阅读说明：本技术 一种滚塑成型模具及其加工工艺 (Rotational molding die and machining process thereof ) 是由 江洁 赵海波 于 2019-08-27 设计创作，主要内容包括：本发明公开了一种滚塑成型模具及其加工工艺,可以实现开发出一套材料-结构-工艺相互耦合的设计体系,通过玻纤增强聚乙烯树脂及辅助料的材料准备,并采用大型复杂铝合金模具单元分割组合成型的方法,对全塑车身模具进行三维单元分块,利用铝合金铸造成型技术制造铝合金微元,可以将形状负责的全塑车身模具化整为零,降低了车身模具整体加工的难度,提高了模具的使用寿命,并保证了制品的表观质量,在工艺上引进了定向加热的新型控温手段,在保证模具全局温度均匀的微观控制下,可以实现对部分重点区域的定向加热,不但能生产出壁厚均匀高质量产品壁厚均匀,甚至将局部区域加厚,提高产品的力学强度和产品的使用寿命。(The invention discloses a rotational molding die and a processing technology thereof, which can realize the development of a material-structure-technology mutual coupling design system, carry out three-dimensional unit blocking on an all-plastic body die by the material preparation of glass fiber reinforced polyethylene resin and auxiliary materials and adopt a method for cutting, combining and molding a large-scale complex aluminum alloy die unit, manufacture aluminum alloy microelements by using an aluminum alloy casting molding technology, can break the all-plastic body die with the shape charge into parts, reduce the difficulty of the whole processing of the body die, prolong the service life of the die, ensure the apparent quality of a product, introduce a novel temperature control means of directional heating on the technology, realize the directional heating of partial key areas under the microcosmic control of ensuring the global temperature uniformity of the die, not only can produce products with uniform wall thickness and high quality and uniform wall thickness, even the local area is thickened, the mechanical strength of the product is improved, and the service life of the product is prolonged.)

1. the utility model provides a rotational moulding forming die, includes the mould body, its characterized in that: the mould comprises a mould body and is characterized in that a full-plastic car body cavity is dug at the inner end of the mould body, the mould body comprises a plurality of mould subunits (1), the mould subunits (1) are assembled through bolts and nuts, each mould subunit comprises a multi-point temperature control subunit (1a) and a single-point temperature control subunit (1b), temperature control cavities (4) are dug at the inner ends of the multi-point temperature control subunits (1a) and the single-point temperature control subunits (1b), an auxiliary control module (5) is installed at the inner end of each temperature control cavity (4), the auxiliary control module (5) is connected with a central control module (2), a split heat transfer net (7a) is fixedly connected to one end wall, close to the full-plastic car body cavity, in each temperature control cavity (4) of the multi-point temperature control subunit (1a), and at least one temperature control node (6) is fixedly connected to a node of the split heat transfer net (7a), an integrated heat transfer net (7b) is fixedly connected to one end wall of the temperature control cavity (4) of the single-point temperature control subunit (1b) close to the all-plastic vehicle body cavity, only one temperature control node (6) is fixedly connected to a node of the split heat transfer net (7a), and the temperature control node (6) is connected with the auxiliary control module (5).

2. A rotomoulding mould as claimed in claim 1, wherein: the temperature control node (6) comprises a heat conduction ring (61), an electric heating wire (62) and a thermocouple (63) are respectively installed at the inner end of the heat conduction ring (61), the heating end of the electric heating wire (62) is in contact with the inner end wall of the heat conduction ring (61), and the measuring end of the thermocouple (63) is in contact with one end wall, close to the all-plastic automobile body cavity, in the temperature control cavity (4).

3. a rotomoulding mould as claimed in claim 1, wherein: the split type heat transfer net (7a) comprises a plurality of bidirectional heat transfer wires, an adjacent pair of temperature control nodes (6) are connected through the bidirectional heat transfer wires, each bidirectional heat transfer wire comprises a pair of end heat transfer wires (71), and a heat insulation sheet (72) is welded between the pair of end heat transfer wires (71).

4. A rotomoulding mould as claimed in claim 1, wherein: the central control module (2) is connected with a cloud server (3).

