Precision Injection Molding

Precision Injection Molding
Precision Injection Molding
—The notion of precision injection molding and certain specifications on plastic injection molding machine

With the development of information technology and automatic handle technologies, the marketplace for precision injection molding machines have a higher specifications, and the demand quantity is also escalating rapidly.
Common precision injection molding machine has two indicators: 1st is the repetitive error of item dimension, and the other is the product’s repetitive weight error. The former is challenging to examine due to the fact of different size and thickness. The latter represents the plastic injection molding machine’s level of aggregation. An ordinary injection molding machine’s repetitive weight error is about 1%, a greater machine can reach .8%, precision injection molding machine is less than .5%, and it is called ultra-precision machine when the error is much less than .3%.

The distinct requirements on precision molding machine:

Injection pressure ≧ 25 MPa
Injection speed ≧ 300 mm/s
Product size precision .001mm
Item top quality regular deviation coefficient (velocity of variation) ≦ .1%
Opening and closing mould position accuracy:

opening ≦ .03 mm, closing ≦ .01

Injection position accuracy (holding stress end point) ≦ .03 mm
Equilibrium degree of force in tie bar ≦ 1%
Pre-plastic position accuracy ≦ .03mm
Stationary mould and movable mould’s degree of balance
≦ .03 mm when clamping force is zero
≦ .005 mm when clamping force is max
Temperature control accuracy of barrel and screw ≦ ± .five ℃

The concentrate of precision injection molding technology:

Clamping force

In precision injection molding procedure, machine usually needs a higher injection pressure (>250 MPa), or it would be challenging to molding. Nonetheless, note that, in general, precision injection molding products have fairly small dimensions and thickness, so not all products have high specifications on clamping force. Conversely, if the clamping force is also huge, or uneven in 4 corners, or instable, it will lead to uneven molding on mould and then in the end affect the good quality of molding product. Precision injection molding approach requires adjusting clamping force reasonable, conveniently and accurately, overcoming the length and size differences caused by the clamping force unit deformation and the issue of unstable clamping force brought on by space temperature and mould temperature’s modifications.

Plasticizing good quality

Uniformity of plasticizing not only impacts the product molding quality, but also affects the resistance when melting plastic flow via the gate. In order to get a uniform plasticizing, it is required to style particular screw and plasticization technology. In addition, the barrel temperature should be precisely controlled.

Measurement accuracy

To make the plastic solution maintains a higher stability, the injection plastic inject into the cavity each and every time need to be equal, that signifies the screw reset accuracy when feeding should be the same. But in truth, the screw reset positions are unable to maintain the same entirely, the larger diameter of the screw, the larger of system inertia, and the much more difficulty for controlling position accuracy. We usually manage the screw reset accuracy in .3 mm, perfectly in .2 mm.

Injection speed

Injection speed is an important indicator in precision injection molding machine as there is a time distinction from the hot melting plastic start injecting into cavity to finish injection. For the duration of this time, the hot melting plastic begin cool, to make the material at the gate and in the mould cavity cool uniformly, it must select higher speed injection. And to improve injection speed, you need to configure 1 or far more accumulator which can release energy speedily to shorten the time difference. It is advantageous for precision injection molding to increase the original injection speed far more than 3 times, reaching 300~800 mm/s.

Injection stress

Precision injection molding demands a big injection stress to increase the plastic density, decrease shrinkage, and guarantee the product precision. Nevertheless, the injection stress is not the larger the better, over pressure will have flash. In the best injection pressure, the injection cycle time need to not a lot more than .05 seconds.

Holding stress

Holding stress has a wonderful effect on precision plastic. Accurately, holding stress can make a good feeding, lessen the plastic deformation and control the item precision. The stability of holding stress determine the molding precision, unchangeable screw end position determine the holding effect.

Mould temperature

For precision injection molding, the mould cavity temperature need to be controlled in ±1℃, which should use PID control. But for ultra-precision injection molding, this is not sufficient, far more sophisticated technique is to use FUZZF control (fuzzy handle).

(edit by DAKUMAR Machinery Co.,Ltd market02@sinogroupe.com )

Plastic Injection Molding Machines’ manufacturer – Dakumar is a single of the Chinese major innovator for plastic molding machine’s researching and establishing.