9 FAQs on Injection Molding Process Optimization

Today, we talk about the list of questions and answers relating to the injection molding process optimization. If you had other injection molding process optimization methods, please share with us, thank you.

Injection Molding Process Optimization FAQ 1

Question: Briefly describe the working condition of check valve during plasticization, injection, and pressure-holding process;


Plasticizing: open

Injection: Closed

Pressurization: closed

Injection Molding Process Optimization FAQ 2

Question: Briefly explain the relationship between injection speed and injection pressure, holding speed and holding pressure;

A: The relationship between injection pressure and injection speed is as follows:

The speed is dominant between speed and pressure in the injection process parameters, and there is no direct relationship between the two. In production, for example, I set the injection speed of 100mm/s, when the actual pressure of injection is less than the set pressure value, the screw will be molded at the injection speed of 100mm/s.

When the actual injection pressure exceeds the set pressure value, the screw does not achieve the 100mm/s injection speed. The relationship between the actual injection pressure and the injection speed is that the faster the speed, the higher the actual pressure value. The higher the injection speed, the higher the required pressure setting.

A very slow speed also requires a high set of pressure. That is to say, the lowest injection pressure point will not be at the fastest speed, nor at the slowest speed.

9 FAQs on Injection Molding Process Optimization - DGMF Mold Clamps Co., Ltd

Injection Molding Process Optimization FAQ 3

Question: How do you usually solve the problem if the product has scorched spots?


Clean the mold surface.

Find the location of the scorched spot and reduce the injection speed.

Lower the mold temperature.

Lower the clamping force.

Reduce the material temperature.

Sticker on the mold surface (to increase the mold exhaust, generally not recommended).

Injection Molding Process Optimization FAQ 4

Question: Briefly explain what is the effect of mold temperature on product deformation?


In the mold, the main factors affecting the deformation of plastic parts are the pouring system, cooling system, ejector system, etc.

For the control of mold temperature, according to the structural characteristics of the product to determine the temperature difference between the moving mold and fixed mold, mold core and mold wall, mold wall, and insert.

So as to use the different cooling and shrinking speed of the various parts of the control product in the direction of bending to the higher temperature side after demolding, to offset the difference in orientation shrinkage, to avoid the deformation of the product according to the law of orientation.

For the products with the same shape, the mold temperature should be kept the same, so that the cooling of each part of the product is balanced.

Injection Molding Process Optimization FAQ 5

Question: If a product is not completely filled and there are flying edges at the same time during the production process, what are the possible reasons?


Mold problem. (There is a gap between the moving and fixed die kernel against the broken surface)

Poor die exhaust.

Insufficient clamping force of the machine.

There are foreign objects on the mold surface.

Injection Molding Process Optimization FAQ 6

Question: Why is the sucking back process after plasticizing necessary? How to optimize?

A: Suction back or large or small will directly affect the quality of the product, large easily caused by the product surface silver wire, small products are prone to residual instability, product quality instability, mold runner overflow, water spout draw silk, etc. The general experience value should not be less than 5mm.

How to optimize: according to the empirical value in the actual production of the product to see the bad phenomenon on, under the fine adjustment, until playing a qualified product so far.

Injection Molding Process Optimization FAQ 7

Question: What is the effect of the size of the back pressure on the product? How is the setting of backpressure generally done?


If the backpressure is large

The melt pressure at the front of the barrel is too high, the material temperature is high, the viscosity decreases, and it is easy to fill, but it will increase the product outline flying edge.

Long storage time, the melt in the barrel of the long heating time caused by thermal decomposition, the product surface color difference is not good.

Slow screw retreat, long storage time, long molding cycle, affecting production efficiency.

High melt pressure, cold runner mold (needle valve does not affect) is easy to produce salivation, resulting in injection down the mold, cold material in the runner blocking the inlet or cold material spot on the surface of the product.

Screw and barrel mechanical wear and tear, affecting the service life. etc.

In case of small back pressure

The melt density at the front of the barrel is low due to the fast backpressure of the screw, and the air is trapped in the barrel, resulting in a silvery surface of the product.

Poor plasticization, unstable material quantity, product weight, and size change greatly.

The product surface shrinkage, cold material pattern, uneven luster, and other undesirable phenomena.

Air bubbles easily appear inside the product.

Low melt temperature, high viscosity, poor melt flow. etc.

The principle of setting backpressure is from small to large. (Specific reference can be made to the value given by the material supplier and the structural characteristics of the product).

Injection Molding Process Optimization FAQ 8

Question: What should you do when you find that the amount of residual material is unstable?


Check if the three pieces of the screw are intact.

Check if the injection pressure is stable. (whether the inside of the nozzle is clean).

Check if there is any material leakage from the nozzle.

Screw temperature and mold temperature are stable within the allowable deviation value.

Are the loosening and receding value of the screw set too small, resulting in cold material?

Injection Molding Process Optimization FAQ 9

Question: How to find out the reasonable clamping force quickly?


Calculation method: Clamping force = projected area of all products (including runners) X pressure in the mold cavity.

Actual method: First set a clamping force, set an empirical value according to the size of the product and the tonnage of the machine (not too small), when the product has no burrs, gradually reduce the clamping force until the product has burrs, and take the pressure value of the last one (no burrs) that has burrs.

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