Best Cutting Techniques for Aluminium & Copper Metallic Foil
Use a correctly designed machine knife for cutting aluminium and copper foils
Everyone loves sharp knives and blades. But sometimes you can have a too sharp cutting edge. This article is for the converting industry and is about industrial cases where a less sharp blade is desired. Basically slitting and cutting materials such as aluminium and copper foils that require a high grinding angle for slitting and cutting.
- Definition of slitting and cutting
- How to avoid chips, swarfs, burrs, dust powder or delamination when cutting or slitting aluminium or copper metal foils
- Types of foils cut with a slitter: metal foil processing
- What material preferences to consider when slitting & cutting aluminum and copper foils?
- The bodyguard scarf cut, sharpness, and durability in general
- Slitting aluminium metallic foil with industrial razor blades does not work
- Slitting aluminium metallic foil with a sharp circular dished top knife does not work
- Slitting aluminium metallic foil with a less sharp circular dished top knife works well
- Cutting copper foil
- Cutting coated copper
- Cutting laminated metallic foil
Definition of Slitting and Cutting
Slitting is when a machine knife or blade is slitting a material in a production web direction. For slitting you can use razor blades or shear knives. Shear knives or rotary or roll slitting is using a top dish circular knife and a bottom / female circular knife. Cutting is the opposite. Cutting is when you cut a material across the web direction. You can use razor blades for cutting or like scissors you can use a top and bottom knife to cut a material across its length.
How to Avoid Chips, Swarfs, Burrs, Dust Powder or Delamination When Cutting or Slitting Aluminium or Copper Metal Foils
Products such as metal foil, resin, and paper, are usually slit into a fixed width and rolled up. Metallic foil is used for a wide array of purposes, but if it is not properly slit or cut chips, burrs, dust, cutting powder or delamination of the foil may ruin it purpose. It is clear that setting and optimizing slit blades largely depends on operators' experiences. Often the finished product quality is greatly affected by the skill level of the operator. This text is about how to slit and cut metallic foil. We are specifically investigating how to slit and cut metallic foils in aluminium and copper. Read more in blog post 5 Ways to Improve Your Slitting and Cutting.
Types of Foils Cut with a Slitter: Metal Foil Processing
Thin metal foils come in various surface treatments and delivery forms. Virtually all metals can be processed using a slitter, with common choices including copper, copper alloys, nickel, nickel silver, fine silver, and various resistance alloys.
A slitter-rewinder is used to wind and cut rolls of paper, nonwovens, film, adhesive tape, metal foil, and sheets. It employs knives to cut in the direction of the material feed, winding the cut pieces into individual rolls. Top and bottom slitter knives perform the cutting by passing the material between them. Quality is enhanced by selecting different knife angles and materials based on the material's characteristics.
What Material Preferences to Consider When Slitting & Cutting Aluminum and Copper Foils?
Copper foil is a soft metal. It is crucial to minimize cutting powder generation. Copper, being highly ductile, tends to stretch near the cutting surface during slitting. The more stretching and deformation occur, the more likely burrs and chips will be produced.
Similarly, when slitting or cutting aluminum foil, challenges arise due to aluminum's low hardness and deformability. Aluminum and its alloys find widespread use in various industries thanks to their excellent thermal conductivity, electrical conductivity, ductility, and low density. However, the microstructure of aluminum foil makes it tricky to cut efficiently, primarily because of its low hardness and deformability.
The Bodyguard Scarf Cut, Sharpness, and Durability in General
Kevin Costner’s katana, in the classic motion picture The Bodyguard from 1992, cuts objects as the blade is pulled across a material. If an object is simply dropped on the blade like the scarf in the movie, it is unlikely that any cutting will occur. As long as there’s no sliding action, the blade rarely cuts. If a scarf is allowed to slide across the edge, the material could be cut. Still, this classic motion picture amplifies the myth of a really sharp blade being cool to have. In practice such a low grinding angle and extremely sharp blade would be worn out very quickly and not be so practical for Japanese warriors.
