1. Panel;2. Heat shield;3. A plate;4. Lock module;5. Line pressing block;6. B board;7. The iron;8. Push rod fixing plate;9. Push rod bottom plate;10. The base plate;11. Positioning ring;12. The machine's mouth;13. Temperature needle;14. Push tube needle;Support column; 15.16. The ejector sleeve;17. Garbage nails;Heating tube 19. Guide post;Pressure plate; 20.21. Protection block of junction box;22. The guide bush;23. The push rod;24. Limit block;25. Reset;26. Fast reset;27. Moving die inserts;28. Reset lever;Push pipe sleeve; 29.Push tube needle; 30.31. Push rod plate guide sleeve;Push rod plate guide post; 32.33. Push tube needle press block;
Figure 2, Figure 3 and Figure 4 are the mold structure drawings of automobile headlight reflector.Although its basic structure is similar to that of the thermoplastic injection mold, compared with the latter, it has the following typical differences and characteristics:
(1) Reverse mold
The die mentioned here is not inverted die.General mold cavity in fixed mold, mold core in moving mold.Because the mirror plastic core is multi-surface reflection and concentrated light working face, need very low roughness, absolutely cannot set push rod and other ejector device, so the mold must be reversed, that is, the convex core (mirror working face) is set in the fixed mold, the concave cavity is set in the moving mold.
(2) The mold shall be heated by a heating tube and the temperature shall be strictly controlled
The injection molding process of BMC material is completely different from that of ordinary thermoplastic injection molding process. The injection molding machine barrel part needs to be cooled by special refrigerating machine ice water, while the mold cavity core needs to be electrically heated.
The following formula can be used to calculate the total power W of the electric heat pipe required by the fixed mode:
G: The total weight of the fixed die,kg
Cp: Specific heat capacity of mold material, KJ /(kg.°C)
Tm: Temperature required for mold forming: °C
To: Room temperature: °C
Y: Heater efficiency, 0.3-0.5
T: Heating time, h.
Generally, the diameter of the electric heat pipe is 15.8mm, which can improve the mold temperature quickly.According to experience, the heating power of die can be calculated according to (40-50) W/kg.The forming surface of the plastic part is 40-50mm away from the electric heat pipe, and the distance between the two electric heat pipes is 80-100mm.In order to improve the heating efficiency, an 8mm thick bakelwood heat insulation board shall be designed for all sides of the fixed mold. Since the electric heat pipe has no positive and negative poles, it can be connected in series, but each set of temperature controller socket shall not exceed 3.6kW.The temperature of each set of electric heat pipe is controlled by a set of thermocouples. The thermocouple should be in the center of the temperature field of this set of electric heat pipe, and the thermocouple head should be in effective contact with the mold cavity, which is conducive to accurate temperature control.
(3) Mold runner system needs to control temperature
Since the material formed by thermosetting injection mold starts to solidify by chemical cross-linking reaction when it exceeds a certain temperature, the solidified pouring system can only be used as waste material instead of recovery, so it is of great significance to adopt the flow path without the solidified pouring system.Therefore, the sprue sleeve of the mold should be cooled with cold water.In order to reduce excessive shear heat generated during injection molding and improve injection molding speed, fan-shaped diverter channels are generally set in moving molds with a gate thickness of 2.0-2.5mm so as to prevent molten BMC material from curing before filling high temperature cavities.
(4) Requirements for mold parting surface
The viscosity of BMC material is lower than that of thermoplastics. No holes or pits are allowed on the parting surface. The sliding block locking block and pressing block are not allowed to be set at the die core, otherwise it will cause the problem of flash cleaning.
(5) The exhaust of mold cavity needs to be strengthened
Ordinary thermoplastic plastic molding is a physical change process, and thermosetting plastic injection molding is a chemical reaction process, chemical reaction will produce a large number of volatile gas, these gases will produce a lot of resistance to injection molding, resulting in plastic surface bubbles and lack of materials, at the same time the gas compression produced by high temperature burning plastic parts.Therefore, it is particularly important to exhaust the mold cavity of thermosetting injection molding. In general, the parting surface of the mold and the bottom of the insert of the fixed mold shall be equipped with high-temperature sealing ring, and the end of the feed flow of the fixed mold cavity shall be vacuated to overcome the forming defects, which is also convenient to improve the injection speed.
(6) High precision of plastic parts
The light distribution of the reflector is very high, and the roughness of the reflector, machining and assembling precision are very high.In addition to the edge lock of mould blank and the positioning of guide post, it is also necessary to design the positioning of mould kernel stop to ensure the reliable three-stage positioning of the mould.The polyhedron has a small area of light distribution grain, so manual polishing cannot be carried out. Precision five-axis high-speed CNC machining machine must be adopted, and the spindle speed of the machine tool can reach more than 20000 RPM.Adopt advanced CAM technology and special cutting tools, choose reasonable processing technology, one processing in place.Cavity precision is required to be 0.01-0.02mm, cavity surface roughness is 0.05-0.10 micron.
3.1 Design of forming parts
The molding parts and template of this mold adopt integral body, commonly known as the original body.Compared with the split-type structure, its advantages are compact structure, good strength and rigidity, small mold volume, and avoid the cumbersome procedures such as opening frame, matching frame and manufacturing inclined wedge.
The inner surface of the headlamp reflector is required to be very high, and the roughness is small. Thimble and inlay marks are not allowed, so it must be molded by fixed mold. The outer surface has relatively low requirements and is molded by moving mold.
