Gear Hobbing Machine for Sale from a list of used hobbing machines in industrial metalworking machinery auctions. Make your selection, compare specs and prices and buy the best deal!
What is a Gear Hobbing Machine : Gear manufacturing processes can be grouped in two categories: Gear forming & Gear generation. In gear form cutting, the cutting edge of the cutting tool has a shape identical with the shape of the space between the gear teeth. Form milling & Broaching are the gear forming processes. In gear generating, the tooth flanks are generated as an outline of the subsequent positions of the cutter, which resembles in shape the mating gear in the gear pair as in gear hobbing & gear shaping. Gear hobbing is a machining process in which gear teeth are progressively generated by a series of cuts with a helical multi point cutting tool called as hob. Hobbing is the most preferred industrial process for cutting gear teeth than any other teeth forming processes. Almost teeth of all types of gears like spur, helical, worm, sometimes special forms are cut using hobbing machines. The hob and the gear blank rotate continuously just as in the meshing of two gears until all teeth of the gear blank are cut.
The cutting of a gear with a hobbing machine is a continuous operation and four to five teeth can be cut at a time on a progressive basis. To start cutting a gear, the rotating hob is fed inward until the proper setting for tooth depth is achieved, then cutting continues until the entire gear is finished. A proportional feed rate is always maintained between the gear blank and hob. The metal is removed from the blank as the hob generates the tooth form. The generating process requires an accurate relationship between various elements of the machine in order to achieve the desired results. The work table rotates in a definite relationship with the rotation of the hub. Index change gears are responsible for the timing of this relation. But in the case of hobbing helical gears, the rotation of the work table is slightly advanced or retarded in relation to the rotation of the axial feed screw with the help of another set of change gears namely differential change gears.
Hobbing vs Shaping
Gear hobbing and shaping are the two major gear generating processes as discussed above. Hobbing produces a series of radial flats based on feed rate of hob across the work while shaping produces a series of straight lines parallel to the axis of the gear. The accuracy of the resultant gears produced by hobbing is with respect to tooth spacing and runout whereas it depends on the tooth form in the case of shaping. Stacking can make hobbing faster than shaping even for gears with narrow face widths. But narrow width jobs can be generated in lesser times with high speed stroking in gear shaping. Hobbing has a major disadvantage of not able to machine internal gears when compared to its counterpart.
Types of Hobbing Machines
The gear hobbing process can be classified into three different types according to the directions of feeding the hob for gear cutting as:
Hobbing with Axial Feed: In this process the gear hob is fed against the gear blank along the face of the blank and parallel to its axis. This kind of feed is used mainly for making spur and helical gears.
Hobbing with Radial Feed: The hob and gear blanks are set with their axis normal to each other in this method. The rotating hob is fed against the gear blank in radial direction or at right angles to the axis of the gear blank. Worm wheels are made predominantly using this method of feeding.
Hobbing with Tangential Feed: In this kind of feeding, the hob is held with its axis horizontal but perpendicular to the axis of the gear blank. The hob is set at full depth of the tooth and then fed forward axially. Thus, the hob is fed tangential to the face of gear blank.
Advantages and Limitations
Some of the prominent advantages of the process of gear hobbing machines are: Gear hobbing is a fast and continuous process so it is realized as economical process as compared to other gear generation processes like shaping. It involves lower production cycle time thereby leading to higher productivity. The process is capable of making a wide variety of gears like spur gear, helical gears, worms, worm gears, splines, sprockets, etc. Indexing process is highly simplified and any number of teeth with consistent accuracy and precision can be made with ease. Also the indexing process is continuous and there is no intermittent motion subsequently eliminating the rise of errors. Gear hobbing is the exclusive process used for generating a special type of gear called harringbone gear. It is highly suitable for both batch and mass production. Several gear blanks, mounted on the same arbor, can be processed simultaneously which leads to cycle time reduction.
Because of the nature and profile of the hob, there is no overheating of the cutting tool as there is ample amount of time available to dissipate the heat. In addition to above mentioned various advantages, one of the major limitation of the process of gear hobbing is that the manufacturing of internal gears is not possible. Some of the splines and serrations require one tooth blocked or removed, which cannot be generated in a gear hobbing machine. If you are looking for buying used hobbing machines then look no further, start your search for hobbing machines for sale on Trade Machines metalworking machines auction. Its easy to select and compare the hob machine from other manufacturers with the specs provided.
Manufacturers of Hobbing Machines
Some of the leading gear hobbing machine manufacturers in the world are: EMAG Maschinenfabrik, MAG, Gleason, STROJIRNY CELAKOVICE, Kashifuji, TOS a.s, FELSOMAT, Vanguard Machinery International, Drake manufacturing Services, Monnier & Zahner AG and Affolter.