Analysis of the Design Considerations of Four-point Right-angle Shears

A right-angle shearing machine is a machine tool with two right-angled blades that can cut the sheet at a right angle. Fully servo-controlled right-angle shearing machine and CNC turret punching machine, automatic loading and unloading device, stacking device, sorting device, etc. form a CNC punching and shearing composite line, which can automatically complete the punching and shearing process, and the processed workpiece can be directly transferred to the bending, Welding and other processes, the system has the advantages of the high utilization rate of the plate, no frame material, high quality of parts and corners, stable frame material state in the whole process, easy to realize automatic control, and low workpiece processing cost. Punching and shearing equipment can be used as independent production equipment, or it can be important equipment for material processing in smart factories. It has been frequently used to produce various products, such as elevator door panels, heating and ventilation equipment, and electrical switch cabinets.

●Common Main Transmission Structure

The main transmission structure of the CNC right-angle shears mainly includes four types: hydraulic type, clutch-type, single-point servo ball head type, and four-point servo drive type. The hydraulic structure needs to be equipped with a hydraulic oil cooling system. The leakage of hydraulic oil and waste oil treatment will cause certain environmental pollution. In addition, the oil pump in the hydraulic station works continuously, which will generate a lot of heat energy loss. The shearing machine does not cut. It also consumes electricity at times, resulting in a lot of energy consumption. The clutch-type structure motor is always in working condition, and the energy consumption is high. In addition, the sheer stroke of the shearing machine needs to be adjusted on-site. The adjustment method is a mechanical adjustment, the adjustment speed is slow, and the accuracy is not easy to be guaranteed.

The single-point servo ball-head servo motor drives the ball screw to directly drive the upper tool post to realize the shearing of the sheet. This structure is relatively compact, eliminates the intermediate transfer link, and can complete more efficient and energy-saving cutting work. However, when cutting, the knife holder will generate large lateral forces in two directions, and the knife holder has the risk of turning over. This single-point ball head structure cannot overcome this drawback. All the lateral forces are generated by the knife holder. The rear upright guide rail bears, when the tool post cuts different thickness or different strength sheet materials, different lateral forces will be generated, and the guide rail will also deform to different degrees, which will affect the cutting accuracy in both directions. To avoid excessive lateral force, the maximum cutting length of the machine tool of this structure will be limited.

The four-point servo-driven structure is driven by four-point dual-servo motors. It has the characteristics of adjustable stroke, anti-eccentric load, and energy saving. Compared with other main transmission structures, it has obvious advantages. This article uses the main transmission method of right-angle shears as the research object, Analyze and explain the precautions in the design process.

●Structure Composition And Principle

The four-point servo-driven right-angle shearing machine is mainly composed of a frame, an upper knife holder, a lower knife holder, a driving device, a pressing device, a lubrication system, and a cooling system. Two sets of shear blades installed at right angles are installed in parallel on the upper and lower sides. On the X-axis and Y-axis of the tool post, the plate can be cut at right angles in the horizontal plane.

The four-point servo-driven right-angle shearing machine is mainly composed of a frame, an upper knife holder, a lower knife holder, a driving device, a pressing device, a lubrication system, and a cooling system. Two sets of shear blades installed at right angles are installed in parallel on the upper and lower sides. On the X-axis and Y-axis of the tool post, the plate can be cut at right angles in the horizontal plane.

The anti-eccentric load principle of the four-point servo-driven right-angle shearing machine is: at the moment the upper tool post cuts the sheet, the two sets of driving devices are synchronously controlled by servo motors. The synchronous driving device is extremely rigid, and the inclined wedge is like a rigid constraint. Pushing the upper tool post balances the turning tendency caused by the shearing force at any point so that the upper tool post will make the knife deformation very small under the action of the shearing force, thereby ensuring the cutting quality.

●Rail Assembly Analysis

The upper blade of the four-point servo-driven right-angle shearing machine is located in the middle of the frame. The four-sided guide assembly is difficult and costly. Therefore, the upper blade holder in the industry mostly adopts double-sided guidance. The two guide assembly surfaces are perpendicular to each other. There are two ways to assemble guide rails: close to the blade and away from the blade, as shown in the figure.

In the picture, the upper knife frame and the ram are connected by screws, and the guide rail and the frame are connected by screws. During the process of cutting the sheet, the reaction force of the sheet on the upper blade is not only the vertical shearing force, but also the horizontal direction. The thrust is generated by the upper and lower blades squeezing the sheet.

