Introduction
With the continuous development of modern life and the constant improvement of peoples living standards, peoples requirements for the quality of panel furniture are also constantly increasing.In the production of panel furniture, edge sealing is a very important and frequently used link, but it is also the process where product quality problems are most concentrated.
The most intuitive point when judging the quality of a piece of panel furniture is the edge sealing quality of the furniture. As the latest seamless edge sealing technology, laser edge sealing technology can ensure that the efficiency of production and processing is improved. At the same time, the panel furniture after edge sealing can have a perfect appearance and be loved by people. Optimizing the board edge banding process not only improves the overall quality of the product in terms of process but also brings huge commercial value to production and sales companies.
1.rocess analysis of laser edge banding technology
1.1 Laser edge banding technology process
Flow Laser edge banding technology requires a special edge banding strip for laser edge banding. The edge banding strip has a polymer layer with special properties coated in advance. During the processing, the edge banding strip passes through the laser equipment on the edge banding machine and is exposed to radiation. The functional layer formed by the special polymer is irradiated with high energy.
In laser beam irradiation, at this time, the polymer in the functional layer absorbs a large amount of energy, resulting in rheology. This special polymer layer appears macroscopically molten and has excellent adhesive properties. Subsequently, the edge banding strip is pressed onto the side edge of the workpiece through the pressure roller device so that the edge banding strip and the workpiece are adhered together. Finally, the edge trimming process completes the entire edge sealing process.
1.2 Comparison between laser edge banding technology and other edge banding processes
The most common edge banding technology currently on the market is hot melt adhesive edge banding. This type of edge banding machine is the most traditional edge banding equipment. It has a separate glueing system. The glueing system heats and melts the hot melt glue in advance. When preparing for edge sealing, the glueing system passes the melted hot melt glue through the glue coating roller and spreads it flatly on the edge banding strip.
Then, the pressure roller is used. The system immediately tightens the edge banding strip on the other side to complete the edge banding process. This machine is usually simple to operate and low in price, so many small furniture factories often choose this processing and production method when they need more funds.
This edge-sealing technology also has many shortcomings and defects: it takes a long time to heat hot-melt adhesive, and the processing efficiency could be higher, which increases energy consumption and processing costs to a certain extent; it is difficult to control the amount of hot-melt adhesive. It is easy to cause contamination to the workpiece and requires time-consuming and laborious cleaning of the workpiece.
When using hot melt adhesive, a special heating storage system is required, and the glue needs to be replaced every time the product changes colour. To improve the shortcomings of traditional hot-melt adhesive edge sealing technology, hot air edge sealing technology provides a new processing idea for edge sealing technology.
The edge banding strip is coated with a layer of hot melt adhesive in advance, and a hot air system is used instead of the glue application system. The process is to spray a strong hot air flow through a hot air delivery pipe to stimulate the adhesive on the edge banding strip coating. The mixture becomes sticky after being heated and melted, and the edge sealing material is connected to the board through a pressure roller system.
The biggest breakthrough of the hot air edge banding process is changing the traditional glue application method, which avoids problems such as glue overflow when the edge banding machine is used, easy contamination of the workpiece, time-consuming and laborious replacement of the glue box, etc. This edge-banding technology can make the entire equipment clean, tidy, and easy to operate, improving the edge-sealing effect.
There are also some problems in the actual use of hot air edge banding technology: only part of the hot air sprayed is absorbed by the adhesive of the edge banding strip, and the rest is wasted; the working environment has high requirements, and air humidity and indoor temperature will all affect it. To ensure edge sealing quality, the wind speed and pressure must be adjusted according to the edge banding strips material, thickness, and colour, which is not easy to control.
Compared with the above two processing methods, laser edge banding technology is the latest seamless edge banding technology, and its workflow is similar to the hot air edge banding process principle. This technology mainly uses a special polymer coating to replace traditional hot melt adhesive to ensure higher strength of edge sealing; it uses laser beams instead of hot air to input energy into the functional layer of the edge banding strip, solving the problem of hot air energy input.
The problem is that the machine has lower requirements for the processing environment during processing. The laser edge sealing process ensures production accuracy and greatly improves the quality of edge sealing. At the same time, the factorys production efficiency is improved, and the defective rate of products is reduced.
