Sewing department in apparel industry is perennially striving to improve poor needle running time, which has an alarmingly low global benchmark of 20-30% of the total shift time. Garment workers traditionally waste time in picking up and disposing the component, handling and transporting material apart from sewing. These factors, combined with higher wages and technological advances, prompted Inge Davidson, technician and co-owner of the Eton Shirt Factory, Sweden in 1967 to address these inefficient material-handling procedures by developing an indigenous hanging conveyor system, where components can be sewn while hanging and small parts can be easily engaged and disengaged. When the system was first developed it was called “workplace system”. Over the years it has been given many different names – Material Handling System, Hanging System, Mover and Unit Production System (UPS).
Although Davidson’s objective was to enable sewing components in hanging condition, gradually the system associated itself with unit production system in sewing, where all components of one garment is kept in one tray/trolley/basket or hanger. Overhead material handing system (OMHS) in combination with UPS, provides for improved efficiency, by eliminating highly unproductive material handling procedures. A survey by Clemson Apparel Research, USA, reveals that the implementation of UPS and overhead material handling system as a percentage of total sewing capacity varies from a low of 9% of total capacity to a high of 92%. In a polo-shirt manufacturing plant, approximately 90% of the sewing operations are achievable on a OMHS.
How does it work?
Irrespective of how the cut components of a single garment passes through a line of operators, whether in a tray, polybag or on hangers, the system of manufacturing (sewing) is called unit production system (UPS), wherein one unit of garment is processed in one place. Incidentally, h anger is the most popular and prevalent form of component carrier being used to move the single product between workstations.
The overhead material handling system requires a reduction in work-in-process levels and a change in the management philosophy of a sewn product plant from “high work-in-process is efficient” to “low work-in-process levels allow quick response”. The system eliminates ‘bundle handing’ (tying and untying of bundles) and allows all the material needed for a specific garment to be transported as a unit directly to the sewing machine of any workstation. When an operation is completed at one workstation, the system either mechanically or automatically sends the unit on to the next work station.
In fact, the basic reason why overhead material handling system was invented was to reduce associated handling time during sewing with sewing operations to be performed, while components were in hanging condition. The basic logic was – more the operations that can be performed in hanging condition, more the time saved.
As a thumb rule, overhead material handling systems are generally not installed in small part sections; the reason behind this is two-fold: firstly, small parts need to be tucked in and tucked out from hanger during sewing, thereby defying sewing in hanging condition. Secondly, small parts are usually done in parallel with other operations; and installing overhead material handling system in small part section will convert the parallel operation to sequential, resulting in increased throughput time.
With every workstation, there may be adjustable chains for flexible height of hanger (e.g. in Eton) or standard hanger height (e.g. in INA and Smart-MRT) or fixed length of hanging chain where garment components can be hung in clips in variable height as per requirement (e.g. Switchtrack). These different options have their unique advantages and disadvantages. While standard hanger height is beneficial for sewing of components that require detaching component from hanger and re-inserting sewn component to hanger, adjustable chain is beneficial for sewing of components in hanging condition. With overhead material handling system, the resulting width of the sewing line ranges from 3 metre to 4 metres, which is almost equivalent to any PBU line with central service table.
Entire frame for INA and Smart-MRT is made of specialized aluminium to be rust free, whereas the connectors are made in specialized alloy to withstand wear and tear. The frame of Eton is made of special grade rust proof steel. While aluminium gives you lighter construction, thereby better for installation in multistoried building, both offer durability. Some installations are floor mount, some are ceiling mounted and some can have either. In addition to an easier pick-up and a free disposal at each workstation, the overhead material handling system reduces the time the garment is normally idle between workstations.
The modern overhead material handling systems are modular, which makes it very easy to adjust for every customer’s specific needs. There are no fixed designs or welding of parts. Individual stations, or even entire systems, can be moved and reconfigured as circumstances change.
The varying needs of both the apparel and textile industry are met by two different system platforms; one designed for lighter products of the apparel/textile segment such as shirts, jeans, ladies’ blouses, bathrobes and bed sheets and the other for heavier and bulkier products such as quilts, large rugs, mattresses, office seating, etc. In the systems meant for heavier products the grip of hanger is specially designed in such a way that fabric component can be engaged or disengaged easily without damaging and/or distorting the fabric. In case of garment components kept hanging for long time, dimensionally unstable fabrics are also prone to distortion.
Computerization of overhead material handling system
With the passage of time many upgradations have come about in the system which include automatic loading devices, pick-ups and work delivery robots and real time production control software provided for immediate ‘up to the minute’ accurate information on production and labour cost. After completing any operation, operator presses a button to actuate dispatch of that hanger to next designated operation, while a new hanger automatically comes for sewing. Hangers are fitted with unique bar codes or RFID tags and there are scanners in the hanger pathway, hence movement of hanger from one operation to another updates completion of the previous operation and WIP calculation in the central database.
