11/28/2023 0 Comments Thread forming taps for aluminum![]() ![]() Forming taps need larger holes because the roots of the tap extrude material inward to form thread crowns.īefore testing thread strip-out strength, 0.25-in. This represents a diameter increase of 8% for the cutting taps and 3.4% for the forming tap. for a forming tap for 75% engagement - up to 0.617 in. ![]() Tap-hole diameters varied from the ANSI B1.1 minimum recommended diameter - 0.5708 in. Spiral taps, on the other hand, have angled lead-in flutes that guide continuous cuttings up and out the back of the hole. Plug taps have little or no lead-in and are used primarily for tapping blind holes. Both spiral and plug-type cutting taps were used, in addition to a thread-forming tap. We precision bored 5/8-in.-18 UNF tap holes into the ID of the tube stock to create 1.75-in.-long specimens. The basic material properties were 91-ksi yield strength, 99.7-ksi tensile strength, and 27% elongation before break. AK steels have finer grains and see less work hardening during plastic deformation. The “AK” stands for “aluminum killed,” meaning aluminum helped remove oxygen that causes bubbling in the molten steel while ingots formed. The tubes were ASTM A513/SAE 1026AK steel - mild plain carbon steel with 0.26% carbon and a maximum of 1% manganese. We fabricated specimens from tube stock with 1-in. To test this theory, we bored and tapped holes in tube stock, varying thread-forming techniques and diameters, then tested them. This includes light alloys and steels with tensile strengths up to 174 ksi and hardnesses below 35 to 40 on the Rockwell C scale. The prevailing wisdom says formed threads are the way to go for strength if the material is soft enough for cold forming. in diameter may be more susceptible to incorrect dimensions because they are fabricated by boring or turning, not with standardized drill bits. The process is generally taken for granted since drill and tap geometries are standardized and repeatable. Whether threads are cut or formed, fabricating them takes two steps: drilling or boring a tap hole and cutting or forming the threads. But internal threads are a different story, especially when internal-thread material is weaker than the bulk material or thread dimensions are incorrect. In fact, the first three threads have been shown to take up 81% of the axial force. It’s well known that the external threads of properly fabricated bolts are stronger than the bolt itself. Recent tests show there are some nuances to the strength of internal threads. Once the hole diameter and thread type are set, there’s little need to consider the strip-out strength of the internal threads, right? Wrong. Specifying internal screw threads isn’t the most thrilling task for engineers. Simulia, University of Tulsa, “The nuts and bolts of specifying fastener torque,” Machine Design, July 9, 1998, /MDFastenerTorque Incompletely formed threads in oversized tap holes can appear good to go/no-go gauges.Cut threads are much more tolerant of oversized holes than cold-formed threads.Cold-formed threads are no stronger than cut threads when holes are correctly sized.So I don't think that min specs are good enough for ID formed threads. 002 undersize and cut tapped - they wouldn't'a never failed IMO. They stripped out as the formed peaks rolled over and played dead. I have seen rolled threads fail that were on low limit or just outta spec. On ID threads - leaving a big valley in the middle does not IMO give as good'a threads. I know that formed threads are known to be stronger - but that premise is on OD threads that are ran to or very near 100% all the time. ![]() IMO this is NOT anywhere's near the same as a solid thread with cut threads. well - even if you doo have the minor in spec - a formed minor anywhere's close to min spec will have two very distinct peaks with quite a valley between. (You may have to think aboot the process for a while to understand that.)ī) As per the QC comment. Reason being that you are pushing up into such a small area now - and you are pushing up from an ever bigger area. As you get closer and closer to 100% threads - each. 003 is prolly true at one particular point of the size ratio - but that is always gunna be a moving target ratio. ![]() I want to challange some of Pros comments tho:Ī) The. I don't ream my holes - but I don't generally run 6-32 either. 001 counts for a lot more on a form tap that a cut tap. I say ream as drill/ream as Pro said - to hold size best on the small pitch sizes - but also to use a decimal reamer for the RIGHT size on a really small pitch as each. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |