What is Gear Hobbing Machine Process?

 

 

Hobbing machines provide gear manufacturers a fast and accurate method for cutting parts. This is because of the generating nature of this particular cutting process. Gear hobbing is not a form cutting process, such as gashing or milling where the cutter is a conjugate form of the gear tooth. The hob generates a gear tooth profile by cutting several facets of each gear tooth profile through a synchronized rotation and feed of the work piece and cutter.

 

As the hob feeds across the face of the work piece at a fixed depth, gear teeth will gradually be generated by a series of cutting edges, each at a slightly different position. The number of cuts made to generate the gear tooth profile will correspond to the number of gashes of the hob. Simply put, more gashes produce a more accurate profile of the gear tooth.

 

The hobs several cutting edges will be working simultaneously, which provide significant potential for fast cutting speeds and/or short cycle times. With this realization, one can see the hobbing process’s advantage over other cutting processes.

 

All gear hobbing machines, whether mechanical or CNC, consist of five common elements.

1. A work spindle to rotate the work piece

2. A cutter spindle to rotate the cutting tool, the hob

3. A means to rotate the work spindle and cutter spindle with an exact ratio, depending on the number of teeth of the gear and the number of threads of the hob

4. A means to traverse the hob across the face of the work piece

5. A means to adjust the center distance between the hob and work piece for different size work pieces and hobs

 

 

While the hob and work piece are rotating, the hob normally feeds axially across the gear face at the gear’s tooth depth to cut and produce the gear. In conventional hobbing, the direction of feed matches the direction of the cutting motion. Alternatively, in climb feeding, the feed is opposite to the direction of the cutting motion. Generally, conventional hobbing produces a better finish, whereas climb hobbing yields better tool life. For either method, the cutting forces of the hob should be directed towards the work spindle and not the tailstock.

 

Gear Hobbing Basics

Gear hobbing is a diverse and wide-ranging process that can be used to create several different gear types: Helical, worm and spur gears are some of the most common, but others are possible as well. It's carried out using a special form milling machine, one that contains a tool known simply as a hob.

The hob is the tool that directly generates the teeth for both gears and splines, and it does so with relative simplicity compared to other gear manufacturing types. It allows for high-volume production of these gear types.

 

The final words

To cut a helical gear, a standard hob cutter can be used. Mechanical hobbing machines provide a differential motion through a series of change gears to generate a gear tooth helix. Today, CNC hobbing machines electronically provide this necessary differential to produce helical gears. Contact gear hobbing machine supplier for a quote!

How Gear Hobbing Works

 

 

A gear hobbing machine contains two skew spindles. One of these spindles houses the hob, while the other houses the gear blank. The angle at which these spindles are placed relative to each other depends largely on the type of gear being manufactured.

 

Once the spindles are placed at the proper angle, the machine is set up to begin rotating the shafts at a speed ratio that suits the gear type. As the shafts rotate, the hob gradually cuts the teeth into the gear with the proper depth. To facilitate faster production, manufacturers can stack multiple blanks on the spindle together, allowing the hob to cut teeth into multiple gears at once.

 

Just like there are multiple different angles, speeds, and techniques manufacturers can use to customize the process, there is also a wide variety of hobbing machines available for use. Most hobbing machines specialize in distinct applications. Hobbing machines are built to handle gears of a particular size and come in two different varieties: single-threaded and multi-threaded hobs. Multi-threaded machines allow for increased production, but they aren’t as precise as single-threaded machines.

 

 

Hobbing is one of the most fundamental processes in gear manufacturing. Its productivity and versatility make hobbing the gear manufacturing method of choice for a majority of spur and helical gears.

 

One of the most important concepts  to understand about gear hobbing is that it is a generating process. The term generating refers to the fact that the shape of the gear tooth that results is not the conjugate form of the cutting tool. Rather, the shape of the tooth is generated by the combined motions of workpiece and cutting tool. During hobbing, both the hob and the workpiece rotate in a continual, timed relationship.

 

For a spur gear being cut with a singlestart hob, the workpiece will advance one tooth for each revolution of the cutter. When hobbing a 20-tooth gear, the hob will rotate 20 times, while the workpiece will rotate once. The profile is formed by the equally spaced cutting edges around the hob, each taking successive cuts on the workpiece, with the workpiece in a slightly different position for each cut. Several cutting edges of the tool will be cutting at the same time.

 

During this rotation, the hob is typically fed axially with all the teeth being gradually formed as the tool traverses the work face.

 

The hob itself is basically a worm with gashes cut across it to produce the cutting edges. Each cutting tooth is also relieved radially to provide chip clearance behind the cutting edge. This also allows the hob face to be sharpened and still maintain the original tooth shape. In its simplest form, the hob tooth takes on the shape of a straightsided rack tooth. The final profile of the tooth is created by a number of flats blending together. The number of flats corresponds to the number of cutting gashes which pass the workpiece tooth during a single rotation. Thus, the greater the number of gashes in the hob, the greater the number of flats along the profile, which improves the “smoothness” of the tooth profile.

 

Geepro Machinery

WUXI GEEPRO GEAR HOBBING MACHINE has been one of the professional gear hobbing machine manufacturer and supplier in China since 2007.

