How to choose materials for machining gears

When designing an individual gear or a gear train, to choose materials for machining gears is regarded as the most important factor. There are many different types of raw materials commonly used in gear manufacturing, and each has the distinct advantage that its mechanical properties make it a superior choice. The main types of materials are copper alloys, iron alloys, aluminum alloys and thermoplastics. Let's learn in detail about the types of materials for machining gear in the article below.

1. Types of gear processing materials

Copper alloy

When designing a device that must withstand corrosive environments or needs to be non-magnetic, copper alloys are often the best choice. The three most common copper alloys used in gears are brass, phosphor bronze, and aluminum bronze.

Brass is an alloy of copper and zinc. The amount of zinc varies in different brass alloys and its presence changes the ductility of the alloy. Low zinc content maintains high ductility in brass alloys, while higher zinc concentrations will reduces the ductility of the alloy. The brass alloy's copper base contributes to ease of machining and has antibacterial benefits. Gears commonly manufactured from brass alloy are cylindrical gears and gear racks that will be used in low load environments such as tool drive systems.

Phosphor bronze is another copper alloy that combines copper with tin and phosphorus. The addition of tin to copper increases the alloy's strength and improves its corrosion resistance. The addition of phosphorus improves both the wear resistance and hardness of the alloy. Increased resistance to corrosion and wear makes phosphor bronze alloys an excellent choice for high-friction drive components. Worm wheels are manufactured with this alloy because it resists wear caused by friction created when the wheel engages with the worm, and it can resist deterioration caused by lubricants.

Aluminum bronze is the third copper alloy found in gears. This alloy combines copper with aluminum, iron, nickel and manganese. Aluminum-copper alloys are more wear-resistant than phosphorus-copper alloys, and they also have superior corrosion resistance. The addition of iron improves the wear resistance of this alloy. Nickel and manganese add to its corrosion resistance. Aluminum-copper alloys can resist corrosion caused by oxidation, exposure to salt water, and exposure to organic acids. The additional wear resistance of these alloys allows the design of gears that can handle significantly greater loads than similarly sized gears made from phosphor bronze alloys. Typical gears manufactured from aluminum bronze alloys include cross-shafted helical gears (worm gears) and worm gears.

Iron alloy

When gear design requires outstanding material strength, iron alloys are the best choice. In its raw form, gray iron can be cast and machined into gears. Typically, cast iron is used in applications where phosphor bronze is a suitable alternative but the application is not limited by the material's magnetic field. Steel is an alloy of iron, carbon and other trace elements. There are four main names for steel alloys. These are carbon steel, alloy steel, stainless steel and tool steel. Carbon steel alloys are used for most types of gears because they are easy to machine, have good wear resistance, can be hardened, are widely available, and are relatively inexpensive. Carbon steel alloys can be classified into mild steel, medium carbon steel and high carbon steel. Mild steel alloys have a carbon content of less than 0.30%. High-carbon steel alloys have a carbon content greater than 0.60%, and medium-content steels are in between. These steels are a good choice for spur gears, helical gears, gear racks, bevel and worm gears.

Carbon steel can be induction hardened or laser hardened to a maximum hardness of HRc 55. Alloy steels such as AISI 4140 contain additional elements such as aluminum, chromium, copper and/or nickel. These other elements, when alloyed with iron and carbon, produce steel that is harder, easier to machine, and more resistant to corrosion than regular carbon steel. These alloys are commonly used to make cylindrical gears, helical gears, gear racks, spiral bevel gears and worms.

In addition to induction and laser hardening, these alloys can be carburized or case hardened. The maximum hardness of these alloys is HRc 63. The added strength allows gears of the same size to withstand additional loads and resist wear for more cycles. Stainless steel alloys have a minimum chromium content of 11% and are alloys of many trace elements including nickel, manganese, silicon, phosphorus, sulfur and nitrogen. They are divided into magnetic ferritic stainless steels, non-magnetic austenitic stainless steels, martensitic and precipitation hardening. Austenitic stainless steel is designated as 300 series stainless steel, while ferritic stainless steel is designated as 400 series stainless steel. The most common type of stainless steel is alloy 304. It contains 18% chromium and 8% chromium. nickel.

For gears, 303 stainless steel is often used. In alloy 303, the chromium content is reduced to 17% and 1% of the alloy is sulfur. Because of the addition of sulfur, alloy 303 has improved machinability compared to alloy 304. When improved corrosion resistance is needed, alloy 316 is a better choice. This alloy has 16% chromium, 10% nickel and 2% molybdenum; Alloys 316 and 303 are used for cylindrical gears, helical gears and bevel gears. Gear racks are typically made from alloy 304. 440C is the most common ferritic stainless steel and 17-4PH is the most common precipitation hardening stainless steel.

