Spiral Powder Metal Gears - Gear Movement Powder metal gears are made through a powder metallurgy process. Over the years, many advancements have been made in this process, which in turn has led to the increasing popularity of powdered metal as a gear material.
Powder metal gears are used in many industries, but are most commonly used in the automotive sector. Typical automotive applications include engine parts such as sprockets and pulleys, transmission components, oil pump gears and turbocharger systems. Powder metallurgy can be used to produce spur gears, helical gears, and bevel gears.
What is powder metallurgy?
Powder metallurgy is a process for forming metal parts. The process is divided into three steps:
1.mixed metal powder
2.Compact the powder to the desired shape
3.Shape compacted by heat under controlled conditions
The end result is a metal part that is nearly identical to the desired shape and requires little or no machine finishing, depending on the level of accuracy required.
Materials used to make powder metal gears
The powder metallurgy process starts with the collection of metal powder particles.
Metal powders are engineering materials that meet a wide range of performance requirements. Understanding powder is crucial in powder metallurgy as it is a critical input in producing the final metal part.
Powders are produced by solid-state reduction, atomization (gas, water or centrifugation), electrolysis or chemical treatment of metallic materials.
Fogging is the typical method used today. It involves converting molten metal into a spray of droplets, which then solidifies into a powder. Water atomization is the most common form of atomization because it produces irregularly shaped particles, which facilitates compaction for powder metal part production.
Metal powders are divided into elemental powders, partially alloyed powders or pre-alloyed powders. Elemental powder is the granular form of pure metal powder. They are the building blocks for making alloys and composite materials. Partially alloyed powders are mixtures of elemental powders of different materials mixed together, while pre-alloyed materials are alloyed states produced by atomizing a combination of metals.
In most cases, the powder mix, whether elemental or pre-alloyed, also contains additives (lubricants or binders) to extend tool life, help parts eject from compaction molds, or to hold metal parts in place prior to the sintering process together. These additives are removed from the parts that require the sintering process.
The geometry of an individual powder is determined by particle shape and internal structure, particle size and distribution, and surface area. Particles come in a variety of shapes, including spherical, irregular, flake, dendritic and sponge-like. The distribution of particle sizes in a powder affects compaction because smaller particles will fill the voids between larger particles. This size combination improves compaction density and material properties.
These are critical parameters in powder metallurgy as they determine the behavior of the powder during mold filling, compaction and sintering. These factors must be optimized to achieve the required strength and density both in the green stage and in the final sintered part.
Advantages and disadvantages of powder metal gears
The main reason powder metal gears are preferred over more traditional gear materials is cost. In high-volume production, making gears from powdered metal is cheaper than making gears from iron or steel. First, less energy is used in the manufacturing process and there is little material waste. Manufacturing costs are also generally lower, given that many powder metal parts don't require much (if any) machining.
Other attractive features of powder metals relate to their material structure. Due to the porous composition of powder metal gears, they are lightweight and generally run quietly. Additionally, powder materials can be uniquely blended to create unique properties. For gears, this includes the opportunity to impregnate porous materials with oil, thereby creating self-lubricating gears.
Powder metal gears have some disadvantages, however. One of the most significant issues is that powdered metal is not as strong as other materials and wears out faster than other materials. There are also dimensional limitations when using powder metal materials to keep gears manufacturable and effective. Producing powdered metal gears at low to medium volumes is also generally not cost-effective.
Mechanical finishing of powder metal gears
We have already said that the need for mechanical finishing of powder metal parts is reduced. But of course, in some cases, powder metal gears require additional processing. For example, gears used in some critical applications require high precision that cannot be achieved with powder metallurgy processes.
Why P/M machining gears?
The P/M process is ideal for manufacturing spur, helical and bevel gears. In addition, some racks and helical face gears were produced. Applications include gear motors for household appliances, as well as tractor transmissions, crane drives and various automotive components such as oil pumps, balance shaft adjusters, power window regulators and seat adjusters, starter motors, distributors and headlight activators.
