iSixSigma

Screw torque

Six Sigma – iSixSigma Forums Old Forums General Screw torque

Viewing 25 posts - 1 through 25 (of 25 total)
  • Author
    Posts
  • #49143

    walden
    Participant

    Hi
    I need help trying to improve my process. Every now and then we get a screw that does not has the appropiate torque. How can I poka yoke this process and make sure that the screw gets the right torque the first time? Any ideas? This station is handled by an operator, on a manual converyor, I have no automation at all.
    Thanks!
    Chris

    0
    #167438

    Adam L Bowden
    Participant

    Screw torque – a lot of variables here.Ideally re-design the assembly so that the screw torque is not a
    critical factor – i.e if you are tightening down on a gasket to make
    it a sealed joint then consider changing it for an o-ring seal or just
    use a sealing compound.If you are stuck with the design then maybe look at stabilizing the
    “female” thread quality by rolling it rather than cutting it, pick a
    better quality screw, make sure the female thread is not “dead
    ended” to trap swarf, ensure screws are aligned when inserted, add
    good quality and calibratable torque drivers, if pneumatic drivers
    are used then consider adding in a pressure reg and possible
    reservoir to eliminate/minimize pressure drops in the lines to the
    driver. Some people also either use a screw lubricant or “loctite”
    hydrauliic lock on the screws to make it more consistent.Hope this helps – Ideally re-design of the assembly provided for a
    much more cost effective solution. My 2c worth.Adam

    0
    #167478

    Glenn
    Participant

    Back to basic , please tell me the process of the operator?Glenn

    0
    #167481

    Six Sigma Shooter
    Member

    Let’s really get back to the basics.Β  Have you sat down with the operator(s) and the manufacturing and design engineers to do a cause and effect and 5 whys?Β  We can give you all the ideas in the world, but the best solutions will come from your own team of people who really understands the design, manufactuingΒ / assembly requirements and processes.
    Shooter

    0
    #167482

    Adam L Bowden
    Participant

    my guess would be…
    – pick up screw
    – put screw on assembly
    – pick up driver
    – drive in screwwhat do you think ?

    0
    #167483

    Six Sigma Shooter
    Member

    Just some additional thoughts.Β  I have found that screws are often used when other fastenersΒ / securing methods would work, such as quick turn fasteners and rivets, sonic weld for plastic parts,Β or a redesign for a snap in function, similar to battery covers and such.Β  Prevailing torque screws might be an option to explore, as well.

    0
    #167484

    Glenn
    Participant

    Firstly we should guess, secondary are we testing the torque? Glenn

    0
    #167488

    Craig
    Participant

    How many times have you seen someone’s gas cap dangling from their car going down the highway? How many times have you locked your keys in your car? How many times have you seen someone driving off with their cup of coffee on the roof of their car? Should we add cup holders to the roof of the car, just in case?
    Human error is a tough challenge. Even if you automate, there are risks. My gut feel is to design the process such that the operator is more methodical. I’d have to know how many screws, the differing torque values, whether all are done by one personΒ  at a single station, etc. Simple things like color coding helps too. (Red bin for a particular type of screw, red handle on the torque wrench)
    RoundΒ up the operators andΒ try using the FMEA approach. Link failure modes to the inputs and determine the effects on the output. (Input: correct torque setting for wrench, Failure modes: wrench out of cal, operator chooses wrong wrench, etc.)
    I would try the simple solutions first, and monitor results.

    0
    #167491

    Six Sigma Shooter
    Member

    Good input hacl.Β  The simple solutions are often the best and usually come from the people who work in the process.Β  Automation often has problems that end up being more complex and costly than the original problem we were trying to solve.Β 
    I like the cup holders on the roof idea.Β  I hear the new TaTa car (list price of $2,500) is looking into that as it’s the only place they have room for them.
    Best wishes,
    Shooter

    0
    #167492

    GrayR
    Participant

    Chris — have you tried preset torque wrenches or screwdrivers for your operator?
    Β 
    Β 

    0
    #167510

    walden
    Participant

    Thank you all for replying back.
    The process is as follows: Operator get a thrust washer, operator gets 1 screw and drives it by hand on our frame, operator gets screw #2 and #3 and drives them by hand too, only the first 2 turns, operator gets pneumatic driver (Deprag) and drives the 3 screws in, then he let the subassembly go.
    Β 

    0
    #167511

    walden
    Participant

    I agree with you, but we have found that this is an opertator related issue and therefore we need to think what to do with the station and stop relying on the operator. Installing an air tank to reduce the variation on the air psi it’s a great idea.

    0
    #167512

    walden
    Participant

    Thanks, I appreciate your inputs.

    0
    #167513

    walden
    Participant

    Well, the operator uses a pneumatic Deprag driver that has the torque preset.