This plastic part is one of the most important exterior parts of automobile, and it is a high-gloss part, the surface needs vacuum electroplating.In the design of this mold, we must first pay attention to the selection of mold materials.Due to poor flutility of BMC material, overflow tank needs to be designed around the moving template cavity, and push rod needs to be designed at the bottom of the overflow tank to facilitate the discharge, as shown in FIG. 11.The BMC thermosetting material is filled with glass fiber, and the mold needs to have high wear resistance, hot red hardness, heat resistance and fatigue.Due to the strict light distribution requirements of the mirror, the core should have good polishing performance.Therefore, the mold fixing material USES German 2344ESR hot tool steel with excellent hardenability, quenching hardness of 48 ~ 52HRC.The steel material remelted by vacuum electroslag improves the crystal uniformity of steel and the polishing effect is excellent.The fixed mold is often polished by hard chromium plating to reduce surface roughness, improve wear resistance and prevent corrosion.Moving mold, moving mold inserts are made of German 2344HT hot tool steel, quenching hardness of 48 ~ 52HRC.
The insertion Angle of the fixed die on the insertion part of this mold is guaranteed to be above 7 degrees at least. In order to ensure the accurate positioning of the fixed die, the fixed die adopts the positioning of the four-angle stop and the surrounding edges.Due to the need for accurate positioning at the insertion place, the fixed die needs to be tightly matched when fitting the die. In order to make the die beautiful and match the mold, a 5-degree wear-resisting block is designed in the fixed die, so as to avoid the occurrence of ugly grinding of the mold by the fitter.At the same time, wear-resistant block design, convenient fitter mold matching, to ensure the beauty of the mold.
This mold design also achieved the following points:
1) The parting surface is smooth without sharp Angle, thin steel, wireless or point sealant;The surface sealing adhesive is constructed, and the surface method such as extension, sweep and mesh is used in the parting. The parting surface is constructed according to the shape of the plastic part. The parting surface of the vehicle lamp mold is highly required, and the wrinkling of the constructed surface is not allowed.The parting surface constructed can effectively ensure CNC machining accuracy, without EDM Angle cleaning, parting surface is not easy to run burr.High speed machine is needed when the auto lamp mould parting surface polishing tool, and the spindle speed of the machine tool is guaranteed to be above 20000 RPM at least.
2) The fitting part of insert and moving die is designed with appropriate technology of turning R Angle or avoiding vacancy at the end of the stop, which simplifies the processing procedure and reduces the processing time to improve the processing efficiency.
3) Design R angles of all non-forming corners to prevent stress cracking. Process R angles shall be no less than R5. Design a relatively large process R Angle as far as possible according to mold size;Sharp edges on the mold are easy to cause accidental injury to the operator. The edges that are not involved in forming or cooperating should be designed with C or R angles, and a larger chamfer should be designed as far as possible according to the size of the mold.
4) Avoidance of parting surface: The width of parting surface is 40MM, and 1MM should be avoided for the fixed die in the area outside parting surface, so as to effectively reduce processing time.The avoidance of parting surface not only refers to the peripheral parting surface, but also includes large area parting surface.Special note: the width of the parting face of the die includes the exhaust slot.The pressure block should be designed in the large area of space to ensure the uniform force of the mold, to avoid the mold from running in the long term production. When the perforated area of the mold is designed to avoid the air, the exhaust hole should be designed in the fixed or moving mold to facilitate the discharge of compressed air when the fixed or moving mold is closed.
5) The parting surface shall be constructed according to the shape of the plastic parts, and the plastic parts shall be optimized when necessary.For medium and large mold, pressure plate groove should be opened as far as possible to facilitate CNC machining.When designing parting surface, try to simplify mold processing and make it smooth and smooth. The parting surface is made without thin steel, sharp Angle and reasonable insertion Angle.
6) The parting surface is smooth and flat, and it is forbidden to have many small broken surfaces when UG parting (CNC machining is easy to snap and the machining accuracy is reduced). Try to use extension surface, mesh surface and sweep surface to build the parting surface, or first extend 10-20mm glue sealing surface, then make stretch surface and transition surface, and the glue sealing surface is designed according to the tonnage of injection molding machine and the size of mold.
7) The parting surface or all the piercing angles shall be designed above 7 degrees to improve the service life of the mold.
3.2 Gating system design
The mold casting system adopts "ordinary runner + fan-shaped gate".Because the plastic part is BMC material, the flow is poor, when designing the runner, the runner should be thick and short.In order to reduce excessive shear heat generated during injection molding and improve injection molding speed, fan-shaped diverter channels are generally set in moving molds with a gate thickness of 2.0-2.5mm so as to prevent molten BMC material from curing before filling high temperature cavities.
3.3 Design of temperature control system
Automobile headlight reflector is one of the most important exterior parts of automobile and also one of the plastic parts with the highest appearance requirements. Therefore, the design of temperature control system has a great influence on the molding cycle and product forming quality of the mold.Because the plastic parts are made of BMC material, the injection molding process of BMC material is completely different from that of ordinary thermoplastic injection molding process. The injection molding machine barrel part needs to be cooled by special refrigerating machine ice water, while the mold cavity core needs electric heating.
The layout of heating pipes is similar to that of waterways and Wells, and can be designed as vertical layout or horizontal layout.The forming surface of the plastic part is 40-50mm away from the electric heat pipe, and the distance between the two electric heat pipes is 80-100mm.In order to improve the heating efficiency, an 8mm thick bakelwood heat insulation board shall be designed for all sides of the fixed mold. Since the electric heat pipe has no positive and negative poles, it can be connected in series, but each set of temperature controller socket shall not exceed 3.6kW.The temperature of each set of electric heat pipe is controlled by a set of thermocouples. The thermocouple should be in the center of the temperature field of this set of electric heat pipe, and the thermocouple head should be in effective contact with the mold cavity, which is conducive to accurate temperature control.See Figures 5 and 6.