A Guide to CNC Materials: classification selection machining

If you are engaged in machining, product design, or manufacturing-related work, you must be familiar with “CNC machining”, and CNC materials, as the foundation of CNC machining, directly determine the performance, cost, and processing difficulty of the final product. Many friends will encounter similar questions in actual work: “Which metal material is suitable for aviation parts?” “What should I do if the knife is always glued when processing plastics?” This article will help you systematically master the core knowledge of CNC materials from basic classification to practical application to problem solving, avoiding pitfalls.

1. CNC material basics and classification: understand what “usable materials” are

When you first start out with CNC machining, the most confusing thing is “what materials can be machined”. In fact, the classification logic of CNC materials is very simple – according to the material properties, and then combined with the key characteristics to determine whether it is suitable for processing. The following is a clear explanation of common types and core parameters, and you can choose directly against your needs.

1. Divided by material type: 5 categories of commonly used materials

2. Key characteristics: 4 parameters that must be looked at before selecting materials

The choice of material should not only look at “what material it is”, but also pay attention to its core characteristics, which directly affects the subsequent processing and product use. When I was selecting materials for a medical device company, I ignored “thermal conductivity”, which caused the initial sample to deform during sterilization, and later replaced it with 304 stainless steel, which has better thermal conductivity.

• Material hardness and strength: Materials with high hardness (such as hardened steel) are difficult to process and require more wear-resistant tools; Materials with high strength, such as titanium alloys, are suitable for load-bearing components, but attention should be paid to cutting force control during machining.
• Material density and weight: Aviation and automotive fields are weight-sensitive, so low-density materials (such as aluminum alloy density 2.7g/cm³, which is only 1/3 of steel) are usually chosen; Heavy machinery, on the other hand, requires high-density materials to ensure stability.
• Thermal and electrical conductivity: When processing plastics, materials with poor thermal conductivity (such as PEEK) are prone to local overheating and sticking knives; Electronic parts need to consider conductivity, such as copper for conductive terminals.
• Material price and availability: Titanium alloy has good performance but high price (about 200 yuan/kg), and aluminum alloy can be considered for mass production; Also pay attention to whether the material is easy to purchase, for example, special grades of stainless steel may need to be ordered 1-2 weeks in advance.

3. Material standards: avoid buying “substandard materials”

Formal processing must use materials that meet the standards, otherwise there will be potential safety hazards. Common standards include ASTM (American Society for Testing and Materials) and ISO (International Organization for Standardization), such as ASTM B348 for aerospace titanium alloys and ISO 20858 for food contact stainless steels. I have encountered customers who used non-standard “304 stainless steel” to process tableware, and when testing, they found that the nickel content was not up to standard, and the final product could not be marketed, resulting in a great loss.

2. CNC material performance and selection: how to choose the “most suitable” material

Knowing the classification and characteristics of materials, the next step is “how to choose”. Many people will fall into the misconception that “the better the performance, the better”, but in fact, the core of material selection is “balancing demand and cost” – not only to meet the requirements of product use, but also not to waste money. The following is a set of “material selection methodologies” that I have used in the industry for 5 years, combined with specific cases to help you implement them.

1. Clarify your core needs first: 3 key questions to help you locate them

Ask yourself 3 questions before choosing materials to quickly narrow it down:

1. What working conditions does the product have to withstand? (e.g. whether it is subjected to force, whether it is exposed to corrosive liquids, and the operating temperature range)
2. What are the requirements for machining accuracy? (e.g. tolerance ±0.01mm or ±0.1mm)
3. What is the approximate budget? (In mass production, material costs usually account for 30%-50% of the total cost)

For example, an auto parts factory wants to make a bracket around the engine, and the working condition is “withstand a certain vibration, the temperature does not exceed 150°C, and the batch is 1000 pieces”. The core requirement is “high temperature resistance, certain strength, and controllable cost”, and finally chose 6061 aluminum alloy – which not only meets the temperature requirement of 150°C, but also has sufficient strength, the price is 30% lower than steel, and the processing efficiency is also high.

2. Key performance indicators: Don’t just look at “hardness”, these 5 indicators are more important

• Material mechanical properties: including tensile strength (the maximum tensile force that the material can withstand before it breaks), yield strength (the tensile force at which the material begins to deform). For example, for load-bearing shafts, materials with high yield strength (such as 45# steel, yield strength ≥ 355MPa) are required to avoid deformation in use.
• Corrosion resistance and environmental adaptability: If the product is used outdoors or in a humid environment (such as outdoor lamp housing), choose corrosion-resistant materials (such as 304 stainless steel, aluminum alloy for anodizing), otherwise it will rust in 1-2 years.
• High and low temperature performance: High-temperature resistant materials (such as PEEK, long-term use temperature 260°C) should be selected for high-temperature environments (such as oven internal parts); In low-temperature environments (such as cold chain equipment), avoid low-temperature brittle materials (such as ordinary ABS, which is prone to cracking below –20°C).
• Material machinability: Simply put, it is “good or not to process”. For example, aluminum alloy is easier to process than stainless steel because of its low hardness, low cutting force, 50% higher machining efficiency, and less tool loss.
• Surface roughness and finish: If the product is an appearance part (such as a mobile phone case), choose materials that are easy to process with high finish (such as pure aluminum, acrylic), and avoid materials with rough surfaces such as wood and foam.

