Main Technical Parameters
Basic parameters of an injection molding machine effectively reflect size of products it can mold, its production capacity, and provide an assessment of type, grade range, and quality of processed materials. They also serve as basis for designing, manufacturing, selecting, and using injection molding machines. Main parameters of an injection molding machine include injection volume, injection pressure, injection rate and injection time, plasticizing capacity, clamping force, mold opening and closing speeds, idle cycle time, and basic dimensions of mold clamping system.

 

Injection volume is one of important performance parameters of an injection molding machine. It reflects processing capacity of machine to a certain extent, indicating maximum range of products that machine can mold. Injection volume is generally expressed in two ways: injection volume and injection mass.
Injection volume refers to maximum volume that injection system can inject during one maximum injection stroke of injection screw or plunger under no-load injection conditions. Theoretical injection volume (cm³) standards for injection molding machines in China include 16, 25, 40, 63, 100, 160, 200, 250, 320, 400, 500, 630, 800, 1000, 1250, 1600, 2000, 2500, 3200, 4000, 5000, 6300, 8000, 10000, 16000, 25000, and 40000, among others.
Injection mass refers to maximum mass that injection system can inject during one maximum injection stroke of injection screw or plunger under no-load injection conditions. It is usually expressed in grams (g) as mass of molten material that can be injected in one injection cycle using PS as standard material (density p = 1.05 g/cm³).

Injection pressure refers to force exerted by screw or plunger on a unit area of material during injection molding, measured in MPa. Injection pressure plays a crucial role in injection molding, enabling molten material to overcome flow resistance through nozzle, runner, and mold cavity, providing necessary filling speed, and compacting melt. Magnitude of injection pressure affects melt flow, size and structure of molded product. During molding, injection pressure depends on factors such as mold runner resistance, product shape, plastic properties, plasticizing method, plasticizing temperature, mold structure, mold temperature, and required product precision. In actual production, required injection pressure should be adjusted within allowable range of injection molding machine.

To obtain dense, uniform, and high-precision products, molten material must be rapidly filled into mold cavity within a short time. Besides sufficient injection pressure, it must also have a certain flow rate. Parameters used to describe speed of molten material filling mold include injection rate and injection time. Injection rate refers to volumetric flow rate achievable per unit time during injection. Injection time refers to the shortest time required for screw or plunger to complete one maximum injection stroke.

Plasticizing capacity refers to amount of material that a plasticizing device can plasticize per unit time. Generally, plasticizing capacity of a screw is related to screw speed, drive power, screw structure, and material properties. Plasticizing device of an injection molding machine should be able to provide a sufficient amount of uniformly plasticized molten material within a specified time. Plasticizing capacity should be coordinated with the entire molding cycle of injection molding machine; otherwise, capacity of plasticizing device cannot be fully utilized. If plasticizing capacity is high but injection molding machine's idle cycle time is long, increasing screw speed, increasing drive power, improving screw structure can all improve plasticizing capacity and plasticizing quality. Generally, theoretical plasticizing capacity of an injection molding machine is about 20% greater than actual required amount.

Clamping force refers to maximum clamping force applied to mold by clamping mechanism of injection molding machine. Under this force, mold should not be pushed open by molten material. It reflects, to some extent, size of products that injection molding machine can process and is an important parameter. Some countries use maximum clamping force as specification designation for injection molding machines.

Opening and closing speeds are parameters reflecting working efficiency of injection molding machine. They directly affect length of molding cycle. To ensure smooth opening and closing of moving platen and to prevent damage to plastic product during ejection, and to prevent damage to mold due to foreign objects inside mold or loose or detached inserts, moving platen needs to operate at a slow speed. However, to improve production capacity and shorten molding cycle, moving platen needs to operate at a fast speed. Therefore, operating speed of moving platen varies throughout molding process; that is, it is fast at first, then slow when closing mold, slow at first, then fast, slow again when opening mold. Furthermore, position of speed variation needs to be adjustable to adapt to production needs of products with different structures.

Idle cycle time refers to time required to complete one cycle of operation without plasticizing, injection, holding pressure, cooling, or product removal. It consists of mold movement, injection unit forward and backward movement, mold opening, and switching time between actions; sometimes it is directly expressed as mold opening and closing time. Idle cycle time reflects performance of mechanical, hydraulic, and electrical components (e.g., sensitivity, repeatability, stability), and also indicates working efficiency of injection molding machine; it is a parameter characterizing the overall performance of injection molding machine.

Basic dimensions of mold closing system directly affect range of products that can be processed, installation and positioning of mold. These mainly include: platen dimensions and tie rod spacing, maximum opening distance between platens and moving platen stroke, maximum (minimum) mold thickness, and mold adjustment stroke.
Platen dimensions and tie rod spacing are key parameters representing mold mounting area. Platen dimensions of injection molding machine determine length and width of injection mold. Platen area is approximately 4 to 10 times maximum molding area of injection molding machine, and mold can be installed onto platen using conventional methods. It can be said that mold platen size limits maximum molding area of injection molding machine, while tie rod spacing limits mold size.

 

Maximum opening distance between mold plates is a characteristic parameter indicating maximum height of product that injection molding machine can process. It refers to maximum distance Lmax that can be achieved between fixed and moving mold plates during mold opening, including mold adjustment stroke.
Moving mold platen stroke refers to maximum value of moving mold platen's travel distance. For toggle-type mold clamping devices, moving mold platen stroke is fixed; for hydraulic mold clamping devices, moving mold platen stroke varies with thickness of installed mold. Generally, moving mold platen stroke should be greater than twice maximum height of product to facilitate product removal. To reduce power loss due to mechanical wear, the shortest possible moving mold platen stroke should be used during molding.
Maximum (minimum) mold thickness refers to maximum (minimum) distance between moving and fixed mold plates when specified clamping force is reached after moving mold platen is closed. If mold thickness of product being molded is less than minimum mold thickness, shims (plates) should be added; otherwise, clamping force cannot be generated, preventing injection molding machine from operating normally. Conversely, same applies; clamping force cannot be generated, and normal production is also impossible.
Mold adjustment stroke is difference between maximum mold thickness (Hmx) and minimum mold thickness (Hmin). To mold products of different heights, mold plate spacing should be adjustable. Adjustment range is 30% to 50% of maximum mold thickness.