Technology for Back Pocket Attachment on Jeans

To set better benchmarks in terms of productivity and quality in the apparel industry, automatic machines, robots, and AI are edging their way in. As order quantities keep getting smaller and lead time shorter, the leaders in the space invest in new technologies that boost efficiency and help keep consumer prices for jeans and other “fast fashion” products low. As per Zion Market Research, the global denim jeans market is expected to reach approximately USD 85.4 billion by 2025, at a CAGR of around 3.7% between 2019 and 2025.[1] The process of sewing accounts for more than half of the labour time in the standard production process of denim trousers, sewing automation will be the biggest driver for reducing labour, accounting for about 21 to 46 percent [2]. This article elaborates on the use of sewing automats for attaching back pockets in denim, and the advantages (technical & financial) it can offer.

jeans back pocket
Figure -1: Jeans back pocket

Performing critical operations in garments require a high skill set. They are more prone to defects and rework when manually operated, ruining the aesthetics of the garment. Attaching back pockets on denim is one of the crucial operations. Pockets are not only functional but also contribute to the aesthetics of the garment, forming an important part of fashion. Since they are very prominent in garments, perfect workmanship is imperative, especially when functionality is combined with decoration. 

Back pocket attachment is a two-step process- firstly creasing and pressing the edges, followed by attaching the patch pocket at the correct position. The use of specialized sewing automats to perform this operation can help achieve superior quality along with high productivity. Owing to the levels of automation, the operation of back pocket attaching has been discussed under three levels of technology- basic, intermediate, and advanced.

Back Pocket Attaching Machine - Basic Level

The basic level of technology involves creasing and sewing operations being performed manually and is controlled by the skill of the operator. The equipment used in this level of technology includes iron for pressing and lock stitch machines. The operator first places the pre-hemmed patch pocket on a template and folds the three edges. To mark the creases, it is ironed. Then, the pocket is placed correctly on the back panel as per the marking and attached using a single needle lock stitch machine, followed by the second stitch (Figure 2). The total SAM of these operations is 1.95. Sewing line manufacturing denim using the basic level of technology produces approximately 1600 pairs of jeans in a day (8 hr shift). 

Manual Operation to Fold and Attach Back Pocket
Figure 2: Manual Operation to Fold and Attach Back Pocket[3]

The number of operators required to carry out these operations -
  • A helper to perform the creasing using iron
  • Operator 1 to attach the back pocket using lockstitch machine
  • Operator 2 to perform the 2nd stitch using lockstitch machine
Back pocket attaching in jeans is done generally by double line of stitching, but not parallel stitching lines. Therefore even though pocket attaching and topstitch operations could be done in combination by a double-needle lock stitch machine, it cannot be used to get a similar look. When stitched using single needle sewing machine, the quality depends on operator skill and any inconsistency in spacing between sewing lines will be visually unappealing. Secondly to achieve perfection operator will be slower at the basic level. The efficiency of the operator is around 65-70%. Thus, to combat the issues of quality and productivity, jeans manufacturers are opting for higher levels of technology as discussed further. Table 1 shows specifications of two models of SNLS machines that can be used for sewing denim jeans, and specifications of a typical ironing unit is mentioned in Table 2.

Table 1: SNLS Machines in Basic Level of Technology
Basic Level of Technology- SNLS Machine
Parameter
Units
JUKI
Brother
Model No.

DDL-9000C
S-7300A-305P
Max. sewing speed
SPM
5000
4500
Max. stitch length
mm
5
7
Needle Bar Stroke
mm
30.7
35
Feed Dog Height
mm
0.8

Lift of the Pressure Foot
mm
1st step: max.8.5
2nd step: max.13.5
Presser bar lifter: 6
Knee lifter: 16
Size of Bed
mm
517 X 178

Machine head drive

Compact AC Servo motor
AC servo motor
Power Consumption
VA
520
450
Power Consumption
kW
0.442
0.3825
Cost
INR
92,000

Table 2: Specifications of a Vacuum Ironing Unit
Basic Level of Technology- Vacuum Ironing
Dimensions
inches
30 x 48 x 36
Weight
kg
60
Voltage
V
230
Power
kW
0.37
Cost
Rs
20600

Jeans Back Pocket Attaching Machine - Intermediate Level

With the up-gradation in technology, semi-automatic machines ease the work of the operator; ensure more accurate work, as well as speed-up the process. Automatic pocket creasing machines and semi-automatic pocket attaching machines have been considered as the intermediate level of technology. An operator creases the back pocket using the pocket creasing machine; the creased pocket is then taken to the pocket attaching machine, which is handled by another operator.

The specifications of pocket creasing machine and pocket attaching machines (for pre-creased pockets) are shown in Table 3 and Table 4 respectively.

