Two-Stage Pressing for Fuel Cell Interconnector Moldings
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Solution Overview
Problem
The production of complex moldings with knob-like and/or web-like elevations, such as interconnectors for fuel cells, faces challenges with non-uniform density and dimensional stability due to the difficulty in pressing powdery materials, especially chromium-based alloys, which are brittle at lower temperatures and exhibit high and irregular shrinkage during the production process.
Innovation Solution
A two-stage pressing process is employed, where the boundary surfaces of the disk-like or plate-like basic body are pressed to the approximate final shape in the first stage, while the elevations are pressed to an oversize with a specific angle of inclination, followed by a second stage where the elevations are compacted to the final shape with an enlarged angle, using different press dies in each stage to achieve uniform compaction and adequate strength and gas-tightness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single-stage pressing process is used to produce moldings with knob-like and/or web-like elevations from powdery raw materials, then the production process is simple, but the density is non-uniform and dimensional stability is poor
Solution Approach 1:
The pressing process is divided into two distinct stages: a first pressing stage that forms the basic body with elevations at an oversize, and a second pressing stage that compacts the elevations to their final dimensions. This segmentation allows each stage to optimize for different requirements - the first stage for overall shape formation and the second stage for density uniformity and dimensional precision of the elevations.
Solution Approach 2:
The first pressing stage performs preliminary forming of the basic body and elevations to an oversize, creating a preform that requires less material removal and enables more uniform compaction in the second stage. This preliminary action reduces the compaction pressure needed in the final stage, improving density uniformity across the complex geometry.
2Manufacturing precision
If material-removing machining is used to produce the final shape from a semifinished product, then dimensional accuracy can be achieved, but the production cost is very high
Solution Approach 1:
The two-stage pressing process performs preliminary shaping to near-final dimensions, minimizing the amount of material that needs to be removed by subsequent machining operations. The first stage creates the basic geometry and the second stage refines the elevation dimensions, so that only minor finishing operations are needed, dramatically reducing machining costs while maintaining dimensional accuracy.
Solution Approach 2:
The process controls the angle of inclination of the elevation side surfaces during pressing to optimize the balance between direct pressing capability and subsequent machining requirements. By adjusting pressing parameters and elevation geometry, the process minimizes material removal while achieving the required final dimensions.
3Temperature
If chromium-based alloys are used for high temperature fuel cell interconnectors, then high temperature performance is achieved, but the materials are brittle at lower temperatures and difficult to press
Solution Approach 1:
The two-stage pressing process uses different pressing parameters for each stage, with the first stage using lower pressures to form the oversize preform and the second stage using optimized pressures to compact the elevations. This parameter optimization enables successful pressing of brittle chromium-based alloys that would be too difficult to press in a single stage with high pressure.
Solution Approach 2:
Dividing the pressing operation into two stages reduces the peak pressure requirements and allows the brittle material to be handled more gently during the first forming stage, then compacted effectively in the second stage. This segmentation prevents material failure while achieving the required density and strength.
4Shape
If powder injection molding techniques are used to produce complex components, then shaping capability is improved, but material density is inadequate and dimensional stability is poor due to high and irregular shrinkage
Solution Approach 1:
The process optimizes the angle of inclination of the elevation side surfaces and the projection dimensions in each pressing stage to control shrinkage behavior. By carefully selecting these geometric parameters, the process achieves uniform compaction and minimizes irregular shrinkage, resulting in adequate material density and improved dimensional stability after sintering.
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 moldings with improved homogeneity, density, and strength, overcoming the limitations of single-stage pressing methods by allowing for the use of difficult-to-press powders and ensuring economic production on a larger scale.
Implementation Method 1
pressing and sintering powdery raw materials close to the final shape
Implementation Method 2
pressing and sintering powdery raw materials close to the final shape
Data Source
AI summary
The invention relates to a process for producing a molding, comprising a disk-like or plate-like basic body -5- having a large number of knob-like and/or web-like elevations -4-3- which merge into the basic body -5- with inclined side surfaces, by means of pressing and sintering powdery raw materials close to the final shape.According to the invention, the pressing is carried out in a two-stage pressing operation. In the first stage the boundary surfaces of the basic body -5- are pressed to at least the approximate final shape as far as the transition regions of the elevations -3-4- and, at the same time, the elevations -3-4- are pressed to an oversize. The projection h′ of the elevations -3-4- from the basic body -5- is greater by 10%-150% as compared with the projection h from the basic body -5- in the finally pressed state. Their side surfaces form an angle of inclination α′ in the range from 90°-150° with the respectively adjacent boundary surface of the basic body -5-. In the second stage, the elevations -3-4- are pressed to at least approximately the final shape, the angle of inclination α′ being enlarged to a value α which lies in the range from 95°-170°.