This is injection mold, don't say I haven't seen it yet!

Time：2020-11-25 16:46:56 / Popularity： / Source：

Mold injection molding is a processing method used in mass production of some complicated parts. Specific principle refers to: plastic raw material melted by heat is pushed by screw of injection molding machine into cavity of plastic mold under high pressure, after cooling and solidification, plastic molded product is obtained.
Plastic mold is composed of a movable mold and a fixed mold. Movable mold is installed on movable mold plate of injection molding machine, and fixed mold is installed on fixed mold plate of injection molding machine. During injection molding, movable mold and fixed mold are closed to form a pouring system and cavity. When mold is opened, movable mold and fixed mold are separated to take out plastic product.
Injection mold is a tool for producing plastic products; it is also a tool for giving plastic products a complete structure and precise dimensions. Injection molding is a processing method used in mass production of certain complex-shaped parts. Specifically, it refers to high-pressure injection of plastic melted by heat into mold cavity by injection molding machine, molded product is obtained after cooling and solidification.

Mold composition

Although structure of mold may vary widely due to variety and performance of plastics, shape and structure of plastic products, type of injection machine, basic structure is same. Mold is mainly composed of a gating system, a temperature control system, forming parts and structural parts. Among them, gating system and molded parts are parts that are in direct contact with plastic, change with plastic and product. They are the most complex and the most variable parts in plastic mold, requiring the highest processing finish and precision.
Injection mold is composed of a movable mold and a fixed mold. Movable mold is installed on movable mold plate of injection molding machine, and fixed mold is installed on fixed mold plate of injection molding machine. During injection molding, movable mold and fixed mold are closed to form a gating system and cavity. When mold is opened, movable mold and fixed mold are separated to take out plastic product. In order to reduce heavy workload of mold design and manufacturing, most of injection molds use standard mold bases.
When single parting surface injection mold is opened, movable mold and fixed mold are separated to take out plastic part, which is called a single parting surface mold, also called a double plate mold. It is the simplest and most basic form of injection molds. It can be designed as a single-cavity injection mold or a multi-cavity injection mold according to needs. It is the most widely used injection mold.
Double parting surface injection mold: Double parting surface injection mold has two parting surfaces. Compared with single parting surface injection mold, double parting surface injection mold adds a middle plate that can be moved locally in fixed part of mold (also called a movable gate plate, which is equipped with gates, runners, other parts and components required by fixed mold), so it is also called a three-plate (movable plate, intermediate plate, fixed plate) injection mold, which is often used in single-cavity or multi-cavity injection molds with point gate feeding. When mold is opened, intermediate plate is separated from fixed mold plate at a fixed distance on the guide post of fixed mold, so that casting system condensate can be taken out between two mold plates. Double parting surface injection mold has a complex structure, high manufacturing cost, and difficult parts processing. Generally, it is not used for molding of large or super large plastic products. Do you think it is okay to process square hole of mold like this?
Injection mold with lateral parting and core pulling mechanism, when plastic part has side holes or undercuts, it is necessary to use a laterally movable core or slider for molding. After injection molding, movable mold first moves down for a certain distance, and then inclined section of bending pin fixed on fixed mold plate forces slider to move outward, and at the same time, push rod of demolding mechanism pushes pusher plate to make plastic part come off core.
Injection molds with movable forming parts due to special structure of plastic parts, injection mold is required to be equipped with movable forming parts, such as movable punches, movable concave molds, movable inserts, movable thread cores or rings, etc. , It can be removed from mold together with plastic part when demolding, and then separated from plastic part.
Automatic thread unloading injection mold: For plastic parts with threads, when automatic demolding is required, a rotatable thread core or ring can be set on mold, using mold opening action or rotation mechanism of injection molding machine, or setting a special transmission device to drive threaded core or threaded ring to rotate, thereby removing plastic part.
Runnerless injection mold: Runnerless injection mold refers to method of adiabatic heating of runner to keep plastic between nozzle and cavity of injection molding machine in a molten state, so that there is no condensate in gating system when mould is opened and plastic part is taken out. The former is called adiabatic runner injection mold, and the latter is called hot runner injection mold.
Right-angle injection molds: Right-angle injection molds are only suitable for angle injection molding machines. Difference from other injection molds is that feeding direction of this type of mold is perpendicular to opening and closing directions during molding. Its main runner is layout on both sides of parting surface of moving and fixed molds, and its cross-sectional area is usually constant. This is different from molds used in other injection molding machines. In order to prevent wear and deformation of nozzle of injection molding machine and inlet end of main runner, replaceable runner inserts can be provided at the end of main runner.
In most injection molds, ejection device is installed on the side of movable mold, which facilitates work of ejector device in opening and closing system of injection molding machine. In actual production, because some plastic parts are limited by shape, it is better to leave plastic part on the side of fixed mold for molding. This makes plastic part eject from mold, and it is necessary to set a release on the side of fixed mold mechanism

Gating system

Gating system refers to part of runner before plastic enters cavity from nozzle, including main runner, cold slug, runner, and gate.
Gating system is also called runner system. It is a set of feed channels that lead plastic melt from nozzle of injection machine to cavity. It is usually composed of a main runner, a runner, a gate and a cold material cavity. It is directly related to molding quality and production efficiency of plastic products.

