Definition: Temperature set on material pipe to ensure smooth molding.
Function: To ensure good plasticization (melt) of the polymer, smooth mold filling and molding.
Setting principles:
(1) It will not cause plastic decomposition and carbonization. (2) It will rise from feeding section to nozzle. (3) Nozzle temperature should be slightly lower than temperature of front section of barrel to prevent "drooling phenomenon" that may occur in straight-through nozzle. (4) Required temperature varies depending on type of material. (5) It will not have a bad impact on quality of product.

 

Each type of plastic has a different flow temperature. Same type of plastic has different flow temperatures and decomposition temperatures due to different sources or brands. This is due to different average molecular weights and molecular weight distributions. Plasticization process of plastics in different types of injection molding machines is also different, so barrel temperature is also different. Barrel of injection molding machine has 5 to 6 heating sections, and each raw material has its appropriate processing temperature (for detailed processing temperatures, please refer to physical property table provided by material supplier).

 

Nozzle temperature should not be too low, otherwise it will cause premature coagulation of melt and block nozzle, or premature coagulation of melt will be injected into mold cavity, affecting performance of product.

Definition: Surface temperature of mold cavity that product contacts.
Function: Controls cooling rate of product in mold cavity and apparent quality of product.
Setting principles:
(1) Consider properties of polymer. (2) Consider size and shape of product. (3) Consider structure of mold and runner system

Definition: Temperature required to dry polymer in advance to ensure molding quality
Function:
(1) Remove moisture from raw materials (2) Ensure quality of finished product.
Setting principles:
(1) Polymer will not decompose or agglomerate (polymerize). (2) Drying time should be as short as possible and drying temperature should be as low as possible so as not to affect drying effect. (3) Drying temperature and time vary depending on raw materials.

Time from end of mold opening to the end of mold opening after next injection cooling is called molding cycle
Molding cycle directly affects labor productivity and equipment utilization. Therefore, in production process, relevant time in molding cycle should be shortened as much as possible while ensuring quality.

 

Definition: Time required for plastic melt to fill cavity, excluding auxiliary time such as mold opening and closing.
Function: Filling time (injection time) is determined by factors such as injection pressure, injection speed and product size.
Setting principles:
(1) Make injection time as short as possible while ensuring product molding. (2) Injection time is affected by factors such as material temperature and mold temperature.
Filling time in injection time is directly inversely proportional to filling rate. Although filling time is very short and has little impact on molding cycle, adjustment of filling time has a great effect on pressure control of gate, runner and cavity. Reasonable filling time helps melt to fill ideally, is of great significance for improving surface quality of product and reducing dimensional tolerance. Filling time should be much lower than cooling time, about 1/10~1/15 of cooling time. This rule can be used as a basis for predicting the total molding time of plastic parts.

When injection molding process is about to end, screw stops rotating and only moves forward. At this time, injection molding enters holding stage.
Definition: To prevent plastic from flowing back after injection and to compensate for shrinkage during cooling, pressure is applied after injection is completed.
Function:
(1) To prevent melt from flowing back after injection. (2) Compensation for shrinkage during cooling.
Setting principle:
(1) Holding time varies with thickness of product. (2) Holding time varies with temperature of melt. The higher temperature, the longer time required, while the lower temperature, the shorter time required. (3) To improve production efficiency, holding time should be as short as possible while ensuring quality of product.
During holding process, nozzle of injection molding machine continuously feeds material into cavity to fill volume vacated by shrinkage of part. If cavity is filled and pressure is not maintained, part will shrink by about 25%, especially ribs will shrink too much and shrinkage marks will be formed. Holding pressure is generally about 85% of maximum filling pressure, which should be determined according to actual situation. Holding time in injection time is time of pressure on plastic in mold cavity. It accounts for a large proportion of the entire injection time, generally about 10-120 seconds (up to 5-10 minutes for extra thick parts). Holding time before melt freezes at gate has an impact on dimensional accuracy of product. If it is later, it has no effect.
Holding time also has an optimal value, which is known to depend on material temperature, mold temperature, and size of main runner and gate. If size of main runner, gate and process conditions are normal, pressure value that results in the smallest fluctuation range of product shrinkage rate is usually used as standard.