    0
    #167517

    Six Sigma Shooter
    Member

    What about the operator is the issue?Β  You already have a preset torque device, so what is the issue with the process that makes you believe that a pneumatic regulator will solve the problem if it is, as you say, a problem with the operator?Β  Are they maliciously just not doing their job on purpose?
    I would say it is more likely a systems issue.Β  If it comes down to a lack of SOPs, a lack of knowledgte /Β training, operator fatigue, line moving too fast, these are all systems issues.Β  The worker is powerless to do anything about them.Β  It is very easy – and typical – to blame the operator.Β 
    Shooter

    0
    #167519

    walden
    Participant

    I agree with you, I don’t want the operator to solve the problem, but I want him to pay attention to what he is doing and to raise his hand when he sees a problem. It is also very easy from an operatorΒ stand pointΒ to say I can’t do anything I am just an operator.Β We are not firing him, we are trying to help him by adding systems to his station to prevent this kind ofΒ situations.
    I apprecitate your inputs.
    Thanks a lot!

    0
    #167522

    Six Sigma Shooter
    Member

    So, you are saying that you know the process and the problems better than the operator?Β  Bolderdash!Β  Being dismissive of the operator when it comes to their process is a critical mistake.Β  If they don’t want to participate in solving the issue, fine.Β  If they aren’t even asked is a hugeΒ error on your part.

    0
    #167534

    Taylor
    Participant

    Chris
    Trying to understand, as I believe everyone that is replying. What exactly is the problem.

    Is the operator missing theΒ  Screw, Not torqueing all 3?
    Is the operator torqueing all, but incomplete?
    Is the thread bad?
    Is the thread Dirtly?
    Is the screw bad?
    Is the screw Dirty?
    Is the driver failing randomly?
    Several options available for torque driving units. One incorporates red & Green lights that single the operator torque has been met. Somewhat pricey, but work great. the lights are in the hand unit, so very visible while driving the screw. They are electric programmable units, that work off number of turns to met a specific torque range,Β we found during our project that no air unit would perform at the level of consistancy we needed.
    Β 

    0
    #167536

    walden
    Participant

    Chad
    We know for sure the operator drives the 3 screws in, however we’ve had 2 reocurrences during the last year, wereΒ 1 bolt falls out (not the same position), with the FMEA analysis that we follow we’ve isolated the problem to the operator not being able to determine if the driver reached the toque that it is set on it. One of the replies I got on this forum was to add an air tank to minimize air drops which they can happen without us knowing about it. We will try this option. I appreciate everyones inputs on this, and I will keep you posted for any reocurrences.
    Thank you all!!
    Chris

    0
    #167589

    GrayR
    Participant

    Chris — you missed the point on the use of a poke yoke (re: C. Vader’s comments). You have to poke yoke the root cause to prevent the problem from occuring again. A screw with inappropriate torque is the result, but your FMEA provides only a potential cause for the problem (may not be the actual cause for these two failures).The improvement to use an extra air tank also seems like it misses the boat(?) How does an extra air tank help the “operator determine if the driver reached the torque it was set on”? You originally asked the Forum to provide a “poke yoke” method. Poke Yoke are devices for identifying a problem to the operator. There are two types of poke yoke devices: control systems which automatically stop the part from being processed and warning systems which warn the operator to stop the part. Adding an extra air tank is a preventive measure but it is not a poke yoke device. I think you need to use Chad Vader’s questions if you want to move toward a poke yoke solution.

    0
    #167593

    No one
    Participant
    #167620

    walden
    Participant

    This is a great website!, I liked the punching and marking torque wrenches, we are getting some of these for some other applications in our process.
    Thanks for the hint!

    0
    #167719

    mcintosh
    Participant

    Try an electric screw gun.Β  We’ve had alot of success with Georges Renault brand.Β  The cost will pay for itself in one quality issue at the customer.
    Β 

    0
    #167894

    Delfino
    Participant

    Dear ChrisWe have 3 screwdrivers that can help you with a pokayoke system:please see in:http://depragusa.com/catalog/Handtools.htmcheck for:
    minimat F (pneumatic, screw count and pokayoke)
    minimat QC (Pneumatic with torque transducer and data colletion and F pokayoke funtions)
    minimat E (Electronic driver, torque, angle, time and speed control, pokayoke funtions, etc.)If you have any question, please call me back

    0
    #167924

    Sparhawk
    Member

    I’m sorry I can’t give make or model (it was Japanese), but we used an electric driver with pre-set torque, and a screw counter with interlocks into the assembly jig. Once the lid closed, the jig locked and the driver became “active”, the operator then had a time limit to put all the screws in at the torque setting. Once complete the lid was released, the driver became “inactive” and the part can be removed.The problem we had that if there was a problem, a key was needed to re-set the unit. This key was left in the machine, so it defeated the purpose of having all the interlocks. We had to make sure the line leader only had the key, and always asked “why” if they needed to use it.

    0
Viewing 25 posts - 1 through 25 (of 25 total)

The forum ‘General’ is closed to new topics and replies.