High Precision Machining Aerospace

How to choose the right CNC machining material？


The materials are wrong, all in vain! In order to produce satisfactory products, the choice of materials is the most basic step and the most critical step. CNC machining can choose a lot of materials, including metal materials, non-metallic materials and composite materials.

Common metal materials include steel, aluminum alloy, copper alloy, stainless steel and so on. Non-metallic materials are engineering plastics, nylon, bakelite, epoxy resin and so on. Composite materials are fiber reinforced plastic, carbon fiber reinforced epoxy resin, glass fiber reinforced aluminum and so on.

Different materials have different physical and mechanical properties, and the correct selection of the right material is critical to the performance, accuracy and durability of the part. Starting from my own experience, this article will share with you how to choose low cost and suitable materials among many processing materials.




Determine the actual application requirements of the product

First, we need to determine the end use of the product and its parts. For example, medical equipment needs to be disinfected, lunch boxes need to be heated in the microwave oven, bearings, gears, etc., need to be used for load-bearing and multiple rotational friction.


Transform the application requirements of the material into the characteristics of the material

After determining the use, starting from the actual application needs of the product, the use of the product is investigated, and its technical requirements and environmental requirements are analyzed, and these needs are transformed into the characteristics of the material. For example, parts of medical equipment may have to withstand the extreme heat of an autoclave; Bearings, gears and other materials have requirements for wear resistance, tensile strength and compressive strength. Mainly can be analyzed from the following points:

01 Environmental Requirements

Analyze the actual use scenario and environment of the product; For example: What is the long-term working temperature of the product, the highest/lowest working temperature, respectively, belonging to high temperature or low temperature? Are there UV protection requirements indoors or outdoors? Is it in a dry environment or a humid, corrosive environment? Etc.

02 Technical Requirements

According to the technical requirements of the product, the required capabilities are analyzed, which can cover a range of application-related factors. Such as: the product needs to have conductive, insulating or anti-static which of the capabilities? Is heat dissipation, thermal conductivity, or flame retardant required? Do you need exposure to chemical solvents? Etc.

03 Physical Performance requirements

Analyze the required physical properties of the part based on the intended use of the product and the environment in which it will be used. For parts subjected to high stress or wear, factors such as strength, toughness and wear resistance are critical; For parts exposed to high temperatures for a long time, good thermal stability is required.

04 Appearance and surface treatment requirements

The market acceptance of the product depends largely on the appearance, the color and transparency of different materials are different, the finish and the corresponding surface treatment are also different. Therefore, according to the aesthetic requirements of the product, the processing materials should be selected.

05 Processing performance considerations

The machining properties of the material will affect the manufacturing process and accuracy of the part. For example, although stainless steel is rust resistant and corrosion resistant, its hardness is high, and it is easy to wear the tool during processing, resulting in very high processing costs, and it is not a good material to process. The plastic hardness is low, but it is easy to soften and deform during the heating process, and the stability is poor, which needs to be selected according to actual needs.


Find materials that match the characteristics

Because the actual application requirements of the product are composed of a number of contents, there may be multiple materials that meet the application requirements of a product; Or the situation where the optimal selection of different application requirements corresponds to different materials; We may end up with several materials that meet our specific requirements. Therefore, once the desired material properties are clearly defined, the remaining selection step is to search for the material that best matches those properties.

The selection of candidate materials begins with a review of material properties data, of course, it is not possible to investigate thousands of applied materials, and there is no need to do so. We can start from the material category, and first decide whether we need metal materials, non-metallic materials or composite materials. Then the previous analysis results, corresponding to the material characteristics, narrow the selection of candidate materials. Finally, the material cost information is used to select the most suitable material for the product from a number of candidate materials.

At present, Honscn has selected and launched a number of materials suitable for processing, which have been a popular choice for our customers.





Introduction to the properties of metal materials


Metallic materials refer to materials with properties such as luster, ductility, easy conduction and heat transfer. Its performance is mainly divided into four aspects, namely: mechanical properties, chemical properties, physical properties, process properties. These properties determine the scope of application of the material and the rationality of the application, which is an important reference for us to choose metal materials.The following will introduce two types of metal materials, aluminum alloy and copper alloy, which have different mechanical properties and processing characteristics.




