‘HIDDEN LOSS FACTORS’ IN OVERHEAD MATERIAL HANDLING SYSTEM
MISMANAGEMENT OF UPS CAN DO MORE HARM
Overhead material handling system, in sewing or popularly called as Unit Production System (UPS), is a favourite among many garment manufacturers in Asia. On an average, cost per sewing workstation can be US $ 1,000 to US $ 4,000 for implementing overhead material handling system in sewing. But it seems cost is no deterrent for many garment manufacturers. If we ask ourselves why any organization would like to implement overhead material handling system on shopfloor? The answers can be manifold – to increase productivity, to reduce operator handling time, to reduce the throughput time (which is a myth), for better accountability of WIP, to reduce soiling of pieces, reduce floor space utilization and increase vertical space utilization, virtually everything that a factory manager can wish for. But in reality, what is achieved can be far different from what is promised or claimed, if the system is dealt with mismanagement. The article is a research project carried out by a NIFT student under the guidance of Dr. Prabir Jana, NIFT Delhi, which shows that an overhead material handling system could also be disadvantageous if not implemented properly.
Afactory was chosen for analysis where the same style was running in both – the PBU system as well as the UPS system – using overhead material handling. On management’s request, the advantages and disadvantages of both the systems on six different parameters were analysed. These parameters were floor area utilization, throughput time, WIP, balance efficiency ( line utilization), labour productivity and SMV.
Floor Area Utilization
The very first shock that hit was when the floor area utilization under the two systems were analysed. There were two types of UPS layout in the factory: Type 1 and Type 2 as shown in the figure below. There were six lines of Type 1 and two lines of Type 2. Similarly, there were six lines of PBU Type 1 and three lines of PBU Type 2.
UPS actually increases throughput time. This is because in PBU, you work simultaneously on one garment, but in UPS, the system becomes linear and is bound to take more time. – Dr. Prabir Jana, NIFT, Delhi
The average area occupied by one sewing machines in the two systems was calculated and compared in the table below. Against the claim, it was shocking to see that the UPS system utilizes about 1.8 times more floor space than its equivalent PBU system. No doubt, the floor area in the line was neat and clean; the WIP counting was easy, but floor area utilization was almost double. Although the organization was able to utilize the vertical space, the typical pre- U-shaped overhead rail made the floor space utilization very poor. Incidentally, all the computerized overhead material handling systems have rigid pre- designed structures resulting in very little options for the manufacturers to change the layout structures.
Shorter the throughput time, the better the response time (or lead time)
In order to understand which of the two systems give a shorter throughput time, it was decided to calculate the throughput time by noting down the date and time of loading a particular hanger ( in case of UPS) and a
All the computerized overhead material handling systems have rigid pre-designed structures resulting in very little options for the manufacturers to change the layout structures.
Overhead material handling system should be implemented only in assembly section where the half-finished sewn component is larger in size and possible to sew in hanging condition. Sewing in hanging condition reduces pick up and dispose of time resulting in reduced SMV in UPS system.
particular bundle ( in case of PBU) in a line and unloading time and date of the same hanger/bundle. We calculated the time for five hangers/bundles each day for three days and for three different styles. To the management’s surprise, the average throughput time for the UPS system came out to be approximately six times higher than the PBU system. “I am professing this point for last so many years ( against the claim of overhead material handling system suppliers) that UPS actually increases throughput time. This is because in PBU, you work simultaneously on one garment, but in UPS, the system becomes linear and is bound to take more time. Although six times may be a little too high in this factory, factory can try to keep it under check by reducing the amount of WIP drastically,” avers Prabir Jana.
Lower the Work in Progress, lower the throughput time
Ideally, low WIP means low overall cost of garment. Work in Progress ( WIP) was calculated in the line by noting the initial WIP, daily input and output for continuous 15 days for one line each. The average WIP for UPS came out to be 386 against an average of 432 pieces for PBU system. The only thing happening right in the factory for UPS is low WIP.
The reason behind maintaining higher WIP in PBU is cushioning for the non-transparency of counting the actual WIP in the line, but in UPS, no pieces are hidden in boxes or trolleys, and it is easy to count the hangers. This transparency enables the company to maintain low WIP in the UPS line. This is also a unique case to prove that only lower WIP cannot ensure quicker throughput. The linearity of all operations and higher SMV have outweighed the advantage of low WIP finally resulting in higher throughput time for UPS.
Better the line utilization, better the productivity
In the next step, three months data on line utilization and labour productivity was taken into account to be measured. Utilization of lines for 8 hour shift was calculated using the formulae ( Output X SMV) / ( Manpower X 480) X 100.
It came as a shock to an extent to see that PBU was featuring better both in terms of utilization and labour productivity. It was interesting to note that the mean SMV that is provided by the company for the UPS line was consistently higher than the PBU line.
The mistake the company did was in implementing overhead material handling system in every sewing operation of the style, which resulted in multiple problems. In the first phase, overhead material handling system should have been implemented only in assembly section where the half-finished sewn component is larger in size and possible to sew in hanging condition. Sewing in hanging condition would have reduced pick up and dispose of time resulting in reduced SMV in UPS system. If overhead material handling system was implemented only in assembly section, the small parts preparation could have followed PBU and hence parallel processing would have occurred, resulting in reduced throughput time. Sewing small parts using overhead material handling system increases the pick up and dispose of time, hence leading to increased SMV.
Every factory should emphasize on judicious use of technology rather than a showcase (to impress buyers or fellow manufacturers).
The floor area in case of UPS is neat and clean, but it utilizes almost double floor area compared to PBU (photo for representation purpose only)
Against all the claims, PBU system of production features optimum floor utilization, low throughput time and high productivity (photo for representation purpose only)