Methods of Fabric Cutting:
During cutting, separate garment components are cut out from the fabric spreading in accordance with their shape and number determined by the marker. Fabric cutting is completed by different types of fabric cutting machines. In most of the cutting methods, a sharp blade is pressed against the fibers of the fabric to separate them. The cutting knife has to present a very thin edge to the fibers, to shear the fibers without exerting a force that will deform the fabric. The act of cutting dulls the blade, which should be sharpened frequently.
Fully Manual Methods:
1. Hand shears – Hand shears are commonly utilised for cutting single or double fabric plies. The lower blade passes under the plies; however, the consequent distortion of the fabric is temporary and accurate cutting to the line can be attained only with practice. The major drawback in this method is that it is a time intensive one and incurs a higher labour cost per garment.
2. Short knife – It pierces through the fabric; 10 to 12 fabric layers could be accurately cut. Heavy weight or denser fabrics have to be used for cutting using this short knife as it distorts several fabric layers while cutting through the fabric.
Manually Operated Power Knives:
Portable power knives are normally moved manually through a lay by means of an operator. Two main kinds of power knives are vertical straight knives and round knives. Construction-wise, both the knives have a base plate, power system, handle, cutting blade, sharpening device and blade guard. The round knives operate with a single force as the circular blade makes contact with the fabric, but the vertical knives cut with an up-and-down action. A straight blade will always maintain a perpendicular contact with the lay (90°) so that all the fabric plies in a spread could be cut at the same time. However, this will not be the case for a rotary knife blade as it contacts the spread at a certain angle. In both cases, the fabric that has to be cut is kept stationary and the knife blade fixed on the machine is moved by an operator to cut the fabric.
The basic elements of manually operated power knives are given below:
- Knife blades – Knife blades have a major influence on the quality of the cut. The performance of the knife blades are influenced by factors such as the blade edge, surface texture of the blade, fineness of the blade edge and blade composition. Blade edges may be straight with a flat surface, saw-toothed, serrated or wavy surface. Straight edge blades are used for general-purpose, serrated blades to reduce heat generation during cutting, wavy edges for cutting plastics and vinyl, and saw-type blades for cutting canvas.
- Base plate – It supports and balances the equipment. It guides the knife along the cutting table and raises the spread off the table for contact with the blade. It is normally supported by bearing rollers at the bottom to facilitate easy movement of the base plate.
- Power system – The power required to cut a lay depends on the lay height and fabric weight (grams per square metre, GSM). The motor horsepower determines the cutting power of the blade; higher horsepower increases machine power as well as the motor weight.
- Sharpening devices – Blades become blunt very quickly while cutting higher spread height or heavy weight fabrics which leads to frayed or fused edges. Sharpening devices such as emery wheels, abrasive belt sharpeners or stone could be used on the machine.
- Handle – It is used to guide and impel the knife through the spread. The operator stabilises the fabric plies on the other hand, which is ahead of the knife to prevent bunching of the fabric.
The different types of power knives are described below:
1. Straight knife fabric cutting machine:This is the most frequently used equipment for cutting garments in bulk. It comprises a base plate, vertically moving blade, an upright, a motor for providing the power for cutting the fabric plies, a handle for the cutter to direct the blade, and a sharpening device.
Typically, the height of the knife blade varies from 10 to 33 cm and strokes vary from 2.5 to 4.5 cm. The straight knife is versatile, portable, cheaper than a band knife, more accurate on curves than a round knife, and relatively reliable and easy to maintain. In a few cases, a straight knife system is used as the preliminary process to cut the lay and then a band knife is used for accurate cutting as the final process.
2. Servo assisted straight knife cutting machine:A development from a straight knife machine has a travelling suspension system which supports the knife from the top, hence heavy base plate and rollers could be changed with a small, flat base (Figure-1). These servo knife systems provide a higher degree of cutting precision than the previous version of unsupported straight knife systems, with the requirement of less operator skill.
3. Round knife cutting machine:The basic elements of a round knife are analogous to a straight knife except it has a round blade. The blade diameter varies from 6 to 20 cm. Round knives are not appropriate for cutting curved lines especially in high lays as the circular blade could not cut all the plies at the same point as well as the same time as in a vertical blade. Hence, it could be utilized only for cutting straight lines rather than curved ones.
4. Band knife cutting machine:It is normally engaged for accurate cutting of garment components. It consists of an electrically powered motor and a constantly rotating steel blade mounted over it . In this cutting system, the knife is stationary which moves through a small slot provided in the table and the fabric has to be moved manually to the blade area for accurate cutting.
5. Fabric die cutting machine: The die is a knife blade in the profile/shape of a pattern margin, including notches (Figure-2). It involves forcing a firm blade through a fabric lay. Free-standing dies normally have two categories. One kind is a strip steel, which cannot be sharpened and must be replaced when worn and another one is forged dies, which can be resharpened but the cost is five times higher than strip steel. The position of the tie bars, which hold the die, determines the depth of the cut. Free-standing gives higher accuracy of cutting and is used for cutting the small components of larger garments like collars and pockets.
