How to choose the appropriate fixture according to the model and specification of injection molding machine?

According to the model and specification of the injection molding machine, the selection of the appropriate picking fixture should be combined with the core parameters of the injection molding machine, such as tonnage, mold opening stroke, template size and maximum allowable modulus, and at the same time match the characteristics of plastic parts and production requirements to ensure that the fixture is compatible with the equipment and operates efficiently. The following are the specific selection methods and steps:

First, clear the core parameters of injection molding machine (basic basis)

First of all, it is necessary to master the key specifications of the injection molding machine, which directly determine the size, weight, movement space and bearing capacity of the fixture:

Influence of injection molding machine parameters on fixture selection points

Tonnage (clamping force) Tonnage determines the size of plastic parts (usually, the larger the tonnage, the greater the size/weight of plastic parts) and affects the load capacity of fixtures. Small tonnage (≤100 tons): the weight of the fixture is ≤5kg, which is suitable for small plastic parts (such as mobile phone accessories);

Large tonnage (≥500 tons): The fixture should bear ≥20kg, and high-strength materials (such as steel+aluminum alloy combination) should be selected.

The distance between the moving die and the fixed die after the die opening stroke determines the depth and movement space of the fixture. Small mold opening stroke (≤300mm): the fixture should be compact to avoid interference with the mold;

Large mold opening stroke (≥1000mm): The fixture can be designed with a longer extension arm (rigidity should be ensured to prevent shaking).

Template size (tie bar spacing) determines the maximum horizontal/vertical size of the fixture, so as to avoid interference with tie bars, templates or molds. For example, when the distance between tie rods is 500×500mm, the maximum width/length of the fixture shall be ≤450mm (with a safety gap reserved).

The maximum bulk modulus affects the thickness of the mold and indirectly determines the space where the fixture extends into the mold (the larger the bulk modulus, the thicker the mold and the more compact the internal space). For injection molding machines with large bulk modulus, the fixture should be designed to be more "slim" to avoid colliding with the side of the mold.

Ejection mode (ejector pin/top plate) The position and stroke of the ejector mechanism determine the picking path of the fixture (such as grabbing from above or grabbing from the side). Small plastic parts ejected by thimble: the fixture can be designed to grab vertically downward;

Large plastic parts ejected from the top plate: the fixture may need to be grabbed from the side or obliquely.

Second, according to the "automatic adaptation ability" of the injection molding machine, choose the fixture driving mode.

The automatic interface of injection molding machine and auxiliary equipment (such as air source and power supply) determine the driving type of fixture;

Small injection molding machine (≤100 tons): Generally, the space is limited, and most of them are simple and automatic. Pneumatic fixtures (simple structure and low cost) are preferred, such as cylinder-driven mechanical jaws or vacuum suction cups (the injection molding machine is required to provide air source interface, and the air pressure is ≥0.5MPa).

Medium and large injection molding machine (≥200 tons): It can adapt to more complicated fixtures. If high-precision control (such as adjustable clamping force and multi-position action) is required, electric fixtures (such as servo motor drive) can be selected, but it is necessary to confirm whether the injection molding machine has sufficient power interface and control system compatibility (such as PROFINET and EtherCAT communication protocol).

High-speed injection molding machine (cycle ≤5 seconds): For fast response of fixture, vacuum sucker+quick response valve (vacuum establishment time ≤0.3 seconds) or lightweight mechanical gripper (opening and closing time ≤0.2 seconds) are preferred to avoid slowing down the production pace.

Third, combining the matching between the characteristics of plastic parts and the parameters of injection molding machine

Even if the parameters of the injection molding machine are the same, the weight, size, shape and material of the plastic parts will also affect the fixture selection, which needs to be judged in coordination with the equipment parameters:

Weight of plastic parts vs tonnage of injection molding machine/manipulator load

The tonnage of injection molding machine determines the maximum weight of plastic parts that can be produced (for example, a 100-ton injection molding machine usually corresponds to the weight of plastic parts ≤500g, and a 500-ton injection molding machine corresponds to ≤5kg).

