Introduction
Material selection is one of the most critical decisions in machining. It directly affects product performance, manufacturing efficiency, and cost. Two material families dominate the field: plastics and metals. Each offers distinct advantages and limitations. Choosing the wrong material can lead to premature failure, excessive costs, or manufacturing delays.
According to industry data, metals account for 65% of the global machining materials market, while plastics represent 35%. However, engineering plastics are growing at 8.5% annually—significantly faster than metals at 2.3%. This growth reflects expanding applications where plastics offer compelling advantages.
This guide compares plastics and metals across three core dimensions: material properties, machining processes, and application suitability. You will learn when to choose each material, how they perform in different environments, and how to balance cost, performance, and manufacturability.
What Are the Key Material Differences?
Physical and Chemical Properties of Plastics
Plastics offer unique characteristics that make them ideal for specific applications.
Physical properties:
- Low density: 0.9–1.5 g/cm³—about 1/5 to 1/8 of steel and 1/3 to 1/2 of aluminum
- Good toughness: Polycarbonate (PC) impact strength is 250 times that of ordinary glass
- Excellent electrical insulation: Breakdown voltage typically above 10 kV/mm
- Low thermal stability: Most engineering plastics deform at 100–150°C
- Moderate strength: Tensile strength typically 40–80 MPa (compared to steel at 400+ MPa)
Chemical properties:
- Corrosion resistance: Polypropylene (PP) withstands most strong acids and alkalis; PTFE resists aqua regia
- No oxidation: Plastics do not rust; no additional anti-corrosion treatment needed
- Chemical sensitivity: Some plastics absorb moisture or swell in certain solvents
Physical and Chemical Properties of Metals
Metals remain the go-to choice for high-strength and high-temperature applications.
Physical properties:
- High mechanical strength: Tensile strength 400–1000+ MPa
- Excellent thermal stability: Steel melting points above 1500°C
- Good thermal and electrical conductivity: Ideal for heat transfer and electrical applications
- High density: Steel ~7.8 g/cm³, aluminum ~2.7 g/cm³—significantly heavier than plastics
- Dimensional stability: Minimal deformation under load or temperature change
Chemical properties:
- Variable corrosion resistance: Most steels rust in humid or acidic environments
- Requires surface treatment: Plating, painting, or passivation needed for corrosion protection
- Stainless and titanium alloys: Good corrosion resistance but higher cost
Performance During Machining
The behavior of plastics and metals during cutting differs significantly. These differences affect tool life, cycle time, and surface quality.
| Aspect | Plastic Machining | Metal Machining |
|---|---|---|
| Cutting difficulty | Low; low cutting resistance; minimal burrs | High; high cutting resistance; burrs require deburring |
| Thermal deformation risk | High; softening and deformation if overheated | Low; heat-resistant; minimal thermal deformation |
| Tool wear | Low; less demanding on tool hardness; long tool life | High; requires hard tool materials; frequent replacement |
| Dimensional stability | Moderate; depends on material (POM stable; PA absorbs moisture) | High; consistent dimensions after machining |
Real-world example: A precision machining factory produced identical gears from POM (plastic) and steel.
| Parameter | POM (Plastic) | Steel |
|---|---|---|
| Cutting speed | 150 m/min | 80 m/min |
| Tool life | 5,000 pieces | 2,000 pieces |
| Post-processing | None | Deburring required |
The plastic gear machined faster, with longer tool life and no secondary operations—a clear efficiency advantage.
How Do Machining Processes Differ?
Processing Methods for Plastics
Plastics offer multiple processing routes, each suited to different production needs.
| Method | Best For | Key Characteristics |
|---|---|---|
| CNC machining | Precision parts, medium volumes | Tolerances to ±0.01 mm; high accuracy |
| Injection molding | High-volume production | Complex shapes; low per-unit cost; high initial tooling |
| Laser cutting | Thin parts, intricate shapes | Smooth edges; no burrs; high precision |
| 3D printing | Custom parts, low volumes | Complex geometries; rapid iteration; no tooling |
Key advantages: Plastic processes are generally simpler, require lower temperatures and pressures, and need minimal pretreatment. This makes them accessible for small and medium enterprises.
