Q
How to select and verify the accuracy and stability of injection molding machine?
A

Choice of power mode for injection molding machine

2002 years ago in the production of injection molding machine is essentially the traditional quantitative pump injection molding machine, the type injection molding machine is quantitative pump using ac generators to provide power injection molding, injection molding machine in action when push valve hydraulic oil pump rotation action, implement open, lock mould, plastic, injection, shot before and after moving, thimble, before and after pulling shoot glue of pumping action.When the injection molding machine without action or need to pressure flow is small, the system through the relief valve will be redundant hydraulic oil back into the tank, that is to say, the full load motor and oil pump works, the equipment needed for energy distribution is controlled by the overflow valves, resulting in injection molding process, most of the energy is to "flow" go in vain.

Since 2004, variable pump injection molding machine began to appear on the injection molding machine market stage.Variable pump injection molding machine mostly USES proportional variable pump (screw pump, plunger pump, gear pump) as the driving element, belongs to the typical positive displacement speed regulation system.The system is composed of load-sensitive proportional variable pump, proportional relief valve, proportional speed regulating valve, pressure feedback valve, flow feedback valve and so on, which has more obvious energy-saving effect compared with the driving quantitative pump injection molding machine.

After 2008, widely used in injection molding machine servo energy-saving injection molding machine manufacturing, the system consists of dc motor, controller, and other components of the feedback system, oil pump, truly a "need to how much energy system power supply", servo motor can do servo closed-loop control, than traditional quantitative pump injection molding machine and energy consumption of variable pump injection molding machine.

Generally speaking, the servo energy saving injection molding machine compared to variable pump injection molding machine energy saving 10-30%, than the traditional quantitative pump injection machine energy saving 30-70%.

The all-electric injection molding machine developed in recent years can separate each action of the injection molding machine, and each reciprocating action is controlled by a servo motor, which can achieve lower power consumption.

Figure compares the energy consumption of different injection molding machines

Therefore, generally speaking, the injection molding machine produced by injection molding machine manufacturers, from the consideration of energy consumption can choose quantitative pump injection molding machine, variable pump injection molding machine, servo energy saving injection molding machine and full electric injection molding machine.At present, the domestic injection molding machine power configuration is the same, choose the same system of the injection molding factory basic not big difference, difference between the single biggest reason, however, are mostly concentrated on the issue of using dynamic size, more power can provide higher parameter selection range and clamping force control, but the injection molding machine configuration and mechanical failure is more likely to lead to leakage, and needs more layers of tubing and machinery with rigidity, injection molding machine cost part will also rise.

Selection of injection pressure for injection molding machine

Injection pressure of injection molding machine Pi=P*A*s/Ao

P = System working pressure (MPa)

A = Effective cross-sectional area of injection piston (cm2)

S = Number of injection cylinders (generally 2)

Ao= Cross-sectional area of screw or feed cylinder plunger (Cm2)

From the above formula can be seen, the product needs higher injection pressure, such as some engineering materials, the optimal method is to increase the system pressure, or increase the area of the cylinder and increase the number of injection cylinder (this is very small), and is to reduce the diameter of screw.

Therefore, when the injection molding machine manufacturers give us the choice of screw injection molding machine, large diameter screw injection pressure are lower, suitable for general plastic processing;The smaller the screw diameter, the greater the injection pressure, the more suitable for processing engineering plastics;When we need to use more injection pressure, injection cylinder diameter must be larger to meet the requirements;Single cylinder injection pressure is not as high as double cylinder injection pressure.

Usually, because of the space limit of injection molding machine, injection piston rod diameter can not be unlimited increase, screw diameter can not unlimited decrease, more injection cylinder in injection balance can not be guaranteed, so generally can only choose 2 injection cylinder, so the normal standard injection molding machine injection pressure to reach 250MPa has been very large.If processing products and materials need higher injection pressure, more often through increasing the system pressure to achieve, before the quantitative pump injection molding machine USES 140MPa oil pump, now injection molding machine generally USES 175MPa oil pump, foreign injection molding machine more use is 220MPa system pressure oil pump.The servo motor of the all-electric injection molding machine can provide more than 450MPa injection pressure, which has a natural advantage in precision molding.

In the selection of injection molding machine, engineering materials and precision parts as much as possible to choose high injection pressure injection molding machine.

Injection rate and injection rate selection

The injection speed of the injection molding machine is the distance that the screw moves forward per second in cm/ SEC: S=Q/A

That is: injection speed = pump discharge ÷ injection cylinder effective area

S: Injection velocity cm/ SEC

A: Injection cylinder effective area cm2

Q: Pump discharge volume CC/REV (ml /rev)

We usually say 300 fire rate, 500 fire rate, 1000 fire rate injection molding machine, generally refers to this speed.As can be seen from the formula, when the diameter of the oil cylinder is small, the injection speed is larger; when the displacement of the oil pump is large, the injection speed is larger.

On what products do we have more urgent requirements for injection molding speed?When the product is thinner, we require a higher injection rate to fill the mold as quickly as possible.To improve the injection speed, on the one hand, it is to increase the pump displacement, on the other hand, it is to reduce the diameter of the cylinder.Many customers in the choice of injection molding machine, injection molding machine manufacturers are required to increase the pump displacement of one or two levels, is generally considered for this.And increase cylinder diameter has an obvious side effects, the injection pressure will decrease because of the increasing oil cylinder diameter, when we produce thin-walled products, in order to overcome the material flow resistance need higher injection pressure, but in order to improve the filling speed to reduce the injection pressure, the method of most is not desirable, the general plastic this method is not recommended.

Injection rate refers to the plastic capacity injected by the injection molding machine into the air per second. The unit is Cm3 / SEC:

V=S*A

V: Injection rate cm3/ SEC

S: Injection velocity cm/ SEC

A: The cross-sectional area of the screw or barrel is cm2

The injection rate is a unit volume representation of how much material can be injected per second, and the larger the number, the more you can inject into the mold.In some thick-wall heavy products, this parameter is very meaningful, for general products and thin-wall products, injection speed can better represent the performance of injection molding machine.

Injection molding machine machinery and lubrication system

The injection molding machine system is generally composed of a frame, three plates, Corinth column, injection molding system, ejector system, mold adjusting system, etc. The domestic injection molding machine frame is generally made of welded steel, three plates are cast iron, Corinth column, mold adjusting gear, ejector mechanism and so on are basically purchased and assembled from professional manufacturers.Quality assured injection molding machine manufacturers, many of its suppliers are supplied by the same several manufacturers, the difference in quality is not big.The parts designed and manufactured by ourselves or manufactured by external partners are mainly on the rack, three big plates and oil circuit plates, etc., which are directly controlled by the injection molding machine manufacturer for their quality and cost.

By comparing several injection molding machines of similar models and different manufacturers, we can know which one has the higher production cost.The clamping mechanism of injection molding machine and the rack shooting table account for 90% of the total weight of the machine. When the machine weight of one injection molding machine manufacturer is heavier than that of another injection molding machine manufacturer of similar models, the cost of this manufacturer is naturally higher than that of another manufacturer.As an industrial product, heavier equipment means a more stable foundation and a more reliable working life, which is qualitatively different from crafts.So, when we buy the injection molding machine, do not ignore the weight of the injection molding machine itself this index.

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