Extrusion Additive Manufacturing of Thixotropic Metal Alloys
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Solution Overview
Problem
Existing extrusion-based additive manufacturing methods for metal alloys, particularly thixotropic aluminum alloys, face challenges in maintaining the semi-solid state and preventing material aging and demixing, leading to inefficiencies and potential clogging during the layer-by-layer application process.
Innovation Solution
The apparatus employs a feeder system with a heatable die and preheating devices, including an induction coil and resistance heating, to maintain the semi-solid state of the metal alloy, using the bar-shaped starting material as pistons and minimizing the heating surface to prevent material aging, along with an ultrasonic generator to ensure uniform distribution and prevent demixing, while maintaining an inert gas environment to prevent contamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the heating surface is enlarged to improve heating efficiency, then the heating rate increases, but material aging occurs in the form of globulite enlargement in the metal structure
Solution Approach 1:
The heating system applies different heating methods to different zones: induction heating for rapid temperature rise and resistance heating for precise temperature maintenance. This localized heating approach allows efficient heating without excessive heating surface contact time that would cause globulite enlargement.
Solution Approach 2:
The starting material is preheated using induction heating before entering the die channel, which reduces the temperature gradient and prevents thermal shock. This preliminary action prepares the material for extrusion without requiring excessive heating during the actual extrusion process.
2Ease of operation
If the metal wire is supplied to a liquefier to produce melt, then the material becomes fluid for extrusion, but the material may age and demix during processing
Solution Approach 1:
The material is heated to specific temperature ranges to achieve partial melting without complete liquefaction. The temperature is precisely controlled to maintain the semi-solid state with optimal liquid-solid ratio, preventing demixing while ensuring sufficient fluidity for extrusion.
Solution Approach 2:
The extrusion process operates continuously with constant propulsion force applied through the gear conveyor or worm conveyor. This continuous action prevents material stagnation and demixing that would occur with intermittent processing, maintaining homogeneous composition throughout the extrusion.
3Ease of manufacture
If the starting material is heated to produce semi-solid state, then the material becomes processable, but contamination by reactive gases such as oxygen and carbon dioxide may occur
Solution Approach 1:
The die channel and heating zones are purged with inert gas (argon or nitrogen) to create an oxygen-free environment. This prevents oxidation and contamination of the semi-solid aluminum alloy during heating and extrusion, maintaining material purity while enabling processability.
4Productivity
If high pressing forces are applied to extrude the semi-solid material, then the extrusion speed increases, but the starting forces must be particularly high which requires complex propulsion devices
Solution Approach 1:
The bar-shaped starting material itself serves as the piston for extrusion. The material is fed in bar form and pushed through the die channel using its own structural integrity, eliminating the need for complex external propulsion mechanisms while maintaining high extrusion speeds.
Solution Approach 2:
A simple gear conveyor or worm conveyor acts as an intermediary to translate rotational motion into linear propulsion force. These relatively simple mechanical devices provide the necessary starting forces without requiring complex hydraulic or pneumatic systems.
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 allows for precise control of the liquid and solid material ratio, minimizing material aging and clogging, and ensuring consistent extrusion, enabling efficient layer-by-layer application of thixotropic metal alloys with improved mechanical properties.
Implementation Method 1
a preheating device in the form of an induction coil including a cap for field concentration, which encloses the channel
Implementation Method 2
a heater in the form of resistance heating for producing the semi-solid processing state of the preheated starting material
Implementation Method 3
Ultrasonic transmitters are deployed in order to prevent retention on the walls of the die
Data Source
AI summary
An apparatus and a method for an extrusion-based additive manufacture of products from thixotropic metal alloys, with a feeder (2) for the starting material, wherein the starting material is in bar form (3), with a preheating device in the form of an induction coil (8) including a cap for field concentration (7), which encloses the channel (6), with a heater (10) for producing a semi-solid processing state of the preheated starting material, which likewise encloses the channel (6), with an afterheater (13) in the region of the die (11) and with an adjustable workpiece table (15) for the product to be built up layer by layer.