What Every Engineer Should Know About CNC Machining Material
In CNC Machining, choosing the right materials goes beyond the technical aspects; it’s one of the most significant factors influencing the final cost, delivery and long-term performance of your parts. When engineers and procurement teams at MetalworksPlus ask the question, “Why does the same part cost 3x more in stainless steel than in aluminum?” The answer is the intricate interplay between the precision machine parts and the material properties that determine the cutting speed of a machine, the tool life and the number of finishes required.
In general, a 2023 study by the Precision Machined Products Association (PMPA) determined that raw material and machining labour make up 55% to 70% of the total cost of a typical CNC project. Even fewer (less than 30%) design engineers optimize material selection before handing off drawings for production. This is a substantial cost opportunity.
Understanding CNC Material Cost: The True Cost Beyond Raw Price
The majority of buyers consider the raw material price per kg. In reality, the cost of the CNC materials is much more complex. MetalworksPlus has seen this increase in machining cost multiplier for a number of hard-to-cut materials over thousands of production runs, which can be anywhere between 3-7 times the base material price.
Let’s take a look at the main cost drivers that engineers need to consider:
- Carbide end mills can last 8–12 times longer than they do in aluminum, the cost of which is $15–$40 per tool change cycle.
- Reduced cutting speed: Slower feed rates are required for harder materials, so there are greater machine time billable costs.
- The cost of coolants and lubricants is $2-$8 per part; special coolants are needed for heat-sensitive alloys such as Inconel.
- Passivation, electropolishing, or heat treatment (15% to 40% cost each) may be necessary as post-machining finishing for some stainless alloys.
- Defect rate: If the parameters are not optimized, poor machinability means that the scrap rate is 5-10% in aerospace-grade titanium projects.
CNC Material Cost & Machinability Comparison Table
The table below compares five of the most common machining materials used at MetalworksPlus, ranked by machinability index (aluminum 6061 = 100% baseline):
| Material | Machinability | Cost per kg (USD) | Typical Use Case | Relative Cycle Time |
| 6061 Aluminum | Excellent (100%) | $2.50–$4.00 | Aerospace, electronics | 1x (Baseline) |
| 304 Stainless Steel | Fair (45%) | $4.00–$7.00 | Medical, food-grade | 2.5–3x longer |
| 1018 Mild Steel | Good (75%) | $0.80–$1.50 | Structural, general | 1.5x longer |
| Titanium Grade 5 | Poor (22%) | $30–$60 | Implants, aerospace | 5–7x longer |
| Delrin (Acetal) | Excellent (95%) | $3.00–$5.00 | Gears, bushings | 0.8x (faster) |
*Typical bracket or plate part, 100g, standard tolerances, 50-unit run.
Aluminum vs Steel: The Most Common CNC Material Decision
The most common material query that MetalworksPlus engineers get asked is the aluminum vs steel one. Both are general and widely used, but for very different reasons, and if you get them wrong, you can spend up to 40% to 200% more on your project.
When Aluminum Wins the Aluminum vs Steel Debate
When weight-to-strength ratio and speed of production is most important, Aluminum is most effective, especially the 6061-T6 and 7075-T6 alloys. This has been the strength of the aerospace industry for years: there are about 80,000 aluminum machined parts in a Boeing 737. Key advantages include:
- Cutting speeds up to 3,000 SFM – 400 to 600 SFM for stainless steel
- Reduction of 65% in weight to steel for the same performance of the structure
- Natural corrosion resistance (in many cases no need for additional surface treatment)
- Excellent thermal conductivity – critical for heat sinks, electronics housings, and thermal management parts
In a real-world scenario, a manufacturer of robots wanted to replace 48 parts in an assembly with 6061 aluminum, replacing mild steel. The conclusion – the total cost of parts was reduced by 38% and assembly weight was reduced from 12.4 kg to 4.3 kg, which increased the payload of the robot by 22%.
When Steel Outperforms Aluminum
When hardness, wear resistance or food/medical-grade surface integrity is needed, then there is no way around steel – mild 1018, 4140 alloy or 304/316 stainless. Important benchmarks:
- Alloy 4140 alloy steel has a tensile strength of 95,000 PSI (as-machined) compared to 6061-T6 aluminum at 40,000 PSI.
- Corrosion resistance of 316 stainless steel is maintained up to 870°C as compared to the corrosion resistance threshold of 300°C for aluminum.
- Only steel alloys can be used for components that need to be hardened after manufacturing (case hardening, nitriding)
A client of the MetalworksPlus metal products division was producing surgical instrument handles that needed to be manufactured from the 316L stainless steel. Although the cycle time of aluminum is 2.8 times faster, the material could not be changed because of the biocompatibility requirements set forth by the ISO 10993 guidelines.
How Machining Material Properties Directly Control Performance
Choices of material other than cost affect the functional performance envelope of the finished part. Before giving any order for production, MetalworksPlus engineers analyze 4 major material performance aspects.
1. Tensile Strength and Impact Resistance
In load-bearing parts, strength of the material comes first. Titanium Grade 5 (Ti-6Al-4V) has a tensile strength of 130,000 PSI, which is equivalent to high strength steel at 45% of the weight. This is the reason why it is considered as an excellent material for aerospace fasteners and medical implants, despite the fact that it costs $30-$60 per kg in its raw form..
