Common problems in injection molding

 

1. What are the reasons for warpage and shrinkage of injection molded products?

 

Answer: 1. The temperature of the barrel is too low;

2. The molding cycle is too short;

3. The injection pressure is too high;

4. The injection speed is too fast;

5. The pressure holding time is too long;

6. The mold temperature is not uniform, the cooling system of the mold should be adjusted, and the cooling circuit should beset reasonably;

7. The gate section is too small;

8. The design of the ejection mechanism is unreasonable, and the ejection area and ejection point should be increased as much as possible;

9. The mold strength is insufficient, so try to increase its rigidity.

 

 

2. When ABS uses a black masterbatch, the product is easy to break and peel. How to solve it?

 

Answer: Too much toner is used in the pigment of the masterbatch, causing the product to peel off. The masterbatch pigment can be replaced.

 

3. How to control the white product with many black spots and color mixing?

 

Answer: 1. Raw materials. In the process of mixing and batching, pay attention to clean, prevent impurities and dust from mixing;

2. Machine.

(1) The inside of the barrel should be cleaned, whether there is a carbonized layer and glue on the screw;

(2) Whether the screw head, nozzle flange and nozzle parts are tight, the inner wall is smooth and there is no dead angle phenomenon;

(3) Whether the screw head is worn, whether the screw installation center meets the requirements, and whether there is a swing phenomenon.

 3. Mould. The mold runner has no sharp angle, and the pour point should not be too small.

 

4. What are the reasons and troubleshooting methods for injection molding products' lack of injection?

 

Answer: The main reasons and troubleshooting methods of injection molding products are:

1. If the melt temperature is too low, increase the temperature of the barrel and nozzle appropriately;

2. The molding cycle is too short and should be extended appropriately;

3. The injection pressure is low and should be increased appropriately;

4. The injection speed is too slow and should be increased appropriately;

5. The holding time is too short and should be extended appropriately;

6. Insufficient material supply, increase the material supply;

7. The screw back pressure is low and should be increased appropriately;

8. The structure size of the gating system is too small, so the gate and runner section should be enlarged appropriately;

9. Poor venting of the mold, vent holes should be added to improve the venting performance of the mold;

10. The mold strength is insufficient, so the mold rigidity should be improved as much as possible.

 

5. What effect does the temperature of the feed inlet of the injection machine have on the product?

 

Answer: The too high or too low temperature at the feed inlet will cause the unstable material return of the machine, make the feed volume unstable, and affect the size and appearance of the product.

 

6. What are the steps to set the injection molding process?

 

Answer: The steps to set the injection molding process:

1. Set the melt temperature;

2. Set mold temperature;

3. Set the screw conversion position and speed;

4. Set back pressure;

5. Set the injection pressure to the maximum value of the machine;

6. Set the holding pressure;

7. Set injection speed;

8. Set the pressure holding time;

9. Set the sample cooling time;

10. Set the mold opening time;

11. Set the ejection board stroke;

12. Minimize the holding time.

 

7. What are the main reasons for flash in injection molded products?

 

Answer: The main reasons for the flashing of injection-molded products are:

 1. The template is not flat or deformed due to insufficient rigidity of the template;

2. The clamping force is not enough, and the mold is not locked;

3. The injection pressure is too high;

4. The raw material MFR value is too high and the melt viscosity is low;

5. The material temperature and mold temperature are too high.

What are the factors affecting precision injection molding?

 Precision injection molding generally refers to a process that requires high precision and surface quality of molded parts. It is also believed that precision injection molding refers to an injection molding process with a dimensional accuracy of 0.01 to 0.001 mm. In recent years, with the rapid development of electronics, medical care, communications, automobiles, and other industries, people’s requirements for high precision and high performance of plastic products are increasing day by day. Traditional plastic molding processes have been difficult to meet the current high standards. At the same time, injection molding is one of the most important plastic molding methods. Therefore, the precision injection molding technology has received more and more attention, which has made the precision injection molding technology continue to advance and new technologies continue to emerge.

Precision injection molding requires products not only to have high dimensional accuracy, low warpage deformation, excellent transfer characteristics, but also excellent optical properties, etc. Therefore, it is important for injection molding machines, injection molds, molding processes, and raw materials. Performance and formula have special requirements, and there are many factors that affect precision injection molding.