5. The process of manufacturing a rotational molding die according to any one of claims 1 to 4, wherein: the method comprises the following steps:

Step one, preparing plastic raw materials: extruding and granulating polyurethane resin powder and an auxiliary agent in advance, adding the polyurethane resin powder and the auxiliary agent into an auxiliary material bag, metering and dispersing polyethylene and glass fiber by using a mixer, and stirring and mixing to obtain powdery glass fiber reinforced polyethylene resin;

step two, rotational molding preparation: sequentially assembling and closing a plurality of die subunits (1) to form a die body, sending a preheating signal to a secondary control module (5) through a central control module (2), and controlling corresponding temperature control nodes (6) to start heating up to preheat the die body by the secondary control module (5);

Step three, rotational molding: starting a double shaft of a rotational molding machine to rotate, firstly circulating hot gas in an oven for 3 times, then adding glass fiber reinforced polyethylene resin into a mold body, heating to 250-350 ℃, maintaining the heating time for 30-45min, acquiring a temperature value in real time by a thermocouple (63) and feeding the temperature value back to an auxiliary control module (5), wirelessly transmitting the temperature value to a central control module (2) by the auxiliary control module (5), feeding a temperature control signal back after data processing and analysis are carried out on the central control module (2), controlling an electric heating wire (62) by the auxiliary control module (5) to carry out temperature regulation, realizing temperature control circulation, opening an auxiliary material bag after the glass fiber reinforced polyethylene resin melts and covers the inner wall of the mold, releasing a foamed polyurethane material, heating and rotating to enable the polyurethane material to form a compact glass fiber reinforced polyethylene layer;

Step four, cooling and mold opening: and (5) obtaining the full-plastic vehicle body (8) by adopting a four-step cooling method.

6. The process of claim 5, wherein the rotational molding die comprises the following steps: in the first step, the glass fiber accounts for 10% -12% of the polyethylene content, and the length of the glass fiber is 3-3.5 mm.

7. The process of claim 5, wherein the rotational molding die comprises the following steps: the preheating temperature in the second step is 150-200 ℃, and the preheating time lasts for 10-15 min.

8. The process of claim 5, wherein the rotational molding die comprises the following steps: and in the third step, the temperature control node (6) directionally heats the weak part and the key part of the all-plastic vehicle body (8) on the premise of keeping the overall temperature of the mold body uniform, so that the temperature of partial areas is slightly increased.

9. The process of claim 5, wherein the rotational molding die comprises the following steps: and in the third step, the flow speed of hot gas in the oven of the rotational molding machine is changed for 20-50 times per minute, and the hot gas is nitrogen, carbon dioxide or inert gas.

10. The process of claim 5, wherein the rotational molding die comprises the following steps: the four-step cooling method is divided into four stages:

the first stage is cooling in the heating chamber, i.e. the heating chamber is stopped heating, and the temperature of the product is slowly reduced from about 320 ℃ to about 230 ℃;

In the second stage, heat preservation and pressure maintaining are carried out in a heating chamber, namely the temperature of the product is kept at 230 ℃ for 10min, and the interior of the product is inflated and pressurized for about 10s under 0.2 MPa;

the third stage is forced air cooling, namely after the mould is removed from the heating chamber, reducing the temperature of the vehicle body product from about 230 ℃ to about 60 ℃ by using the forced air cooling;

and the fourth stage is clamp shaping, namely, the product is taken out after the plurality of mould subunits (1) are sequentially disassembled, the product is fixed by a shaping clamp, the product is cooled to room temperature and kept for 5 to 6 hours, and the inside of the product is inflated and pressurized to about 6Mpa in the shaping and cooling process.

