Question

Discuse the gear industry in general.. this is an introduction or overview to an essay.

Answer 1

MANUFACTURING:

Gear manufacturing refers to the making of gears. Because of their capability for transmitting motion and power, gears are among the most important of all machine elements. Special attention is paid to gear manufacturing because of the specific requirements to the gears. The gear tooth flanks have a complex and precise shape with high requirements to the surface finish. Gears can be manufactured by most of manufacturing processes discussed so far (casting, forging, extrusion, powder metallurgy, blanking). But as a rule, machining is applied to achieve the final dimensions, shape and surface finish in the gear. The initial operations that produce a semi finishing part ready for gear machining as referred to as blanking operations; the starting product in gear machining is called a gear blank.

VARIOUS PROCESSES CAME UNDER GEAR MANUFACTURING TECHNOLOGY:

Gear Forming Process:

Gear manufacturing can be divided into two categories namely forming and machining. Forming consists of direct casting, molding, drawing, or extrusion of tooth forms in molten, powdered, or heat softened materials and machining involves roughing and finishing operations.

Casting:

Sand casting, die casting and investment casting are the casting processes that are best suited for gears.

Sintering or P/M process:

The powder metallurgy technique used for gear manufacture.

Accuracy similar to die-cast gears

Material properties can be Tailor made

Typically suited for small sized gears

Economical for large lot size only

Injection Molding:

Injection molding is used to make nonmetallic gears in various thermoplastics such as nylon and acetal. These are low precision gears in small sizes but have the advantages of low cost and the ability to be run without lubricant at light loads. Injection molded gears are used in cameras, projectors, wind shield wipers, speedometer, lawn sprinklers, washing machine.

Extruding:

Extruding is used to form teeth on long rods, which are then cut into usable lengths and machined for bores and keyways etc. Nonferrous materials such as aluminium and copper alloys are commonly extruded rather than steels. This result in good surface finishes with clean edges and pore free dense structure with higher strength.

Stamping:

Sheet metal can be stamped with tooth shapes to form low precision gears at low cost in high quantities. The surface finish and accuracy of these gears are poor.

Forging:

Forging is the shaping of metal using localized compressive forces. Forging is often classified according to the temperature at which it is performed: ‘”cold,” “warm,” or “hot” forging. Forged parts can range in weight from less than a kilogram to 580 metric tons. Forged parts usually require further processing to achieve a finished part.

Gear cutting process:

Gear cutting is the process of creating a gear. The most common processes include hobbing, broaching, and machining; other processes include shaping, forging, extruding, casting, and powder metallurgy. Gears are commonly made from metal, plastic, and wood.

Broaching:

For very large gears or splines, a vertical broach is used. It consists of a vertical rail that carries a single tooth cutter formed to create the tooth shape. A rotary table and a Y axis are the customary axes available. Some machines will cut to a depth on the Y axis and index the rotary table automatically. The largest gears are produced on these machines.

Hobbing:

Hobbing is a method by which a hob is used to cut teeth into a blank. The cutter and gear blank are rotated at the same time to transfer the profile of the hob onto the gear blank. The hob must make one revolution to create each tooth of the gear. Used very often for all sizes of production runs, but works best for medium to high.

Shaping:

The old method of gear cutting is mounting a gear blank in a shaper and using a tool shaped in the profile of the tooth to be cut. This method also works for cutting internal splines. Another is a pinion-shaped cutter that is used in a gear shaper machine. It is basically when a cutter that looks similar to a gear cuts a gear blank. The cutter and the blank must have a rotating axis parallel to each other. This process works well for low and high production runs.

Gear Finishing Process:

When high precision is required secondary operation can be performed to gears made by any of the above roughing methods. Finishing operations typically removes little or no material but improves dimensional accuracy, surface finish, and or hardness.

Shaving:

Shaving is similar to gear shaping, but uses accurate shaving tools to remove small amounts of material from a roughed gear to correct profile errors and improve surface finish.

Grinding:

In grinding, a contoured grinding wheel is run over machined surface of the gear teeth using computer control. With a small amount of metal removal high surface finish is obtained. Grinding is used to correct the heat-treatment distortion in gears hardened after roughing. Improvement in surface finish and error correction of earlier machining are added advantages.

Burnishing:

In burnishing, an especially hardened gear is run over rough machined gear. The high forces at the tooth interface cause plastic yielding of the gear tooth surface which improves finish and work hardens the surface creating beneficial compressive residual stresses.

Lapping and Honing:

Lapping and honing both employ an abrasive-impregnated gear or gear-shaped tool that is run against the gear to abrade the surface. In both cases, the abrasive tool drives the gear in what amounts to an accelerated and controlled run-in to improve surface finish and the accuracy.

GEAR MATERIAL:

In order for gears to achieve their intended performance, life and reliability, the selection of a suitable gear material is very important. High load capacity requires a tough, hard material that is difficult to machine; whereas high precision favours materials that are easy to machine and therefore have lower strength and hardness ratings. Gears are made of variety of materials depending on the requirement of the machine. They are made of plastic, steel, wood, cast iron, aluminium, brass, powdered metal, magnetic alloys and many others. The gear designer and user face a myriad of choices. The final selection should be based upon an understanding of material properties and application requirements.

Plastic Gears

Steel Gears

Cast Iron Gears

Wood Gears

Powdered Metal Gears

Copper Gears

Brass Gears

Aluminium Gears