Showing posts with label Cutting. Show all posts
Showing posts with label Cutting. Show all posts
19 May 2010

Feature of Straight Knife Cutting Machine | Structure of Straight Knife Cutting Machine

Straight Knife Cutting Machine:
Straight knife cutting machine is the world’s most popular and most versatile. Available in all standard electrical configurations, with the largest variety of sizes and blade speeds in the industry. It is widely used in Bangladeshi garment industry.
Straight knife cutting machine
Feature of Straight Knife Cutting Machine:
  1. Suitable for mass trimming cotton, woolen, linen leather and chemical fiber goods, etc.
  2. Neat cutting, small-curvature radius curvilinear cutting.
  3. Low noise, stable running, easy to operate and high efficiency.
  4. Incorporated with an auto knife-grinding device, easier to operate.
Structure of Straight Knife Cutting Machine:
The Straight knife cutting machine consists of a base plate, an up right stand to hold the vertical blade, motor, a handle for moving assembly, a sharpening device and a handle to transfer the whole assembly from one place to another.

Two kinds of power are required to operate a straight knife. Motor power drives the reciprocating blade and operator power drives the knife through the lay. Normally the available blade heights very from 10 cm to 33 cm and normally available strokes vary from 2.5 to 4.5 cm. The greater the blade movement the faster the blade cuts the fabric and more easily the operator can move the machine.


1. Knife
2. Sharpener
3. Motor
4. Fabric presser
5. Base plate
6. Moving handle
7. Transport handle

The most important consideration is selecting a straight knife is the power required from the operator to move the knife is the power required for the operator to move the knife through the lay. Operator effort is affected by the weight of the motor, the shape of the stand, handle height, stroke, sharpness of blade and the base plate movement.

The normal blade has a straight edge that varies from coarse to fine depending upon the type of fabric being cut. Wavy edged knifes are used to reduce the heat generation and hence can be used for cutting synthetic materials without fusing difficulties. The speed of the blades can also be adjusted by having variable speed mechanism.

The straight knife is a common means of cutting lays in conventional cutting rooms because it is versatile,, portable, chapter than a band knife and easy to maintain. Even if a band knife is used for main cutting operation, a straight knife will be used to separate the lay into sections for easier handling. 
 
 
8 March 2010

Cutting Fabric | Requirements of the Cutting Process | Technique of Fabric Cutting

Fabric Cutting:
Cutting is the major operation of the cutting room, when the spread fabric is cut into garment components. Of all the operations in the cutting room this is the most decisive, because once the fabric has been cut, very little can be done to rectify serious mistakes. Cutting can be done manually using powered knives or by computer-controlled system.

Fabric cutting
Requirements of the Cutting Process:

1. Precision of cut- It depends on :
  • Methods of cutting employed.
  • Marker planning- distance between two pattern pieces.
  • Marker marking- correct marking by pen/pencil.
  • Condition of cutting equipment- machine, blade etc.
  • Skill and motivation of the operator.
2. Clean edge- Free from fraying.

3. Unfused edge- High temperature produced during cutting can fuse fabric edges by melting. Unfused edges can be ensured by taking the following measures:
  • Well sharpened blade.
  • Use of anti-fusion (heat absorbent) paper.
  • Spraying silicon lubricants on the blade.
  • Less cutting speed.
  • Reducing the height of the lay.
4. Support of the lay- using a polyethylene sheet or nylon bristle under the bottom ply
5. Consistent cutting- all plies should be of same dimension

Cutting Techniques:
1) Manually Powered Knife:  
Rotary blade- small instrument, electrically operated octagonal blade, very sharp edge, grinding wheel attached, fabric should be clamped before cutting. Suitable for relatively gentle curve cutting & for less ply height
 
Straight blade- straight reciprocating blade of upto 13" height and 0.5" width could be sharpened by attached grinding wheel. Most commonly used, could be used for larger depth of fabric, high cutting speed, sharp corners could be cut; but blade deflection occurs and higher the depth of fabric greater the possibility of deflection
 
Band knife- endless loop of flexible blade, one side sharpened, thinner than straight knife, machine stationary whereas the fabric moves, much more accurate cut for smaller parts, suitable for cutting sharp corners. Not suitable for large parts, more fabric wastage as block piece of fabric is required; workload is high due to stationary cutting machine.
 
Die cutter- suitable for smaller garment parts like shoulder pads, very accurate for sharp corners & circular patterns. Not suitable for larger parts, difficulty in producing dies (labour, time), higher fabric wastage due to use of block pieces

2) Computerized Technique
  • Knife cutter
  • Laser cutter
  • Water jet
  • Plasma jet
Choice of Cutting Technique:
The following points should be considered while choosing cutting techniques:

1. Availability of cutting machines.

2. Number of plies or spread height- band knife for upto 6" height, straight knife for higher height.

3. Type of garment parts- straight knife & knife cutter for bigger parts, band knife for sharp corner, die cutter for small parts like pockets.

4. Type of fibre in the fabric- laser cutter should not be used for thermoplastic fibres, water jet is suitable for low absorbency fibres like polyester.

5. Cutting speed required- computerized method for higher speed.

6. Quality of cutting- computerized techniques for high quality cutting.

7. Volume of production- straight knife & computerized techniques for higher volume

8. Cost of cutting. 
 
 
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