You are now at: Home » News » English/Business War Think Tank » Text

Basic injection molding knowledge that injection molding technicians must know

Enlarged font  Narrow font Release date:2021-01-08  Browse number:12
Note: The injection molding machine can be divided into four major systems, the four major systems are: injection system, mold opening and closing system, hydraulic transmission system, and electrical control system.

A. Fill in the blank questions: (1 point for each question, 134 points in total)

1. The injection molding machine can be divided into four major systems, the four major systems are: injection system, mold opening and closing system, hydraulic transmission system, and electrical control system.

2. The temperature in injection molding is: barrel temperature, mold temperature, drying temperature, hydraulic oil temperature, and ambient temperature.

3. The clamping methods of the injection molding machine are: direct pressure type, crank type, etc.

4. The time in injection molding refers to: injection time, pressure holding time, cooling time, cycle time, low pressure protection time, etc.

5. Common types of Japanese injection molding machines include: Nissei, Nippon Steel, Fanuc, Sumitomo, Toshiba, etc.

6. The screw of the injection molding machine is divided into three sections: the first section is the feeding section, the middle section is the plasticizing section, and the rear section is the metering section.

7. The glue port of the model can be divided into: point glue, fan glue, submerged glue, hot runner, straight glue, etc.

8. The chemical name of PC material is: polycarbonate, commonly known as bulletproof rubber, molding temperature 260-320℃, drying temperature 100-120℃.



9. The main components of plastic raw materials are resin. Four commonly used engineering plastics are: PC, ABS, PA, and POM.

10. The glass transition temperature of PC is 140℃, the shrinkage rate is 0.4%-0.8%; the drying temperature is 110±5℃

11. According to the reasons, the types of plastic products can be divided into: thermal stress, tissue stress, and partial stress.

12. There are three methods for inspecting the internal stress of products: instrument, impact, and medicine;

13. The total heat of the heat source in the injection metering process: convection heat, conduction heat, shear heat, friction heat;

14. The correct connection method of the mold transportation waterway should be: one in and one out peer-to-peer connection;

15. What are the three major categories of back pressure: plasticizing capacity, plasticizing quality, and plasticizing precision;

16. The cleaning time of the mold surface during the production process: 2H/time

17. The four recognized engineering plastics are: PC, POM, PA, PBT.

18. The normal setting of screw loosening when forming high-precision products on a 100T machine is: 3—5MM

19.7S refers to: tidying up, rectifying, sweeping, cleaning, literacy, safety and saving.

20. The filling time of the daily report during the production process is: 2H/time.

21. In the process of loading the mold, the mold whose nozzle depth exceeds 40MM, needs to replace the extended nozzle

22. Internal stress is the stress generated in the material due to crystallization, orientation, shrinkage and other reasons in the absence of external force

23. The screw of the injection molding machine can be divided into conveying section, compression section and metering section

24. When there is a quality abnormality in production, the team leader will ask the technician to deal with it within 10 minutes after receiving the quality abnormal information. If the technician cannot solve it within 1 hour, he should report to the foreman. If the foreman cannot solve it within 2 hours, he should report to the section manager. If the section chief cannot solve the problem within 4 hours, he should report to the economics (deputy) manager.

25. What forms do mold repairs need to be done during the production process? Mold repair form, mold batch management form, production daily report.

26. Usually the pouring diversion of the mold is composed of the main runner, the runner, the gate and the cold slug well

27. Common defects affecting injection molded products include batch peaks, lack of glue, shrinkage, flow marks, weld marks, deformation, stress marks, and dimensional changes.

28. The heat source of the pre-plastic metering process _ friction heat and viscous heat inside the plastic, heating of the heating element.

29. Usually the injection volume is best set between 30%~85% of the maximum injection volume of the injection molding machine.

30. If the mold temperature is different, the gloss of the product will be different. When the mold cavity is a textured surface, if the mold temperature is higher, the sol fits the cavity surface tighter, and the injection molded product looks more elegant, otherwise the gloss will be more consistent. The mold temperature is constant.