Processing Methods for Metals
Metal machining relies primarily on traditional subtractive processes.
| Method | Best For | Key Characteristics |
|---|---|---|
| Turning | Cylindrical parts (shafts, sleeves) | High precision; fast material removal |
| Milling | Flat surfaces, grooves, complex contours | Versatile; handles complex geometries |
| Drilling | Holes and through-features | Precision hole size and position |
| Grinding | Finishing high-precision parts | Achieves fine surface finishes; tight tolerances |
| Forging/Casting | High-volume, near-net shapes | Requires secondary machining for precision |
Key challenges: Metal processes require rigid machines, skilled operators, and often multiple operations. High-precision work demands specialized equipment and careful process control.
Efficiency and Cost Comparison
Plastic machining generally offers higher efficiency and lower costs across several dimensions.
| Cost Factor | Plastic | Metal | Advantage |
|---|---|---|---|
| Raw material cost | 1/3 to 1/2 of steel | Baseline | Plastic |
| Processing energy | 1/5 to 1/3 of metal | Baseline | Plastic |
| Tool wear cost | 1/4 of metal | Baseline | Plastic |
| Production efficiency | 1.5–2× faster cutting speeds | Baseline | Plastic |
| Post-processing | Minimal | Deburring, polishing often required | Plastic |
Data point: A machinery factory processing chemical pipes found that PP plastic had 45% lower comprehensive cost compared to steel pipes for the same application.
Where Are Plastics and Metals Used?
Plastic Applications Across Industries
Plastics excel where lightweight, corrosion resistance, and electrical insulation are priorities.
| Industry | Materials | Applications |
|---|---|---|
| Automotive | PP, PA, PC | Bumpers, interior panels, engine covers, lightweight structural parts |
| Electronics | PC, POM, PVC | Smartphone housings, computer cases, keyboard buttons, wire insulation |
| Medical | PC, PTFE, PLA | Surgical instrument shields, artificial blood vessels, disposable consumables |
| Chemical | PP, PTFE, PVDF | Storage tanks, pipes, fittings in corrosive environments |
Case study: An electric vehicle manufacturer replaced metal body parts with plastic components, reducing vehicle curb weight by 120 kg and increasing driving range by 15%.
Metal Applications Across Industries
Metals dominate where strength, stability, and high-temperature performance are essential.
| Industry | Materials | Applications |
|---|---|---|
| Aerospace | Titanium alloys, aluminum alloys | Fuselage structures, engine components, landing gear |
| Machinery | Steel, cast iron | Machine tool spindles, gearboxes, heavy-duty transmissions |
| Construction | Structural steel | Bridge supports, building frames, load-bearing structures |
| New energy | Copper, aluminum | Battery terminals, power cables, busbars |
Case study: An aerospace company uses titanium alloy for aircraft engine blades. These components operate reliably in high-temperature, high-pressure environments with a service life exceeding 10,000 flight hours.
Advantages and Disadvantages in Specific Applications
The choice between plastic and metal often depends on the specific application requirements.
| Application | Plastic Pros | Plastic Cons | Metal Pros | Metal Cons |
|---|---|---|---|---|
| Lightweight automotive parts | Light weight; low cost | Limited strength | High strength | Heavy; higher cost |
| Electronic insulation | Excellent insulation; machinable | Lower thermal conductivity | Not applicable | Conducts electricity |
| High-precision transmission | — | Limited to low-load applications | High strength; dimensional stability | Higher cost |
| Corrosive environment | Corrosion-resistant; low maintenance | Lower temperature limits | Needs anti-corrosion treatment | Shorter service life |
How Do You Choose Between Plastic and Metal?
Decision Framework
The choice between plastic and metal should be based on three core factors:
- Performance requirements: Strength, temperature, load, environment
- Working environment: Corrosive, high-temperature, electrical, outdoor
- Cost budget: Material cost, processing cost, lifecycle cost
When to prioritize plastic:
- Lightweight construction is critical
- Corrosion resistance is required
- Electrical insulation is needed
- Cost sensitivity is high
- Loads are low to moderate
When to prioritize metal:
- High mechanical strength is essential
- Operating temperatures exceed 150°C
- High precision and dimensional stability are required
- Heavy loads or impact resistance are needed
- Thermal or electrical conductivity is required
Hybrid Approaches
In some applications, combining plastic and metal offers the best of both worlds. Examples include:
- Metal core with plastic overmold: Structural strength with ergonomic surfaces
- Plastic housings with metal inserts: Lightweight enclosures with threaded metal connections
- Composite structures: Strategic use of each material where it performs best
Yigu Technology’s Perspective
At Yigu Technology, we view plastics and metals not as competing materials but as complementary tools in the manufacturing toolbox. The key is matching material properties to application requirements.
