|Title of Invention||
A METHOD TO SLIT SHEETS AND SYSTEM THEREOF
|Abstract||The method detailed provides approach to develop Software solution taking into consideration the required data and the constraints.|
|Full Text||Coverage & Back Ground Coverage
The Coverage of the solution is related to Electrical Transformer Core manufacturing (distribution and or power). The Core manufacturing is consisting again of preparation of individual sheets of different widths, cut to size, hole punched and then of stacking to form the core. The solution which is under discussion is that of preparation of individual sheet widths out of rolls of thin magnetic material (cold rolled grain oriented) before being fed into cut to length+hole punching lines. Subsequent to cut to length and hole punching, the individual sheets (as per drawings) are stacked to form the core of a 3 phase Transformer.
The author of the solution, I C.L.VISWANATH have worked in the Transformer manufacturing Industry for a long time. Initially I was associated with specialists in setting up the Transformer Lamination manufacturing section of which the slitting line was one followed by cut to length and hole punching lines. Having worked initially in preplanning, I am aware of the construction of the core and the inputs of different widths. The complete calculation under 2 is based on this experience.
The actual situation as to when I came into picture of providing an optimized solution was much later. That is when I was GM Computer aided Management systems (CAMS). As head of this division I took upon myself along with 2 of my colleagues /Consultants to provide an optimized solution for conserving Raw material. After prolonged discussions over a period of 3-4 months I came out with the approach which I discussed with my 2 other colleagues who are basically software persons without domain knowledge (which I had in plenty). They accepted the approach and went ahead with providing the computer based software solution. As such I claim that the intellectual property rights in this are mine only. I did not get any compensation for this from the enterprise.
Optimised Transformer Core Lamination Coil Slitting Solution
(Also suitable to other situations where any thin material in coil confirm is required to be slit into different widths)
1.1 Electrical Transformers' Cores are essentially built (out of thin sheets) in stepped construction of different widths with the outer edges lying on the periphery of circle dia D of the Core as shown below. The material used is cold rolled grain oriented (CRGO) thin magnetic Silicon steel. The material is supplied in coil form. Each coil could be max. 3 T minimum 1.7 T. Thickness is 0.28 mm Uniform, Specific gravity is 7.89 gms / cm3. The material could cost more than Rs. 100/kg. Width of the coil is normally 1000 mm. While transporting the edges could be spoiled to an extent of 2-3 mm. A trimming allowance of 5 mm on each side is desired to be provided.
1.2 The coils as received from rolling mills are loaded on Decoiler. The width is passed through the slitter where widths between two pair slitting rollers could be adjusted upwards of 30 mm to 600 mm (600 mm is the max. width normally required for large power transformers and 30 mm is the minimum width for distribution Transformers of 50KVA and above). The slit coils are wound on mandrels mounted on recoilers. In one slitting program there could be min. 2-3 widths or as many as max No of recoilers. These slit widths are further loaded on automatic cutting lines where cutting to length, whole punching and notching (depending on design) is processed. The process on automatic cutting lines is outside the scope of the slitting solution in question.
1.3 It may be further noted that the slitting process is a shearing process where no material is wasted by way of generation of scrap: The scrap in the optimized solution could be the trimming width of 10mm, plus any width less than the minimum width required.
1.4 It may be also noted that large no of small transformers are required, where as large transformers are required in comparatively small numbers. The result (for a period) could be, small widths would require small quantity of weights and large widths would require large quantity of weights depending on product mix for the period.
E.g.: t4 of say 100mm would consist of 100 /0.28= 357 sheets. Length could be 1000 mm, width W4 of say 120 mm starting from Wi of 60 mm
1.5 A diagram (not to dimensions) of 3 phone transformer core (5steps) is given below. A cross section of a similar core (7 steps) is given above under 1.4.