Aluminum alloy

Aluminum alloys are a good alternative to iron alloys in applications requiring a high strength-to-weight ratio. Aluminum alloys typically weigh one-third the weight of steel alloys of the same size. The surface finish called passivation protects the aluminum alloy from oxidation and corrosion. This is similar to rust on steel alloys; however, it coats the surface, protecting it from further damage. Aluminum alloy is more expensive than carbon steel but cheaper than stainless steel. However, they are easy to machine, thus offsetting the increase in material costs.

Aluminum alloys cannot be used in high temperature environments because they begin to deform at 400°F. Common aluminum alloys used in transmissions are 2024, 6061, and 7075. 2024 aluminum alloy is a cousin to aluminum bronze because it is also an alloy of aluminum and copper. However, in this case, the ratio is reversed. Copper in 2024 gives this alloy high strength but greatly reduces corrosion resistance. Aluminum 7075 combines zinc and magnesium with aluminum to form a high-strength, load-bearing alloy. Aluminum 6061 is an alloy of aluminum, silicon and magnesium. It is a medium strength aluminum alloy that has good corrosion resistance and is weldable. All three of these aluminum alloys can be heat treated to improve their hardness. Gears made from aluminum alloy include cylindrical gears, helical gears, straight tooth bevel gears and gear racks.

Thermoplastic

Thermoplastics are the best choice for gears where weight is the most important criterion. Gears made from plastic can be machined just like metal gears; however, some thermoplastics are more suitable for production through injection molding. One of the most popular injection molded thermoplastics is acetal. This material is also known as polyacetal or polyoxymethylene (POM). Polyoxymethylene is available in two forms: It is produced as a copolymer (POM-H) or produced as a copolymer (POM-C). Gears can be made from either type of polymer. These can be cylindrical gears, helical gears, worm gears, bevel gears and gear racks.

The advantages of POM are its dimensional stability over a large temperature range, low coefficient of friction, and creep resistance. It is an excellent material for wear-resistant surfaces because it is self-lubricating, but POM is a poor material for shock-loaded applications due to its brittleness. For these types of applications, nylon is the better choice. Nylon 6/6 is a polyamide composed of two monomers with six carbon atoms per monomer. Nylon is very good at absorbing vibrations, but when exposed to moisture, it becomes dimensionally unstable. Nylon also undergoes dimensional changes when subjected to significant changes in temperature. Like acetal, nylon has a low coefficient of friction. Nylon has high mechanical strength. Nylon can be manufactured with molybdenum impregnated into it to provide self-lubricating properties. Nylon can also be manufactured with fiberglass or carbon fibers embedded into the material for added durability. Nylon is an excellent material for all types of gears including worm gears, rack gears, spur gears and straight tooth bevel gears.

Unobtainium
There is a gear material that has not yet been developed. It is the ideal material for all gear designs. This material is called unobtainium. This material is extremely light, has a harderness than natural diamond, has a friction coefficient of 0.001, is dimensionally stable in all environments, does not corrode or rust, is easy to process and has low material costs. crude is 1 cent. per pound. Once invented, it will make all other materials obsolete and will greatly improve the efficiency of gear drives.

2. Choose suitable materials in gear machining

Choosing the right material for manchining gears depends on the following factors:

Mechanical properties

The material must have excellent mechanical properties such as tensile strength, fatigue strength, toughness, durability, etc. However, this depends on the product you are processing. For example, plastics do not need harsh mechanical properties in the right product.

Friction

Gears must be in conjunction with each other, i.e. in contact with each other or other parts, to operate. As a result, suitable materials must have a significant coefficient of friction. Furthermore, you can improve friction by using appropriate post-processing mechanisms.

Manufacturing capabilities

Additionally, the material must be highly manufacturable using the processes outlined in the next section. This will reduce production costs and make production very efficient. Additionally, it will slightly improve accuracy and precision.

Hopefully this article has provided useful information for you on how to choose materials for machining gears to best prepare for your production.

If you are looking for a gear processing machine supplier, please contact us. VISC specializes in distributing outstanding gear processing machines for many applications. With more than 13 years of experience as an industrial processing solution consultant in combination with leading machine manufacturing experts in the world. VISC ensures we provide advice that effectively meets your unique needs.

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