For most machined parts, aluminum is the cheapest and fastest metal to cut. Stainless steel usually costs two to three times more for the same geometry, and titanium four to six times more. Very little of that gap comes from the price of the raw bar. Almost all of it comes from how long each metal takes to cut and how quickly it destroys tooling.
That single fact should shape how you specify parts. A designer who understands why titanium is slow to machine can often get titanium performance out of a cheaper metal, or can redesign a titanium part so it costs 30 percent less without losing anything functional. This guide compares aluminum, stainless steel and titanium across the factors that actually decide a quote: machinability, cost, achievable tolerance, finishing options and lead time.
The short answer
| Metal | 最适合 | Weak point | Typical machining cost |
| 铝 | Lightweight structures, enclosures, heat sinks, prototypes, high-volume runs | Low hardness, poor wear resistance, limited service temperature | Baseline (1x) |
| Stainless steel | Corrosion resistance, strength, food and medical contact, wear surfaces | Heavy, work hardens, slower to cut | Roughly 2x to 3x |
| 钛 | Strength-to-weight, biocompatibility, chemical and marine exposure, high temperature | Expensive stock, slow cycles, long material lead times | Roughly 4x to 6x |
Those multipliers are indicative rather than fixed. Part geometry, batch size, tolerance and finishing all move them. A simple flat plate in 316 might cost only 1.5 times its aluminum equivalent, while a thin-walled titanium housing with deep pockets can exceed 6x.
How the three metals compare on paper
Material properties explain almost every downstream decision, from cutting speed to whether a part needs a coating. These are typical published values for the common grades used in precision work.
| 年级 | Density (g/cm3) | Yield (MPa) | Thermal cond. (W/m.K) | Modulus (GPa) | Expansion (um/m.K) | 注释 |
| 6061-T6 | 2.70 | 276 | 167 | 69 | 23.6 | Weldable, anodizes well, best all-round value |
| 7075-T6 | 2.81 | 503 | 130 | 71.7 | 23.6 | Aircraft grade, not conventionally weldable |
| 304 | 8.00 | 215 | 16.2 | 193 | 17.3 | General purpose stainless |
| 316L | 8.00 | 170 to 205 | 16.3 | 193 | 16.0 | Better chloride resistance, common in medical |
| 17-4 PH | 7.80 | 1170 (H900) | 18 | 197 | 10.8 | Hardenable, high strength, tough to machine |
| Ti Grade 2 | 4.51 | 275 | 16.4 | 105 | 8.6 | Commercially pure, more forgiving to cut |
| Ti-6Al-4V | 4.43 | 880 | 6.7 | 114 | 8.6 | Grade 5, the workhorse titanium alloy |
Two numbers in that table matter more than the rest. Thermal conductivity of 167 for 6061 against 6.7 for Ti-6Al-4V is why titanium is hard to cut. And the density column shows something engineers regularly get backwards: titanium is not a lightweight metal. At 4.43 g/cm3 it is roughly 60 percent heavier than aluminum. What titanium offers is strength per unit weight, not low weight.
Machinability is what you are really paying for
Raw material is a small share of most quotes. Machine time and tooling are the bulk of it, and each metal behaves differently at the cutting edge.
Aluminum cuts fast because it carries heat away
Aluminum is soft, and its high thermal conductivity means the chip removes most of the heat generated at the cutting edge. Tools last a long time, spindle speeds are high, and material removal rates are the best of any common engineering metal. This is why aluminum is the default for prototypes and why per-part price drops so sharply at volume.
Stainless steel work hardens as you cut it
Austenitic stainless grades such as 304 and 316 harden locally when deformed. If a dull tool rubs rather than shears, the surface it just passed over becomes harder, and the following pass is worse. The practical response is a rigid setup, sharp positive rake tooling, generous and uninterrupted feed, and enough stock left for a clean finishing pass. Cutting speeds drop to a fraction of aluminum, and tool consumption rises noticeably.
The differences between grades are real too. 303 machines far more freely than 304 because of its added sulphur, while 316 cuts slower again. If you are weighing the two most common options, our breakdown of 304 and 316 stainless steel for CNC machining covers where the extra cost of 316 is justified and where it is not.
Titanium fights back on three fronts at once
The machinability of titanium is poor for reasons that compound. Heat has nowhere to go, so it concentrates at the cutting edge instead of leaving in the chip. Titanium is also chemically reactive at temperature and will gall onto tooling. And its elastic modulus is roughly half that of stainless, so thin walls and slender features deflect away from the cutter and spring back afterwards, which hurts both accuracy and surface quality.
