Bolt Hole Threads with Flattened Crests for Automated Assembly
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Solution Overview
Problem
The existing bolt hole design with fishmouth-shaped crests often inhibits proper engagement of start threads between bolts and bolt holes, particularly in automated assembly due to raised corner portions and central depressions, leading to mis-threading issues.
Innovation Solution
A bolt hole design with improved start threads featuring flattened crests and increased minor diameters at valleys, created using a tap with a crest altering thread section that reduces or eliminates the fishmouth shape, ensuring proper engagement and alignment during automated assembly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional tapping process is used to create threads in bolt hole, then threads are formed efficiently, but fishmouth-shaped crests with raised corner portions and central depressions are created that inhibit proper bolt engagement
Solution Approach 1:
The tap is divided into two distinct thread sections: a first thread section that creates threads with conventional geometry, and a second thread section with altered geometry (flattened crests, reduced corner portions, eliminated central depressions). This segmentation allows different portions of the thread to serve different functions - the first section provides efficient material displacement while the second section ensures reliable bolt engagement without fishmouth defects.
Solution Approach 2:
The thread geometry is made non-uniform along the length of the tap. The second thread section has specifically modified local characteristics (flattened crests, increased minor diameter) compared to the first thread section. This local quality change ensures that the critical engagement zone (created by the second section) has optimal geometry for preventing fishmouth formation and ensuring reliable bolt connection.
2Productivity
If automated assembly is used for bolting operations, then assembly speed is increased, but mis-threading issues occur due to improper engagement of start threads with fishmouth-shaped crests
Solution Approach 1:
The tap creates threads with pre-modified geometry in the second thread section before the bolt engagement process begins. The flattened crests and eliminated central depressions are formed in advance during the tapping operation, ensuring that when automated assembly occurs, the bolt start threads can properly engage with the pre-prepared improved thread geometry without mis-threading issues.
3Ease of manufacture
If fishmouth-shaped crests are present in thread design, then material flow during tapping is facilitated, but raised corner portions and central depressions prevent proper bolt thread engagement
Solution Approach 1:
The thread geometry parameters are changed in the second thread section compared to conventional threads. Specifically, the crest geometry is flattened, corner portions are reduced, and minor diameter is increased. These parameter changes maintain manufacturability while eliminating the fishmouth effect that prevents proper bolt engagement, thus improving ease of operation.
Data Source
AI summary
In a part having a surface, a bolt hole is provided extending into the part from the surface. Threads in the hole have crests with a fishmouth shape at the crests defined by a central concave portion and raised corner portions at ends of the concave portion. At least one start thread preceding the threads with the fishmouth shape crests is provided having a substantially flat crest without the fishmouth shape. A tap for manufacturing the threaded bolt hole has a first thread section and a second thread section. The second thread section has a plurality of threads for creating at least one improved start thread in the hole to be threaded, minor diameters at valleys between the threads of the second thread section being greater than minor diameters at valleys between threads of the first thread section or major diameters at crests of the threads of the second thread section being greater than major diameters at crests of the first thread section.