Haochen20 years of focus on multimode cavities and small spacing hot runner

1、 Fill in the blank question:(1 point per question, a total of 20 points)

1. The viscosity of ABS and PP materials is sensitive to shear rate (injection rate), but not to material temperature. Increasing material temperature has no significant effect on improving their flowability;

2. Only when the plasticization of the molten material inside the barrel reaches (molecular isomorphism (viscous flow)）When in the state of injection, it can be injected into the mold to produce high-quality rubber parts;

3. Thermoplastics are divided into two types: crystalline plastics and amorphous (non crystalline) plastics. When injecting crystalline plastics, it is necessary to strictly control the mold temperature and injection process conditions in order to control their crystallinity and shrinkage rate, and to stabilize the size and quality of the rubber parts;

4. The three states of plastic refer to: glass state, (high elastic state), and viscous flow state, while (crystalline) plastic does not have a high elastic state during the plasticization process;

5. The screw of injection molding machines is generally divided into three types: A-type screw, B-type screw, and C-type screw. For engineering plastics, it is better to choose (A-type) screw;

6. Before designing an injection mold, it is necessary to understand the performance of plastic, (injection molding process conditions), the size of the injection molding machine, and the quality requirements of the rubber parts;

7. The core of injection molding lies in the mold, the core of the mold lies in the design, and the core of the design lies in the third tier. The "three streams" refer to: material flow, (airflow), and heat flow;

8. The mold should have "three multiples" and "three connections". "three multiples" refer to: more water channels, (more exhaust), and more positioning; The "three connections" refer to: (channel connections), airway connections, and waterway connections;

9. Mold designers must understand the relevant properties of plastics, such as melt index (FMI), flow length ratio, shrinkage rate, temperature resistance, thermal stability, crystallinity, overflow gap, (thermal conductivity (thermal conductivity)), and mold temperature, in order to design a good mold;

10. When designing the mold, it is necessary to consider not only the balance of glue injection but also the balance of expansion force, as well as the balance of heat absorption and release;

11. If the exhaust effect of the injection mold is not good, it will cause a series of problems. The exhaust channel must be connected to (air), and the length of the overflow gap (sealing position) of the exhaust slot should not exceed (1) mm;

12. The location, form, size, and quantity of the gate have a significant impact on the quality of injection molding and rubber parts, and should be given special attention;

13. The purpose of mold testing is not only to produce qualified samples and submit them to customers for signature, but also to verify the quality of mold design and establish standard injection molding process conditions to ensure smooth and stable injection molding production, and achieve a state of "high quality, high efficiency, and low consumption";

14. If we do not attach great importance to the maintenance of injection molding molds, a series of problems will occur during the injection molding production process, such as blocked exhaust systems, rusted waterways, crushed mold surfaces, increased mold and machine failures, easy wear of mold and moving parts, increased flash of rubber parts, and unstable quality of injection molding parts;

15. The prerequisites for automation and unmanned injection molding are: plastic should be OK, molds should be OK, injection molding machines should be OK, peripheral equipment should be OK, injection molding process conditions (parameters) should be OK, environment should be OK, and human concepts should be OK;

16. Pressure maintaining can be divided into ineffective pressure maintaining and effective pressure maintaining. (Effective pressure maintaining) refers to the pressure maintaining performed before the flow channel and gate are frozen and sealed, in order to continuously add enough adhesive to the mold and improve shrinkage.

17. The main work of the injection molding workshop is to control the plastic (water containing material), optimize and control the opening and closing mold parameters, optimize and control the injection molding process conditions (parameters), maintain the mold and injection molding machine (including peripheral equipment), and provide training for personnel in various positions;

18. The surface shrinkage of injection molded parts is mainly caused by the blockage of the filling channel (pre freezing and sealing), rather than insufficient holding pressure;

19. The shrinkage rate of crystalline plastics is greater than 1.0%, mainly due to not only cooling shrinkage but also (crystallization shrinkage) during molding;

20Hot runnerThe main functions of molds include reducing raw material loss, reducing runner resistance, shortening injection molding cycles, and reducing manual processing of gates.