The answer is slow speeds, heavy constant feed, sharp coated tooling, high pressure coolant and very rigid workholding. Complex titanium parts also benefit disproportionately from 5轴数控加工, because reaching the part from multiple angles in one setup avoids the repositioning errors that titanium is least forgiving of.
| Metal | Typical carbide cutting speed | Practical consequence |
| 6061铝合金 | 300 to 900 m/min | Long tool life, high removal rates, short cycles |
| Stainless 304 / 316 | 80 to 180 m/min | Slower cycles, higher tool cost, finish pass discipline |
| Ti-6Al-4V | 30 to 60 m/min | Long cycles, frequent tool changes, rigid setups required |
Those ranges assume modern coated carbide, adequate coolant and a rigid machine. Actual parameters vary with tooling, depth of cut and part stiffness, so treat them as a comparison rather than a recipe.
What titanium machining cost is actually made of
When buyers see a titanium quote for the first time, the usual assumption is that the metal is expensive. It is, but that is only part of the story. A useful way to think about titanium machining cost is four separate contributors:
- Cycle time. Cutting speeds four to ten times lower than aluminum translate directly into machine hours, which is normally the single largest line on the quote.
- Tooling. Shorter tool life means more inserts and end mills consumed per part, and more machine stoppages for tool changes.
- Raw stock. Titanium bar and plate cost several times more per kilogram than aluminum, and titanium is denser, so the same billet volume weighs more.
- Material waste. Machining a part from solid removes most of the billet. On a pocketed structural part the scrap can outweigh the finished component several times over, which matters far more when the stock is expensive.
That fourth point is where design changes pay off. Reducing overall envelope, avoiding deep unnecessary pockets and choosing near-net stock sizes can cut a titanium quote meaningfully without touching a single functional dimension.
Tolerance and dimensional stability
All three metals comfortably hold general tolerances to ISO 2768-m, and tighter callouts down to the low micron range are achievable on suitable features. Our precision CNC machining service holds tolerances to plus or minus 0.005 mm where the geometry and material allow it, and the material choice affects which features qualify.
- Aluminum has the highest thermal expansion of the three at 23.6 um/m.K. On a long part, measuring warm off the machine and again at 20 degrees C can produce a meaningfully different reading. Temperature control during inspection matters more than most people expect.
- Stainless work hardening makes the final pass critical. Too little stock left for finishing and the tool skates over a hardened layer, producing poor finish and dimensional drift.
- Titanium has the best dimensional stability across temperature of the three, at 8.6 um/m.K, but the worst behaviour during cutting. Springback on thin sections is the usual reason a titanium feature misses tolerance.
The practical rule applies across all three metals: apply tight tolerances only to functional features. A blanket tight callout on an entire drawing raises cost on every metal, and on titanium it raises it steeply.
Finishing options differ more than people expect
Material choice quietly determines which surface treatments are available to you, and this catches designers out late in a project when the appearance has already been approved.
| Metal | Common treatments | Not available |
| 铝 | Type II and Type III anodizing, conductive anodizing, chemical conversion coating, bead blasting, brushing, polishing, powder coat | Passivation in the stainless sense |
| Stainless steel | Passivation, electropolishing, bead blasting, brushing, mirror polishing | Anodizing in the aluminum sense |
| 钛 | Anodizing by oxide interference colour, passivation, bead blasting, polishing | Dyed anodizing, most conventional plating |
Titanium anodizing is worth understanding because it works differently. Rather than absorbing dye, the oxide layer refracts light, and colour is controlled purely by layer thickness. Colours are limited to what the process produces, and matching a specific brand colour is not realistic. Aluminum is the opposite case, with a wide colour range and mature process control, which is one reason it dominates consumer-facing enclosures. Our guides to black anodizing for CNC aluminum parts 以及 machined surface finish selection go deeper on the practical trade-offs.
Lead time is often a material problem, not a machining problem
Aluminum in common grades and sizes is widely stocked, so material rarely delays an aluminum job. Stainless in 304 and 316 is usually available in standard bar and plate, with occasional delays on unusual sections or 17-4 PH in specific conditions.
Titanium is different. Grade 5 in a specific plate thickness or bar diameter is not always on the shelf, and sourcing can add days or weeks before a machine ever starts cutting. If a project timeline is tight, confirming titanium stock availability early is more useful than negotiating machine time. Finishing adds to this on all three metals, since anodizing, passivation and electropolishing are typically outsourced batch processes with their own queues.