Main runner

It is a passage in mold that connects nozzle of injection molding machine to runner or cavity. Top of main runner is in a concave shape and is connected to nozzle. Inlet diameter of main runner should be slightly larger than nozzle diameter (0.8mm) for injection molding overflow, and to prevent inlet diameter from being determined according to product size, generally 4-8mm. Diameter of main runner should be expanded inward at an angle of 3° to 5° to facilitate demolding of runner.

Cold feed hole

It is a cavity located at the end of main runner to trap cold material generated between two injections at the end of nozzle to prevent clogging of runner or gate. Once cold material is mixed into cavity, diameter of cold slug hole is about 8-10mm and depth is 6mm. In order to facilitate demolding, bottom is often borne by demolding rod. Top of demolding rod should be designed in a zigzag hook shape or a recessed groove, so that sprue can be pulled out smoothly during demolding.

Shunt

It is channel connecting main runner and each cavity in multi-slot mold. In order to make melt fill cavities at the same speed, layout of runners on mold should be symmetrical and equidistant. Shape and size of cross-section of runner have an impact on the flow of plastic melt, product demolding and difficulty of mold manufacturing.
In terms of flow of first-level feed, size of runner with a circular cross-section is the smallest. However, because specific surface of cylindrical runner is small, it is unfavorable for cooling of runner redundant, and runner must be opened on two mold halves, which is labor intensive and difficult to align.
Therefore, trapezoidal or semicircular cross-section runners are often used, and they are opened on half of mold with a stripping rod. Runner surface must be polished to reduce flow resistance and provide a faster filling speed. For most thermoplastics, width of runner cross-section is no more than 8m, extra large can reach 10-12m, and extra small be 2-3m. Cross-sectional area should be shortened as much as possible under size that meets needs to increase excess of runner and extend cooling time.

Gate

It is a channel connecting main runner (or branch runner) and cavity. Cross-sectional area of runner can be equal to main runner (or branch channel), but it is usually reduced. So it is the smallest cross-sectional area in entire runner system. Shape and size of gate have a great influence on quality of product.
Role of gate is:
A. Control material flow speed:
B. It can prevent backflow due to early solidification of melt stored in this part during injection:
C. Passing melt is subjected to strong shear to increase temperature, thereby reducing apparent viscosity and improving fluidity:
D. It is convenient to separate product and runner system. Design of gate shape, size and position depends on nature of plastic, size and structure of product. Generally, cross-sectional shape of gate is rectangular or circular, cross-sectional area should be small and length should be short. This is not only based on above effects, but also because it is easier for small gates to become larger, and it is difficult for large gates to shrink. Gate location should generally be selected where product is thickest without affecting appearance.
Design of gate size should take into account properties of plastic melt. Cavity is space in mold for molding plastic products. Whole components used to form cavity are called molded parts.
Each molded part often has a special name. Molded parts that make up shape of product are called female molds, and ones that make up internal shape of product (such as holes, grooves, etc.) are called cores or punches (also called male molds). When designing molded parts, first determine overall structure of cavity according to properties of plastic, geometry of product, dimensional tolerances and requirements for use.
Second is to select parting surface, gate, vent position and demolding method according to determined structure.
Finally, according to size of control product, design of each part and combination of each part are determined. Plastic melt has a high pressure when it enters cavity, so molded parts must be selected reasonably, checked for strength and rigidity.
In order to ensure that surface of plastic products is smooth, beautiful and easy to demold, roughness of surface in contact with plastic should be Ra>0.32um, and it should be corrosion resistant. Formed parts are generally heat treated to increase hardness, and are made of corrosion-resistant steel.

Temperature control system

In order to meet mold temperature requirements of injection process, a temperature adjustment system is required to adjust mold temperature. For injection molds for thermoplastics, a cooling system is mainly designed to cool mold. Common method of mold cooling is to place a cooling water channel inside mold, and use circulating cooling water to take away heat of mold; in addition to use of hot water or steam in cooling water channel, heating of mold can even install electric heating elements in and around mold.

Molded parts

Refers to various parts that constitute shape of product, including movable molds, fixed molds and cavities, cores, molding rods, and vents. Molded part consists of a core and a cavity mold. Core forms inner surface of product, and concave mold forms outer surface shape of product. After closing mold, core and cavity constitute cavity of mold. According to process and manufacturing requirements, sometimes core and die are combined by several pieces, and sometimes they are made as a whole, inserts are only used for parts that are easily damaged and difficult to process.