The laser edge sealing processing process almost only retains the necessary processing processes. This ensures that the laser edge banding process can maximize processing efficiency. The glue layer of laser edge sealing is usually only 0.1~0.2 mm thick, and the final effect of edge sealing can achieve truly seamless and perfect edge sealing. The laser edge banding machine can manually select and set the laser intensity, irradiation duration, feed speed, etc., according to the thickness of the workpiece and laser coating thickness of the edge banding material.
During the actual operation, you generally only need to enter or scan the model of the edge banding strip and give the feed speed of the plate. The machine can automatically set the parameters. The disadvantage is that the current laser edge banding has a high production cost because the edge banding strip is a special edge banding strip. For most small and medium-sized enterprises in my country, it is likely that there is equipment that can be bought but not used.
The problem, therefore, has yet to be widely accepted by domestic manufacturers. On the consumer side, there are also problems, such as an incomplete understanding of laser edge banding and low acceptance.
1.3 Material selection of laser edge banding strip
Laser edge banding technology can be applied to the most common edge banding materials on the market at this stage. It requires processing on the conventional edge banding and applying an appropriate thickness of polymer colloid with adhesive function in advance. Layer. Commonly used materials for edge banding include copolymers of three monomers, including acrylonitrile, butadiene, and styrene (ABS), polypropylene (PP), polyethene (PVC), and polymethylmethacrylate (PMMA).
The thickness of the edge banding strip is usually 0.4~1.2 mm, and the thickness of the commonly used laser edge banding strip is 0.5~3.0 mm. The thickness of the colloid functional layer can vary according to different bonding requirements. Normally, the functional thickness is 0.2 mm, which provides the best bonding and no traces. Basic selection requirements for edge banding strips:
The thickness of the edge banding strip should be selected based on product requirements and the performance of the edge banding equipment; the width of the edge banding strip corresponds to the plate thickness series, and special needs can be customized according to the thickness of the workpiece; the edge banding strip The colour should meet the requirements of the overall product design.
2.Structure of laser system
2.1 Selection of laser and its light-emitting principle
Usually, lasers are composed of three parts: laser working material, pump source and optical resonant cavity. According to different working materials, lasers can be divided into gas, solid, liquid, semiconductor, etc. Their main characteristics are that many gas laser working materials can produce lasers of various frequencies and have good coherence.
However, due to the low gas density, the laser output power is correspondingly small; the characteristics of solid lasers are exactly the opposite. , it can generate ultra-high power pulses, but there are few types of working materials, poor coherence and high price; the biggest feature of liquid laser is that the wavelength of the laser is continuously adjustable within a certain range, easy to prepare, low cost, but stable Relatively poor; semiconductor lasers have the characteristics of small size, lightweight, simple structure, and the output power is also small.
For the laser in the laser edge banding machine, the output power does not need to be too large. Still, the excitation method used by the laser must be able to convert electrical energy into laser energy. It must have continuous and stable output, good coherence, a volume that takes work to pass, and a series of requirements. CO2 gas lasers and semiconductor lasers meet the above requirements.
In comparison, CO2 gas lasers require more frequent maintenance, the device is relatively large, and the output power efficiency is relatively low when used. Usually, a semiconductor laser is chosen, a laser diode, essentially the same as a light-emitting diode (LED) and composed of a PN junction and two electrodes. The main difference is that LDs laser is coherent, while LED is incoherent.
Suitable working materials and special structures are required to achieve the inversion distribution of non-equilibrium carriers near the PN junction. Currently, heavily doped GaAsPN junctions are generally used, represented by P+ N+. In the energy level structure of a heavily doped P+ N+ junction under zero bias voltage, EC is the conduction band, EY is the valence band, EF is the Fermi level with regular carrier distribution, and QV is the barrier height.
When the PN junction is subjected to a forward voltage, the barrier potential height drops to q(VN-V), and V is the external bias voltage. At this time, electrons will be forced from the N region to enter the P region through the PN junction, and holes will enter the N region in the opposite direction. At this time, the holes near the PN junction will spontaneously recombine with non-equilibrium electrons, emitting a certain amount of energy.
The wavelength of photons is a phenomenon called spontaneous emission. When the photons generated after spontaneous recombination pass through the semiconductor, they can stimulate the nearby emitted electron-hole pairs to recombine and generate new photons, that is, stimulated emission. Increasing the injected current, when it is large enough, that is, qV>Eg, can break the balanced particle distribution, reverse the particle number, and achieve a carrier reversal distribution in the junction area.
The spontaneous recombination of non-equilibrium carriers in the injection region produces radiation photons, and these photons will cause the non-equilibrium carriers in the inversion state to produce stimulated recombination and emit stimulated emission photons.
