Green-State Ceramic Threading with Shrinkage Scaling
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Solution Overview
Problem
Threading ceramic materials, such as silicon nitride, is challenging due to their high strength and toughness, which makes internal or female thread formation difficult and expensive, especially in small diameters, requiring specialized and costly grinding processes.
Innovation Solution
Threading the ceramic material in its 'green' or unfired state using a tap with a scaling factor to account for shrinkage during firing, followed by machining to remove cracks and achieve the desired shape and size, eliminating the need for expensive grinding equipment and processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If threading is performed on fired ceramic material using grinding processes, then thread formation is achieved in high strength material, but manufacturing cost and process complexity increase significantly
Solution Approach 1:
The threading operation is performed on the green ceramic body before firing, when the material is still relatively soft and easily machinable. This preliminary action eliminates the need for difficult post-firing grinding operations on hardened ceramic material, significantly reducing manufacturing complexity and cost while maintaining the ability to form accurate threads.
Solution Approach 2:
The patent exploits the change in material properties between the green state (soft, pliable) and fired state (hard, strong). By performing threading when the material parameters are favorable (green state), the process avoids the difficulties of machining hardened ceramic, resolving the contradiction between material strength and ease of manufacture.
2Ease of manufacture
If threading is performed on green ceramic material before firing, then manufacturing cost and process complexity decrease, but crack formation may occur during tapping
Solution Approach 1:
The patent converts the potential harm of crack formation into a beneficial process feature by designing the threading operation to create controlled surface cracks that are subsequently removed during machining. This approach allows easy threading while maintaining reliability, as the cracking issue is transformed into a manageable step in the manufacturing process.
Solution Approach 2:
Surface cracks formed during tapping are removed through subsequent machining operations. This extraction of defective material eliminates the reliability issue caused by cracking, allowing the benefit of easy green-state threading to be realized without compromising final product quality.
3Manufacturing precision
If tap size is selected based on desired final thread size without scaling, then thread size accuracy is simplified, but shrinkage during firing causes dimensional inaccuracy
Solution Approach 1:
The tap size is pre-calculated to account for shrinkage that will occur during firing. By performing this scaling calculation in advance, the patent ensures that threads formed in the green state will have the correct dimensions after firing, maintaining manufacturing precision while adding only minimal complexity to the tap selection process.
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 method allows for efficient and cost-effective threading of ceramic materials by leveraging their pliability in the green state, ensuring accurate thread sizes post-firing while minimizing crack formation and post-firing machining difficulties.
Implementation Method 1
the step of compressing the ceramic powder into a block may comprise using a cold isostatic pressing process to compress the ceramic powder into the block
Implementation Method 2
The block may then be fired. This firing may reduce a size of the block
Data Source
AI summary
Methods for threading ceramic materials, such as ceramic materials used for spinal implants or other biomedical implants. In some implementations, an expected rate of shrinkage of the block upon undergoing a firing process may be determined. A scaling factor may then be applied using the expected rate of shrinkage to select a tap having a size larger than a desired thread size. A green block may then be tapped with the selected tap to form a threaded opening in the green block. The block may be machined in order to remove cracks caused by the tapping process and/or to form the block into a desired shape/size. The green block may then be fired, which may result in a reduction of a size of the block and a size of the threaded opening.