Setting and adjustment of die casting process parameters

In die casting production, the setting and adjustment of machine process parameters directly affect the quality of products. One parameter may cause multiple defects of the product, while the same defect of the same product may be related to multiple parameters. It is required to carefully analyze the impact of changes in process parameters on the casting formation during trial die casting production. Die casting manufacturers usually assign special personnel to set and adjust machine parameters.

1、 Setting and Adjustment of Main Process Parameters of Horizontal Cold Chamber Die Casting Machine

The following takes the CSC280 horizontal cold chamber die-casting machine produced by Jiexun Mechanical Equipment Co., Ltd. as an example to explain the setting of main process parameters in die-casting production.

1. Setting of main process parameters

(1) Feeding time: the feeding time is in direct proportion to the casting wall thickness. For large casting quality, slow injection speed and long time required, the feeding time can be appropriately increased, generally more than 2s. The movement time of the two speed punch is equal to the filling time.

(2) Opening time: generally, the opening time is more than 2s. The opening time of the thicker and thinner die castings is longer than that of the thinner die castings, and the opening time of the complex die castings is longer than that of the simple die castings. At the beginning of the adjustment, the time can be a little longer, and then shortened. Note that the working procedure of the machine is to open the mold (mold) first, and then open the safety door, so as to prevent the casting not completely cooled from splashing and injuring people.

(3) Ejection delay time: on the premise of ensuring that the product is fully solidified and molded without sticking to the mold, the ejection delay time shall be reduced as much as possible, generally more than 0.5s.

(4) Jacking delay time: the jacking delay time shall be reduced as much as possible under the premise of ensuring the smooth removal of the casting, generally more than 0.5s.

(5) Energy storage time: generally about 2s. When setting, operate the machine for automatic circulation. Observe whether the pressure can reach the set value at the end of the energy storage time. Reduce the energy storage time as much as possible on the premise that the set pressure can be reached.

(6) Number of thimbles: set the number of thimbles according to the requirements of the mould.

(7) The pressure parameters shall be set to minimize the working pressure on the premise that the machine can work normally and the casting product quality can meet the requirements.

The following factors shall be considered when selecting and setting injection specific pressure:

1) The structural characteristics of die castings determine the setting of pressure parameters.

① Wall thickness: thin wall parts, injection pressure may be higher than that; For thick wall parts, the pressurization ratio can be higher.

② Complexity of casting geometry: for complex parts, high specific pressure shall be selected; The shape is simple, and the pressure is lower.

③ Process rationality: good process rationality, lower than pressure.

2) The characteristics of die casting alloy determine the setting of pressure parameters

① Crystallization temperature range: large crystallization temperature range, select high specific pressure; The crystallization temperature range is small and the specific pressure is lower.

② Liquidity: good liquidity, select a lower injection specific pressure; Poor liquidity, injection pressure is higher than pressure.

③ Density: high density, injection specific pressure and pressurization specific pressure shall be high; The density is small, and the injection specific pressure and pressurization specific pressure are selected to be smaller.

④ Specific strength: the specific strength is required to be greater, and the pressure ratio is higher.

3) The gating system determines the setting of pressure parameters

① Runner resistance: the runner resistance is large, mainly due to the long runner, many turns, and the small thickness of the inner gate under the same sectional area. The specific pressure for pressurization should be larger.

② Heat dissipation speed of runner: the heat dissipation speed is fast, and the injection pressure is higher than the pressure; The heat dissipation speed is slow, and the injection pressure is lower than the injection pressure.

4) The setting of pressure parameters determined by the overflow system

① Exhaust duct distribution: the exhaust duct distribution is reasonable, and the injection specific pressure and pressurization specific pressure are selected higher.

② Sectional area of exhaust duct: the sectional area of exhaust duct is large enough, and the pressure injection is higher than the pressure separation.

5) The inner gate speed is required to be high, and the injection speed is higher than the press dressing speed.

6) The temperature difference between the temperature alloy and the die-casting mold (die) is large, and the injection pressure is higher than the pressure; The temperature difference is small, and the injection pressure is lower than the pressure.