Table 3: Automatic Pressing-Creasing Unit Specifications
Intermediate Level of Technology- Automatic Creasing Machine
Parameters
Units
NGAI SHING
SOKIEI
SIP Italy
Model No.
NS-9085-D-L
BY-P102
001-SIP
Dimensions
mm
840x970x1470
1000x725x1260
2050x1650x1400
Gross Weight
kg
350
272
450
Pressing- Iron 
Width 
and Length
mm
250 x 250
250 x 250

Average Production
Capacity
pockets/ hour
250-300
300-450
400
Die Change Time


3 minutes

Power

AC 220V, 50HZ, 
Single Phase
AC 220V, 50HZ, Single Phase
AC 220V, 50HZ, Single Phase
Power Consumption
kW
4.2
3.4
10
Price


3,50,000


Automatic pocket creasing machines mechanize the process of folding the edges and ironing the pocket. The pocket cloths are folded with fine, sharp creases, without any material slippage or bulging. These machines offer high productivity as the workstations have twin independent creasing-pressing stations for double production (Figure 3). Each station can be adjusted with different temperature and cycle time. Thus, these automatic pressing units are highly efficient products, reliable, provide easy handling and use by unskilled workers, and have a low running cost. However, these machines are not suitable for stretch denim fabrics.

Automatic Pressing-Creasing Unit for Patch Pockets
Figure 3: Automatic Pressing-Creasing Unit for Patch Pockets

Table 4: Semi-Automatic Pocket Attaching Machine Specifications
Intermediate Level of Technology- Pocket Attachment Machine
Parameters
Units
JUKI
Vi.Be.Mac
Model No.

AP-874S
VBM 2516V4 DCT
Sewing Head

single
double
Stitch Type

301
301
Max Sewing Area
mm X mm
250 X 250
305 X 250
Clamp Sewing Area
mm X mm

250 X 247
Stitching Length
mm
0.16
from 0,1 to 20
Max Sewing Speed
SPM
4000
2500
Process time
seconds/ pocket
9.9

Daily Production
no. of pockets/ operator
2237

Time Required To Change Clamps

5 minutes
5 minutes
Storage Of Pattern Data In The Memory

Max. 999 pattern
512 patterns internal memory + USB
Power Consumption
VA
820

Power Consumption
kW
0.697



Semi-Automatic pocket setters have been specifically designed for being capable of placing the next sewing pocket while engaging in placing the current pocket (preliminary folded) on the garment body and sewing it. They are available in single sewing head as well as double sewing head (for multi-colour thread). The machine is equipped with direct-drive lockstitch programmable electronic pattern sewing head, by adopting a simple template clamp which is easily exchangeable. These pocket setters ensure high quality and high production efficiency can be reached without the need of any skilled operator. The productivity the machine offers is 1200 pairs/8-hour shift, which is nearly five times the number produced in basic level by the same number of operators manually. Semi-Automatic pocket setter units are shown in Figure 3.
Semi-Automatic Pocket Setter Unit
Figure 4: Semi-Automatic Pocket Setter Unit (for Pre-Creased Pockets)
Related article: Jeans waistband attaching machine

Jeans Back Pocket Attaching Machine - Advanced Level

Automated solutions ensure good and consistent quality with high output performance. Although the first thought of an automat seems to be a matter of investment and concern, manufacturers need to focus on an enlarged analysis, understanding the technicalities in detail and thinking of medium and long term goals. The fully-automatic workstation that makes all the pocket setting processes such as creasing of a pocket, placement of the pocket on the panel, sewing, bar-tack, and stacking automatic come under the advanced level of technology. 

A single operator can perform all these operations consecutively in a single workstation. For operating this machine, minimum operator training is required. The operator first loads the pocket in a creasing clamp and then loads the trouser leg component in the loading area. Then the operator presses the actuator, the creasing clamp first creases the pocket then comes down and positions the creased pocket onto the trouser leg. 

A separate jig then grasps the pocket plus the leg assembly, carries to the sewing head and the attaching is accomplished by the stationery sewing head in two nonparallel sewing bursts and bar-tacking at both ends. (Jana, 2018) The machine is equipped with an integrated folding station and stacker to collect the stitched pieces. 

Maximum efficiency can be achieved due to automatic creasing, attaching and stacking. These machines are equipped with software having a large capacity memory capable of storing bulk data. The machine runs at a speed of 4000 stitches/min and has a cycle time of 9.2 seconds producing an output of 1300 pairs of medium-sized pockets in an 8-hour shift. The machine speed remains constant even when sewing through corners or bar-tack. Sewing parameters can be changed via the user-friendly touch control panel. The pocket style jig can be changed in less than five minutes without requiring a tool, thus supporting small-lot production flexibly.

In both the lower levels of technology, the folding devices were not suitable for stretch denim fabric, but fully automatic machines are equipped with a cold folding device which is the unique solution for such fabric. The versions of these machines have single and two sewing heads. Two sewing heads can produce extra 25% as compared to single head pocket setter unit. Also, two sewing heads give the opportunity to stitch a pocket with two different colour threads. Specifications of fully automatic pocket attaching machine (single and double head) are shown in Table 5.