Definition: Time required for product to cool and solidify without deformation after demolding
Function:
(1) Allow product to solidify. (2) Prevent product from deforming.
Setting principle:
(1) Cooling time is an important part of cycle time and should be kept as short as possible while ensuring product quality. (2) Cooling time depends on temperature of melt, mold temperature, product size and thickness

 

Definition: It refers to residence time (usually measured in minutes or seconds) of plastic resin in injection device roller of injection molding machine during injection molding process. In other words, residence time is the time it takes for plastic resin to move from roller hopper to nozzle tip. Long residence time will cause plastic to decompose, increase plastic fluidity, and change plastic's properties.
Setting principle: Maximum residence time of plastic resin (in processing stage) will be noted in physical property table, so that end user can be aware of above requirements, so that plastic can be processed under correct conditions and maintain its material properties before and after processing time.

Definition: Time required to dry raw materials in advance using drying equipment
Function:
(1) Improve surface gloss, improve bending and tensile strength, avoid internal cracks and bubbles. (2) Improve plasticizing ability and shorten molding cycle. (3) Reduce moisture and humidity in raw materials.
Setting principles:
(1) Drying time varies depending on raw materials. (2) Drying time should be set appropriately. If it is too long, drying efficiency will be reduced and even raw materials will agglomerate. If it is too short, drying effect will be poor.

Definition: Maximum pressure generated at injection port at screw tip, which is closely related to oil pressure generated in injection cylinder
Function: To overcome flow resistance of melt from nozzle--runner--gate--cavity, to increase speed of melt filling mold and to compact melt to ensure that cavity is filled and desired product is obtained.
Setting principles:
(1) Must be within rated pressure range of injection molding machine. (2) Try to use low pressure when setting. (3) Try to avoid using high pressure at high speed to avoid abnormal conditions

 

Injection pressure is provided by hydraulic system of injection molding system.
In current production, injection pressure of almost all injection machines is based on pressure applied by plunger or the top of screw to plastic (converted from oil circuit pressure). Pressure of hydraulic cylinder is transmitted to plastic melt through screw of injection molding machine. Under pressure, plastic melt enters vertical runner (also main runner for some molds), main runner, branch runner of mold through nozzle of injection molding machine, and enters mold cavity through gate. This process is injection molding process or filling process.
Existence of pressure is to overcome resistance in flow process of melt, or conversely, resistance in flow process needs to be offset by pressure of injection molding machine to ensure smooth progress of filling process.
During injection molding process, pressure at nozzle of injection molding machine is the highest to overcome flow resistance of melt throughout process.
Afterwards, pressure gradually decreases along flow length to front wave front of melt. If exhaust inside mold is good, final pressure at the front end of melt is atmospheric pressure.
There are many factors that affect melt filling pressure, which can be summarized into three categories: (1) Material factors, such as type and viscosity of plastic. (2) Structural factors, such as type, number and position of gating system, shape of mold cavity and thickness of product. (3) Process factors of molding.

Definition: Pressure that plastic creates in melt cavity during plasticizing process. During melting and plasticizing process of plastic, molten material continuously moves toward front end of barrel (inside metering chamber), more and more, gradually forming a pressure that pushes screw backward. In order to prevent screw from retreating too quickly and ensure that molten material is evenly compacted, it is necessary to provide screw with a reverse pressure. This reverse pressure that prevents screw from retreating is called back pressure.
Function:
(1) Increase specific gravity of melt. (2) Make melt plasticized evenly. (3) Reduce gas content in melt and improve plasticizing quality.
Setting principles:
(1) Adjustment of back pressure should take into account properties of plastic raw materials. (2) Adjustment of back pressure should refer to apparent quality and dimensional accuracy of product.
Size of this pressure can be adjusted by overflow valve in hydraulic system.
In injection, size of plasticizing pressure needs to be changed according to design of screw, requirements of product quality and type of plastic. If these conditions and screw speed remain unchanged, increasing plasticizing pressure will strengthen shearing effect, that is, it will increase temperature of melt, but it will reduce efficiency of plasticizing, increase backflow and leakage, and increase driving power.
In addition, increasing plasticizing pressure can often make temperature of melt uniform, colorant mixes evenly and discharge gas in melt.
In pressure curve operation in general plastic molding, plasticizing pressure should be determined as low as possible while ensuring quality of product. Specific value varies with type of plastic used, but it rarely exceeds 20 kg/cm2.
Use of high back pressure is conducive to dispersion of colorants and melting of plastics, but it also prolongs screw retraction time, reduces length of plastic fibers, and increases pressure of injection molding machine. Therefore, back pressure should be lower, generally not exceeding 20% of injection pressure.

