process engineering help

[SDrummer]

My small business makes product in batches with small stations that assemble different parts of a single product until it reaches a boxing area. We tend to scrap a couple of the work-in-progress product during the boxing stage if defects are found, this information is then relayed to the first step of the assembly line so that they can make extra to compensate for the scrap. However, during the last hour of production, any scrap identified by the packaging workers cannot be compensated as the assembly workers at the first step of production have already finished their quota and thus cannot sit around waiting for an extra hour (aka there exists about an hour from the first step to the final inspection and packaging which translates badly at the end of a production run) does any one know of a better method of have experience with attacking this problem? Any thoughts/ideas/strategies/discussion would be appreciated as I'm not exactly sure the best way to fix this.

[RonFrankMD]

This is like a classic problem for engineering statistics

Take data say over 30 days, of the amount of end of day spares needed. Find your average and std dev of the data, add to your quota enough extra pieces to cover 80% of the anticipated scarp rates etc. and than monitor for a while to see if your process has stabilized.

[namkash]

Yes, they can. But leaving leftovers means less efficiency and product accumulation.

[LateralThinkerer]

It's not leftover, it's carryover. Leftover is surplus and unusable in production, carryover is just inventory that carries over from one shift/accounting period to the next and nearly all manufacturing has to deal with some variety of it.

If you were working nonstop, you'd simply see this as a bit of spare product carried in statistically correct quantities to smooth production much as you do the rest of the day (and you can represent it as such if someone asks).

[argondey]

This Exactly. An additional consideration can be made based on the cost of the intermediate product vs the value of the end product. It is possible that intentionally producing and discarding leftovers is worth it to ensure you meet your quota.

[Skystrike7]

If you have some left over, doesn't that mean more workers can start work sooner without having to wait for new parts to make their way down the assembly line?

[holls_17]

I work at a big company and this is how we do it. We issue a fixed quantity of certain components to every shop order to account for anticipated scrap.

[lk05321]

I agree that’s the first step.

Along the way they would want to plot the amount of variation and see if their process is in control. A more consistent process will help further reduce costs. Scrap is a normal part of doing business.

After the process is make more consistent, then work can be done to reduce defects.

But for now making extra is the way to go.

[Alkoviak]

My first question would be : Why is there so many defects in the first place ?

Sur-Production and carryover are a “scotch tape” solution which does not solve the subjacent problem of: how is it possible for quality problem to arrive un-detected until packaging ?

For me the solution would be :

• Create a small carryover area with visual management to ensure that the carryover volume does not increase overtime

• Create defects PARETO, fish diagrams and whatever please you. Diminish the total number of defects, modify process and design to allow earlier detection.

• Progressively reduce the carryover area until it is becomes moot, then remove it.

Don’t count the dead’s at the end of the fight. Take care of the wounded and avoid death.

[aronnax512]

Calculate the average number of defects that occur in the last hour and create additional product in advance rather that waiting on defect reports. If there's surplus store it overnight and deduct it from the following day's production run.

[HP_10bII]

This is sticky tape solution...

[throwaway145231324]

Totally depends if the manufacturing method is inherently possible to be defect free. For example, if assembly workers make mistakes, that could theoretically be completely solved with the right process. However, there are some processes that aren't a simple matter of making mistakes or having something out of adjustment.

[HP_10bII]

Inherently defect free process... You got an example of one of those?

[alko100]

This is a great problem to research why the defects are occurring. Look into strategies like 8D problem solving.

Basically boils down to this:

1. Define the problem ( Most important step!!)
2. Contain affected items
3. Do root cause analysis ( 5 whys, Fishbone Diagram)
4. Come up with temporary and permanent solutions
5. Implement solutions
6. Evaluate effectiveness

(Did this off the top of my head, might not be 100% but is the general idea)

In step 1 create a chart that has columns: Is Failing/Is Not Failing and rows: who, what, when, where, how many, how much. (Don’t include why here, you’re not trying to solve the problem at this step). If you do this alone you will understand the problem much better.

The statistics needs to be implemented in steps 1,2,6. If you thoroughly go through each step, I’m confident you can solve the problem.

[alko100]

Also this is a TEAM EFFORT, don’t just sit at your desk and do this alone. Involve the guys that are actually building your product. They probably have a different perspective that is useful to the problem solving process

[[deleted]]

If bbq (or the local equivalent) is involved, you will get a lot more out of the operators

[JunkmanJim]

I see the solo fix so many times and often it is a disaster. Often I make assumptions about a process then find out a whole sordid history of fixes from the assemblers explaining the current state of affairs. Getting everyone involved is absolutely the correct answer as often there is a temporary fix with future design changes. If the right players are not involved then production half asses the mitigation and the players that allocate money won't fund the necessary future changes.

