Mold design considerations

- Jul 11, 2017-

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⑴ plastic shape and wall thickness design should be considered particularly conducive to the flow of flow filled cavity, try to avoid sharp corners, gaps.

⑵ stripping slope should take large, with glass fiber 15% desirable 1 ° ~ 2 °, with glass fiber 30% desirable 2 ° ~ 3 °. When the demoulding angle is not allowed to avoid forced stripping, should adopt the horizontal classification structure.

⑶ pouring system cross-section should be large, straight and short process, in order to facilitate the uniform dispersion of fiber.

⑷ design of the feed port should be considered to prevent the lack of filling, anisotropic deformation, uneven distribution of glass fiber, easy to produce welding marks and other adverse consequences. The inlet should be taken as thin slices, width, fan, ring and multi-point form of the feed port to make the flow of turbulence, glass fiber evenly dispersed to reduce the anisotropy, it is best not to use needle-like inlet, Mouth section may be appropriate to increase its length should be short.

⑸ mold core, cavity should be sufficient rigidity and strength.

⑹ mold should be hardened, polished, the choice of wear-resistant steel, easy to wear parts should be easy to change.

⑺ top should be uniform and powerful, easy to repair.

⑻ mold should be equipped with exhaust gas trough, and should be located in the easy weld parts.


Mold temperature setting

⑴ mold temperature affect the molding cycle and forming quality, in the actual operation of the material is the use of the minimum mold temperature began to set, and then according to the quality of the situation to properly increase.

(2) Correctly speaking, mold temperature refers to the temperature of the cavity surface when the forming is carried out. It is important not only to maintain the proper temperature but also to make it evenly distributed in the mold design and forming conditions. The


⑶ Uneven mold temperature distribution, will lead to uneven shrinkage and internal stress, so that the molding port prone to deformation and warping.

⑷ increase the mold temperature can get the following results;

① increase the crystallinity of the molded product and the more uniform structure.

② to shrink the shape of more fully, after the contraction reduced.

③ improve the strength of molded products and heat resistance.

④ reduce the internal stress residue, molecular alignment and deformation.

⑤ reduce the flow resistance when filling, reduce the pressure loss.

⑥ make the appearance of the shape more shiny.

⑦ increase the chance of forming a flash.

⑧ increase near the gate site and reduce the chance of the remote gate parts depression.

⑨ reduce the degree of significant line

⑩ increase the cooling time.

 

Metering and plasticization

⑴ in the molding process, the amount of control (measurement) and plastic uniform melting (plastic) is the ** machine plasticizing unit (Plasticizing unit) to serve.


① heating cylinder temperature (Barrel Temperature)

Although the melting of plastic, about 60 - 85% is due to the rotation of the screw generated by the heat, but the molten state of the plastic is still affected by the temperature of the heating cylinder, especially near the nozzle area of the temperature - the temperature of the front area High when the prone to drop material and remove the pieces when the phenomenon of wire.

 

② screw speed (screw speed)

A. The melting of plastic, generally due to the rotation of the screw generated by the heat, so the screw speed is too fast, the following effects:

Thermal decomposition of plastic.

B. Glass fiber (plus fiber) shortened.

C. Screw or heating tube wear accelerated.

The same time as the above-

B. Speed setting can be measured by the size of its circumferential speed:

Circumferential speed = n (speed) * d (diameter) * π (pi)

Usually, low viscosity thermal stability of the plastic, the screw rod rotation of the circumferential speed can be set to 1m / s up and down, but the thermal stability of the plastic, it should be as low as 0.1 or so.

 

C. In practical applications, we can try to reduce the screw speed, so that the rotary feed can be completed before the mold.

 

③ back pressure (BACK PRESSURE)

A. When the screw is rotated, the pressure accumulated in the melt at the front of the screw is called the back pressure. When the molding is carried out, it can be adjusted by adjusting the oil withdrawal pressure of the hydraulic cylinder. The following effects:


A. More homogeneous melting of the melt.

B. Toner and filler are more evenly dispersed.

C. Exit the gas from the blanking port.

D. The measurement of the feed is accurate.


B. back pressure level is determined by the viscosity of plastic and its thermal stability, too high back pressure to extend the feed time, but also because of the increase in rotation shear force, easy to make plastic overheating. Generally 5-15kg / cm2 is appropriate.

 

④ loose back (SUCK BACK, DECOMPRESSION)

A. screw rotation before the start of the feed, so that the appropriate withdrawal of the screw, you can make the mold in front of the melt pressure reduction, which is called before the loose, the effect of the nozzle to prevent the melt on the screw pressure, and more for the hot runner Mold forming.

B. screw rotation After the end of the feed, so that the appropriate withdrawal of the screw, you can make the front screw melt pressure reduction, which is called after the loose, the effect can prevent the nozzle part of the drop.


C. shortcomings, it is easy to make the main channel (SPRUE) sticky mold; and too much loose, you can inhale the air, so that the occurrence of gas marks marks.

