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The basic knowledge of injection molds, the most complete collated knowledges

Postview: 270 Date: July 17, 2019

Mold overview:

The phrase “Mold is the mother of industry” is familiar to everyone. The importance of molds is increasingly recognized by people, and mold design and mold manufacturing technology have made great progress.

The innovation of mold processing technology, the wide application of various new mold materials, the standardization and specialization of mold parts, etc., all force us to adapt to the development of molds faster and more compliant.

The speed increase requires the design section to be completed in about 3 days. The accuracy is improved. It is required to consider the processing methods of each part in the design process, and try to use the processing method with high precision and low processing cost.

The improvement in accuracy and speed is in line with each other. The increase of speed will inevitably require the improvement of precision; the improvement of precision will inevitably lead to the increase of speed.

Hot runner system

2. Inclined top barb mechanism

3. Sleeve ejection mechanism

4. Slider outer hook mechanism

5. Internal thread automatic screw-out demolding mechanism

6. Three-plate mold, needle point into the glue, sleeve ejection mechanism

7. Side wall latent feeding mechanism

8. Buried injection mechanism

9. Thimble latent feeding mechanism

10.Hub barb mechanism

11. Injection molding machine workflow

Basic structure of plastic mold

Plastic molds can be divided into: guiding system, supporting system, forming part system, pouring system, cooling system, ejector system and exhaust system according to the overall functional structure.

Definition: A plastic flow path in the mold from the injection nozzle to the cavity. It consists of a main channel, a runner, a gate, and a hole.

Related some Chinese and English

CAV.NO No. No. 模NER RUNNER

GATE gate CAVITY cavity

(1) Mainstream:

1. Definition:

The main flow path refers to the section from the portion where the nozzle of the injection machine contacts the mold to the branching path.

2. Design considerations:

(1). The shape of the end face of the main flow path is usually circular.

(2). In order to facilitate demolding, the mainstream road is generally made with a slope, but if the main channel passes through multiple boards at the same time, we must pay attention to the slope of the hole and the size of the hole on each block.

(3). The design of the mainstream channel size should be based on the flow characteristics of the plastic material.

(4). Mainstream roads are mostly conical in design. (As shown in the figure), pay attention to:

A. Small end diameter D2=D1+(0.5~1mm)

B. Small end ball radius R2=R1+(1~2mm)

(where D1 and R1 are the diameter of the injection exit of the injection machine and the radius of the ball of the injection head, respectively)

3. Sprue cover

Since the main channel is in contact with and collides with high temperature plastics and nozzles, the main channel portion of the mold is usually designed as a detachable replacement bushing, referred to as a casting sleeve or a sprue bushing.

(1). Its main role is:

A. It is convenient to enter the positioning hole when the mold is installed, and it is well positioned on the injection molding machine to match the nozzle hole of the injection molding machine, and can withstand the back pressure of the plastic, and will not be pushed out of the mold.

B. As the mainstream of the pouring system, the plastic in the barrel is transferred into the mold to ensure that the flow reaches the cavity vigorously and smoothly, and there should be no plastic overflow during the injection process, and at the same time, it is convenient to prevent the main flow of the aggregate.

(2) The structural form is monolithic and split

Integral: the shoulder is integrated with the main part of the main road

Split type: the shoulder is made separately from the main part

Japanese industrial standard: JIS

China’s industrial standard: SJB

(two). Split runner:

Definition: A section between the main flow path and the gate. It is the transition section of molten plastic flowing into the cavity from the main flow path. It is also the transition section of the casting system through the change of the sectional area and the plastic turning, which enables the plastic to be smoothly converted.

Section design

A. The general design section is circular

B. Generally, it is U-shaped, V-shaped, trapezoidal, and regular hexagonal in terms of processing convenience.

C. The cross-sectional shape and size of the runner should be determined according to the molding volume of the plastic part, the wall thickness of the plastic part, the shape of the plastic part, the plastic process characteristics, the injection rate, the length of the runner, and other factors.

