CNC Machining of soft rubber threaded rollers
Soft rubber threaded rollers are key components in the printing, packaging, and textile industries, used in conveying, calendering, or printing processes. Their surfaces are typically machined with precision threads to ensure uniform material conveyance or accurate pattern transfer. Soft rubber has a low hardness (typically 30-60 Shore A), high elasticity, and is easily deformed. This can easily lead to surface tearing and insufficient thread precision during turning, necessitating specialized tooling, clamping methods, and cutting parameters to ensure quality.
The material properties of soft rubber thread rollers significantly affect turning processes, necessitating targeted processing strategies. Soft rubber has the characteristics of high elasticity, low hardness, and low strength. During cutting, the material is prone to plastic deformation, making it difficult to form continuous chips, resulting in burrs, tears, or depressions on the machined surface. Furthermore, rubber has poor thermal conductivity, and cutting heat is difficult to dissipate, which can easily cause local temperature increases, causing the material to soften or even melt, affecting the profile accuracy of the thread. Furthermore, the friction coefficient between soft rubber and metal tools is high, making it prone to tool sticking, further deteriorating surface quality. To address these characteristics, sharp tool edges must be used during turning to reduce extrusion deformation of the material caused by cutting forces; the cutting temperature must be controlled to avoid softening the material; and a suitable cutting fluid must be selected to reduce friction and tool sticking.
The selection and geometric design of turning tools for soft rubber threaded rollers are crucial for ensuring CNC machining quality. Tool materials with excellent wear resistance and a low coefficient of friction should be selected. High-speed steel tools (such as W18Cr4V) offer sharp cutting edges and excellent toughness, making them suitable for turning soft rubber. Carbide tools (such as YG8), while hard, are prone to micro-chipping at the cutting edge and require fine grinding before use. Tool geometry should be designed to minimize cutting forces and extrusion deformation. The rake angle should be 15°-25°; increasing the rake angle improves tool sharpness and reduces extrusion on the rubber. The clearance angle should be 10°-15° to reduce friction between the flank face and the workpiece. The lead angle should be 45°-60° to reduce radial cutting forces and avoid workpiece deformation. The tool tip radius should be kept as small as possible (0.1-0.3mm) to prevent extrusion marks. The cutting edge should be passivated, with a radius of 0.01-0.03mm to ensure sharpness while preventing chipping. For thread turning, the tooth angle of the tool must be consistent with the designed angle of the thread, and the surface must be polished with an Ra value of no more than 0.025μm to reduce tool sticking.
The clamping method for soft rubber thread rollers must prioritize minimizing deformation and ensuring accurate positioning. Due to the low rigidity of soft rubber materials, excessive clamping force during clamping can cause elastic deformation in the workpiece, leading to springback during unloading after processing, affecting thread accuracy. Therefore, flexible clamping methods should be employed, such as using an expansion mandrel or chuck jaws with a rubber coating, to increase the contact area and reduce the clamping force per unit area. For thread rollers with a large aspect ratio, two-end support (one clamping and one supporting) is required, supplemented by a steady rest. The steady rest’s support blocks should be made of a low-hardness material (such as copper or nylon) to avoid damage to the workpiece surface. The support force should be adjusted to prevent workpiece bending without causing noticeable deformation. Before clamping, the end faces of the thread roller must be machined to ensure coaxiality between the center hole and the axis to improve positioning accuracy. Additionally, process chucks can be installed at both ends of the workpiece to minimize the impact of clamping on the thread processing area. The process chucks can be removed after processing is complete.
The selection of cutting parameters for soft rubber thread roll turning requires a balanced consideration of surface quality and processing efficiency. Cutting speed significantly impacts rubber processing quality. When the speed is too low, tool-material contact time is prolonged, resulting in significant extrusion and prone to surface tearing. When the speed is too high, cutting heat increases, causing the material to soften and stick to the tool. Therefore, the cutting speed is generally controlled between 10-30 m/min, with lower values (10-20 m/min) for high-speed steel tools and higher values (20-30 m/min) for carbide tools. The feed rate should be determined based on the thread pitch and precision requirements. For rough turning, the feed rate is 0.1-0.3 mm/r, while for finish turning, it is 0.05-0.1 mm/r. A smaller feed rate can reduce plastic deformation and produce a smoother surface. The depth of cut should be limited to no more than 1 mm per cut for rough turning and 0.1-0.3 mm for finish turning to avoid workpiece deformation due to excessive cutting forces. Cutting fluid is generally not used during turning to prevent the rubber material from expanding after absorbing the liquid. However, for high-speed cutting or situations where the tool is prone to sticking, compressed air cooling or special rubber cutting oil (such as silicone-based lubricant) can be used to reduce friction and cool down.
Quality control and troubleshooting of common problems in turning soft rubber threaded rollers are crucial for ensuring product performance. The machined threads must be inspected for parameters such as pitch, profile angle, and surface roughness. Pitch tolerance is generally controlled within ±0.05mm, profile angle tolerance within ±1°, and surface roughness Ra less than 3.2μm. If surface tearing or burrs occur, this could be due to a blunt tool edge, low cutting speed, or excessive feed rate. Regrind the tool, increase the cutting speed, or reduce the feed rate. Thread profile distortion could be caused by workpiece clamping deformation or an inappropriate tool angle. Adjust the clamping force or resharpen the tool. If tool sticking occurs, reduce the cutting speed, improve the tool surface finish, or use compressed air cooling. For high-precision threaded rollers, manual grinding or polishing can be performed after finish turning to further improve surface quality, but care must be taken to avoid damaging the thread precision. Through effective process control, the turning quality of soft rubber threaded rollers can meet application requirements and ensure stable performance in conveying, rolling, and other processes.
