Blog 20: Gear Basics: Gears Manufacturing

Introduction:

A gear is a rotating, circular mechanical part with equally spaced teeth around a cylindrical or conical surface. In the case of gears and cogs, an inserted tooth (called a gear) meshes with another toothed part to transmit torque. Gears are used in machines to transmit motion, and change speed, and direction. Different gear combinations can be used to achieve different speeds. It can be used to increase torque, adjust speed, change the direction of travel, etc. Two or more gears that move alternately are called gears. The advantage of gears is that the gear teeth prevent slippage. By connecting pairs of these elements, they are used to transmit rotation and force from the drive shaft to the driven shaft. There are multiple methods for gear manufacturing.

There are many other power transmissions such as belt drives, chain drives, cable drives, etc., but the main advantage of gear systems is that there is little or no slippage between the driving and driven elements. Gears are operated in pairs. The gear or toothed component attached to the shaft or base component of the machine is called the driving gear (i.e. the gear that provides the initial rotational input) and the gear that rotates with that shaft component is called the driven gear (i.e. , the gear or geared component that is acted upon by the driving gear and exerts its final performance). Depending on the gear pair design and construction, the direction of rotation or motion can change as a result of motion transmission between the input and output shafts. Additionally, if the gear sizes are unequal, the machine or system can experience a mechanical advantage and vary the output speed and torque.

Materials Used to Produce Gears

There are no gear material restrictions. The earliest ones were wooden, and you can find gear in a variety of materials throughout the industry. From large industrial gears made of steel and iron to small toy plastic gears. The combination of materials is infinite.
Nevertheless, the following items are most commonly used in gear manufacturing and gear molding processes.
• cast iron
• Steel
•bronze
• plastic
Gears have very specific material selection criteria. Materials with appropriate tensile strength and durability should be selected according to the application.
In addition, since the gears must be in constant contact, the coefficient of friction must also be taken into account. Finally, you should also choose materials that are easy to process. Gear manufacturing requires extreme precision and accuracy, making it more difficult to work with strong materials that are less manufacturable.
The materials listed above provide the perfect balance of these properties for your application. For this reason, it is frequently found in most passageways you come across.

Common Gear Manufacturing Processes

Gear production is quite complicated because of the precision it demands. Today, gear manufacturing is an industry in itself that relies on multiple processes, both traditional and modern, to ensure the right balance between cost, quality, and operations.

Here’s a list of common gear-cutting and manufacturing processes along with their apparent advantages and disadvantages.

1 – Casting

Casting is a simpler process in which the teeth are made by machining but is primarily used to make gear blanks or cylinders. However, its mass production capabilities and relative simplicity make it a viable overall gear manufacturing process for many applications.
However, there is one area where casting is the industry’s most preferred manufacturing process. This is a very large gear production. Machining methods and other gearing methods are not practical for large diameters. In general, larger gears are most often spur gear types. So casting would be a very good option due to its relative simplicity.
Among the most common casting methods, shell casting, die casting, sand casting and chill casting are the most common for gear manufacturing. Other methods are of limited use in some applications. However, the above are the most common in the industry.

2 – Forging

This is another molding process that can provide both blanks and prepared gears depending on your needs. Forging works best when the gear is relatively simple.
In theory, forging is a good gear manufacturing process for high-performance applications for one simple reason. Forging requires heat treatment. This means that the resulting gear has better fatigue properties. However, the enormous force required by the forging process limits the size and thinness of this process. Forging is generally suitable for gears 6 to 10 inches in diameter. It depends on the type of  Precision forging. You may or may not need to machine the gears at the end.

3 – Extrusion and cold-drawing

This is another versatile and simple gearing process. Although extrusion requires fewer tools, it is not the most economical process.
Extrusion, as the name suggests, is the process of passing a heated metal profile through a pre-defined smaller die. The result is a rod of the desired shape with a hardened and smooth outer surface.
The cold drawing process is very similar to the extrusion process. There are two differences. During extrusion, the blank is pushed into the die and pulled by the die. Another difference is temperature. Cold drawing does not heat the billet. This improves mechanical properties at the expense of cost.