  

Stability of the molding parameters set

 

1, prior confirmation and preparation

⑴ confirm the material drying, mold temperature and heating cylinder temperature is set correctly and reach the machinable state.

⑵ check the opening and closing mode and the top of the action and distance settings.

⑶ ** The pressure (P1) is set at 60% of the maximum value.

⑷ Keep the pressure (PH) set at 30% of the maximum value.

⑸ ** speed (V1) set at the maximum of 40%.

The screw speed (VS) is set at about 60 RPM.

⑺ The back pressure (PB) is set at about 10 kg / cm2.

⑻ loose retreat set at 3mm.

⑼ The position of the holding switch is set at 30% of the screw diameter. For example, φ100mm screw, set 30mm.

⑽ measurement stroke is slightly shorter than the calculated value.

⑾ ** total time is shorter, the cooling time is slightly longer.

The same time as the above-

2, manual operation parameter correction

⑴ blocking mold (to confirm the rise of high pressure), ** forward.

⑵ to manual ** until the screw is completely stopped, and pay attention to stop the position.

⑶ screw rotation feed.

⑷ to be cooled after the mold out of the molding.

⑸ repeat ⑴ - ⑷ steps, the screw finally stopped in the screw diameter of 10% - 20% of the position, and the molding material without short shot, burr and whitening, or cracking and so on.


3, semi-automatic operation parameters of the amendment

⑴ measurement stroke correction [measurement end point] ** pressure will be increased to 99%, and the holding pressure is temporarily adjusted to 0, the measurement end point S0 forward transferred to the occurrence of short shot, and then transferred to the occurrence of flash, Point to select location.

The same time as the above-

⑵ out of the speed of the correction of the PH back to the original level, the ** speed up and down to find out the occurrence of short shot and burr individual speed, with the middle point for the appropriate speed [this stage can also enter the multi-speed corresponding to the appearance of the problem Parameter setting].

The same time as the above-

(3) to maintain the pressure to adjust the upper and lower adjustment to maintain the pressure to find the surface of the depression and the individual pressure, with the middle point for the choice of pressure.

The same time as the above-

⑷ the holding time [or ** time] correction gradually extend the holding time until the weight of the molded article is clearly stable for the obvious choice.

The same time as the above-

⑸ cooling time correction gradually reduce the cooling time, and confirm the following circumstances can be met:

1, the molded product is ejected, caught, trimmed, the packaging will not be whitened, cracked or deformed.

2, mold temperature balance can be stable.


⑹ plasticized parameters of the amendment

① to confirm whether the need to adjust the back pressure;

② adjust the screw speed, so that the measurement time is shorter than the cooling time;

③ to confirm whether the measurement time is stable, you can try to adjust the heating ring temperature gradient.

④ to confirm whether the nozzle drip, the main channel is the occurrence of pig tail or sticky mold, finished product with or without gas marks and other phenomena, the appropriate adjustment nozzle temperature or loose distance.

The same time as the above-

⑺ multi-stage pressure and multi-stage fire rate utilization


① In general, the injection should take the principle of high speed without affecting the appearance, but should be carried out at a lower speed before switching between the gate and the holding pressure;

② pressure should be used to gradually decline, in order to avoid the deformation of the molded product is too high, so easy to deformation of molded products.

  

Practical tips:

Mold and injection molding machine a good match

A. Mold positioning circle standardization and versatility;

B. The ratio of the radius of the ball of stone to the radius of the ball of the shot shall be standardized and versatile;

C. Through the plastic nozzle aperture and the nozzle with the aperture to be reasonable;

D. 1 in the mold must be set in four directions hanging die hole;

   

2 hanging pole pole or rings can make the mold smooth lifting;

E. Mold on the water transport joints in the upper and lower mold as far as possible free disassembly.

  

L mold in the production of high efficiency

A. All molds should be considered in the design of automated production;

B. Minimize the nozzle;

C. Effective balanced cooling system;

D. Cavity, core steel to ensure adequate hardness.

  

L Practical mold maintenance plan:

A. Mold maintenance in the production process;

B. 3-5 million beer comprehensive maintenance;

C. Pre-production mold inspection and oil preparation.

  

The basic structure of plastic injection molding machine


Plastic injection molding technology is based on the principle of die-casting from the late nineteenth century and early twentieth Century developed, is currently the most commonly used plastic processing methods. The method applies to all thermoplastics and partially thermosetting plastics (about 1/3 of the total plastic).

 

The working principle of injection molding machine


The working principle of the injection molding machine is similar to that of the injector, which is the injection of the plasticized molten state (ie, viscous) into the closed cavity by means of the thrust of the screw (or plunger) The process of obtaining the finished product after curing.


Injection molding is a cycle of the process, each cycle mainly include: quantitative feeding - melt plasticization - pressure injection - charge cooling - Kai-picking. Remove the plastic parts and then closed the mold, the next cycle.

 

The structure of the injection molding machine


The injection molding machine is divided into plunger type injection molding machine and screw type injection molding machine according to the plasticization method. According to the machine transmission mode, it can be divided into hydraulic, mechanical and hydraulic - mechanical (connecting rod) type, and in recent years Motor type; according to the operation is divided into automatic, semi-automatic, manual injection molding machine.