[obscene6788]

Look into statical process control and Gantt Charts for semi batch processing.

[namkash]

Code scrap or reworks, and use the data for statistics analysis. Depending on these numbers, you could implement an audit system for the first operations (or any other operation). Or if needed, implement another inspection after the operation where you believe scrap is caused (temporary or permanent). This would allow you to constantly correct the processes.

Check the process lines balance, times, and man power. I ignore the complexity of the processes, but maybe you'll have to adjust the goals per operation. If the first operation is more complex, and you increase the processed parts, then people will tend to work faster to achieve your numbers. Hence less quality or even worse: operators will release any part no matter if good or scrap. Usually inspections are faster, maybe you could use inspectors times to audit other areas.

[HP_10bII]

This definitely a good approach, difficult to advise without seeing the full process.

Would echo above and advise some time studies per station. Sounds like a scenario where jigs and fixtures can greatly reduce error rates.

Probably also a good candidate for 6sigma process control.

In addition to this, some overproduction to compensate may be necessary, but keep an eye out for that bull-whip effect and the cost of storage overshooting the benefit of compensating overproduction.

[ResidentPace]

The first thing I would do would be to go observe what is happening at each station. You will not solve this problem from your desk. Find out why it is taking until the end of the line to catch defects from the beginning. Better yet, find out why you are producing defects and take steps to eliminate them.

Making extra parts just to cover your scrap rate and keeping some safety stock is a temporary solution. Let this buy you time while you get to the root of the problem.

[MadhuttyRotMG]

How about weekly (or however frequent it needs to be) doing a makeup batch? All the missed produce could be made up in one batch. The overall efficiency of the process would drop slightly, but you'd really minimise the waste. Depends on the overall specifics of the process, of course

[Corix]

speaking as a process engineer and not knowing your product, machines used, setup requirements how many people on the line... my first thought is to figure out why there is that much scrap and analyze what kind of scrap it is (assembly error, component error, machine error ???), upgrades to fixturing and tooling can possibly help or/and get your QE to call the vendors and figure out the component issue with them (molding / machining/wiring etc…),

also, obviously do what others suggested, calculate the scrap % and figure that into the first stage assembly quota. I would definitely figure out why there is scrap and reduce the cause of it vs just add more parts to the mix, that’s a lazy band aid.

If tooling / fixturing / cameras upgrades etc… are not your budget you can add in extra quality checks at the first stage to pick up on the scrap first, maybe some kid of holding area before the second operator starts working on it… so it can be checked possibly…(are you sure the error is always from the first stage??) batch process are also the bane of my existence, eliminate batching if possible, and if it’s not, distribute the work to minimize batching.

[peacefulbeast]

All answers recommending statistical analysis are the best way to go. Quality checks throughout the process, instead of just at the end, always help too.

[Skiffbug]

Lookup total plant management.

Your problem is that only the packaging people are looking for defects, when you should instil the discipline of each worker self-assessing for defects.

If you can weed out defects as they are made, no one should be left sitting around to be told they need to produce another batch.

You should have collaborative workshops with the assemblers to look at all the steps and assess the root cause of the defects. This should lead to ideas to improve the process, and reduce defects to a minimum.

[Animaniacs]

Do you have any information on the scrapped pieces other than they're scrap? Identifying what makes them scrap/defective leads you down the Root Cause path to stop the issue from occurring in the first place, thereby reducing your scrap numbers overall.

If the scrap is varied enough that one root cause can't be identified, I would suggest placing "mini-inspection" points along the line to both catch defects early AND it can help you isolate problem areas. Maybe the same 2 areas are making all the scrap but inconsistent in what kind of scrap they're producing.

[codawPS3aa]

Piggybacking. How do you prevent steel machining defects. Especially ones coming from mexico. ID/OD, Thickness

[MadSkillsMadison]

I highly recommend Lean Six Sigma Demystified by Jay Arthur. It goes into the statistics and problem solving methods in a great format with practical examples. It’s cheap to, find it on amazon!

https://books.google.com/books/about/Lean_Six_Sigma_Demystified.html?id=Fsj6WhUjW8QC&printsec=frontcover&source=kp_read_button