Pop Quiz: Designing a t-shirt sewing cell
Here’s a different kind of challenge for you -beginning industrial engineering using the simple example of t-shirts. Are you excited yet? Don’t go away, it could be fun and you may be surprised at how well you do. But first I want to tell you about a free Juki app for iPhone and iPad (HT: Jessica Montoya) because it can be used as a sort of cheat sheet and also, I am using some of the images from it (without permission) but Juki may look the other way if I plug it. Then again they may not, they’re tightening down their IP. But anyway, the app is pretty neat.
The Item List screen loads a selection of products to choose from. You pick an item and the application loads a schematic of the product with its seams in call outs listed by number. Below the schematic, each number lists the kind of machine you need to form the seam along with the model numbers. The model numbers themselves are also hyperlinks so you can read about the machine, its specifications et cetera.
Now back to our challenge which comes in two parts. You don’t need the application to do this challenge and can instead, follow the provided links above. For what it’s worth, I didn’t use the app to come up with what I think is an optimal solution.
Part one: examine the schematic of the product (the tee shirt) or use your noggin and figure out what kinds of machines you need. You can be very general, you don’t have to list machine model, just say “overlock”, “cover stitch”, “single needle” or whatever. I will tell you that for the purposes of this exercise, the tee is not made of tubular knit so there are side seams. Also, the shoulder seams are taped.
Part two: now figure out the ratio of machines needed. For example, let’s say someone is starting a tee shirt sewing factory with six stitchers and they plan to buy six machines. How many of each machine should they buy? Four overlocks, one coverstitch and one chainstitch (4:1:1)? Or should they buy two of each (2:2:2)? Or none of the above? Why or why not?
If you haven’t figured it out by now, this is a real life example. The person starting the factory has made good choices about the needed machines but not with appropriate ratios. In my opinion that is. So being that he is a good sport, I’m posting this challenge to see how many people will come up with responses similar to my own (because of course I think I am right). I also want to read how people have rationalized their decisions (because I could be wrong).
If you needed a nudge to work the problem, consider how many of each seam type there is and how long it is likely to take. Keep this in mind to prevent bottlenecks while also realizing that some machines are much more costly than others. Meaning, a 2:2:2 ratio would certainly avoid bottlenecks (mostly) but some machines might be underutilized while incurring greater purchasing expense. For example, the cover stitch machine is roughly 4 times the cost of an overlock.
So good luck and I look forward to reading your comments. Oh, and we have a prize for a winner! Lisa Bloodgood has donated two books as a give away. The winner can pick which one they want. The two titles are Pattern making in Fashion and Pattern making in Practice (same author).