When using a CNC oscillating knife cutting machine to cut various highly air-permeable materials such as knitted fabrics, EVA foam, automotive sound-absorbing cotton, filter materials, mesh cloth, non-woven fabric and felt, users often face the problem of difficult material fixation. Combining a vacuum adsorption system with the film covering auxiliary method is the best solution to effectively fix air-permeable materials.
Why Is It Difficult to Secure Air-Permeable Materials in CNC Oscillating Knife Cutting?
Working Principle of the Vacuum Adsorption System
The basic principle of a vacuum adsorption table is as follows:
The vacuum pump extracts air from under the table → forms negative pressure → presses the material tightly on the table using atmospheric pressure difference.
Theoretical formula: Adsorption force = Pressure difference × Effective area
For non-air-permeable materials, negative pressure can be maintained stably, for example, at -20kPa ~ -60kPa.
Air-permeable materials (such as garment fabrics and foam) are hard to fix because they have a large number of internal pores, through which air continuously enters the table, making it impossible to build up stable negative pressure.
According to the porous media seepage theory (Darcy’s Law) in *Fluid Mechanics*, the air permeability of porous materials is proportional to their porosity. The higher the porosity, the better the air circulation, and the harder it is to maintain negative pressure.
Reference: Fox & McDonald’s Introduction to Fluid Mechanics. https://www.wiley.com
This means: air-permeable materials are not “unable to be adsorbed”, but the continuous air leakage prevents the formation of a stable negative pressure state.
Why airtight materials are easy to adsorb: Airtight materials such as leather, gaskets or PVC sheets cannot be penetrated by air. The vacuum pump extracts the air underneath, and the external atmospheric pressure (about 101 kPa) presses vertically on the material surface, generating a huge downward pressure.
Why porous materials leak air: Materials such as various fabrics allow air to pass freely through the small holes on them. As soon as the vacuum pump extracts a little air, external air immediately replenishes it, making it impossible to form a stable pressure differential, which leads to “poor adsorption”.
Physical Properties of Air-Permeable Materials
High porosity: The porosity of EVA foam and sound-absorbing cotton can reach 60%-95%, allowing air to circulate unimpeded and forming “air leakage channels”. As a result, the vacuum pump needs to continuously extract air to maintain adsorption.
Low material density: Low density means small mass per unit area. For example, the density of ordinary EVA is about 30–80 kg/m³, making the material very light. Vibration caused during cutting by the oscillating knife can easily lead to material displacement.
Loose structure: Fibers of mesh cloth or non-woven fabric are loosely interwoven. The high-speed reciprocating motion of the oscillating knife (usually 0–18,000 strokes per minute) generates a strong impact force. If the material is not firmly fixed, problems such as interlayer slip, edge warping, uneven cuts and aperture deviation will occur.
The Impact of Cutting-Induced Vibration on Material Stability
The oscillating knife cuts materials through high-frequency reciprocating motion, which generates a vertical lifting force at a high frequency of up to 18,000 strokes per minute. If the adsorption force is insufficient to offset this lifting force, the material will jump up and down with the blade, resulting in frayed cut edges.
The strong downward impact force of the cutter will also cause micro-displacement of the material. As micro-displacements accumulate, dimensional errors will gradually expand, leading to a decline in cutting accuracy.
Relevant mechanical vibration research (Springer, Mechanical Vibrations in Manufacturing Systems) points out that high-frequency vibration has a dynamic displacement effect on lightweight materials. Source: https://link.springer.com
Common Wrong Methods to Fix the Material Securing Problem
Blindly Increasing the Vacuum Pump Power
Poor material adsorption is not necessarily caused by low vacuum pump power. For air-permeable materials, simply increasing the vacuum degree (negative pressure value) is meaningless, because stable vacuum cannot be maintained no matter how much air is extracted; what is really needed is a large air flow.
If the vacuum pump flow is insufficient to compensate for the leaked air in time, stable adsorption cannot be maintained even with a high negative pressure value. Blindly increasing the vacuum suction will instead lead to higher noise, increased energy consumption and rising costs.
Manual Material Pressing or Tape Fixing
Some factories may press the material edges with heavy objects, fix materials with tape or even press the material by hand. This will reduce automation efficiency, and tape is easy to leave residue on the material or be cut by the blade and wrap around the tool head. Pressing by hand also brings potential safety hazards, which may cause accidental injury to operators, and at the same time lead to unstable cutting quality.