Users often choose P/M to manufacture gears because of its multiple process advantages:
• Provides true involute tooth profile and full fillet radii.
• Easily incorporate weight relief holes to reduce part weight, Figure 1.
• Because the material is porous, it helps make the transmissions quiet (the porosity dampens sound) and allows them to self-lubricate (through oil impregnation).
• Gears can be combined into a single unit with other mechanical elements such as cams, ratchets, drive lugs, or other gears. Examples are shown in Figures 2, 3 and 4.
• Gears can be manufactured with radii at blind corners, eliminating the undercut clearance required to cut gears and providing additional strength at the radii.
• Almost no mechanical processing is required, and the material utilization rate is close to 100%.
• Gears can be produced with integrally mounted shafts, either as short trunnions or with machined steel shafts bonded to the gears during the sintering process.
Limitation
P/M gears have certain limitations in strength and size. One such limitation is that the impact resistance of the gear teeth is reduced by approximately 50% due to porosity and the contact fatigue strength is reduced by 33% compared to forged steel gears. Manufacturers can partially offset this limitation by increasing the density of gear teeth through double pressing and double sintering. Alternatively, high temperature sintering or case hardening can be used.
The compaction process occurs in the vertical direction, producing relatively dense teeth in spur gears because the teeth are parallel to the gear centerline. But other types of gears, such as bevel and helical gears, have teeth that are at an angle to the centerline. Therefore, the vertically oriented compaction process is less efficient and produces smaller tooth densities in these gears compared to spur gears. In this case, copper infiltration is often used to increase the density of the gear teeth (and the corresponding mechanical properties).
Another limitation of P/M gears is their tooth flank width. The amount of powder that can be used in most compactors limits the gear face width to less than 3 inches. In addition, friction losses between the powder and the mold result in reduced density along the face width, with the lowest density in the middle. View. The larger the face width, the greater the density attenuation.
These density differences can lead to dimensional changes during sintering and heat treatment. Large density changes can cause deformation, especially with larger gears.
Keep improve
Powder metal gear manufacturers, with the help of powder producers and process equipment suppliers, are developing methods to improve the dimensional control and mechanical properties of powder metal gears.
Size control
One way to improve the dimensional consistency of P/M gears (spur and helical) is to roll the surface of the sintered gear over the main gear. This roll forming operation can increase the AGMA quality grade of Q6 gears to Q9. Surface rolling has produced AGMA Q9 gears in diameters ranging from 12 to 28 and tooth counts from 10 to 56. One P/M gear manufacturer achieved extended gear life, reduced noise levels, reduced wear and enhanced durability through this process.
Another method that is gaining favor is sinter hardening, which reduces the distortion typically associated with conventional quenching and tempering heat treatments of conventional steels. The sintering hardening method eliminates the need to reheat the gear and subject it to rapid oil quenching. In contrast, cooling in a sintering furnace achieves the required mechanical properties without losing dimensional accuracy. Higher alloy steels are required to achieve the desired results in sintering hardening. But the higher cost of these steel alloys can be completely offset by eliminating the quench hardening process.
Increased tooth density
Since the durability of permanent magnet gears is related to the bending strength and contact fatigue strength of the gear teeth, many studies have focused on increasing the tooth density. Here are some examples:
• Roll compaction densification. The rolling process described earlier to improve dimensional control also makes the gear tooth surfaces more dense. Hitachi researchers reported that rolled case-hardened AISI 4600 P/M steel achieved a 32% improvement in bending fatigue strength and a 3.5-fold improvement in contact fatigue strength. The contact fatigue strength of rolled P/M steel reaches 96% of the strength of case-hardened forged AISI 4118 steel.
• Warm compaction. This method is an extension of the traditional room temperature compaction process, increasing the compaction temperature to approximately 300 F. Warm compaction enables part densities in the range of 7.3 to 7.5 g/cm3 (93 to 95% of the density of conventional machined steel) that could previously only be achieved with two pressings and two sinterings. Warm compaction can result in cost savings of up to 25% compared to dual pressing and dual sintering processes. This new method works for both spur and helical gears. Preliminary results show a 30% improvement in tooth strength compared to traditional compaction and sintering; when warm compaction is combined with high-temperature sintering, improvements exceed 50%.
