Multi-Diameter Tubular Body Cold Forging Flaw Removal
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Solution Overview
Problem
Cold forging methods for multi-diameter tubular bodies often result in internal flaws like cracks on the rearward-facing annular ledge surface, which is critical for supporting elements in gas sensors and spark plugs, due to poor metal flow at the 'fillet corner' formed during deep hole forming.
Innovation Solution
A deep hole forming punch with a protrusion having an outside diameter smaller than the inside diameter of the small-diameter hole portion is used to form the large-diameter hole portion, allowing the internal flaw to be partially removed as punching scrap during the formation of the small-diameter hole portion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If deep hole forming is performed with a conventional punch to create the large-diameter hole portion, then the multi-diameter tubular body can be formed, but internal flaws such as cracks occur on the rearward-facing annular ledge surface due to poor metal flow at the fillet corner
Solution Approach 1:
The invention performs preliminary action by forming a depression at the bottom of the large-diameter hole portion before punching the small-diameter hole portion. This depression is created by the protrusion on the deep hole forming punch, and it serves as a pre-positioned feature that enables subsequent removal of internal flaws during the punching operation. The protrusion is designed with specific dimensions (outside diameter smaller than the inside diameter of the small-diameter hole portion) to create this depression in advance.
Solution Approach 2:
The invention converts the harmful effect of internal flaws (cracks) into a beneficial outcome by designing the punching process to remove the flawed material. The protrusion creates a depression that positions the internal flaws within the material to be punched out. What was originally a defect (poor metal flow causing cracks) becomes an opportunity to remove contaminated material and create a cleaner, more reliable ledge surface.
2Reliability
If the outside diameter of the protrusion is made smaller than the inside diameter of the small-diameter hole portion, then internal flaws can be removed as punching scrap, but the depression formed by the protrusion becomes larger
Solution Approach 1:
The invention applies parameter changes by optimizing the outside diameter of the protrusion relative to the inside diameter of the small-diameter hole portion. By setting the protrusion diameter to be smaller than the final hole diameter, the patent creates a controlled depression size that balances two requirements: large enough to generate and position internal flaws for removal, but small enough to leave sufficient material for structural integrity. This parameter relationship (protrusion diameter < small-hole diameter) is the key controlled variable.
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 reduces the occurrence of internal flaws on the rearward-facing annular ledge surface, enhancing the structural integrity and accuracy of the multi-diameter tubular body.
Implementation Method 1
forming the large-diameter hole portion by subjecting the preliminary hole to deep hole forming
Implementation Method 2
forming the rearward-facing annular ledge surface and the small-diameter hole portion by punching out a bottom surface of the large-diameter hole portion
Data Source
AI summary
A multi-diameter tubular body is cold-forged by forming a large-diameter hole portion in a formed body having a preliminary hole through subjection of the preliminary hole to deep hole forming and by punching out the bottom surface of the large-diameter hole portion to thereby form a small-diameter hole portion. Since a punch having a central protrusion on its forward end surface is used, an internal flaw is generated by dead metal in the inner circumferential surface of a depression, formed by the protrusion, in the bottom surface of the large-diameter hole portion. An outside diameter of a protrusion of a deep hole forming punch is rendered smaller than an inside diameter of the small-diameter hole portion to be formed later by punching out the bottom surface of the large-diameter hole portion. As a result, the internal flaw is removed when the small-diameter hole portion is formed.