Plastic Machinability Chart Guide: Compare Materials and Optimize Processing

Imagine you are tasked with producing a batch of precision plastic gears for an automotive project. You carefully select a material, set the mold temperature, and start the production, but the parts come out warped or the mold does not fill completely. What went wrong? Often, the answer lies in not fully understanding the material’s machinability.

In the plastics industry, a plastic machinability chart acts as a vital guide, systematically presenting the processing characteristics of different plastics. From newcomers navigating their first projects to seasoned engineers optimizing complex production lines, effectively using this chart can save time, reduce waste, and improve part quality.

Let’s dive into the world of plastic machinability charts and uncover the insights they provide for smarter, more efficient manufacturing.

1. Key Parameters in the Plastic Machinability Chart

A plastic machinability chart contains multiple parameters, each highlighting a specific aspect of plastic processing behavior. Key indicators include:

Melt Flow Rate (MFR)

Melt flow rate (MFR) measures the flowability of molten plastic under standard temperature and pressure, expressed in g/10 min. Higher MFR indicates better flowability, making the plastic easier to fill complex or thin-walled molds.

Conversely, plastics with lower MFR are more challenging to process and better suited for thick-walled or high-strength components like pipes or structural panels.

Thermal Stability

Thermal stability describes a plastic’s resistance to degradation, discoloration, or performance loss at elevated temperatures. Indicators in the chart include decomposition temperature and Vicat softening point.

• Decomposition temperature: Higher values mean the material can withstand higher processing temperatures.
• Vicat softening point: Indicates the temperature at which plastic softens under a specified load, essential for evaluating thermal performance and suitable operating range.

Different plastics exhibit distinct thermal behaviors, which directly influence processing choices.

Shrinkage

Shrinkage refers to the dimensional reduction of plastic parts after cooling from the molten state, expressed as a percentage. Factors affecting shrinkage include plastic type, processing parameters (temperature, injection pressure, and cooling time), and part geometry.

Shrinkage is often anisotropic, meaning it can vary by direction. Accurate shrinkage knowledge is essential to ensure dimensional precision in molded components

Mechanical Properties

Mechanical properties, such as strength, stiffness, toughness, and hardness, dictate how plastics respond to forces during processing and in service.

• High-strength plastics like PC or PA require higher injection pressures to fill molds and minimize internal stress.
• Tough but less rigid plastics like PE or PP need careful cooling control to prevent brittleness or deformation.

Processing parameters should always align with the material’s mechanical characteristics.

2. Plastic Machinability Chart: Comparing Common Engineering Plastics

Plastics vary widely in molecular structure and physical properties, influencing both processing and application. The table below summarizes the key parameters of commonly used engineering plastics, providing a quick reference for manufacturing decisions:

This plastic machinability chart simplifies material selection and helps you align plastic properties with intended processing methods.

3. Common Plastic Processing Methods

Plastic manufacturing involves primary forming and secondary machining. Each method serves different purposes and is suited to specific plastics:

Injection Molding

Injection molding converts plastic pellets into high-precision, complex parts suitable for large-volume production. It is ideal for plastics such as ABS, PC, PA, PP, PE, and POM. This process supports intricate geometries and fast cycle times, typically 10–60 seconds, but careful control of mold temperature, injection speed, and cooling is essential to prevent warping and ensure dimensional accuracy. Typical products include phone housings, keyboards, and automotive components.

Extrusion

Extrusion produces continuous profiles like pipes, sheets, or films by forcing molten plastic through a shaped die. It is suitable for plastics such as PVC, PP, PE, PS, ABS, and PET. Extrusion allows cost-effective, high-volume production, though uniform cooling and die design are crucial to maintaining consistent dimensions. Typical products include piping, films, and sheets.

Blow Molding

Blow molding creates hollow parts by inflating softened plastic inside a mold using compressed air. It works well with PE, PET, PVC, and PP. The process is efficient for bottles and containers, with high material utilization, but precise control of air pressure and cooling is needed to avoid wall thickness variations. Typical products include beverage bottles, automotive tanks, and cosmetic containers.

3D Printing (Additive Manufacturing)

3D printing builds parts layer by layer, offering high design freedom for complex geometries. It supports plastics like PLA, ABS, PETG, TPU, resins, and PA powders, depending on the technology. This method is ideal for rapid prototyping and small-batch production, but layer adhesion, shrinkage, and print orientation must be carefully managed. Typical applications cover consumer products, medical devices, and automotive and aerospace parts.

CNC Machining

CNC machining is a precision subtractive process using mills, lathes, and routers. It suits rigid plastics such as ABS, PC, PA, POM, and PMMA. The method offers high precision (±0.01 mm) and flexibility for complex or custom parts, but tool selection, cutting speed, and fixture design are important to minimize burrs and deformation. Typical products include optical mounts, precision gears, and medical device components.

The choices you make in heating, molding, or cutting are small, but they ripple through every part’s performance, showing that process understanding matters as much as material selection.

4. Processing Challenges in Plastic Machining

Even with a clear plastic machinability chart, real-world production often presents challenges that can affect part quality and efficiency. Understanding why these issues occur and how to address them is essential for smooth manufacturing.

Warping

Warping occurs when different areas of a part cool and shrink unevenly, causing distortion. Materials with high shrinkage rates, such as ABS or PA, are more prone to this problem, especially in thick or complex geometries. To minimize warping, engineers can optimize mold design, adjust cooling rates, or select plastics with lower shrinkage characteristics.

Short Shots

A short shot happens when molten plastic fails to completely fill the mold cavity, leaving incomplete parts. This often results from plastics with high viscosity or inadequate injection pressure, such as POM or highly filled composites. Solutions include increasing injection pressure, raising melt temperature, or redesigning the mold to improve flow paths.

Stress Cracking

Stress cracking refers to cracks that appear under mechanical or chemical stress after molding. Plastics like PC or PMMA can be sensitive to residual stress induced by rapid cooling or uneven packing. Preventive measures involve controlling cooling rates, using proper gate locations, and applying post-processing annealing to relieve internal stresses.

By anticipating these challenges and referring to the plastic machinability chart, engineers can predict potential issues, choose suitable materials, and adjust processing parameters accordingly. The result is higher-quality parts, reduced scrap rates, and a more predictable production process.

Conclusion

The plastic machinability chart is more than just numbers. It is a practical guide that connects material science with real-world manufacturing. By understanding MFR, thermal stability, shrinkage, and mechanical properties, engineers can move from reactive adjustments to proactive process control.
Before starting production, consider the following questions:

• What flowability does my part geometry require?
• What mold temperature aligns with surface finish needs?
• How should I compensate for shrinkage to maintain dimensional accuracy?

Answering these questions with the help of the plastic machinability chart transforms you from a passive material user into a strategic manufacturing problem solver. Consulting a knowledgeable supplier like the Beska team, who understands both the materials and the machining processes, can further ensure optimal material selection, precise processing, and high-quality production results.

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