• Rotary pressing. In the process, a small press applies rapid, repetitive loads on the sintered gear teeth, several teeth at a time. This repeated loading causes intense localized plastic flow and densification in the tooth. The density of gear teeth is reported to be in excess of 7.6 g/cm 3 (97% dense), resulting in excellent fatigue and wear properties.
• Australian Rolling. The rolling process involves rolling the gear against the main gear during a heat treatment process. After heating, gears made of low-alloy steel are quenched to a temperature just above the martensitic transformation, then plastically deformed by rolling, and then finally quenched to room temperature. Ausrolling conventional powder metallurgy steel reduces surface porosity from 14% to less than 2% and increases rolling contact fatigue strength by more than 10 times. The Penn State researchers also claim that the process resulted in significant improvements in gear accuracy and surface finish.
Which industries are using powder metal gears?
Powder metal gears are a popular choice for different industries, including:
Agriculture
Power transmission
Fluid handling
Ocean
Material handling
Lawn and Garden
Leisure
Electromagnet
Powder metal gears are widely used in these industries because they can be manufactured repeatedly and uniformly, making their production cost-effective. They are also porous, which reduces weight and dampens sound to meet the unique needs of different applications.
Powder metal gears are manufactured through resin or oil impregnation, which adds self-lubrication to extend their life and improve efficiency.
Examples of powder metal gears
The three most common types of powder metal gears are spur gears, helical gears, and bevel gears. Spur gears are cylindrical components with straight teeth used in applications where mechanical motion needs to be transmitted and torque, power and speed controlled. They are simple, cost-effective, durable gears that provide constant speed to drive a variety of industrial applications.
Helical gears are cylindrical gears with helical teeth. They have greater overlap than spur gears and are best suited for applications requiring quietness and limited vibration. A pair of helical gears have similar helix angles but opposite helical directions.
Bevel gears are toothed rotating components used to transfer shaft power or mechanical energy between intersecting shafts. These axes can be vertical or at an angle. This results in a change in the shaft power of the rotating shaft. These gears can also increase or decrease torque because they have opposite effects on angular velocity.
Other common types of powder metal gears include:
Gear
Combination
Spiral bevel
Shelf
Common Applications of Powder Metal Gears
Due to their durability and versatility, powder metal gears are commonly used in the following industries:
Medical
Car
Appliance
Electrical tools
Outdoor power equipment
Ocean
Lawn and garden equipment
Precautions for powder metal gears
Gear quality can reach AGMA grade 8 without the need for secondary operations
•The tooth shape of the powder metal gear is pressed into the body by a precision mold, and we do not have the cost of repairing the teeth.
•Forming gear teeth in precision molds means excellent consistency from part to part
•Gear IDs can have spline shapes, mounting keyways, D-shapes, virtually any shape without expensive broaching
•Gear teeth can be shaped to your preference, with root radii formed entirely in precision molds for maximum strength and no secondary machining required
•Helical gears with helix angles up to 20 degrees
•One piece flange and hub gear available
•Powder metal gears can be integrally hardened and, depending on density and raw material type, can also be case hardened
•For applications such as powder metal pump gears, we can provide you with ready-to-use gears that are fully machined to extremely tight tolerances and surface treatments
•Tools are required, usually with a short payback period and a one-time fee, and then H&Z will maintain the tools for the life of the part
Conclusion
As a precision gear manufacturer, H&Z is able to perform a variety of finishing operations on powder metal gears. This includes precision gear grinding of spur and helical gears. Finishing techniques such as precision gear grinding produce precise tooth shapes and high-quality surface finishes.
We can also perform gear cutting operations, cutting gear teeth from powder metal blanks. This operation is particularly useful when producing helical gears, since angled teeth are difficult to form using powder metallurgy.
H&Z has advanced manufacturing machinery and a skilled workforce to meet all your gear manufacturing needs. If you have questions or contact us today for a quote.
Related reading recommendation