4 – Powder metallurgy

Powder metallurgy is an advanced process that has made great strides in recent years. Today it is used for several manufacturing processes including gear manufacturing.
So how does powder metallurgy work? From a point of view, it’s pretty simple. However, there are many subtleties. It all starts with metal powder. The first step is to take all the powder and give it the final shape you want. Once you are done, the next step is to make sure the whole build is fairly compact. This improves mechanical properties. Gently heat the entire setup and you’re done.
Powder metallurgy is very efficient, simple, and suitable for mass production. The product is ready to use, so you don’t have to worry about post-processing. However, the resulting gear cannot carry very heavy loads and is limited in size.
In addition, powder metallurgy equipment has a very high initial cost, which is unfavorable for low-volume production.

5 – Blanking

Stamping is a process very similar to extrusion, but with limited 3D capabilities. This gear-forming process uses sheet metal to create the desired shape using multiple molds. Various types of gear can be made using the stamping process. However, spur gears give the best results.
Today, stamping processes in gear manufacturing are used in several industries for lightweight applications. For example, office equipment, hydraulic equipment, small medical equipment, and other applications with light load requirements.

6 – Gear Machining

Machining is among the most common gear manufacturing processes because of its versatility. Traditional machining was quite common for gear cutting and manufacturing but the advancements in CNC machining have propelled its popularity.

The following 4 gear cutting methods are the most common across the industry.  

Hobbing

Hobbing utilizes a conical cutting device called a hob. Both the hob and the workpiece turn as the hob rotates around the gear blank. So far, external spur and helical gears are the only products you can create from hobbing.

The process is quite versatile and quick. You can also increase your production rates by processing multiple stacks together. However, it requires more skills and precision.

Shaping

Shaping is an advanced gear-cutting and manufacturing process that develops gears that Hobbing can’t handle. The cutter can be of any shape like a pinion, rack shape, or single-point shape. It looks quite similar to gears and works by cutting into the blank at your required shape. You can create internal or cluster gears with the shaping process.   

Broaching

Broaching is perhaps the quickest method of gear form-cutting. It relies on a multi-teeth tool with embedded cutters that go deeper than its predecessor. This results in smaller, incremental cuts that are easier to make and quickly give you the required shape without compromising the precision.

This gear manufacturing process is typical for internal gears but you can use it to make external teeth as well. For that, you’ll need a specialized tool for pot broaching that allows you to replicate the same precision and efficiency.

Milling

This is a basic gear-cutting method where you produce individual gear teeth sequentially. It is however quite versatile, especially when you involve a CNC milling machine. While you can make any type of gear on a milling machine, the precision of this method leaves a lot to be desired. That’s why milling is not as common as it was before.

However, the recent developments in the CNC domain and multi-axis have changed things. Gear manufacturing on milling machines is becoming more and more common. So, things will get even better with time.   

Gear Manufacturing Post-processing

Depending on the gear manufacturing method you used, your gears will need some post-processing before they are 100% ready. That post-processing can range from heat treatment for improved fatigue characteristics to dimensional correction and surface finishing.

Here are the 5 most common surface finishing processes that are common in gear production.

Grinding: Just as its name suggests, grinding is a common surface finishing process that gives you a smooth finish throughout the surface. You can perform it intermittently or continuously, and it won’t affect the results.

Lapping: This process is for sensitive gears where you need extreme precision. Lapping uses small abrasive particles to smooth out a surface at low or medium speeds.

Honing: This is another common process that polishes the surface and makes it smooth. Moreover, you can also correct some minor errors in your tooth geometry.

Shaving: This process removes extremely thin layers from the surface to achieve a smooth profile. Shaving is generally expensive, so it’s rarely used in gear production.

Burnishing: In its essence, burnishing is the process of using compression to smooth out the surface

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