Fig.1 Square thread parameters
Our factory specializes in the external machining of bed nuts for the J53-300 friction press. The nut is composed of a steel jacket (material ZG45) and a copper nut. The nut cover is connected to the brass nut using an M265×4 thread and a pin mechanism. The copper nut features a four-start square thread with a bore of 630mm, having the following specifications (see Figure 1): pitch of 44mm, lead of 176±0.07mm, outer diameter of Ø227D7+0.6mm, mean diameter of Ø191D4+0.09mm, and a helix angle of 14°25'. This type of four-line square thread is non-standard and presents significant challenges during processing. To address this, we designed and manufactured a specialized turning tool that employs a combined cutting and extruding process to form the threads (see Figure 2).
1. Arbor 2. Rear pressure plate 3. Sliding bearing 4. Tool 5. Front pressure plate
6. Press screw (M16) 7. Countersunk screw (M10)
Figure 2 Four-wire thread forming tool structure
The tool is used as a final finishing tool. The front part (approximately 3mm) of the two edges of the tool head acts as a cutting edge, while the rear portion performs light extrusion. During the machining process, the two side blades create a negative clearance of about 1°, and the back corner (about 0.5mm wide) ensures tight contact between the tool flank and the workpiece surface, reducing vibration and improving cutting smoothness. Additionally, it provides a slight calendering effect, enhancing the surface finish of the workpiece. The top edge of the tool has a negative rake angle of 3°, which helps guide the chip toward the top edge, preventing surface scratching.
Behind the side blade (on the right side of the top surface), a crescent-shaped groove is ground, increasing the rake angle of the blade. This allows the two front edges to maintain equal angles, ensuring stable cutting and avoiding the "sickle" phenomenon. When machining the copper nut, the workpiece speed is set at 50r/min, and three cutters are used: the first roughing cutter has a width of 8mm with a larger front rake and a feed rate of 1.5mm; the second roughing cutter has a width of 15mm, also fed 1.5mm per pass; the third is a finishing tool (see Figure 3), with a width of 16±0.2mm and a feed of 3mm per pass.
Figure 3 Finishing tool
Before cutting, a groove is first machined on the workpiece. The first tool is placed in the center of the groove to ensure balanced cutting on both sides. However, during the start of cutting or when the cut is completed, uneven force can cause the first thread to be too small and the last one to be oversized. To solve this issue, the blank is made slightly larger than the final size, and then cut from both ends to achieve uniform dimensions. This approach significantly improves the accuracy and quality of the threaded surface.
I beam
I Beam,Steel I Beam,Metal I Beam,Stainless Steel I Beam
Shandong Shifeng Metal Products Co., Ltd. , https://www.qfgygs.com