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Plant Streamlining Series
Functions and utilization of the sewing machine with an automatic thread trimmer
DLN9010
DLN9010
Labor costs are showing an upward tendency in many countries due to the rapid increase in crude oil prices. Sewing plants have to achieve an increase in productivity with greater urgency.
JUKI launched its lockstitch machines with a thread trimmer in 1969. In the 70's, lockstitch machines with a thread trimmer spread rapidly among sewing plants in Japan. As a result, "lockstitch machine = lockstitch machine with an automatic thread trimmer" became the standard. The basic performance of the sewing machine with a thread trimmer is that it is capable of automatically trimming the thread. Now, let's check the advantages of the lockstitch machine with a thread trimmer for sewing plants.
Sewing Research Institute
Hiroyasu Asai

1. Evolution of the sewing machine with an automatic thread trimmer
<Basic functions of the lockstitch machine with a thread trimmer>
During the corner stitching process in sewing work, the operator needs to stop the machine with its needle down (with the needle penetrating the material) to change the direction of stitching. At the end of sewing, the operator needs to raise the needle and pull out the thread to trim it. Normally, therefore, when sewing with a lockstitch machine, the operator has to operate the pulley and/or to trim the thread with a pair of scissors when sewing a corner part of the material and at the end of sewing. When sewing with a lockstitch machine with a thread trimmer, the operator is not required to carry out the aforementioned actions since the machine automatically performs them.
While the lockstitch machine with a thread trimmer makes a half revolution from the "needle-down stop position" to the "needle-up stop position," the thread trimmer works to activate the trimming knife. The lockstitch machine with a thread trimmer, therefore, has (1) a thread trimming knife function for trimming the thread, (2) a needle position control function (stop with the needle up/down, etc.) and (3) a function for controlling the machine's number of revolutions.

<The lockstitch machine with a thread trimmer is evolving>
The lockstitch machine with a thread trimmer these days is provided not only with the previously mentioned basic functions, but also with lots of additional functions, including those described below, to evolve into a substantially easier-to-use machine in comparison to the regular lockstitch machine.
  • Touch-back switch is installed near the needle entry zone
  • The machine automatically performs reverse stitching by the specified number of stitches
  • The machine automatically stops when it finishes sewing of the specified number of stitches
  • Maximum speed restriction, which enables the easy setting of a speed suitable for the material
  • The pedal which drives the machine can be operated with a lighter pressure and is able to change the startup speed of the machine
  • Easy-to-use machine allows inexperienced operators to fully utilize its capabilities in a short period of time
  • The machine is provided with an automatic presser lifting feature which lifts the presser foot using a light-to-operate knee switch
  • A subclass model which employs a non-lubricating mechanism for totally preventing oil stains on sewing products
  • The latest 9000 Series has a bobbin winder which is located near the operator (the bobbin winder is mounted on the machine head)
  • The dial for adjusting stitches is ergonomically designed for achieving ease of operation
  • The distance from machine arm to needle is increased for easier handing of the material being sewn
  • Air is blown from the clearance between the pulley and the main body in order to prevent thread from tangling
The new needle-feed machine (DLN9010) has been designed to be adaptable for use as a lockstitch machine by exchanging the gauges. Lots of improvements have been employed to achieve ease of operation for users and to improve the effectiveness of the machine.


2. Effects of the introduction of the lockstitch machine with a thread trimmer for sewing plants

Let's see the lockstitch machine with a thread trimmer in terms of the benefits (effects) of its use in sewing plants.

(1) Increase in productivity (reduction in processing time)
Operations become easier by introducing lockstitch machines with a thread trimmer, thereby reducing the working hours. The effect greatly varies depending on the operator, process in which the machine is used and material to be sewn. In some cases, the increase in productivity in the entire production line exceeds 20 %. By comparing and analyzing the operating activities between the regular lockstitch machine and the one with a thread trimmer, a difference in the processing time can be grasped. The effect of using the lockstitch machine with a thread trimmer is obtained based on the activity in different processes and the resulting productivity calculations. The results are summarized in Table 1.