2、 Multiple choice fill in the blank questions - multiple choices are allowed (1 point per question, a total of 30 points)

1. If the locking force is not controlled (the locking force is too large), it will cause 100 harms without any benefits, and will cause the following adverse consequences (A, B, C);

A. Poor mold exhaust B, increased mold failures C, increased injection molding machine failures D, fewer flash edges of rubber parts E, increased depth and size of rubber parts

2. The melt viscosity of the following (C) plastics is sensitive to both melt temperature and shear rate;

A. PA B, ABS C, PS D, PMMAE, PC

3. Injection molds that are easy to adjust should have the following characteristics (A, B, C, D, E);

A. The glue inlet channel is unobstructed B, the glue replenishment channel is unobstructed C, the exhaust effect is good D, the glue inlet is balanced E, and the expansion force is balanced

4. If the return spring of the top needle plate of the mold is broken and installed on the machine for injection production, which of the following adverse problems will occur (A, B, C, D, E);

A. Accelerated needle burning/breaking B, imbalanced ejection C, rubber side pulling (drag) D, rubber deformation E, inclined top prone to burning

5. When the temperature of the melt is reasonable, which of the following changes (A, B, C) will occur in the plastic inside the barrel during the plasticization process of the melt;

A. Heating softening B, degassing C, melting plasticization D, adiabatic compression E, molecular chain fracture

6. In general, which physical changes (A, B, C, E) occur after molten plastic is injected into the mold cavity;

A. Adiabatic expansion B, molecular orientation C, cooling solidification D, mold temperature rise E, crystallization of crystalline plastics

7. The basis for setting injection molding process conditions (A, B, C, D);

A. Performance B of plastic, wall thickness C of adhesive parts, thickness D of flow channels, mold structure E, and experience of technical personnel

8. Which of the following problems may occur when the pressure is too high: (A, B, C, E);

A. Adhesive mold B, white top C, flash (burrs) D, reduced weight E, high internal stress

9. Which of the following problems can occur if the back pressure is too low: (A, B);

A. Low plasticizing heat B, poor degassing C, high melt density D, long plasticizing time E, slow screw retreat

10. The basis for setting injection speed parameters is: (A, B, C, D, E);

A. Mold exhaust effect B, thickness of rubber parts C, mold temperature D, appearance quality of rubber parts E, thickness and length of flow channels

11. On the premise that other injection molding process conditions remain unchanged, too fast injection speed may lead to the following adverse phenomena: (B, C);

A. More obvious fusion line B, trapped gas burning C, increased flash D, reduced internal stress E, difficulty in filling the molten material

12. The main factors that affect the cooling time of injection molds are as follows: (A, B, C, D);

A. Wall thickness B, water pressure C, water temperature D, plastic thermal conductivity E, injection pressure size

13. The basis for setting the injection pressure is: (A, B, C, E);

A. Number of gates B, position of gates C, mold temperature D, injection amount E, flow resistance

14. The injection molding department should choose the right dryer. If the plastic is not fully dried, which of the following adverse phenomena (A, B, C, D) will occur during plasticization and injection molding;

A. Silver streaks appear on the surface of the adhesive B, the melt is prone to hydrolysis C, the strength of the adhesive decreases D, flash (overflow) E, and the viscosity of the melt increases

15. The cross-sectional shapes of the diversion channel include trapezoidal, circular, U-shaped, semi-circular, rectangular, etc. Among them, (C) has the highest efficiency;

A. Trapezoidal section B, U-shaped section C, circular section D, rectangular section E, semi circular section

16. If the exhaust effect of the mold is not good, in addition to burning and missing glue, it will also cause the injection molded parts to produce the following adverse phenomena (A, B, D, E);

A. High internal stress B, excessive flash C, flow pattern (cold material pattern) D, adhesive mold E, bright printing

17. To prevent the screw holes on the machine board from slipping, it is necessary to limit the length of the sleeve when driving code mold screws: code mold screws with a diameter of (C) are suitable for L=40-45CM;

A. M16 B, M18 C, M20 D, M24

18. When installing the lifting ring, it is necessary to use a lifting ring with a suitable diameter, and the depth of the threaded part must be above the (B) aperture (10-12 turns);

A. 1x B, 2x C, 3x D, 5x

19. During the injection molding production process, if there is a sudden problem with the quality of the rubber parts, it is mainly caused by the following abnormalities (A, B, C, E);