The bearing capacity of fixture should be ≥ 1.5 times of the weight of plastic parts (safety factor), and the rated load of manipulator should include the weight of fixture+the weight of plastic parts. For example: 5kg plastic parts+3kg fixture, the load of manipulator should be ≥8kg, and it is necessary to confirm whether the load parameters of the supporting manipulator of injection molding machine meet the standard.

Size of plastic parts vs opening stroke/template size of injection molding machine

For long plastic parts (such as pipes with a length of 1m), the mold opening stroke should be ≥ plastic part length+safety distance (≥100mm), and the fixture should be designed as "long arm type", but the length of the long arm should not exceed the template spacing of the injection molding machine to avoid collision with the pull rod.

Large flat plastic parts (such as car bumper) need to match the maximum cavity size of injection molding machine, and the fixture adopts multi-suction cup array (the number of suction cups is calculated according to the area, and there is at least one suction cup per 100×100mm area), and the layout of suction cups should avoid the weak parts of plastic parts (such as edges and holes).

Shape of plastic parts vs picking space of injection molding machine

Deep-cavity plastic parts (such as trash cans): The opening stroke of the injection molding machine should be deep enough, and the fixture should be designed as "deep", such as lengthening the gripper or sucker rod, but the volume of the fixture should not exceed the internal space after opening the mold (the interference between the fixture and the mold can be simulated by 3D modeling).

Special-shaped plastic parts (such as inverted buttons and bosses): If the space for taking parts is narrow after the injection molding machine is opened, the combined fixture (such as "mechanical gripper positioning+vacuum-assisted adsorption") is preferred, giving consideration to stability and spatial adaptability.

Fourth, refer to the special functions and additional devices of injection molding machine.

Special design of some injection molding machines requires fixture adaptation;

Injection molding machine with rotating template: The fixture should have rotating function (such as 90/180 turnover), and the rotating radius should be less than or equal to the rotating space of injection molding machine template to avoid interference with fixed parts.

Multi-cavity mold injection molding machine: If the mold is multi-cavity (e.g. 8 cavities and 16 cavities), the fixture should be designed for multi-position synchronous grasping (e.g. 8 groups of suction cups or jaws), and the grasping spacing of the fixture should be consistent with the spacing of the mold cavities (error ≤0.5mm), otherwise it will lead to grasping dislocation.

Injection molding machine with core-pulling mechanism: Core-pulling action will occupy part of mold opening space, so it is necessary to reserve the movement path of core-pulling mechanism in fixture design to avoid interference (the position and stroke of core-pulling can be confirmed by the mold drawings of injection molding machine).

V. Verification and testing

After selecting the fixture, the following steps are needed to verify the adaptability:

Size simulation: use CAD software to simulate the assembly of 3D model of fixture with 3D model of injection molding machine template and mold, and check whether there is interference during mold opening/closing (focus on the distance between fixture and pull rod, ejector pin and core-pulling mechanism, with a safety gap of ≥50mm).

Load test: Test the running speed and stability of the manipulator under the condition of no-load and full load (fixture+plastic parts) to ensure that the maximum load and acceleration limit of the manipulator of the injection molding machine are not exceeded (usually the manipulator acceleration is less than 5m/s).

Compatibility test: connect the fixture and the control system of the injection molding machine, and test the signal linkage (such as "the fixture is successfully grasped → the injection molding machine closes the mold" and "the vacuum is insufficient → the shutdown alarm") to ensure the normal communication.

summary

The core logic of selecting the clamping fixture is to match the driving mode and structural design with the "space limitation (mold opening stroke, template size)" and "performance limitation (load, speed)" of the injection molding machine as the boundary and the "grasping requirements (weight, shape, accuracy)" of the plastic parts as the core. When necessary, the fixture supplier can be required to provide customized solutions based on specific injection molding machine models, and provide simulation test reports to ensure efficient compatibility between fixtures and equipment.