Sintered Body Cooling with Thermal Resistors and AE Detection
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Solution Overview
Problem
In discharge plasma sintering methods, sintered bodies formed from isotropic graphite molds often experience cracking due to thermal stress and rapid cooling, which existing technologies fail to effectively prevent.
Innovation Solution
A manufacturing device and method utilizing a mold with isotropic graphite punches and spacers, interposed with thermal resistors of higher thermal resistance than the mold components, along with an acoustic emission detection system to monitor and determine crack occurrence during cooling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If discharge plasma sintering is performed using isotropic graphite molds and punches, then high density and fine grain structure can be achieved, but thermal stress during cooling causes cracking in the sintered body
Solution Approach 1:
A thermal resistor (made of material with lower thermal conductivity than the punches and die, such as alumina or zirconia) is introduced as an intermediary component between the isotropic graphite punches and the sintered body. This thermal resistor mediates the thermal contact, reducing the rate of heat transfer from the sintered body to the punches during cooling, thereby minimizing thermal stress and preventing cracking while still allowing effective sintering
Solution Approach 2:
The thermal resistance parameter of the contact interface between the punch and sintered body is changed by introducing the thermal resistor. This modifies the cooling rate parameter, making it more gradual and uniform, which prevents thermal shock and cracking while maintaining the benefits of plasma sintering
2Productivity
If rapid cooling is applied after sintering to increase productivity, then manufacturing efficiency improves, but thermal shock causes cracking in the sintered body
Solution Approach 1:
The thermal resistor serves as a thermal buffer that controls the cooling rate. It allows heat to be removed from the sintered body at a controlled, gradual rate rather than rapidly, preventing thermal shock and cracking while still enabling efficient production cycles
Solution Approach 2:
The thermal resistor is positioned in advance between the punch and sintered body to provide thermal cushioning during the cooling phase. This pre-positioned thermal barrier protects the sintered body from sudden temperature changes and mechanical stress during cooling
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 solution effectively suppresses cracking in sintered bodies by controlling thermal shock and enabling early detection of cracks through acoustic emission analysis, ensuring higher quality and reliability of the sintered products.
Implementation Method 1
the plurality of thermal resistors are interposed between the first punch and the first spacer, between the first spacer and the first ram, between the second punch and the second spacer, and between the second spacer and the second ram, wherein the plurality of thermal resistors have greater thermal resistance than thermal resistance of the die, the first and second punches, and the first and second spacers
Implementation Method 2
an acoustic emission (AE) wave detecting unit configured to detect an AE waveform from the sintered body, while the sintered body formed in the cavity of the die is cooling; and a crack occurrence determining unit configured to determine whether a crack has occurred in the sintered body using the detected AE waveform
Implementation Method 3
discharge plasma sintering is performed on the molding material by applying a voltage, while performing pressing
Data Source
AI summary
In a manufacturing method for a sintered body, a mold device including a die, first and second punches, first and second spacers, first and second rams, and a plurality of thermal resistors is used. The manufacturing method includes an operation of loading raw material powder into a cavity of the die and then sintering the raw material powder, while pressing and molding the raw material powder in the uniaxial direction using the first and second punches, to form a sintered body and an operation of cooling the formed sintered body. In the operation of cooling the formed sintered body, an acoustic emission (AE) waveform is detected from the formed sintered body, and it is determined whether a crack has occurred in the formed sintered body using the detected AE waveform.