A. Change in mold temperature B, change in return ratio C, no cutting D, change in process conditions E, nozzle or gate blockage

20. The experiment proves that the addition ratio of a single return material is within (B), and the effect on the strength of its plastic products is not significant (the effect is below 10%);

A. 10% B, 25% C, 40% D, 50% E, 60%

21. The particle size of the crushed nozzle material should be 6-8mm. If the particle size is uneven, what problems will be caused during injection molding production (A, B, C, D, E);

A. Unstable cutting B, inconsistent drying quality C, inconsistent plasticizing quality D, unstable material extraction E, unstable rubber part quality

22. When inspecting the newly purchased injection molding machine, we should focus on the following elements: (A, B, C);

A. Fluctuation of the end point position of glue injection B, stability of melt temperature C, accuracy of mold opening and locking D, machine size E, ejection speed

23. Which color do you think is the best for the return spring of the injection mold needle plate? (C);

A. Brown B, Green C, Yellow D, Blue E, Red

The top three factors that affect the quality stability of injection molded parts are: first, (C), second, (A), and third, (D);

A. FMI B of plastics, injection molding machine C, injection molding mold D, injection molding process parameters E, workshop ambient temperature

25. If a small mold is placed on a large machine for injection molding production, which of the following adverse problems will occur: (A, B, C, E);

A. Poor dimensional stability of injection molded parts B, poor control of mold locking force C, high power consumption D, high injection pressure E, easy decomposition of molten materials

The main factors causing shrinkage (shrinkage marks) on the surface of injection molded parts are: (C);

A. The holding pressure is too low, B, the back pressure is too high, C, the glue filling channel is blocked, D, the injection molding speed is too fast, E, the holding time is too long

27. During the injection molding production process, the reasons for the nozzle leakage of the injection molding machine are: (B, C, D);

A. The heating ring is burnt out B. The nozzle is not properly aligned C. The nozzle head R and the hole are uncomfortable D. The back pressure is too high E. The nozzle temperature is low

28. The main reasons for the long time and difficulty in adjusting the machine during the new mold trial are: (B, C);

A. Poor machine adjustment level B, too small mold gate C, poor mold exhaust effect D, poor injection molding machine E, poor plastic performance

29. The more cooling channels in injection molds, the following results will be achieved: (A, B, E);

A. Good temperature uniformity of the mold B, short cooling time C, difficult machine adjustment D, easy deformation of the rubber parts E, uniform cooling shrinkage of the rubber parts

For molds with multi-stage flow channels, the diameter of the main flow channel head should be: (B) the straight diameter of the last stage flow channel.

A. Equal to B, greater than C, less than D, no relationship

3、 True or False:(0.5 points for each question, a total of 15 points) Please mark "√" and "false" in the parentheses after each question below“ ×” Symbol for:

1. The quality of injection molding is mainly determined by the concept of the injection molder. The practice of one injection molding machine is the same as that of one hundred injection molding machines; （√）

2. The injection molding workshop is not used for machine adjustment, but for production. We need to find ways to achieve a state of no machine adjustment; （√）

3. High quality injection molded parts are designed, injected, managed, and controlled, rather than perceived by QC; （√）

4. The fusion lines (water marks) generated by the hole positions of injection molded parts cannot be improved（×）

5. During mold transfer production, the cleaning of the injection molding machine barrel and screw needs to be carried out during start-up production; （×）

6. The vast majority of injection molding defects are caused by the inability of molten material to enter the mold and the inability of gas to be discharged; （√）

7. When there are defects in the rubber parts during injection molding production, we need to immediately adjust the machine to improve it; （×）

8. The locking force is not used to adjust the flash, the smaller the locking force, the better,Generally, it does not exceed 50% of the maximum locking force of the injection molding machine; （√）

9A good injection molding machine is sure to inject good products; （×）

10. Plastics that require high drying conditions often have high water absorption; （×）

11. When converting transparent PC material for injection molding production, PMMA nozzle material can be used to clean the material barrel and screw; （×）

12. The water ripples on the surface of injection molded parts only occur when injecting transparent rubber parts; （×）

13. The longer the working years of injection molding technicians, the higher their injection molding technical level and salary should also be higher; （×）

14. When most plastics stay in high-temperature barrels for more than 15 minutes,Timely cooling and insulation work should be done well（√）;