Aluminium alloy

There are more than 1000 aluminum alloy grades registered in the world, each brand name and meaning are different, different grades of aluminum alloy in hardness, strength, processability, decoration, corrosion resistance, weldability and other mechanical properties and chemical properties there are obvious differences, each has its strengths and weaknesses.

hardness

Hardness refers to its ability to resist scratches or indentations. It has a direct relationship with the chemical composition of the alloy, and different states have different effects on the hardness of aluminum. The hardness directly affects the cutting speed and the type of tool material that can be used in CNC machining.

From the highest hardness that can be achieved, 7 series > 2 series > 6 series > 5 series > 3 series > 1 series.

intensity

Strength refers to its ability to resist deformation and fracture, commonly used indicators include yield strength, tensile strength and so on.

It is an important factor that must be considered in product design, especially when aluminum alloy components are used as structural parts, the appropriate alloy should be selected according to the pressure under.

There is a positive relationship between hardness and strength: the strength of pure aluminum is the lowest, and the strength of 2 series and 7 series heat-treated alloys is the highest.

density

Density refers to its mass per unit volume and is often used to calculate the weight of a material.

Density is an important factor for a variety of different applications. Depending on the application, the density of aluminum will have a significant impact on how it is used. For example, lightweight, high-strength aluminum is ideal for construction and industrial applications.

The density of aluminum is about 2700kg/m³, and the density value of different types of aluminum alloy does not change much.

Corrosion resistance

Corrosion resistance refers to its ability to resist corrosion when in contact with other substances. It includes chemical corrosion resistance, electrochemical corrosion resistance, stress corrosion resistance and other properties.

Corrosion resistance selection principle should be based on its use occasion, high-strength alloy used in a corrosive environment, must use a variety of anti-corrosion composite materials.

In general, the corrosion resistance of series 1 pure aluminum is the best, series 5 performs well, followed by series 3 and 6, and series 2 and 7 are poor.

processability

The machinability includes formability and machinability. Because formability is related to the state, after selecting the grade of aluminum alloy, it is also necessary to consider the strength range of each state, usually high strength materials are not easy to form.

If the aluminum is to be bent, drawn, deep drawing and other forming processes, the formability of the fully annealed material is the best, and on the contrary, the formability of the heat-treated material is the worst.

The machinability of aluminum alloy has a great relationship with the alloy composition, usually higher strength aluminum alloy machinability is better, on the contrary, low strength machinability is poor.

For molds, mechanical parts and other products that need to be cut, the machinability of aluminum alloy is an important consideration.

Welding and bending properties

Most aluminum alloys are welded without problems. In particular, some 5 series aluminum alloys are specially designed for welding considerations; Relatively speaking, some 2 series and 7 series aluminum alloys are more difficult to weld.

In addition, the 5 series aluminum alloy is also the most suitable for bending a class of aluminum alloy products.

Decorative property

When aluminum is applied to decoration or some specific occasions, its surface needs to be processed to obtain the corresponding color and surface organization. This situation requires us to focus on the decorative properties of materials.

Aluminum surface treatment options include anodizing and spraying. In general, materials with good corrosion resistance have excellent surface treatment properties.

Other characteristics

In addition to the above characteristics, there are electrical conductivity, wear resistance, heat resistance and other properties, we need to consider more in the selection of materials.


Copper alloy

Orichalcum



Brass is an alloy of copper and zinc. Brass with different mechanical properties can be obtained by changing the content of zinc in brass. The higher the content of zinc in brass, the higher its strength and slightly lower plasticity.

The zinc content of the brass used in the industry does not exceed 45%, and the zinc content will be brittle and make the alloy performance worse. Adding 1% tin to brass can significantly improve the resistance of brass to seawater and Marine atmosphere corrosion, so it is called "navy brass".

Tin can improve the machinability of brass. Lead brass is commonly referred to as easy to cut national standard copper. The main purpose of adding lead is to improve the machinability and wear resistance, and lead has little effect on the strength of brass. Carving copper is also a kind of lead brass.

