The fiercely competitive global market requires gear manufacturers to constantly push the limits of improving production efficiency and reducing production costs, which means that high-speed hobbing processes made of high-quality materials and protected by high-performance coatings must be used. Due to the high price of advanced tools, some production workshops are reluctant to use high-efficiency hobs, because they do not comprehensively analyze all aspects of the production process to determine the correct cost calculation method-from calculating the total cost to calculating each piece of machining cost.
In order to achieve higher gear cutting efficiency, the design of the hob is tending to develop an efficient, multi-head shank hob. The hob with shank is made of integral tool steel and has a smaller diameter, usually longer than the hob with holes. When they are installed on the hobbing machine, they are positioned by the shank necks at both ends, rather than being installed on the mandrel like a hob with holes. For example, the design concept of Leitz Fette indexable carbide heavy-duty cutting hobs is to use economical indexable carbide inserts combined with the well-known advantages of rolling cutting, which can be used at high cutting speeds within a specified time. Removal of large amounts of metal, regrind and recoating are necessary for traditional hobs, but not necessary here. Greatly saves the cost of grinding and tool change, which will reduce the investment of machine tools, thereby reducing the construction of the plant, and really save a lot of costs for users; Gleason Corp. (Gleason Corp.) Genesis shank hob uses D The driving mechanism uses the entire surface contact of the hob key to transmit torque. In general, the plane-to-plane drive mechanism used on most machine tools is prone to slight misalignment on the contact surface under the torque generated by high-stress line contact.
Integral shank hobs are usually used to process worm gears, and the diameter of the hob is required to be relatively close to the diameter of the worm gear being processed. The optimized designed hob with shank is most suitable for high-volume, high-efficiency machining. Large-diameter, high-pitch gears (such as gears for truck gearboxes or mining machinery) are usually processed with hole hobs.
For hob with shank and hob with hole, the factors that can shorten the cutting time include increasing feed rate, hob speed and increasing the number of hob heads. In order to optimize hob performance, hob designers try to use small diameter hobs, because at a given surface speed (sfm), the smaller the diameter of the hob, the higher the cutting speed. Because the hob with a shank has a smaller diameter and no holes, it has a larger length than a hob with a hole of a similar diameter, so more movable cutting areas can be obtained, and the hob can cut more every time it passes Multiple artifacts. The hob with sharp cutting teeth moves along its axial direction into the cutting zone.
Glenn Schlarb, design manager at Gleason, explained, “The high productivity of the shank hob is the result of more moving positions along the hob in each pass, and due to the use of high wear resistance The hob material and tool coating increase the number of hob passes, so that each hob can process more workpieces. ”
Hobbing can be used with or without coolant. However, many users prefer dry hobbing because it eliminates environmental pollution and saves the costs associated with handling coolant. In order to protect the cutting edge under high-speed dry hobbing conditions, dry hobbing requires the hob to use a high-quality coating with high temperature stability and low thermal conductivity.
Because the hob with a shank adopts an integral structure, and there are fewer parts to install it on the hobbing machine, its assembly rigidity is better than that with a hole. The hob can detect its sharpening, installation and measurement accuracy when it is installed between the centers. Compared with the hob with a hole, the hob with a shank eliminates the cumulative radial jump error between the hole and the mandrel, and the sway error caused by the spacer and the mounting nut.
The high-quality steel grades used in the manufacture of shank hobs have high wear resistance and a high level of room temperature hardness and red hardness at high cutting temperatures. Although high-quality steel and coatings are more expensive than materials with lower performance, small-diameter shank hobs with higher cutting speeds can be manufactured, which can shorten the machining cycle time and reduce the cost of each piece. Under appropriate machining conditions, this cost-effectiveness per piece is usually greater than the increase in the cost of each tool, which can reduce the total cost of each piece of machining.
In the hobbing process, it is very important to use a suitable tool coating. It can increase productivity and reduce machining costs. In some machining occasions, the tool life can be doubled, which can not only save tool costs, but also reduce tool changes. Times to shorten downtime.
Dr. Dennis Quinto, technical director of Oerlikon Balzers Coating, pointed out that the preparation of the cutting edge has an important influence on the performance of the coating, which is usually a factor of the tool performance that is not well controlled. Sharp cutting edges can produce less cutting force and lower cutting heat, but the thinner coating will increase the risk of cutting edge chipping, so it is only suitable for small feed rate cutting; passivated cutting edges The upper coating is thicker and has more stable chipping resistance, but the cutting force generated is also larger; the cutting edge after chamfering and passivation treatment has the most stable chipping resistance, so it is very suitable for hard and brittle tool materials ( Such as cemented carbide) and high feed rate cutting.
Since the cutting speed and cutting depth should be reduced with the increase of the tensile strength of the workpiece material in the hobbing process, the appropriate coating can increase the cutting speed (in some cases, it can also increase the feed rate). PVD coating can protect almost all hobs. The standard TiN coating is effective for low-speed hobbing with lubricant; TiCN coating can increase the hardness and wear resistance of the hob, suitable for machining abrasive workpiece materials; TiAlN coating is developed for dry cutting, has excellent Toughness and high temperature resistance. The new AlCrN coating recently developed for dry cutting has more excellent wear resistance, heat resistance and oxidation resistance.