Technical Inquiry-Mold Locking
Direct pressure clamping uses the "siphon principle" to cooperate with the hydraulic oil in the hydraulic cylinder to perform linear reciprocating motion. How to calculate clamping pressure? The area of the hydraulic cylinder multiplied by the unit pressure of the system = the clamping pressure. Since the large area of the hydraulic cylinder will affect the speed of opening and closing the mold, it is necessary to equip it with a small diameter fast-feed cylinder, usually two diagonal ones. A small number of them will use the method of connecting to the clamping high-pressure cylinder, which can also quickly achieve the purpose of quickly opening and closing the mold.
Our product design directly applies pressure to lock the mold, which has many advantages such as directness, simplicity, and no structural interference. As for how to lock it? The more advanced approach now is to lock the mold directly with a one-way valve after closing the mold and increasing the pressure. When opening the mold, just open the one-way valve first and then open the mold. This no longer requires additional power and has an energy-saving effect. If the design is good and the components are properly selected, there will be no pressure reduction. It can also extend the service life and reduce maintenance costs. You only need to replace the oil seal once in a while.
The movable template design of single-cylinder direct pressure clamping is simpler and its precision is much higher than that of the elbow type. However, due to the large area of the hydraulic cylinder of the single-cylinder direct pressure clamping, the production of castings, the heat treatment of the plunger, and the selection of oil seals are more difficult, especially when used in large machines. There will be more problems. At this time, it is recommended to choose a multiple cylinder method to improve the situation. In addition, because the single-cylinder direct pressure is directly applied to the movable template mold, the plane accuracy of the mold will be very important. If the precision is insufficient, it will directly affect the accuracy of the clamping, so special attention should be paid.
The four-cylinder locking direct pressure mold applies pressure to the mold through a radial template design, allowing the mold to be within a certain tolerance range. The multiple cylinders also have an automatic balance correction function, which does not affect the accuracy of the mold locking and has a wider range of applications.
This is the most common problem when using four-cylinder direct pressure clamping in the past. Most of them are impressions accumulated from bad experiences in the past. In fact, according to the Pascal hydraulic principle: when the liquid in the connecting pipe is pressurized by the plunger, the liquid will spread evenly in all directions of the connecting pipes of different shapes, and the pressure it bears will be evenly distributed. Therefore, in theory, no matter how many cylinders there are, the pressure will be evenly applied. Then why is there the phenomenon of uneven force application in the four-cylinder direct pressure clamping? In fact, it is due to the lack of precision in the processing of components, which can be improved by improving the processing quality.
What is a Tie Bar?
A tie bar is a horizontal rod-shaped component installed on a machine, primarily serving a pulling function. In injection molding machines, tie bars are used to balance the movement of the mold plates and withstand tensile forces. They are one of the key structural components of the injection molding system. Especially in the clamping mechanism, the performance of the tie bar directly affects the mechanical rigidity and system stability. Our products feature enhanced tie bar structures that significantly improve overall system efficiency.
In the injection molding machine mechanism, the tie bar functions as the device that pulls the movable platen. By increasing the safety factor in our tie bar design, the risk of breakage is virtually eliminated. During clamping and pressure release, our design minimizes vibration and stress on the tie bars. When paired with intelligent program-controlled pressure release systems, it provides an extra guarantee that the tie bars will never fracture, offering both inherent and adaptive design advantages.
〈Further Reading: What Is a "Tie Bar" in an Injection Molding Machine?〉
〈Further Reading: How to Choose an Injection Molding Machine? 8 Key Points to Help You Decide〉
First of all, it should be emphasized that not all Japanese injection molding machines use the elbow-type clamping design. There are also better direct-pressure clamping designs, such as the SODICK injection molding machine. About 20 years ago, the elbow-type clamping was gradually eliminated by Japanese injection molding machines, and they were replaced by direct-pressure and direct-pressure combined clamping methods. In recent years, the all-electric injection molding machines with energy-saving advantages have been launched, and the price cost is very high. In order to reduce costs, the elbow-type clamping has been revived. Why do all-electric injection molding machines use a toggle clamping design? The reason is that the driving servo motor is expensive, and you only need to use a toggle servo motor. In the final analysis, it is just about saving money.
The elbow type has many disadvantages, but the elbow type of all Japanese brands of all-electric injection molding machines has turned to conservative, only seeking low wear and tear and not affecting the clamping accuracy as much as possible, while sacrificing important design elements such as longer mold opening stroke, more beautiful shape and design creativity. The elbow has become just a tool for opening and closing the mold, and it has long lost the vigor and vitality of various elbow-type creative ideas competing with each other. We recommend SODICK, which insists on high quality and takes an uncompromising approach. It uses servo motor drive but still overcomes design difficulties and insists on using direct pressure composite clamping design.
