Sintered Gear Tooth Portion Density Gradient
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Solution Overview
Problem
Existing methods for enhancing the density of sintered gears, such as hot forging and cold forging, face challenges like increased weight, loss of damping capacity, and complexity, while rolling methods struggle with uniform densification and long processing times, especially for gears with short modules or shaft holes.
Innovation Solution
A method involving a sintered gear with distinct high and low density areas, where the high density area is formed over the tooth flank and tooth bottom land with a density of 7.6 Mg/m3 or more, and a low density area with a density of 7.3 Mg/m3 or less, along with an intermediate area, allowing for improved wear resistance and rigidity without excessive weight or production complexity, using a process that includes powder preparation, compacting, sintering, recompressing, and heat treatment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If hot forging is used to enhance density, then wear resistance is improved, but weight increases and damping capacity is lost
Solution Approach 1:
The invention applies local quality by creating a high density area specifically in the tooth portion (tooth flank and tooth bottom land) while maintaining lower density in other portions. This is achieved by forming a compact with a tooth portion having a thickness shorter than other portions, then compressing only the tooth portion during recompression. The tooth portion achieves a density of 7.6 Mg/m3 or more, while other portions maintain density of 7.3 Mg/m3 or less, providing wear resistance where needed without increasing overall weight.
2Strength
If cold forging is used to enhance density, then wear resistance is improved, but device complexity and production cost increase
Solution Approach 1:
The invention merges the compacting process with the tooth profile formation process. The die cavity is designed to directly form the tooth profile during compacting, eliminating the need for separate forging operations. The compact is compressed in the die cavity to form the tooth profile, and then the sintered body is recompressed to densify the tooth portion. This integration reduces device complexity and production cost compared to separate cold forging operations.
3Strength
If cold forging is used to enhance density, then wear resistance is improved, but manufacturing precision deteriorates due to flange formation
Solution Approach 1:
The invention extracts the excess material removal step by designing the die cavity to match the final gear outer diameter. The compact is compressed to have the same outer diameter as the finished gear, eliminating the need to form and subsequently remove flanges. This direct formation approach maintains manufacturing precision and size accuracy while achieving the desired density in the tooth portion.
4Strength
If rolling is used to enhance density, then wear resistance is improved, but productivity decreases due to long processing time
Solution Approach 1:
The invention replaces the gradual mechanical rolling process with a direct compression process. Instead of rolling the sintered body multiple times to densify the tooth flank, the invention compresses the sintered body in a die cavity to directly form the tooth profile and then recompresses it to densify the tooth portion. This substitution reduces processing time and improves productivity while achieving the same wear resistance enhancement.
5Strength
If rolling is used to enhance density, then wear resistance is improved, but manufacturing precision deteriorates due to insufficient densification in short module gears
Solution Approach 1:
The invention applies compression in the thickness direction (another dimension) to densify the tooth portion, rather than relying solely on rolling in the radial direction. By compressing the tooth portion which has a thickness shorter than other portions, the invention achieves effective densification even in short module gears where rolling amount is insufficient. The recompression process applies pressure perpendicular to the tooth flank surface, ensuring uniform densification regardless of module size.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method achieves high wear resistance, rigidity, and fatigue strength while maintaining a low overall density, enabling efficient mass production and reducing the burden on production equipment, allowing for the use of sintered gears in high-pressure applications.
Implementation Method 1
the mixed powder is compacted to have a density less than 7.3 Mg/m3
Implementation Method 2
The compact is sintered at a temperature of 1000 to 1200° C.
Implementation Method 3
The compact is sintered at a temperature of 1000 to 1200° C.
Implementation Method 4
the tooth portion is compressed and densified in the thickness direction in a recompression process
Implementation Method 5
a heat treatment step for heating the recompressed body at a temperature range of 850 to 950° C. for a predetermined time, and quenching the recompressed body from the temperature range, and tempering the recompressed body
Data Source
AI summary
A sintered gear comprises: plural tooth portion having a tooth flank and a tooth bottom land; a high density area formed over entire surface of the tooth portion, the high density area having a density of 7.6 Mg/m3 or more and formed with a depth of 1 mm or more from the surface; a low density area formed in deeper area than the high density area, the low density area having a density of 7.3 Mg/m3 or less; and an intermediate area formed between the high density area and the low density area, the intermediate area having a density gradient in which the density is gradually decreased from the high density area to the low density area.