31. The larger the screw compression ratio, the denser the pellets will be, the faster the heat transfer between pellets, the better the diffusion effect of the powder, but the greater the conveying resistance and the smaller the amount of plasticization.

32. The main function of the anti-pinch valve is to prevent the backflow of plastic during the injection molding and pressure holding stage.

33. Too late holding pressure switch will cause the injection pressure to increase, and even flash.

34. POM is abbreviated as polyoxymethylene in Chinese. It is a semi-crystalline material with good dimensional stability. The melting temperature can be set between 190-210℃, and the mold temperature should be greater than 90℃.

35. If the plastic part shrinks, the first step should be the minimum residual quantity.

36. Point out the names of the parts of the filling system: 1. Nozzle, 2. Screw head, 3. Non-return ring 4. Barrel 5. Screw 6. Heating ring 7. Cooling ring. The screw of the injection molding machine can be divided into conveying section, compression section and metering section

37. The total heat of the heat source in the injection molding measurement process: convection heat, conduction heat, shear heat, friction heat;

38. Plastic raw materials can be divided into thermoplastic plastics and thermosetting plastics according to their different thermal reactions.

39. When the hydraulic injection molding machine is running, the temperature of the hydraulic oil should be controlled between 20-65°C.

40. For molds with three-platen mold and four-platen mold that have external buckle and limit pull, you must pay attention to setting the ejection distance

41. Internal stress is the stress generated inside the material due to crystallization and orientation in the absence of external force.

B. Multiple choice questions (2 points for each question, 40 points in total)

1. The following crystalline plastics are (C)A. ABS B.PMMA C.PA66 D.PVC



2. Compared with non-crystalline plastics, crystalline plastics (A) A. Crystalline shrinkage is greater B. Amorphous plastic shrinkage is greater



3. In precision injection molding, the general residual quantity is set to (B) A.0-2MM B.3MM-5MM C.7MM-10MM



4. For PC materials, (A) should be used to improve fluidity. A. Increase injection temperature B. Increase injection speed



5. When the surface quality of the product is required to be high or when it is required to avoid viscosity dissipation and swirling defects during injection, ______ injection rate and ______ pressure are often used. (C) A. high, low B. high, high C. low, high D. low, low



6. Injection molding is a molding method of production efficiency (C). A, low B, general C, high



7. After adding glass fiber to PA, the fluidity of its melt is (C) compared with the original PA. A, unchanged B, increase C, decrease



8. The barrel temperature when ABS is injected is (A). A, 180~230℃ B, 230~280℃ C, 280~330℃



9. The temperature distribution law of the barrel of the injection molding machine is from the hopper to the nozzle direction (A). A, gradually increase B, gradually decrease C, high at both ends and low in the middle



10. The arc radius of the nozzle is larger than the radius of the main sprue, it will produce (A). A. Melt overflow B, product flash C, product defect D, all of the above



11. The main reason for the difficulty in demolding injection molded products is (C). A. The temperature of the melt is too high. B. The cooling time is too long. C. The mold structure is unreasonably designed.



12. When injecting thermoplastics, if the mold temperature is too high, the product will be produced (C). A. The product sticks to the mold B, the product has a fusion pattern C, the product has flash



13. The method to be used for the clamping position and speed program is (A): A, slow-fast-slow B fast-medium-slow C slow-medium-fast D slow-fast-medium



14. The viscosity of PC material is (B), and its metering speed should be set according to (B); A high viscosity B medium viscosity C low viscosity



15. In the following parameters, (D) can close the injection mold tightly. A, injection pressure B, holding pressure C, cavity pressure D, clamping force



16. When the mold temperature is high, the qualitative quality should be (D); A good deformation B good dimensional stability C good shrinkage D good appearance



17. The quality of the overfilling position is easy to appear (B); A is trapped B, the burr C is large in size



18. PC material, low mold temperature, low filling pressure, product is easy to appear (B); A large clamping line B lack of glue C unstable quality



19. Which process conditions are relatively ideal when injecting thin-walled products (C); A fast B slow C fast short shot



