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Automotive interior panel injection mold design Mar 17, 2018

With the development of society, people are demanding more and more cars. Not only do they require the car to have good performance, but they also require a good profile and a comfortable and beautiful interior and exterior trim. In order to save energy consumption and make cars lose weight, plastic parts have become an indispensable and important part of modern automobiles. Automotive interior panels produce injection-molded parts, which are large in size and have high dimensional and assembly accuracy requirements. Nowday we use CAD/CAE/CAM technology for mold design and manufacturing, accelerating the speed of mold design and manufacturing, reducing the number of trials, resolving common defects, and quickly and efficiently manufacturing qualified products to improve the economic efficiency of the company.Following is the processing .

 

1 plastic parts process analysis

The material of the automotive interior panel must have good aging resistance, impact resistance, flame retardant and comprehensive mechanical properties. In addition, the plastic part has a large size and a complex structure, so the material must also have good fluidity to satisfy the charge. Model requirements. After comparison, polypropylene (PP) can meet the above requirements, good fluidity at the time of injection, and easy molding, but the shrinkage rate is large, the shrinkage rate is 1% to 2%, and defects such as shrinkage holes, dents and deformation are easily generated. Internal stress is prone to occur when solidification speed is high. Therefore, attention should be paid to controlling the molding temperature and appropriately reducing the cooling rate. Otherwise, the surface of the plastic part will lose gloss or the plastic part will warp. The main process parameters of polypropylene injection are: melting temperature is 220-275°C, care should not exceed 275°C; mold temperature is 40-80°C, 50°C is recommended, the degree of crystallization is mainly determined by the temperature of the mold

2. Mold structure analysis

Plastic parts are relatively complex in shape, large in size and large in production volume. Comprehensive consideration of the above factors, the use of a two-cavity, symmetrical distribution of the mold structure, due to the complex shape of the surface of the plastic parts, and many irregular surfaces, so in the design of the parting surface, the main part of the plastic surface is The extended surface of the largest outer contour is divided by the UG NX injection mold guide mold splitting tool. Due to the large outer shape of the plastic parts, the size of the parting surface is correspondingly large. When the mold is actually used, the pressure surface of the mold is too wide. Requires a larger injection molding machine, pressure surface is too small, affect the life of the mold. Under normal circumstances, the width of the bearing surface is 30 mm, and the part over 30 mm is designed to avoid an air gap of 1 mm. The cavity side and the core side are designed as o. 5 mm, at the same time can effectively reduce the number of CNC milling man-hours.

2.2 gating system design

The mold uses a two-cavity, balanced flow channel layout structure. The gate is selected on a reinforcing rib on the inside of the plastic part. The submerged gate is used to lubricate the gate on the top bar to ensure the appearance of the surface.

2.3 Molding Part Design

The structure of the core is relatively complex. From the consideration of the processing technology and accuracy of the mold, the core is made into an integral embedded structure. The core contains a plurality of inserts, the insert can be replaced, the service life of the mold is improved, and the mold is reduced. The processing cost [1]. The cavity adopts an integral embedding structure and is partially made of inserts and inserts. The assembly and disassembly are convenient and easy to maintain and replace.

2.4 Inclined Mechanism Design According to the structural characteristics of the product, this mold needs to design 8 oblique roof structure, in which the inner groove depth and the sliding block connection head are flattened and screwed, and the screws are required to be removed from the back of the mold. Push plate through holes to facilitate mold maintenance. The split-type structure is designed so that the slope of the back of the oblique roof body is greater than the degree of inclination of the diagonal guide rod. ~3. , Prevent the back of the inclined roof body from generating friction with the punch, and the two sides of the inclined roof are required to be designed with the slope. In general, the slope is 3 degrees.

2.5 Cooling system design The temperature of the injection mold has an important influence on the filling flow of the plastic melt, solid set, production efficiency, and the shape and dimensional accuracy of the plastic parts [1]. After many considerations, the circulating cooling water passage is used, and the diameter of the cooling water passage is 10 mm. The fixed mold part is introduced into the fixed mold cavity insert to set up a circulating cooling water passage (see FIG. 8 ), and a spacer-type circulating cooling water passage is also added to the fixed mold part to control the mold temperature within the required temperature range. Shorten the molding cycle based on the quality of plastic parts. The moving mold part is driven by a movable platen to insert a moving mold insert and a straight-through cooling water channel (see Figure 9). An “O”-type seal ring seal shall be added between the fixed template and the fixed mold cavity insert, the movable mold plate, and the dynamic mold core insert to prevent water leakage.

2.6 Exhaust system Exhaust from the mold parting surface is very important for the production of qualified products. It is required to design exhaust ducts on the parting surface, the slider, and the periphery of core inserts that need to be vented. Exhaust slots are generally designed at the plastic-filled end and are designed for easy processing on the core side or cavity side.

2.7 Ejection Mechanism and Guide and Positioning Mechanism Design 2.8 Mold Working Principle The ejector mechanism is designed as an ejector ejector, using a 10 mm ejector pin. At the same time, eight inclined-head mechanisms are provided in the mold. The top is mainly involved in ejecting the product by moving the ejector plate fixing plate. The mold design purchases the standard mold frame. The external dimensions of the mold frame are 800 mm×800 mm×650 mm, including the guide mechanism. The guide mechanism includes a guide post and a guide bush. The guide post and the corresponding guide bush are selected according to the size structure of the mold frame.

3 Conclusions The UG NX's own M01dWizard module is used for automotive interior panel injection mold design. The MoldWizard module includes supply information for a number of mold carriers, as well as intelligent components and mold carriers. It can be used to quickly design mold structures and greatly reduce The time for designing, customizing, and refining mold parts for injection molds has improved design efficiency. At the same time, it provides a data model for the processing of mold parts and three-dimensional coordinates, and the most important thing is to ensure the accuracy of the products after injection molding, reduce the number of tryouts, and shorten the design and production cycle of molds. In the design of the mold structure, it is necessary to match with its own specific process environment. Due to the large size of the product, it is designed as a hot runner injection mold structure, which improves the fluidity of the plastic in the injection molding process. The filling effect is good, no short shots and other phenomena occur, and the formed runner system is saved, and the molding cycle of the plastic parts is shortened at the same time. The mass production of plastic parts proves that the structure of the mold is rationally designed, concise and practical, and the plastics produced meet the quality requirements.