Batch, UPS and Modular (Modular pt.1)

Posted by Kathleen Fasanella on Jul 24, 2007 at 12:45 pm / Lean Manufacturing, Operations, Process Reviews, Production / Trackback

Continuing from parts one, two and three, we’ve come to modular. Modular is TSS, team or lean sewing and I’ve written about it ad nauseum. As a refresher, team sewing means (usually) U shaped pods of machines. One operator makes an entire product moving from machine to machine in the cell sequence. Rather than regurgitate what I’ve previously written, in this entry, I’ve decided to highlight a case study (pdf) provided by our colleagues at Cal State Pomona. There are some good things about the study which are important as teaching samples but there are also problems. The gravest inconsistency is that their test cell wasn’t really lean as we’ve come to define the term. Specifically, they had assigned stitchers to given machines rather than having cross trained operators using each machine in turn to complete the product. I guess their system could more aptly be described as a hybrid of PBS aka bundle (assigned machines) UPS (various operators processing one at a time) and lean (stand up, U shaped cell). Still, this kind of set up may be an option for you if cross training your operators is unmanageable at the level you find yourself. Minimally, there’s a good discussion of the migration of PBS stitchers orienting to a UPS system so we can call it a good start. There’s also a link to a much longer version of this paper at close but I’m using the short one for discussion purposes.


First off, this document like the chart from yesterday, represents a seller’s proposition (the school performs work for hire and training services) claiming that bundling (PBS ) systems results in WIP through put of 4-6 weeks. I find this very hard to believe. Logistically, it’s impossible. Production managers are well known to make mistakes but they just aren’t that stupid. The only way 4-6 weeks worth of WIP is going to accumulate is if needed inputs are missing reflecting either a purchasing, delivery or scheduling (lots are too large) problem. Even then, someone would have put a hold on the whole lot pending delivery of the needed inputs allowing production to proceed on other items. Summary: you don’t need to exaggerate the excesses of a competing system to score points for yourself, especially when you can prove your point otherwise.

The principles of modular manufacturing include:

  1. Set-up of all equipment necessary to complete the entire assembly of a single garment (or a sub-assembly of a single garment) into a U-shape work unit. The premise for modular manufacturing is complete unit processing instead of the single operation processing found in PBS.

  2. Operators in the module are cross-trained and work as a team to keep the production moving at the required rate. All operators can work at more than one workstation and move from station to station as required to keep production moving forward.

The particular strengths of this paper are the descriptions of team training and the process of conversion to TSS which is useful for people who want to make the transition. However, there are significant problems with the summarized results. For example, page 5 of this document shows a set-up of the module operation for a short sleeve shirt. The needed machines are listed and organized according to its placement in the cell’s operation (the latter being another strength of this paper).

The last chart shows the module’s efficiency which is listed as 12 completed units per hour (96 per day) making for 480 units per week for the total of 6 operators. While this paper’s authors cite these figures as successful, I don’t think you’d find a production manager in the industry who would consider 2 units per worker per hour -for a short sleeve shirt- to be anything approaching efficiency. It would be more typical in a PBS system (in my experience) to produce this rate of garment completion with fully lined sportcoats; a garment inarguably more complex than a shirt. Drawing this out to it’s logical conclusion, the labor costs of such a shirt would amount to a minimal calculation of $2.50 per unit (then) -assuming the pay scale was tied to minimum wage- which even at minimum wage, is extremely high. In a PBS system sewing sportcoats, workers earned twice this rate, the total paid for sewing was $5 +/- per unit for the same half hour, making for an average hourly wage of $9.73 to $11.27 as these garments took an average of 28 minutes sewing time. Related: this explains why stitchers don’t want to work in an inefficient system. They make less money.

Another difficulty is the breakdown of machine assignments per worker. Worker A is operating machines numbered 1, 2 and 3, Worker B is assigned machines 4 and 5 et cetera. Now, as far as any experience I’ve had suggests, the beauty of a TSS system is that all operators operate all machines so I’m not certain how this test lab has determined this system to be a lean TSS model. Rather, the machine assignment per worker is more typical of a PBS model (although machines on a PBS floor are aligned in rows rather than cells). Now, I’ve seen men’s work jackets (long sleeve, zip front, 2 set pockets) being constructed with the TSS system on the floor of the Bobbin Show with a completion time of under 7 minutes. The latter was truly one of the most impressive displays I’ve ever seen so it would be unfortunate if one were to interpret the efficacy discussed in this paper as a standard of TSS efficiency. By the way, the stitchers in this last example were not harried to any extent, having the time to converse with booth visitors and answering questions while they went about constructing the jackets.

While I realize there are contradictions in this referenced paper, I would be very dismayed if any of you got the idea that the resources provided by Cal State’s Apparel Technology & Resource Center (ATRC) were anything less than impressive. I am definitely impressed by the wealth of information and resources available -for free no less- at their site and I’d strongly encourage you to visit and read papers of interest in their reference library. That said, you may have difficulty navigating some aspects of the site. Two problems I noted were not being able to register on the site (unlikely to be processed). The other major difficulty is navigating to the “Reference Library” from the left side bar as this bounces you to a registration page (which doesn’t process). The work around for the site is to type in a keyword using their “Keyword Navigator” at the top of the page. Skip all other strategies. Your search will produce a list of hyperlinked documents according to sub-headings.

Another way this study is useful is if you wanted to manufacture this type of shirt. It’s all laid out for you. The number of machines, models etc. Shown are fourteen different machines being used by six workers.

There is a longer version of this report, 73 pages worth. (select acrobat to open it). There are two other documents similar to this one:

  • A151393 Cal Poly Apparel Manufacturing Demonstration – Year 4 and 5 Final Technical Report

  • A958963 DLA Demonstration All Service Maternity Battle Dress Uniform – Coat & Slack Year 3

but I can’t find a free download. If you can find a work around, let me know. If it helps the research fanatics in our midst, I found the first document here.

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