CUTTING SYSTEMS IN GARMENTS FACTORY; AUTOMATED, NUMERICALLY CONTROLLED

Automated cutting is the best system for fabric lay cutting in garments. Automated cutting more faster than manual cutting system. Automated cutting system is operated by computerized numerically controlled cutting system. Required low labor cost and the lowest man power for automated cutting system.

Objectives of Automated cutting system:
 -Equipments and their operations
 -Recent development in equipments and techniques

 The four types of automated cutting systems are:
(I) blade cutting,
(II) Laser cutting,
(III) Water jet cutting, and
(IV) Plasma jet cutting.

Electronic microchips control the cutting device, travel pattern, and speed. Computer-generated markers are stored and used to guide the operation of the cutting head. Printed markers are not required for cutting but may be used to assist with bundling. The primary advantage of computerized cutting systems is the accuracy of the process.

Automatic Blade Cutting is the most highly developed and widely used computerized cutting system. Systems are specific to the standard volume to be cut. Numerically controlled knives cut multiple plies with great accuracy and speed. Information can be downloaded directly to the cutting system when needed. Easy data entry and instant communication with the main control unit allow technicians to preprogram multi-step commands, set parameters, and start the process with a single keystroke.

The central control unit operates the components of the system such as the cutting head, cutter carriage, knife sharpening, and conveyorized cutting table. A cutting head is a sophisticated mechanical component with the capacity to cut, mark, and drill as dictated by the computer. Automatic knife sharpening is done at preset intervals during the cutting operation. The cutter carriage moves the cutting head and provides lengthwise and crosswise motion during the cutting operation. The reciprocating blade can be adjusted to the height of the spread and density of the fabric. Knife speed automatically adjusts to the forward speed of the cutting head. As the cutting head slows for corners, curves, or notches, the reciprocating blade also slows to reduce heat and possible fusing. Most reciprocating knife systems use a vacuum to hold down the fabric. Placement of plastic film over a spread helps compress the fabric into a firm stationary lay-up when the vacuum is applies. The effect of the vacuum is to reduce the height of the spread and eliminate fabric movement during cutting. An intensified vacuum force is automatically applied to the area directly under the knife to further restrict material shifting

Laser Cutting focuses a powerful beam of light projected onto a minute area to cut fabric by vaporization. The fine, V-shaped beam is only 0.004 of an inch. The beam cuts without pressure on the fabric, which is a major advantage for some types of fabric. The fabric remains immobile during the cutting operation.

Lasers cut with incredible speed (twice that of automatic knife cutting), accuracy, and multidirectional ability, but with some heat emission. Laser-cut edges are sharp and clean. The heat produced tends to seal fabric edges, which can be an advantage for fabric that ravels and a disadvantage for cutting multiple plies as edges may fuse together. Laser-cut garment parts are easier to assemble, as they are consistent in size with smooth sharp edges to align.

Water Jet Cutting is another computer-operated, multidirectional method that has limited usage at this time. Water jet cutting is performed by propelling a tiny jet of water (0.0010-0.0015 inch) through fabric at very high pressure (70,000 pounds per square inch). The forward edge of the jet stream shears the fabric as it moves along the cutting line but does not wet the fabric, generate airborne contaminant, or exert an appreciable force on the ma-terial. The water jet will cut multiple plies without fusing, but it may fray and tangle the yarns of some fabrics, which makes it difficult to separate the plies. It is used when heat build up must be avoided and water absorption is not important. At the present time its use is limited to cutting leather and vinyl fabrics.

Plasma Jet Cutting is a computer-operated, high-speed, single-ply cutting device that offers many of the same features of a laser cutter but at a lower price. Along with the plasma jet cutting system, Investronica has developed a Matching System for automatic matching and cutting of striped, checked, or printed fabric. A TV camera reads the fabric on the conveyor, and a digital image processor decides the best way to match and layout the pattern pieces based on determined matching rules. Matches can be made among different prints, selvages, and fabric characteristics. This system eliminates recutting parts for more precise matching.

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GARMENTS SEWING MACHINE FUNDAMENTALS- PRINCIPLES OF STITCHING (MECHANIZATION PROCSS)

Sewing machine is an important part of apparel and garments manufacturing technology. Production of garments factory depends on the performance of sewing machine and principles of stitching. Principles of stitching and perfection of stitching depends on the quality of sewing machine.

Mechanization is the process of replacing human labor with machines. Mechanization of the garments sewing process encouraged mass production of apparel garments product. Garments sewing that had long been performed by hand sewing machine could be done more rapidly by garments sewing machine. By about 1900, most garments sewing processes could be performed by machine

Automation is a state of operating without external influence or control. In manufacturing of garments and apparels it is often viewed as highly desirable because it eliminates the potential for garments workers error. Automated garments sewing systems are capable of feeding themselves cut garments parts from a stack, completing multiple sewing tasks, and delivering finished parts of garments. Automated equipment for garments sewing may be cost effective for some apparel manufacturers, while the high costs of acquisition, installation, and maintenance are prohibitive to others.