Exhaust vent

It is a trough-shaped air outlet opened in mold to discharge original gas and gas brought in by molten material. When melt is injected into cavity, air originally stored in cavity and gas brought in by melt must be discharged out of mold through exhaust port at the end of material flow, otherwise product will have pores, poor connection, uncompleted filling of mold, and even accumulated air will burn product due to high temperature and compression.
Under normal circumstances, vent hole can be located at the end of melt flow in the cavity or on parting surface of mold. Only a shallow groove with a depth of 0.03-0. 2mm and a width of 1.5-6mm is inserted into die. During injection, there will not be a lot of molten material in vent hole, because molten material will cool down, solidify there and block channel. Opening position of exhaust port should not be facing operator to prevent accidental spraying of molten material and hurting people. Also use matching gap between ejector rod and ejector hole, matching gap between ejector block, stripper plate and core to exhaust.

Structural parts

It refers to various parts that constitute mold structure, including: various parts for guiding, demolding, core pulling and parting. Such as front and rear splints, front and rear buckle templates, bearing plates, bearing columns, guide columns, stripping templates, demolding rods and return rods.

1. Guide parts

In order to ensure that movable mold and fixed mold can be accurately aligned when mold is closed, a guide part must be provided in mold. In injection mold, four sets of guide posts and guide sleeves are usually used to form guide parts. Sometimes it is necessary to set mutually coincident inner and outer cones on movable mold and fixed mold to assist positioning.

2. Launch agency

During mold opening process, an ejection mechanism is required to push or pull out plastic products and aggregates in runner. Push out fixed plate and push plate to clamp push rod. A reset rod is generally fixed in push rod, reset rod resets push plate when moving and fixed molds are closed.

3. Side core pulling mechanism

Some plastic products with undercuts or side holes must be parted laterally before being pushed out. After lateral cores are pulled out, they can be demolded smoothly. At this time, a side core pulling mechanism is required in mold.
Common defects of injection molds and their adjustment methods

Injection mold assembly defects	Cause	Adjustment method
Mold opening and closing Ejection reset Not moving well	1. Guide post and guide sleeve of mold base do not slide smoothly, and fit is too tight 2. Lifter, thimble does not slide smoothly. 3. Return spring has insufficient elastic force or preload.	1 Repair or replace guide post and guide sleeve. 2 Check and repair matching of lifter and thimble. 3 Add or replace spring.
Mold and injection Machine does not match	1. Position of positioning ring is wrong, size is too large or too small. 2. Width of mold is too large; height of mold is too small. 3. Position of ejector hole of mold is wrong; Position of hole is forced to be reset, and size is wrong.	1. Replace positioning ring; adjust position and size of positioning ring. 2. Change tonnage of first-class injection molding machine; increase thickness of mold. 3. Adjust position and size of ejector hole; adjust position and size of reset hole.
Part is difficult to fill Difficult to pick up	1. Gating system is blocked, runner cross-section size is too small, gate layout is unreasonable, and gate size is small. 2. Limit stroke of mold is not enough, core pulling stroke of mold is not enough, and ejection stroke of mold is not enough;	1. Check runners and gates of each section of gating system, and trim related parts; 2. Check whether each limit, core pulling and ejection stroke meet the design requirements, and adjust the stroke that does not meet the requirements;
Mould transport Blocked or leaking	1 Mold water channel is blocked, connection mode of water inlet and outlet pipe joints is wrong. 2 Sealing performance of water sealing rubber ring and water pipe joint is not enough.	1. Check connection mode of water inlet and outlet pipe joints of cooling system and various sections of water channels, repair relevant parts; 2. Check sealing rubber ring and water pipe joint, repair or replace related parts;
Quality of parts is not good: 1. Has flash 2. There is a shortage of materials 3. There is a top white 4. Has drag flowers 5. Large deformation 6. Big rank 7. Obviously dissolving wiring	1. Fit clearance is too large; 2. Material is not smooth and trapped; 3. Pin is too small and ejection is uneven; 4. Slope is too small, there are burrs, and hardness is insufficient; 5. Uneven injection pressure and insufficient product form strength; 6. Processing error; 7. Far from gate, mold temperature is low.	1. Reasonably adjust clearance and parting surface of grinding work part; 2. Partially add glue and exhaust; 3. Increase pin and distribute it evenly; 4. Trimming burrs, adding slope and nitriding; 5. Trimming gate, uniform pressure, strengthen product strength; 6. Reprocessing; 7. Improve gate and increase mold temperature.

Gud Mould Industry Co., Ltd