ADVANCED COIL PROCESSING

INTRODUCTION:

Sheet metal working holds a special place in many consumer durable and engineering industries. Use of sheet metal has increased steadily due to various advantages it offers viz reduced material consumption and suitability for mass production. Automotive, electrical, and furniture industries are the main users of sheet metal.

In India sheet working was introduced long back, but its full potential was not completely exploited due to number of reasons. The major amongst those were lack of quality-sheet metal supplies, absence of reliable sheet service centers, comparatively low labor costs and other financial constraints.

However, the scenario has changed in last 5 to 6 years with increasing market demand for end products and technology upgradation started by many industries. Many new concepts in sheet metal working viz transfer presses, roll forming, etc have made their entry into Indian industry. However, the potential of coil processing is not fully exploited to achieve the productivity, considering the manufacturing cost of the end product.

The topic discusses the various possibilities of coil processing lines instead of stand alone press operations.

NEW DEVELOPMENTS IN COIL PROCESSING:

Over the past few years, a number of coil processing solutions are locally developed and mastered by Godrej. Some are listed below:

1.      Mini cut-to-length cum slitting line (Freedom Lines)

2.      Flexible punching & folding lines (FPL)

3.      Auto blanking lines(ABL)

4.      Press feeding lines with progressive tooling (PFL)

These solutions have proved to enhance the productivity of the press shops in a dramatic way. The concepts are discussed below.

Freedom Lines

Freedom Lines are small cut-to-length lines with slitting option. This range is developed to enable the sheet metal users to make the coil processing in-house and free them from the traditional constraints.

Getting the rectangular blanks from steel processors meant extra cost, more inventories, more variety of sheets stored and dependence on external setups. On the other hand, in-house slitting and cut-to-length lines (CTLL) are a costly proposition which only a few bigger companies can afford.

The Freedom Series Lines have solved this problem completely. The investment in the line is very low compared to steel center lines. Also, the line flexibility to operate in any of the following modes (refer fig.1):

·         Only cut-to-length mode

·         Slit-cut mode

·         Slit & rewind mode

·         Slit-cut + rewind mode 

FLEXIBLE PUNCHING & FOLDING LINES: 

Numbers of components going in the appliances, panels, furniture typically involve operations like punching and bending. These are being produced starting from the rectangular sheet. The sheets are corner notched on presses or on big punching benches. This is followed by bending operations on press brakes.

The entire operation can be done on a flexible punching line starting from the coil. The coil is unwound, straightened and fed to punching stations are. The required numbers of hydraulic/pneumatic tools are used to make corner and punch holes. The system is very flexible as the sheet feeding and actuation of tools is controlled by a computer program. This also makes the entire line compact (refer figure3) and quickly adaptable to any shape and size of the part.

The line can also be provided by a folding unit after the punching stations. This takes care of end folds.

After the cut-off, one gets complete or semi complete panel ready. A number of operations are saved in the process (refer figure4).

Use of prepainted sheets on this line is possible with a little more investment. This saves further, space requirement and inventory in the press shop.

Automatic Control System:

In automatic control system for forming and auxiliary feed motions, the whole cycle of motions required to complete a particular job is automated. This includes automatic transition from one motion to another. The forming and auxiliary feed motions in machine tools are automated primarily with the aim of achieving:

1.      higher productivity

2.      greater reliability  of the product quality,

3.      greater safety.

Autoblanking line concept:

The concept of coil processing press lines is not new in itself. It is being widely used for many sheet metal parts of small size, e.g. electrical laminations, bearing elements, packaging, etc. However, the concept is limited to small parts whereby feed lengths are very small. The feeder used to feed sheet to the press is either conventional roll feed of gripper feed or pneumatic feeder.

In case of larger components, however, the sheet metal coil is first cut on the cut-to-length line. Subsequently, the rectangular sheets are then blanked on the press. The blanked components (shaped blanks) are further punched/notched before they are ready for subsequent forming/bending operations (refer figure 5). However, this process is labors oriented, involves a longer cycle and has much wastage. The same can be avoided by having a coil processing line to get the components of required shape; such a line requires an independently driven, fast acting feeder like servo feeder.

The term “Auto Blanking Line” implies a blanking line equipped with servo feeder and can handle wider sheets and longer feed lengths, to give blanks of required shapes. Such a line replaces number of operations (see Figure 5). It can reduce the costs and cycle times to a great extent.

The line consist of the decoiler, leveler, AC servofeeder, blanking press, conveying and stacking system (refer Figure 6). Also to increase the flexibility and productivity of the line it can be provided with coil skid and coil car, edge cropping shear, snubber, sheet support and loop bridge, quick die change system, etc.

The line can be used to get blanks of any required shapes using either the blanking tool or cut-off tool (after punch/cut operation) in the press. The sheet is fed to the press is required feed length, by AC servo feeder which gives a very fast and accurate feeding. The programming faculty provided gives very good flexibility to the line. Along with the other accessories provided, this feature helps to reduce the line change over time drastically.