Most brasses have good color, processability, ductility, and are easy to electroplate or paint.

Red copper



Copper is pure copper, also known as red copper, has good electrical and thermal conductivity, excellent plasticity, easy hot pressing and cold pressure processing, can be made into plates, rods, tubes, wires, strips, foil and other copper.

A large number of products that require good electrical conductivity such as electrocorroded copper and conductive bars for the manufacture of EDM, magnetic instruments and instruments that must be resistant to magnetic interference, such as compass and aviation instruments.

No matter what kind of material, a single model basically can not meet all the performance requirements of a product at the same time, and it is not necessary. We should set the priority of various performance according to the performance requirements of the product, the use of the environment, the processing process and other factors, reasonable selection of materials, and reasonable control of costs under the premise of ensuring performance.


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Imagine you’re designing a custom part for your project—maybe a bracket for a car’s electrical system or a housing for a small sensor. You’ve narrowed down the material to either aluminum (metal) or ABS (plastic), but now you’re stuck: Do you use CNC turning or milling? And will the process work the same for both materials?

This is the exact confusion most teams face. Metal and plastic behave very differently under CNC tools, and picking the wrong process (or pairing the wrong material with a process) can lead to wasted time, scrapped parts, and higher costs. A plastic part that works with milling might crack if you try turning it; a metal shaft that needs turning could end up lopsided with milling.

Honscn has spent 15+ years figuring out how to match materials to processes—we’ve helped clients fix botched projects where a supplier used the wrong CNC method, and we’ve streamlined workflows by picking the right tool for the job from day one. In this guide, we’ll break down the key differences between metal and plastic CNC machining, when to choose turning vs. milling, and how Honscn takes the guesswork out of the decision. We’ll even share two real client stories to show how this works in practice.


First: Metal vs. Plastic CNC Machining—The Big Differences That Matter
Before diving into turning and milling, let’s start with the basics: Metal and plastic don’t just look different—they react differently to being cut, shaped, and finished. These differences change everything from the tools we use to the speed of the process.

1. Material Hardness & Tool Wear
Metals (like aluminum, stainless steel, or brass) are harder and more abrasive than plastics (like ABS, PEEK, or nylon). This means:


Metal needs tougher tools: We use carbide or high-speed steel (HSS) tools for metal—they hold up against the friction. For example, milling aluminum requires a carbide endmill that can withstand 300–400°C (572–752°F) heat.
Plastic needs sharper, gentler tools: Dull tools can “smear” plastic instead of cutting it (think of trying to cut butter with a blunt knife). We use polished carbide tools for plastic—they slice cleanly without melting or warping the material.

Tool wear is a big cost factor too. A carbide tool for stainless steel might last 500 parts before needing replacement; the same tool for ABS plastic could last 2,000 parts. If you use a metal tool on plastic without adjusting, you’re wasting money on premature tool changes.

A client once came to us with a problem: They’d used a stainless steel tool to mill ABS plastic sensor housings, and the tools were wearing out in 300 parts (instead of 2,000). We switched them to a polished plastic-specific carbide tool—their tool life jumped 6x, and they saved $800/month on tool costs.

2. Heat & Warping Risks
Cutting generates heat—and metal and plastic handle heat in opposite ways:


Metal dissipates heat (mostly): Aluminum and steel can handle high temperatures, so we can run CNC machines faster (e.g., 10,000 RPM for aluminum milling) without warping the part. We still use coolant to prevent tool overheating, but the part itself stays stable.
Plastic melts or warps easily: ABS starts to soften at 105°C (221°F)—way lower than metal’s tolerance. If we run the machine too fast, the tool’s friction melts the plastic, leaving rough edges or distorted shapes. For plastic, we slow down (e.g., 5,000–7,000 RPM for ABS milling) and use air cooling (not liquid coolant, which can soak into plastic and cause swelling).

One auto parts client tried to mill plastic clips at the same speed as aluminum—80% of the clips warped, and they had to scrap the whole batch. We adjusted the speed and switched to air cooling—their next run had a 99.5% pass rate.

