9 Q&A on injection molding process

1. briefly describe the operating status of the check valve during plasticization, injection, and pressure-holding.

Plasticizing: open

Injection: closed

Holding pressure: closed

2. briefly describe the relationship between injection speed and injection pressure, holding speed, and holding pressure.

The relationship between injection pressure and injection speed is as follows.

The speed is dominant between speed and pressure in injection process parameters, and there is no direct relationship between the two.

In production, for example, set the injection speed of 100mm/s, when the actual pressure of injection is less than the set pressure value, the screw is molded at the injection speed of 100mm/s. When the actual injection pressure exceeds the set pressure value, the screw does not reach the injection speed of 100mm/s. The relationship between the actual injection pressure and injection speed is that the faster the speed the higher the actual pressure value. The higher the injection speed, the higher the pressure you are required to set.

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

3. 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 mold exhaust, generally not recommended.

4. briefly explain the influence of mold temperature on product deformation?

In terms of mold, the factors that affect the deformation of plastic parts are mainly the pouring system, cooling system, and ejector system.

For the control of mold temperature, the temperature difference between moving mold and fixed mold, mold core and mold wall, mold wall, and insert should be determined according to the structural characteristics of the product, to control the different cooling and shrinking speed of each part of the product.

The products tend to bend to the higher temperature side of the traction direction after demoulding to offset the orientation shrinkage difference and avoid deformation of the products according to the orientation law. For products with identical shapes, the mold temperature is maintained accordingly, so that the cooling of each part of the product is balanced.

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

There is a gap between the die kernel and the broken surface of the moving and fixed die

Poor die venting

Insufficient clamping force of the machine

Foreign matter on the mold surface

6. Why is the back-off process necessary after the plasticization is completed? How to optimize it?

The back suck or large or small will directly affect the product quality, large is easy to cause the product surface silver wire, small is easy to have the residual amount of unstable products, unstable product quality, mold runner overflow, water spout extraction, and so on. The general experience value should not be less than 5mm.

How to optimize: according to the empirical value in the actual production to see the bad phenomenon of the product up and down fine-tuning, until no overflow and hit the qualified products.

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

High backpressure.

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 profile 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

Small backpressure.

The screw is backed off quickly, the melt density at the front of the barrel is small, the air is trapped, and the product surface is silvery.

Poor plasticization, unstable material volume, product weight, and size change

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 fluidity, etc.

Backpressure setting: the principle 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)

8. when you find that the amount of residual material is not stable, what should you do?

Check whether the three pieces of the screw set are intact

Check whether the injection pressure is stable and whether the inside of the nozzle is clean

Check if there is any material leakage from the nozzle

Are the screw temperature and the temperature of the mold temperature stable within the allowable deviation value?

Is the loosening and releasing the value of the screw set too small, resulting in cold material

9. 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

Practical method: First set a clamping force, set an empirical value (not too small) according to the size of the product and the tonnage of the machine, 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.