2. The arrangement of the runners is in the form of balanced feed and unbalanced feed. Balanced feeding is to ensure that the feed inlets are fed at the same time. The unbalanced feed is that the feed inlets cannot be fed at the same time, and the mold flow analysis is generally used for evaluation.

(three). gate

1. Definition: The gate is also called the inlet or the inner runner. It is the narrow part between the runner and the plastic part, also called the shortest part of the casting system;

2. Function : It can make the flow velocity of the molten plastic conveyed by the runner flow to generate an ideal flow state, sequence, and quickly fill the cavity, and also play a role of preventing the melt backflow by closing the cavity, and After molding, it is convenient to separate the gate from the plastic part.

3. The form of the gate:

Inner gate

Ordinary side gate (edge ​​gate):

Outer gate

Fan-shaped gate: commonly used to form a sheet-shaped plastic part with a large width

Flat seam gate

Ear guard

Gap gate

General point gate

Latent gates (most of my company use this method)

Ring-type gate

Spoke gate

Claw gate

Garden ring gate

3>. Choice of gate location

(1) The gate is selected to have the closest distance to the barrier.

(2) The size and position of the gate should be chosen to avoid jetting and creeping.

(3) The gate shall be opened at the thickest part of the plastic part.

(4) The position of the gate should be selected so that the plastic flow is the shortest and the flow direction is minimized.

(5) The choice of gate location should be beneficial to the discharge of gas in the cavity.

(6) The choice of gate location should reduce or avoid the weld line of the plastic parts to increase the weld fastness.

(7) The position of the gate should be selected to prevent the flow from deforming the cavity, the core and the insert.

(4). Cold material hole

1. Structure :

The cold material hole is used for storing the cold material head generated during the injection interval, preventing the cold material from entering the cavity and affecting the quality of the plastic part, and allowing the molten material to smoothly fill the cavity, and the cold material hole is also called the cold material well.

2. Pulling form:

(1) hook shape (form) pull rod

(2) spherical pull rod

3. Conical pull rod

4. Pull the material hole: A. With the top rod; B. Without the top rod

What expertise is required for structural design?

Personal insights are for reference only!

I. Mold aspect

For any newcomer to make a structure, at least understand the principles of the mold (plastic mold / die-cast mold / metal mold);

A. Mold manufacturing process (that is, you should consider whether you can mold, how to mold, whether it is convenient for mold manufacturing, and affect the service life of the mold, etc.)

B. The working principle of the mold (that is, you should consider whether the mold release mode of this product will affect the normal production in the future; such as injection molding defects, low production efficiency, etc.)

2. Product function

A. First of all, you have to figure out the type of product you are facing; (home appliances, communication or actual) because each type of its industry security standard / test standard is different; these will affect you Drawing later.

B. Secondly, as far as possible to meet the product function, the simplification of the drawing should be used as much as possible, taking into account the ease of manufacture and maintenance of the mold in the future;

3. Other relevant knowledge

A. Have a relevant understanding of the injection molding process; (such as often white / top height / trapped gas / water line / gas pattern / bubble / flower / shrink, etc.)

B. Be familiar with the knowledge of plastics/hardware; the characteristics of different materials are different; so it is very important to select the materials for each part of the design, which will affect the cost, reliability, etc. of the products you design in the future. ;

Causes of defects in injection molded parts and their remedies

Filling dissatisfaction

1. Characteristics of injection molded parts defects

The injection molding process is incomplete because the cavity is not filled with plastic or the molding process lacks some detail.

2. Reasons for possible problems

(1). Insufficient injection speed.

(2). Plastic shortage.

(3). The screw does not leave the screw pad at the end of the stroke.

(4). Run time changes.

(5). The temperature of the shooting tank is too low.

(6). Injection pressure is insufficient.

(7). The nozzle part is sealed.

(8). The heater outside the nozzle or the shooting tank cannot operate.

(9). The injection time is too short.

(10). The plastic is attached to the throat wall of the hopper.

(11). The capacity of the injection molding machine is too small (ie, injection weight or plasticizing ability).

(12). The mold temperature is too low. (13). Anti-rust oil that does not clean the mold.

(14). The retaining ring is damaged, and the melt has a backflow phenomenon.

