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How to Reduce Torque Miss Defects on Engine Assembly Line

08/16/2015 6:00 AM

I am looking out for opinion to error proof a process so that torque would not get missed on a particular screw on an engine assembly line. This should ensure that all screws are torqued.

I use DC Tool on my line and I already have an interlock for the number of tightenings that the tool has to go, which is working fine. The chance of error in this is-

Let's say I have 10 screws to be torqued on a particular station, but operator torques one screw twice and miss the other one, even then the condition of tool is satisfied.

I am looking out for options to control such defects .....

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#1

Re: How to reduce torque miss defects on Engine assembly line

08/16/2015 7:25 AM

Presumably the screw torquing tool must be indexed to all ten locations in your example. Make the program logic so that each location is satisfied by a successful torque measurement before moving to the next location.

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#13
In reply to #1

Re: How to reduce torque miss defects on Engine assembly line

08/19/2015 10:29 AM

Thanks a lot for reply.

I already have this feature of a successful torque measurement. I am using a Cleco Cordless DC Tool, and it may not be easy to index to every screw, if the tool is not tied to something like reaction arm

My issue is to implement something that would help me identify if one of the screw is double torqued, and the next screw is not missed.

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#2

Re: How to reduce torque miss defects on Engine assembly line

08/16/2015 7:56 AM

I do hope you are not supplying the current auto industry.

This problem is one that was solved many years ago by mistake proofing. There are multiple solutions for you to choose from.

Auto loading screwdriver. Means that every screw is torqued before it is released from the driver head. Under torque, over torque, crossed threads andmany other faults eliminated by the driver not releasing the part and requiring intervention.

Fully automatic process. Torque driver mounted on XY system with Z axis controls and auto torque settings on driver. Can have bolts pre- \started by person if so desire, or auto loading per previous.

If you are supplying current auto industry, I suggest you contact your customer "mistake proofing" group for thier input. They will usually support suppliers by providing workshops to a combined FMEA program and then help Poka-Yoke your rpocess for a couple ofthe identified failure modes. If done properly, this actually gains you points in their quality system reviews as continuous improvement and a few other areas.

Previous employer was in auto component supply worldwide and I was one Quality representative inthedesign teams.

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#14
In reply to #2

Re: How to reduce torque miss defects on Engine assembly line

08/19/2015 10:36 AM

This application is different wherin screws are in different orientationand not only along X-Y direction. The tool (Cleco Cordless Tool) that I am using has a feature that indicates whether the screw is torqued or not, quite well.

My issue is this-

I have an interlock in the tool whcih indicates that per engine, if the number of screws that are required to be torqued are done or not, but this condition also gets satisfied if I torque one of the screw twice and leave another one. I am looking out of asolution to control this.

Thanks for reply.

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#3

Re: How to reduce torque miss defects on Engine assembly line

08/16/2015 8:10 AM

You might think about a pen-type barcode scanner. At an earlier stage in assembly, you place a small, unique barcode label at each torque site. Attach the barcode pen to the screwdriver, so that the operator can scan the barcode and then immediately torque the screw. This would allow a system that records each screw being torqued.

There are a lot of bar code scanner companies that can help you with this.

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#4

Re: How to reduce torque miss defects on Engine assembly line

08/16/2015 9:52 AM

Keep records, frequency and qualitative/descriptive defects. (Statistician can help later on delay and product defects)--pertaining to quality and how to improve the condition in the total aspect.

Talk to your team, supervisor, engineer. --have a chitchat "root cause" what is causing such.

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#5

Re: How to Reduce Torque Miss Defects on Engine Assembly Line

08/16/2015 12:40 PM

You need to decide whether you are trying to "Reduce Torque Miss Defects" (and how much reduction), or "error proof".

The only way to take human error out of the equation, is to take human beings out of the process. Automate in that case.

If you are trying to reduce errors, and/or you cannot automate, then some of the sugestions above will help. Don't forget employee education as part of that effort. A modest motivational incentive would go a long way. This doesn't have to be expensive, just something like a free lunch for the shift/team that has the least defects each month, quarter... That also provides self regulation within that group, since they will have a tendency to monitor each others work.

