Ways to Improve Production Efficiency of Injection Molding

Injection molding factories want to become bigger and stronger, and injection molding people want to live a better life. To achieve these two points, the prerequisite is that the factory must make money and have considerable profits.

But how can injection molding have considerable profits?

Shortening the injection molding production cycle and improving production efficiency are the most important and direct way.

The injection molding production cycle is composed of injection holding time, material storage time, cooling time, mold opening and locking time, core pulling and ejection time, picking time, and cycle time.

Injection holding time and storage time

It depends on the nature of the plastic, the shape of the product and the quality requirements. It is related to many factors such as injection pressure, injection rate, screw revolution, back pressure and temperature. We need to seek the shortest time under the premise of ensuring quality.

Product cooling and screw metering and storage are carried out at the same time. When estimating the storage time of injection molded parts, it is generally calculated by taking between 70% and 80% of the maximum plasticizing capacity (cubic centimeters/s) of the injection molding machine.

The holding time is the time elapsed from the time the cavity is filled to the end of the feeding and holding pressure. The length of the holding time depends on the product’s requirements for appearance shrinkage, size and deformation.

Cooling time

Cooling time refers to the time elapsed from the end of holding pressure to the opening of the mold. The length of cooling time is affected by factors such as product shape, wall thickness, mold cooling water design, mold temperature, and melt properties. Under the premise of ensuring better product quality, the cooling time should be shortened as much as possible.

When the product is constant, the design of mold cooling water is the key factor affecting the length of cooling time. Therefore, in the mold review meeting for the mold opening, injection molding technicians must confirm whether the water transport of the mold is reasonable.

When adjusting the machine, if the cooling time of the product is too long when the cooling conditions of the mold are finalized. There is a little trick: set the pressure of the tail section to a small pressure, low speed, and set a time for cooling, which can reduce a lot of cooling time.

Reference table for cooling time corresponding to glue position thickness of commonly used plastic products▼

Material

Cooling time(S)

1mm thick

2mm thick

3mm thick

4mm thick

5mm thick

ABS

1.8

7

15.8

28.4

44.4

PS

1.3

5.4

12.1

21.4

33.5

HDPE

2.9

11.6

26.1

46.4

72.5

LDPE

3.2

12.6

28.4

50.1

79

PA66

1.6

6.4

14.4

25.6

40

PC

2.1

8.2

18.5

32.8

51.5

PMMA

2.3

9

20.3

36.2

56.5

POM

1.9

7.7

17.3

30.7

48

PP

2.5

9.9

22.3

39.5

61.8

Soft PVC

2.2

8.9

20.1

35.7

55.8

Hard PVC

2.7

10.7

24.3

43

67.3

Time for molding opening and clamping

Affected by the size of the machine and the structure of the mold, the core pulling (row position) on the mold, the mold unlocking pin, the three-plate mold, etc. will all affect the total time of mold opening and clamping.

  • 80T~200T take 2~8 S
  • 200T~500T take 3~10 S
  • 500T~1000T take 8~15 S

Ejection time

The ejection time is affected by the ejection speed, ejection stroke, and pick-up method (automatic, manual, robotic). Automatic drop is generally only used for small products with low appearance requirements (internal parts), with the general ejection time of 0.5-2S.

Pickup time

When the robot picks up the product, after the product leaves the range of the mold, the mold can start to close the moving parts, and the time for picking out the item is generally 3-8S.

Under certain conditions, taking products by hand is faster than taking products by robots (this requires the factory’s workshop culture and employee benefits are good enough).

Reference table for cooling time corresponding to glue position thickness of commonly used plastic products▼

Improve Production Efficiency of Injection Molding-Mold opening

Requirements for Continuous Improvement in Injection Molding Production

(1) Shorten the cycle and improve production efficiency! (Cooling conditions, mold opening and clamping speed, position, manipulator action, mold, etc.)

(2) In the injection molding cycle, except for the injection and pressure holding time, others are useless time, which should be minimized as much as possible.

(3) After 2 hours of normal production of the first piece, it is necessary to improve and shorten the cycle by 2~3 seconds. After half a shift of normal production, go back and improve and shorten the cycle by 2~3 seconds until the best quality is achieved.

(4) Optimize product appearance: shrinkage, air marks, clamping lines, rough edges, shiny, etc. Improve customer experience.

(5) 80% of the causes of bad defects in injection molding products are mold problems, and 70% of mold problems are caused by design.

Problems found by injection molding technicians in production must be put forward in written form to mold engineering, project engineering, and mold repairers when making parts, such as: poor cooling effect, water entry form, position, exhaust position, size, demoulding form etc.

Confirm cooling conditions▼

Cooling conditions

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