Postpress: Analysis of factors that affect die-cutting performance

1. Influence of processing quality and assembly accuracy of each component

Judging from the individual technical parameters of the die-Cutting Machine, the difference between domestic die-cutting machines and foreign die-cutting machines is small, but there is a large gap between the die-cutting speed, accuracy, stability, and reliability. Mainly due to the limitations of the domestic manufacturing technology, many parts of the rough processing, the error range is relatively large, the assembly is also not accurate enough, resulting in the machine is not running fast enough and die-cutting accuracy is not high enough. For example, the matching and manufacturing accuracy between the intermittent mechanism and the main drive system and the chain row directly affects the speed of the machine. If the assembly accuracy is not enough, the precision of the cutting will be affected and the noise will increase. Another example is the matching of the pressure mechanism of the toggle lever and the moving platform. Because there is relative movement, there must be a gap. If the gap is determined irrationally, it will cause impact load, generate vibration, cause noise increase, and then affect the speed and precision of die cutting.

2. Effect of paper feeding speed and positioning mechanism

At present, the paper-feeding method commonly used at home and abroad is continuous paper feeding, that is, there is always a partial overlap between the front sheet and the back sheet. This method is smooth and fast. However, the speed of paper feeding is high, and the paper will have a large impact force when it is against the forward gauge, which will easily cause the paper to curl or bounce, resulting in inaccurate positioning and reduced accuracy. Therefore, an ideal die-cutting machine should minimize the speed of paper movement on the paper-feeding table while ensuring the cutting speed, thereby reducing the paper's impact on the front gauge, ensuring accurate positioning, and improving die-cutting precision.

The print is positioned by the positioning mechanism prior to die cutting. The positioning mechanism of the die cutting machine consists of a front gauge, a side gauge, a front abutment mechanism, and a backrest gauge mechanism. The positioning mechanism has a crucial influence on the accuracy of the die cutting machine.

Before the paper enters the gripper row, it is positioned by the front gauge and the side gauge. The role of the front gauge is to longitudinally position the paper. If there are multiple front gauges installed, only two positioning functions are used. Accurately on the same level, it must play an auxiliary role; otherwise, it will cause over-positioning and reduce the positioning accuracy. The height of the front gauge is adjustable, the height of the gauge is moderate, the height of the front gauge is moderate, and the front gauge is adjusted too high, which can cause the front edge of the paper to bend, which affects the positioning accuracy. The front gauge is adjusted too low and the paper cannot reach the front gauge. Does not achieve positioning effect. Lateral gauges are used for lateral positioning of the paper. There are usually two side gauges, but only one when working. In order to ensure accurate positioning, the side pull roller pressure should be appropriate. Pulling the paper roller too much pressure will cause the side of the paper to bend; if the pressure is too small, it may cause the paper to not be pulled out, affecting the positioning accuracy. In addition, due to the fixed positioning time, the positioning time of the front gauge and the side gauge will also affect the positioning accuracy, and thus affect the accuracy of die cutting, so we must reasonably allocate the positioning time of the front gauge and the side gauge.

After the paper is positioned, the paper is conveyed to the molded part by the feed roller for die-cut indentation. The feed line is fixed on the intermittent conveyor chain. To ensure the precision of die cutting, it must stay in the exact position. Therefore, when the feed dog row moves to the end of the paperboard, the front abutment mechanism pulls the tooth row shaft to a determined position and completes the front positioning of the feed dog row. When the transport chain evacuates the transporter between the platform and the lower platform of the molded part, the rear abutment mechanism toggles the row of teeth to the positioning point for accurate positioning. Therefore, the front gauge and back gauge mechanism directly affect the die cutting accuracy.

3. Influence of the intermittent mechanism, chain, and paper feed

The movement of the feed roller is an intermittent motion controlled by an intermittent mechanism. Flat press die cutting machine intermittent mechanism generally adopts parallel indexing cam mechanism. Compared with other intermittent mechanisms, it has the following characteristics: reliable movement; smooth transmission; follower movement law depends on the contour of the cam; the dial can achieve the desired Movement and good dynamic performance, the positioning of the turntable in the interval is completed by the curve groove of the cam, no additional positioning device is required. When the machine is running at a high speed, the cam profile is affected by the speed, acceleration, inertia size and direction of the follower, causing machine vibrations. This vibration is transmitted to the chain, and the rapid start and stop can cause jitter in the feed bar row. This affects the speed and accuracy of the entire machine. Therefore, on the basis of dynamic analysis, it is also necessary to dynamically design the cam profile to ensure the smooth movement of the intermittent mechanism itself.