A 3 Phase Transformer Core Construction Core Dia D (mm)
Window Height L (mm) window width A (mm) No of steps 5(could be 7 also shown under 1.4) 2. Generating data from documentation & Production program
2.1 It is generally in practice in Transformer manufacturing Industry (for the same grade of material) to determine the total requirement of different widths and their weights, converted from standard rating and their corresponding widths and weights multiplied by the No. of Transformers within the considered program of say a week or 2 weeks. The data could be worked out as follows
By adding up all the requirements (of different ratings for the same grade of material and the corresponding Nos) for the period, we arrive at the following
consolidated requirement (weight in kg) of Yi, Y2, Y3 Z„ (by adding up all
weights under each respective widths). Net weights required of each width is after subcontracting respective available slit coils weights.
Total requirement Zi+Z2+Z3+ +Z„ of slit material in kgs
The above is the starting input compiled out of design documentation (for each core corresponding to each rating) and the production program for the period.
3. Other conditions to be fulfilled.
3 .1 The optimized solution should provide a solution where total raw coil weight
(Z0) should not exceed (Z,+Z2+Z3+ Zn) / (Desired utilization factor say 0.95)
or in other words Z0x0.95 wt 3 .2 As an aid to continuously check the output, the slitter is required to be provided with a running meter, which measures the length in meters of the sheet, which passes. This meter could be set is zero for every slitting program.
3.3 Each slitting program could be in terms of full coils or fraction there of depending on need. The setting, even though, involves an hour or two it is desired to minimise the material generated which is not required for the program.
3.4 The normal requirement could be of the order of 100 Tons plus for 1 week.
3.5 Unutilised coils from the previous program should be minused from the current program requirement.
3.6 The No of recoilers could be limited. Hence the No of different widths in a set up cannot be more than the No recoilers.
4.1 Convert Wt (kg) of each width (wl-w2 etc) to corresponding equivalent length in Meters as below
Width Net wt Required in kgs Equivalent length in Meters
W, Zx U
W2 Z2 L2
w3 z, u
Wn Zn Ln
Apply formula Li= Wixtx7.8 where l, js in Meters W in mm and t in mm.(thickness of sheet 0.28mm) Figure 7.8 is corresponding to specific gravity of steel in gms/cubic cms
4 .2 Arrange all widths (mm) and lengths (m) in ascending order of widths and
corresponding Lengths as follows
"Widths (mm) I Wn I Wf 1 I Wv
Lengths (m) | Ln Lf Ly
Note while W„, Wf and Wn are in increasing order, Ln, Lf need necessarily be
in any order however it could be noticed that lengths of smaller widths could be longer (this depends on product in mix).
4.3 Pick the width whose length is the smallest of the lot. Let it be Wx with length L (min)
4.4 Make combination of other widths with Wx being the 1st, such that the sum total of al widths in each combination is less than the coil widths minus 2 edge trimming widths. Check also if the difference of each combination is such as to accommodate one more widths (of the selected) whose length together is more than the minimum. If so select. However the No of widths in each combination should not exceed the No of recoilers.
4.5 select amongst the combinations one such combination whose sum total is the highest. However satisfying the condition under 4.4
4.6 List the widths and lengths of this combination as follows
4.7 Subtract Lxof each of the widths of the combination from the total requirement. Arrive at the balance requirement (in fact the output under 4.6 is the 1st of the slitting program)
4.8 At the end of step 4.7 we are back in position under 4.2 repeat 4.2 to 4.7. The result will be the 2nd slitting program (as under 4.6)
4.9 Repeat 4.1 to 4.7 as many times as we are not left with any width to be cut.
4.10 Examine the last few slitting programs for optimal use of the material. If the Utilisations are such that they are less and there is scope for improvement by adding popular widths, a decision has to be taken if it is desired to add popular widths to increase Utilization. In that case select which widths to be added however the length should not exceed the length of the widths already included.
It may be noted that only step 4.10 is manually driven where as other programs are operatable with out any addition of widths.(not required immediately)
The logic that is covered under 4.1 to 4.10 is operatable manually. However it is generally known that the data in respect of widths and lengths could be very large which makes manual calculation very tedious. As such it is recommended computer software is developed to take into consideration all the calculations and come out with a set of optimized solutions or slitting programs.
