DED Thermal Control Using Secondary Heating and Cooling
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Solution Overview
Problem
Current additive manufacturing methods fail to effectively control thermal gradients and cooling rates globally within the build, leading to defects, residual stresses, and suboptimal mechanical properties in materials like high carbon steel and titanium, due to their focus on local melt pool phenomena.
Innovation Solution
The integration of a secondary heating and cooling system with a dynamic thermal model into Direct Energy Deposition (DED) machines, utilizing a secondary heat source, cooling source, and thermal measurement devices to actively control temperature gradients and cooling rates across the build, ensuring uniform microstructure and mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If current control methods focus only on local melt pool phenomena, then processing simplicity is maintained, but thermal gradients and cooling rates cannot be controlled globally within the build
Solution Approach 1:
The build is divided into multiple zones with independent temperature control. Multiple heating elements are positioned at different locations (bottom, sides, top) to independently control thermal conditions in different regions of the build chamber, enabling global thermal gradient management while maintaining manageable system complexity through modular control.
Solution Approach 2:
A dynamic thermal model acts as an intermediary between the control system and the physical build. The model predicts temperature distribution and thermal gradients, allowing the control system to adjust heating element parameters proactively to maintain desired thermal conditions without direct real-time measurement of every point in the build.
2Strength
If rapid cooling is applied to achieve smaller grain size or desired material phase, then material properties are improved, but high residual stresses and distortion occur
Solution Approach 1:
The cooling rate is dynamically adjusted based on real-time temperature monitoring and the dynamic thermal model. The system transitions from static, uniform cooling to dynamic, spatially-varying cooling rates that adapt to the evolving thermal state of the build, allowing rapid cooling where beneficial for microstructure while slowing cooling where stress accumulation occurs.
Solution Approach 2:
Different regions of the build receive different cooling rates tailored to their specific requirements. The system applies localized thermal management where rapid cooling is applied to achieve desired microstructure in specific areas, while other regions experience slower cooling to minimize stress, creating spatially-varying thermal histories throughout the build.
3Stress or pressure
If uniform cooling is applied throughout the build, then residual stresses are reduced, but non-uniform microstructure and dimensional integrity cannot be achieved
Solution Approach 1:
The build is divided into multiple zones with independent temperature and cooling control. Heating elements and cooling mechanisms are positioned to independently manage thermal conditions in different regions, allowing the system to reduce overall residual stress through controlled cooling while maintaining dimensional integrity through localized thermal management of critical features.
Solution Approach 2:
The system uses real-time temperature monitoring and the dynamic thermal model to continuously adjust heating and cooling parameters. This feedback control allows the system to maintain desired temperature profiles that balance residual stress reduction with dimensional integrity, adjusting cooling rates based on actual thermal conditions rather than applying uniform cooling.
4Manufacturing precision
If the build strategy is optimized for thin features, then those features are properly formed, but adjacent thicker features become overheated
Solution Approach 1:
The system applies spatially-varying heating and cooling to different regions of the build. Thin features receive targeted heating and controlled cooling to ensure proper formation, while adjacent thicker features receive different thermal management to prevent overheating. Each region's thermal history is independently optimized for its geometric characteristics.
Solution Approach 2:
The thermal management system dynamically adjusts heating and cooling parameters based on real-time temperature measurements and the dynamic thermal model. This allows the system to adapt cooling rates and heating power to the specific thermal state of different build regions, maintaining appropriate temperature gradients for thin features while preventing excessive heat accumulation in thicker features.
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
This solution enables precise control of thermal gradients and cooling rates, reducing defects, residual stresses, and optimizing mechanical properties by maintaining desired temperature profiles throughout the build process, resulting in improved dimensional integrity and material quality.
Implementation Method 1
a secondary heat source, separate from any heat source associated with the additive manufacturing system, for directing a heat flow to a selected portion of the build
Implementation Method 2
The cooling source is configured to cool the build by one of forced convection, spray cooling, and via a material auxiliary to the build
Implementation Method 3
The material auxiliary to the build comprises a cryogenic material
Data Source
AI summary
A system for making a build using directed energy deposition is provided. The system includes a primary heat source; a processing nozzle movable relative to the build for delivering a metal powder, a carrier gas for the metal powder, and a shield gas to the build; a melt pool sensor for providing information regarding a temperature of a melt pool of the build; a secondary heat source separate from the primary heat source positionable relative to the build for delivering heat to a selected area of the build; a cooling source positionable relative to the build for delivering a cooling fluid to a selected area of the build; and a control system for operating the primary heat source, the secondary heat source and the cooling source to maintain a desired temperature profile for the build. The system preferably includes a temperature sensor for providing a temperature profile of the build. The temperature control system preferably includes a programmable controller configured to control the secondary heat source and the cooling source to conform the temperature of the build to the desired temperature profile. In one embodiment, the programmable controller is pre-programmed with a dynamic thermal model of a thermal history of the build for each time step.