Do you know 30 common problems and countermeasures in injection moulding process?

1. Product has a sharp edge (flashing edge) when it start production, cause of lack of material after a period of production and solution.

When machine is turned on, hot melt in injection tube of injection molding machine has a long heating time, low melt viscosity, good fluidity, and product is prone to produce sharp edges. After a certain period of time, melt continues to take away heat, resulting in insufficient melt, high viscosity and poor fluidity, which makes product lack of material. After a period of production, gradually increase temperature of tube to solve it.

2. In production process, product lacks material, sometimes increasing injection pressure and speed is invalid. Why?

After a period of production, melt continuously takes away heat, resulting in insufficient melt, high viscosity and poor fluidity, which makes product lack of material. Increase tube temperature to solve it.

3. Causes and solutions of product oval.

Ellipse of product is caused by uneven pressure of product, which causes uneven pressure around product and makes product ellipse. Three gates of injection are used to make product evenly.

4. Precision product requirements for molds.

Mold material is required to have good rigidity, small elastic deformation and small thermal expansion coefficient.

5. Purpose of product acid resistance test.

Product acid resistance test is to detect internal stress of product and position of stress point of internal stress in order to eliminate internal stress of product.

6. Reasons and solutions for easy cracking of metal inserts in products.

Inserts are placed in the product. When hot melt encounters cold inserts during injection, it will form internal stress, which will reduce product strength and crack easily. During production, inserts are pre-heat treated.

7. Reasonability and selection method of mold exhaust point.

If mold exhaust point is unreasonable, not only exhaust effect will not be achieved, but product deformation or dimensional change will be caused, so mold exhaust point should be reasonable. Selection of mold exhaust point should be set at the place where product is full of melt at the end and product is trapped.

8. Reasons and solutions for brittle products.

Product is easily brittle because product uses too many nozzles and inferior materials to cause product to be brittle, or material stays in pipe for too long, causing material to age and make product brittle. Increase proportion of new material and reduce number of times for recycled nozzle material. Generally, it cannot be more than three times to avoid melt material staying in material pipe for a long time.

9. Reasons and solutions for occurrence of pan fiber in glass fiber products.

It is because melt temperature is low or mold temperature is low, injection pressure is insufficient. As a result, glass fiber cannot be well combined with plastic, so that fiber appears. Increase melt temperature and mold temperature to increase injection pressure.

10. Effect of inlet temperature on product.

Too high or too low temperature at the feed port will cause machine to return to instability, make feeding amount unstable, affect size and appearance of product.

11. Reasons and solutions for white spots in transparent products.

White dots in transparent products are caused by cold glue entering product or by dust in material. Increase nozzle temperature, add cold material wells, pay attention to preservation of raw materials to prevent dust from entering.

12. What is injection capacity of injection molding machine.

Shooting capacity PW = Shooting pressure (kg/cm2) * Shooting volume (cm3)/1000

13. What is injection horsepower of injection molding machine?

Injection horsepower PW (KW) = injection pressure (kg/cm2) * injection rate (cm3/sec) * 9.8 * 100%

14. What is injection rate of injection molding machine?

Injection rate V (cc / sec) = л/4 * d2 * rd2: tube diameter r: material density

15. What is injection force of injection molding machine?

Injection thrust F (kgf) = л/4 (D12-D22) * P * 2D1: cylinder inner diameter D2: piston rod outer diameter P: system pressure

16. What is injection pressure of injection molding machine?

Injection pressure P (kg/cm2) = [л/4 * (D12-D22) * P * 2] / (л/4 * d2)

17. What is plasticizing ability of injection molding machine?

Plasticizing capacity W (g/sec) = 2.5 * (d/2.54) 2 * (h/2.54) * N * S * 1000/3600/2h = Depth of front end of screw (cm) S = Density of raw material

18. What is system pressure? What is difference with injection pressure?

System pressure (kg / cm2) = The highest working pressure set in hydraulic circuit. Injection pressure refers to actual pressure of injection molding machine. Two are not equal.

19.Requirement of hydraulic oil for injection molding machine:

(1) Proper viscosity and good viscosity performance

(2) Good lubricity and rust resistance

(3) Good chemical stability, not easy to gasify into colloid

(4) Good foaming

(5) Less corrosive to parts and seals

(6) Ignition point (flash point) is required to have a low freezing point.

20. Influence of hydraulic oil viscosity on injection molding machine?

When system working environment temperature is high, oil with higher viscosity should be used. On the other hand, oil with lower viscosity should be used. When system working pressure is high, oil with higher viscosity should be used because it is difficult to seal at high pressure and leakage is main problem;

Conversely, system has a lower working pressure, oil with a lower viscosity should be used. When operating speed of working parts of hydraulic system is high, flow rate of oil is also high. At this time, pressure loss will increase and leakage will be relatively reduced, oil with a lower viscosity should be used. Conversely, when moving speed of working parts is low, oil with higher viscosity should be used.

21. Loose settings.

Loosening correct position = moving position of rubber ring + offside distance of screw.

22. Importance of loose position setting

If loosening position is set too large, return material will absorb oxygen, oxidize rubber material and generate air bubbles. If position is set too small, pressure in barrel is high, shear force is too high to decompose melt, and nozzle is drooling. Position error cannot exceed 0.4mm.

23. Setting of melt position

Melt position = product weight/(maximum stroke/maximum melt amount)

24. Main advantages of gas assisted injection molding (GAM)

Core of thick material can be evacuated to make a hollow pipe, which can save material and shorten cycle time.

Use of gas in injection molding can evenly distribute pressure. When plastic is cooled and solidified, gas can compensate volume shrinkage of plastic through expansion.

Reduce internal stress of molded product, thereby improving shape stability, eliminating deformation and warping.

25. Piston rod has a small outer diameter in the middle and a large end?

Due to overheating of middle hole needle, product shrinks unevenly, resulting in a small middle diameter of piston rod and two large ends. Middle hole needle can be made of phosphor copper material with fast heat dissipation, and mold is vented in the middle of product.

26. Cracking problem after spherical silk printing

Due to stress on product surface, it causes cracking after silk printing. Increasing mold temperature and reducing stress, annealing can be used to eliminate stress.

27. Problem of easily broken edge of spectacle frame

Residual internal stress at nozzle side of large injection pressure and holding pressure causes product to break easily. Try to reduce injection pressure and holding pressure, increase mold temperature to solve it.

28. Easy to burst when four pillars of appliance shell are screwed

Due to existence of a water line in column, product assembly column is susceptible to bursting. Increase exhaust of mold and mold temperature appropriately, speed up injection speed to reduce water entrapment line.

29. Product deformation problem

Product deformation is mainly caused by imbalance caused by heat shrinkage, or due to internal stress of product.

30. Transparent PC case bubble problem

Insufficient drying of raw materials, uneven thickness of product, poor venting of mold, and easy decomposition of raw materials may cause product bubbles. Fully dry, increase mold exhaust, and minimize uneven thickness.