The most commonly used method in preforming gear blank is casting or forging that is then followed by pre-machining to prepare the material to finally achieve the desired dimensions. The next step is the production of teeth through machining and by secondary finishing if needed. The teeth of spur gears, for instance, are made by forming where the profile of each tooth is obtained as the replica of the form of the cutting edge used to cut through the preformed material. Conversely, the process of generation is done in which the complex tooth profile is achieved through the use of a simpler form of cutting edges through rolling type, tool, hobbing, gear shaping, and so on.
In the case of spur gears, the straight toothed gear can be made in a shaping machine. Since the productivity and product quality is poor in this process, and so it is being used only, if at all, for creating a few teeth on pieces of gears when needed for repair and maintenance purposes. As for the production of gear teeth through milling, it is characterized by many things. This includes the use of ordinary milling machines, slow speed and feed, low production rate which is needed to index following the machining of every tooth gap. For manufacturing large gears or modules, end mill cutters are utilized for better manufacturing results.
What Happens During Manufacturing And Finishing of Bevel Gears
In the manufacture of bevel gears, the gear blanks are first being preformed through forging or casting and then followed by machining to desired dimensions using lathes or by a special machine specially designed for the task. The teeth are then produced in the gear blank by machining. The form of the teeth and the volume of production are what dictates the type of machining and machine tool to be used in creating the gear. In this case, the following guidelines are usually considered when machining straight toothed bevel gears.
- In forming through a milling cutter, the process involved low productivity and quality, making it suitable for productions that require less volume and precision.
- In generation, there is high accuracy and finish which it applicable for mass manufacturing. During this process, the internal flanks of two teeth of straight toothed bevel gear adjacent to each other are created with involute profile of the cutting edges that are rotating as they cut through the gear blank.
It is worth noting at this point that the teeth of hypoid and spiral bevel gears are created by very similar generation process with the cutters resembling the face milling cutter. In order for both gears to have good performance, stay longer, and run smooth, they need to have high surface finish and to be accurate in forms and dimensions. More importantly, they need to be wear resistant that can be achieved through the employment of gear teeth finishing that could be done right after almost precise preforming and machining.
Typically, smaller gears that are created through cold rolling don’t need additional finishing works. In case, they do, a little bit of finising might be enough such as lapping right after the hardening process. But if you need machined and hardened bevel gears, then they are most likely need to be finished for high accuracy.