15. The reason why the POM material and PA 66 injection molded rubber parts are relatively hot during demolding is due to insufficient cooling time; （×）

16. Whether the injection mold or injection molding machine (including peripheral equipment) cracks or deforms, they are all caused by excessive or uneven stress; （√）

17. Injection mold maintenance refers to regularly wiping the mold surface, exhaust groove, top needle oil, lubricating oil, and rust prevention oil during the production process; （×）

18. Any problems that arise during the injection molding production process should not occur and can be controlled and improved; （√）

19. The flow length ratio of molten material refers to the ratio of the length of molten material flowing from the gate into the mold to the wall thickness of the adhesive part; （×）

20When the dimensional accuracy and quality requirements of injection molded parts are high, it is not allowed to arbitrarily change the injection molding process parameters during the injection molding production process; （√）

21. During the injection molding production process, there are many problems and mold failures, and everyone is busy and tired, with high pressure, indicating that we have not done the right/good job; （√）

When injecting plastic with poor thermal stability, it is advisable to choose an injection molding machine that can achieve a maximum injection volume of over 80% for injection molding; （√）

23. The position of pressure maintaining switch should be smaller than the position where the screw stops at the end of injection molding, in order to enter the pressure maintaining and glue replenishing state; （×）

24The machine adjustment is carried out during the mold trial, and standard injection molding process conditions should be established during the mold trialUsed for injection molding production; （√）

25. Crystalline plastic injection molding is prone to nozzle blockage, mainly due to improper nozzle form and low nozzle temperature; （√）

26. During injection molding, the temperature of the injection mold has the same effect as the injection speed, both of which regulate and control the changes in the viscosity of the molten material; （√）

27. All thinking and behavior of injection molding workers are determined by the properties of plastics, and we must be familiar with the properties of plastics; （√）

The relationship between injection molds and injection molding processes is: injection molding processes are combined with injection molds; （×）

29. To engage in injection molding, it is necessary to have a systematic approach and focus on every aspect of the work in order to achieve good results; （√）

30. Under the condition of overcoming the resistance of the moving template, the lower the low-pressure protection pressure, the better, in order to have a protective effect on the mold. （√）

4、 Please fill in the performance values of various plastics in the table below?(6 points)

Plastic name	Crystallinity	decomposition temperature	Thermal deformation temperature	Screw speed prm	Permissible moisture content	thermal stability
ABS	wrong	240-260 ℃	75-85 ℃	80-100	<0.15%	Poor
POM	yes	220-225 ℃	150-160 ℃	90-110	<0.20%	Not good
PC	wrong	330-350 ℃	135-150 ℃	80-100	<0.02%	Poor
PA66	yes	290-300 ℃	185-210 ℃	110-120	<0.15%	preferably

5、 What can the injection molding department do to completely control the machine's nozzle material (return material) to meet the crushing requirements?(6 points)

Answer: Firstly, everyone in the injection molding workshop needs to recognize that if the control of the machine nozzle material is not good, it will cause a series of problems. Everyone should have a strong awareness of strictly controlling the quality of the machine nozzle material;

2. The injection molding department should develop a "machine position nozzle material control specification";

3. Each team in the injection molding department must strictly implement the "machine position nozzle material control specification";

4. To use a rubber box without holes and with a cover to load the machine's water outlet material;

5. The machine nozzle material cannot be left on the injection molding workshop site for a long time (no more than 1 hour), and needs to be crushed in a timely manner. It is best to use the machine side material for timely recycling and utilization;

6. It is necessary to include the control of the machine position nozzle material in one of the work contents of the injection molding department's management/technical personnel during machine inspection;

7. It is necessary to include the control of the machine nozzle material in the handover work of the injection molding department's management personnel, technical personnel, and machine workers;

8. It is necessary to include "control of machine position water inlet material" as one of the inspection tasks of the quality inspection personnel (IPQC) during machine inspection;

9. When the shredder is free, he/she should also go to the injection molding workshop to inspect the quality of the machine's nozzle material;

10. In the pre shift morning meeting, all employees should be trained on the "control requirements for machine position water inlet materials", and checked and supervised for implementation;

11. Incorporate the control status of each team on the quality of machine nozzle materials into their performance evaluation.