20. The mold temperature is high, and the material temperature is high, and the product is prone to condition (B); A trapped air B batch front C deformation



C. Indefinite multiple-choice questions: (3 points for each question, 15 points in total)



Eliminate the weld line of the product: (A C D E F) A increase the resin temperature B reduce the mold temperature C increase the injection pressure D accelerate the injection speed E improve the exhaust F improve the resin flow
2. The method to improve the warping deformation of the product is: (ACFG) A, reduce the pressure B, increase the holding pressure C, shorten the holding time D, increase the injection E, reduce the cooling time F, reduce the mold temperature G, and slow down the ejection speed



3. The physical properties of PA66 should be: (A), (B); A, crystalline, B, thermal, C, non-crystalline, D, non-thermal



4. PMMA physical properties should be (C), (D); A crystalline B thermal effect C non-crystalline D non-thermal effect



5. Turn on the hot runner temperature in advance (B); when the personnel need to leave (C) turn off the hot runner A 5 minutes B 10 minutes C 15 minutes D 20 minutes



D. True or False (Question 1 point, 8 points in total)



1. The cooling setting process starts from the gate "holding pressure" until the product is demolded. After the holding pressure is removed, the melt in the cavity continues to cool and shape, so that the product can withstand the deformation allowed during ejection. ()



2. only daily production report needs to be made during the product proofing process ()



3. The frequency of CTQ inspection during the production process is 6/time ()



4. Increase mold temperature, reduce post-shrinkage, and reduce dimensional changes (right).



5. The best injection speed distribution makes the melt flow through the gate area at a slower rate to avoid spray marks and excessive shear stress, and then increase the flow rate to fill most of the mold cavity with the melt. (Correct)



6. In fully automatic production, if the manipulator does not take out the product, the manipulator alarms, first turn off the manipulator alarm. (wrong).



7. The quality of products produced during the day and night is different. The problem lies in the unstable temperature of the mold and the environment. (Correct)



8. The larger the cross-sectional area of the flow channel, the more conducive to the transmission of pressure, and the more obvious the feeding effect. (wrong)

E. Questions and answers: (5 points for each question, 10 questions in total)

What are the reasons for the silver wire?
Answer: 1. Cold rubber friction production; 2. The material is not completely dried; 3. The pressure is too small; 4. The resin is decomposed; 5. The mold temperature and material temperature are low; 6. The filling speed is slow.
2. The heating time of the hot runner is too long, and it will start production again. What should you do as a technician at this time?

Answer: First, shoot the 3-4 molds with the material tube empty, then align the nozzle with the nozzle, then open the mold, and block the back mold with a piece of cardboard to prevent the decomposition of the material from being shot to the back mold. It is difficult to clean up. If you don’t pay attention, it will cause the pressure mold. .



3. Why clean the PL surface during normal production? why?

Answer: The surface of the mold in normal production is prone to static electricity. Some rubber scraps and iron scraps fall to the edge of the die when the mold is opened and closed, which may cause damage to the die.



4. What are the critical factors that appear on the parting surface?

Answer: The mold temperature and material temperature are too high, the filling pressure is high, the filling speed is fast, the holding pressure is fast, the holding pressure is large, the filling position is switched too late, the clamping pressure is insufficient, and the machine tonnage is large.



5. What are the factors that cause unstable quality and size?

Answer: The mold temperature is too high, the cooling time is short, the ambient temperature is unstable, the cooling water temperature is unstable, the actuating oil temperature is unstable, the countercurrent ring is damaged too much, the barrel temperature is abnormal, the cold glue head is too much, resin particles Uneven in size.



6. Mold protection, what aspects should you consider as a technician foreman?

Answer: The sensitivity of the limit switch, the low-voltage clamping force, the low-voltage clamping speed, the low-voltage clamping position, and the clamping monitoring time are set to be slower, smaller, and better.



7. Why can't the machine be stopped at random when adjusting the dimensional accuracy when it is turned on?

Answer: There will be resin temperature and viscosity difference. There will be differences in mold temperature, difficult to control the dimensional accuracy, resulting in long adjustment time, material loss, and low production efficiency.