(2) The machine is free from operator habits
For machines which employ a clutch motor, the operator controls the number of revolutions by operating the foot pedal. As a result, the machine is likely to adapt to the operating habits of the operator. When an operator has to use a machine which has been used by another operator, it takes him/her time to become familiar with the machine and operate it as usual. In addition, in this case, the operator is likely to make mistakes during work until he/she gets used to the machine.
For the lockstitch machine with a thread trimmer, the number of revolutions is electronically controlled. This means that the machine does not adapt to the operator's habits. This is advantageous to any operator since he/she is able to immediately operate the machine with a thread trimmer at his/her own pace. In addition, the supervisor may be free to change jobs assigned to operators, thereby facilitating production line management. This is a great benefit to a sewing plant which employs a various-kind small-lot production system.

(3) Easy setting of the sewing speed
A buyer's first concerns are the purchase price and quality. For the buyer, an important theme is that the plant "is really capable of producing products of a consistent quality." In recent years, materials have become more and more diversified, including soft or light-weight types which need to be sewn at a lower speed. The lockstitch machine with a thread trimmer is provided with a maximum sewing speed limiting function. This function also works to prevent defective products. The sewing machine with an automatic thread trimmer is a piece of equipment with an enourmous appeal to buyers.
The machine's speed limiting function is also advantageous to sewing plants as they can smoothly proceed with the training of new recruits by using the function.

(4) Reduced frequency of troubles in sewing
Sewing machine failures or troubles directly contribute to reduced productivity. Important points of a sewing machine are ease of maintenance, minimal failures and consistent operation. JUKI's thread trimming mechanism is of the horizontal type for cutting the thread by nipping. This mechanism demonstrates consistent performance since it is rarely affected by the thread count or thread tension.
The machine is also provided with a presser-foot micro-lifting mechanism for improving the consistency in seam quality. his mechanism is another advantageous point to sewing plants which use light-weight materials with respect to the prevention of troubles in sewing.

<Summary>
A factor responsible for the popularization of the lockstitch machines with a thread trimmer is the effect of increasing productivity. At the same time, the machine is also evaluated as being easy to operate and use. In Japan, the lockstitch machines with a thread trimmer had been introduced in a period when the labor shortage and increased wages were becoming serious. Sewing plants in Japan competed with each other in introducing the lockstitch machines with a thread trimmer as a strong weapon which helped secure a work force and ensure its stability.
Thereafter, the Japanese apparel industry has undergone further improvements in quality and diversification of materials. Each sewing plant has been aiming at the manufacturing of products making the best out of its features. To support the achievement of this aim, subclass models for the lockstitch machine with a thread trimmer, such as a bottom & variable top-feed machine and needle-feed machine have become popular. For the bottom and variable top-feed machine, not only its capabilities of sewing beautiful gatherings or of handling slippery materials for increasing productivity and ensuring consistent quality, but also its strategic benefits such as differentiation from competitors and substitution of skilled techniques have received attention.
The effect of any piece of equipment varies depending on how it is used. It is important for sewing plants to continue to investigate how to make the most out of the equipment for ensuring its superiority in terms of the increase in productivity, consistency in quality and securing of manpower.

Table 1 Example of a reduction in working hours (Actual value)
Type of product Process name Skill level Net working time (in sec) Reduction in time (in sec) Reduction ratio
Regular lockstitch machine Machine with a thread trimmer
Men's shirts Pocket setting A 27.5 25.8 1.7 6.1%
Pocket setting B 32.6 28.5 4.1 12.5%
Pocket setting (vtr) A 46.0 38.0 8.0 17.4%
Counter stitch collar bottoms A 33.3 31.4 1.9 5.7%
Counter stitch collar bottoms A 34.0 32.3 1.7 5.0%
Counter stitch collar bottoms A 36.4 32.4 4.0 10.9%
Tacking sleeve plackets A 18.1 14.2 3.9 21.5%
Tacking sleeve plackets A 23.4 15.7 7.7 32.9%
Double stitch collars B 10.6 6.0 4.6 43.3%
Slacks Runstitch welt of hip pockets C 36.4 33.7 2.7 7.4%
Topstitch lower welt of hip pockets B 11.3 9.5 1.8 15.9%
Counterstitch edge of hip pockets B 7.4 6.5 0.9 12.1%
Topstitch upper welt of hip pockets B 21.1 17.5 3.6 17.0%
Topstitch edge of side pockets A 16.5 16.0 0.5 3.0%
Counterstitch edge of side pockets A 6.5 5.2 1.3 20.0%
Reinforcing stitch top and bottom of side pockets A 18.2 13.0 5.2 28.5%
Sew stay to side pockets B 14.7 10.5 4.2 28.5%
Sew ticket pocket to side pockets B 13.5 11.0 2.5 18.5%
Sew bottom of side pocket bags B 12.3 8.0 4.3 34.9%
Topstitch side pocket bags A 14.1 12.5 1.6 11.3%