Robotics is the most advanced form of automation in garments sewing operation. Robots are computerized, reprogrammable, multifunctional manipulators designed to move materials, parts, tools, or specialized devices through variable programmed motions for the performance of a variety of tasks. Flexible reprogrammability is one of the hallmarks of robotic automation. This manufacturing flexibility differentiates robotics from fixed-purpose, hard-wired automation, which has to be torn apart and reconfigured for every new application.

Garments sewing and Apparel pressing equipment may be either general or special-purpose. General-purpose garments sewing machines are manually operated by garments worker and can perform a variety of sewing operations. Special-purpose garments sewing machines are designed to perform a specific garments related or sewing related operation and more likely to be semiautomatic or automatic machine.













 





Objectives of garments sewing machine:
 -Discuss issues related to equipment selection
 -Explain mechanization and automation relative to special- and general-purpose garments sewing machines
 -Examine the basic components of garments sewing machines and work aids

GARMENTS SEWING MACHINE FUNDAMENTALS:
A basic garments sewing machine or apparel sewing head, as it is sometimes called, consists of the fundamental parts required to form a stitch, sew a seam, or perform a specific garments sewing operation. The major components of a basic garments sewing machine include a sewing casting, a machine lubrication system, a stitch-forming system, and a garments feed system. The speed at which a sewing machine can operate depends on the engineering of the garments machine’s components.

The Sewing Casting:
The sewing machine casting is the metal form that provides the exterior shape of the garments machine. Shapes vary with the bed type, the garments sewing function that is to be performed, and how piece goods are to be presented to the needle. The casting houses the internal workings, such as the gears, cams and shafts, that operate the stitching and feeding mechanisms of the sewing machine.

Bed Type:
The bed is the lower portion of the sewing machine under which the feed mechanisms and loopers are located. Sewing machines are frequently described by bed types.

Different Types of Machine Beds:

Types of Garments Sewing Machine	Sewing Stitch Type	Features and Uses
Flat bed sewing machine (basis type)	Lockstitch sewing, Chain stitch sewing	The large working area allows a wide range of sewing application; the material can easily be guided around the needle and the presser foot. This basic type garments sewing machine used for all kinds of flat sewing operation.
Raised bed sewing machine	Lockstitch sewing, Chain stitch sewing	The bedplate is in the form of a plinth. It facilitates the assembly of pre-sewn parts and is especially suitable for the fitting of accessories and special attachments. This is the basic form for various specialized garments sewing machines such as buttonholers.
Post bed sewing machine	Lockstitch sewing, Chain stitch sewing	This type of sewing machine has an increased working height. Special sewing applications are found in the working of three-dimensional products. e.g. shoes and bags. The post makes it easier to work on tight curves and corners, to sew in sleeves and to complete large, half-assembled products.
Cylinder bed sewing machine	Lockstitch, Chain stitch	This type of garments sewing machine has an increased working height and a bed in the shape of a horizontal arm. It is especially suitable for sewing on tubular parts, such as cuffs, sleeves, and trouser legs, and also for button sewing and bar tacking. This sewing machine is used extensively in the making of clothing from knitted fabrics.
Side bed machine	Chain stitch, Over-edge	Machines which are specialized for sewing at edges need only a small working area

CUTTING AND CUTTING ELEMENT OF GARMENTS IN APPAREL FACTORY

Cutting is the production process of separating (sectioning, carving, severing) a spread into garment parts that are the precise size and shape of the pattern pieces on a marker. The cutting process may also involve transferring marks and notches from the marker to garment parts to assist operators in sewing. Chopping or sectioning a spread into blocks of piece goods may precede precision cutting of individual pattern shapes. This is often done to allow for accurate matching of fabric design or easier manipulation of a cutting knife.

CUTTING AND CUTTING ELEMENT OF GARMENTS IN APPAREL FACTORY

Fabric pieces may be cut to predetermined lengths for matching patterns or for additional processing such as screen printing. Spreads of plaid fabrics may be presectioned into blocks so the design of the fabric can be perfectly matched before cutting to the shape of the pattern piece. Presectioned pieces may also be garment parts knitted to specific finished lengths such as sweater bodies. Presectioned pieces such as leather or other specialty fabrics may be and cut as a single ply or laid up and cut as a multiple-ply spread. 


Objectives of cutting:
 -Understanding of the cutting process
 -Cutting equipments and their operations

Cutting often is carried out in two stages: rough cutting (separating the individual pieces) and the final cutting (accurate cutting of the individual shapes). Different types of cutting tools have different degrees of precision.