3. Remedy

(1). Increase the injection speed.

(2). Check the amount of plastic in the hopper.

(3). Check if the injection stroke is set correctly and change if necessary.

(4). Check if the check valve is worn or cracked.

(5). Check whether the operation is stable.

(6). Increase the temperature of the melt.

(7). Increase back pressure.

(8). Increase the injection speed.

(9). Check the nozzle hole for foreign matter or unplasticized plastic.

(10). Check all the heater layers and check the energy output with an ammeter.

(11). Increase the screw forward time.

(12). Increase the cooling capacity of the throat of the hopper or reduce the temperature of the rear area of ​​the shooting tank.

(13). Use a larger injection molding machine.

(14). Appropriately increase the mold temperature.

(15). Clean the rust inhibitor in the mold.

(16). Check or replace the check ring.

Injection molded parts size difference

1. Characteristics of injection molded parts defects

The change in weight during the injection molding process exceeds the production capacity of the mold, injection molding machine and plastic combination.

2. Reasons for possible problems

(1). The plastic in the injection cylinder is not uniform.

(2). The range of temperature or fluctuation of the shooting tank is too large.

(3). The capacity of the injection molding machine is too small.

(4). The injection pressure is unstable.

(5). The screw reset is unstable.

(6). Changes in operating time and inconsistent solution viscosity.

(7). The injection speed (flow rate control) is unstable.

(8). A plastic type that is not suitable for the mold is used.

(9). Consider the effects of mold temperature, injection pressure, speed, time and pressure on the product.

3. Remedy

(1). Check for sufficient cooling water to flow through the hopper throat to maintain the correct temperature.

(2). Check for poor quality or loose thermocouples.

(3). Check if the thermocouple used with the temperature controller is of the correct type.

(4). Check the injection molding volume and plasticizing capacity of the injection molding machine, and then the actual injection quantity and the hourly injection.

The amount of plastic used was compared.

(5). Check if there is stable molten hot material for each operation.

(6). Check the backflow prevention valve for leaks and replace if necessary.

(7). Check if the wrong feed setting.

(8). Ensure that the screw is stable at each operation return position, that is, no more than 0.4mm change.

(9). Check the inconsistency of the operation time.

(10). Use back pressure.

(11). Check if the hydraulic system is operating normally and the oil temperature is too high or too low (25-60oC).

(12). Select the type of plastic suitable for the mold (mainly considering shrinkage and mechanical strength).

(13). Re-adjust the entire production process

Shrink marks

1. Characteristics of injection molded parts defects

Usually related to surface marks (please refer to the “holes” section), and it is formed by shrinkage of plastic from the mold surface.

2. Reasons for possible problems

(1). The melting temperature is not too high or too low.

(2). Insufficient plastic in the cavity.

(3). The surface of the contact plastic is overheated during the cooling phase.

(4) The flow path is unreasonable and the gate cross section is too small.

(5). Whether the mold temperature is compatible with the characteristics of the plastic.

(6). The product structure is irrational (enhanced into the ancient high, too thick, obviously thick and thin

One).

(7). The cooling effect is not good, and the product continues to shrink after demolding.

3. Remedy

(1). Adjust the temperature of the shooting tank.

(2) Adjust the screw speed to get the correct screw surface speed.

(3). Increase the amount of injection.

(4). Ensure the correct bedding is used; increase the screw forward time; increase the injection molding

Pressure; increase injection speed.

(5). Check if the stop valve is installed correctly, because abnormal operation will lead to pressure

Force loss.

(6). Reduce the mold surface temperature.

(7). Correct the flow channel to avoid excessive pressure loss; according to actual needs, appropriate expansion

Large cross section size.

(8). Appropriately control the mold temperature according to the characteristics of the plastic used and the product structure.

(9). Improve product structure if allowed.

(10). Try to get enough cooling for the product.

Smudge marks and injection lines

1. Characteristics of injection molded parts defects

Usually related to the gate area: its surface is dull and sometimes streaks are visible.

2. Reasons for possible problems

(1). The melting temperature is too high.

(2). The mold filling speed is too fast.

(3). The temperature is too high.

