Over the years as the Unit Production System became popular in Asian countries, more and more organizations started using it. However the ‘myths’ behind advantages of Unit Production System are still misconstrued and often misunderstood. In this article, Prabir Jana, Professor of NIFT, tries to de-mystify these myths whilst putting its net advantages in correct perspective.
Myth 1:
Unit Production System means overhead material handling system
- First, ask yourself a question. Why am I going for Unit Production System? Am I looking for benefit accrued out of UPS or overhead material handling system?
- Unit Production System is becoming popular in Asian countries; more and more organizations are using it. However the ‘myths’ behind advantages of UPS are still misconstrued and often misunderstood.
Yes, it is true that Inge Davidson, who invented Unit Production System, also invented overhead material handling system for transporting cut components on the sewing floor. However, we need to understand that Unit Production System (UPS) is basically a manufacturing system with typical characteristics while overhead material handling system is merely an enabler (equipment) to help the system perform. UPS may be defined as a sewing practice where all cut components of one garment are bundled together and passed through a line of operators. The operator reaches out to the components, performs specific functions, puts the sewn piece back into the bundle and passes it to the next operator. Hence, the essence of UPS is “All cut components of one garment should be in one bundle”.
However, talking specifically of the overhead handling system, this eliminates practical bundle handling, i.e. tying and un-tying of bundles, while allowing the cut components to be easily transported as a unit directly to the sewing machine or workstation through an overhead conveyor system.
The word ‘bundle’ usually makes us visualize big and small cut components, rolled and tied by one cloth string. However, it is not necessary that the ‘bundle’ should always be ‘bundle’ in literary meaning; all cut components of one garment may be in a single tray, in one polybag or hung on a hanger, and the trey or hanger is passed from one operator to another.
Therefore, whether it is the bundle, tray, polybag or hanger, it is the system of manufacturing (sewing) which is called unit production system where one unit of garment is processed in one place.
Incidentally hanger is the most popular and prevalent form of ‘bundle’ being used: Thus UPS is synonymous with overhead material handling system.
Myth 2:
Unit Production System reduces ‘throughput time’
Throughput time can be defined as time lapsed between the first sewing operation on the cut components to the last to complete any garment. When we talk of “reduction in throughput time”, there is always the question of what it is being compared to. If the answer is progressive bundle unit (PBU), then the statement is wrong! There is a popular belief that the UPS system increases the efficiency of the shop floor while radically reducing the work-in-progress thereby reducing the throughput time. However, factually UPS does not reduce throughput time; rather increases the same when implemented in complete line.
However, let us understand the PBU system first: PBU is defined as a sewing practice where the same cut components of one garment are bundled together (20 cuffs or 20 yokes are bundled together) and these stacks are then passed through a line of operators. Each operator is supposed to open his bundle, perform the specific functions, and make a fresh bundle of the sewn components which he passes on to the next operator.
For example an operator receives one bundle of 20 creased pockets and another of 20 fronts. He will attach the 20 pockets to the 20 fronts and make a new bundle (of sewn pocket fronts) and pass on to next operator. In the PBU system, while one operator is working on pocket attachment, at the same time another operator may work on the collar of the same garment, and a third works on the cuff and so on. Therefore, all operators work parallel to each other. So, if the total work content of any garment is 20 standard minutes, then throughput time (sewing from start to finish) may be lesser than 20 minutes depending on how many operations can be done parallel.
But when working on UPS all components of one garment are at one place and that bundle/tray/hanger can be with only one operator at any given point of time. Multiple sewing operations can’t be done in a parallel manner in the UPS; thus theoretically sewing the same garment in UPS from start to finish will take equivalent to 20 minutes and not less than that.
Myth 3:
Unit Production System reduces work in process in sewing line
Factually UPS does not have any direct relation with work in process (WIP) in sewing line. However if we analyze the results of few implementations then the above myth may sound to be true. WIP is a buffer in a line maintained for three purposes:
- First, balance the output (varying workplace) of different operations.
- Second, ensure supply to next operation in case of a machine breakdown.
- Third, uninterrupted line-function in case of absenteeism.
While the first reason can be definitive calculation, the other two represent the ‘just in case’ scenario, in true sense, as a replacement of lack of information. If we can make correct forecast of machine breakdown and/or absenteeism, then we don’t need to keep WIP due to uncertainty. In traditional PBU system, WIP is maintained in cartons/ trolleys/bins where bundles are piled up one over other. Thus, counting and analyzing WIP in a line is cumbersome, thereby resulting in unaccounted pieces and thus increasing uncertainty and to maintain increased WIP.
When accompanied by overhead material handling system, UPS actually makes the WIP visible; you can easily count (or it gets automatically counted) how many chains or hangers are there between any two operations. Increased visibility of WIP reduces uncertainty, thus one can operate with reduced WIP.
Now you may be able to better relate with second myth. As WIP is directly related to throughput, reduced WIP will eventually reduce throughput.
Ask Yourself
The basic reason why UPS accompanied by overhead material handling system was invented was to reduce associated handling time during sewing; sewing operations were imagined to be performed while components were in hanging condition. More the operation that can be performed in hanging condition, more the time saved. As a thumb rule refrain from installing UPS in a small part section; the reason behind this is that small parts need to be tucked in and tucked out from hanger during sewing, thereby defying sewing in hanging condition. Moreover small parts are usually done in parallel operations. Thus, installing UPS in assembly section serves you two benefits: possibility of hang-in-sewing and maintaining throughput time.
While UPS may enable you to skip ticketing functions and less chances of shade mix up in sewing, an overhead material handling system will accrue benefits like cleaner pieces for whites (no spillover from cartons, no trampling, no dart), non-crushed components for pre-formed jackets (no tying-untying of bundles, so no creases) and reduced handling time during sewing. Handling time reduction remained a grossly ignored priority for maximum installations either due to ignorance or distorted briefing by UPS vendors.
