Object: Industrialization of the advanced mixing process of metal powders for the additive manufacturing sector (Cold Spray, SLM, etc.)
Co-funded by POR CAMPANIA – FESR 2014-2020 – DECRETO N°225 del 07/08/2018 – CUP: B32C18000070007 – SURF: 17048BP000000024 – UNIONE EUROPEA | Fondo Europeo di Sviluppo Regionale
The fluidization bed mixing technique assisted by acoustic fields consists of a dual action of a pressurized gas and a sound pressure field. These actions mix metal powders for production of components with high level of customization both in shape and material, using additive technologies such as Cold Spray and 3D printing.
The final goal of the POWMIX project was to design and manufacturing an industrial-scale reactor capable of producing homogeneous (on a micrometric scale) mixes of metal powders, whose composition is defined on the customer needs and the operating specifications of the component.
This mixing system integrates fluidized bed mixing technique with acoustic fields which act as a forcing system in order to allow and/or optimize the separation and aggregation between the different agglomerates of powder (clusters), ensuring the homogeneity of the mixture made.
The activities included the complete design and production of the fluidized bed mixing system assisted by acoustic fields:
- 3D Design
- Design verifying
- Drawing Set
- Testing and Calibration
The advanced mixing system is composed of:
– fluidization reactor: it is the main element of the plant, there are the elemental powders to be mixed.
– Support structure: it constitutes the plant frame and guarantees the handling of the reactor for the loading / unloading of the powders.
– Generation and propagation system of the acoustic field: it supplies the powders bed with acoustic waves (forcing) for the realization of the process.
– Management and monitoring system: it constitutes the interface of the plant and allows a continuous quality control on the process.
To perform the operations of fluidization and powders mixing, nitrogen is injected from the bottom inside the fluidized bed reactor. The flow rate of the process fluid is continuously monitored by an MFC sensor (Mass Flow Controller). Through a distribution plate (sintered bronze) the flow permeates through the powder bed making it fluid (fluidization), ie:
– denser objects when into a fluidized bed sink;
– under inclination of the reactor, the free surface of the solid remains horizontal;
– making side holes in the duct involves the continuous release of bed material.
The pressure drop of the nitrogen flow is measured through pressure transducers placed upstream and downstream of the bed.
The acoustic field generation and propagation system consists of:
– wave generator: capable of producing the desired shape, amplitude and frequency signal.
– signal amplifier: capable of generating a signal with an intensity of around 150 dB.
– loudspeaker: installed on the head of the reactor for acoustic signal reproduction
– microphone: to monitor the sound field supplied to the dust bed.
The feedback on cluster composition (homogenization of the mixture) is obtained through optical sensors placed inside the fluidization chamber.
The system thus designed allows to process more than 100 kg of metal powders for the realization of custom mixtures.