Hollow Metal Part Forging With a Lost Mandrel for Variable Cavities
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Solution Overview
Problem
Conventional methods for manufacturing hollow parts from high-value metallic alloys like Ti alloys and nickel-based superalloys are inefficient, as they require significant material wastage and costly machining processes, especially for large parts with variable internal diameters.
Innovation Solution
A method involving a 'lost mandrel' made of a material with flow stress comparable to the alloy, allowing for deformation during forging to create internal spaces without material removal, followed by machining to finalize the mandrel's configuration, reducing material waste and machining needs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If conventional forging and die-forming with subsequent machining is used, then hollow parts can be manufactured, but significant material is wasted as chips and machining costs are high
Solution Approach 1:
A hollow billet is prepared in advance with a hollow section before the main forging operation. This preliminary action allows the final part to be formed with minimal material removal, as the hollow geometry is already established in the billet rather than being created by subtractive machining after forging.
Solution Approach 2:
The manufacturing process is segmented into distinct stages: preparing a hollow billet, inserting a mandrel into the hollow section, and then performing the final forging operation. This segmentation allows each stage to be optimized independently, with the hollow billet preparation focusing on minimizing material waste and the forging stage focusing on achieving the final geometry.
2Adaptability or versatility
If hot expansion with a punch is used, then seamless tubes with constant cross-section can be manufactured, but variable cross-section hollow parts cannot be produced
Solution Approach 1:
The hollow billet is prepared in advance with the desired hollow geometry before the final forging operation. This preliminary action enables the subsequent forging process to accommodate variable cross-sections while maintaining dimensional accuracy, as the hollow section provides a framework that guides the deformation of the metal during forging.
Solution Approach 2:
The method allows for changes in the geometric parameters of the hollow section during the forging process. The hollow billet and mandrel configuration enables the cross-section to vary along the length of the part while maintaining control over the final dimensions through the forging process parameters.
3Strength
If rigid mandrels are used in forging, then reusable tools can be employed, but the mandrels cannot be deformed during the process
Solution Approach 1:
A consumable mandrel made of a material different from the billet material is used. This mandrel is designed to be deformed along with the billet during forging and is subsequently removed, typically by melting or other removal processes. The mandrel does not need to maintain its structural integrity throughout the entire process, as it is intended to be consumed or removed after serving its purpose of defining the internal geometry.
Solution Approach 2:
The process involves two different materials: the billet material and the mandrel material. The mandrel is made of a material that is suitable for being deformed and removed, while the billet is made of the final part material. This composite approach allows each material to be optimized for its specific function during the manufacturing process.
4Loss of substance
If foundry sand filling is used, then internal cavities can be created, but the filling material cannot be reused and acid removal creates safety and waste issues
Solution Approach 1:
The mandrel is designed as a consumable component that is removed after serving its purpose. By using a mandrel material that can be easily removed (such as through melting or other removal processes), the need for acid dissolution is eliminated, avoiding the safety and waste disposal issues associated with acid handling.
Solution Approach 2:
The chemical removal process (acid dissolution) is replaced with a mechanical or thermal removal process. The mandrel can be removed by mechanical means such as drilling or by thermal means such as localized melting, eliminating the need for chemical acids and associated safety and waste management concerns.
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 minimizes material loss and machining costs while achieving precise dimensional control and complex internal geometries, making it suitable for large, high-value alloy parts.
Implementation Method 1
co-forging to achieve a simultaneous deformation of the billet and of the lost mandrel with a homothety ratio K
Implementation Method 2
a punch is applied to at least one of the ends of the billet to expand at least a portion of the billet and create at least one internal space in the billet
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
Method for producing a hollow part (17; 21; 46) made of a metal material, characterised in that it comprises the following steps: - preparing a billet (1; 18; 33) of the metal material of the hollow part (17; 21; 46), and at least one sacrificial mandrel (2; 19; 34, 35) made of a material which has a yield stress in the range from -30% to +20% of the yield stress of the material of the billet (1; 18; 33), preferably in the range from -15% to +10%, ideally in the range from -5% to +3%; - applying a punch (10) on at least one of the ends of the billet (1; 18; 33) in order to produce the expansion of at least a portion of said billet (1; 18; 33) and to create at least one internal space (12; 20; 36, 37) inside said billet (1; 18; 33); - inserting the sacrificial mandrel (2; 19; 34, 35) in said one internal space (12; 20; 37) of the billet (1; 18; 33); - clamping the sacrificial mandrel (2; 19; 34, 35) in said billet (1; 8; 33); - producing, by co-forging, a simultaneous deformation of said billet (1; 18; 33) and of said sacrificial mandrel (2; 19; 34, 35), with a homothetic ratio K; - and machining in order to remove the sacrificial mandrel (2; 19; 34, 35). Use of the method for manufacturing a landing gear rod or beam.