Technical Field

the invention relates to the technical field of mold processing, in particular to a rotational molding mold and a processing technology thereof.

background

The main direction of the development of the automobile material technology in the world is light weight and environmental protection. The reduction of the weight of the automobile is one of the most effective measures for reducing the emission of the automobile and improving the combustion efficiency, and the self weight of the automobile is reduced by 10 percent, and the consumption of fuel oil can be reduced by 6 to 8 percent. In developing a more economical, safer and lighter vehicle, materials are a key element. Aluminum alloys, high strength steels, synthetic plastics and ceramics have become competing partners in certain applications over the years. Among these materials, plastics have the lowest specific gravity, which is 36% lighter than aluminum alloys and 78% lighter than steel, and have good mechanical properties, corrosion resistance and easy processing, and have been regarded by the automotive engineering community. Therefore, increasing the usage amount of plastic materials in automobiles becomes a key to reduce the cost and the weight of the whole automobile and increase the effective load of the automobile.

the plastic is a high molecular material which takes synthetic resin as a matrix, is added with different additives and is molded into products with various shapes under the action of certain temperature and pressure. Plastics are of various types, and are classified into thermosetting and thermoplastic types according to thermal properties; can be divided into general plastics, engineering plastics and high-performance engineering plastics according to the application range. Plastics are used in almost all automotive assemblies, and it is customary in the industry to divide them into interior (trim) parts, exterior parts and functional parts (other structural parts). The automobile safety and comfort improvement system provides great technical support for improvement of automobile safety, comfort, light weight, recycling and the like.

in modern vehicle body design, the aim of light weight is generally achieved by structural optimization and material replacement. On one hand, the light weight of the vehicle body is realized through structural improvement, namely, based on a finite element analysis method, by applying topological optimization in a conceptual design stage, applying shape optimization in a basic design stage and applying size optimization in a detailed design stage, the designed structure is ensured to meet basic performance requirements, and materials can be saved to the maximum extent, so that the overall quality is reduced, and the optimal structure is obtained; on the other hand, the light weight design of the vehicle body is realized by adopting a material replacement method, namely, the aim of reducing the quality of parts is fulfilled by applying high-strength or low-density materials, such as high-strength steel, aluminum alloy, magnesium alloy, plastic, composite materials and the like. The structural optimization design and the introduction of novel materials on the vehicle body inevitably promote the improvement of the vehicle body manufacturing process level, so that the aim of light weight design is fulfilled through the research of novel manufacturing technology which is adaptive to the modern vehicle body design.

The development trend of the automobile composite material automobile body is gradually changed into an integral composite material frameless automobile body, and various processes are provided for forming an automobile body covering part. The composite material vehicle body is formed by injection molding, so that the design difficulty of a mold is high, and the processing cost is high; the car body is formed by adopting a resin transfer molding process, so that a complex car body structure is difficult to form, and a plurality of car bodies made of composite materials need to be bonded into a whole; the method of the hand lay-up forming process is adopted, so that the automobile forming efficiency is low, the process is complicated, and the automobile industrialization is difficult to realize.

Referring to fig. 10, the rotational molding process is to add plastic raw materials into a mold, then the mold is continuously rotated along two vertical axes and heated, so that the plastic raw materials in the mold are gradually and uniformly coated and fused on the whole surface of a mold cavity under the action of gravity and heat energy to be molded into a required shape, and then the product is obtained through cooling, shaping and demolding, and is convenient to mold a product with a complicated shape, a hollow shape and a large size under the condition of no additional stress. In recent years, with the innovation of composite materials and rotational molding die technology, products which cannot be molded by the traditional composite material special molding process (such as blow molding, injection molding, extrusion molding and the like) can be molded by rotational molding, such as large-sized products with complex structures. The rotational molding method is suitable for molding large members with relatively closed complex shapes, can mold complex structures such as wall surface concave-convex structures, double-layer wall surface structures and the like, and can realize one-step molding of the inner and outer covering parts of the automobile body.

