Injection molding machine controls

The preceding considerations led to an endeavor to try and bridge simulation with injection-molding machine controllers. The aims of this endeavor are twofold ... 

To ensure consistency, the two critical areas for control specific to injection molding are shot size control and temperature control on the injection system, i.e., screw portion for the reciprocating screw machines, and both the screw and ram sections for the screw/ram machines. As mentioned previously, for temperature and cure control, the use of microprocessor controls has significantly improved the performance of injection molding machines, including control of the shot size. 

An injection molding machine is operated by hydraulic power and equipped with an dectric motor and hydraulic pump. The maximum hydraulic oil pressure is ca 14 MPa (2000 psi). A hydraulic cylinder opens and closes the mold and holds the mold dosed during injection another cylinder forces the screw forward, thereby injecting the mdt into the mold. A separate hydraulic motor turns the screw to plasticate, homogenize, and pressurize the mdt. Control of these movements is a combined function of the hydraulic and electrical systems (35—37). 

Injection molding machines can control machine elements only with feedback from sensed process data. A fundamental difficulty in polymer processing is that very few of the final part properties can be ascertained within the molding cycle. Instrumentation does not yet exist, and may never exist, to yield information about... 

Blends produced under the Eref trade name include both alloys rich in PP and alloys rich in PA where PA is PA-66 or PA-mXD6 (a semicrystalline PA, made by polycondensation of m-xylylenediamine and adipic acid). A compati-bilizer is added in order to provide optimal adhesion between PP and PA. Injection molding machines used for injecting PA are recommended, with peripheral screw speeds of 3-10 m/min. Cooling time can be estimated as 2.5xe seconds where e is the wall thickness in mm. Melt temperature for flame retarded grades must be well controlled and not exceed 270°C. 

The operation of the injection and clamp units and other components of the injection molding machine (opening and closing of the mold and melting and injection of the polymer material) requires power, which is supplied by an electric motor. The orderly delivery of this power depends on auxiliary systems the hydraulic and control systems. The hydraulic system, the muscle for most maehines, transmits and controls the power from the electric motor to the various parts of the maehine. Maehine functions are regulated by a careful control of the flow, direction, and pressure of the hydraulic fluid. The elements of the hydraulic system for most injection molding machines are essentially the same fluid reservoir, pumps, valves, cylinders, hydraulic motors, and lines (Figure 11.8). 

The size of injection molding machines is usually specified in terms of injection capacity and clamp force. These factors are not directly related. Other important variables are the L D (length to diameter) ratio, barrel size, plasticizing rate, injection rate, and injection pressure. Major components of injection molding machines include the injection unit, the clamp unit, and the machine base which contains the power and control units. 

The main component of an injection-molding machine are (1) the injection unit which melts the molding material and forces it into the mold (2) the clamping unit which opens the mold and closes it under pressure (3) the mold used and (4) the machine controls. 

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