Die-less cutting-Part 3 (Laser Jet)
3. Laser Jet Cutting
Laser cutting is fast, flexible and cost effective. Lasers are capable of cutting steel, stainless steel, super alloys, copper, aluminum, and brass. They also cut non-metallic materials such as Leather, ceramic, quartz, plastic, rubber, wood and certain composite structures. The laser is so fast and repeatable that it is particularly ideal for high production volumes. The laser beam actually vaporizes the material in its path. This results in a clean, smooth edge. Laser cutter can cut 250- 400 patterns per hour. Laser cutter contains a vacuum duct which the smoke generated is exhausted. It also contains electric control cabinet and laser power supply enclosure.
Now a days Laser machines are used to engrave the design on leather parts.
Process: Laser cutting is nothing more than cutting with a miniature computer controlled torch. Focused laser light is used as the heat source to both melt and vaporize material in its path. Assist gases are also used to aid in additional heat generation and material removal. As a result, a very narrow and consistent path or “kerf” is created. Many materials, whether hard, soft, ferrous or non-ferrous can be precisely cut with a laser, by varying power, feed rate, focus, gas type and pressure, etc
It is important to clarify how laser cutting actually works and how the process can differ depending on the material. Many people have common misconception that laser cutting works like a small “torch” and simply burns through everything it touches. For non-metallic materials the focused laser beam actually vaporizes the material it contacts. If oxygen is not available, the process does not cause oxidation or burning. For cutting thin non-metallic materials, inert gasses such as nitrogen or argon are used with the gas-assist nozzle. This can virtually eliminate oxidation and produces edges that are free from charring. Laser cutting produces a “heat affected zone” (HAZ). Paper products and leather, as well as natural and synthetic textiles, can easily be cut with a laser. The lack of thickness, coupled with their high combustion ability minimizes the power output requirements of a laser to no more than a few hundred watts. The resultant edges are clean and free from fraying. Most fabrics can be easily cut with a CO2 laser. The resultant cut is a sealed edge free from loose fibres. For this reason lasers are often used for cutting fabrics used in medical applications or where sealed edges are required.
The typical laser cutter contains the following parts
- Cutting gas: Compressed gas is required to disperse the vapours from the cutting point and also to cool the focusing lens. Typically, compressed air is all that is required, although for some applications it is useful to cut with nitrogen.
- Cooling water: The quantity of cooling water depends on the laser power requirement. For example, if you need a 100W laser, a minimum of 9-10 liters/minute is usually required.
- Exhaust: The exhaust serves to draw the cutting vapours. The exhaust is also useful if you are cutting a light fabric, as it holds the material to the cutting plane.
* No part distortion – Due to small Heat Affected Zones (HAZ).
* No tool wear – Due to the non-contact cutting process.
* Ability to cut most materials – Due to the non-contact cutting process.
* Efficient part nesting capability – Due to narrow “kerf” width and programming flexibility.
* Fast, inexpensive prototyping – Due to little or no hard tooling.
* Rapid design changes – Due to narrow “kerf” width.
* Cost competitive – Due to low fixture costs, high feed rates, multi-axis capability and minimal downtime, high processing speed
Disadvantages : While cutting paper pattern, some machines leave burning edges which reduces the strength.
Video Source : Prakash Laser
So, What is the best cutting tool ?
There is no single answer to this question.
- Early 70s: Laser cutters for pattern cutting, water jet for insole and outsole materials and reciprocating knives for linings and fabrics.
- Early 80s: Laser cutters for pattern cutting emerged that offered improved performance and reliability at lower cost. (Ex. L-34, L023 laser cutters by Gamata)
- In 90s and after the trend has been toward sample cutting. The Footwear industry like many others is placing emphasis on reducing the time it takes to get product to market. The time it takes to go from concept to sample or prototype is now under pressure to reduce waiting time for dies, and to reduce the time it takes to get new style through acceptance process. Now a days Laser machines are used for both engraving (complicated designs) and cut the part at the same time.
Drag knife is useful in leather cutting or in other single ply cutting such as patterns. In case of cutting samples the reciprocating knife or drag knife is the most versatile cutting tool. Some NC cutting systems also incorporate auxiliary tools to perform special operations. These include notching tools, routers, punches, drills and marking pens for stitch marking. (Ex. Lectra Vector 2500 cutter)
The laser is effective for cutting paper and cardboard patterns, and other synthetic materials where the slight ‘burned’ edge effect are not exposed or are not important.
The water jet is useful in cutting leather hides, insoles, and bottom materials. Knife cutting is occupies 80% of the market and 20% by water jet and 10% by laser jet.
So, before the ‘best tool’ can be identified, the application must be specified.
One of the basic justification for NC cutting has been the improvement in material utilisation. This improvement is difficult in case of natural materials like hides due to their irregular shapes and defects and properly align parts with the directional characteristics of the material. Companies like developed a technique to digitize the boundary of the material and defects. The parts are then automatically placed in the material to avoid the flaws and to provide the proper orientation while maximizing material utilization.
Comparison between different cutting systems
|Water jet||Laser Jet||Conventional|
|Method||Mechanical (micro chipping)||Thermal||Mechanical|
|Tool||No stable in shape||Stable in shape|
|Material||Any material||Material that absorbs light energy||Hard materials cannot be cut|
|Laminates||Can cut all laminates||Cannot cut all laminates||Cutting laminates often difficult|
|Burr||No burr||No burr in most materials||Burr may form|
|Deformation||No material deformation||No material deformation||Material deformation may be occur|
|Fumes||No fumes||Fumes may arise while cutting plastics||No fumes|
|Speed||Lower than laser||Faster than water jet||Slow|
|Kerf||Low||Low||Higher than others|
|Thick ness||Upto 15”||Upto 5/8”|
Source: Class notes prepared by A.V.Suresh, Ex.Sr . Technical officer, CFTI, Agra for students, while he was working in CFTI, Agra