Benefits From Our Advantages:

• Professtional Sales Engineers

• Stable Performance of Machines

• Reasonable Price For Users

• Long Life After-Sales Service

We provide high speed high accuracy gear machinery and other workpieces solutions with premium quality service to global users. Contact us now!

Gear Hobbing Machine: Everything You need to Know about Gear Hobbing

 

 

Gear hobbing has been an integral part of gear making. Whereas milling would be used to produce the basic gear shape, gear hobbing performs the much more intricate task of shaping the gear. Various facets of gear teeth emerge once hobbing is complete, including its thickness, profile and addendum.

Gear hobbing is a specialised process of gear cutting, spline cutting and sprocket cutting. The central equipment in the gear hobbing process is the milling machine. This gear hobbing machine does the task of cutting the spline or teeth using a series of cuts using a hob. Gear hobbing is often used for spur gear and helical gear making, because of its ease of use and cost effectiveness.

 

Construction Of Gear Hobbing Machine

Hob– In this process, the gear blank is rolled with a rotating cutter called a hob. Gear hobbing is done by using a multipoint cutting tool called gear hob. It looks like a worm gear having a number of straight flutes all around its periphery parallel to its axis. These flutes are so shaped by giving proper angles to them so that these work as cutting edges.

In gear hobbing operation, the hob is rotated at a suitable rpm and simultaneously fed to the gear blank.

The gear blank is also kept as revolving. Rpm of both, gear blank and gear hob are so synchronized that for each revolution of gear bob the gear blank rotates by a distance equal to one pitch distance of the gear to be cut.

The motion of both gear blank and hob is maintained continuously and steady. A gear hob is shown in Figure and the process of gear hobbing is illustrated in Figure

The hob teeth behave like screw threads, having a definite helix angle. During operation the hob is tilted to helix angle so that its cutting edges remain square with the gear blank.

Gear hobbing is used for making a wide variety of gears like spur gear, helical, hearing-bone, splines and gear sprockets, etc.

 

Types Of Hobbing Process :

The process of gear hobbing is classified into different types according to the directions of feeding the hob for gear cutting. The classification is described as given below.

• 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 is used to make spur and helical gears.

• Hobbing with Radial Feed

In this method the hob and gear blanks are set with their axis normal to each other. The rotating hob is fed against the gear blank in radial direction or perpendicular to the axis of gear blank. This method is used to make the worm wheels.

• Hobbing with Tangential Feed

This is also used for cutting teeth on the worm wheel. In this case, the hob is held with its axis horizontal but at the right angle to the axis of the blank. The hob is set at full depth of the tooth and then fed forward axially. The hob is fed tangentially to the face of the gear blank.

 

 

The process of gear hobbing is as follows:

• The gear hobbing machine is checked for any mechanical issues. This includes the synchronisation of the rotating gears for the workpiece and the hob.

• The gear hobbing machine has two skew spindles, one of which has the gear blank while the other one has the hob.

• The spindles are set at an angle from each other, depending on the type of teeth to be set on the gear blank.

• The two spindle shafts are then rotated proportionally with the hob cuts on the gear blank. Having them properly rotating is the key to making the right gear teeth on the gear blank.

• The hob would then be applied to the gear blank until the correct tooth depth has been reached.

• The hob is then run through the gear blank’s axis of rotation as a final step.

• The process is repeated for each gear blank, which is often stacked one atop another. The rotation ensures identical gear spindle depth and a consistent number of teeth on each gear blank.

• The completed gears are removed from the milling machine.

• The central tool to gear hobbing is the hob, a worm-shaped cutter. The hob makes successive cuts on the gear blank to create the gear teeth. In order for the cutting to be precise, the gear blank and the hob must be synchronised in the rotation.

 

The 5 Advantages of Gear Hobbing

Gear manufacturing gives us lots of options. There are a handful of different processes we can use to make dozens of different gear types from dozens of different materials. Accordingly, when we choose a gear manufacturing method, it’s because it’s the best one for the job.

Gear hobbing is just one way we can manufacture gears. It relies on a special form milling machine with a tool known as a hob, which generates the teeth in both gears and splines. So what are the advantages of this process?

• Speed. Some gear manufacturing processes take a long time, but gear hobbing is relatively fast. The machine is simple, so it doesn’t require as much operational attention, and for some gears, we can stack multiple units to hob them all at the same time.

• Precision. That said, not just anyone can operate a hobbing machine. With the right expertise, hobbing can be highly precise, resulting in high quality gears.

• Flexibility. There’s more than one type of hob—and more than one type of hobbing machine. There are countless variations that cater to specialized applications, so you always have options available.

• Applications. While hobbing is often used for spur gears, the process can be used for a variety of other gears, such as cycloid gears, helical gears, worm gears, ratchets, splines, and sprockets (as long as you have the right tools for the job).

• Related processes. One of hobbing’s only weaknesses is that it does not work for internal gears (with inward-facing teeth). However, there’s a related process called shaping that can be used instead—with all the same advantages of hobbing.

 

Geepro Machinery

WUXI GEEPRO GEAR HOBBING MACHINE has been one of the professional gear hobbing machine manufacturer and supplier in China since 2007.

Benefits From Our Advantages:

• Professtional Sales Engineers

• Stable Performance of Machines

• Reasonable Price For Users

• Long Life After-Sales Service

We provide high speed high accuracy gear machinery and other workpieces solutions with premium quality service to global users. Contact us now!