Fabric Cutting Optimization (Part 1 in a Series on Cutting Optimization and Automation)
- For example, if the whole garment grade is 1 inch and 4 patterns make up this item, then the tolerance must be much less than the grade. It is easy to calculate; take 1 inch divided by 4 patterns which give us a grade of 1/4 inch per pattern... 1/8 inch on each side of the pattern. Then, the cutting tolerance must be much less than the grade of 1/8 inch which usually means that the cutting tolerance must be no more than 1/16 inch on either side of the pattern for the item to fit as designed.
- So, on a specification sheet, it is not uncommon to see a measurement of 8.5 inches +/- 1/16 inch. Cutting the pattern must include seam allowance to successfully assemble the item. The seam allowance should relate to the stitch type being used in assembly. So, to optimize cutting, the pattern, grading, seam allowance, assembly, and fabric type all contribute to successful cutting.
- Cutting productivity is the result of cutting speed, the number of plies spread, and the first quality yield. Straight lines cut faster than curved lines. Adding notches and internal cuts slow all cutters and must be used sparingly and as instructions to those who are in assembly. In many cases, the notches and internal cuts distinguish between cutting systems.
- In many cases, spreading has been automated. It is a matter of programming the spread length and height. These spreaders must perform, and they are priced to yield an ROI of about one year. The spread length will determine the time required to cut as the height, notches, internal cuts, etc. will be in the “marker”.
- As the industry moves more and more toward “cut-to-order” the Cut Order Planning function is busy optimizing spread height, spread length, cutting time, first quality yield, etc. The last time I looked, there are about 47 parameters used by Cut Order Planning to optimize the cut. As a general rule, all items to assemble the final product must be in place before taking the fabric out of inventory to make the product.
- I like to think of cutting as with three options:
- 1) Manual cutting systems
- 2) CNC low ply cutters
- 3) CNC high ply cutters
- Manual Cutting Systems In this first article, we look at the Manual Cutting Systems which include: Round Knives, Straight Knives, Suspended Straight Knives, Bandsaws, Shears, Scissors, Hand-Held Cutting Tools, Power Driven or Battery Driven, and Dies.
- There is a trend to use more “battery” power for manual cutting systems since there are no cords and fewer wiring harnesses to be installed. If a traditional wiring harness is available, it will tend to dictate the type of cutting tool.
Clearly, there is not one solution for all spread heights, so it is recommended that end users who vary spread heights choose differing heights of straight knife cutters. The type of blade can vary depending on the type of material being cut. For example, if the plies of fabric fuse together at the cut edge, a wavy blade might be needed. Alternatively, air jets directed to the blade may be sufficient to keep it cool and therefore allow the plies to be easily separated.
Please do not send fused plies to the assembly room as there will be a loud noise coming therefrom. If automation is a part of the assembly, it will be a disaster.
One of the advantages of straight knives is their precision in making notches. Of course, training is needed to prevent cutting the notch too deep yet allowing it to be easily seen by the assembly operator. As a rule of thumb, the notch depth should not be more than half the seam allowance. This means that the Manual Cutter operator needs to know the seam allowance(s) for the part being cut.
Suspended Straight KnivesSuspended straight knives are readily available but are rarely shown at trade shows now. Apart from the ergonomic principles of ease of cutting, a suspended knife will have a smaller ‘platform’ and supposedly more accurate cutting. Suspended knives can also fit the ‘trolly’ duct as a power source and can cut the length of the spreading table.
In all cases above, the spread stays on the table and the cutter moves the knife in and out of the spread.
Bandsaw CuttingBandsaw cutting is also a manual cutting method where the bandsaw is a continuous blade that does the cutting. In this case, the cutting operator must bring the part(s) to the blade. This type of cutting is often found in sweater manufacturing where the operator will cut out the neckline (for example) for a stack of sweater blanks. It is also used in R&D to cut fabric precisely to the pattern shape but only one ply.
For manual cutting, it is an OSHA (Occupational Safety & Health Administration) requirement for the operator to have a cut-resistant glove covering the hand closest to the blade. www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.138.
ShearsNo discussion on cutting would be complete without a sentence on shears. Shears can be found in most customized cutting rooms. It is often faster to use shears to cut custom products such as suits and shirts/blouses when the quantity is one.
Die CuttingDie cutting is often found for high-volume items. The pattern shape is formed into a metal shape that is the die. Often a foundry is needed to bend and weld the die shape. Die cutting may be found marketed by companies such as www.bierrebi.com/en/. Manual cutting is not going away anytime soon. It does not mean that it is the best system, but many firms do not want to invest in training automated cutters and CAD users but rely on manual systems.
A challenging yet desirable evaluation of the differences between manual methods and technology-driven methods is needed on an ongoing basis. We all know that manual methods have shortcomings yet they have major benefits. How do we reconcile these pros and cons to become a vibrant and productive cutting room?