Large Thin-Wall Plastic Panel CNC Machining Case Study

Project Background

Plastic components are widely used in electronics, electrical, medical, automotive, and industrial instrumentation due to their lightweight, insulation, and design flexibility. However, large thin-walled plastic parts are prone to deformation during CNC machining, making precision and surface quality challenging to control, and placing high demands on equipment, tooling, and machining strategy.

Recently, WayKen worked on a set of thin-walled plastic parts made from POM and PC. The combination of large dimensions and thin wall sections made deformation control a key concern throughout machining. By carefully managing the overall process, the final parts maintained good dimensional stability and surface consistency. Let’s take a closer look at the part.

Key Machining Considerations for Large Thin-Walled Panels

Large thin-walled plastic panels are prone to deformation during machining. Success depends on understanding the part structure, material properties, and tight tolerances.

Structural Characteristics

The parts measure 609 mm × 457 mm × 5 mm, with a wall thickness of only 5 mm, classifying them as typical large thin-walled structures.

The upper cover requires double-sided milling, where controlling tool marks and preventing stress concentration or progressive deformation is critical.

The lower cover features a large hollow cavity, requiring significant material removal. This greatly reduces structural rigidity and makes the part highly susceptible to deformation during machining.

Material Properties and Processing Considerations

The initially specified material is PC, relatively brittle and prone to cracking, which increases the difficulty of precision machining. During cutting, PC is sensitive to heat buildup, burr formation, and edge defects.

In the second production run, the material was changed to POM. While POM offers better machinability, it has poorer dimensional stability, especially in large-area cutting. As internal stresses are released, warping can easily occur, requiring additional care in machining strategy and process control during the second run.

Accuracy Requirements and Deformation Control

Thin-walled parts are highly sensitive to deformation caused by the release of internal stresses during machining. For this industrial panel, 2D flatness had to be controlled within 0.05 mm, while other critical dimensions were required to remain within ±0.1 mm.
Meeting these tight tolerances demanded careful planning of machining sequences, optimized tool paths, and effective stress management throughout the entire process.

Machining Strategy Focus

Based on this analysis, the part’s structural features and material behavior introduce a high risk of residual stress and deformation, directly impacting flatness and dimensional accuracy.

Therefore, the machining strategy was specifically designed to prioritize deformation control and stress relief, ensuring that the final components consistently meet stringent dimensional and surface quality requirements.

Machining Strategies for Plastic Thin-Walled Structures

A targeted strategy of optimized fixturing, stepwise cutting, and stress relief ensured flatness and dimensional accuracy for the large thin-walled components.

1. Pre-Machining Deformation Prevention – Annealing

Before CNC machining, we performed annealing on the large thin-walled PC and POM parts as a preparatory measure against deformation. Annealing effectively relieves internal stresses, helping the parts maintain dimensional and geometric stability during multiple machining operations on both sides, thereby laying a solid foundation for subsequent high-precision processing.

2. Optimized Fixturing for Large Thin-Walled Plastics

The way large thin-walled plastic parts are fixtured has a major impact on machining results. Improper clamping can cause uneven forces during cutting, leading to warping, displacement, and compromised dimensional or surface quality.

For this project, we implemented a hybrid clamping solution combining vacuum suction with flexible pressure fixtures, providing dual fixation to ensure the parts remain flat and stable throughout high-speed cutting and multiple tool changes.

3. Precision Cutting Strategy: Stress and Deformation Control

We optimized the tool paths from conventional linear passes to spiral trajectories and employed dynamic cutting in combination with sharp tools for step-by-step material removal. This approach reduces the contact area during cutting, effectively minimizing machining-induced stress.

Through this precision cutting strategy, even large thin-walled parts achieve strict compliance with hole locations, flatness, and overall dimensional accuracy, significantly enhancing machining stability and the quality of final assembly.

4. High-Precision Machining Strategy: Deformation Control and Accuracy Assurance

We adopted a “stepwise roughing + multiple stress-relief cycles + finishing” approach to manage deformation and achieve high precision. We adopted a “two-stage roughing + multiple stress-relief cycles + precision machining” approach to control deformation and achieve high dimensional accuracy.

4.1 Upper Cover Machining

The upper cover has an extremely thin wall and requires double-sided milling, making it highly susceptible to deformation. We first performed two consecutive roughing passes, removing equal amounts of material from both sides simultaneously to avoid stress concentration from one-sided cutting.

After each roughing pass, the part was allowed to rest for 24–36 hours to fully relieve residual stresses. Following the two roughing–rest cycles, overall deformation was effectively controlled. With the structure stabilized, the final precision machining was carried out, ensuring flatness within 0.05 mm and meeting strict dimensional tolerances.

4.2 Lower Cover with Deep Cavity

The deep-cavity lower cover requires large-area material removal, which can easily cause severe deformation. Cutting only on one side would create stress concentration and warping. To address this, we pre-machined a mirror structure on the backside, allowing both sides to remove equal amounts of material and balance stress from the start.

The process included two roughing passes, each leaving a small material allowance, with stress relief applied between passes to reduce deformation risk. Final precision machining was then performed on the stabilized part to achieve the required dimensions.

Deformation and Flatness Inspection Before Shipment

The final machined parts demonstrated excellent control of deformation. Before shipment, our quality inspection team measured deformation using feeler gauges, ensuring all parts remained within the expected limits. Flatness was then verified separately with a CMM. These careful inspections ensured that the final results fully met the customer’s requirements.

Feedback & Support

After receiving the parts, the customer confirmed that flatness, dimensional accuracy, and assembly performance fully met expectations, with no deformation issues observed.

At WayKen, we support customer projects with practical process planning, deformation-aware machining strategies, and reliable CNC capabilities for plastic and metal parts, helping ensure stable quality from prototyping through small-batch production.