Fig.1 Square thread thread parameters

Our factory specializes in the external machining of bed nuts for the J53-300 friction press. The nut assembly consists of a jacket made from ZG45 material and a copper nut. The nut cover is connected to the brass nut via an M265×4 thread, which is driven by a pin. The copper nut features a four-start square thread with a bore of 630mm, and its thread parameters are shown in 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'. As a non-standard thread type, the four-start square thread presents significant challenges during processing. To address this, we developed and manufactured a turning tool that utilizes a combined cutting and extrusion process to form the threads (as shown in Figure 2). The tool has several key design features. To accommodate the large aperture requirements, the tool holder is equipped with a sliding bearing at its head. During radial feed, the arbor moves within the flat bore of the sliding bearing. Since the sliding bearing maintains contact with the inner hole during the cutting process, it enhances the rigidity of the cutter bar and minimizes vibration.

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

This tool serves as the final finishing tool. The front part of the two edges on the tool head, approximately 3mm in length, acts as the cutting edge, while the rear part performs light extrusion. During processing, the side blades form a negative rake angle of about 1°. The back corner, which is about 0.5mm wide, ensures that the flank face of the tool tightly fits against the workpiece’s thread surface, reducing vibration and improving cutting smoothness. It also provides a slight calendering effect, enhancing the surface quality of the workpiece. The top edge of the tool has a negative rake angle of 3°, and both side edges have a similar negative edge angle of 3°, which helps guide the chips toward the top edge during cutting, preventing surface scratches. Additionally, a crescent-shaped groove is ground behind the side edge (on the right side of the top surface), increasing the rake angle of the blade and ensuring the two front edge angles are equal. This helps maintain stable cutting and prevents the formation of a sickle-shaped chip. When machining copper nuts, the workpiece rotates at 50r/min, and three cutting tools are used in sequence. The first roughing tool has a width of 8mm, a larger front rake, and a feed rate of 1.5mm. The second roughing tool has a width of 15mm, with a feed of 1.5mm per pass. The third tool is the finishing tool (as shown in Figure 3), with a width of 16±0.2mm and a feed of 3mm per pass.

Figure 3 Fine knife

Before cutting, a groove is machined into the workpiece using a grooving tool. The first tool is placed in the center of the groove to ensure even material distribution on both sides. When starting the cut or when the cut is nearly complete, excessive force on one side can cause the first thread to be too small and the last one too large. To avoid this issue, the blank is initially machined slightly oversized, allowing for a balanced cut at both ends. This method ensures consistent thread dimensions and improves overall machining accuracy.

Angle Steel

Angle Steel,Angle Iron,Stainless Steel Angle,Stainless Steel Angle Iron

Shandong Shifeng Metal Products Co., Ltd. , https://www.qfgygs.com