According to the current actual production, the difficulties of precision injection molding mainly include the following aspects:

(1) Plastic shrinkage rate: When designing precision plastic products, the shrinkage rate of plastics should be considered.

(2) Product shape and size: The shape and size of the plastic part have a great influence on the accuracy of the part. Production practice shows that the more complex the shape and the larger the size of the product, the lower the accuracy.

(3) Mold structure: The accuracy of injection molded parts is closely related to the number of mold cavities and production batches. It also shows that the precision of the single-cavity mold structure is higher than that of the multi-cavity mold structure, and the precision of small batch production is higher than that of large batches.

(4) Mold processing accuracy: Since the injection molded product must be molded in the mold cavity, the accuracy of the product will never exceed the accuracy of the mold cavity. Under normal circumstances, the accuracy of injection molded products is one to two tolerance levels lower than the accuracy of the mold. As far as the current mold manufacturing technology is concerned, most of the mold cavities are manufactured by high-speed milling, grinding, polishing, or electrical machining, etc. These processing methods can achieve the highest precision required.

(5) Injection molding machine: Because precision injection molding has higher precision requirements for products. Therefore, they generally need to be carried out on a special precision injection molding machine. The injection power of the precision injection molding machine must be large, the control accuracy must be high, the response speed of the hydraulic system must be fast, and the mold clamping system must have sufficient rigidity.

Selection of precision injection molding plastics The shrinkage rate of plastic products fluctuates greatly during molding. In addition, due to the different types of polymers and additives used in different plastics, their flow performance and molding performance during injection molding will be different. There are big differences. Due to factors such as the manufacturer, the factory season, and environmental conditions, there are also problems with the stability of the shape and size of the products molded by them.

Therefore, in addition to having good flow properties and molding properties, precision injection molded plastics also require shape and dimensional stability. Otherwise, the accuracy of the product is difficult to guarantee. Therefore, when injection molding precision plastic products, we must consider the variety of plastics and their molding properties, and choose materials with low shrinkage and good long-term stability as much as possible.

Injection molding operation requirements

 

First, the quality requirements of plastic products

1. After injection molding, the product structure must be guaranteed to be complete, and there should be no shortage of materials or materials.

2. The surface of the product is bright in color, uniform in color, and full.

3. The surface of the product is not filled with defects such as flowers, impurities and black spots.

4, The shape of the product is regular, with no deformation, distortion, and obvious bubbles inside the product.

  5,The product can be matched with the relevant parts and normal, can not be separated without external force.

6. For products that need to be assembled, after assembly, the operator needs to perform a self-test to ensure that the product meets the quality requirements. Not allowed

Not installed, missing, and broken.

Second, plastic products trimming requirements

1. The feeding port of the product is generally cut off with a trimming knife, and the cutting position cannot be clearly whitish.

2. When trimming the knife, when trimming the product, the force should be repaired from the inside out when repairing the product. The direction of the force is not allowed to be blocked by the other hand.

3. When the product is trimmed, the force on the shank should be even, ensure that the force can cut off the product as much as possible, the long front of the batch, the middle does not stagnate, once repaired to the end, to ensure the finished the appearance of the edge after trimming

 4. The surface of the product that has been trimmed is not allowed to have wavy lines and unevenness.

5. For the part where the inlet is removed, the trimming should be smooth, and slight scratches caused by improper trimming in the range of φ10 are allowed. Other parts are not allowed to have scratches due to improper trimming.

6. For the height of the draping height greater than 0.2mm, it should be trimmed (unless the adjustment of the injection parameters can be solved), especially the flank on the edge of the outline of the product must be removed.

7. For different products, it is recommended to use different types of trimming knives to ensure product quality and improve trimming efficiency.

8. It is not allowed to damage other qualified surfaces due to improper trimming operation (such as causing good surface scratches, cuts, etc.).

 

Third, product stacking and handling

1. The height of the product stacked on the pallet should not exceed 1.2mm. The number of products in the same specification must be the same. Finally, it is bundled with a winding die. For small products placed in the tote, the height of the product should be 10CM at the tote, and the loading weight of the tote should not exceed 25Kg.

 

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