Pre-Bent Substrate Clamping for DED Residual Stress Control
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Solution Overview
Problem
Directed energy deposition (DED) processes in additive manufacturing, particularly for titanium and titanium alloys, face significant challenges with residual stress and distortion due to thermal gradients and incompatible strain fields, leading to geometric inaccuracies and potential failure, with existing methods being costly and inefficient.
Innovation Solution
The use of a pre-bent substrate with a curved clamping mold and controlled thermal pre-bending, combined with pre-heating and a gas jet cooling system, to minimize residual stress and distortion by inducing uniform thermal gradients and stress distribution during the DED process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional DED processes are used to manufacture metal parts, then additive manufacturing freedom and material utilization are improved, but residual stress and distortion increase leading to geometric inaccuracies
Solution Approach 1:
The substrate is pre-bent to a predetermined curvature before the DED process begins. This preliminary action creates a pre-stressed state that counteracts the thermal gradients and residual stresses that will develop during additive manufacturing, thereby maintaining geometric accuracy while preserving manufacturing freedom
Solution Approach 2:
The substrate curvature is changed from flat to pre-bent, altering the mechanical state of the substrate. This parameter change in the substrate geometry allows the DED process to proceed with improved dimensional stability, reducing distortion and maintaining manufacturing precision
2Productivity
If high thermal energy is applied during DED to melt and deposit metal layers, then material deposition efficiency is improved, but thermal gradients and residual stress increase causing distortion
Solution Approach 1:
The pre-bent substrate acts as a counterbalancing element that provides opposing mechanical stress to the thermal stress generated during high-energy DED processing. This allows aggressive deposition parameters to be used while the pre-bent substrate compensates for the resulting distortion
Solution Approach 2:
The predetermined substrate curvature serves as a pre-established cushion against the harmful effects of thermal gradients. By preparing the substrate in advance with the appropriate curvature, the system is pre-cushioned against the distortion that would otherwise result from high thermal energy input
3Speed
If rapid cooling is applied after metal layer deposition to reduce cycle time, then manufacturing speed is improved, but thermal shock and residual stress increase leading to cracking and distortion
Solution Approach 1:
The substrate is pre-bent before deposition to create a stress state that compensates for the effects of rapid cooling. This preliminary preparation allows aggressive cooling rates to be used without causing thermal shock damage, as the pre-bent substrate absorbs the stress differential
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 approach results in reduced residual stress and distortion, enhancing the dimensional accuracy and mechanical properties of DED-manufactured components, allowing for larger, more complex parts to be produced within specified tolerances and reducing material waste and manufacturing costs.
Implementation Method 1
The pre-bending of the substrate includes inducing steep through-thickness thermal gradients in the substrate
Implementation Method 2
Owing to localized heat and cooling cycling, as the thermal source melts a metal material and deposits each new metal layer and re-melts previously solidified metal layers, large amounts of welding-induced residual stress can arise and accumulate during DED of metal preforms
Implementation Method 3
Thermal expansion and contraction can occur as a result of transient thermal excursions and steep thermal gradients that can be present during DED
Data Source
AI summary
Provided are a curved clamping mold and systems and methods using the curved clamping mold for manufacturing objects, especially titanium and titanium alloy objects, by directed energy deposition. The methods include thermally pre-bending the substrate onto which the object is to be manufactured to form a pre-bent substrate, attaching the pre-bent substrate to a jig using the curved clamping mold as an underlying support, pre-heating the substrate, and forming the object on the pre-heated, pre-bent substrate using a directed energy deposition technique.