Tapping problems - 3/8" hot roll pickled & oiled steel - seeking expertise

rstocum

Involved In Discussions
#1
My company makes a high volume part where we tap M8 x 1.25 (6) places in 3/8" hot roll pickled & oiled steel. We laser cut the blank including the hole pattern that gets tapped. We tap the part while its flat and then form it in a press brake. No bend lines occur near the hole pattern. We recently had a return from the customer of 16 pieces for oversize thread. I have inspected the return parts and found 5 of them oversize. The nogo goes more than 2 turns into the hole, or goes all the way through. The other 11 parts pass in the sense that the nogo either does not start, or goes no more than 1 turn into the hole. I am confident that the pilot hole size is correct. The laser has failure modes that can cause the holes to be oversize, but if those failure modes occur, all the holes on every part after the failure would be oversized. I know that I am not dealing with that scenario.

I have two concerns that my own experience does not address:
1) That 2 turns max (for metric threads) of the nogo is permissible is tribal knowledge as far as I know. I was trained to this "standard" in a previous life. I thought it was common knowledge in fabrication, but it may not be for the customer. I plan to ask the customer to verify their gage is in calibration, and let them know the parts pass my gage, which is brand new. If it becomes a matter of interpretation of the nogo entering the hole at all, do I have a leg to stand on by saying the nogo is allowed to start, but not go further than two turns?​
2) All 6 holes are tapped in succession by the same tap, unless the tap squeals from wear or breaks. Broken & worn taps are replaced immediately. Some of the parts that failed have holes that failed and holes that passed on the same part. I have no knowledge of a failure mode that can account for this. One part has 5 failed holes and one good one, another part has 1 failed hole and 5 good ones, yet another has 3 failed and 3 good. The failed parts all came from the same batch, shipped on the same purchase order, so I know they were tapped on the same shift. Needless to say, I am having trouble formulating ideas to test for root cause. Does anyone here know what kind of tap related failure could account for this?​
 
Elsmar Forum Sponsor

Golfman25

Trusted Information Resource
#2
Without seeing our print or forming setup, my gut feeling is the forming may be causing a problem. Of course that would probably make the hole oval which would interfere with your gage?
 
#3
How are you tapping the parts? Are you fixturing the plate on a CNC mill or are you using a Drill Press of some sort to tap? Are all the holes tapped on the same machine? Is it a forming or cutting tap? Does you tap have an H value (H3, H7, ....) for cutting oversize? Are chips building up on the tap causing issues? This is some of the things I thought up quickly that may cause oversized tapped holes, but I can't say anything without a print or something.
 

rstocum

Involved In Discussions
#4
None of the bend lines are near the holes. The forming is not distorting the holes. The parts are large enough that they don't move during tapping, so they are not fixtured. They rest on a 2x4 frame and are tapped by a mobile tapping unit called a flexarm. The motive force for the rotation of the tap is hydraulic, and the initial downward pressure is supplied by human arm power. The flexarm unit holds the tap vertical and does not allow the tap to drive at an angle. The class of fit is 6H. We use a standard cutting tap, TiAlN coated, supplied by MSC. All holes are tapped on the same machine. I regret that I cannot share a print due to confidentiality agreements, but the screen snip attached shows the hole detail. There are no notes or special instructions on the print regarding the threaded holes.

I see your point about chip buildup, Rexton. If chips are dragged into the cut during tapping, perhaps they are causing the thread form to cut oversize? I will be inquiring about tapping fluid to see if it is the right substance to use in our material, with our current taps.

I asked our operators if the part could be at an angle to the tap arm and cause this problem. They said the frame holds the part in the correct orientation, and if the part were not located correctly in the frame so that the tap approached the hole at an angle, the tap would squeal and the problem would be immediately obvious.
 

Attachments

Golfman25

Trusted Information Resource
#5
None of the bend lines are near the holes. The forming is not distorting the holes. The parts are large enough that they don't move during tapping, so they are not fixtured.
I guess I would ask, "how do you know?" Has it been tested and verified?
None of the bend lines are near the holes. The forming is not distorting the holes. The parts are large enough that they don't move during tapping, so they are not fixtured. They rest on a 2x4 frame and are tapped by a mobile tapping unit called a flexarm. The motive force for the rotation of the tap is hydraulic, and the initial downward pressure is supplied by human arm power. The flexarm unit holds the tap vertical and does not allow the tap to drive at an angle. The class of fit is 6H. We use a standard cutting tap, TiAlN coated, supplied by MSC. All holes are tapped on the same machine. I regret that I cannot share a print due to confidentiality agreements, but the screen snip attached shows the hole detail. There are no notes or special instructions on the print regarding the threaded holes.

