| 1. IntroductionWith the application of CNC, EDM and CAD/CAM system, the shape of mold surface can basically processing automation. However, mold polishing processing is mainly depended by skilled workers to complete at present. It does not only pose high technical requirements on workers, but also requires considerable time and vigour, and the quality of polished surface is difficult to keep steady.End Effector is fixed at the end of polishing machine, used to install the polishing process head, which plays an important role in the mold polishing process. End Effector can not only improve the overall structural stiffness, but also compensate the position error automatically and adapt to a variety of shapes of surface.Developing an End Effector suitable for a general CNC machining equipment has great significance in reducing production costs shortening the manufacturing cycle and improving the competitiveness of die products.The paper is summarizes domestic and foreign related polishing technologies and End Effector's development, with VTP in End Effector's design and developing process. UG software is used to create solid model and fit assembling, finite element analysis software ANASYS is also used to carry on static analysis of End Effector's key components, ADAMS software to carry on the machining process simulation of 6°and 12°inclined plane, comparative analysis of the effects of processing speed limit in different angles oblique, as well as the parameterized technology of ADAMS to analyze processing speed limit at different spring stiffness.2. Polishing End Effector model establishmentPolishing End Effector is mainly composed of support, spindle and polishing head. Support is used to connect End Effector to CNC equipment, and it's the fundamental installer for other parts. The spindle is used to transmit the torque of motor. Polishing head consists of three parts: round head screw, grinding head, coat. Grinding head is connected to coat through thread, which can change different particle size according to the needs of polishing process. Round head screw and grinding head are connected by ball-joint to ensure the grinding head has enough freedom to adapt to the changes in free-form surfaces. After parts design, using the assembly function of UG, introducing constraints, finished assembly model of polishing End Effector is shown in Figure 1.Fig 1 Polishing End Effector3. Polishing End Effector static analysis of key parts Spindle is the key force-bearing part in polishing End Effector, bearing torque generated by tangential grinding force, moment by radial grinding force and the axial force. Spindle easily brings in bending and torsion. We need to ensure its strength and stiffness to meet the requirements in the design.Import the spindle model as Parasolid format into ANSYS, define element's attribute, meshing and set up the spindle of the finite element model, applied constraints and loads at the corresponding position, calculated and the results display in the Fig 2 and Fig 3. As shown in the Fig 2, the maximum deformation happened at the end of the spindle. The main reason for this result is the spindle using the cantilever-type support structure, the main force applied at the end of the spindle. The maximum deformation is 0.364×10-4m, which will not lead to significant deformation on the spindle. The stiffness of the spindle meets design requirements.As shown in the Fig 3, the maximum stress occurred in the keyway. This result is mainly attributed to the spindle to transmit torque through the keyway and the keyway position prone to stress concentration. The maximum stress is 48.4MPa, the material of spindle is 45 steel, yield limitσs is 360MPa. The strength of the spindle meets design requirements.The analysis of the support is similar to the spindle. Fig 4 and 5 show the deformation and stress of the support respectively. Seen from Fig 4 and Fig 5, the maximum deformation and stress occurred in the screw. This result is mainly attributed to the torque and bending moment being transmitted by the bolt. The maximum deformation is 3.7×10-7m, will not lead to significant deformation on the support. The maximum stress is 10.3MPa, the material of support is Q235-A, yield limitσs is 235MPa. The strength of the support meets requirements.4. Polishing End Effector virtual prototyping model establishment After setting up the model of End Effector by software UG, conversion the model to the dynamics simulation software ADAMS2003 by Parasolid format. Establish virtual prototyping model in ADAMS, including setting of working environment,modify model color,rename components,add constraints,impose drivers,build springs, and applies ADAMS bringing model examination tool to exam the restraints and the degree of freedom, thereby completes the virtual prototyping model. The virtual prototyping model of polishing End Effector is shown in Fig 6. Processing of inclined plane, with the increase in spindle speed, the grinding head has the danger of popping up from the inclined plane. In order to ensure the safety of the polishing process, measuring the limit of the spindle speed is particularly important. There are Planar between the grinding head and workpiece, when the Z direction constraint force of the workpiece on the grinding head is zero, the speed of the spindle is the limited speed for processing. Using Sensor function of ADAMS, Sensor Event Definition is the Z direction constraint force of the workpiece on the grinding head, Event Evaluation is taken when the force is zero. Define the Sensor Motion: event occurs, simulation stop. In order to extract the constraint force of the workpiece on the grinding head, use ADAMS function JOINT, JOINT return a certain direction constraint force or moment of kinematic pair. Function format: JOINT (Joint Name, On This Body, Force Component, Along About Axes), Joint Name is the name of kinematic pair, the value of On This Body is 0 or 1, respectively I Marker and J Marker constraint force, Force Component refers to the direction of force component, can get 1～8, 1 and 5 refer to constraint force and constraint torque amplitude, followings are the constraint force and constraint torque of six degrees of freedom, Along About Axes refers to the reference coordinate system to determine the direction of axis, Enter 0 express the Global Coordinate System. Set the spindle start to accelerate form stationary at the angular acceleration 5r/s2, simulation time is 10s, simulation step is 1000, simulation stop, information window as in Fig 7 pops up. As shown in the window, when the simulation time arrives at 8.8509525998, the sensor makes the simulation stop. At this time, the spindle's rotational speed is approximately 44.2r/s.Change the inclined plane angle of workpiece to 12°, while follow the other steps similarly as above with 6°inclined plane machining simulation. Sensor stops the simulation, information window as in Fig 8 pops up.As shown in the window, when the simulation time arrives at 7.4149979848, the sensor makes the simulation stop. At this time, the spindle's rotational speed is approximately 37.1r/s.Comparing the results, it can be seen that increase in the slope angle reduces the speed limit. The main reason for this is when the spindle rotates at the same speed, greater the slope angle, the Z direction inertia force of the grinding head becomes greater.Add contact between the grinding head and workpiece, deactivate the Planar between the grinding head and workpiece, and set the spindle rotates at 5r/s, feed rate at zero. Simulation time at 1s, and simulation step at 100, the grinding head angular velocity is shown in Fig 9. As shown in Fig 9, there is a minor rotation of the grinding head. The angular velocity of grinding head is always positive, which proves that the rotation direction of the grinding head is in the same direction as the spindle. The minor rotation of the grinding head around its own axis is beneficial to uniform wear.In order to analyze the effects that different spring stiffness at the limit processing speed, the spring stiffness as Design Variables needs to be defined. Control the range of the variables at (1.0, 3.0), in the range realizes five levels of implementation of the simulation analysis. Determine the Target Object as the spindle speed, choose the type of Target Object as the last simulation value, using the last simulation scripts.A simulation information window as Fig 10 can be seen in the simulation processing,When the simulation is finished, run the PostProcessor module, the results of the parametric analysis can be seen in Fig 11. From the figures, we can see the spindle speed limit at each level. The unit of the speed is deg/sec, converted are 42.75,43.55,44.25,45,45.8, unit r/s. Also can be seen from the figures, the limits of the spindle speed with the spring stiffness shows similar increase as in a linear function.6. Conclusion1) This paper establish 3D solid model for polishing End Effector and parametric design. UG NX4.0 is used for End Effector assembly. The model can be established to provide a foundation for the next generation polishing End Effector research and reference.2) Carry on static analysis of polishing End Effector key parts by the ANSYS; make the conclusion that the stiffness and strength of parts are meet design requirements.3) Carry on machining simulation of 6°and 12°inclined plane by the ADAMS. Using Sensor function of ADAMS to measure the limit of the spindle speed. Comparing the results, the increase in the slope angle reduces the speed limit. Proved that the minor rotation of the grinding head around its own axis is beneficial to uniform wear.4) Using the parametric analysis function of ADAMS to analyze the effects that different spring stiffness at the limit processing speed, draw conclusion that the limits of the spindle speed with the spring stiffness shows similar increase as in a linear function. |
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