(4). Related to plastic properties.

(5). There is a cold material at the nozzle mouth.

3. Remedy

(1). Reduce the temperature in the first two zones of the shooting tank.

(2). Reduce the injection speed.

(3). Reduce the injection pressure.

(4). Reduce the mold temperature.

(5). Most of the parts produced with PE will have a ray pattern, which can be used according to the requirements.

Modify the position of the inlet.

(6). Avoid generating cold material as much as possible (control the nozzle temperature).

Adhesive

1. Characteristics of injection molded parts defects

The nozzle is held by the mouthpiece.

2. Reasons for possible problems

(1). The nozzle cover and the nozzle are not facing Huai.

(2). The plastic inside the nozzle sleeve is overfilled.

(3). The nozzle temperature is too low.

(4). The plastic is not completely solidified in the nozzle, especially the nozzle with a large diameter.

(5). The arc surface of the nozzle sleeve is improperly matched with the circular arc surface of the nozzle.

The flow path of “winter mushrooms”.

(6). The flow path is not enough to pull out the slope.

3. Remedy

(1). Re-position the nozzle and nozzle cover.

(2). Reduce the injection pressure.

(3). Reduce the screw forward time.

(4). Increase the nozzle temperature or use a separate temperature controller to heat the nozzle.

(5). Increase the cooling time, but a better way is to use a nozzle with a smaller nozzle

The sleeve replaces the original nozzle sleeve.

(6). Correct the mating surface of the nozzle sleeve and the nozzle.

(7). Appropriately increase the extraction slope of the flow channel.

Hole

1. Characteristics of injection molded parts defects

It can be easily seen in the “air trap” of a transparent injection molded part but can also be found in opaque plastics.

This is related to thickness and is often caused by plastic shrinkage leaving the center of the injection molded part.

2. Reasons for possible problems

(1) The mold is not fully filled.

(2). The abnormal operation of the stop valve.

(3). The plastic is not completely dry.

(4). The speed of pre-molding or injection is too fast.

(5). Certain special materials are produced using special equipment.

3. Remedy

(1). Increase the amount of shots.

(2). Increase the injection pressure.

(3). Increase the screw forward time.

(4). Reduce the melting temperature.

(5). Reduce or increase the injection speed. (For example, plastics for amorphous materials should be increased.

Add 45% speed).

(6). Check if the check valve is cracked or not working.

(7). Drying conditions should be improved according to the characteristics of the plastic to allow the plastic to dry thoroughly.

(8). Properly reduce the screw speed and increase the back pressure, or reduce the injection speed.

Injection molded parts bent

1. Characteristics of injection molded parts defects

The shape of the injection molded part is similar to the cavity but is a distorted version of the cavity shape.

2. Reasons for possible problems

(1). Bending is due to excessive internal stress in the molded part.

(2). The mold filling speed is slow.

(3). Insufficient plastic in the cavity.

(4). The plastic temperature is too low or inconsistent.

(5). The injection molded part is too hot when it is ejected.

(6). The cooling is insufficient or the temperature of the fixed and fixed molds is inconsistent.

(7). The structure of the injection molded parts is unreasonable (such as the reinforcing ribs are concentrated on one side, but the distance is relatively small

far).

3. Remedy

(1). Reduce the injection pressure.

(2). Reduce the screw forward time.

(3). Increase the cycle time (especially the cooling time). From within the mold (especially

Thicker injection molded parts) immersed in warm water (38oC) immediately after ejection

The pieces slowly cool down.

(4). Increase the injection speed.

(5). Increase the plastic temperature.

(6). Use cooling equipment.

(7). Appropriately increase the cooling time or improve the cooling conditions, as far as possible to ensure that the movement, set

The mold temperature of the mold is the same.

(8). According to the actual situation, it is allowed.