I see your point about chip buildup, Rexton. If chips are dragged into the cut during tapping, perhaps they are causing the thread form to cut oversize? I will be inquiring about tapping fluid to see if it is the right substance to use in our material, with our current taps.

I asked our operators if the part could be at an angle to the tap arm and cause this problem. They said the frame holds the part in the correct orientation, and if the part were not located correctly in the frame so that the tap approached the hole at an angle, the tap would squeal and the problem would be immediately obvious.
I guess I would ask, "how do you know?" Has it been tested and verified? You're at the point where all the "easy" stuff seems to been accounted for. You may want to go back an independently verify to see if any of the assumptions may be wrong.
 
#6
I guess I would ask, "how do you know?" Has it been tested and verified?


I guess I would ask, "how do you know?" Has it been tested and verified? You're at the point where all the "easy" stuff seems to been accounted for. You may want to go back an independently verify to see if any of the assumptions may be wrong.
I agree with Goldman, I believe doing some testing, such as checking all the tapped holes with a gage after tapping and then again after forming.

Also to clarify, I did not mean the thread class 6H, but the tap class of cut. I am not sure if this is used outside the US, but taps are readily available here that cut oversized in order to account for plating (and are designated with H#, e.g. H6). If an oversized tap was accidentally purchased it could cause issues with thread size.

As for 2 turn NOGO standard, ISO 1502 should cover it. (It came up in a quick google search and I don't have a copy of the standard.)
 

outdoorsNW

Involved In Discussions
#7
How often is the tap changed?

Even if you did not order the wrong tap by mistake, could mixed stock from the supplier cause the problem?
I have seen enough mixed stock for other types of items to think mixed stock might have occurred.

Also, is the squealing a reliable indicator of an angled tap 100% of the time, or does the tap squeal only in some circumstances?
 

Al Rosen

Holed-up in a Hotel in South Florida
Staff member
Super Moderator
#8
iso1502 said:
7.2.2 NOT GO screw plug gauges

c) The NOT GO screw plug gauge, when screwed by hand without using excessive force, may enter into both ends of the threaded part, but by not
more than two turns of thread. If it can be screwed in by more than two turns of thread, the workpiece thread does not comply with the specification. The NOT GO screw plug gauge shall not pass completely through a workpiece with a length of thread of three threads or less.
 

rstocum

Involved In Discussions
#9
I agree with Goldman, I believe doing some testing, such as checking all the tapped holes with a gage after tapping and then again after forming.

Also to clarify, I did not mean the thread class 6H, but the tap class of cut. I am not sure if this is used outside the US, but taps are readily available here that cut oversized in order to account for plating (and are designated with H#, e.g. H6). If an oversized tap was accidentally purchased it could cause issues with thread size.

As for 2 turn NOGO standard, ISO 1502 should cover it. (It came up in a quick google search and I don't have a copy of the standard.)
The holes are verified with the go/nogo at the threading operation, and I am verifying them myself post forming. The closest bend is 4 inches away from the nearest hole. Steel in this thickness does not move in any way we can measure that far from a bend.

A quick double check of our taps shows they are all the same Guhring tap in the proper size. Some have a bit of wear, but nothing drastic.

I was completely unaware of an ISO standard governing thread acceptance. Thank you.
 

rstocum

Involved In Discussions
#10
How often is the tap changed?

Even if you did not order the wrong tap by mistake, could mixed stock from the supplier cause the problem?
I have seen enough mixed stock for other types of items to think mixed stock might have occurred.

Also, is the squealing a reliable indicator of an angled tap 100% of the time, or does the tap squeal only in some circumstances?
Yes, at this time I cannot rule out operators using taps that are close to their "end of life", but not obviously done yet. We have never done any kind of study to determine when taps should be discarded, or how many holes our preferred tap can do in the materials we use them in. I will see if I can production on board to look at that. Thank you.

The tap squeals when it encounters too much resistance to engagement. This happens when the tap is presented to the hole at an angle, and when it has too much wear on the cutting edges. If the holes were undersize, or the edges of the holes were hardened due to improper laser cut settings the tap would also squeal. Sometimes the tap simply breaks before making any unusual noise at all.
 