PORTABLE CUTTING KNIVES:
Portable knives can be moved to and through a spread by an operator. There are two main types of portable knives:
(i) vertical reciprocating straight knives and (ii) round knives. Structurally and mechanically the two types of machines share many similarities. Structurally, both types of knives have a base plate, power system, handle, cutting blade, sharpening device, and blade guard. Round knives operate with a one-way thrust as the circular blade makes contact with the fabric, and vertical knives cut with an up-and-down action. Circular cutters and straight knives are pushed by hand through the stationary material.

CIRCULAR CUTTERS:
Circular cutting tools use a rotating circular blade. The smallest devices (power shears) is used for cutting single ply lays and for cutting fabric plies to length during manual spreading. Depending on the size of the device it is possible to cut to a depth of about 10mm. The larger circular cutter is used mainly for dividing a lay into sections. It is suitable only for cutting in straight lines or very gradual curves, in depths of about 150mm.

STRAIGHT KNIVES:
A straight knife cutter has a vertical blade, which reciprocates up and down. It is capable of both coarse and precise cutting to a depth of about 300mm. Corners and curves can be cut accurately. Since all of the layers are cut at the same place (unlike a circular cutter), and provided that the knife is held vertical, then all of the pieces cut from a lay are identical.
Vertical straight knives with reciprocating blades are the most versatile and commonly used cutting devices. Reciprocating blades have a vertical cutting action. Blades vary in length from 6 to 14 inches. Blade length and the adjustable height of the blade guard are factors in determining the spread depth that can be cut. The 90-degree angle of the narrow, thin blade to the cutting surface makes this knife a good choice for accurately cutting sharp corners, angles, and curves.
Vertical straight knife machines make only lateral cuts into a spread therefore cannot be used to cut out areas from the center of garment parts.

Basic Components of Portable Knives:
Blades are mounted in a vertical position at a 90-degree angle to the cutting surface. Blades vary in shape, size, cutting action, and fineness of the cutting edge. A straight blade contacts the spread at a 90-degree angle; assuming the blade and spread are kept vertical, all plies are cut at the same time. A rotary blade does not cut all plies evenly at the same time. A round blade contacts the spread at an angle; thus, the top ply is cut before the bottom ply.

(i) Knife blades can have a major affect on the quality of the cut. Factors that affect the performance of a blade are the blade edge, surface texture of the blade, coarseness or fineness of the blade edge, and blade composition. Blade edges may be straight with a flat surface, saw-toothed, serrated, or wavy with a striated surface. Straightedge blades with a flat surface are general-purpose and the most widely used, while the other types are more specific to certain types of fabrics. Striated blades are used to reduce heat buildup during cutting, wavy edges are used for plastics and vinyls, and saw-type blades are use for cutting canvas.

(ii) The base plate is the foundation that supports and helps balance the cutting mechanism. Bases vary in shape and size, depending on the size and weight of the knife it supports and the maneuverability needed. The base plate guides the knife in relation to the table surface and elevates the spread off the cutting table for contact with the blade. Base plates are supported by bearing rollers to facilitate maneuverability and ease of movement. Edges of the plate are sloped and the front curved to easily slide under the bottom ply and provide less fabric distortion and drag as it is maneuvered during cutting. The base plate helps maintain the position of the blade at a 90-degree pitch.

(iii) The power system controls the motor and the potential cutting speed. The amount of power needed to cut a spread depends on the height of the spread and the density of the fabric to be cut. The horsepower of the motor determines the amount of thrust or cutting power of the blade. Higher speeds allow operators to move knives faster. Greater horsepower increases machine power but it also may increase weight of the motor, which must be balanced by the blade housing and base plate. Larger, more powerful knives, which may weigh approximately 35 pounds, are often more cumbersome, heavier, and harder to manipulate and maneuver. Motors with variable speeds provide more versatility.

(iv) Sharpening devices appropriate for the specific blade type are found on almost all mechanized cutting equipment. Blades dull quickly when cutting deep spread or dense fabric. As a blade becomes dull, it creates friction and may cause rough, frayed, or fused edges. Sharpening devices may be stone or emery wheels or abrasive belt sharpeners. Cutting blades are sharpened frequently during the cutting operation simply by touching the control.

(v) All manually operated cutting devices have a handle for the operator to grip, guide, and propel the knife through the spread. The operator's other hand is used to stabilize the plies ahead of the knife to prevent bunching of fabric.

(vi) A blade guard, when positioned at spread height, rests on the top ply to help stabilize the spread and to protect the operator's hand. Metal mesh gloves are available as a safety device for cutters using vertical knives.

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