Table 5: Specifications of Fully Automatic Pocket Attaching Machine

Advanced Level of Technology- Fully Automatic Pocket Attaching Machine
Parameters
Units
SIP Italy
JUKI
PFFAF
PFFAF
Model Number
PS342-FG2SIP
AP-876
3588
3589
Stitch Type
301
301
301
301
Complete cycle time
secs
6
10
9
12
Average production
pairs/ 8 working hours
1200
1100
1200
1300
Sewing head utilized
two heads
single head
single head
two heads
Max. Sewing Speed
SPM
3000
4000
4000
4000
Stitch Length
mm
3.5
0.05 - 12.7
Power Consumption
kW
1.4
1
Sewing Area
mm
250 X 250
250 X 250
250 X 250
Dimensions of the workstation
cm
290x170x140
192x120x 170
192x120x170
Price
INR
30,64,000
20,80,000
19,60,000
39,20,200

As discussed earlier, for operating this automat, the operator skill required is low. However, it is unethical to lower the salary of the already existing operator if a new machine is brought in the manufacturing unit. Thus, to have a better return on investment, instead of 1:1 man to machine ratio, 1:2 ratio can be configured. For 1:1 ratio (single head machine), the SAM value for a single operation is 0.430, and that for 1:2 ratio drops down to 0.248. (Mondal, 2019). A helper transports the completed pieces from the stacker to the next operation of jeans sewing. Models of fully automatic back pocket setters are shown in Figure 5.

Fully Automatic Back Pocket Setter
Figure 5: Fully Automatic Back Pocket Setter

ROI Calculation for different technology level

To evaluate the efficiency of investing in higher technology, Return on Investment (ROI) and Payback Period are suitable performance measures. However, these two factors are not solely responsible for decision making to make an investment. There could be several other reasons for technology up-gradation, one being their goal to be state-of-the-art manufacturers.

The formulas used for ROI and payback period calculation are:
  • Production per annum= (Shift hrs X 60 X Working Days X Months X Operator Efficiency) / SAM
  • CM Price per Pocket= (Sewing Cost/ Total SAM of Garment) X Pocket Setting SAM
  • Cost Output per annum= Production per annum X CM Price per Pocket
  • No. of Machines Required= Production Target/ Production per operator per day
  • CM Price per Machine= Cost Output per Annum X No. of Machines
  • Cash Inflow= CM Price from Machines – Total Machine Running Expense per Annum
  • ROI for 1st Year= Cash Inflow/ Depreciated Value of Machine after 1 Year
  • Payback Period= Total Machine Cost (Investment)/ Cash Inflow

Key Performance Indicators

Key Performance Indicators are crucial to direct the team in a project by creating an analytical basis for decision making. With a matrix depicting the KPIs that automation improves (Table 6), it can aid one in making correct decisions for the betterment of the organization.

Table 6: Key Performance Indicators

Parameter
General Purpose M/C
Semi-Automatic Pocket Setter
Fully-Automatic Pocket Setter
Comparison of 
Basic & Advanced
Daily Production
200
1500
1400
Increased 7 fold
Process Time
120 s
38 s
23 s
Process time reduced by more than a minute
Manpower
8 + 2
1 + 1
1 + 1
No. of Operators reduced by 7
No. of Machines
8
1
2
No. of machines significantly reduced
No. of Processes
3
2
1
No. of Processes reduced by 2
Power Consumption
Rs. 32428
Rs. 20452
Rs. 9984
Annual power consumption one-third
Suitability for diff. material (stretch fabric)
No
No
Yes
Stretchable denim fabric can be processed

Jeans back pockets being a very visible component in the garment, its finished quality carries much importance to add value to the product. As technology is being upgraded, it offers various advantages such as higher productivity, increased production, consistent quality, lower total power consumption, reduced manpower, and a title of having state of the art manufacturing technology. Owing to the requirements of buyers for consistent quality, quick style changes, shorter lead times, and improved manufacturing process, it is surely a wise decision to invest in a higher level of technology- sewing automats.

References
  • Jana, D. P., 2017. Automation has now become relevant and 'affordable'. Industry 4.0, December, pp. 17-19.
  • Jana, P., 2018. Automation in Sewing Technology. In: R. P. Rajkishore Nayak, ed. Automation in Garment Manufacturing. s.l.: Woodhead Publishing, pp. 199-236.
  • Mondal, P., 2019. Sewing Automat Solution for Jeans Manufacturing. Annual Journal of TANTU Textile Alumni Association, September, Volume 7, pp. 30-33.
[1] https://www.zionmarketresearch.com/report/denim-jeans-market
[2] https://sourcingjournal.com/denim/denim-innovations/levis-laser-automation-denim-124738/
[3] https://www.thelaststitch.com/how-to-sew-jeans-back-pockets/

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