Common injection molding product defects:

phenomenon

cause

Treatment

Lack of product

Filling dissatisfaction

1. The injection speed is insufficient. 2. Plastic shortage. 3. The screw does not leave the screw pad at the end of the stroke. 4. The running time changes. 5. The temperature of the shooting tank is too low. 6. Insufficient injection pressure. 7. The nozzle part is sealed.8. The heater outside the nozzle or the shooting tank cannot operate. 9. Injection time is too short. 10. The plastic is attached to the throat wall of the hopper. 11. The capacity of the injection molding machine is too small (ie injection weight or plasticizing ability). 12. The mold temperature is too low. 13. There is no anti-rust oil for cleaning the mold. 14. The retaining ring is damaged and the melt has a backflow phenomenon.

1. Increase the injection speed. 2. Check the amount of plastic in the hopper. 3. Check if the injection stroke is set correctly and change if necessary. 4. Check if the check valve is worn or cracked. 5. Check whether the operation is stable. 6. Increase the melt temperature. 7. Increase back pressure. 8. Increase the injection speed. 9. Check the nozzle hole for foreign matter or unplasticized plastic. 10. Check all heaters and check the energy output with an ammeter. 11. Increase the screw forward time. 12. Increase the throat area of ​​the hopper or lower the temperature of the rear area of ​​the shooting tank. 13. Use a larger injection molding machine. 14. Appropriately increase the mold temperature. 15. Clean the rust inhibitor in the mold. 16. Check or replace the retaining ring.

Injection molded parts size difference

1. Input the plastic in the shooting tank is uneven. 2. The range of temperature or fluctuation of the shooting tank is too large. 3. The capacity of the injection molding machine is too small. 4. The injection pressure is unstable. 5. The screw reset is unstable. 6. Changes in operating time and inconsistent solution viscosity. 7. The injection speed (flow control) is unstable. 8. Use a variety of plastics that are not suitable for the mold. 9. Consider the effects of mold temperature, injection pressure, speed, time, and pressure holding on the product.

1. Check for sufficient cooling water to flow through the hopper throat to maintain the correct temperature. 2. Check for poor quality or loose thermocouples. 3. Check that the thermocouple used with the temperature controller is of the correct type. 4. Check the injection molding volume and plasticizing capacity of the injection molding machine, and then compare it with the actual injection quantity and the amount of plastic injection per hour. 5. Check if there is a stable molten hot material for each operation. 6. Check the backflow prevention valve for leaks and replace if necessary. 7. Check for incorrect feed settings. 8. Ensure that the screw is stable at each return position, ie no more than 0.4mm.9. Check the inconsistency of the operation time. 10. Use back pressure. 11. Check if the hydraulic system is operating normally and the oil temperature is too high or too low (25-60 ° C). 12. Select the type of plastic suitable for the mold (mainly considering the shrinkage rate and mechanical strength). 13. Readjust the entire production process.

Shrink pattern

1. The melting temperature is not too high or too low. 2. There is not enough plastic in the cavity. 3. The surface of the contact plastic is overheated during the cooling phase. 4. The flow path is unreasonable and the gate cross section is too small. 5. Whether the mold temperature is compatible with the characteristics of the plastic. 6, the product structure is irrational (strengthen into the ancient high, too thick, obviously thick and thin). 7, the cooling effect is not good, the product continues to shrink after demolding.

1. Adjust the temperature of the shooting cylinder. 2. Adjust the screw speed to get the correct screw surface speed. 3. Increase the amount of injection. 4, to ensure the use of the correct bedding; increase the screw forward time; increase the injection pressure; increase the injection speed. 5. Check that the stop valve is installed correctly, as abnormal operation will cause pressure loss. 6. Reduce the mold surface temperature. 7. Correct the flow path to avoid excessive pressure loss; appropriately expand the cross-sectional size according to actual needs. 8. Appropriately control the mold temperature according to the characteristics of the plastic used and the product structure. 9. Improve product structure if allowed. 10. Try to get enough cooling for the product.

How to easily distinguish the pros and cons of the product:

Look at the appearance

1, see if the product is complete, whether it is deformed

2, whether the color is uniform, whether there is obvious color difference, whether the color is bright and translucent

Touch product

1. Touch the surface of the product to make it smooth, and whether there are burrs around the handle and the handle.

2. Is the assembly part proper and the stacking code is safe?

3. Whether the product has been naturally aging, the aging is reflected in the product becoming hard and brittle, and the high quality product is soft and has

toughness

weigh

1, weighing the weight, from the raw material polymerization process and physical properties, the light weight indicates low crystallinity, high purity, impurities

less

2. Products with the same structure and uniform wall thickness are produced using the same raw materials and processes. In addition to the above two characteristics, the weight is better.