3. Surface Finish Needs
The finish you want often depends on the material:


Metal often needs post-processing: Milled aluminum might have a matte finish (Ra 1.6μm) right off the machine, but if you need it shiny (Ra 0.8μm) for a visible part, you’ll need polishing or anodizing. Stainless steel might need passivation to prevent rust.
Plastic can get smooth finishes direct from the machine: Polished tools and slower speeds let us get a smooth finish (Ra 0.8μm) on ABS or PEEK without extra work. This saves time—no need for sanding or painting unless you want a custom color.

4. Tolerance Limits
Both materials can hit tight tolerances, but plastic has a catch:


Metal holds tolerances better long-term: An aluminum bracket with ±0.01mm tolerance will stay that way for years—metal doesn’t expand or contract much with temperature changes.
Plastic shifts with temperature/humidity: ABS can expand 0.2–0.4% if it absorbs moisture, which means a ±0.01mm tolerance might drift to ±0.02mm in humid conditions. For plastic parts that need tight tolerances (like sensor housings), we dry the material before machining and use heat-treated plastics (like glass-filled PEEK) that are more stable.

CNC Turning vs. Milling: When to Pick Which Process
Now that you know how metal and plastic differ, let’s talk about the two most common CNC processes: turning and milling. The key difference comes down to shape—what does your part look like?

What Is CNC Turning? (Best for Rotational, Symmetrical Parts)
Turning uses a rotating tool and a stationary cutting tool (or vice versa) to shape parts that are round or symmetrical around an axis. Think of a lathe: the part spins, and the tool cuts away material to make shapes like shafts, sleeves, or bolts.

When to Use Turning:

Parts that are round or cylindrical: Shafts for car transmissions, plastic bushings for door hinges, metal sleeves for wiring.
Simple, symmetrical features: Grooves, threads, or tapers (e.g., a tapered metal pin for aligning two parts).
Fast, low-cost for rotational parts: Turning is faster than milling for round parts—you can make a metal shaft in 2 minutes, vs. 5 minutes with milling.

Material Notes for Turning:

Metal turning: Works great for aluminum, brass, and stainless steel. We use coolant to keep tools cool and parts smooth.
Plastic turning: Possible, but trickier. We need slow speeds (3,000–5,000 RPM) and sharp tools to avoid melting. Turning is good for plastic bushings or knobs, but not for complex shapes.

A car repair shop needed 500 metal shafts for a transmission repair kit. We used turning—each shaft took 2.5 minutes to make, and we delivered all 500 in 3 days. If we’d used milling, it would have taken 6 days and cost 30% more.

What Is CNC Milling? (Best for Complex, Irregular Shapes)
Milling uses a rotating cutting tool to remove material from a stationary part. It’s like using a router to carve wood—you can make flat surfaces, holes, slots, and complex shapes (like brackets with multiple holes or curved edges).

When to Use Milling:

Parts with irregular shapes: Aluminum brackets for car engines, plastic sensor housings, metal mounting plates with multiple holes.
Complex features: Slots, pockets (recessed areas), or non-symmetrical holes (e.g., a bracket with holes at different angles).
Parts that need precision in multiple directions: Milling machines (especially 5-axis mills) can cut from multiple angles, making parts that fit into tight spaces (like under a car’s dashboard).

Material Notes for Milling:

Metal milling: 3-axis mills work for simple brackets; 5-axis mills for complex parts (like aerospace components). We adjust speed based on metal hardness—slower for stainless steel, faster for aluminum.
Plastic milling: Ideal for complex plastic parts (like ABS sensor housings). We use air cooling and sharp tools to prevent warping. Glass-filled plastics (like glass-filled nylon) are great for milling—they’re strong and hold tolerances well.

A consumer electronics client needed 1,000 plastic housings for a car GPS. The housing had a curved edge, two holes for mounting, and a recessed area for the screen—perfect for 3-axis milling. We delivered all 1,000 in 5 days, with zero warping.

The Gray Area: When to Use Both (Hybrid Processes)
Some parts need both turning and milling. For example:


A metal bolt: Turn the cylindrical shaft (turning), then mill the hexagonal head (milling).
A plastic knob: Turn the round base (turning), then mill a slot for a screwdriver (milling).

