1 First of all, we should fully understand the technical requirements of users such as mold structure, material, hardness and accuracy, including whether the shrinkage rate of molded plastic materials is correct and whether the three-dimensional modeling of products is complete, and make reasonable treatment and analysis.
2. Fully consider shrinkage cavity, flow mark, draft angle, weld mark and crack of injection molded products.
3. On the premise of not interfering with the product function and pattern forming of injection molded parts, simplify the processing method of the mold as much as possible.
4. Whether the selection of parting surface is appropriate, the mold processing, molding appearance and deburring of molded parts should be carefully selected.
5. Whether the pushing mode is appropriate, whether the push rod, stripper plate and push sleeve are adopted, and whether the positions of the push rod and stripper plate are appropriate.
6. Whether the side core-pulling mechanism is appropriate, flexible and reliable, and there should be no jamming phenomenon.
7. How to control the temperature is more suitable for plastic products, what kind of structure is used for circulating temperature-controlled oil, warm water and coolant, and whether the size, quantity and location of coolant holes are appropriate.
8. Whether the gate form, size of runner and water inlet, gate position and size are appropriate.
9, the influence of various modules and mold core heat treatment deformation and the selection of standard parts is appropriate.
10. Whether the injection quantity, injection pressure and clamping force of the injection molding machine are sufficient, and whether the aperture of nozzle R and sprue sleeve match properly.
Wait, it should be strictly controlled from the initial stage of the product.
Second, the control of process manufacturing.
Although the design stage has been fully considered and arranged, there are still many problems and difficulties in actual production. We should try our best to meet the original design intention in production and find more effective and economical technical means in actual processing.
1. Choose economical machine tools and equipment to make 2D and 3D machining schemes.
2. We can also consider a series of production process requirements and solutions, such as auxiliary preparation of suitable fixtures in production, rational use of tools, prevention of deformation of product parts, prevention of shrinkage fluctuation of product parts, prevention of demoulding deformation of product parts, improvement of mold manufacturing accuracy, reduction of errors, and prevention of changes in mold accuracy.
3. Here, I would like to mention the reasons for the size error of molded parts of the British Plastics Association (BPF) and its proportional distribution:
A: the mold manufacturing error is about 1/3, b: it is about 1/6 caused by mold wear, c: it is about 1/3 caused by uneven shrinkage of molded parts, and d: it is about 1/6 caused by inconsistency between the predetermined shrinkage and the actual shrinkage.
The total error is =A+B+C+D, which shows that the manufacturing tolerance of the mold should be less than 1/3 of the dimensional tolerance of the formed part, otherwise it is difficult for the mold to ensure the geometric size of the formed part.
(3) General production control
It is a common problem and phenomenon that the geometric dimensions of plastic parts fluctuate after molding;
1, the control of material temperature and mold temperature, different brands of plastics must have different temperature requirements, the poor fluidity of plastic materials and the use of more than two mixtures will lead to different situations, and it is usually easy to control the plastic materials within the optimal flow value range, but the control of mold temperature is more complicated. Injection molded parts with different shapes, sizes and wall thickness ratios have certain requirements for cooling. Mold temperature controls the cooling time to a great extent, so try to keep the mold at an allowable low temperature to shorten the injection cycle and improve production efficiency. If the mold temperature changes, the shrinkage rate will also change, the mold temperature will remain stable, and the dimensional accuracy will also be stable, thus preventing defects such as deformation, poor gloss and cooling spots of molded parts, and making the physical properties of plastics in the best state. Of course, there is also a debugging process, especially the molded parts with multiple cavities are more complicated.
2. Adjustment and control of pressure and exhaust:
Appropriate matching of injection pressure and clamping force should be determined when debugging the mold. The air in the gap between the mold cavity and the core and the gas generated by the plastic must be discharged from the mold through the exhaust slot. If the exhaust is not smooth, there will be insufficient filling, resulting in weld marks or burns. These three kinds of molding defects sometimes appear in the same place. When there is a thick wall around the thin-walled part of the plastic part, insufficient filling will occur when the mold temperature is too low. If the mold temperature is too high, there will be scalds, and usually there will be weld marks at the scalded parts at the same time. The exhaust slot is often neglected and is generally in a small state. Therefore, as long as there is no burr, the depth of the exhaust shoulder should be as deep as possible, and a large exhaust slot should be opened behind the shoulder, so that the gas passing through the shoulder can be discharged from the mold quickly. If necessary, the exhaust slot is opened on the ejector pin. The reason is the same. One is that there is no waste edge, and the other is exhaust.
3. Auxiliary molding control of injection molding parts size
Due to the different shapes and sizes, some plastic parts will be deformed and warped in different situations with the change of temperature and the loss of pressure after demoulding. At this time, some auxiliary fixtures can be used for adjustment, and remedial measures can be taken in time after the molded parts are taken out of the mold, and good correction and adjustment effects can be achieved after natural cooling and shaping. If strict management is ensured in the whole injection molding process, the size of injection molded parts will be controlled very well.