Metal Powder Injection Moulding Internal Cavity Support
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Solution Overview
Problem
The metal injection molding (MIM) technique faces challenges in manufacturing parts with internal cavities, particularly those with non-self-supporting complex forms, as the grains of metal or alloy powder are not sufficiently linked to support significant stresses during sintering, leading to deformation or collapse, and existing methods fail to achieve precise tolerances and non-deformable nuclei within these cavities.
Innovation Solution
A method involving a ceramic green core, prepared with a thermoplastic binder, is used to create internal cavities, where the core is coated with an anti-adhering layer and remains in place during sintering to support the part, ensuring dimensional stability and allowing for the removal of the core post-sintering through chemical dissolution or dropping, enabling the production of complex parts with internal cavities without deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional MIM technique is used to manufacture parts with internal cavities, then the manufacturing process is simple, but the part deforms or collapses during sintering due to insufficient grain linkage to support stresses
Solution Approach 1:
A sacrificial core made of soluble material is introduced as an intermediary element within the mold cavity. This core serves as a temporary support structure during the molding and sintering processes, preventing collapse of the internal cavity. The core is specifically designed to be dissolved or removed after sintering, leaving the desired internal cavity in the final part.
Solution Approach 2:
The sacrificial core is placed in the mold cavity before the metal powder mixture is injected. This preliminary placement creates a pre-formed internal cavity structure that guides the metal flow and provides structural support during subsequent sintering, preventing deformation before the sintering stress can cause collapse.
2Stability of the object's composition
If hard ceramic nuclei are used to create internal cavities in MIM parts, then the cavity structure is maintained, but the nuclei cannot deform to follow the withdrawal of the room during sintering, causing deformation of the finished part
Solution Approach 1:
The core material is specifically selected to have different physical and chemical properties compared to the metal matrix. The core is made of a soluble material that can be dissolved after sintering, allowing it to remain as a non-deforming placeholder during the process while enabling precise cavity formation in the final part without the deformation issues of hard ceramic nuclei.
3Ease of manufacture
If the binder is removed before sintering, then the metal grains are exposed, but the grains are not sufficiently linked to support significant cantakes during sintering, leading to room collapse
Solution Approach 1:
The sacrificial core is placed in the mold cavity before the metal powder mixture is injected and before binder removal. This core provides structural support during the binder removal process and throughout sintering, preventing collapse of the internal cavity while the metal grains are being linked together. The core acts as a temporary scaffold that remains until the metal structure is sufficiently strong.
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 the successful manufacture of parts with internal cavities and non-self-supporting complex forms, maintaining dimensional stability and avoiding collapse, while enabling the removal of the core without damaging the part, thus overcoming the limitations of previous MIM techniques.
Implementation Method 1
preparing a mixture of a metal or metal alloy powder and a thermoplastic binder such as a wax or a polymer. It is ensured that in this mixture, the particles, metal or alloy grains are coated with the thermoplastic binder
Implementation Method 2
the delineation is made by thermal heating the green piece, usually in a controlled atmosphere oven
Implementation Method 3
During sintering, the room is heated, up to a temperature close to the metal melting temperature or the metal alloy but less than this melting temperature. Sintering causes a reduction, a removal, homothetic of the play because the grains of metal or alloy powder bind between them by diffusion thus causing a densification of the room
Data Source
Figure 1~4
AI summary
The invention relates to a method for producing, by a metal powder injection moulding (MIM) technique, a part consisting of at least one metal and/or at least one metal alloy comprising at least one internal cavity, in which a green core made of a mixture of at least one powder of at least one ceramic and a thermoplastic binder is used.