Using a Single-Zone Vacuum Table
Single-zone adsorption means the entire table extracts air uniformly. Uncovered areas will continuously leak air, dispersing the effective adsorption force and reducing vacuum efficiency. For example, if only a small 0.5-meter material is cut on a 3-meter-long table, single-zone adsorption will cause the remaining 2.5-meter area to leak air entirely.
The Core Solution for a CNC Oscillating Knife Cutting Machine to Secure Air-Permeable Materials: Film Covering Method
What Is the Film Covering Method?
Film covering method: After laying the air-permeable material on the table, cover its surface with a layer of airtight plastic film (PE film).
Why Can Covering the Material Surface with a Film Instantly Improve Adsorption Force?
After covering the air-permeable material with a film, the object adsorbed by the vacuum system changes from “air-leaking fabric” to “airtight film”.
Principle: Atmospheric pressure acts directly on the film surface, and the film then uniformly transmits the pressure to the air-permeable material below.
Effect: Even fishing net cloth with extremely large meshes can be firmly fixed after film covering. The adsorption force can usually be increased by 3 to 5 times.
How to Choose the Right Cover Film?
Material: PE (polyethylene) film is recommended, as it is soft and has a certain ductility.
Thickness: 0.02mm – 0.05mm is suggested. Too thin a film is easy to tear, while too thick a film will increase cutter resistance.
Cost: Extremely low. Although an extra process is added, the cutting accuracy of the material is guaranteed. Compared with the losses caused by material scrapping, this method is very cost-effective.
Other Optimized Solutions for a CNC Oscillating Knife Cutter to Secure Air-Permeable Materials
Zoned Vacuum Adsorption System
Uniform adsorption on the entire table is a huge energy waste for cutting small-format materials. Choose a model with zoned adsorption, which divides the table into 6-8 independently controlled adsorption zones. Only open the valves of the zones covered with materials and close the idle zones to reduce ineffective air leakage.
This can concentrate the limited vacuum flow on the working area and significantly improve local suction. Engineering practice shows that multi-zone control can increase the effective adsorption efficiency by 20%-40% (public test data from equipment manufacturers).
High-Flow Vacuum Pump Instead of Simply High Negative Pressure
Selection suggestion: For cutting air-permeable materials, priority should be given to a high-flow fan (such as a turbo fan), rather than a vane pump that maximizes vacuum degree, because what we need is to quickly extract the continuously infiltrating air.
Honeycomb-Structured Adsorption Table
Advantages: The honeycomb aluminum plate structure can evenly distribute suction, reduce air diffusion, avoid local collapse, and provide a larger air passing cross-sectional area at the same time.
Auto Film Feeder
Automation: Install a film roll rack on the crossbeam. The machine automatically covers a layer of film while laying the material, without manual film laying, greatly improving efficiency.
Different Fixing Solutions for Various Air-Permeable Materials
EVA Foam Cutting
Pain point: The closed-cell structure is air-impermeable, but the material is easy to be sucked flat (compression deformation), and the size becomes larger after rebound after cutting.
Suggestion: Film covering is not suitable. Use a frequency converter to reduce the vacuum pump speed and find the critical point between “firm adsorption” and “no deformation”. Or use a milling cutter for processing to reduce downward pressure.
Automotive Sound-Absorbing Cotton Cutting
Pain point: Extremely fluffy with high porosity, making it impossible to adsorb at all.
Suggestion: Film covering is a must. Use an automatic film roll rack to cover a layer of film after laying a layer of material. The film is used to compact the fluffy cotton and ensure the consistency of cutting dimensions.
Filter Material and Mesh Cloth Cutting
Pain point: Large meshes that even expose the table, leading to complete air leakage.
Suggestion: Film covering + sacrificial layer. Lay a layer of air-permeable felt at the bottom to protect the table, and cover a film on the top. Cut the film together with the material during cutting.
Various Garment Fabric Cutting
Pain point: Easy to stretch and deform, and single-layer fabric is too light.
Suggestion: Multi-layer adsorption. Lay 10-20 layers at a time and cover the top layer with a film. Use vacuum pressure to compress the multi-layer fabric into a tight whole to prevent interlayer slip. However, a pneumatic oscillating knife should be selected for such multi-layer cutting.
