Multi-function diagnostic instrument panel injection mold design
Time：2022-02-09 20:33:59 / Popularity： / Source：
The former Fourth Ministry of Machinery Industry of my country formulated SJ 1372-78, which has become industry-recognized guiding standard. On this basis, GB/T 14486-1993 "Engineering Plastic Molded Plastic Parts Dimension Tolerance" was issued in 1993, it was revised again in 2008, and it was renamed "Molded Parts Dimension Tolerance Table".
Since there are many factors that affect dimensional accuracy of plastic parts, it is very important to reasonably determine dimensional tolerances in design of plastic parts. Generally speaking, under premise of ensuring use requirements, accuracy should be designed to be lower.
At present, there is no uniform dimensional tolerance standard for plastic parts in the world, but various countries have their own specified tolerance standards. For example, German standard is DIN16901; Swiss standard is VSM77012; French standard for plastic parts is NF T58-000; European general standard is DIN ISO 2768 tolerance table, which can be used as a reference when designing molds for export to Europe.
Due to different materials and processing methods of product, dimensional accuracy of plastic parts is different from that of mechanical products. Size of plastic parts is restricted by plastic materials. At the same time, its accuracy is also affected by material shrinkage fluctuations, mold manufacturing accuracy, injection technology, wear of molded parts, and thermal changes during mold parts assembly and use. Therefore, it is much more difficult to control accuracy of plastic parts than to control accuracy of other electromechanical products. It is particularly important to improve accuracy of plastic parts and control molding .
Dimensional accuracy of plastic part is also related to structure of plastic part. For example, difference in accuracy is different in mold structure design due to whether there is a lateral core pulling mechanism. Unreasonable ejection mechanism will cause ejection deformation. Compared with open plastic part structure, there is still a difference in shrinkage deformation, and plastic part itself also has installation elastic deformation.
According to role of plastic product in the entire product and assembly relationship, size of plastic product can be divided into: functional size; assembly size; free size.
Strict dimensional tolerances and geometric tolerances have brought technical difficulties to inspection. Difference between inspection of plastic parts and mechanical parts is that rigidity of plastic parts is poor. Sometimes, when shape of plastic part is irregular, it is difficult to straighten part. Excessive force during testing may also cause plastic parts to deform. Therefore, in view of this situation, plastic parts inspection needs to design inspection fixtures when necessary. Testing fixtures are mostly made of aluminum alloy, which is light and convenient to be placed on testing table or surface of three-coordinate instrument.
Panel plastic parts of multifunctional diagnostic instrument are small-size precision plastic parts. There are multiple button holes on the top of plastic part, and surface is required to be flat. There are 4 places on the side of plastic part that need to be designed with slider cores. Mold design diagram is shown in Figure 2. Mold base is a standard simplified fine nozzle mold base FCI3550. Simplified nozzle has 4 guide posts less than standard nozzle. Therefore, long side of mold base has a wider space, which is convenient for designing slider.
A slight modification in function of mold can lead to fully automatic injection molding and therefore increase labor productivity. Fully automatic injection molds usually produce better and more stable quality, reduce defective products. In most cases, life of mold can also be increased.
Fully automatic operation: Injection molding machine repeatedly completes the entire cycle of programmed molding function, only stops when machine or mold fails or is manually closed. Plastic parts and runner system of pouring system will automatically fall down or be removed by a robot.
When three-platen mold is fully automatic injection molding, long nozzle material is easily deformed and turned over, loses its original position, which makes it difficult to grasp by manipulator. Therefore, an anti-rotation column needs to be designed on aggregate of gating system, as shown in Figure 2. Another idea is to let nozzle material of three-platen mold automatically fall, but if there is a wire drawing phenomenon, automatic drop will fail, nozzle material may hang in the air, injection molding will fail when mold is closed again. Therefore, for fully automatic injection molding of three-platen mold, nozzle material should be grasped by a manipulator as much as possible.
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