The chain is a flexible piece and the pins are connected between the links. Therefore, the pitch error is large. For a long time, due to the wear, the chain will naturally elongate, and the error will increase, which will cause instability to the transmission, affect the position of the positioning point of the paper feeding tooth row, and thus affect the precision of die cutting. When working, the chain should not be too tight or too loose. Too tight the chain wears up and shortens the service life of the chain. Too loose the chain is vibrating and the noise increases.

The paper feed is used to transport paper. The flat press and die cutting machines use solid tooth rows, which are easily deformed during high-speed operation of the machine, affecting the positioning accuracy, and because of its high quality, it is in the process of rapid transit and instantaneous stop. , Due to large inertia, it is not easy to stop, affecting the stability of machine operation and die-cutting accuracy. Therefore, changing the solid tooth row into a higher hardness hollow row is the direction of future development. In addition, the grippers generate noise during work, causing vibrations in the row of teeth, which in turn affect the speed of die cutting, but also affect other components. Generally, the following measures can be taken: (1) The plug clearance should be as small as possible; (2) The gripper should be staggered with the regulatory plate; (3) The dental caries angle should be adjusted appropriately. In addition, the pressure of the gripper will affect the precision of die-cutting, and the pressure of the gripper will cause the paper to be damaged; if the pressure is too small, it will cause the paper to slip or slip during the transfer process; the pressure between the grippers is not Both may cause the paper to be skewed when it is die cut.

4. The influence of the chain guide

During the die-cutting process, the paper is driven through the chain. In addition to the chain wheel and the sprocket, the chain passes through and rotates. The guide rail positions it and controls the direction of movement of the chain and the teeth row. Therefore, when installing and debugging the guide rail, it is necessary to ensure that the guide rail is of appropriate thickness and can be embedded in the chain. The distance between the upper and lower guide rails must ensure the smooth passage of the chain. If the distance is too small, it will increase the transmission resistance and affect the transmission speed. In severe cases, it may even damage the machine. If the distance is too large, the chain will easily jump during movement and affect the transmission accuracy. Impact die-cutting accuracy. In addition, the trajectory of the guide rail and the length of the chain have a certain influence on the performance of the machine.

5. Influence of the transmission system

The main drive system of the die-cutting machine is driven by the motor to drive the worm and the worm gear. The transmission performance of the main drive system has a direct or indirect influence on the cutting speed and accuracy. The worm gear is a kind of gear, and the gear transmission has the characteristics of smooth transmission, strong bearing capacity, good thermal processability, and high efficiency. The most common transmission gears are spur gears and helical gears. Compared with the two, the helical gears have better stability and coincidence coefficient. At present, helical gears are widely used in die-cutting machines, but their pressure angles will affect the smoothness of their transmission. When the worm gear and the worm mesh at the indexing circle, the backlash between the gear teeth and the gear teeth is suitable, the worm gear is stable, the lubrication is sufficient, and the worm gear is in the best working condition. Otherwise, the backlash is too large, will make the worm gear drive unsteady, causing vibration; the backlash is too small, is not conducive to the flow of lubricating oil, accelerate the wear of the gear, when serious worm gear and worm will mesh "top teeth", affect the transmission Accuracy, in turn, affects die-cutting speed and accuracy.

6. Influence of pressure mechanism

Die cutting is done under pressure, so the most important mechanism of the die cutting machine is the pressure mechanism. At present, the most used pressure mechanism in China is a double toggle mechanism, which has a transmission characteristic that the active platform can reach the highest limit position (also referred to as “dead point”) twice during one revolution of the crank. During die-cutting, the upper platform consisting of the upper plate frame and the die-cut plate does not move, and the lower platform gradually rises from the lowest point to the highest point through the main drive system and the toggle pressure mechanism and reciprocates. When the moving platform reaches the "dead-center", the die-cutting pressure is maximum. At this moment, the elbow is straight and the pressure will be transmitted to the base vertically. The connecting rod and the crank are not subjected to force, which effectively reduces the load peaks of the connecting rod and the crank. In order to ensure the quality of die-cutting, the entire platform should be stressed evenly when pressurized. Therefore, the working surfaces of the upper and lower platforms must be parallel. Therefore, the reasonable design and optimization of the length of the components are particularly important. If the design is unreasonable, unfavorable factors such as non-uniform die-cutting pressure and excessive idle stroke will affect the speed and accuracy of die-cutting.

