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How Should Thin-Walled Plastic Parts Be Removed Without Deformation After Molding?

2026/09/18 By le zhan

How Should Thin-Walled Plastic Parts Be Removed Without Deformation After Molding

Although thin-walled plastic parts are rigid enough to be ejected from the mold cavity, they remain hot and relatively soft, so they cannot withstand concentrated gripping forces, excessive acceleration, torsional stress, or imprecise removal paths.

This places extremely high demands on automated removal technologies in thin-wall injection molding. Cartesian injection molding robots must not only be capable of rapid part extraction but also able to apply force at appropriate locations, synchronize precisely with the mold-opening position, and avoid violent vibrations.

The guidelines from Autodesk Moldflow also emphasize this fundamental principle: “Molded parts must possess sufficient rigidity to withstand ejection forces without excessive warping or ejection marks. Although ejection at higher temperatures can shorten cooling time, it also increases the risk of deformation.”(Source: Autodesk Moldflow)

Therefore, for thin-walled plastic parts, the removal stage is not simply about speed, but about achieving a removal process that is fast, precisely synchronized, well supported, and controlled in force application.

Why Do Thin-Walled Plastic Parts Deform During Removal?

Immediately after molding, thin-walled plastic parts have relatively low flexural stiffness. Although thin-walled areas typically cool faster than thick-walled areas, they also resist external forces less well. Consequently, if a Cartesian robot gripper is used improperly or accelerates too rapidly, large flat surfaces, narrow ribs, long edges, and lightweight shells are all prone to bending deformation.

The first cause of deformation is premature removal.

If the part’s temperature is too high, the polymer has not yet developed enough rigidity to resist forces from vacuum suction, fixture pressure, gravity, or acceleration.

This raises an important issue: while extending the cooling time can improve rigidity, it also increases the molding cycle time. Therefore, a well-designed take-out robot should allow the part to be removed immediately once it reaches a mechanically stable state, without adding unnecessary cooling time.

Why Do Thin-Walled Plastic Parts Deform During Removal

Excessively Concentrated Gripping Force May Cause Deformation in Thin-Walled Plastic Parts

The second issue concerns force distribution.

Placing a large vacuum pad at the center of a flexible panel may cause localized tensile deformation. Similarly, if mechanical clamps are positioned too close to thin edges, they may cause the product to bend or leave indentations.

Therefore, end-effectors used to remove thin-walled parts should typically distribute the applied force across multiple stable areas rather than concentrating it at a single point. Instead of a single, powerful suction point, the end-effector can utilize multiple small suction cups distributed around areas of higher structural strength. The goal is to support the part’s geometry while keeping local stress low.

Deformation Caused by Excessively Abrupt Robot Movements

The third issue concerns the robot’s motion characteristics.

Even with the correct gripping position, rapid acceleration or sudden changes in direction can generate inertial forces that cause high-temperature parts to bend.

Therefore, the take-out robot must combine high speed with stable motion.

The robot should enter the mold quickly, grasp the part, and exit promptly to keep the molding cycle time unaffected. However, once it contacts the product, its acceleration, deceleration, and motion trajectory must be strictly controlled. Excessive vibration at the robot arm or EOAT may also exacerbate deformation. For this reason, in thin-walled part applications, the robot’s rigidity, servo response speed, positioning accuracy, and low-vibration structural design are critical.

Inaccurate removal paths may lead to warping

The fourth reason is a deviation between the Cartesian robot’s path and the actual ejection position.

After thousands of cycles, the mold does not always remain in exactly the same mechanical position. Slight variations in the mold opening stroke, ejector mechanism movement, or the injection molding machine’s operating condition can alter the actual removal position. If the product shifts slightly but the robot continues to follow a fixed path, the end-of-arm tool may pull the product sideways. This can result in a collision with the mold and an off-center grasp. For thin-walled plastic parts that are still hot, these deviations can cause permanent deformation.

