Tuesday, May 24, 2011

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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Wish you good luck......................................................

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