Thread starter Similar threads Forum Replies Date
W Standard for Internal Thread / Tapping Length Other ISO and International Standards and European Regulations 8
P Cutting and Tapping Titanium Material - What tap material is recomended Manufacturing and Related Processes 3
H Tapping Brass Inserts - Taps breaking too frequently Manufacturing and Related Processes 12
K Problems with process equipment ISO 13485:2016 - Medical Device Quality Management Systems 4
A Feedback of typical maintenance problems with LMI digital probes Inspection, Prints (Drawings), Testing, Sampling and Related Topics 0
S New problems exporting to Germany - February 2019 ISO 13485:2016 - Medical Device Quality Management Systems 7
C Resource allocation problems in Software DFMEA FMEA and Control Plans 4
Marc Problems - Contacting Us about Problems (How To - Etc.) Elsmar Xenforo Forum Software Instructions and Help 0
Marc Youtube - Viewing problems Elsmar Xenforo Forum Software Instructions and Help 4
O How do reduce the risk of suppliers having similar problems? Supplier Quality Assurance and other Supplier Issues 4
L Problems while documenting the SOUPs used for the software we are developing IEC 62304 - Medical Device Software Life Cycle Processes 4
W Problems with our new Auditor (a Ph.D. with four months experience) ISO 13485:2016 - Medical Device Quality Management Systems 25
L Relying on Suppliers - Most Quality and Warranty problems are caused by Suppliers Supply Chain Security Management Systems 5
M The biggest gaps and problems in QMS or Quality in Automotive Misc. Quality Assurance and Business Systems Related Topics 3
I Request an FDA GUDID Account - Problems Other US Medical Device Regulations 3
S Document Review Problems ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 9
L How to avoid Nonconformance Reoccurrence problems IATF 16949 - Automotive Quality Systems Standard 20
C Software Process Implementation Problems ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 8
K Bottle Labeling Machine Problems - Non conformance in FCMG industry Nonconformance and Corrective Action 8
T Contacting the Supplier's CB vs a Supplier Audit - Nonconformance Problems AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 4
Peter Fraser Problems and Deficiencies with the ISO 9001:2015 Draft ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 12
B Quality problems that cost Millions of dollars (or euros, or pounds, etc.) Quality Manager and Management Related Issues 7
AnaMariaVR2 How Open Innovation is Solving Some of NASA?s Trickiest Problems World News 0
T A survey on problems during ISMS implementation - need help IEC 27001 - Information Security Management Systems (ISMS) 2
S Common Electric Fan Motor Problems Reliability Analysis - Predictions, Testing and Standards 3
M Problems with Competence/Skills Matrix (6.2 Human Resources) AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 5
ScottK Is anyone else having problems uploading Proprietary Names into the DRLM? 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 9
M FDA Warning Letter - Product Association with Search Engine Results - Problems Ahead? US Food and Drug Administration (FDA) 10
M Problems with Unrealistic Customer Expectations Customer Complaints 12
AnaMariaVR2 Chronic Regulatory Compliance Issues Causing Drug Shortages & Safety Problems Pharmaceuticals (21 CFR Part 210, 21 CFR Part 211 and related Regulations) 1
Q Method on how to cause people to solve problems Benchmarking 5
Oldrice Aerospace Registrar Problems - Starting Over? AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 13
M 8.2.4 Problems with Monitoring and Measurement of Product AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 3
R Problems with Supplier - Always with 100% Sorting - No Corrective Actions Supplier Quality Assurance and other Supplier Issues 22
G Product Returns are above average for Labeling Problems Quality Manager and Management Related Issues 4
V Supplier's First Run had Plating Problems - Can they Strip, Re-Plate and PPAP them? APQP and PPAP 14
1 A New Job - Replaced a QM who passed away - BIG Problems Quality Manager and Management Related Issues 25
N English as a Second Language - English problems with Legal Terms Contract Review Process 2
Uriel Alejandro Problems with the Employee Skills Matrix - Document Control System Quality Manager and Management Related Issues 8
L Avoiding Recurrence of the Supplier?s Quality Problems Supplier Quality Assurance and other Supplier Issues 5
M Problems implementing ISO 13485 for Software-Only Medical Device Manufacturers? ISO 13485:2016 - Medical Device Quality Management Systems 4
B How can I resolve Chronic Nonconformance Problems? ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 8
S Problems with the application of EN 62366:2008 IEC 62366 - Medical Device Usability Engineering 13
F Can you tell me if this table is correct? Gage R&R Problems Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 12
D Quality Metrics to use to solve Problems Quality Tools, Improvement and Analysis 5
P Self Motivation - How to keep it when overwhelmed with problems? Career and Occupation Discussions 13
S Systemic Problems Identified in Audit and How to Fix Them IATF 16949 - Automotive Quality Systems Standard 10
T Lollipop Production Line Problems - Defectives and Root Cause Analysis Reliability Analysis - Predictions, Testing and Standards 6
T Big problems with Inspection - Manual Operation - Needs experts Inspection, Prints (Drawings), Testing, Sampling and Related Topics 27
C Efficient Supplier Development and Problems with Buyers Supplier Quality Assurance and other Supplier Issues 5

Similar threads

Top Bottom