8. In normal production, the temperature and pressure cannot be modified at will. Why?

Answer: The pressure affects the flow oil temperature, the cold water temperature, the barrel temperature, the mold temperature and other changes for a long time, usually more than 3-4H to be stable, if there is a modification, the quality must be continuously //confirm/i/ied.



9. When the quality is abnormal, if the process parameters need to be modified, what time should be released before analysis?

Answer: First of all, the pressure holding time should be released, and the analysis should be started from the rubber sheet.



10. The quality is unstable, which aspects can be seen from the machine?

Answer: The filling position, filling time, measuring time, filling actual pressure and machine quality management table can be seen.



F. Analysis questions: (10 points for each question, 6 questions in total)

What are the preparations before injection molding?
1) Input of standard molding conditions

2) Preheating and drying of materials

3) Preheating of the mold

4) Cleaning of the barrel



2. What are the factors that cause dimensional instability of plastic parts?

Answer: The factors that cause dimensional instability of plastic parts are:

1) The electrical and hydraulic system of the injection machine is unstable;

2) The feeding amount is unstable;

3) Uneven plastic particles and unstable shrinkage;

4) The molding conditions (temperature, pressure, time) change, and the molding cycle is inconsistent;

5) The gate is too small, the size of the multi-cavity feed port is inconsistent, and the feed is unbalanced;

6) Poor mold accuracy, unstable movement of movable parts and inaccurate positioning.



3. In the design of injection mold, what is the role of mold temperature adjustment?

1) Temperature adjustment refers to cooling or heating the injection mold.

2) Temperature adjustment is not only related to the dimensional accuracy of the plastic part, the mechanical properties of the plastic part and the surface quality of the plastic part, but also the injection production efficiency. Therefore, the mold temperature must be controlled at a reasonable level according to the requirements. In order to achieve high-quality plastic parts and high productivity.



4. What is plastic shrinkage, and what are the basic factors that affect plastic shrinkage?

Answer: After the plastic is taken out from the mold and cooled to room temperature, the characteristic of dimensional shrinkage is called shrinkage. Since this shrinkage is not only caused by the thermal expansion and contraction of the resin itself, but also related to various molding factors, the shrinkage of the plastic part after molding is called molding shrinkage. The main factors affecting the shrinkage rate include:

1) Plastic varieties;

2) Plastic part structure;

3) Mold structure;

4) Molding process.



5. Please briefly describe the role of back pressure. (10 points)

1) Ensure that sufficient mechanical energy can be generated to melt and mix the plastic

2) Exclude volatile gases including air from the material pipe

3) Mix the additives (such as toner, color masterbatch, antistatic agent, talcum powder, etc.) and melt evenly

4) Make the flow diameter different and help homogenize the melt of the screw length

5) Provide uniform and stable plasticized materials to obtain accurate product quality control



6. If black spots are often produced when producing white or transparent products, how will you solve it? (Please briefly describe your solution ideas) (20 points)

1) Adjust the material preparation process: avoid contamination of raw materials and set appropriate drying conditions;

2) Change the mold design: too narrow vertical runners, runners, gates and even the wall thickness of the plastic parts may generate excessive shear heat, which will cause the overheated material to become hotter and cause cracking. You can try to increase the vertical Runners, runners, gates;

3) Clean mold and screw regularly: the runner system and screw surface should be cleaned or polished regularly to avoid accumulated dirt;

4) Select the specifications of the molding machine suitable for the mold: If you select the screw suitable for the plastic used, the injection volume is generally maintained within 20%-80% of the specifications, and check whether the heating plate or heater is invalid;

5) Adjust molding conditions: such as lowering the heating temperature of the barrel, lowering the back pressure and screw speed, etc.

 
 
[ News Search ]  [ Add to Favourite ]  [ Publicity ]  [ Print ]  [ Violation Report ]  [ Close ]

 
Total: 0 [Show All]  Related Reviews

 
Featured
RecommendedNews
Ranking