Fabric cutting

 

1. 1. Cutting is a preproduction process of separating a spread into garment parts that are of precise size and shape of pattern pieces on a marker. Cutting Quality: Cutting contributes to the quality, efficiency and cost of subsequent operations, including handling, fusing and sewing. It can be judged by the accuracy and condition of cut edges and precision of cut garment parts.
2. 2. Accurate cutting facilitate sewing and improve cutting quality. Inaccurate cutting may cause sewing operator to compensate by stretching or easing to make adjoining parts the same length. Factors that cause cutting inaccuracies are Wide or vague lines on the marker Imprecise following of lines on the marker Variation in cutting pitch Shifting of the spread Fabric bunching up or pushing ahead of the knife Improper equipment Improper cutting sequence as parts are cut.
3. 3. Cutting pitch: It is the angle at which the cutting device contacts the spread. Maintaining the cutting device at vertical position with pitch of 90 degree create uniformity. Condition of cutting edges: Smooth edges and precise corners are easier to align and position during the sewing operations. Edges that are frayed, jagged, scratched and fused are difficult for operators to pick up, align and sew accurately. The condition of edges is affected by Appropriateness of cutting equipment The shape being cut Condition of the equipment
4. 4. Cutting Equipments: There are two major types of cutting equipments: Operator controlled cutting systems Automatic, Numerically controlled cutting systems
5. 5. Operator controlled cutting systems Hand Shears Portable cutting machine Vertical straight knife Rotary knife End cutter Stationary cutting machines Band knife Die Cutter Servo cutting machine Specialized cutting machine Stripe cutting machine Automatic cutting systems Automatic blade cutting Laser cutting Water jet cutting Plasma jet cutting
6. 6. Operator controlled cutting systems Manually operated systems depend on the skills of operator to position, manipulate and guide the fabric or cutting device. Operator controlled equipment may be portable or stationary. Hand shear: It is used normally for cutting of single or double plies The lower blade passes under the plies and distortion of fabric might be occur. Both left handed and right handed shears are available Disadvantage of method is time consumption and consequent high labor cost per garment so not used at mass level It is useful for made to measure garments
7. 7. Portable Cutting Machines: Portable knives can move to and through a spread by an operator. There are two types Vertical reciprocating straight knives Round knives Structurally and mechanically the two types of the machine share many similarities Both types have the base plate, power system, operating handle, cutting blade, sharpening device and blade guard.
8. 8. Vertical straight knife cutting machine: It is used where the quantities for cutting does not justify purchase of computer controlled system. It is versatile and blade has a vertical cutting action. The element of knife are base plate usually on rollers for ease of movement, an upright or stand carrying a straight or vertical blade and an electric motor, a handle and a sharpening device. The cutting blades are available with different edge characteristics like straight edge blades, wavy edge blades, saw type and coated blades.
9. 9. The base plate slides under the bottom most layer of fabric. Various types and sizes of base plates are available such as small, medium and large. Blade height vary from 4 to 14 inches. The 90° angle of blade to the cutting surface make it suitable for accurately cutting sharp corners, angles and curves. The greater the blade movement, the faster the blade cuts the fabric and more rapidly and easily the operator can push the machine
10. 10. Rotary or Round Knife Cutting Machine: It can be identified by round blade that cuts with a downward turn at leading edge. The element of machine are base plate, electric motor, a handle and a circular blade. The cutting capacity is determined by the radius of blade, motor size and speed. Blade diameter vary from 2.25 to 8 inches.
11. 11. It can not be used around tight curves and sharp edges. May be used for large radius curves. This is not suitable for cutting curved lines in high lays because the blade does not strike all the plies simultaneously at the same point as the vertical point does. Therefore it is used only to cut straight lines.
12. 12. Rotary or Round Knife Cutting Machine (End Cutter): The element of end cutter are same as round knife machine except base plate including a rail onto which the cutting head moves back and forth on the cutting table, lifting mechanism to lift the rail after cutting each ply. This is used to cut single ply during spreading process. Used only for straight cuts.
13. 13. Operator Controlled Cutting Systems: Stationary Cutting Machines: Stationary cutters are those cutting machines that have blades that remain in fixed position The two types of stationary cutters are band knife and die cutters Operator must move the fabric to the machine for cutting action
14. 14. Band Knife Machine: It comprises a series of three or more pulleys, an electric motor with a continuously rotating steel blade mounted on them. One edge of the blade is sharpened. The band knife passes through a slot in the cutting table in a fixed position and the section of the lay to be cut is moved pass it. The operator position and guide the fabric around the knife.
15. 15. Pieces to be cut are first cut on a block and then cut exactly on band knife. Heavy cardboard may be placed on top of a section block to provide a guide for cutting specific shapes. Band knives are used for highly accurate cutting. Band knife blade is finer and narrower than reciprocating blades so they can be used to cut tight curves.
16. 16. Die Cutting: Dies are preshaped metal outlines with one cutting edge. Die cutting involves uses of a die to cut out a specific garment part or trim from a single piece or small block of fabric. Die cutting involves placement of fabric, positioning the die on the fabric and engaging the machine to press the die on the fabric. Dies can also be used to cut parts from centre of fabric Die cutting is labor intensive when dies placed manually. Only a small area of fabric cut at one time and die must be repositioned each time.
17. 17. Servo cutting machine: It is between manual and automatic cutting machines. This machine has servo motor with adjustable speed and a system that supports the knife perpendicular to cutting table. It can combine vertical cutting and band knife cutting in one machine.
18. 18. Specialized Cutting Machines: Stripe cutter: Stripe cutter may cut or cut and roll stripes or bindings from knit tubular yardage, cut bias stripes from woven. Stripe cutter is used to measure and cut lengths of material as ribbon, tape, elastic and strapping.
19. 19. Automatic Cutting Machines: Automatic blade cutting: These are used to cut large number of plies with great accuracy and speed. Information can be sent directly to the cutting machine. The central control unit operates the components such as cutting head, cutter carriage, knife sharpening and conveyorized cutting table. Automatic knife sharpening is done at intervals during cutting. The reciprocating blade can be adjusted to the height and density of fabric
20. 20. Laser Cutting: Laser cutting focuses a powerful beam of light projected onto a minute area to cut fabric. 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 fabrics. The fabric remain immobile during cutting. Laser cut with high speed, accuracy and multidirectional ability but with some heat emission. The heat produce can seal fabric edges which can be advantage for fabric that ravels and disadvantage for cutting multiple plies as edges fuse together. The handling operation of laser cutting is labor intensive as well as parts must be handled individually.
21. 21. Water Jet cutting: It is computer operated multidirectional cutting method. Water jet cutting is done by propelling a tiny jet of water(0.0010-0.0015 inch) through the 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 . It can cut multiple plies without fusing but it can fray and tangle the yarns of some fabrics. It is used when heat build up is avoided but water absorption is not important. At present time its uses are limited to cut leather and vinyl fabrics.
22. 22. Plasma Jet Cutting: It is computer operated, high speed, single ply cutting device that offers same features as laser cutting but at lower price. ATV camera reads the fabric on the conveyor and a digital image processor decides the best way to match and lay out the pieces based on predetermined matching rules.
23. 23. Cut parts identification: It involves identifying and marking parts for further operations. Through out the sewing operation it is essential that each garment be assembled from the parts that have been cut from the same ply of the fabric, which is ensured by shade marking each piece in the lay. Ticketing: Each piece or garment part is ticked with a style number, size and ply number. Plies are numbered sequentially. Garment parts are grouped and bundled for the specific production system to be used.