(8) Setting of injection speed

The injection speed is divided into slow injection speed (also known as the first speed of injection), fast injection speed (also known as the second speed of injection), and pressurized movement speed.

The slow injection speed is usually selected within the range of 0.1~0.8m/s, the movement speed increases gradually from 0, and the fast injection speed is proportional to the inner gate speed, which is generally adjusted from low to high. Under the condition that the casting quality is not affected, the lower fast injection speed, namely the inner gate speed, is appropriate.

The pressurization movement takes a very short time. Its purpose is to compact the metal and make the casting structure compact. When adjusting the pressurization speed, it is generally observed that the pressure indication of the injection pressure gauge rises evenly in a diagonal line during the pressurization movement, and the die casting products are free of looseness.

(9) Position adjustment principle of one speed and two speed transfer inductive switch

1) The conversion of one speed and two speed movement shall be carried out after the injection ram passes through the pouring port of the pressure chamber

2) For small thin-walled castings, the first speed is generally shorter and the second speed is longer

3) For large castings with thick wall, the first speed is generally longer and the second speed is shorter

4) Adjust the conversion point according to the casting quality (such as flash, under casting, bubble, etc.).

(10) Adjustment of metal liquid temperature The alloy liquid temperature can be displayed and set from the panel of the electrical box of the machine. The pouring temperature of various alloy liquids is different, and the pouring temperature of thick wall castings is lower than that of thin wall castings for products with different structures of the same die casting alloy.

(11) Selection of pouring amount Each pouring amount shall be selected so that the thickness of the residual material produced is within the range of 15~25mm, and the ladle amount of each alloy liquid shall be stable.

(12) The mold temperature control refers to the temperature when the die casting mold (mold) is closed. For different alloy liquids, the mold temperature is different, generally limited to 1/2 of the alloy solidification temperature. In die casting production, the most important thing is the stability and balance of the mold (die) working temperature, which is one of the important factors affecting the quality and efficiency of die castings.

The process parameters of each action of the hydraulic system of the machine, such as pressure, speed, stroke, starting point and ending point, time of each action and total time of the whole working cycle, have certain technical parameters. The commissioning personnel must be familiar with the technical performance of the machine, carefully analyze the structure, function, performance and commissioning range of all components according to the hydraulic system diagram, find out the actual position of the hydraulic components on the equipment, and understand the mechanical, electrical Hydraulic interrelationship.

2. Adjustment of main process parameters

(1) Precautions for machine adjustment

1) Only the adjustable parameters indicated in the machine operation manual can be adjusted. The pressure regulation shall be carried out according to the requirements of the operating instructions, and shall not be greater than the specified pressure value. Try to prevent excessive pressure regulation, which may lead to increased oil temperature or damage to components.

2) It is not allowed to adjust the working pressure of the system when the actuating elements (hydraulic cylinder, hydraulic motor) are in motion.

3) Before pressure regulation, check whether the pressure gauge is damaged. If abnormal, adjust the pressure after the pressure gauge is replaced.

4) Before pressure adjustment, loosen the adjusting nut on the pressure regulating valve to be adjusted. After pressure adjustment, tighten the fastening nut of the adjusting screw to avoid loosening.

(2) Adjustment skills of main process parameters

1) The speed of the opening (mold) and closing (mold) slow speed sections is controlled by the adjusting screw on the left side of the slow oil valve. Turn the screw clockwise to slow down the opening and closing (mold) slow speed section, and turn the screw counterclockwise to speed up the opening and closing (mold) slow speed section. After proper adjustment, tighten the fixing nut.

2) Adjustment of opening and closing (mold) constant speed (i.e. fast speed) section

① The speed of the open type (mold) constant speed section is controlled by the adjusting screw on the right side of the open and close type (mold) reversing valve. If the screw is tightened clockwise, the speed will slow down; if the screw is loosened anticlockwise, the speed will speed up. After proper adjustment, tighten the fixing nut.

② The speed of the closing (mold) constant speed section is controlled by the adjusting screw on the left side of the opening and closing (mold) directional valve. Turn the adjusting screw clockwise to slow down the speed of the closing constant speed section, and turn the adjusting screw counterclockwise to speed up the closing constant speed section. After proper adjustment, tighten the fixing nut.