Injection molding principle

First, what is injection molding:

The so-called injection molding is the plastic material in the barrel of the injection molding machine through the external heating and the shear heat generated by the rotation of the screw to plasticize the resin material into a melt, after applying a certain pressure, the melt is injected to have a certain The items produced in the shaped cavity after cooling and setting are injection molded.

Second, the process of injection molding, that is, the cycle of injection molding:

Mode locking

Sit

Shot glue

Holding pressure

Melt + cooling

Eject

Mold

Seat

Third, the three basic elements of injection molding:

Machines – including injection molding machines and auxiliary machines.

Mold

material

Fourth, the five major elements of the injection molding process:

1, temperature:

A,

Temperature: For the hydraulic machine, it is the heat energy generated by the frictional movement of the hydraulic oil of the machine. It is controlled by the cooling water. When starting the machine, it is necessary to confirm that the oil temperature is around 45 °C. If the oil temperature is too high or too low Both will affect the transmission of pressure.

B,

Material temperature: the barrel temperature, which is set according to the shape and function of the material and product. If there is a file, set it according to the file.

C,

Mold temperature: This temperature is also an important parameter. Its height has a great influence on the performance of the product. Therefore, the function and structure of the product must be considered when setting, and the material and cycle should be considered.

2, speed:

A,

The speed setting of the opening and closing mode, the setting of the opening and closing mode is generally based on the principle of slow-fast-slow, so the setting mainly considers the machine, the mold and the cycle.

B. Ejection setting: It can be set according to the structure of the product. It is better to use a slow speed to eject some of the structure and use it to quickly release the mold and shorten the cycle.

C, the rate of fire: according to the size of the product, the structure to set, if the structure is more complex and thinner can be fast, if the structure is simple, the wall thickness can be used slowly, but also according to the performance of the material, from slow to fast setting.

3. Pressure:

A,

Injection pressure: depending on the size of the product, the thickness of the wall, from low to high, other factors are considered during commissioning.

B,

Holding pressure: The holding pressure is mainly to ensure the shape and stable size of the product, and the setting is also set according to the structure and shape of the product.

C,

Low pressure protection pressure: This pressure mainly protects the mold and minimizes the damage of the mold.

D,

Clamping force: refers to the force required to mold the mold to high pressure, some machines can adjust the clamping force, and some can not.

4. Time:

A,

Injection time: This time setting must be longer than the actual time, and it can also play the role of injection protection. The setting value of the shooting timing is about 0.2 seconds larger than the actual value. The setting should be considered with pressure, speed, The temperature is matched.

B,

Low-voltage protection time: When this time is in the manual state, first set the time to 2 seconds, and then add about 0.02 seconds according to the actual time.

C,

Cooling time: This time is generally set according to the size and thickness of the product, but the melting time should not be greater than the cooling time, so that the product can be fully shaped.

D,

Holding time: This time is the time to ensure the size of the product after the injection is completed. The time to cool the gate before the melt is reversed under the pressure of holding pressure can be set according to the size of the gate.

5. Location:

A,

The position of the opening and closing mold can be set according to the corresponding speed of the opening and closing mold. The key is to set the starting position of the low pressure protection, that is, the starting position of the low pressure should be the point that most likely protects the mold without affecting the cycle. The termination position should be The position where the front and rear molds are in contact at the time of slow mold clamping.

B,

Ejection position: This position can satisfy the complete demoulding of the product. It should be set from small to large increment. Pay attention to set the retraction position to “0” when loading the mold, otherwise the mold will be damaged.

C,

Melt position: Calculate the material amount according to the product size and screw size, and then set the corresponding position.

D,

The V-P position should be determined by the Short-Short method to find the V-P position (ie, the V-P switching point).

In short: these five elements are complementary when debugging, and must be linked to each other to set up debugging.

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