Plasticization: On
Injection molding: off
Holding pressure: off

Relationship between injection pressure and injection speed is as follows:
In injection molding process parameters, speed is dominant between speed and pressure, and there is no direct relationship between the two.
In production, for example, injection speed of 100mm/s is set. When actual injection pressure is less than set pressure value, screw will be molded at injection speed of 100mm/s. When actual injection pressure exceeds set pressure value, screw cannot reach injection speed of 100mm/s. Relationship between actual injection pressure and injection speed is that the faster speed, the greater actual pressure value. The higher injection speed, the more pressure you are required to set.

 

A high set pressure is also required at very slow speeds. That is to say, point with the lowest injection pressure will not be at the fastest speed, nor will it be at the slowest speed.

Clean die surface
Find point position of focal spot and reduce injection speed
Lower mold temperature
Reduce clamping force
Reduce material temperature
Die surface sticker, increase mold exhaust, generally not recommended

In terms of molds, main factors affecting deformation of plastic parts are gating system, cooling system and ejection system.
For control of mold temperature, temperature difference between movable mold and fixed mold, mold core and mold wall, mold wall and insert should be determined according to structural characteristics of product, so as to control difference in cooling and shrinkage speed of each part of product.
After product is demolded, it tends to bend in the direction of traction on the side with higher temperature to offset difference in orientation shrinkage and prevent product from deforming according to orientation law. For products with exactly same product shape, mold temperature should be kept consistent accordingly, so that cooling of all parts of product is balanced.

There is a gap between movable and fixed die cores by broken surface
Poor mold exhaust
Insufficient clamping force of machine
There is a foreign body on mold surface

Whether back suction is large or small will directly affect quality of product. If it is large, it is easy to cause silver threads on the surface of product. If it is small, it is easy to have unstable residual quantity, unstable product quality, overflow of mold runner, wire drawing at nozzle, etc. . General experience value shall not be less than 5mm.
How to optimize: According to experience value, actual production to see bad phenomenon of product, fine-tune up and down until there is no overflow and qualified product is produced.

 

High back pressure:
Melt pressure at the front end of barrel is too high, temperature of material is high, viscosity decreases, and it is easy to fill, but it will increase flash of product outline.
Storage time is long, and heating time of melt in barrel is long, resulting in thermal decomposition, and color difference on the surface of product is poor.
Screw retreats slowly, storage time is long, and molding cycle is long, which affects production efficiency.
When melt pressure is high, mold of cold runner (needle valve is not affected) is prone to drooling, causing cold material in the runner to block glue inlet or cold material spot on the surface of product when the lower mold is injected.
Mechanical wear of screw and barrel is large, which affects service life.
Low back pressure:
Screw retreats quickly, melt density flowing into front end of barrel is small, air is trapped, and surface of product is silvery
Poor plasticization, unstable material volume, large changes in product weight and size
Product surface shrinkage, cold grain, uneven gloss and other undesirable phenomena
Bubbles are prone to appear inside product
Low melt temperature, high viscosity, poor melt flow, etc.
Back pressure setting: principle is from small to large (for details, please refer to value given by material supplier and structural characteristics of product)

Check whether three-piece screw set is in good condition
Check whether injection pressure is stable and whether inside of nozzle is clean
Whether nozzle is leaking
Whether screw temperature and temperature of mold temperature machine are stable or not within allowable deviation value
Whether loosening value of screw is set too small, causing cold material

Calculation method: clamping force = projected area of all products (including runners) X pressure in cavity
Practical method: first set a clamping force, set an empirical value according to size of product and tonnage of machine (not too small). When product has no burrs, gradually reduce clamping force until product has burrs, take pressure value of last (without burrs) with burrs.
Other flaws:
There are various plastic raw materials used in injection molding process, types and forms of mold designs are also varied. In addition, operator's familiarity with a specific injection molding machine, as well as operating skills and practical experience of workers are also different. At the same time, objective environment will also vary with seasons, these objective and subjective conditions jointly determine occurrence of defects in injection molded products.
Generally speaking, there are three main aspects to evaluate performance of plastic products:
First, appearance quality, including integrity, color, gloss;
Second, accuracy between size and relative position,
Third, mechanical properties, chemical properties, electrical properties, etc. corresponding to application.