The conveying and stacking system will be generally an integral part of the line. The blanks falling through the die are transported out of the press on the belt conveyors and are dropped on a stacker-pallet. The stacker and pallet-stack disposal system will be engineered to suit the individual components.

Press feeding line with progressive tool:

Press feeding lines need not be only for blanked components as in lamination lines or autoblanking lines. They can also be used for getting the end product which needs forming/bending operations.

This is possible using a progressive tool with a number of operating stations. The typical operations sequence involves:

·         Punching, piercing in the beginning;

·         Cracking followed by any forming operations;

·         Cut-off at the end.

The feeder can be selected considering feed lengths and speeds. It could be gripper feed, pneumatic feeder or servo feeder as the application demands.

The process can be applied to a number of small and medium sized parts which otherwise go through independent press operations. This gives dramatic reduction in cycle time, inventories, material handling and manpower requirement.

BENEFITS OF COIL PROCESSING:

The traditional method of working with metal involves getting the pre-cut rectangular sheets from the market and processes them through a number of press operations like blanking, forming, punching, sizing, trimming, etc. Replacing the same by a coil processing line/system (some possible solutions are discussed in the subsequent section) gives a number of quantifiable benefits over the traditional method.

·         The line can combine various operations, viz cutting to length, blanking to shape, notching, punching, etc.

·         Reduction in total cycle time.

·         Reduction in work in process (WIP).

·         Reduction in manpower.

·         Reduction in scrap percentage due to avoiding edge trims and nesting.

·         Reduction in material handling as inter-stage storage and handling is eliminated.

·         Space requirement can be brought down with proper planning

·         Flexibility of operation, faster response time.

·         Productivity – operator independent production rate, better monitoring.

·         Consistent quality.

·         Enhanced operator safety.

·         Lesser dependence on vendors.

The only hindrances as perceived by the managements seem to be the quality of the sheet metal coils and initial investment necessary to upgrade the existing facilities. Both these factors need close scrutiny to arrive at appropriate technology selection.

Emergence of a number of rolling mills has improved the quality of the local coils available in the market. Also the coils are now available in required widths, weights unlike in the old days when only mother coils were available to the users. This has removed many constraints from the coil processing. The investment decision of course needs to be made considering the benefits/savings possible.

JUSTIFICATION OF INVESTMENT:

The change of manufacturing process to coil processing can give tremendous boost to productivity and streamline the operations. This however needs some initial investment to be done in the equipment. This needs to be weighed against the benefits of the new process. One can find the payback period or simply find out the production cost/piece considering all visible and not so visible costs.

The justification will come from a number of direct and indirect savings mentioned above However, the remaining benefits can also give additional justification for the investment.

A simplified analysis for getting payback period can be done on following lines

·         Document the earlier process of manufacturing the part and the new envisaged process.

·         Determine the production volumes considering the future requirements.

·         Collect data on investments in both the processes. Consider-

Equipment Cost:          Consider the effect of higher production rates available on line processing. A single line can replace a number of standalone presses. Sometimes a coil line can become cheaper than all the presses considered together.

Tooling Cost:                standalone presses will need a number of different tools, whereas the coil line will need one tool which will be little complicated and hence costly.

Cost of floor space:     the coil line is a space saver, particularly if one considers the space required, not only for the equipment but also for in-process storage and RM storage

·         Analyse the various costs and savings. Various likely savings are listed below:

Raw material rate difference: The coil is cheaper than the rectangular blanks. Consider total consumption to arrive at saving.

Reduced Raw Material Consumption: The coil processing reduces the scrap percentage, as edge trims are avoided and nesting is done. Consider this along with rate to arrive at material price.

Reduced interest cost: The interest cost on WIP or inventories needs to be evaluated considering the cycle time reduction. Typical reduction from 6 weeks to 1 week inventory levels is possible. Also, the inventory will be now in coil from which is cheaper.

Manpower cost reduction: In many of the coil lines there is considerable reduction in manpower as against standalone presses operation. One or two people can oversee a line. The roll is mainly monitoring and tool/coil/stack changes as per the production plan.

 Other savings:            The coil processing also reduces material handling between various operations. The rejections will also reduce as there is better control over the entire processes. An attempt should be made to capture these in cost/savings terms.

The experience shows that in many cases the payback periods are within 2-3 years and sometimes even lesser. Also, there are many qualitative benefits like streamlined process, better control on operations, ability to respond to changes in production plans. These need to be emphasized even if not easily quantifiable.

Thus proper selection of process to get the required end product should give better productivity and reduced part per component. Economic justification as above can be prepared to put up the case. 7

CONCLUSION:

The potential of sheet metal processing can be fully exploited with coil processing. A number of coil processing solutions discussed give a number of benefits to the user. The coils available in the market have improved in quality and can be ordered to the required size. The investment for the coil lines can lead to continuous savings resulting in lower manufacturing cost/price for the end product.

Thus availability of coil processing technology locally coupled with availability of good coils, for a fresh look in the traditional processes by the Indian industries.