Real time production control goes hand-in-hand with the overhead material handling system concept as all relevant management and performance information like machine occupancy, operator performance, WIP status, balance efficiency is automatically generated and presented through the software. It helps the customers make better decisions on a real time basis, thereby conquering their next hurdle, even faster. The computerization of overhead material handling system has two significant benefits: firstly, the opportunity for human error is reduced; and secondly, the data collection is automatic and does not consume productive operator time.
However, the main benefits that accrue from an overhead material handling system can come only if the users have an in-depth knowledge of how to handle the system. Operators need to be provided professional training in handling of both hardware and software. Current overhead material handling system software is available to allow a company to link several overhead material handling system lines together, and also to tie in to off-line operations to track whether operator is working or not in seat. There is also a historical link to each product after it has been completed and this information is useful when similar products are brought to the line again.
How it will benefit users?
An overhead material handling system will accrue many benefits like no requirements for ticketing; cleaner pieces of whites, as there is no spillover from cartons, no trampling, no darts; non-crushed components for pre-formed jackets (no tying-untying of bundles, so no creases) and reduced handling time during sewing. A study by Clemson Apparel Research, Clemson University, USA, confirms that the key advantages of overhead material handling system are increased productivity and efficiency, improved quality, reduction in direct and indirect costs, reduced WIP inventories, as well as a reduction in operator fatigue due to the ergonomic advantages, as components are presented to sewing operator in an ergonomic manner, so that operator posture and hand movements are improved.
The ‘one-piece’ (one unit per carrier/hangar) flow makes it easier to process smaller batches and still get an economically efficient manufacturing process, as the WIP is less. The overhead material handling system also offers substantial reduction in throughput time, turnover, absenteeism probably due to better working conditions and space utilization. The shortening of throughput times enables any quality problems to be identified much quicker; operators can concentrate on sewing, and with all parts hanging, the amount of in-process creasing is reduced drastically resulting in less final pressing. Not only does the productivity improve, but also production can be planned and controlled down to each individual garment.
Overhead material handling system causes a reduction in direct labour content (9.7%) through ergonomic garment handling by the operator and its automatic removal upon completion of the sewing cycle. Further, there is a complete elimination of bundle handling costs, time, effort and cost in pulling piecework tickets and completing clerical duties.
Overhead material handling system leads to a significant improvement in quality of product (by an average of 60.4%), mainly because of the drastic reduction of work-in-process. Problems are not ‘hidden’ in bundles and tend to show up quickly. Also, this improvement in quality, directly affects operator productivity since more garments are sewn correctly the first time and fewer defects must be corrected. The reduction in defects (by 11.1%) results in savings in the number of off-line repair people, mender carriers, etc. There is a better overall appearance of the products due to garments being hung versus tied in bundles and stored. These garments tend to require less inspection, cleaning and pressing. All of this results in a better quality product.
The use of overhead material handling system also leads to improved operator’s productivity (by an average of 18.4%) and less fatigue, since operators neither have to pick up heavy bundles nor stretch to pick up and dispose of garments. Additionally, since there is no bundle handling, which tends to break the operator’s rhythm, productivity is higher. The UPS also helps to pace operators by automatically positioning the next garment.
Another added benefit of overhead material handling system is that it has a positive effect on operator annual labour turnover rate, which has been seen to reduce by 29.5%. It also improves the operator’s satisfaction and morale indirectly, as the combination of a high-tech environment, the potential for increased earnings, and increased team feeling seems to contribute to higher morale.
While many may argue that with the dramatic reduction of WIP levels, errors and imbalances are revealed quicker, which may pose problems; in reality this may in fact be a positive as corrective measure can be taken faster. The only real challenge is to train supervisors and operators correctly for optimum utilization.
Recommendations from Users
Current users of overhead material handling systems offered the following suggestions:
When starting a new overhead material handling system, the plant must provide training to the supervisors to balance the system.
Involve the mechanics and maintenance technicians from the start.
Never take hangers off system to create a balance. This will only prolong the problem and will negate the system’s advantages.
Plan a comprehensive training programme for both managers and production operators.
Avoid the tendency to take out too much of the labour content, which will cut the piece rates (If his earning depends on piece rate) and reduce operator earnings. This will certainly create morale problems, when operator cooperation is most critical.
Don’t try to install overhead material handling system initially throughout the plant. There is a need to draw from the bundle line for the initial production (small parts preparation) operators.
Don’t use utility operators for style changes. It is important to teach all operators to become flexible from the start of the UPS installation.
In a style shop, introduce a variety of styles in the beginning; don’t try to protect the UPS operators from the inevitable operation changing.
Do a good job selling the concept to the production team indicating that the system will be a challenge and rewarding to all.
Pay production operators on average while UPS piece rates are being developed.
Start using the computer system immediately so that management can maintain control and utilize the full benefits of the system.
Before deciding on a system suitable to your requirement, talk to and visit as many companies as possible, which are presently using UPS.
Make sure features stated by the vendors have been proven in the field.
Put all machines on casters to aid machine repair and quick style changes.
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