Choosing the right metal for your part
Sound CNC machining material selection comes down to identifying which single property the part genuinely cannot compromise on, then choosing the cheapest metal that satisfies it.
Choose aluminum when
- Weight matters but loads are moderate, as in enclosures, brackets, robotics frames and optical mounts.
- Thermal conductivity is a functional requirement, as in heat sinks and cold plates.
- You need a wide range of cosmetic finishes and colours.
- You are prototyping and want the fastest, cheapest functional part that still behaves like metal.
- Volume is high and per-part cost is the deciding factor.
Choose stainless steel when
- The part meets food, pharmaceutical or surgical hygiene requirements.
- It faces moisture, steam, cleaning chemicals or marine exposure and 316L earns its cost premium.
- You need strength and wear resistance and weight is not critical.
- Service temperature exceeds what aluminum can tolerate.
- You need high strength in a hardenable grade, which is where 17-4 PH fits.
Choose titanium when
- Strength-to-weight is genuinely the binding constraint, typically in aerospace structures and high-performance assemblies.
- The part contacts human tissue or blood, where Grade 5 and Grade 23 are the established implant materials.
- Chemical or seawater exposure would attack even stainless.
- The part runs hot enough that aluminum loses strength.
- Low thermal expansion is required for dimensional stability across a wide temperature range.
If none of those apply, titanium is usually an expensive way to buy properties the part will never use. Testing that honestly before tooling up is one of the most valuable things a design review can do.
Five material decisions that quietly waste money
- Specifying titanium for weight saving. Titanium is heavier than aluminum. If the part is not strength limited, 7075-T6 will usually be lighter and far cheaper.
- Bolting titanium directly to aluminum. The two sit far apart galvanically, and in a damp environment the aluminum corrodes. Isolating washers, coatings or a material change solve it, but only if caught at design stage.
- Defaulting to 316 when 304 is sufficient. 316 costs more, cuts slower and is genuinely better in chloride environments. In dry indoor service it often buys nothing.
- Choosing 7075 for a part that must be welded or exposed to weather. 7075 is not conventionally weldable and has lower corrosion resistance than 6061. Strength alone is the wrong basis for the choice.
- Applying one tight tolerance band to the whole drawing. Tolerance is a cost multiplier on every metal, and it stacks hardest on titanium and hardened stainless.
Making the call on your next part
A workable sequence is to list the properties the part cannot compromise on, then pick the cheapest metal that meets all of them, then check finishing and stock availability before releasing the drawing. Most cost overruns on machined parts trace back to a material chosen for a property the part never actually needed, or to a finish that the chosen metal cannot accept.
If you are still weighing options, sending the model with your requirements rather than a fixed material is usually the faster route. XY加工 machines all three families, from 6061 and 7075 through 303, 304, 316L and 17-4 PH to Grade 2 and Ti-6Al-4V, and returns design-for-manufacturability feedback within 24 hours. You can review the full materials range or send a drawing through our 数控加工服务 to see the same part quoted in more than one metal before you commit.
常见问题
Q: Is titanium stronger than stainless steel?
A: Not always. Ti-6Al-4V yields around 880 MPa, well above 304 or 316, but 17-4 PH in the H900 condition exceeds it. Titanium wins decisively on strength per unit weight rather than on absolute strength.
Q: Why is titanium machining so expensive?
A: Mostly machine hours. Poor thermal conductivity keeps heat at the cutting edge, forcing cutting speeds four to ten times lower than aluminum. Add short tool life, costly stock and high material waste, and the quote rises quickly.
Q: Can aluminum parts be used outdoors without treatment?
A: Bare aluminum forms a natural oxide layer but will dull and pit over time, especially near salt air. Type II or Type III anodizing, or a chemical conversion coating, is normally specified for outdoor and marine service.
Q: Which of the three holds the tightest tolerance?
A: All three can hold tight tolerances on suitable features. Titanium offers the best dimensional stability across temperature, aluminum is easiest to machine accurately, and stainless sits between the two provided the finishing pass is properly planned.
Q: Is 7075 aluminum always better than 6061?
A: No. 7075 is significantly stronger but is not conventionally weldable, costs more and has lower corrosion resistance. For enclosures, brackets and general structural work, 6061-T6 remains the better balance of cost, machinability and durability.