Only by doing so can the machine position nozzle material (return material) be completely controlled to meet the recycling requirements.

6、 Please analyze the blue injection molded parts with 16 cavities of hardware and soft glue in Figure 1. During the injection molding process, some are missing glue and some have flash edges, which are the root causes of three people being unable to start production and propose effective improvement measures (only one person)?(6 points)

Answer: This problem is mainly due to the incorrect form of the mold flow channel, and the thin distribution channels and gates at all levels. When the molten material enters the flow channel, it will quickly cool down. Before the molten material fills the mold cavity, the flow channel and gates will freeze and seal in advance, causing some mold cavities to lack glue. A worker needs to peel off the hardware inserts inside the missing glue products. When there is a shortage of glue in the plastic parts, the injection molding technicians are forced to increase the injection speed and pressure to force the molten material into the mold, resulting in the production of burrs. One worker needs to use a nail clipper to process the burrs, while the other worker needs to start the operation, resulting in a total of three workers required for the machine to produce; Secondly, the imbalanced feeding of glue into each cavity of the mold can also cause this phenomenon (some have missing glue and some have flash edges).

Improvement measures:Firstly, change the flow channels at all levels of the mold to circular shapes, and thicken the gate by 0.15mm. Then, balance the feeding of glue into each cavity of the mold. Reduce the injection pressure during injection molding, slow down the end injection speed, and there will be no shortage of glue or flash during injection molding. Only one worker needs to start the machine.

7、 What are the prerequisites for achieving good reproducibility of injection molding process conditions without adjusting the machine during mold transfer production?(8 points)

Answer: The prerequisites for mold transfer without machine adjustment are as follows:

1. Firstly, do a good job in planning and scheduling the injection molding machine, which should be the same as before;

2. The brand and batch of plastic raw materials should be the same as much as possible;

3. The quality of the water outlet material (return material) should be absolutely pure;

4. The particle size of the crushed nozzle material (return material) needs to be uniform and consistent, and its powder needs to be removed;

5. The proportion of added nozzle material (return material) needs to be consistent;

6. The mixing time needs to be consistent;

7. The drying quality of plastic raw materials (water containing materials) should be consistent;

8. The temperature of the molten material should be the same as last time;

9. The mold temperature needs to be the same as last time;

10. The locking force needs to be the same as last time;

11. Other plasticizing parameters and injection molding process conditions need to be the same;

12. The hydraulic oil temperature of the hydraulic injection molding machine should be the same;

13. After sufficient molding, the maintenance work of the injection mold should be done properly.

8、 Why do many injection molding workshops have many problems, high waste, unstable quality, low efficiency, and everyone is busy and tired?(9 points)

Answer:Due to the traditional injection molding concept of "relying on experience to do things and following the problems", there is no systematic thinking and focus on itThe work in various stages does not attach importance to process control, and the personnel in various departments and positions have not done their work properly or well,Accumulation can cause many problems.The specific reasons are as follows:

1. The product design and new product development work were not done properly;

2. There are problems in the design of the "three streams" of injection molds;

3. There are also issues with the steel and mold processing accuracy of injection molds;

4. The new mold trial did not introduce a "scientific mold trial system", did not identify and improve mold problems, and did not ensure good mold quality;

5. The selection of injection molding machines and PMC scheduling are not suitable;

6. The plastic raw materials and nozzle materials are not well controlled;

7. There are problems with the quality of crushed materials, mixing time, baking quality, and supply chain;

8. Neglecting the setting and optimization of opening and closing mold parameters and ejector pin parameters;

9. Neglecting the setting, optimization, and control of injection molding process parameters;

10. Inadequate attention is paid to the maintenance of injection molds and injection molding machines (including peripheral equipment);

11. Not valuing the measurement and control of "three temperatures" - melt temperature, mold temperature, and hydraulic oil temperature;

12. The pre job training for personnel in various positions is not in place, and their work abilities and quality are relatively low.

13. The management of the injection molding workshop is not in place, and the job responsibilities of personnel in each position are not clearly defined. A set of scientific, systematic, and comprehensive work processes and standards (work standards) have not been established for the work of personnel in each position;

14. The best way to solve problems without the concept of preventing them from happening and the control of the injection molding process is to avoid any problems.