although the rotational molding technology of the all-plastic automobile body has been developed, the defects of the all-plastic automobile body are obvious, on one hand, the all-plastic automobile body is complex in structure, strict in size requirement, high in precision requirement of the surface of the automobile body, difficult in design and processing of an integral mold, high in processing and maintenance cost of the mold, and large in processing and manufacturing difficulty of the all-plastic automobile and the mold thereof, on the other hand, the rotational molding mechanism is adopted, plastic raw materials in the mold are under the action of gravity and heat energy, particularly the heat energy is considered, and at present, hot air convection, open fire direct burning and liquid heat conduction are generally in 3 heating modes in rotational molding. Wherein the hot air convection heating mode is clean and safe, and the temperature field in the rotary molding equipment oven is easy to control. However, because the hot air in the rotary molding equipment oven is constantly in a motion change state, and because the structure of the car body is large in size and complex in shape, effectively controlling the hot air temperature field in the working area of the car body mold in the rotary molding equipment oven is the key for ensuring the integral one-step molding of the all-plastic car body, secondly, in the rotary molding process, the temperature has a great influence on the powder in the rotary molding mold, and the uniformity of the surface temperature of the mold has a great influence on the uniformity of the wall thickness of the product. The uniform and symmetrical product is formed by the rotational molding process, and the uniformity of the wall thickness of the product is easy to realize; it is difficult to maintain uniform wall thickness in asymmetric and severely embossed products. The all-plastic vehicle body structure belongs to a deep concave structure, has more concave-convex characteristics on the surface, and has slow air flow in the interior, so the macroscopic control effect in the prior art is very little, and the forming quality and the development of the all-plastic vehicle body are restricted.

Disclosure of Invention

1. technical problem to be solved

aiming at the problems in the prior art, the invention aims to provide a rotational molding die and a processing technology thereof, which can realize the development of a set of design system of material-structure-technology mutual coupling, carry out three-dimensional unit blocking on a full-plastic vehicle body die by the material preparation of glass fiber reinforced polyethylene resin and auxiliary materials and adopting a method of large-scale complex aluminum alloy die unit division combined molding, manufacture aluminum alloy infinitesimal by using an aluminum alloy casting molding technology, can break the full-plastic vehicle body die with the shape responsible for the whole part, reduce the difficulty of the whole processing of the vehicle body die, have convenient installation and combination, improve the efficiency of die filling and demoulding, have convenient maintenance, improve the service life of the die, ensure the apparent quality of products, introduce a novel temperature control means of directional heating on the technology, ensure the microcosmic control of the uniform overall temperature of the die, the directional heating to partial key area can be realized, the wall thickness of the high-quality product with uniform wall thickness can be produced, even the local area is thickened, the mechanical strength of the product is improved, and the service life of the product is prolonged.

2. Technical scheme

In order to solve the above problems, the present invention adopts the following technical solutions.

A rotational molding mold comprises a mold body, wherein an all-plastic vehicle body cavity is dug at the inner end of the mold body, the mold body comprises a plurality of mold subunits, the mold subunits are assembled through bolts and nuts, each mold subunit comprises a multi-point temperature control subunit and a single-point temperature control subunit, temperature control cavities are dug at the inner ends of the multi-point temperature control subunit and the single-point temperature control subunit, an auxiliary control module is installed at the inner end of each temperature control cavity and connected with a central control module, a split heat transfer net is fixedly connected to one end wall, close to the all-plastic vehicle body cavity, of each temperature control cavity of the multi-point temperature control subunits and the single-point temperature control subunits, at least one temperature control node is fixedly connected to a node of the split heat transfer net, an integrated heat transfer net is fixedly connected to one end wall, close to the all-plastic vehicle body cavity, of each temperature control cavity of the, the node of the split heat transfer net is only fixedly connected with one temperature control node, and the temperature control node is connected with the auxiliary control module.

Furthermore, the temperature control node comprises a heat conduction ring, an electric heating wire and a thermocouple are respectively installed at the inner end of the heat conduction ring, the heating end of the electric heating wire is in contact with the inner wall of the heat conduction ring, the measuring end of the thermocouple is in contact with one end wall, close to the all-plastic automobile body cavity, in the temperature control cavity, the electric heating wire is used for directly heating the mold subunit, the temperature rise speed is high compared with that of a hot air convection method, accurate control is easy, and the thermocouple is used for collecting the temperature value of a specified area in real time and feeding the temperature value back to the auxiliary control module.

furthermore, the split type heat transfer net comprises a plurality of bidirectional heat transfer wires, and a pair of adjacent temperature control nodes are connected through the bidirectional heat transfer wires, each bidirectional heat transfer wire comprises a pair of end heat conduction wires, a pair of heat insulation sheet end heat conduction wires are welded between the end heat conduction wires and used for conducting heat to enlarge the temperature control area of the temperature control node, and the heat insulation sheets are used for insulating heat to limit the temperature control area of the temperature control node.

