(1) Rough machining This sequence is the process of converting a blank into a semi-finished product.In order to reduce costs and improve processing efficiency, the Czech Skoda W200H digital floor boring machine is arranged to use φ 200mm cutter head, φ 315mm three-face milling cutter and φ 25mm cutter head for processing.First, use a φ 200mm cutter head to machine the 6 sides of the rack, leaving a 10mm machining allowance on one side, then use a φ 315mm three-sided edge milling cutter on the universal angle head to cut straight grooves along the tooth profile, and then stand the workpiece sideways, Use the φ 25mm cutter head to process the tooth surfaces on both sides according to the folded line, leave 10mm machining allowance on each side, and turn to the next sequence, so that most of the machining allowance can be quickly removed, which is more rough than the φ 25mm cutter head. Grooving efficiency increased nearly 3 times.
(2) The first semi-finishing rack is quenched and tempered and returned to the 3m×8m CNC gantry milling machine for semi-finishing.Place the workpiece flat on the table for two clamping operations.During the alignment process, it was found that each rack was deformed to the concave center of the tooth side, and the deformation amount was 3 to 5 mm.This is mainly caused by the large machining amount removed from the tooth profile side during roughing.After evenly considering the machining allowance, semi-finishing the outer profile and tooth shape, leaving a 5mm allowance on each side, and transferring to the next sequence for artificial aging.
(3) After the second semi-finishing rack is artificially aged, the internal residual stress will be fully released.The main processing contents of this sequence include semi-finishing tooth shape, contour surface and processing of each handle hole.On the CNC gantry milling machine, according to the clamping method shown in Figure 2, a φ 250mm right-angle cutter head on the universal angle head is used to process the tooth shape, and the cutter is divided into 2 to 3 passes, leaving a 1mm machining allowance on one side, and then the workpiece is turned 180 °, process the bottom surface to a machining allowance of 1mm, and turn to the next sequence for natural aging for 5 days.The semi-finishing operation allows the racks to be machined in groups on the same machine, which reduces the overall cycle time.
(4) Control method of finishing The equipment and processing method used in this process are the same as those in the previous sequence, the difference lies in the control of the machining accuracy of the rack.First, clamp the bottom surface of the workpiece toward the machine tool spindle, and place the equal-height bolster at the bottom. After alignment, it can be gently clamped, and the bottom surface is processed to a machining allowance of 0.3mm. Then the workpiece is turned 180° and placed on the equal-height bolster. To machine the tooth shape, first machine the top surface of the tooth to the size of the drawing.Due to the high requirements of tooth thickness and tooth pitch accuracy, in the process of finishing tooth shape, the method of measuring while machining is used to control the tooth shape accuracy.When selecting the diameter of the measuring rod, the contact point between the outer circle of the measuring rod and the tooth profile should fall on the index line and its vicinity. Generally, it is selected according to the diameter of the measuring rod D=(1.68～1.72)m, where m is the end face Modulus (mm).After calculating the roundness, use a measuring rod of φ (80±0.01) mm for measurement.The specific control method is: according to the size required by the drawing, draw the distance h between the highest point of the top of the standard measuring rod and the tooth crest, as shown in Figure 3.In the process of processing, first, one side of the inclined surface of all teeth is processed to meet the requirements of the drawing, and then the measuring rod is placed in the first tooth valley, and the actual distance h' between the measuring rod and the tooth top is measured by using a dial indicator. The difference between h' and h is Δh, then the machining allowance A of the cutter head along the length direction of the rack can be calculated according to the formula A=2Δhtan25°.After finishing the first tooth, the machine ram travels 152.4mm along the length direction of the rack to process the second tooth, and then processes each tooth and the size in the length direction. The tooth surface is processed in three passes, and then R15 ball is used. The knife cleans the root of the tooth.After the tooth shape is processed, the workpiece is turned over to remove the thickness and width of the machining allowance, and the assembly is carried out in the next sequence.