Types Of Hob Cutter

According to different purposes, hobs cutters are divided into gear hobs, worm gear hobs, non-involute developed hobs and custom hobs, etc.

types of hob cutter

 

1. Gear Hob

 

Gear hobs for producing spur and helical gears with the highest precision, including finishing, pre-shaving, and pre-grinding of various profiles, such as with or without lobes, half-top teeth and top cuts.

 

1.1 What is a gear hob cutter?

 

 

What is a gear hob cutter

 

Gear hobs are commonly used tools for machining external spur and helical cylindrical gears. During processing, the hob is equivalent to a helical gear with a large helix angle, the number of teeth of which is the number of heads of the hob, and the workpiece is equivalent to another helical gear, which meshes with each other according to a pair of helical gears and rotates at a fixed speed ratio. , The tooth profile of the gear is enveloped by the tooth profiles of the adjacent positions of the sequential cutting. Most of the commonly used hobs are single-headed (see thread), and in mass production, multi-headed hobs are often used in order to improve efficiency.

1.2 Classification of gear hobs

 

1) According to different structures, gear hobs can be divided into two types: integral hobs and insert hobs.

2) According to the purpose, it can be divided into rough machining hob and finishing hob.

3) According to the material cut by the hob, it can be divided into high-speed steel hob and carbide hob.

4) According to the number of thread heads of the hob, it can be divided into single-head hob and multi-head hob.

5) In addition, according to the characteristics of the workpiece to be processed, various improvements can be made to the structure of the gear hob and the geometry of the hob tooth profile, typically small pressure angle hobs, wave-shaped edge hobs, different Equal-tooth high-speed hobs, full-cut hobs, etc., as well as front-shaving hobs, front-grinding hobs, and front-shaving hobs. The cutter teeth of the latter two are relatively narrow so that after hobbing to the depth, the tooth thickness of the workpiece still has a margin for grinding or shaving.

 

1.3 High-speed steel gear hob

 

The small and medium modulus gear hobs made of high-speed steel generally adopt an integral structure.

For hobs with a modulus of more than 10mm, in order to save high-speed steel, avoid forging difficulties and improve the metallographic structure, the insert structure is often used. There are many structural forms of the insert hob, and the commonly used one is the insert rack structure, that is, the tooth part is made of high-speed steel in the form of a rack, and is fastened to the cutter body after heat treatment.

 

1.4 Carbide gear hob

 

Using cemented carbide to make hobs can significantly increase cutting speed and gear-cutting efficiency.

Solid carbide hobs have been widely used in the watch and instrument manufacturing industry to process various small modulus gears. Solid and insert carbide hobs of medium modulus have been used to machine cast iron and Bakelite gears. Carbide hobs with a modulus of less than 3 mm are also used for machining steel gears.

Carbide hobs can also process hardened gears (hardness HRC50-62). This kind of hob often adopts a single-tooth welded structure with a negative rake angle of 30° and scrapes off a layer of tooth surface during cutting.

 

1.5 How to choose a gear hob?

 

The precision of the gear hob has 5 precision grades, which are: 3A, 2A, A, B, and C; the corresponding precision of the processed gear also has 5 grades, which are: 6, 7, 8, 9, 10; The precision of pre-, pre-grinding and pre-shaving hobs is generally A-level and B-level. Of course, in addition to precision matching, there are some things to pay attention to, as follows:

 

(1) Choose according to the precision of the gear being machined.

 

It is recommended to use integral hobs for gears with grade 7 precision and above, and blade hobs for others.

 

(2) Choose according to the hardness of the gear being processed.

 

If the tooth blank hardness is >300HBW, it is recommended to use a blade hob.

 

(3) Choose according to gear batch and efficiency.

 

If the batch is large and has high-efficiency requirements, the blade hob is used.

 

2. Worm gear hob

 

Worm gear hob

 

2.1 What is a Worm Gear Hob?

 

Worm gear hobs are commonly used worm gear machining tools.

The worm gear hob processes the worm gear, which simulates the meshing process between the worm and the worm gear. Therefore, the type and main size of the basic worm of the worm gear hob must be the same as the original worm: the worm is from Archimedes, and the basic worm of the worm gear hob must also be It is Archimedes; the worm is expressed by the axial modulus, and the worm gear hob must also be expressed by the same axial modulus; the hob’s tooth profile angle, thread lead angle, helical direction, number of heads, The tooth pitch and the diameter of the indexing cylinder are also equal to the original worm, so the worm gear hob is often dedicated. When the outer diameter is large, the hob is made into a sleeve type; when the outer diameter is small, the hob is made into a handle structure integrated with the mandrel

The most important thing about worm gear hobs is the worm type, which adopts single-head or multi-head hole and shank types, and the lead angle is generally up to 45°.

The hob has two cutting methods: tangential feed and radial feed.