The key here is to do the processes in the right order—usually turning first (to make the base shape), then milling (to add complex features). This saves time and ensures precision.

Honscn handles hybrid parts in-house—no need to send your part to two different shops. We’ll turn the base shape, then move the part to a milling machine (often on the same production line) to add the final features.

How Honscn Helps You Pick (and Execute) the Right Process
The biggest mistake we see clients make is picking a process based on “what they’ve used before” instead of “what the part needs.” A client might try to mill a round shaft (wasting time) because they’ve never used turning, or use turning for a complex plastic housing (ending up with a lopsided part).

Honscn takes the guesswork out of this with three key advantages:

1. Material-Process Matching (We Don’t Force a One-Size-Fits-All)
We start with your part’s design and material, then recommend the best process—no bias toward one machine or another. Here’s how it works:


Step 1: Free Design Review: You send us your CAD file (even a sketch works), and we look at:

Material (aluminum? ABS? PEEK?)
Shape (round? Irregular? Symmetrical?)
Tolerances (±0.01mm? ±0.1mm?)
Quantity (10 prototypes? 10,000 production units?)


Step 2: Process Recommendation: We tell you exactly which process to use, and why. For example:

“Your aluminum shaft is round—turning will be 30% faster and cheaper than milling.”
“Your ABS housing has curved edges and multiple holes—3-axis milling is the way to go, with air cooling to prevent warping.”


Step 3: Cost & Timeline Estimate: We give you a clear quote and timeline, so you know what to expect.

A startup making a car diagnostic tool came to us with a design for a metal probe. They wanted to mill it (since they’d used milling for plastic parts before), but the probe was a simple cylindrical shape. We recommended turning—they saved 25% on cost and got the parts 2 days earlier.

2. In-House Equipment for Both Processes (No Outsourcing)
We have 12 CNC machines in total—6 turning centers (for rotational parts) and 6 milling machines (3-axis and 5-axis for complex parts). This means:


No handoffs to other shops: If your part needs both turning and milling, we do it all in-house. You don’t have to coordinate with two suppliers or worry about parts getting lost in transit.
Consistent quality: The same team handles your part from start to finish. They know the material’s quirks (e.g., “this ABS needs 5,000 RPM”) and the process’s requirements (e.g., “this aluminum shaft needs coolant at 20°C”).
Fast turnaround: We can switch between processes quickly. For example, we made 200 hybrid parts (turned shaft + milled head) in 4 days—if we’d outsourced one process, it would have taken 8 days.

A car parts distributor needed 500 hybrid metal bolts (turned shaft + milled hex head). We did the turning first (2 minutes per shaft), then moved the bolts to a 3-axis mill (1 minute per head). All 500 were done in 3 days, with 100% quality checks.

3. Expertise in Tricky Materials (Plastics, Heat-Treated Metals, etc.)
We don’t just work with “easy” materials—we specialize in the ones that other shops avoid:


Heat-sensitive plastics: We’ve mastered machining PEEK (which melts at 343°C/649°F) and PVC (which releases toxic fumes if heated too much). We use specialized ventilation and temperature controls to keep parts and workers safe.
Hard metals: Stainless steel (316L) and titanium are tough to machine, but our 5-axis mills and carbide tools handle them with ease. We’ve made titanium brackets for car exhaust systems that hit ±0.005mm tolerances.
Composite materials: Glass-filled nylon or carbon-fiber reinforced plastics (CFRP) are great for car parts (strong, lightweight), but they’re abrasive. We use diamond-coated tools to prevent wear—something most shops don’t offer.

A luxury car manufacturer needed 100 carbon-fiber reinforced plastic (CFRP) brackets for their door panels. Other shops turned them down because CFRP is abrasive and hard to machine. We used diamond-coated milling tools and slow speeds—all 100 brackets passed their tolerance checks, and the client now orders 1,000 every quarter.

Real Client Stories: How Honscn Fixed Process & Material Mistakes
Let’s look at two clients who started with the wrong process or material—until we stepped in.

Story 1: Auto Repair Shop (Wrong Process for Metal Shafts)
A Texas-based auto repair shop needed 200 metal shafts for a batch of vintage car transmission repairs. They’d hired a shop that used milling (since the shop didn’t have turning equipment) to make the shafts.