Furthermore, the central control module is connected with a cloud server, case analysis is carried out by uploading data to the cloud server, and an optimal temperature control scheme is optimized and formulated by utilizing a big data integration mode, so that the forming quality is improved.

A processing technology of a rotational molding die comprises the following steps:

Step one, preparing plastic raw materials: extruding and granulating polyurethane resin powder and an auxiliary agent in advance, adding the polyurethane resin powder and the auxiliary agent into an auxiliary material bag, metering and dispersing polyethylene and glass fiber by using a mixer, and stirring and mixing to obtain powdery glass fiber reinforced polyethylene resin;

step two, rotational molding preparation: sequentially assembling and assembling a plurality of die subunits to form a die body, sending a preheating signal to the auxiliary control module through the central control module, and controlling the corresponding temperature control nodes to start heating up to preheat the die body by the auxiliary control module;

step three, rotational molding: starting a double shaft of a rotational molding machine to rotate, circulating hot gas in an oven for 3 times, adding glass fiber reinforced polyethylene resin into a mold body, heating to 250-350 ℃, maintaining the heating time for 30-45min, acquiring a temperature value in real time by a thermocouple, feeding the temperature value back to an auxiliary control module, transmitting the temperature value to a central control module by the auxiliary control module in a wireless manner, processing and analyzing data by the central control module, feeding a temperature control signal back, controlling an electric heating wire by the auxiliary control module to adjust the temperature, realizing temperature control circulation, opening an auxiliary material bag after the glass fiber reinforced polyethylene resin is melted to cover the inner wall of the mold, releasing a foamed polyurethane material, heating and rotating to enable the polyurethane material to form a foaming layer on the compact glass fiber reinforced polyethylene layer;

step four, cooling and mold opening: and (5) obtaining the full-plastic vehicle body by adopting a four-step cooling method.

furthermore, in the first step, the glass fiber accounts for 10% -12% of the polyethylene content, the length of the glass fiber is 3-3.5mm, the strength and the modulus of the product are greatly improved, the elongation at break is reduced, and the stability of the size of the car body and the mechanical property of the car body are improved.

further, the preheating temperature in the second step is 150-200 ℃, the preheating time lasts 10-15min, the overall heating is firstly carried out on the die body through preheating, and the uniform temperature is kept, so that on one hand, the uniform flowing of the glass fiber reinforced polyethylene resin under the thermodynamic action is facilitated, and on the other hand, the influence caused by rapid temperature change is avoided.

Furthermore, the temperature control node in the third step directionally heats the weak part and the key part of the all-plastic automobile body on the premise of keeping the overall temperature of the mold body uniform, so that the temperature of a partial area is slightly increased, the temperature of the mold area is rapidly increased, the surface temperature of the mold is adjusted, the mold temperature of the automobile body mold is balanced, the product achieves the expected effect, the weak part of the all-plastic automobile body is directionally heated, high-quality products (uniform wall thickness) can be produced, even a local area is thickened (such as the wall thickness of a front bumper and a rear bumper), and the mechanical strength of the product and the service life of the product are improved.

Further, in the third step, the flow speed of hot gas in the oven of the rotational molding machine is changed 20-50 times per minute, the hot gas is nitrogen, carbon dioxide or inert gas, the flow speed of air close to the rotational molding die is low, and the temperature is low; the flowing speed of the wall surface of the oven close to the air inlet and the air outlet is higher, and the temperature is higher. The air flow rate in the furnace is accelerated, and the temperature change gradient of the air in the furnace can be reduced. But the taper phenomenon of the high and low air flow temperature is not effectively improved, and the temperature of the die is not uniform enough.

