Abstract: Traditional three-plate die-casting machine uses clamping cylinder to push hinge mechanism, and generates clamping force through amplification effect of hinge mechanism. Size of clamping force is affected by many factors, and it is difficult to adjust appropriate clamping force. Clamping force of traditional two-plate die-casting machine is directly provided by four large clamping cylinders installed at tail of two plates. Guide column passes through piston hole of clamping cylinder. Diameter of a single cylinder is large, cost is high, it is difficult to assemble and maintain. Two-plate machine with a multi-structure clamping cylinder structure invented in this paper divides a large cylinder into several small cylinders and arranges them around guide column. It is easy to assemble and maintain, and cost is low.

Traditional die-casting machine's clamping mechanism is a three-plate five-link hinge clamping mechanism. It generates clamping force by amplifying force of clamping cylinder through hinge. Compared with two-plate type mold opening and locking mechanism, shortcomings of this mechanism are mainly as follows: 1) Mechanism has three plates, so weight of mechanism is large and length direction is also large; 2) Its force is amplified and transmitted through a five-link machine hinge, which is complicated to calculate; 3) Clamping force is greatly affected by change of mold temperature, and mold parallelism is required to be high; 4) There are many moving parts, many moving pairs that wear each other, and maintenance workload of machine is large.

Two-plate die-casting machine has only two plates, head plate and second plate. At four corners of tail of second plate, there are four clamping cylinders symmetrically distributed, and guide column passes through hole in the center of clamping cylinder piston. See Figure 1.

 

Clamping cylinder of traditional two-plate die-casting machine includes following large parts: clamping cylinder body, clamping piston, clamping cylinder cover, brake sleeve, brake block, rear locking cylinder, etc., as well as related guide columns, second plates and other parts. See Figure 2.

 

Cylinder body and cylinder cover of mold locking cylinder are fixed to second plate by screws. Mold locking piston is a double-rod structure. Diameter d1 on the side close to second plate is smaller, and it forms a mold locking cavity with inner diameter D of mold locking cylinder cylinder body; diameter d2 on the side away from second plate is larger, and it forms an open mold cavity with inner diameter D of mold locking cylinder cylinder body; tail end of diameter d2 side is fixed to mold locking piston by two open-edge rings. Two open-edge brake blocks are installed in brake sleeve. Movement of brake block is pushed by extension and contraction of rear lock cylinder piston rod, so as to realize meshing and separation of tooth grooves on brake block and tooth grooves on guide column. Position of piston in cylinder is read by mold locking stroke control device. Mold locking stroke control device is shown in Figure 3.

 

See Figure 2. Piston rod of rear lock cylinder extends outward, driving two brake blocks to move outward, and brake blocks are separated from guide column. Two plates can be moved to any position and then stop. Rear locking cylinder conducts a trial brake. If it can smoothly engage with guide column, mold opening and locking action can be performed. If it cannot smoothly engage, piston rod of rear locking cylinder extends outward, brake block and guide column are separated. Mold opening cavity of locking cylinder is filled with oil. Because weight of two plates is large and there are other mechanisms to keep it immobile, clamping piston moves forward a specified distance (this distance is generally half of difference between slot width and tooth width), brake sleeve fixedly connected to clamping piston and brake block contained in brake sleeve also move forward, then brake is tested. Repeat above actions until brake can be held smoothly. After brake is held, brake block and guide column have no arbitrary relative axial movement (maximum relative axial movement is difference between slot width and tooth width). When mold is to be locked, locking cavity is filled with oil. Because locking piston cannot move backward, locking cylinder and two plates are pushed to move to the left, resulting in a locking action. Clamping force Flock = Plockπ(D2-d12)/4, where Plock is oil pressure of clamping cavity. As long as we accurately control oil pressure, we can accurately control clamping force of entire machine. When opening mold, oil enters mold opening cavity, clamping piston cannot move to the left, pulls cylinder cover, clamping cylinder and two plates connected together move to the right, thereby realizing mold opening action. Mold opening force Fopen = Popenπ(D2-d22)/4, where Popen is oil pressure of mold opening cavity. Figure 4 is a screenshot of three-dimensional model of structure.

For traditional single clamping cylinder structure, if it is for a large die-casting machine (with a clamping force of more than 6,000 tons), because real clamping force is only annular cavity in the middle, then diameter of a single clamping cylinder will be quite large (for a 6,000-ton die-casting machine, cylinder diameter reaches 1100mm). Cost of each part is very high, seals inside are not commonly used, price is high, and supply cycle is long, which has an adverse effect on production and maintenance. In response to these disadvantages, our company has developed a multi-cylinder clamping cylinder structure, which divides 4 large cylinders into 4 groups of cylinders, each group of cylinders consists of several small cylinders. As shown in Figure 5, there are 6 small cylinders in each group. For super-large die-casting machines, each group can also be divided into 8 or even more small cylinders. Structure of a single group of cylinders is shown in Figure 5.

