Reamer toothing
A reamer is a tool used for finishing and semi-finishing holes. Its main function is to improve the dimensional accuracy and surface quality of the hole and reduce the surface roughness of the hole. The toothing of the reamer is a key process in the reamer manufacturing process, which directly affects the cutting performance, service life and processing quality of the reamer. The toothing of the reamer refers to the processing of teeth with certain geometric parameters on the reamer body. These teeth include the cutting edge, the rake face and the flank face, which together constitute the cutting part of the reamer. The quality of the toothing depends on factors such as tooth profile accuracy, tooth pitch uniformity, and the accuracy of the front and back angles. These parameters need to be precisely designed and controlled according to the reamer material, the processing material and the processing requirements.
There are two main methods for creating teeth on reamers: machining and electro-discharge machining (EDM). Machining is the most common method, and includes milling and grinding. Milling involves milling tooth grooves into the reamer body using a milling cutter, creating the teeth. This method is efficient, low-cost, and suitable for mass production. Milling requires selecting the appropriate milling cutter based on the reamer’s tooth profile parameters (such as tooth angle, rake angle, and clearance angle), and using an indexing mechanism to ensure uniform tooth pitch. High-speed steel (HSS) reamers are typically milled with a HSS cutter; carbide reamers use carbide or ceramic cutters. Grinding involves grinding the teeth after milling to improve profile accuracy and surface quality. It is suitable for reamers with high precision requirements. Grinding eliminates machining errors introduced during milling, sharpening the cutting edges and improving the reamer’s machining accuracy and service life. Electrospark machining is suitable for cutting teeth on reamers with complex shapes or high material hardness. It uses the electric spark discharge between the electrode and the workpiece to erode the material to form tooth grooves. It has the advantages of high machining precision and no restrictions on material hardness, but it has low efficiency and high cost. It is generally used for the manufacture of reamers with special requirements.
The design of reamer tooth geometry is a core element of the toothing process, primarily encompassing rake angle, clearance angle, tooth profile angle, and pitch. The rake angle, defined as the angle between the rake face and the base plane, influences the sharpness of the cutting edge and the magnitude of cutting forces. A larger rake angle results in a sharper cutting edge and reduced cutting forces, but also reduces tooth strength. A smaller rake angle increases tooth strength but also increases cutting forces. The choice of rake angle should be determined based on the properties of the material being processed. A larger rake angle (e.g., 5°-10°) is recommended for machining plastic materials to minimize deformation and friction, while a smaller rake angle (e.g., 0°-5°) is recommended for machining brittle materials to maximize tooth strength. The clearance angle, defined as the angle between the flank face and the cutting plane, primarily influences friction between the flank face and the workpiece surface, as well as tooth wear. A larger clearance angle reduces friction and increases tool durability, but reduces tooth strength. A smaller clearance angle increases tooth strength but increases friction. Typical clearance angles for reamers range from 6°-10°. The tooth profile angle refers to the angle between the teeth within the base plane, which determines the reamer’s tooth shape. For cylindrical reamers, the tooth profile angle is typically 60° or 90° to ensure sufficient tooth strength and chip space. The pitch refers to the distance between adjacent teeth. The pitch should be evenly distributed to ensure uniform cutting force and reduce vibration. The pitch size is determined by the reamer’s diameter and number of teeth. Reamers with larger diameters generally have a larger pitch and a higher number of teeth.
Sharpening and finishing a reamer after tooth cutting significantly impacts its performance. The goal of sharpening is to sharpen the cutting edge and ensure that the cutting edges of each tooth are aligned on the same circumference, ensuring uniform hole diameters during reaming. Sharpening primarily involves rake face grinding and flank face grinding. Rake face grinding adjusts the rake angle, while flank face grinding adjusts the clearance angle and straightness of the cutting edge. High-precision grinding equipment, such as a universal tool grinder, should be used, along with appropriate grinding wheels, such as aluminum oxide wheels for high-speed steel reamers and silicon carbide wheels for carbide reamers. After sharpening, the cutting edge should be inspected to ensure it is free of defects such as chipping and burrs. Finishing procedures include deburring and chamfering. Deburring removes burrs generated during tooth cutting and sharpening to prevent scratches on the workpiece surface during reaming. Chamfering is a slight chamfering of the cutting edge tip to enhance its strength and prevent tip chipping. For reamers with higher precision requirements, balancing tests are also required to eliminate the imbalance caused by uneven teeth and avoid vibration during high-speed rotation, which affects the processing accuracy.
During the reamer toothing process, the following points need to be noted to ensure the quality of toothing: First, the appropriate toothing method and tool should be selected according to the material of the reamer. For example, for reamers made of high-strength alloy materials, electric spark machining or carbide tools should be used for milling. Second, the reamer body should be pre-treated before toothing, such as tempering, to improve the hardness and toughness of the tool body and reduce deformation during the toothing process. Third, the cutting parameters, such as cutting speed and feed rate, should be strictly controlled during the toothing process to avoid deformation of the tool body or tooth profile error due to excessive cutting force or high cutting temperature. Finally, after the toothing is completed, a comprehensive quality inspection should be carried out, including tooth profile accuracy, pitch deviation, rake angle and back angle values, to ensure that all parameters meet the design requirements. Through reasonable toothing process and strict quality control, high-performance reamers can be manufactured, thereby ensuring the accuracy and efficiency of reaming processing and meeting the processing requirements of high-precision holes in mechanical manufacturing.
