Research On Multi-Link Drive Mechanism Of A High-Speed Precision Press

In China High-speed precision presses for lead frame manufacturing rely on imports.In order to get rid of the dependence and improve technology level of domestic high-speed precision presses a multi-link drive mechanism which is composed of crank-slider mechanism, rhombic mechanism, elbow-bar mechanism and dynamic balancing mechanism is taken as an object of study. The following studies have been carried out:1. Kinematic equations for the drive mechanism of a multi-link high-speed precision press were established and the calculation program was also written based on Matlab software environment. Compared with the crank-slider mechanism the multi-link mechanism has the advantage of extending the stamping time by 80%, increasing nominal force by 55.3% under the same driving torque and reducing the slider acceleration to 61.6% at nominal pressure stroke. The mechanical advantage is 1.55 times of crank-slider mechanism.2. The variations of the slider’s displacement, speed, acceleration and pressure angle which help to guide the design were studied when the length of rods and the coordinates of fixed hinge points changing. The error transmission function equations for the rod length and fixed hinge points’coordinates were deduced and the error transmission function factors at bottom dead center (B.D.C) obtained by calculation which help to control the B.D.C dynamic accuracy. Coordinate yH and x18 could be used as B.D.C compensation points and the ratio of B.D.C change and compensation input is rounded to the 1.3778 and 0.3576.3. The dynamical equations for the driving mechanism when the nominal force and inertial force acting on separately were established and the calculations which provide load data for stiffness design of some parts were carried out. Calculation results (600spm, similarly hereinafter) show that the maximum torque required to overcoming the inertial force occupies 68.84% of the torque required to overcoming stamping force. As the machine speed raising the torque needed to overcome the inertial force increases also. And at the speed of 800spm, the torque required to overcome inertial force will exceed the torque required to overcome stamping force. The torque required to overcome stamping force is reduced 19.73% when the torques combined and the rates continue to increase with speed increasing. Approximately 30.21% of nominal force acted on the vertical direction of yH position when punching. Since the vertical inertial force is 77.14% of stamping force at top dead center (T.D.C) this position is unsuitable for compensation within the entire stroke. And the contrary is that only 5.97% of nominal force acted on the horizontal direction of x18 position when punching and the inertial force is 11.42% of stamping force.4. The reverse balancing mechanism is taken as the press’s dynamic balance mechanism and its kinematics and dynamics equations were established also. Calculations indicate that the maximum vertical inertial force of toggle 8 acted on crown shrunk by 88.4%, the minimum shrunk by 98.5%, the value reduced by 97.6%at B.D.C when the dynamic balance mechanism used. Meanwhile the torque needed to overcome inertial forces increases to 1.96 times and the torque required to overcome nominal force decreased 16.2%. The vertical inertial force of toggle eight exerted on crown fluctuates between-2kN～2kN in the crank corner 60°～300° interval when the mass of upper die increasing gradually from 180kg to 340kg. The inertial force acted on yH is 80.74% of stamping force and the horizontal inertial force exerted on x18 only 16.9% of stamping force at T.D.C when the dynamic balance mechanism used. According to the compensation relationships and the stresses acted on joint yH and x18, the latter is more appropriate. Since it is difficult to guarantee the synchronism in the design, and structure is not easy to layout the joint yH is chosen as B.D.C compensation position which also play a role in stroke adjustment.5. Considering the inertial forces, the calculation formula of ideal drive torque for high-speed precision presses was established, simplified and amended. The two items in the formula were multiplied by the coefficient k1 and k2. The coefficient k1 reflects the sensitivity of the torque needed to overcome nominal force on speed and k2 is a dimensionless coefficient which related to the torque needed to overcome inertial forces. The coefficient C1 which reflects the sensitivity of mechanism to the torque needed to overcome the inertial force is slider’s velocity and acceleration of the product with 3 power ratio of the crank angular velocity. The value of k1, k2 and C1 is different for different driver types and design parameters. The torque needed to overcome inertial forces can be reduced by lower C1.And the ideal drive torque variations are studied by changing the radius of the crank when the stroke is same by adjusting other rod’s length.6. The dynamic simulation model for the multi-link high-speed precision press was established (ideal model and the model with friction) based on ADAMS software environment. The simulation results show that impact of gravity on the drive torque is small and can be ignored. The friction of hinge point will lead to a significant increase in work and the average power. And the power needed to overcome inertial forces will larger than that of nominal force due to friction. Taking the minimum RMS and maximum vertical inertial force acted on joint P18 as the goal the optimized mass of slider 12 are obtained and the masses close to equal.7. The technical solutions and parameters for the multi-link high-speed precision press were given based on the above studies. Some of the major parts such as the crankshaft, the crown and the sliders were analyzed by using the Simulation Professional module in the 3D software Solid Works. Analysis showed that the stress, displacement of the above-mentioned parts meet to the design requirements. The prototype was dual-channel tested by using measurement system of B.D.C absolute value. Test results show that B.D.C gradually downward shift in 3h and there is a slight increase in process. The parallelism errors of the slider 10 at B.D.C are less than 34μm within the test speeds with abnormal data removing. The parallelism error at B.D.C gradually increases with the speed increasing. The B.D.C gradually upward shifts with the air spring pressure increasing.