Our experience:
- We machine both plastics and metals daily, from PEEK medical components to titanium aerospace parts
- We help clients evaluate trade-offs: a 45% cost reduction with plastic may justify slightly lower strength in some applications
- We offer DFM feedback that considers material behavior—accounting for plastic moisture absorption or metal work hardening in process planning
Recent example: A chemical processing client needed corrosion-resistant pump housings. The original design specified stainless steel, which required expensive machining and frequent replacement due to pitting. We proposed PTFE plastic housings with stainless steel internal inserts for strength. The hybrid design reduced weight by 60%, cut material cost by 40%, and extended service life from 2 years to over 10 years.
We believe the future of manufacturing lies in intelligent material selection—choosing plastics where their advantages shine, metals where strength and stability are non-negotiable, and hybrid structures where both are needed.
Conclusion
Plastics and metals each offer distinct advantages in machining. Plastics provide lightweight construction, corrosion resistance, electrical insulation, and cost efficiency—especially in low to moderate load applications. Metals deliver high strength, thermal stability, dimensional accuracy, and conductivity for demanding environments.
The choice is not simply “plastic vs. metal” but rather matching material properties to application requirements. Consider performance needs, operating environment, and cost constraints. When in doubt, consult with machining experts who understand both material families.
As modified plastics improve in strength and temperature resistance, their application scope continues to expand. The trend is toward intelligent material selection—using each material where it performs best, and combining them when complementary properties are needed.
FAQ
For high-precision parts, should I choose plastic or metal?
If precision is extremely high (within ±0.005 mm) and the part bears load, choose metal (steel, aluminum). If precision requirements are moderate (±0.01–0.02 mm) and loads are low, choose high-precision plastics like POM or PC—they offer higher machining efficiency and lower cost.
Can plastic replace metal in high-temperature environments (above 150°C)?
Ordinary plastics cannot. Special high-temperature plastics like PTFE and PEEK can operate at 200–260°C. Above 260°C, metal materials (stainless steel, titanium) are required.
Do plastic machined parts have shorter service life than metal?
Not necessarily. In normal environments, metal parts generally last longer. In corrosive environments, plastic parts (PP, PTFE) can last 5–10 times longer than non-corrosion-resistant metals, with lower maintenance costs. Material modification can further extend plastic service life.
Is plastic or metal more cost-effective for small-batch custom parts?
Plastic is generally more cost-effective. For small-batch customization, plastics can be CNC machined or 3D printed with short lead times (1–3 days) and low tooling costs. Metal machining typically requires custom tooling and longer lead times (5–7 days) with higher costs. Choose metal only when parts must withstand heavy loads.
How do I prevent plastic parts from deforming during machining?
Use sharp tools to minimize heat generation. Apply air cooling rather than flood coolant for most plastics. Reduce feed rates for finishing passes. Allow material to stabilize at room temperature before final dimensions. For hygroscopic plastics like nylon, dry material before machining to prevent moisture-induced swelling.
Contact Yigu Technology for Custom Manufacturing
Need expert guidance on material selection for your next machining project? Yigu Technology machines both plastics and metals, helping clients choose the right material for performance, cost, and manufacturability.
- Plastics: POM, PC, ABS, PEEK, PTFE, PP, nylon, acrylic
- Metals: Aluminum, steel, stainless steel, titanium, brass, copper
- Capabilities: CNC milling (3, 4, 5-axis), CNC turning, Swiss-type turning
- Quality: ISO 9001 certified; in-process inspection; CMM verification
- Volumes: Prototyping to high-volume production
Contact our engineering team to discuss your application. We will provide material recommendations, DFM feedback, and a manufacturing plan optimized for your requirements. Let us help you make the right material choice—the first time.