3. Cost and certification: Don’t overlook “hidden costs” and “compliance”

• Balance cost and performance: It’s not that better performance is more cost-effective. For example, for ordinary mechanical brackets, 45# steel (about 5 yuan/kg) is enough, and there is no need to use titanium alloy (about 200 yuan/kg), and excess performance will only increase the cost.
• Comparison of material suppliers: When choosing a supplier, we should look at three points: (1) whether the material meets the standards (provide a test report); (2) Lead time (whether it can meet the production schedule); (3) After-sales service (if the material has quality problems, whether it can be returned or exchanged). I had previously worked with a supplier who had a three-day production line downtime due to delivery delays, and then switched to a supplier with in-stock to avoid similar issues.
• Material certification: special industries must be certified. For example, aerospace parts require AS9100 certified materials, medical devices require FDA-certified materials (such as PEEK needs to comply with FDA 21 CFR Part 177), and materials without certification cannot be used even if their performance is good.

3. CNC material processing technology: how to “process well” different materials

Once the material is selected, the next step is “how to process”. The processing process of different materials is very different, such as the cutting parameters and tool selection of metals and plastics are completely different, once the parameters are wrong, either the processed parts are unqualified, or the tool loss is fast. The following shares the processing points of different materials, which are all my experience summarized in actual production, and you can apply them directly.

1. Core processing parameters: how to set the speed, feed, and cutting depth

The core parameters of machining are “rotation speed (S), feed speed (F), and depth of cut (Ap)”, and the combination of these three parameters directly affects the machining efficiency and part quality. I have compiled the reference parameters of common materials, which novices can use directly (the specific needs to be fine-tuned according to the machine tool and tool):

2. Matching tools to materials: Don’t “use one knife to process all materials”

If the tool is not chosen correctly, the processing will be “in vain”. For example, if you use a tool that processes aluminum to process stainless steel, the tool will wear out quickly, and there will be burrs on the surface of the processed parts. Here’s a simple matching principle:

• Soft materials (aluminum, plastic, wood): High-speed steel (HSS) tools are used for fast cutting with low cost and high sharpness.
• Medium-hard materials (304 stainless steel, copper): With carbide (WC) tools, the wear resistance is 3-5 times better than that of high-speed steel, and can withstand higher cutting temperatures.
• High-hardness materials (hardened steel, titanium alloy): Ceramic tools or CBN (cubic boron nitride) tools can withstand high temperatures above 1000°C to avoid knife chipping.

I used to help a mold factory solve the problem of “low efficiency in machining H13 mold steel”, originally they used carbide tools, but later switched to CBN tools, the processing efficiency increased by 40%, and the tool life also changed from 10 pieces/handle to 50 pieces/handle.

3. Common problems in machining: how to solve deformation, sticking knives, and poor accuracy

The most troublesome thing during processing is problems, such as material deformation, sticking knives, and substandard accuracy. These problems are not “bad materials”, but poor craftsmanship. Share 3 solutions to high-frequency problems:

• Material deformation: When machining thin-walled parts (such as aluminum alloy shells with a thickness of < 1mm), they are prone to deformation due to excessive cutting forces. Solution: (1) Reduce the cutting depth (from 2mm to 0.5mm); (2) Fixed with a clamp (e.g. vacuum suction cup); (3) Stress relief treatment (such as aluminum alloy aging treatment) after processing.
• Material stickiness and difficulty in chip evacuation: When processing plastics (such as ABS, nylon) or copper, it is easy to stick to the knife, and poor chip evacuation can scratch the surface of the part. Solution: (1) Add coolant (compressed air for plastics, emulsion for metals); (2) Select a tool with a chip flute; (3) Increase the rotational speed (e.g. ABS from 3000r/min to 5000r/min).
• Machining accuracy and tolerance: If the part tolerance is required to be high (such as ±0.005mm), pay attention to 2 points: (1) Preheating the machine tool (idle for 30 minutes after starting the machine to avoid temperature changes affecting the accuracy); (2) Material pretreatment (such as annealing before stainless steel processing to reduce hardness fluctuations).

4. CNC material application fields: “How to choose the right material” in different industries

The needs of different industries vary greatly, such as aerospace pursuing “lightweight and high strength”, medical equipment pursuing “corrosion resistance and biocompatibility”, blindly following the trend of material selection is prone to mistakes. The following is a breakdown by industry, telling you the core needs and material selection logic of each industry, and combining cases to help you understand.

