAB, lDE and points a and e first, as above.
The dimensions of the mechanism designed by the above method are as follows:
LAB=lDE= 100mm, lAE=200mm, LBC = 283 mm, lCF=430mm, the vertical distance between point A and the guide road is 162mm, and the vertical distance between point E and the guide road is 223 mm.
2. Gear mechanism design
The center distance of this gear mechanism is a = 200mm, and the module m = 5mm. The gear mechanism is driven by standard spur gear, Z 1=Z2=40, ha*= 1.0.
Kinematics and dynamics analysis of six-bar and seven-bar mechanisms
The kinematic and dynamic analysis of the mechanism is carried out by graphic method. The motion of crank AB is divided into 12 equal parts, and the scoring points are B 1, B2, …, B 12. For each position of the crank, get the position of point C, and then get the trajectory of point C, and then analyze the speed and acceleration of slider F one by one, draw a speed diagram, and analyze whether it meets the design requirements.
Figure 5-8 shows the corresponding relationship between the velocity of the actuating element of the stamping mechanism and the locus of point C. Obviously, the slider is approximately constant in F4~F8, and this velocity value is about 40% of the maximum velocity of the working stroke. The walking speed ratio coefficient of this mechanism is as follows
Therefore, this institution meets the requirements of sports.
Figure 5-8 Motion and Dynamic Analysis of Seven-bar Mechanism
In the dynamic analysis of the mechanism, firstly, according to the resistance F0 = 5000 N in the working section, the resistance is considered to be constant in the working section, and then the balance torque Mb acting on the crank AB is calculated and multiplied by the angular velocity of the crank to obtain the power of the working section. Considering the efficiency of each drive, the required motor power is 5.3KW, so the determined motor model Y 132S-4 (rated power is 5.5KW) meets the requirements. (The specific process and results of dynamic analysis are omitted).
Seven, the mechanism movement cycle diagram
According to the analysis results of the stamping mechanism and the requirements for the feeding mechanism, the motion cycle diagram of the mechanism can be drawn (as shown in Figure 5-9). When the driving part AB rotates from the initial position by an angle (=90o) (the punch is located at the upper limit point), the punch quickly approaches the blank; When the crank rotates from (=2 10o), the punch presses the blank downward at approximately the same speed. When the crank is turned from to (= 240 degrees), the punch continues to move downward to push the workpiece out of the cavity. When the crank is turned from to (= 285), the punch just exits the lower die and finally returns to the initial position to complete a cycle. The feeding action of the feeding mechanism can only be carried out within the range from when the punch exits the lower die to when the punch contacts the workpiece again. Therefore, the feed cam completes the lift from 300 degrees to 390 degrees at the crank AB, and the crank AB completes the return journey from 390 degrees to 480 degrees. ..
Figure 5-9 Mechanism Motion Cycle Diagram
Seven. Design of feeding mechanism
The feeding mechanism is composed of a disk cam mechanism with oscillating follower and a rocker slider mechanism in series. The size of rocker-slider mechanism should be determined before designing cam mechanism.
Design of 1. Four-bar mechanism
According to the travel requirements of the slider and the size limitation of the stamping mechanism, the size of the mechanism is selected as follows:
LRH= 100mm, LOH=240mm, the vertical distance from o point to slide RK guide rail =300mm, the feed distance is 250mm, and the rocker swing angle should be 45.24o O o.
2. Design of cam mechanism
In order to reduce the size of the cam, the stroke of the swing rod should be less than AB, so the maximum swing angle is 22.62o O. Because the speed of the cam is not high, the constant velocity motion law is selected for both lift and return. Because the cam is fixedly connected with the gear 2, it rotates at the same speed. Used for graphic design of cam profile, base circle radius r0=50mm, roller radius RT =15 mm. ..
Eight. Design of speed regulating flywheel
Equivalent driving torque Md, equivalent resistance torque Mr and equivalent moment of inertia are all functions of crank angle. Draw their curves, and then calculate the moment of inertia JF of the flywheel by graphic method.
Nine, belt drive design
Adopt common V-belt drive. Known power machine is Y 132S-4 asynchronous motor, rated power P=5.5KW, full load speed n 1= 1440rpm, transmission ratio i=2, and it works in two shifts.
(1) Calculate the design power Pd.