A cutting edge can be grinded on one or two sides. A low grinding angle and a single bevel gives a very sharp blade. Higher grinding angle and double bevel means less sharpness but increased durability. A really sharp cutting edge is only optimal for a short time period and materials that need very clean cuts. Then the intention is to replace them. Consider a surgeon using his scalpel or an extra sharp snap-off blade cutting fine paper. However all blades wear down and sharp cutting edges wear down faster. When sharp blades cut material clips from the edge loosens. Depending on how abrasive the material is the more clips are lost. These clips ruin the edge and will give a more and more unclean cut. In the end, it is time to replace them. For industrial usage, a combination of sharpness and durability is essential. In our mind a blade must be sharp enough to do the cutting or slitting but durable to last as long as possible.
Slitting Aluminium Metallic Foil with Industrial Razor Blades Does Not Work
Sollex general recommendation is that when slitting film razor blades give the cleanest slit and cut. However, when cutting metallic foil with aluminium we found that our dear industrial razor blades did not work. Cutting thin aluminium foil with slitting razor blades resulted in uneven edges and a rough cutting surface.
Industrial razor blades are too sharp for cutting the thin aluminium foil. Slitting razor blades perform well when a film is stretched but still flexible and the pressure from the blade makes the material slide in two directions. The difference with cutting aluminium foil is that there is no constant pressure as the material deforms and stretches. As a result the razor blade makes very many small cuts and there is no continued slitting.
Please note that if the metallic would have been laminated with a film keeping it in place, razor blades would work with the cleanest cut.
Slitting Aluminium Metallic Foil with a Sharp Circular Dished Top Knife Does Not Work
A good way to slit or cut metallic aluminium foil is to use a top and bottom machine knives. The bottom knife fixes the material and the top disc knife cuts it. Again, a too sharp top slitting knife generates flakes, burrs and destroys the slit as metallic foil deforms and stretches.
Slitting the aluminium foil with a 30 degree top knife is way too sharp. This low grinding angel was too sharp and resulted in a slit as this picture with. Similar to the razor blades the sharp top knife slits the films in several different directions. The film is too fragile and unstable which makes it go into bits and pieces. Creating small cut flakes that sticks to the knife and destroys the slitting process.
Slitting Aluminium Metallic Foil with a Less Sharp Circular Dished Top Knife Works Well
Solving the problem with slitting aluminium and other soft material foils is a less sharp top knife. A 60 degree top knife works fine for aluminium and copper foil. So in the end the aluminium foil needed to be fixed by the bottom knife and slit with the 60 degree top knife.
Cutting Copper Foil
Copper must be one of the most challenging materials to slit or cut. In itself the copper is a very soft foil. It means that it deforms, stretches and moves if it is not fixed enough. Similar to slitting aluminium, copper bends and tweaks. A too sharp blade may cut partial cuts or create tearing as the copper foil approaches the knife. In Gemba we have found that cutting copper foil also requires a less sharp knife.
Cutting Coated Copper
Cutting coated metallic foil like carbon coated battery copper foil is an even tougher challenge. It is our findings that the soft metallic foil is smooth and slippery, while the carbon coating is hard and easily cracks or generates clips or burrs. To cut such a battery-grade copper foil you need two almost 90 degrees flat knives to keep the film in position. Think more like punching than sharp blades for cutting. We have seen that a too sharp second knife has problems cutting the film and the applied coating ends up in flakes, burr or etc. But a well designed almost 90 degrees vertical knife does the job beautifully.
Cutting Laminated Metallic Foil
Similar to coated metallic foil, a laminated foil presents challenges when being cut. Depending on the layer structure and the type of layers we have found that there are two different approaches to laminated foils. Firstly, if any layer is supportive enough fixing the material foil you can proceed more like cutting a film with a sharp knife. But if the laminated layers are ”all metallic” you need to cut the laminated metallic foil just like the coated. More punching than normal slitting. Use two almost 90 degree knives.