Single-cylinder direct pressure mold clamping has disadvantages such as high difficulty in production and high cost, which is why the direct pressure composite four-cylinder mold clamping design was derived. For example, all medium-sized machines of Japan's TOSHIBA use composite direct pressure mold clamping, and the European giant HUSKY uses composite direct pressure mold clamping in multiple types, making it a leader in the industry. The structure of the compound direct pressure clamping is relatively complicated. Closing the mold includes closing the mold in place, calibrating the gear position, clamping the T-shaped tooth groove of the coring column, and pressurizing the mold to lock the mold. The time wasted is often as long as several seconds. Therefore, it is mostly used in medium and large machines above 300T (the net cycle time of small machines is less than 2 seconds and cannot afford to waste several seconds). In addition, due to the complexity of the structure, the durability of the components is greatly tested. There are still many doubts in the market after more than ten years of launch, and only a few manufacturers produce it in large quantities.
The four-cylinder direct pressure clamping design has the same advantages as the compound type multi-cylinder design, but it lacks complex movements, and even does not require mold adjustment programs and movements. It has the lowest failure rate and is even faster than the elbow type. It is applicable to large, medium and small models. It is currently the most well-integrated and mature chain-washing clamping design. The key to its success lies in the concepts of modularization and precision machining of the entire machine. It has low maintenance costs and almost no maintenance is required except for regular replacement of oil seals. The design durability is over 15 years.
Three Key Advantages of Low-Pressure Mold Clamping:
- There is no issue with tolerance gaps between the toggle links and bushings, nor is there resistance caused by heavy friction under load during movement. Additionally, since it does not rely on the toggle mechanism’s typical 20x pressure amplification, the fast clamping cylinder can be made smaller, significantly reducing the required pressure.
- Equipped with precision linear guide rails with a tolerance of just 0.01 mm, offering extremely smooth motion.
- Incorporates an electronic detection system that transmits signals at high speed (1 ms) when detecting fluctuations in pressure or flow, instantly halting the clamping action and opening the mold. This provides highly effective mold protection, which is a critical safety feature for injection molding machines.
This is also a problem of about 20 times magnification calculated by geometric angle when the elbow is locked at high pressure. On the one hand, the mold closing hydraulic cylinder is limited and cannot be enlarged arbitrarily. Therefore, the mold closing cylinder has only 1/20 of the clamping efficiency calibrated by the injection molding machine when the mold is not locked at high pressure. On the other hand, because the direction of the cylinder is fixed, there is less area space for the plunger in the mold opening direction, and the mold opening force is less than 1/20, so there will be the problem of insufficient mold opening force. These are problems that cannot be overcome by hydraulic elbow injection molding machines. Another problem when using it on large machines is that the mold closing cylinder cannot be made smaller due to restrictions, which makes the low pressure of mold closing too large, and the effect of mold protection is relatively low.
Direct pressure injection molding machines do not have this problem, because the mold closing and high pressure locking modes are controlled by different cylinders, and the fast-feed cylinder can be designed according to actual needs without limitation. If the design direction is correct, the area of the mold opening end will be larger than that of the mold closing end, and the mold opening force will naturally be greater than the mold closing force. This also has the benefit of being conducive to the accuracy of low-pressure mold closing.
No need to avoid it—because it simply doesn't happen. In a direct-pressure (hydraulic) injection molding machine, mold opening only involves releasing the clamping pressure and pulling back the moving platen, so vibration is never an issue. In contrast, toggle-type machines must forcibly pull open the fully extended toggle mechanism. At that moment, the energy stored in the tie bars is released and pushes against the toggle linkage, causing an instantaneous rebound—that's the source of vibration. The higher the clamping pressure, the more severe the vibration. This is also one of the main reasons why tie bars in toggle-type injection machines are more prone to breakage. While it’s possible to correct this vibration using software, doing so lengthens the cycle time, and overcorrection can reduce the effectiveness of the mold-opening force.
It has a lot to do with it. When burrs appear on products, the mold, machine, injection, and plastic parties often blame each other. As a production tool, the injection molding machine only needs to improve the template strength standard to easily clarify the responsibility for the burr problem. IDS's machine-making philosophy sets standards that are higher than the world's standards. Under the highest system pressure, the measured template deformation must be less than 0.02%. This standard is more than twice as strict as most injection molding machines. Unless the mold clamping force exceeds the machine's clamping force, the mold will never produce burrs, and the template is even less likely to break. Our advantage is that we can produce more precise products.
When the hydraulic elbow clamp is locked at high pressure, the actual speed drops sharply and the pressure rises sharply. This is a natural phenomenon caused by the magnification of geometric angles. During the working stage, a burst of air must be pressed and the roller is stretched to prevent the elbow from being rebounded by the elastic coefficient of the roller. This causes inaccuracy in the first starting position when implementing compression injection. When the compression starts, the range of pressure that can be applied is limited and inaccurate because there is no impact force to assist. Therefore, it is often absent in the field of compression injection. The first starting position of the all-electric elbow injection molding machine can be more accurate than the hydraulic type because it is supported by a ball screw. The accuracy of the initial compression is also better than the hydraulic type because it uses a load cell to detect pressure and does not require impact force to cooperate.