What Cutting Problems Are Caused by Unstable Material Fixation?
Dimensional Errors Leading to Rework
Slight material displacement will turn circular holes into ellipses and straight lines into curves. For precision parts such as automotive interiors, the finished products cut in this way will be completely unqualified and require rework, which directly increases time and material costs.
Rising Scrap Rate
Especially for expensive materials such as carbon fiber and Kevlar fabric, any cutting damage will directly cause huge losses.
Example:
Scrap rate rises from 1% to 3%
Material cost: 1 million US dollars
Loss: 1 million US dollars × 2% = 20,000 US dollars
Forced Reduction of Cutting SpeedC
To prevent material deviation, operators have to reduce the cutting speed to 100mm/s or even lower, which may reduce the production capacity of the CNC oscillating knife cutting machine by about 10%-20%, resulting in serious waste of production capacity.
Tool Wear
Material shaking will cause the cutter to cut repeatedly, increasing lateral friction, leading to intensified blade heating and possibly shortening the tool life by more than 30%.
FAQs
Do air-permeable materials require a special CNC oscillating knife cutter?
No.
The machine only needs to meet the following conditions:
- Support zoned adsorption
- Equipped with a high-flow vacuum adsorption system
- Honeycomb-structured table with good airtightness
- Support film covering or be retrofitted with an Auto Film Feeder
Is the PE film used in the film covering method disposable? Is the cost high?
Yes, it is disposable.
The blade will cut the film together with the material during cutting, so it cannot be reused.
Cost is extremely low: Commonly used PE packaging film (0.02mm thick) is very cheap, with a cost of only a few cents per square meter. Compared with the scrapping of the entire material sheet caused by material displacement, this investment is completely worthwhile.
Will film covering affect the cutting speed?
No. The film is extremely thin, and the resistance it brings to the oscillating knife is negligible. On the contrary, because the material is adsorbed more firmly, you can set a faster feed rate, which actually improves the overall efficiency.
My machine has no automatic film roll rack, and manual film covering is too slow. What should I do?
You can install a simple roller bracket on the top of the machine crossbeam or at the end of the table to place the film roll. Just pull the film over to cover the material while pulling the material, without complex automation mechanisms, and it only costs a few dozen US dollars.
When cutting multi-layer fabric, the bottom layer is adsorbed firmly, but the upper layer still slips. What should I do?
This is caused by insufficient interlayer friction.
Solutions:
1. Be sure to cover the topmost layer with a film and use atmospheric pressure to compact the entire stack of fabric.
2. Use a long-blade cutter and appropriately reduce the cutting speed to reduce the dragging force of the blade on the fabric.
Can I freely select the vacuum adsorption zones?
Yes. Current CNC oscillating knife cutting machines are generally divided into 6-8 adsorption zones. The TRUSTER CNC oscillating knife cutter is equipped with 8 adsorption zones, and you can freely select the adsorption zones to turn on/off on the control system (Ruida, TROCEN).
How to quickly judge whether the problem is with the vacuum system or the material?
You can judge through three simple tests:
1. Test the adsorption force with an airtight material (such as a PVC sheet). If it is adsorbed firmly, the equipment is normal.
2. Test the vacuum pressure recovery time. If the recovery time is too long, the air flow is insufficient.
3. Test with the film covering method. If the adsorption force is significantly enhanced after film covering, the problem is caused by the material’s air permeability.
Through comparative tests, the source of the problem can be accurately located.
Will film covering increase tool wear?
Theoretically, it will increase a little resistance, but the impact is very small and almost negligible. The PE film is extremely thin (0.02-0.05mm), so the increase in cutter resistance during cutting is limited, so there is no need to worry about increased tool wear.
Is film covering suitable for all air-permeable materials?
No.
For example:
EVA foam has a closed-cell structure and is not completely air-permeable, but it is easy to be compressed. Excessively high suction from film covering may cause material deformation.
Therefore, the solution should be selected according to the material type:
Extremely air-permeable → Film covering is a must
Semi-air-permeable → Prioritize high-flow adsorption
Easy to deform → Control vacuum intensity
References and Information Sources
Fox, R. W., McDonald, A. T., & Pritchard, P. J. (2015). Introduction to Fluid Mechanics. Wiley.
Springer. (2014). Mechanical Vibrations in Manufacturing Systems. Springer Publishing. https://link.springer.com