Definition: From time mold cavity is filled with plastic, injection pressure applied to plastic in mold cavity is continued until gate is completely cooled and closed. This period of time requires a relatively high pressure to support it. This pressure is called holding pressure.
Function:
(1) Supplement amount of material near gate position, stop unhardened plastic in mold cavity from flowing back under residual pressure before gate is cooled and closed, to prevent shrinkage of part, avoid shrinkage, and reduce vacuum bubbles. (2) Reduce sticking, bursting or bending of part due to excessive injection pressure.
Setting principles:
(1) Holding pressure and speed are usually set to 50~60% of maximum pressure and speed when plastic fills mold cavity. (2) Length of holding time is related to material temperature. The higher temperature, the longer gate closure time and the longer holding time. (3) Holding pressure is related to projected area and wall thickness of product. Thick and large ones require longer time. (4) Holding pressure is related to size, shape and size of gate. Holding pressure switching position, metering length and release stroke are set.

Definition: Clamping force applied to mold by clamping system to overcome expansion force that separates mold during injection and holding stages.
Function:
(1) Ensure that mold does not expand during injection and holding stages. (2) Ensure surface quality of product. (3) Ensure dimensional accuracy of product
Setting principles:
(1) Size of clamping force depends on size of product and size of machine. (2) Generally speaking, the smaller clamping force is, the better, provided that product does not have burrs. (3) Setting of clamping force should not exceed rated pressure of machine.

Definition: Speed at which molten plastic is injected from nozzle into mold under a certain pressure.
Function: (1) Increasing injection speed will increase filling pressure. (2) Increasing injection speed can increase flow length and make product quality uniform. (3) High viscosity and fast cooling speed during high-speed injection are suitable for long-flow products. (4) Smooth flow at low speed and stable product size.
Setting principles:
(1) Prevent mold support and burrs. (2) Prevent burning caused by excessive speed. (3) Try to choose high-speed filling to shorten molding cycle while ensuring product quality.

Definition: Speed of screw when melting plastic during plasticization process
Function: An important parameter that affects plasticizing ability and plasticizing quality. The higher speed, the higher melt temperature, and the stronger plasticizing ability.
Setting principles:
(1) When adjusting melt speed, it is generally adjusted gradually from low to high. (2) Speed of machine with a screw diameter of more than 50MM should be controlled below 50RPM, and speed of machine with a screw diameter of less than 50MM should be controlled below 100RRM.

Definition: After plasticization begins, screw begins to retreat from injection end position under force of plastic melt until retreat limit switch is reached. This process is called metering stroke.
Function: Ensure that there is enough plastic to fill mold cavity to obtain desired appearance and size of product.
Setting principles:
(1) Metering stroke should be set according to size of product and size of machine. (2) Metering stroke should not be too large to prevent excess plastic from staying in material tube for too long and causing carbonization. (3) Metering stroke should not be too small to ensure that there is enough metering for filling and to avoid mechanical damage to screw and nozzle. There should be a buffer of 3~5mm

Definition: Change in position of screw during injection
Function: Combine speed and pressure to control flow state of plastic
Setting principles:
(1) Metering position is determined by filling amount of finished product. Usually, a buffer of 3~5mm is added to this value to determine final setting. (2) Switching point to second speed is usually switched to hot runner and material head position. (3) Switching point to third speed is set with 90% filling degree of molded product. (4) Pressure holding switching point is generally set at the position of 90% filling degree of finished product. (Note: Above four sections are used as an example).

Definition: After screw is pre-molded (metered) in place, it moves back a certain distance in a straight line. This backward movement is called backward loosening, and distance of loosening is called looseness or anti-delay amount.
Function: Function of backlash is to increase specific volume of melt in metering chamber, reduce internal pressure, and prevent melt from flowing out of metering chamber.
Setting principles:
(1) It can be set according to viscosity, relative density and actual situation of plastic raw material. A large backlash will cause melt to mix with bubbles, affecting quality of product. (2) Setting of backlash should be adapted to screw speed and back pressure. (3) For raw materials with high viscosity such as PC, backlash amount can be set.

Definition: After screw is injected, it is not desired to eject all molten material in head of screw. It is desired to leave some to form a sacrificial amount. This amount is buffering amount.
Function:
(1) Prevent mechanical damage accidents caused by contact between screw head and nozzle. (2) Control repetitive accuracy of injection volume.
Setting principles:
(1) Buffering amount should not be too large or too small. If it is too large, there will be too much residual material, resulting in pressure loss and raw material degradation. If it is too small, purpose of buffering cannot be achieved. (2) Determination of buffering amount is generally 3~5mm.