Further, the four-step cooling method is divided into four stages:

The first stage is cooling in the heating chamber, namely the heating chamber stops heating, the temperature of the product is slowly reduced from about 320 ℃ to about 230 ℃, and the disordered molecular structure in the product tends to be ordered and forms crystals;

and in the second stage, the heat preservation and pressure maintaining are carried out in a heating chamber, namely the temperature of the product is kept at 230 ℃ for 10min, and the product is inflated and pressurized for about 10s under 0.2MPa in the period. Experiments show that even if the pressurization time is short, bubbles in the product can be effectively removed;

the third stage is forced air cooling, namely after the mould is removed from the heating chamber, the mould is required to keep biaxial rotation in the process of reducing the temperature of the car body product from about 230 ℃ to about 60 ℃ by the forced air cooling, so as to ensure the uniformity of cooling;

and the fourth stage is clamp shaping, namely, the product is taken out after the plurality of mould subunits are sequentially disassembled, the product is fixed by a shaping clamp, the product is cooled to room temperature and kept for 5 to 6 hours, and the interior of the product is inflated and pressurized by about 6Mpa in the shaping and cooling process so as to achieve the purpose of stabilizing the appearance and prevent or reduce warping and deformation.

3. advantageous effects

Compared with the prior art, the invention has the advantages that:

The scheme can realize the development of a set of material-structure-process mutual coupling design system, the full-plastic vehicle body mould is subjected to three-dimensional unit blocking by adopting the material preparation of glass fiber reinforced polyethylene resin and auxiliary materials and a large-scale complex aluminum alloy mould unit division combination molding method, the aluminum alloy infinitesimal is manufactured by utilizing the aluminum alloy casting molding technology, the full-plastic vehicle body mould with the shape charge can be broken into parts, the integral processing difficulty of the vehicle body mould is reduced, the installation and combination are convenient, the mould filling and demoulding efficiency is improved, the maintenance is convenient, the service life of the mould is prolonged, the apparent quality of a product is ensured, a novel temperature control means of directional heating is introduced in the process, the directional heating of partial key areas can be realized under the microcosmic control of ensuring the global temperature uniformity of the mould, and not only can the products with uniform wall thickness and high quality be produced, even the local area is thickened, the mechanical strength of the product is improved, and the service life of the product is prolonged.

Drawings

FIG. 1 is a schematic structural view of the present invention;

FIG. 2 is a schematic structural view of a body portion of the die of the present invention;

FIG. 3 is a schematic structural view of the all-plastic vehicle body of the present invention;

FIG. 4 is a schematic structural diagram of a multi-point temperature control subunit according to the present invention;

FIG. 5 is a schematic view of a segmented heat transfer network according to the present invention;

FIG. 6 is a schematic diagram of a single-point temperature control subunit according to the present invention;

FIG. 7 is a schematic view showing the structure of an integral heat transfer net according to the present invention;

FIG. 8 is an exploded view of a segmented heat transfer mesh portion of the present invention;

FIG. 9 is a schematic view of the structure of the "solid + foamed + solid" face-to-face bond of the present invention;

FIG. 10 is a schematic view of prior art rotational molding;

FIG. 11 is a schematic structural view of a "solid + foamed + solid" interference type bond of the present invention.

the reference numbers in the figures illustrate:

the automobile body comprises a mold subunit 1, a multipoint temperature control subunit 1a, a single-point temperature control subunit 1b, a central control module 2, a cloud server 3, a temperature control cavity 4, an auxiliary control module 5, a temperature control node 6, a heat conduction ring 61, an electric heating wire 62, a thermocouple 63, a split heat transfer net 7a, a heat conduction wire 71 at the end, a heat insulation sheet 72, an integrated heat transfer net 7b and an all-plastic automobile body 8.

Detailed Description

the technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention; it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments, and all other embodiments obtained by those skilled in the art without any inventive work are within the scope of the present invention.

In the description of the present invention, it should be noted that the terms "upper", "lower", "inner", "outer", "top/bottom", and the like indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of description and simplification of description, but do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and thus should not be construed as limiting the present invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

In the description of the present invention, it should be noted that, unless otherwise specifically stated or limited, the terms "mounted," "disposed," "sleeved/connected," "connected," and the like are used in a broad sense, and for example, "connected" may be a fixed connection, a detachable connection, an integral connection, a mechanical connection, an electrical connection, a direct connection, an indirect connection through an intermediate medium, and a communication between two elements.