5 Logic behind the solution
The pivotal break through is of converting all weights each widths of developed length and trying to see the picture in a two dimensions mode i.e. width and lengths (with constant thickness) The evolved picture is indicative of the possible solution. The same is shown in below
5.1 There is 1 width with minimum length i.e. W7. 5 .2 All other widths other than under 5.1 have higher lengths
5.3 W7 with L7 along with other widths such that the sum total is " 5.4 For clarity the picture with W7 (folly), W3 (partially) and W5 (also partially) knocked off to length of L7 is shown as below
5.5 After the 1st run, out of the remaining data it could be seen that L5-1 is the minimum length with width W5
5.6 Now let us say W5 + W4+W1+W2 could give the best combination where all these would add up to effective coil width W0.
5.7 The third combination could be W3+W2+W6 with L3-1 as minimum length.
5.8 The fourth one could be W6+2W4+2Wi +W2 with L6-2 as min length
5.9 The fifth combination could be W4+W1+W2
5.10 The last combination 2W2+2Wi+other popular widths.
Thus it could be seen that the total area covered under Wi-Wn and Li to L7 represents the total requirement (Area). The optimization could be achieved by navigating with the constraints on building Block by Block principle.
To achieve this the approach is from bottom up. That is why the width with the smallest length is taken as the starting point. To this other suitable widths are added which give the best utilization. Once this is done we are creating the new area after deleting what is covered already for optimization. In this new area again the width with the smallest length is taken and the same exercise is continued till the whole requirement is met.
If on the other hand a mere No crunching exercise on L near program model to create all combinations and select the best set, as per my information, the exercise is either unfeasible and even if it is feasible it would take enormous time on computer itself. Manually it is impossible. Since in actual life situation (unlike what is shown in the diagram earlier) the widths required and the lengths could be very large. Hence the necessity of software program on the lines under 4 could be feasible and operative.
6. Solution is based on own experience
This is borne out of experience. I was one of those 3 top experts who were asked to come out with a solution. The subject was discussed many times over a period of couple of months. I came out with the solution on the lines under 4. The result was, the utilization, which was only 90%, was brought upto 97-98%. This saved enormous raw material (which was then imported) amounting to substantial savings. I proudly say the solution is mine and only mine, others assisted in eveloping the solution on computer. Utilising my logic described above under 4& 5
Diagram drawn for clarity after 1st slitting configuration which gives L2 the lead for next set of combinations
7. In respect of other situations (other than Transformer Core lamination) where widths in mm and Corresponding lengths in meters for the same grade of material are given directly, the application of the optimization solution is (directly) from step 4.2 (i.e. arrange all widths (mm) and lengths (m) in ascending order) and continue there after.
3.1 The solution is to minimise in put raw materials in coil form to meet the required widths & weights
3.2 The solution takes into consideration (if available) already coils of the widths required and the respective weight
3 .3 The solution provides multiple slitting combinations or programs and the length on the assumption that the length if each combination is by itself substantial 3 .4 The solution recognizes the limitation say No of widths depending on No of recoilers provided on the slitting line.
3 .5 The solution is based on converted weights to corresponding lengths (for each width) as means of optimization and also to monitor the output of each combination. For conversion exact thickness and specific gravity have to be inputted into the formula
Wjx t x Where Lj is length in meters corresponding to widths Wi in mm Zi is wt required of width Wi in kg t is thickness of the sheet (CRGO)
D is a constant related to specific gravity (7.8 for steel) for others the constant differs.
The method detailed provides approach to develop Software solution taking into consideration the required data and the constraints.
The Optimised solution provides material Utilisation of the order if 96/-98% for a given period requirement.
While the method was developed for Transformer core lamination manufacturing, it could also cover engineering Industry (especially Automobile Industry) where raw materials in slit coil firm is fed into Automatic Punching and Forming Components out of thin material. The various different width coils are slit from broad coils (cold roll steel sheets) sourced from steel mills.
|Indian Patent Application Number||803/CHE/2004|
|PG Journal Number||37/2011|
|Date of Filing||16-Aug-2004|
|Name of Patentee||CHANGAVI LINGAPPA VISWANATH|
|Applicant Address||20, 1ST CROSS, VANSANTHA NAGAR, BANGALORE-560 052|
|PCT International Classification Number||H01F41/00|
|PCT International Application Number||N/A|
|PCT International Filing date|