Table 1 Supplementary explanation 1
The operation analysis results are gathered based on the following data:
(1) For each product item, the operation by means of a lockstitch machine and that by means of a machine with a thread trimmer are compared. Time required for thread trimming (effect of the use of the machine with a thread trimmer: 2.6 sec per thread trimming)

* Operating time using a regular lockstitch machine
(1) Turn the pulley of the sewing machine at the end of sewing
(2) Stop the machine with its needle up
(3) Draw out the material and trim the thread with a pair of scissors In total, 3.1 sec is required for carrying out the aforementioned steps (1) to (3) in sequence.
* Operating time using the lockstitch machine with a thread trimmer
(1) Depress the pedal using the heel. The machine trims the thread.
The machine time is 0.5 sec.

Difference in time between the two models:
3.1 sec - 0.5 sec = 2.6 sec
Time saving effect of the use of the machine with a thread trimmer: 2.6 sec

Similarly;
Corner stitching (effect of the use of the machine with a thread trimmer is 1.6 sec per location of a corner part).
Reverse stitching (effect of the use of the machine with a thread trimmer is 1.2 sec per reverse stitching operation).

For Table 1, the aforementioned three points regarding the effects are subject to operation analysis and comparison on a process-by-process basis to calculate the reduction in time required for each process. In this case, the operator is assumed to have an average level of skill.

Supplementary explanation 2
The effect of an increase in revenue is calculated by multiplying the increase in the number of products produced along with the increase in productivity by processing fees (provisional values are entered in the CMT table). This represents the direct effect of the use of the lockstitch machine with a thread trimmer for a sewing plant.

Table 2 Provisional calculations of the increase in productivity organized by type of clothing (Provisional calculations by comparison of operation)
Men's jackets Men's jackets Ladies' formal wear, lower garments Men's shirts Slacks Cotton pants Jeans
Comparison of processing time            
Using a regular lockstitch machine 4971 1995 1004 1904 1563 883
Using the machine with a thread trimmer 4568 1778 847 1573 1333 778
Reduction in time 403 217 157 331 230 105
Reduction rate 8.1% 10.9% 15.6% 17.4% 14.7% 11.9%
Comparison in terms of line organization          
Number of sewing machine operators 70 20 50 55 40 30
Quantity of output (daily output/number of pieces)            
Using a regular lockstitch machine 312 222 1103 640 565 872
Using the machine with a thread trimmer 340 249 1308 775 665 1011
Increase in the number of products (daily output) 28 27 205 135 100 139
Increase ratio 9.0% 12.2% 18.6% 21.1% 17.7% 15.9%
Comparison of the number of facilities in use            
Number of regular lockstitch machines in use 33 16 37 34 28 15
Number of machines with a thread trimmer in use 31 14 34 29 26 13
Effect of the increase in revenue and facility investment            
Condition setting            
Price of the machine with a thread trimmer ($) 1400 1400 1400 1400 1400 1400
Processing fee (CMT, $) 5 3 1 2 1.5 1
Provisional calculations            
Investment amount ($) 43400 19600 47600 40600 36400 18200
Increase in revenue (per day, $) 140 81 205 270 150 139
Increase in revenue (25 days, $) 3500 2025 5125 6750 3750 3475
Increase in revenue (per year, $) 42000 24300 61500 81000 45000 41700

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