2.2 What are the points for attention in the selection of worm gear hobs?

 

(1) In the case of meeting the strength requirements of the cutter body, the worm gear hob with a hole sleeve is preferred, otherwise, the integral shank-type worm gear hob is used.

(2) The outer diameter of the worm gear hob is larger than that of the original worm to ensure a radial clearance, and it is used as a compensation value for the reduction of the outer diameter of the hob after regrinding.

(3) While ensuring that the hob teeth have sufficient strength, increase the number of circumferential teeth as much as possible, so that the worm gear tooth surface has a higher surface quality.

(4) The rake angle of the worm gear hob is generally 0°, and the rough machining hob can take a positive value.

(5) The tooth top relief angle in the helical direction of the hob can be selected from 10° to 12°. When the strength of the hob is low, take a small value, otherwise take a large value.

 

2.3 Can gear hobs be used instead of worm gear hobs?

 

The worm gear hob is a special hob designed according to the parameters of the working worm pair. Compared with the gear hob in terms of shape and structure, it has the following characteristics.

(1) The parameters such as the type of worm gear hob, the diameter of the sub-circle, the number of heads, the direction of rotation, and the tooth profile angle should be equal to those of the working worm.

(2) Since the diameter is restricted by the working worm when the strength of the hob is insufficient, the keyway can be opened to the end face, and the hob with the smallest diameter can only be made into a form with a handle.

(3) Since the diameter is restricted by the working worm, the helix angle is often larger, and the structure of the spiral groove is commonly used. Generally, zero rake angle is used to reduce design and manufacturing errors.

(4) Pay attention to the worm gear hob with a cutting cone, most of which need to use a tangential feeding process. Moreover, it is necessary to check whether the parameters of the worm pair meet the radial assembly conditions.

In actual production and processing, the worm gear hob is a special tool with long manufacturing cycle, high precision requirements and high cost. Therefore, under certain conditions, the worm gear processed by the gear hob instead of the worm gear hob can work normally. , and the certain condition here is that the modulus is the same, which involves a lot of data matching. If you want to use the gear hob instead of the worm gear hob, you still need to have a professional tool engineer to guide the implementation.

 

3. Non-involute generating hobs

 

The working principle is the same as the gear hob.

Non-involute generating hobs can also process arc gears, cycloid gears and sprockets, etc.

 

4. Fixed hob cutter

 

Each tooth shape of the fixed hob is different, and only the last tooth is a fine-cutting tooth. The tooth shape is the same as the tooth groove of the workpiece, and the tooth groove of the workpiece is cut by the form milling method, so the fixed hob must be installed in a fixed position relative to the axis of the workpiece. The rest of the teeth on the hob are rough-cutting teeth. The motion relationship during processing is the same as that of the gear hob. Forming hobs avoid the transition curves that occur at the tooth root when machining with generating tools. Ratchet hobs are commonly used custom hobs.

 

5. Involute spline hob cutter

 

 

Involute spline hob cutter

 

Spline hobs can be used to process spline shafts with rectangular teeth, involute teeth or triangular teeth, and their machining accuracy and productivity are higher than those of form milling cutters.

 

6. Rectangular spline hob cutter

 

Rectangular spline hob cutter

 

7. Sprocket hob cutter

 

Sprocket hob cutter

 

8. Hob cutter with special tooth shape

 

Hob cutter with special tooth shape

 

Hobs with special tooth shapes used for various parts can basically be used as long as they are external gears processed by generation.

 

9. Straight tooth synchronous pulley hob cutter

 

Straight tooth synchronous pulley hob cutter

 

Manufactures timing pulley hobs for a wide range of belts and pulleys for involute and HTD profiles; in top-cut and non-top-cut designs.

 

10. Heavy-duty double-cutter hob

 

Heavy-duty double-cutter hob

 

Specially designed double-cut hobs are produced to reduce cutting time by increasing the cutting edge in specially designed grooves. These are designed for gears module 5.5 and up.

Benefit:

Significantly reduced cycle times

easy to implement

Reduced hob wear

Hobs are available for both manual and CNC gear hobbing machines.

 

11. Dry cutting hob

 

Dry cutting hob

 

For high-speed cutting on CNC gear hobbing machines for higher productivity. The length of cutting edge of this kind of hob is very long, and the number of grooves of the hob is more, which can improve the processing life of the hob once sharpened. It is very suitable for use in large-scale automatic production lines. It is recommended to use the hob Specifications such as diameter, number of flutes and heads, and cutting data. The goal is to obtain the shortest cutting time and the longest life.

Advantage:

Reduce cycle time.

Increased number of parts per sharpening.

Less inventory.

Fewer variables for smoother production.

Increase factory capacity without increasing investment in land, machinery and manpower.

Lower cost per component

Application

Dry and Wet Cutting

Hole and Shank Type

single-threaded and multi-threaded

Large-capacity parts, such as two-wheelers, cars, ring gears, sprockets, etc.

easy to implement

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