3) Pressure regulation of low-pressure large flow pump

Start the machine for automatic circulation, manually rotate the adjusting screw on the dual pump flow control valve to adjust the low pressure to a certain value (generally 5 × 106Pa (about 50bar), the low pressure value is read from the low pressure indicator. After proper adjustment, tighten the fixing nut.

4) Adjustment of the two speed working pressure of the feed

The working pressure of the two speed feed is adjusted by the adjusting screw that controls the pressure of the two speed feed. The pressure can be adjusted by manually rotating the adjusting screw on the pressure reducing valve. The pressure indication is read from the two speed feed pressure gauge. This pressure is the feed pressure in the two speed feed movement. The specific adjustment steps of DCC400 horizontal cold chamber die-casting machine are as follows:

① Loosen the adjusting screw on the stop valve to unload the two speed accumulator and then tighten it.

② Unscrew the fastening nut on the adjusting screw of the pressure reducing valve.

③ While holding down the pressure button by hand, slowly adjust the adjusting screw on the pressure reducing valve, and observe that the pointer on the pressure gauge reaches the required value (maximum 1.4 × 107Pa (140bar)).

④ Tighten the fastening nut on the adjusting screw of the pressure reducing valve.

5) Adjustment of working pressure of supercharging movement

The working pressure of the boost movement is regulated by the adjusting screw on the pressure reducing valve that controls the boost accumulator. Turn the adjusting screw on the pressure reducing valve by hand to adjust its pressure. The pressure indication is read from the boost pressure gauge. The specific adjustment steps for boosting pressure of DCC400 horizontal cold chamber die-casting machine are as follows:

① Loosen the adjusting screw on the stop valve to unload the booster accumulator and then tighten it

② Unscrew the fastening nut on the adjusting screw of the pressure reducing valve.

③ While pressing the pressure button, adjust the adjusting screw on the pressure reducing valve, and observe the pointer of the pressure gauge until it reaches the required value.

④ Tighten the fastening nut on the adjusting screw of the pressure reducing valve.

6) Pressure regulation of boost control accumulator

① Loosen the adjusting screw on the stop valve to unload the booster control accumulator before tightening.

② Unscrew the fastening nut on the adjusting screw of the pressure reducing valve.

③ While pressing the pressure button, adjust the adjusting screw on the pressure reducing valve, and rotate the screw clockwise to increase the pressure; Rotate the screw counterclockwise to reduce the pressure. Observe that the pointer of the pressure gauge reaches the required value (6 × 106Pa (60bar).

④ Tighten the fastening nut on the adjusting screw of the pressure reducing valve.

7) Adjustment of one speed of material injection The one speed of material injection is controlled by the left side of the one speed adjustable cartridge valve. Adjusting the screw can change the one speed of movement: rotate the screw clockwise to reduce the speed; Rotate the screw counterclockwise to increase the speed.

8) Adjustment of the second speed of feeding

The speed of the two speed injection valve is controlled by the adjusting handwheel on the two speed cartridge valve. Rotate the handwheel manually to obtain different speeds: rotate the handwheel clockwise to reduce the speed; Rotate the handwheel counterclockwise to increase the speed.

9) Adjustment of pressurization speed The pressurization speed is controlled by the adjusting handwheel on the cartridge valve. Different speeds can be obtained by rotating the handwheel manually: the speed decreases when the handwheel is rotated clockwise; Rotate the handwheel counterclockwise to increase the speed.

10) Speed adjustment of the ejection return hammer The speed of the ejection return hammer movement is controlled by the right side of the ejection switchable valve. Adjusting the screw can change the speed of the return hammer movement: Rotate the screw clockwise to reduce the speed; Rotate the screw counterclockwise to increase the speed.

11) Adjustment of one speed and two speed travel The length of one speed and two speed travel is determined by the position of the two speed induction switch. The length of the two sections of travel affects the forming quality of the casting, such as under casting, flash, bubble, etc. It is generally adjusted according to the product quality in the trial die casting production.