Computerised Methods of Cutting Machine:
1. Computer controlled knife cutting: This method gives the most precise and accurate cutting at high speed. The complete setup of a computerised cutting system is shown in Figure-3. A characteristic computerised cutting system has nylon bristles at the top of the cutting table to support the fabric lay, which is flexible enough to allow penetration and movement of the blade through it. It also allows passage of air through the table to produce a vacuum for decreasing the lay height. The frame/carriage supporting the cutting head has two synchronised servo-motors, which drive it on tracks on the edges of the table. A third servo-motor keeps the cutting head at an accurate position on a beam through the width of the carriage. The cutting head includes a knife, sharpener and a servo-motor to rotate the knife to position it at a tangent to the line of the cut on curves. An airtight polyethylene sheet could be spread over the top of the lay to facilitate vacuum creation in the lay to reduce the lay height. A control cabinet houses the computer and the electrical components required to drive the cutter, its carriage and the vacuum motor.
An operator spreads the fabric lay on a conventional cutting table or cutting table equipped with air flotation or conveyorised cutting table. Perforated paper is spread below the bottom fabric ply to support it during cutting as well to avoid distortion during moving to the cutting table. After loading the disc having the marker plan into the computer, the operator positions the cutting head’s origin light over the corner of the spread (reference point). A motorised drill at the back of the cutting head provides drill holes as required and facilities are available to cut the notches as well. The maximum height is usually 7.5 cm when compressed, with the height before compression, and hence the number of plies, being based on the nature of the fabric.
As the computerised cutting system works on the predetermined instructions from the computer/disc, markers are not compulsory for this type of system. However, to identify the cut garment panels for sorting and bundling, labelling of garment components that are to be cut is required.
2. Fabric laser cutting machine:A laser produces a beam of light that could be focused into a very small point (0.25 mm) to produce high energy density and result in localised increase in temperature. In this system, cutting takes place by way of burning, melting and evaporation. The limited depth of fabric cutting (single or two plies) is the major drawback of this system.
The cutting system comprises a stationary gas laser, a cutting head carrying a system of mirrors to reflect the laser beam to the cutting line, a computer which operates the entire system and a system for removing cut parts from the conveyor carrying the single ply of fabric (Figure-4).
An automatic, single ply, laser cutting system is speedy compared with automatic multiple ply knife cutters, with speeds of 30–40 m/min being realised compared with 5–12 m/min for knife cutting. The main hindrances to utilising laser cutters in the garment industry are the quality of the cut edge (which may become charred and, with thermoplastics, may affect the feel of the edge), the possibility of less than 100% efficient cutting and the requirements to maintain the equipment.
3. Fabric plasma cutting machine:The plasma cutting process was developed to satisfy a demand for high quality accurate cutting on stainless steel and aluminium; however, it could also be utilised to cut textile materials. In this system, cutting is accomplished through a high velocity jet of high temperature ionised gas (argon). This method has the potential to become the faster cutter of single plies, but the cutting method has similar issues as in laser cutting related to quality of cutting.
4. Water jet fabric cutting machine:A high velocity, small diameter stream of water is generated by applying high pressure water to a nozzle (Figure-5). The high pressure water jet acts as a means to cut the fabric, tearing the fibers on impact. As the water jet penetrates succeeding plies in a spread, the energy decreases and cutting capability is also reduced. The water jet spreads out and the cutting point becomes wider at the bottom of the lay. There is a problem of water spotting, wet edges and inconsistent cutting quality.
5. Ultrasonic fabric cutting:In this cutting system, vibration frequencies in the 20 kHz range are used to produce 1/20 mm movement in the blade, small enough to remove the need for a bristle base to the cutting table. Disposable knife blades save sharpening time and last for 10–14 days. Single ply and very low lays can be cut and low vacuum only is needed.
Auxiliary Devices for Fabric Cutting:
Notchers: Notchers are machines used to create notches in the edge of cut components.
- Cold notcher – The cold notcher is a spring-loaded device with a small blade fitted on a plunger. For making a notch in the fabric panels, it is kept at the edge of the panel where the notch has to be produced and by a single downward stroke the notch is cut into the edge of fabric plies.
- Hot notcher – In loosely constructed woven or knitted fabrics, the cut notch will vanish in the edge fraying during handling each component. To make a permanent notch, a hot notcher (Figure-6) is utilised. It uses a vertical heated edge to burn a notch without the danger of melting or scorching into the edge of the bundle.
- Ink notcher – It is analogous to the hot notcher except after burning a notch it leaves a drop of UV marking ink that is visible under UV light.
Cloth drills: Cloth drills are utilised when an identification mark is required inside the body of a panel to illustrate the dart point, pocket location, or location of an inner element such as a pocket or appliqué.
- Cold drill – It cuts a tiny circle of fabric plies as it drills down through the fabric lay.
- Hot drill – It utilises an electrically heated solid shaft for drilling, which leaves a burn mark to create a permanent identification on loosely constructed woven and knitted fabrics. The hot drill machine.
- Thread markers – It uses a needle that penetrates all the fabric plies in the lay. The thread carried by a needle is left in the fabric, which shows a location of a drill hole. This is suitable on loosely constructed woven and knits where use of a hot notch could lead to fabric damage.
- Inside slasher – It is a device used to cut the inside slashes for interior ‘slash’ pockets. The cut is completely inside of the component, thus cutting from the fabric edge becomes impossible. The device has a double edge blade that reciprocates and is inserted from above the part bundle, where the part bundle is moved under the knife.
Original Source: https://clothingindustry.blogspot.com