The Problem:


Milling took 6 minutes per shaft (vs. 2 minutes with turning), so the shop missed their 5-day deadline.
30% of the shafts were lopsided (milling can’t get the same symmetry as turning), so they couldn’t fit into the transmissions.
The cost was $15 per shaft (vs. $10 per shaft with turning)—they overpaid by $1,000.

Honscn’s Solution:


We recommended turning (since the shafts were cylindrical, no complex features).
We used a carbide turning tool and coolant to keep the aluminum shafts smooth.
We made 200 shafts in 3 days (2 minutes per shaft) and checked each one for symmetry.

Results:


100% of the shafts fit into the transmissions.
The shop saved $1,000 (cost dropped to $10 per shaft).
They now order all their metal shafts from us—we’ve done 5 more batches, with zero defects.

Story 2: Electronics Client (Wrong Process for Plastic Housings)
A California electronics company needed 500 ABS plastic housings for a car’s backup camera. They’d used a shop that tried to turn the housings (since turning is faster for round parts).

The Problem:


The housing had a square recess for the camera lens—turning can’t make square features, so the shop had to mill the recess separately (adding 3 minutes per part).
25% of the housings warped during turning (the shop used too high a speed: 8,000 RPM instead of 5,000 RPM).
The total time was 8 days (vs. the 5-day deadline they needed).

Honscn’s Solution:


We recommended 3-axis milling (since the housing had square features and needed precision in multiple directions).
We used a polished carbide tool and air cooling (5,000 RPM) to prevent warping.
We milled the entire housing in one setup—no need for a second process.

Results:


500 housings delivered in 4 days (beating the deadline).
Only 2 housings were rejected (0.4% defect rate).
The client saved $800 (no extra milling step meant lower labor costs).

How to Choose: A Quick Checklist for Your Part
Not sure if you need turning, milling, metal, or plastic? Use this checklist to narrow it down:

1. What’s the Shape of Your Part?

Round/cylindrical/symmetrical → Turning (faster, cheaper).
Irregular/has holes/slots/curved edges → Milling (more flexible).
Both round and irregular → Hybrid (turning first, then milling).

2. What Material Are You Using?

Metal (aluminum, stainless steel, brass):

Round part → Turning (use coolant, carbide tools).
Complex part → Milling (3-axis for simple, 5-axis for tricky).


Plastic (ABS, PEEK, nylon):

Round part → Turning (slow speed, air cooling, polished tools).
Complex part → Milling (slow speed, air cooling, avoid liquid coolant).


Composite (CFRP, glass-filled nylon):

Complex part → Milling (diamond-coated tools, slow speed).



3. What’s Your Tolerance?

Tight (±0.01mm to ±0.05mm):

Metal → Turning or 5-axis milling (metal holds tolerances better).
Plastic → 5-axis milling with heat-treated plastic (e.g., PEEK).


Loose (±0.1mm to ±0.5mm):

Metal → 3-axis milling or turning (either works).
Plastic → 3-axis milling (ABS or nylon is fine).



4. How Many Parts Do You Need?

10–500 parts (small batch):

Turning or milling (either works—pick based on shape).


1,000+ parts (mass production):

Turning (faster for round parts) or automated milling (for complex parts).



Conclusion: The Right Process = Better Parts, Lower Costs
Picking between metal and plastic, turning and milling, doesn’t have to be a guess. It’s about matching the material’s properties to the process’s strengths:


Use turning for round parts (metal or plastic) to save time and money.
Use milling for complex parts (metal or plastic) to get the shape you need.
Let material hardness and heat tolerance guide your speed and tool choices.

Honscn’s job is to make this easy for you. We don’t just machine parts—we help you pick the right path from day one. Whether you’re making 10 metal shafts for a car repair or 10,000 plastic housings for a new product, we’ll recommend the best material, process, and tools to get the job done right (and on budget).

Ready to stop guessing? Send us your part design (even a sketch) and tell us what you need it for. We’ll give you a free process recommendation, a clear quote, and a timeline—no strings attached. Let’s make sure your next CNC project is a success.