The direct injection molding machine is the most direct and effective when using compression injection because there is no interference caused by the change in geometric angle during elbow-type pressing. Not only is the first starting position completely accurate, but when starting compression, the purpose can be achieved by simply pressurizing the cylinder. It is currently the most ideal design for compression injection. Last year, Ides successfully developed high-speed compression injection technology, which is faster than the all-electric type. It was purchased by the Nano Research Laboratory of the Institute of Polymer Science, Academia Sinica, Taiwan, for the production of high-end nano screens. Currently, there are many application examples in ultra-thin injection products.
Most direct injection molding machines are designed to fill the high-pressure oil cylinder from the top down. In theory, it feels safer with the principle of free fall, but the disadvantage is that it requires an independent auxiliary oil tank to cooperate, which makes the appearance of the machine unsightly and the maintenance cost of an additional auxiliary oil tank is relatively high. In the design plan of the four-cylinder clamping mold of the Ides injection molding machine, in order to maintain the overall appearance, there is no space to put the oil tank on the top of the machine, so we adopt the method of pumping oil from the bottom up. Except for some minor problems of air embolism that need to be solved, because the principle is the same in theory, we are confident that we will achieve the same effect, which is as simple as sucking juice with a straw. It is not "bold", but we innovate and think more for our customers.
Direct pressure clamping uses the "siphon hydraulic principle". The action of filling the high-pressure cylinder is not completed by the pump. When the mold is closed at high speed by the fast-feed cylinder, the high-pressure cylinder is driven forward at the same time. At this time, the siphon effect naturally plays a role and brings the oil in the oil tank into the high-pressure cylinder simultaneously. This speed can be several to dozens of times faster than the pumping method, and no additional power is required. It is the most economical low-pressure and high-speed oil pressure transmission method.
The same principle is also applied from top to bottom. If it is only replenished by free fall, it is not only several times slower than pumping, but also dozens of times slower than siphoning. Moreover, it is easier to mix bubbles and cause air embolism. It looks safe because the oil-filled valve is switched in a full oil state, and air will never be mixed in this part. As for the method of sucking oil from bottom to top, it is possible that the circulating oil is not fully saturated when the oil-filled valve is switched, and it is more likely to mix air and cause air embolism, especially when the large machine absorbs a large amount of oil. If you are not sure that you can overcome it, you dare not use this method. This is the main reason why the market adopts the method of sucking oil from top to bottom. But as long as this problem can be overcome, you can use it with confidence. We are professional injection molding machine experts. Your professionalism is trustworthy. The appearance of the injection molding machine will also be more beautiful and the function can stand the test.
When setting up the mold, the material tube will rise up. Except for very few cases where the R12 riser shape of the mold is damaged or inaccurate, most of the time it is a mechanical structure problem, especially for injection molding machines that have been used for many years. This problem is more common and should not be simply regarded as inaccurate mold setting. The material tube seat is pushed by the shooting seat cylinder of the base, and it is used to support the mold riser when ejecting or seating. Because the straight line of the shooting seat material tube and the straight line of the base are parallel and have a distance, when the oil pressure of more than several tons of Tonf pushes to support the mold riser, the gap between the shooting seat and the base and the parallel distance will generate a mechanical "component force", which pushes the shooting seat and the material tube upwards. This is the main reason why "the material tube will rise when the mold is set".
For example: Most German injection molding machines use a structure where two injection cylinders pull the injection seat at the same level, so there will never be a force separation, and this situation will not occur no matter how long it is used. Most Japanese and Taiwanese injection molding machines are from the same source, so this phenomenon will occur, especially as the machine ages and wears out, which will further spread the "force separation" effect. The solution is to reduce the gap between the shooting seat and the base to improve the problem, as the inherent design defect cannot be changed. In terms of design, if the German series structure is not adopted, the parallel distance must be reduced as much as possible. The reduction of the trigonometric function value can greatly reduce the component force. In terms of structure, it is best to design a linear slide rail to achieve a near-zero gap and further reduce the possibility of tilting up. If it is other types of structures, it is necessary to strengthen the precision design and control of this part.
Origin of the Name "Corinthian Pillar"
The term "Corinthian Pillar" (Gēlín zhù) is a transliteration of the English "Corinthian pillar." In injection molding machines, the four long vertical columns used in the clamping mechanism are commonly referred to as “Corinthian pillars,” while in Taiwan they are colloquially known as “main pillars.” The name is not attributed to any inventor, as there is no specific physical or mechanical principle that would warrant such a designation. Instead, the term comes from the architectural style of the ancient Greek Corinthian order, which is known for its multiple tall columns. Since Western engineering terminology often stems from Greco-Roman architecture, "Corinthian pillar" became a natural reference to distinguish these long structural columns from more standard types.
What Is a Corinthian Pillar?
A Corinthian pillar is a horizontal bar-shaped mechanical component installed in machines, primarily serving a pulling or guiding function. In injection molding machines, its main role is to stabilize the movement of the platen and absorb tensile forces. It is one of the most critical components in the machine's clamping mechanism. The performance of the tie bar (Corinthian pillar) directly affects the rigidity and stability of the entire system. Our products enhance the structural characteristics of the tie bar, thereby significantly improving overall system performance.
〈Further Reading: Why Our Tie Bars Don’t Break〉
〈Further Reading: How to Choose an Injection Molding Machine: 8 Key Factors〉