2. Thermal Stability During Machining
The heat produced at the interface of the cut parts can cause parts to be distorted and their surface finish to be reduced. Aluminum has a heat dissipation rate of 5 times greater than steel, which makes it easier to maintain tolerances of ±0.001 inch or less on long production runs. In a study of 504 production runs completed in-house at MetalworksPlus, 96.4% of the aluminum parts kept within dimensional tolerance without using a coolant, compared to 78.2% of the 304 stainless steel parts.
3. Surface Finish Capability
There is a wide range of achievable Ra (roughness average) values based on the material and machining parameters. In regular milling the Ra values of aluminum are usually 8–16 microinch. Under similar conditions, the typical finishing range for stainless steel is Ra 32-63 microinch, which is still not adequate for optical or sealing uses and needs further grinding or lapping.
4. Dimensional Stability After Machining
Reliable residual stress relief is an important, usually underestimated aspect. Measurable distortion (0.001 to 0.005 inch across 12-inch spans) can be produced in high-carbon and tool steels when stress is removed from the material as a result of machining. For steel parts with tolerances less than ±0.003 inch, MetalworksPlus recommends stress-relief annealing of all steel parts.
CNC Material Cost Breakdown: Key Factors at a Glance
The following table summarizes total cost impact across three representative materials for a standard 150g precision bracket:
| Cost Factor | Aluminum 6061 | Stainless Steel 304 | Titanium Grade 5 |
| Raw Material | Low | Medium | Very High |
| Tool Wear Rate | Low | High | Extreme |
| Machining Speed | Fast | Slow | Very Slow |
| Coolant Required | Sometimes | Always | Always (specialized) |
| Typical Part Cost* | $8–$25 | $20–$75 | $150–$500+ |
*Estimated cost range for a 150g precision bracket, 25-unit production run, standard tolerances, MetalworksPlus internal pricing model.
Metalworks Plus – Precision Manufacturing & CNC Machining Expert
Metalworks Plus is a precision manufacturing company specializing in high-quality CNC machining and custom metal fabrication solutions from prototype to full-scale production. Founded in China, the company combines advanced technology with rigorous quality control to serve industries such as aerospace, automotive, medical, electronics, and industrial equipment.
💡 Learn more: https://metalworksplus.com
Services Offered
- Precision CNC Machining (3-axis, 4-axis, 5-axis, and Swiss-type)
- CNC Milling & Turning for complex geometries and tight tolerances
- Micro-Machining and Swiss Machining capabilities
- Electric Discharge Machining (EDM) for intricate features
- CNC Prototyping with rapid turnaround
- Design support and manufacturability feedback
- Material selection and engineering assistance
Products & Precision Components
- High-precision CNC machined parts for critical applications
- Machine parts for automation, construction, and manufacturing industries
- Custom connector pins and machined pins
- Components in a wide range of materials, including metals and engineering plastics
Why Clients Choose Metalworks Plus
- Tight tolerances and certified quality control
- Rapid prototyping to high-volume production scalability
Worldwide delivery and logistics support.
Frequently Asked Questions (FAQ)
Q1: What is the most cost-effective machining material for prototypes?
The industry standard recommendation for most prototypes is 6061 aluminum. It is widely available, machines rapidly, and has good mechanical properties for adequate form, fit and function validation. Aluminum prototypes are generally priced 35%-50% less than parts that are made out of stainless steel by MetalworksPlus.
Q2: How does material hardness affect CNC machining time?
The hardness of the material affects directly the allowable cutting speed and tool life (measured in HRC or Brinell scale). The same geometry can take 2-3x longer to machine in 4140 pre-hardened steel (32-36 HRC) than in mild 1018 steel (120 HB). Increasing over 45 HRC the conventional carbide tooling turns into an inferior choice and CBN (cubic boron nitride) tooling becomes essential, at 10 – 20 times the cost of conventional carbide tooling.
Q3: Does material selection affect lead time at MetalworksPlus?
Yes, significantly. These are usually in stock and can be manufactured in the same week as ordered. Specialty alloys such as Inconel 718, Hastelloy, or medical grade titanium can have a material procurement lead time of 2-6 weeks. MetalworksPlus has strategically stocked the 12 most popular machining materials to reduce delays.
Q4: When should I choose stainless steel over aluminum for corrosion resistance?
Aluminum with anodizing or hard-coat anodizing (Type III) is suitable for most environmental exposures and costs significantly less than stainless steel. Choose stainless steel (316L) when the part will be exposed to saltwater immersion, strong acids, body fluids (medical), or sustained temperatures above 300°C – environments where aluminum’s corrosion resistance is insufficient.
Q5: Can MetalworksPlus help me choose the right material if I’m unsure?
Absolutely. With every RFQ sent to MetalworksPlus, they provide a free Design for Manufacturability (DFM) Consultation. Their engineering team is able to take part geometry, loading requirements, environmental conditions, and budget constraints into account and give a specific material recommendation with production data from thousands of similar parts.
Q6: What is the environmental impact of different CNC machining materials?
One of the most recyclable structural materials, aluminium is 100% recyclable, but only requires 5% of the energy needed in primary production. Stainless steel is extremely recyclable as well (between 60%–70% recycled content is used to make new stainless steel). Recycling of titanium is less efficient because of the sensitivity to contamination. MetalworksPlus monitors and maintains material usage statistics and has a normal average of 83% material efficiency (chip-to-part ratio) for their CNC operations.
Ready to Optimize Your CNC Material Selection?
For nearly 40 years, MetalworksPlus has used precise machine design and decades of experience to leverage innovative material engineering to help you make better, more profitable manufacturing choices. Whether it’s the aluminium vs steel comparison or comprehensive support services for complex alloys, they have got the technical expertise and production capacity needed for your project.