Since losses in materials and cavities always exist, sufficient current intensity must be required to ensure that the gain in the laser is greater than the loss, thereby achieving laser oscillation and emitting good coherent light from the PN junction, which is the required laser light source. In the actual processing and production of the laser edge banding machine, the laser wavelength needed for the laser must be between 900 and 1064 nm, and the energy output power must reach 3 kW.
According to the requirements, a near-infrared laser diode was selected. Since the principle of the laser edge banding machine is to use high-energy laser output power to activate the colloid functional layer on the edge banding strip, more is needed to use a single laser unit. Several laser units are arranged in a certain array to integrate the light beam through the collimating mirror, forming a high-energy laser beam that can be collimated towards the edge banding strip.
Different array methods also affect the quality of edge banding to a certain extent. The practice has proved that when the laser element array is a rectangular spot with the same width and narrowness as the edge banding strip, the special glue on the edge banding strip will be processed under the premise of the same processing speed. Radiation heating of the mass layer is the most complete, and the edge sealing effect is the best.
2.2 Improvement of laser system structure
In the process of laser edge sealing, the laser source is used to irradiate the colloid layer of a special polymer on the edge sealing strip. However, there will be a problem that a small amount of energy emitted by the laser rays is not absorbed, causing an invisible waste of resources. The cost of edge sealing is increased. To solve the above problems, the design of the laser edge sealing equipment is improved. The purpose of this device design is to use the second medium to re-integrate the laser beam and enhance the laser utilization rate.
Those parts that are not absorbed by the edge sealing strip in time are absorbed by the edge sealing strip. The divergent light reflected from the strips can also be reused. The improved laser edge sealing device includes a radiation source (near-infrared laser diode), collimating mirror, radiation, second medium and pressure roller device.
The specific working process is: the laser diode emits radiation as a radiation source, and the ray path is initially integrated through the collimating mirror at the front end of the radiation source and is directly emitted to the A side of the second medium, and then reflected on the B side of the second medium (B side Special substances are required for coating).
At this time, this high-output laser beam enters a bonding gap formed by the relative movement of the workpiece and the edge banding strip and finally accurately irradiates the gel layer of the edge banding strip. Most of the radiation that hits the edge strip can be absorbed by the special polymer of this colloid layer. Some radiation may pass through the edge strip and return to the second medium.
At this time, the radiation will be reflected again in the second medium, and this process will be repeated until the colloid layer on the edge banding strip absorbs all the radiation. As the laser irradiates, the light energy is converted into a large amount of heat energy, the special polymer coating is activated, the colloid layer appears macroscopically molten, and the adhesion performance reaches its best. At this time, the pressure roller device should immediately separate the edge banding strip from the workpiece. Compacting, the two are perfectly bonded together to complete the edge-sealing process.
It should be noted that the second medium used must have a higher optical density than ordinary media. The A side of the second medium must have a high transmittance for laser rays, and the B side needs to be coated with a special coating. A layer of coating is necessary to ensure that the laser emitted by the diode has a high reflectivity so that the propagation direction of the high-output laser radiation beam can be changed through the refraction and reflection of light, ensuring that the radiation from the radiation source can be accurately guided to the edge sealing On the strip.
On the radiation entrance side of the second medium, a mobile device for forming a laser beam is set up, and its radiation edge is equipped with a deflection device. The deflection device has multiple deflection surfaces to ensure the direction adjustment of the laser beam.
A cooling device needs to be installed in the driver of the mobile device so that the radiation beam can be cooled at the outlet and the beam temperature can be adjusted according to the processing requirements. The rational use of the second medium allows the rays not absorbed by the edge banding strip to be reused in time. The utilization rate of the radiation source is improved, and the edge banding efficiency is improved.
This indirectly reduces the production and processing costs and reduces the radiation discharged into the environment. The safety of laser edge banding equipment is increased.
3 Conclusion
Laser edge banding technology is a breakthrough in sheet edge banding. It optimizes the overall processing process, improving the edge banding quality and increasing the production speed. The main problem at this stage is that the processing cost of laser edge banding needs to be lowered, making it unacceptable to most small and medium-sized processing companies. By improving the laser system on the laser edge banding machine, the processing cost can be reduced to a certain extent.
In contrast, the accuracy of processing and the perfection of edge banding are ensured. The wide applicability of laser edge banding to materials means that this technology will be increasingly used in processing and production and will be loved by consumers.