How to Remove Thin-Walled Plastic Parts Without Deformation?

Preventing deformation requires comprehensive control of four factors: ejection temperature, support method, robot motion, and synchronization of the removal actions.

How to Remove Thin-Walled Plastic Parts Without Deformation

Thin-Walled Plastic Parts Must Have Sufficient Rigidity Before Removal

The primary task is to determine the earliest safe ejection timing.

The part does not need to cool completely to room temperature inside the mold; it only needs to have sufficient rigidity to withstand the stresses generated during ejection and robotic handling. However, premature removal may shorten the molding cycle at the expense of an increased scrap rate. Therefore, the practical goal is to achieve:

Shortest cooling time + sufficient part rigidity + stable robotic removal motion

Uniform cooling is crucial; uneven cooling and shrinkage variations generate internal stresses, causing the part to warp after ejection. Robots cannot correct thermally unstable parts, so mold cooling and removal-motion settings should be optimized in coordination.

A well-distributed and repeatable gripping method is required

The end-effector must support the product at a stable position and apply an appropriate gripping force. For vacuum handling, the following factors should be considered:

Number and location of suction points;
Product surface geometry;
Vacuum level;
Part temperature;
Expected acceleration after removal.

Multi-point suction is particularly effective for large, flexible products, as multiple support points distribute the load and reduce the stress on individual localized areas. The gripping layout must also be repeatable. If a Cartesian robot approaches different positions in different cycles, the same set of fixtures may subject the product to varying stresses.

Precise and Low-Vibration Retrieval Motion Is Required

Although high-speed retrieval can shorten mold opening time, speed alone is not the ultimate goal.

Robot motion must balance the following:

Rapid approach + Precise positioning + Stable gripping + Smooth withdrawal

High positioning repeatability ensures that vacuum cups or grippers align precisely with the intended contact areas. High structural rigidity reduces unnecessary oscillations, while servo control allows precise adjustment of acceleration and deceleration. Therefore, the ideal motion profile should employ rapid movement as the robot disengages from the product, while adopting a more controlled motion during the gripping and initial removal phases.

This approach protects thin-walled structures without unnecessarily slowing down the entire molding cycle.

Synchronization of Robot Movements with Mold and Ejector Mechanism Positions Must Be Achieved

The removal sequence should respond to the injection molding machine’s actual status rather than relying solely on fixed time settings. The Cartesian robot should recognize the following sequence of actions:

Mold fully open → Confirm ejection mechanism/part position → Robot enters → Confirm grasping → Controlled removal → Robot exits mold area.

This prevents the Cartesian robot from attempting to remove the part before the mold or ejection mechanism has reached the specified position. The more precisely the robot’s movements are synchronized with those of the injection molding machine, the less unnecessary tensile or torsional force is applied to the part.

How do Topstar Cartesian robots protect thin-walled plastic parts during the removal process?

When designing Cartesian robots, Topstar considers the practical risks of removing high-temperature, thin-walled plastic parts. Our goal is not only to shorten removal time but also to maintain precise positioning, reduce vibration, control removal force, and ensure synchronization between the robot, the mold, and the ejection mechanism. Thin-walled plastic parts are protected primarily through the following three performance features:

  1. High positioning accuracy and low vibration
  2. Mold-opening position compensation and flexible floating control
  3. Multi-point gripping for better support
How do Topstar Cartesian robots protect thin-walled plastic parts during the removal process

Improving the Stability of Thin-Walled Plastic Part Removal

When it comes to the removal stage of thin-walled parts after molding, avoiding deformation during removal is straightforward:

Selecting a Cartesian injection molding robot with precise positioning, smooth, low-vibration motion, synchronized mold tracking, and evenly distributed gripping force enables rapid part removal without deformation. By meeting these conditions, Topstar’s Cartesian injection molding robots not only reduce mold opening time but also ensure that thin-walled plastic parts maintain consistent geometry and quality across all molding cycles.

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