2、 Setting and Adjustment of Die Casting Process Parameters of Hot Chamber Die Casting Machine

1. Setting of main process parameters

(1) Slow injection speed of injection punch

The slow injection velocity shall be as low as possible to reduce the pressure loss caused by the friction and scuffing of liquid metal in the flow process. At the same time, it can keep the metal liquid in contact with the wall surface and avoid air mixing. It is recommended to take 25%~35% of the maximum injection speed of the die-casting machine. The injection time is 0.5~2s, which is too long, and it is easy to cause metal condensation at the nozzle.

(2) The setting of the starting point of the fast injection speed (two speed) of the injection punch The setting of the starting point of the fast injection speed must ensure that the liquid metal flow speed can reach the required value before reaching the inner gate (it has been set in the mold design stage). The starting point is usually 10~70 mm down from the starting point of the injection punch, depending on the die casting machine model and die.

When the starting point is too late, part of the casting cavity is filled at low speed, and the surface quality is seriously affected. If it is too early, the exhaust is insufficient, and the energy of the accumulator is used in advance, which affects the quality of the casting. The ideal position of the turning point from one speed to two speeds is when the liquid metal moves smoothly near the mold inlet.

(3) Setting of fast injection speed (two speed)

Atomization filling is the best mode for filling the mold cavity with liquid metal. At this time, the velocity of liquid metal entering the mold cavity at the gate must be greater than 35m/s. 45~60 m/s for thin wall cast alloy castings.

(4) Setting of filling time

In order to obtain castings with smooth surface and clear contour, it is required to fill the entire workpiece cavity in a very short time. According to the characteristics of the cast alloy workpiece, the filling time should be within 6~40 ms. When the die casting is a mechanical workpiece or the casting surface needs electroplating, the filling time shall be less than 20 ms and the painting time shall be less than 40 ms.

(5) Setting of die casting specific pressure

The die-casting pressure of thin-walled parts, electroplated parts, bearing parts and complex parts should be higher; The runner resistance is large, the runner is long, the direction of rotation is more, the specific pressure should be larger, the internal gate speed is required to be higher, and the specific pressure for die casting should be larger. 13~20 MPa shall be selected for general castings, and 20~30 MPa shall be selected for castings with high requirements.

(6) Setting of holding time and holding specific pressure

Long pressure holding time reduces production speed and affects production; The short holding time makes the shrinkage of the casting in the solidification process can not be fully compensated and reduces the mechanical properties of the casting. The holding time is determined according to the wall thickness and the observation of whether there is a cavity at the inner gate, which should generally be greater than 0.5 s.

The pressure holding ratio is too high, and flash is easy to occur; The holding pressure ratio is too low, and the casting is easy to form voids. The normal holding pressure ratio is 14~35 MPa.

2. Adjustment of main process parameters Take Lijing hot chamber die-casting machine as an example to introduce the adjustment method of main parameters.

(1) Slow adjustment of open type and close type

The opening and closing slow speeds are uniformly controlled by the adjusting screw on the right side of the slow oil valve. If the screw is tightened clockwise, the opening and closing speed will increase slowly; if the screw is loosened counterclockwise, the opening and closing speed will decrease slowly. After proper adjustment, tighten the fixing nut.

(2) Adjustment of open type and closed type constant speed

1) The closing constant speed is controlled by the screw on the left side of the slow oil valve. If the adjusting screw is tightened clockwise, the closing speed will slow down; if the adjusting screw is loosened counterclockwise, the closing speed will speed up. After proper adjustment, tighten the fixing nut.

2) After the closing constant speed meets the requirements, the opening constant speed can be adjusted. The open type constant speed is controlled by the screw on one side of the open type constant speed oil valve. If the screw is tightened clockwise, the opening speed will slow down; if the screw is loosened anticlockwise, the opening speed will speed up. After proper adjustment, tighten the fixing nut.

(3) Adjustment of feed pressure

1) Set the feed pressure:

① Turn the adjusting hand wheel of the pressure reducing valve counterclockwise to make the pressure reducing valve