According to Table 6-6 in [6], the working condition coefficient KA = 1.4.
(2) Selection of Belt Type Select a belt from Figure 6- 10 of [6]
(3) Select the reference diameter of the pulley Select the reference diameter of the small pulley from Table 6-7 of [6]
Take the diameter series values from Table 6-8 in [6] and the reference diameter of the big pulley:
(4) Check the belt speed v.
In the range of (5~25m/s), the belt speed is appropriate.
(5) Determine the center A and reference length of the seat belt.
Within the range of primary center distance
Initial belt length
See Table 6-2 in [6] to select the standard reference length of the A-belt.
Find the actual center distance
Take the center distance as 500mm.
(6) Check the wrap angle of the small pulley
Suitable wrap angle
(7) Determine the number z of belts.
lookup table
Take Z=3.
(8) determining the initial tension
Initial tension of a single common V-belt
(9) Calculate the pressure on the pulley shaft.
Structural design of (10) belt drive (omitted)
X. gear transmission design
The transmission ratio of the gear reducer is ig= 10.285. The standard two-stage cylindrical gear reducer, code named.
ZLY- 1 12- 10- 1 .
Section 2 Design of Actuator and Transmission System of Reinforcement Leveler
I. Design theme
Bar straightening is a preparatory process before machining mechanical parts. If the bar is bent, it is necessary to process small parts with large bars, as shown in Figure 5- 10, which has low material utilization rate and poor economy. Therefore, before machining parts, the bar must be straightened. Now it is necessary to design a short steel bar straightener. Determine the mechanism motion scheme, design the actuator and transmission system.
Figure 5- 10 Bending steel bar to be straightened
Second, the design data and requirements
The bar to be straightened is 45 steel. See Table 5- 1 for other original design data of the bar straightener.
Table 5- 1 Original design data of bar straightener
parameter
Grouping diameter d2
(mm) length l
(mm) Maximum radius of curvature ρ before straightening
Maximum straightening force (mm)
(KN) number of revolutions of steel bar during straightening.
(steering) productivity
(Roots/min)
1 15 100 500 1.0 5 150
2 18 100 400 1.2 4 120
3 22 100 300 1.4 3 100
4 25 100 200 1.5 2 80
Attention: indoor work, I hope the impact vibration is small; The prime mover is a three-phase AC motor, with a service life of 10 year, working for 300 days a year, working for 16 hours a day, maintaining once every six months, and the overhaul period is 3 years.
Third, the determination of working principle
1) Roll and straighten the bar with a flat platen (Figure 5- 1 1). The advantage of this method is simple and easy to operate, but the disadvantage is that the material is not very straight because of springback.
2) Straighten the bar with a grooved press plate. Considering that "correction must be over-correction", the static washboard is made into a groove shape, and the cross section of the dynamic and static washboards is made into the shape shown in Figure 5- 12. This method can not only straighten the bent steel bar, but also bend the straight steel bar, which is not ideal.
3) Straighten with a compression bar. Design a mechanical device similar to that shown in Figure 5- 13. On the one hand, the motor drives the bar to rotate, on the other hand, the pressing amount of the compression bar is gradually reduced by the cam, so as to achieve the purpose of straightening. Its advantage is that the bar can be straightened very straight; The disadvantage is that the productivity is low and the rod needs to be stopped when loading and unloading.
4) Roll and straighten with the chute pressure plate. The longitudinal section of the static washboard is as shown in Figure 5- 14, and its groove depth changes from deep to shallow, and finally disappears. Its working principle is the same as the previous scheme, which makes the reduction gradually, so it can also straighten the bar. Its disadvantage is that the moving washboard moves back and forth, so there is a gap and the production efficiency is not high enough. Although the quick return action of the offset crank-slider mechanism as shown in the figure can be used to reduce the idle loss, the inertia force generated by the moving washboard due to its large mass and reciprocating motion is not easy to balance, which limits the improvement of the running speed of the machine, so the productivity is still not ideal.
5) Planetary rolling straightening. As shown in Figure 5- 15, its moving washboard becomes a roller 1, which makes continuous rotation, and the stationary washboard becomes an arc-shaped member 3, and the groove opened on it becomes shallow from deep to shallow, and finally disappears. This scheme can not only straighten the bar, but also has a high degree of automation and high productivity, so it finally determines this working principle.