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#6

Re: How to Reduce Torque Miss Defects on Engine Assembly Line

08/16/2015 1:43 PM

Somebody needs to 'invent' a thread-sealant that CHANGES COLOR when it reaches a pre-determined "torque" level.

Anybody at LOCKTITE™ working on this?

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#9
In reply to #6

Re: How to Reduce Torque Miss Defects on Engine Assembly Line

08/17/2015 10:41 AM

How are you going to see the thread sealant when it is on the threads inside of a hole?

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#7

Re: How to Reduce Torque Miss Defects on Engine Assembly Line

08/16/2015 5:21 PM

Why not use Machine vision to be certain all fasteners are torqued.

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#8
In reply to #7

Re: How to Reduce Torque Miss Defects on Engine Assembly Line

08/17/2015 9:21 AM

He might be scared on the recent thread Robot a Murder.

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#18
In reply to #7

Re: How to Reduce Torque Miss Defects on Engine Assembly Line

08/19/2015 11:05 AM

Very expensive.....

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#10

Re: How to Reduce Torque Miss Defects on Engine Assembly Line

08/17/2015 1:21 PM

We need a new rating category.

LAA.

For lame a$$ answer.

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#11

Re: How to Reduce Torque Miss Defects on Engine Assembly Line

08/17/2015 1:21 PM

Too bad they don't make these for screws:

http://www.smartbolts.com/dti-smartbolts%c2%ae/

It looks like they only have HHCS starting at 7/16"Ø.

Until you find a more practical solution you could have each operator mark a torqued screw with a mark unique to each operator.

Or it could be as simple as circling the torqued screw with a marker indicating it has been torqued properly and tested.

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#17
In reply to #11

Re: How to Reduce Torque Miss Defects on Engine Assembly Line

08/19/2015 11:03 AM

You are right, but operator does sometimes miss marking also

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#12

Re: How to Reduce Torque Miss Defects on Engine Assembly Line

08/18/2015 5:50 AM

HI, I'm not sure if already another respondent meant this by their answer, but when I was involved several years ago in setting up an automated assembly line, we discussed this very problem with the drive manufacturer - their solution was simple and, I believe, idiot and even malicious proof to some extent - the driver not only records maximum torque but also torque increase v angle (or time) as the fasteners are tightened - it is then easy to detect if an operator in error or otherwise puts the driver a second time onto a fastener as it will not turn before full torque is reached. It is even possible to detect the difference between repeat tightenings of the same fastener in the same hole (if slackened in between by a wench?!!/wrench) - the shape of the rising torque curve is changed somewhat by the bedding in process on first tightening.

hope this helps, good luck,

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#15
In reply to #12

Re: How to Reduce Torque Miss Defects on Engine Assembly Line

08/19/2015 10:53 AM

Hi, Thanks for the reply. You are giving me new ideas to try out, and i think that putting up angle control should work , atleast in some of the cases. I'd also have to check the torque curve.

Thanks

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#16
In reply to #15

Re: How to Reduce Torque Miss Defects on Engine Assembly Line

08/19/2015 11:01 AM

let me know if you get stuck - I may have some records somewhere on the technique / suppliers involved etc..... P I'd also be interested to hear how it goes.

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#19

Re: How to Reduce Torque Miss Defects on Engine Assembly Line

08/24/2015 4:19 PM

The local road vehicle tyre replacement specialist (name withheld) uses "second person check" when applying warranty to the wheel-replacement-on-the-hub torque-application operation.

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#20

Re: How to Reduce Torque Miss Defects on Engine Assembly Line

08/28/2015 7:54 AM

I recently proposed a solution to a customer that usied a tool balancer/torque arm that had position encoders. Atlas-Copco has a model but there are other makers.

The encoder can be programmed with the driver or station controller (PLC) to only allow torquing in a specific sequence or in specific positions.

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