Operation of mold

Clamping/ disconnection of mold must be smooth, without jerks, unwanted sounds. It is necessary to set parameters of the mold protection rationally, protecting tooling from damage in the case part or the gate is hanging. Before locking the mold to the required force (the force preventing the opening of the mold during the specific pressure produced by the injection molding machine), “the mold protection” is set, clamping pressure of movable half mold is lowered, and after passing the protection motion unchecked (5-10 millimeters to the contact of shaping parts), the mold is locked with the necessary effort. This processing method will extend the service time of the mold, helping to avoid hung parts, intrusion of foreign parts.

When working with a mold, it is recommended to use brass, copper chisels, and rubber hammer. After development of the program (cycle) it is necessary to block the water, and blow the cooling system channels with compressed air. Cooling duct and the surface of the mold should be dry.

Installation of the mold in injection molding machine

To operate the mold, it is necessary to choose an economical, suitable for its dimensions automatic molding machine with optimal parameters of clamping force. Before installing the mold, it is necessary to familiarize yourself with its drawings, make sure that the mold is making into dimensions (the distance between the columns, the minimum and maximum closed mold height, and the maximum motion of the movable plate), work out the question of fixing the mold to the plates of the machine, connecting of pushing system, the size of the centering ring. As a rule, the designer already has information at the initial design stage, for which molding machine the mold will be made.

The process of installation

For the installation of the mold, lifting mechanism with the appropriate class of use and loading is used. The molds is grabbed with belts and bring between the IMM columns, forcing it against the fixed plate so that the centering ring enters the tool bore of the fixed plate of the injection molding machine. The work is carried out with dead pump engine of injection molding machine. Next, the mold is fixed with clamping relating to the fixed plate, IMM pump motor is turned on and pass into manual mode, the plates are closed. Turn off the pump, attach the mold to the movable plate of IMM, each half of the mold must be fixed at least at four points. Disconnect the belts, turn on the pump and, in manual mode proceed to adjust the height of the mold. After adjusting the height, set the opening motion of the movable plate, set the mold clamping protection parameters. Connect the cooling or thermostatic system. Next, close the mold, the injection unit is brought until the snout touches the mold sprue bush. It is necessary to ensure adjoining nozzle with the bushing by adjusting the plasticization unit.

Installation of technological modes. Cycle of casting

After the mold is installed, the material is prepared, it is necessary to set the technological modes for manufacturing the product. Modes are selected empirically, depending on the design of the mold, the features of the polymer material, its thermophysical and rheological properties.

Casting temperature

The heating temperatures of the zones of the heating cylinder are differentiated, for materials with high MFI temperature are in the lower zone, for high-viscosity grades temperature range is in the upper zones. The heating of the heating cylinder is caused by means of electric tens. It is necessary to keep the time during which the polymer can withstand the temperature without thermal decomposition. It is necessary to avoid high temperatures.

Clamping of mold. Start of the cycle

Locking force of the mold is provided by the clamping unit of the injection molding machine. The structure of the clamping unit can be hydraulic, with a large diameter of the hydraulic cylinder or knuckle-joint. The locking force is measured in kN, and this parameter is usually entered by the manufacturer in the name of the injection molding machine. The locking force is set so as to exceed the force of opening the mold during injection and hold pressure.

Moving of the injection unit forward with pressing of nozzle to sprue bush

The main task of the injection unit is to melt the polymer, prepare a new dose, inject the material into the mold cavity of the mold and soak in the cooling process. There are three movements of the injection unit: operation without nozzle removal, nozzle withdrawal after injection, nozzle withdrawal after loading and decompression.

Injection

Movement of screw forward along the axis after setting a dose. To prevent over-flow of hot melt from the zone of packing into the loading zone, the screw design has a non-return valve. There are two stages during the injection:
-Filling of the mold. Pressure and speed of injection is set depending on the length of hot melt flow path and wall thickness of the product. Modes are selected smoothly in order to completely fill the cavity of the mold without defects in physical form. The maximum achievable parameters are limited by the technical characteristics for a specific injection molding machine, taking into account its wear.
- Compression of the hot melt after the filling of the mold.

Holding time under pressure

At the end of the filling of the mold, packing phase begins during the holding under pressure. During this period, volumetric and linear shrinkage is compensated by additional material - the point of the screw position in the pre-snout zone. The polymer is cooled from the walls of the mold.

Holding time for cooling without pressure

The time for cooling of the part is the dominant component of the total casting cycle. Depending on the processed polymer material the heat is supplied to the mold or removed. The thermostating affects the quality and economy of production of the part. The temperature of the product must be such that the part is not deformed during extraction and does not warp in the future. Relaxation of the material should be uniform. At the stage of "holding time" on cooling without pressure, the polymer finally hardens, and through the harden gate transfer of the pressure from the injection unit is not carried out. The pressure in the mold gradually decrease.

Loading

The loading stage begins with the holding moment for cooling, the screw rotating around its axis is pulled back, overcoming the pressure and moving the grains from the loading zone to the plasticization zone into the packing zone. Good homogeneity of the material is achieved through the "Back pressure" mode during material loading. To exclude spontaneous outflow of mass from the nozzle (open-type nozzle), "Decompression" is used - forcing the screw back after loading without rotation. The screw is pulled back for a short distance so as not to catch air, which is determined by experience.

Mold opening

The clamping unit opens the mold. The movable plate is retracted to a predetermined opening stroke to allow unchecked extraction of the cast from the mold. Casting is extracted by the pushing system. After the extraction of the part, the cycle is repeated in automatic or semi-automatic mode.

Production engineer fixes all the modes in planning sheet of casting, the sheet is kept at the injection molding machine for a fast change-over.