 

As shown in Figure 5, a group of clamping cylinders consists of six small cylinders, which are distributed in a ring around guide column, and guide column just passes through space formed by these six cylinders. Two of six cylinders are double-acting cylinders, which are used to adjust position of rear locking block relative to guide column and for mold opening. When their right cavity is filled with oil, mold opening action is generated. Their left chamber and left chamber of single-acting cylinder are fed with oil at the same time, and clamping force is generated together under joint action of six cylinders. Moreover, clamping force is generated in 6 complete circular areas. Diameter of a single cylinder is less than 40% of diameter of traditional clamping cylinder. Among 24 cylinders of each machine, 16 single-acting cylinders are exactly same, and 8 double-acting cylinders are also exactly same. Although number of cylinders is large, types of parts are not many, which is conducive to improving production efficiency. Three-dimensional model of clamping cylinder of multi-cylinder structure is shown in Figure 6.

 

Structure of single-acting cylinder in this multi-cylinder structure is shown in Figure 7. This cylinder is simply used to generate clamping force, so structure is simple, that is, plunger, cylinder sleeve, cylinder head and guide sleeve of composite material between cylinder sleeve and plunger. Length of guide sleeve is large, so it can withstand a large eccentric load. It is ensured that under action of clamping force, even if two plates of die-casting machine produce a large deformation, under joint action of plunger, split nut behind clamping cylinder can still mesh well with guide column to ensure normal production of machine.

Structure of double-acting cylinder in this multi-cylinder structure is shown in Figure 8. Left cavity of double-acting cylinder - clamping cavity, generates a clamping force when oil is fed through inlet and outlet ports at the bottom of cylinder; right cavity - mold opening cavity generates a mold opening force when oil is fed. Generally speaking, mold opening force of die-casting machine is 15% of clamping force. In above-mentioned multi-cylinder clamping structure, number of double-acting cylinders is 1/3 of the total number. If diameter of double-acting cylinder piston rod is 0.7 of cylinder diameter, area ratio is about 1/2. At this time, mold opening force is about 1/6 of clamping force. It just meets our commonly used requirements for mold opening force. However, for deep cavity parts, clamping force of workpiece on mold is greater than that of simple structural parts, and the two-plate die-casting machine is often used to form deep cavity parts due to its structural advantages. Therefore, mold opening force of two-plate machine generally reaches about 20% of clamping force. Therefore, piston rod diameter of our double-acting cylinder should be slightly less than 0.7 times cylinder diameter, generally around 0.55 times. At this time, mold opening force is about 23% of clamping force.

 

See Figure 9 (a). Left side of guide column is fixed on head plate, and position of groove on guide column that engages with locking block is determined. When mold is closed, two plates move to the left together with locking cylinder and locking block behind. In extremely unfavorable conditions, piston rod of locking cylinder has completely entered cylinder, and locking block can no longer move to the left. At this time, left side of guide column annular groove and right side of locking block annular groove are aligned, see Figure 9 (b).

 

If locking block is inserted forcibly at this time, friction will inevitably occur between guide post and locking block, or even locking block cannot be inserted. This will affect service life of machine for a long time. In this way, piston of clamping cylinder can only extend a certain distance to the right, groove of locking block will move back one and mesh with groove of guide post. See Figure 9(c).
In order to make teeth of locking block smoothly inserted into groove of guide post, generally speaking, width of groove will be 5-6 mm wider than width of teeth. In this way, under ideal conditions, there is a gap of 2.5-3 mm on each side of teeth and groove. See Figure 9(d).
At this time, distance L2 moved by locking cylinder piston is one tooth pitch plus gap between teeth and groove. Machine also has a maximum clamping stroke L1. However, in this L1, the first small section is to make right side of teeth of locking block fit with left side of guide post groove, and no clamping force is generated. When maximum clamping force is generated, deformation of the entire clamping system will not exceed 10 mm. So far, we can determine maximum stroke L of clamping cylinder.
L=P+C+10+δ(1)
L-maximum stroke of clamping cylinder; P-pitch of annular groove; C-difference between groove width and tooth width (generally 5-8 mm, larger value for large machines); δ-safety margin, generally 10 mm for machines below 6,000 tons, 15 mm for super large machines above 6,000 tons.

Compared with traditional single cylinder structure, this multi-cylinder structure has following advantages: 1) Because cylinder diameter is small, processed parts and purchased parts are of regular size and are easier to obtain, and cost is greatly reduced. At the same time, two types of clamping cylinder structures for 1850-ton die-casting machines were made. Cost of multi-cylinder structure was 27% lower than that of traditional single-cylinder structure; 2) 6 cylinders in each group, cylinders and pistons are connected with pressure plates and other parts. After removing pressure plates, cylinders and pistons can be removed, each cylinder can be installed and disassembled separately. If there is a problem with any cylinder, just remove that cylinder, instead of removing the entire large cylinder and brake at the back as in traditional structure. It takes about 1 hour to install and disassemble a small cylinder, but like traditional large cylinder structure, it takes a day to remove all corresponding connecting parts to install and disassemble a cylinder.