Author: Dr. Anirban Dutta
Serampore, W.B., India
1.0: Definition of Marker:
A marker in apparel production is defined as an optimised template with maximum possible fabric utilisation percentage, either in hard copy or digital format, that includes all the pattern pieces for every size of a specific style number. It is designed according to the required size ratio, fabric width, and table length for the lay lot cutting of fabric, which is a preparatory step for sewing.
2.0: Objectives of Marker Planning:
The Salient and specific objectives of marker planning in apparel production are as mentioned below:
- i) To create a template for cutting fabric layers. Hardcopy of Marker to be placed on the top of the fabric spread. Or alternatively, the Digital copy can be directly fed to the compatible automatic cutting machine.
- ii) To include all the pattern pieces of all the sizes according to size ratio, based upon the production requirement and order-concentration chart.
- iii) To ensure the maximum fabric utilization, i.e. marker efficiency
3.0: Input Parameters or Control Parameters for Marker Planning:
The input parameters or control parameters to be considered, both in case of manual marker planning and computerized marker planning are as listed below with relevant mathematical interpretations.
3.1: Maximum allowed value of Marker length:
The maximum allowed length-value of the marker to be planned depends upon the length of the cutting table. Marker Length is parallel to the longitudinal axis of the fabric, i.e. warp direction in case of woven fabric and Wales direction in case of knitted fabric.
let, the available length of cutting table = T,
then the maximum allowed Marker length = T – 2 x length-wise allowance.
3.2: Marker Width:
The Marker width depends upon the fabric width, i.e. width of the corresponding fabric which is to be cut subsequently. It is obvious that the marker width must be must be less than the fabric width.
Selvedge width = t (In case of woven fabric)
Selvedge allowance = a
Then the Marker Width = WM = WF - 2. (a + t) ----------- (1)
Hence, width-wise allowance = (a + t), which is to be kept in both sides of the fabric while placing the marker.
3.3: Marker Ratio:
The Marker ratio or Size-ratio is the proportional share of each of the sizes under planning, in terms of number of pieces of garment to be cut from one single layer of that Marker.
For example, if the size ratio/marker ratio is S : M: XL = p : q : r , then it is to be planned that total number of garment-pieces to be cut form that marker = p + q + r ( p, q , r must be integer).
And, the size wise distribution of pieces to be cut are as under.
q pieces for the size M
r pieces for the size XL
Here it must be understood that ‘to cut p number of pieces of S-size from a marker’ means that all the required quantities of all the pattern pieces required to stitch p number of S-size garment of that style number must be included there in the marker. For example, to cut 5 pieces of S-size formal shirt from a marker means to cut 5 x 2 = 10 pieces of sleeve pattern, 5 x 1 = 5 pieces of back-pattern , 5 x 4 = 20 pieces of cuff pattern and so on.
4.0 Marker Efficiency %:
Marker-Efficiency percentage is defined as the total area of the marker utilized for placement of pattern pieces expressed as a percentage with respect to the total area of that marker.
Therefore, The Marker Efficiency % = EM = (Total Area of the marker utilized for pattern pieces x 100) / Total Area of the Marker
Or,
EM = (Total area of all the pattern pieces included in the marker X 100) / Total Area of the Marker ------------------------------------- (2)
It is obvious that the marker efficiency% is the key parameter for the reduction of fabric wastage and reduction of the manufacturing cost of a garment in turn. As it is known that around 60 to 70 percent of the manufacturing cost of a garment consists of the fabric cost.
4.1: Mathematical Interpretation of marker efficiency % :
For the mathematical interpretation of the marker efficiency %, let us consider the geometry of marker as represented by the Fig.1.
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| Fig.1: The Geometry of Marker |
As represented by the Fig.1, the Outer rectangle ABCD represents the fabric layer i.e. one single ply of fabric. The Inner rectangle EFGH represents the marker.
Ply length = AB = DC = LP
Marker width = EH = FG = WM
Marker length = EF = HG = LM
Total Area of marker = AM = LM .WM ---------------- (3) (ref. Fig. 1)
Area of the fabric utilized in that marker = Total area of all the patterns pieces in that Market = AP (Let) ------ (4)
So, From equation 2, 3 and 4
The Marker Efficiency% = EM = AP . 100 / AM -------------- (5)
Or, EM = AP . 100 / LM .WM ----------------------------- (6) (By eq.3).
4.2: Calculation of the total area of the pattern pieces:
Now, the most fascinating question arises, how the total area of all the pattern pieces in a marker can be calculated? As it is understood that the patterns are of non-geometrical shape and of course not feasible to calculate area of all the patterns by graphical method.
Well, in case of computerized marker-planning it is easily and automatically done by the marker planning software, by pixel calculation of the digital matrix. But what about in case of manual marker planning ? The following possible options are discussed here.
4.2.1: Option-A:
The instrument called ‘Planimeter’ can be used to calculate the area of the non-geometrical shapes like pattern pieces. This way, the total area of all the pattern pieces can be determined.
4.2.2: Option-B:
Step-1: To weigh all the pattern-pieces (Paper patterns) placed on the marker = w gram (say).
Step -2: Let the GSM of that paper = g
Step-3: Total Area of the pattern pieces = w/g = AP (in Square meter)
5.0: Ply-Efficiency %:
It is clearly understood by the Fig.1 that just the Marker efficiency can not describe the fabric utilization exclusively. Marker efficiency just talks about the fabric utilization in the marker, i.e. in the inner rectangle (EFGH) only. But what about the fabric left between inner and outer rectangles? Those width and length allowances kept are also wasted.
Hence the Ply efficiency % which represents the fabric utilization percentage of a single ply (i.e. in the outer rectangle ABCD) is also required to be calculated.
Similar to the Marker Efficiency % , the Ply Efficiency % = EP can be formulated as :
EP = (Total Area of all the pattern pieces in the ply) x 100 / Total area of that single Fabric Layer (ply)
(AP = Total Area of all the pattern pieces in the marker)
AF = Total area of that single Fabric Layer (ply) used for spreading)
= (AP . 100) / LP .WF (LP = Ply length, WF Fabric Width)
= (Ap . 100) / [LP . {(WM + 2. (a + t)}] ------------ (7) (By eq. 1)
6.0: Calculation of Fabric Consumption From marker
As it is explained in the section 3.3, if the size ratio or marker ratio is S : M: XL = p : q : r , then it is planned that total number of pieces to be cut form that marker = p + q + r.
Now, to generalize it , let , the total number of sizes included in the marker = n
And the Size ratio = s1 : s2 : s3 : ---------: sn
Then , the total number of garment pieces to be obtained from that marker = N
N = s1 + s2 + s3+ ---------+ sn
If the Marker length = LM
Average fabric consumption in that marker = LM /N
And more accurately, considering the ply length = LP , the fabric consumption based upon the marker and ply = LP /N
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