When the guide rail is close to the blade assembly, the force is transmitted to the rack through the nearby ram, and the rigidity of the rack restricts the knife yielding during the shearing process. The advantage is that the deformation of the upper tool holder has little effect, but the disadvantage is the uneven bearing capacity of the ram. , The bearing capacity of the ram near the acting force is large, the guide rail fastening screw tends to stretch under the force, the guide rail is easy to slip when the thick plate is sheared, and it deviates from the initial assembly position.

When the guide rail is far away from the blade assembly, the force is transmitted to the rack through the upper tool holder. Due to the coordinated deformation of the upper tool holder, the bearing capacity of each ram is uniform, and the guide rail fastening screws are not affected by the force and will not deviate from the initial assembly position. Disadvantages In the process of force transmission, the upper tool holder produces a certain deformation. When cutting materials with different thicknesses, the adjustment of the blade gap should comprehensively consider the influence of the deformation of the upper tool holder.

●Shearing Machine Accuracy Guarantee Measures

The cutting quality defects of sheet material mainly include edge collapse, burrs, poor parallelism of opposite sides, poor perpendicularity of adjacent sides, etc., which are related to blade gap, upper and lower blade parallelism, and sheet and blade perpendicularity.

Too small a shear blade gap will increase the shearing force, and at the same time increase the friction between the cutting edge and the edge of the plate, and accelerate the wear of the cutting edge. If the gap is too large, the steel plate of plastic material will have burrs, and the steel plate of brittle material will have a rough fracture. The value of the gap is related to the thickness of the steel plate and the mechanical properties of the steel plate. At present, the shears are mostly equipped with automatic gap adjustment devices.

The poor parallelism of the upper and lower blades will cause the blade gap to change during the operation of the upper blade, and the verticality of the upper blade will also change accordingly. During the cutting process, there will be defects such as edge collapse, burrs, material pulling, and blade banding; The change of the perpendicularity to the blade, in addition to the blade itself, the deformation of the plate itself will also affect it.

●Double Servo Motor Synchronous Control

The four-point servo-driven shearing machine adopts a double-servo drive and semi-closed loop control mode. The motor adopts synchronous control. The gantry synchronous axis is connected to the NC CNC system for unified control. The master and slave motors are simultaneously controlled by the NCU (Numerical Control System Control Unit). Position control. In the idle stroke, the synchronization of the dual servo motors is very good, but during the cutting process, the synchronization accuracy of the dual servo motors fluctuates at a certain moment. The unsynchronization of the dual motors causes the upper tool post and upper blade to tilt, and then Affect processing accuracy. By controlling the allowable fluctuation range of the phase difference of the dual motors, the upper tool post is controlled to run smoothly, thereby ensuring the parallelism of the upper and lower blades.

●The Inclined Wedge is Matched with the Roller of the Upper Tool Post

During the assembly process, the fit of the diagonal wedge and the upper tool holder may not be very close. There are several factors in this.

⑴Assembly error. During the assembly process, the diagonal wedge must fit well with the roller of the upper tool post, and the contact force should be uniform. If the force applied to the upper tool post by the individual wedges is too large, the wedge and roller will appear during operation. gap.

⑵Manufacturing error. The angle of the oblique wedge assembled on the drive device has an error, which is the main reason for the dynamic gap between the oblique wedge and the roller during operation.

⑶Assembly stress. If the double-drive mechanism is connected to the upper tool post in an unreasonable way, or the synchronous motor is not properly cleared before powering on, there will be stress between the double-drive mechanism and the upper tool post. In the idling operation, there will be only one drive The mechanism provides the main power. After a long time, there will be a gap between the other set of wedges and the upper tool post.

●Sheet Sagging

When the right-angle shearing machine cuts large workpieces, such as workpieces larger than 300mm in both X/Y directions, the rigidity of the plate is poor when it is laid flat. Before the cutting starts, the plate sags due to gravity and is far away from the plate in the clamped area Due to the deviation of the deformation from the set position, the shear quality of the adjacent edges of the plate, and the parallelism of the opposite edges deteriorate. The easiest measure is to design a set of supporting mechanisms to limit the sagging of the sheet. Figure 3 shows the most commonly used supporting principle diagram of the shearing machine. The cylinder uses the principle of the lever to push the other end of the supporting roller to move upward, saving assembly space.