7. Influence of die-cutting plate, die cutter and rubber strip

The die-cutting mechanism is the core of the die-cutting machine, and the die-cutting plate and the die-cutting knife and the indentation line are the basic parts of the die-cutting. To ensure high-precision die cutting, it is necessary to use high-quality die-cutting plates, die-cutting knives, and indentation lines.

Good die-cut media requires uniform density, light weight, high hardness, good flexibility, ease of processing, good flatness, strong, not easily deformed. And require die cutter, indentation line embedded die-cut version of the performance is reliable and stable, can ensure that the replacement die cutter, indentation line after the new die cutter, indentation line can still be combined with the die-cut version. At present, most domestic large and medium-sized printing companies use laser die-cutting indentation plates. Although this plate is simple and convenient for loading, it is subject to deformation due to changes in ambient temperature and humidity, which affects the accuracy of die-cutting. In addition, due to the relatively large die-cutting pressure, if the size of the layout is too large and the version of the plate is not used or the plate is not firmly mounted, lateral movement of the plate can easily occur during the production process. In addition, under the great pressure, the horizontal version of the plate may be deformed, and the die-cutting blades are liable to be bent and other undesirable phenomena, resulting in changes in the specifications of the die-cutting plate and affecting the precision of die-cutting.

With the advent of packaging materials, product diversification and unique packaging designs, high-quality die cutters for different die-cutting materials have become a necessary condition for ensuring die-cutting accuracy. The quality of the die cutter mainly depends on the sharpness of the knife edge, the height error of the entire knife, and the situation of the big knife bend. The sharper the knife edge, the smaller the height error of the entire knife, and the smaller the knife bending, the better the quality of the cutting knife. In addition, the thickness of the die cutter must be uniform, and the uneven thickness or beyond the error range will cause the insert to be difficult, deformed, or the cutting line too loose, which will affect the precision of die cutting. The height of the die cutter varies depending on the die-cut packaging material. For example, when the packaging material is a double corrugated paperboard, a peak knife is used; when the packaging material is a single corrugated paperboard, a cardboard, or a thinner paper, the low-peak knife has good stability.

In order to ensure the smooth running of paper, it is necessary to stick a rubber strip at the main knife line, and use the elastic restoring force of the rubber strip to push the printed product from the knife to prevent the printing material from sticking during die-cutting and indentation. When selecting a rubber strip, its height and thickness should be determined according to different products. Usually the height of the rubber strip is about 1~3mm higher than the die-cutting blade, and the specific height should be determined depending on the printing materials. If the rubber strip is too high, the rubber strip may easily hit the warped paper surface when the pressure is applied, causing the paper to shift and cause die cutting inaccuracy. In addition, the hardness of the rubber strip should also be moderate. If the rubber strip is too hard, the die-cutting knife will have a large compressive force when die-cutting, which will cause the knife-edge deformation and affect the product quality; if the hardness of the rubber strip is too small, the rebound force Insufficient, may cause "stencil" or "scattered". Therefore, the thickness and height of the rubber strip should be reasonably selected according to the printing materials, and the rubber strip should be pasted in an appropriate position to ensure that the elastic force is moderate and the adverse effect on the precision of the cutting is reduced.

There are many factors that affect the speed and accuracy of die-cutting. To improve die-cutting speed and accuracy and the stability and reliability of the die-cutting machine, in addition to optimizing the mechanism for designing parts, precision machining of parts and components, and the rational selection of the basis for each part Outside the material, the ideal assembly accuracy is also crucial to improve the stability and reliability of the complete machine.

In addition, the accuracy of equipment installation and commissioning also directly affects its production speed, product quality, stability and reliability. Improper installation and debugging will not only reduce the speed and accuracy of the whole machine, but also bring unexpected consequences and troubles to actual production. Therefore, it must be given enough attention. The quality of machine installation and commissioning is related to the actual operator. Therefore, it is very necessary to actively train employees and improve their quality and technical level.

Source: Chenyi Online

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