Monday, 15 October 2007

cutting-4



The requirement of quality in Cutting

Wherever a knife blade is used, the placement of the pattern pieces in the marker must give freedom of knife movement. It should not restrict the path of knife so that it leads to inaccurate cutting.
For example, a blade, which has width, cannot turn a perfect right angle in the middle of a pattern piece. Space must be allowed for a knife to turn such corners.


A pattern count must always be made at the completion of a marker. This is done to check that the complete menu of patterns has been included. For example, a 12 size trouser marker, where each trouser size has 16 pattern pieces, signifies a complete menu of 192 pattern pieces.

Correct labeling of the cut garment parts is essential. It is the responsibility of the marker planner to code every pattern piece with its size as the marker is made.

2. The requirement of the production Planning

When an order is placed for a quantity of garments , it normally specifies a quantity of each size and color. Size is often given as a ration. For best utilization of cutting room resources, a high lay rather than a low lay gives a lower cutting labour cost per garment. It will also give lower overall cutting time.

Scrambling

The mixing of sizes in a marker is termed as scrambling. Upto a point, the more sizes that are included in a marker, the greater the scope for fabric savings.

Stepped Lay

Some times single, sized markers are used in a stepped lay

Marker Efficiency
It is defined as


A marker planner can improve the marker efficiency by
a. suggesting alterations to pattern
b. suggesting alterations in cloth

Alteration to pattern: In this the seam location is examined and best possible placement of pattern in the marker is made. This is done by shifting the seam so that small parts can be placed in areas which are otherwise wasted
Alteration to cloth: In this the marker planner can select the fabric width.

Methods of marker planning

Manual Marker Planning

It is used for short marker or single sized markers
In this the planner works by moving around the full sized patterns, either directly or on paper.

Manual marker planning in miniature

In this a miniature of marker is produced. With the help of plenimeter, marker efficiency is calculated. After getting the highest marker efficiency, the pattern is again marked back to full size.

Computerised marker planning

In this the planner specifies the following parameters to the computer:

- The width of the fabric
- The pattern pieces to be used
- Size to be included
- Other constraints eg. Matching of the checks.

The system can produces the marker either
- automatically
- interactively

In automatic marking, the placement of pieces are previously defined in computer. That arrangement is called up that gives the highest marker efficiency.

Advantages

Rapid method of obtaining a relatively efficient marker

Disadvantages

There is no guarantee that the best marker is achieved

In interactive marker making, the operator plans markers by interacting directly with the system through a graphic display terminal

Advantages of computerized marking

The quality of marker planning is more consistent than with manual method because
Instructions regarding grainlines are always followed
Butting of patterns is precise with no overlapping
Pattern count is automatic
It provides grading facility
It enables the reproduction of as many copies of a marker as are required.

Disadvantages

Cost of computer equipment is very high

Methods of drawing and duplicating markers:

Once the planning of a marker has been completed, there is need for it to be drawn out in a way that cutter can use and which can be duplicated if multiple copies of the same plan is needed.

The method of drawing markers can be classified as

Drawing the shape of the patterns onto paper by marking around the patterns by hand.
Drawing the shape of the patterns onto paper using a plotter linked to the computer on which the marker was planned
Recording the shape of the patterns, hence its edge on paper by photographic method
Marking directly onto fabric by drawing round the patterns or by spray marking

Hand drawing round patterns onto paper

In this method the marker maker lays out the pattern on paper, the order already planned. He then draws the pattern pieces with a pencil or ball point pen and identifies each pattern with a size code.

Advantages: Most common method of marker making in bulk production

Disadvantages: It cannot be used readily with check fabrics. Because checks are not easily seen through paper, when it is put on the lay

Computer Controlled plotting on paper

After planning the marker on a visual display unit, the marker maker instructs the computer to trace the marker automatically onto paper. Any number of copies can be produced

Photographic system for paper markers

These create paper markers which show pattern shapes but avoid the need to draw round them by hand. In one method marker maker positions the pattern pieces on a light sensitive paper. Ultra violet lamps travel over the marker to expose the pattern which is then developed in ammonia vapour. Accuracy is high. High capital investment is required.

Marking Directly onto fabric

Marking round pattern pieces

Chalk or pencil is here used to mark round pattern pieces by hand. It is most traditional and simplest method. It is economical for single garments and check fabrics. It allows manipulation of the patterns during the marking process. It requires considerable skill. It takes the longest time. Dark coloured chalks can stain light coloured fabrics.

Spray Marking

In this after the pattern pieces are placed on the fabric, the marker maker lowers a net, held taut by a frame, onto the fabric to secure the position of the pattern pieces. A machine with a pump ejecting a fine spray is parsed over the marker. With the whole marker sprayed, the marker maker removes the patterns to leave an unsprayed silhouette. Very good on check fabrics. This method does not work satisfactorily on more sheer, less absorbent fabrics. Machine requires a lengthy cleaning process. While duplicating, successive layers of paint build up on the patterns, until they become so thick they lose accuracy.

Duplicating the patterns on paper

Carbon Duplicating: In this the marker maker lays out the number of plies of paper, interlaced with carbon. As the marker maker marks the top ply, an impression is simultaneously transferred to other copies.
Advantages: It can create upto six or eight copies in addition to the original
Disadvantages: It is a dirty process, particularly when the carbons are new. It can be less accurate in practice, since papers can be moved out of alignment during marking. Cutting lines can become less clear on the lower plies of a high stack. It is not always possible to predict the number of copies required as the time the marker is made.
Non Carbon Duplicating Papers.
Advantages: More copies can be achieved. It saves time by not having to roll out and re-roll carbons.
Disadvantages: Paper cost is high.
Paper combined with disposable carbons
It delivers more copies and saves time. When the cutting room uses only a few copies of each marker, this method pays best because of low capital costs and manual costs. It can provide an acceptable definition of lines, if too many copies are not attempted simultaneously.
Spirit Duplicating or hectograph carbon system
In this carbon is transferred to the underside of the master during marking. This carbon is released onto copy paper during reproduction.
This method can produce upto 40-50 copies per minute. The costs are reduced as more copies are required. It is a wet and messy process. Accuracy can be reduced due to twisting, creasing, shrinking or stretching of paper. Consumes time as copies should be left to dry for five minutes. It is sometimes necessary to remark parts of the marker after a few copies have been run off. It is very difficult to use wider marker as size of machine and difficulties of operations increase.
Pressurised Duplicating
In this method the carbon in the master is transferred to the pressure sensitive paper of the copy by pressurized roller. This method can produce upto 50-60 copies per master. It is more accurate as there is less likelihood of paper twisting and creasing. Paper is more expensive. Special marking pen does not produce very thin line.

Photographic Method
The original marker is copies using ultraviolet light on light sensitive paper. The image is then developed by means of ammonia vapours.
It is the quickest copying method. It ensures good definition of line. It is a cleaner process. The system can duplicate an unlimited no. of copies. It is also convenient to duplicate small quantities as they are required for current production. Removal of ammonia vapors is a problem. It is expensive for a small number of copies.

Perforated markers
In this the marker maker lays out the pattern pieces on light weight pattern card, draws round each piece with pencil and identifies each piece with a size code using a long arm sewing machine which carries a punch in place of a needle, the marker maker punched a series of perforations around the periphery of all the pattern pieces, and punches out the outlines of the size codes. The perforated marker, placed on top of the lay, is dusted with French chalk. The perforated marker can be used many times. Line definition can be poor unless great care is exercised. The cutting knife can cause the chalk dots to vibrate, thus sometimes dissipating the lines. It involves about twice the time of producing a hand drawn marker plus the cost of dusting.





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