(1) ** Injection Molding Machine: This is the most common type. The mold clamping portion and the injection portion are on the same horizontal center line, and the mold is opened in the horizontal direction.

Its characteristics are: short body, easy to operate and repair; machine center of gravity is low, the installation is more stable; products can be used after the top of gravity automatically fall, easy to achieve automatic operation. At present, the market of injection molding machine to use this type.


(2) vertical injection molding machine: the mold part and the injection part of the same vertical center line, and the mold is open in the vertical direction. Therefore, its small footprint, easy to place the insert, loading and unloading mold more convenient, from the hopper into the material can be more uniform plastic. But the product is not easy to automatically drop after the top, must be removed by hand, not easy to achieve automatic operation. Vertical injection molding machine is suitable for small injection molding machine, usually in the following 60 grams of injection molding machine used more large, medium machine should not be used.


(3) angle injection molding machine: its injection direction and mold interface on the same side, it is particularly suitable for the processing center part of the gate marks are not allowed to leave the flat products. It covers an area smaller than the ** injection molding machine, but the insert into the mold is easy to tilt down. This type of injection molding machine should be used for small machines.


(4) multi-mode rotary disc injection molding machine: it is a multi-station operation of the special injection molding machine, which is characterized by a clamping device with a turntable structure, the mold around the shaft rotation. This type of injection molding machine can give full play to the plasticizing capacity of the injection device, which can shorten the production cycle and improve the production capacity of the machine. Therefore, it is particularly suitable for large-volume plastic molding Products, but the mold system is huge, complex, clamping device clamping force is often smaller, so this injection molding machine in the plastic soles and other products in the production of more applications.


General injection molding machine, including injection device, mold clamping device, hydraulic system and electrical control system and other parts.


The basic requirements for injection molding are plasticization, injection and molding. Plasticization is the prerequisite for the realization and assurance of the quality of molded products, and to meet the molding requirements, the injection must ensure that there is sufficient pressure and speed. At the same time, since the injection pressure is high, a high pressure is generated in the mold cavity (the average pressure in the mold cavity is generally between 20 and 45 MPa), and therefore a sufficient clamping force must be obtained. It can be seen that the injection device and the clamping device are the key components of the injection molding machine.

 

Injection process selection:


General injection molding machine can be manually operated, can also be semi-automatic and fully automatic operation.


Manual operation is in a production cycle, each action is by the operator toggle operation switch to achieve. Generally in the test machine when the mold selection.


Semi-automatic operation of the machine can automatically complete a work cycle of the action, but after each production cycle operator must pull the security door, remove the workpiece, and then close the security door, the machine can continue the next cycle of production.


Automatic operation of the injection molding machine in the completion of a work cycle after the action, can automatically enter the next work cycle. In the normal continuous process without downtime to control and adjustment.

 

Normal production, the general use of semi-automatic or fully automatic operation. At the beginning of the operation, the operating mode (manual, semi-automatic or fully automatic) should be selected according to the production requirements and the manual, semi-automatic or fully automatic switch should be activated.


Semi-automatic and fully automated working procedures have been determined by the line itself, the operator only need to change the speed and pressure on the cabinet surface size, the length of time, the number of thimble, etc., not because the operator tuning key Make the work process chaos.


When a cycle of each action is not adjusted properly, you should first select the manual operation to confirm that each action is normal, then select the semi-automatic or fully automatic operation.

  

Preforming action selection


According to the pre-plastic injection before and after the injection is back, that is, whether the nozzle to leave the mold, injection molding machine generally has three options.


(1) fixed feeding: pre-plastic and pre-plastic nozzle are always posted into the mold, the seat does not move.


(2) before the feeding: nozzle against the mold for pre-plastic feeding, pre-finished, the seat back, the nozzle to leave the mold. The purpose of this method is to choose: pre-plastic injection hole with the nozzle to help the nozzle, to avoid the melt in the back pressure from the nozzle outflow, pre-plastic nozzle and mold to avoid prolonged contact with the heat transfer, affecting them The respective temperatures are relatively stable.


(3) after the feeding: injection is completed, the seat back, the nozzle to leave the mold and then pre-plastic, pre-plastic and then move forward. This action is suitable for processing molding temperature is particularly narrow plastic, because the nozzle and mold contact time is short, to avoid the loss of heat, but also to avoid the melt in the nozzle hole solidification.


After the end of the injection, the cooling timer is finished and the preform action starts.

The screw rotates the plastic and squeezes it into the front of the screw head. Due to the action of the check valve from the front end of the screw, the molten plastic accumulates at the front of the barrel and the screw is forced backwards. When the screw retracts to the predetermined position (this position is determined by the stroke switch, the distance of the screw is controlled to realize the quantitative feeding), the preform is stopped and the screw stops rotating.


Followed by a retrogression action, the retraction of the screw for a slight axial retraction, this


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