1. Aerospace: Lightweight + high strength is at the core

Aviation parts have extremely high weight and strength requirements, and for every 1kg weight saved, aircraft can save tens of thousands of dollars in fuel costs per year. Therefore, “high-strength, low-density” types such as titanium alloys (TC4) and carbon fiber composites (CFRP) are preferred.

Case: An airline wants to make a connection for an aircraft landing gear, requiring “tensile strength ≥ 1100MPa and density <5g/cm³”. TC4 titanium alloy was chosen – which meets the strength requirements, has a density (4.5g/cm³) that is 40% lighter than steel (7.8g/cm³), and can withstand temperature variations from –50°C to 300°C, which meets aviation standards.

2. Medical Devices: Corrosion resistance + biocompatibility is key

Medical devices come into direct contact with the human body or pharmaceutical liquids, so the materials must meet the requirements of “corrosion resistance and no release of harmful substances”. Common materials include 304/316 stainless steel (corrosion resistance), PEEK (biocompatible and implantable in the human body), and pure titanium (lightweight and suitable for surgical instruments).

Note: Medical materials must be certified, such as 316 stainless steel to ISO 10993 (biocompatibility standard) and PEEK to FDA certification, otherwise they cannot be used in medical devices.

3. Automotive Industry: Balancing Cost and Performance

Auto parts are divided into “structural parts” and “exterior parts”, structural parts (such as chassis supports) choose high-strength steel or aluminum alloy, and exterior parts (such as body coverings) choose aluminum alloy or ABS with an easy-to-machine and smooth surface.

For example, the battery shell of new energy vehicles needs to be “lightweight, anti-collision, and corrosion-resistant”, usually choose 6061 aluminum alloy – lighter than steel, anodized after processing, can meet corrosion resistance requirements, and the cost is 80% lower than titanium alloy.

4. Electronic product field: appearance + lightweight priority

The shell and internal parts of electronic products (such as mobile phones and computers) are mainly required to be “lightweight, good-looking, and easy to process”. Common materials include ABS (low cost, suitable for mass production), aluminum alloy (good texture, suitable for mid-to-high-end products), acrylic (transparent, suitable for display pieces).

For example, a mobile phone manufacturer’s mid-range model uses an ABS shell with oil spray treatment on the surface, and the cost is controlled at 5 yuan / piece; The high-end model uses 7000 series aluminum alloy, which is CNC integrated molding, which has a better texture, but the cost rises to 30 yuan / piece.

5. Common problems and solutions for CNC materials: Don’t panic when encountering problems

Even if the material selection and process planning are done in the early stage, problems may still occur during the processing process. The following is a compilation of 10 high-frequency problems, each of which gives “cause + solution”, which I have encountered and solved in my actual work, you can directly check it.

6. Yigu Technology’s perspective on the application of CNC materials

In the field of CNC machining, material selection and process adaptation have always been the core links that affect production efficiency and product quality. Yigu Technology has been deeply involved in the industry for many years and found that there are two core pain points in the application of materials in the current enterprises: one is “blind pursuit of high-performance materials leads to cost loss of control”, and the other is “lack of collaborative optimization awareness of materials and processes”.

We believe that the future application trend of CNC materials will revolve around “precise matching” and “green sustainability”. On the one hand, enterprises should choose materials based on the needs of the whole life cycle of products, such as new energy vehicle parts, without blindly using titanium alloy, through the combination of 6061 aluminum alloy and surface treatment process, it can meet the needs of lightweight and corrosion resistance, and reduce costs by more than 50%; On the other hand, material recycling and reuse will become a focus, and we have assisted many customers to establish a waste sorting and recycling system, increasing the recycling rate of metal scrap to 85%, and plastic waste through recycling to reuse non-critical structural parts, which not only reduces costs but also reduces environmental pressure.

In addition, in response to the difficult machining of composite materials, we recommend that companies prioritize mature composite grades (such as CFRP made of T700 carbon fiber cloth), paired with specialized diamond-coated tools, and optimized cutting parameters, which can increase machining efficiency by 30% while reducing material waste.

7. FAQs: Addressing Your Biggest Concerns About CNC Materials

1. For beginners getting started with CNC machining, which material should I prefer?

It is recommended to give preference to 6061 aluminum alloy or ABS plastic. 6061 aluminum alloy has moderate hardness (about HB 95), is not easy to break the tool during processing, and has low tool loss, suitable for practicing cutting parameter adjustment; ABS plastic has low cost, low cutting resistance, and is not easy to damage the tool even if there is an operation error, so you can quickly master the basic machining skills. Avoid using difficult-to-process materials such as titanium alloy and hardened steel from the beginning, which can easily undermine confidence and increase costs.

2. What are the key points to pay attention to when machining medical device parts with PEEK material?

There are three key points in medical PEEK processing: (1) material pretreatment, PEEK is easy to absorb, and needs to be dried at 120°C for 4-6 hours before processing, otherwise the parts are prone to bubbles after processing; (2) Tool selection, use carbide tools or diamond-coated tools, and avoid using high-speed steel tools (fast wear and affect accuracy); (3) Cleaning requirements, the processing environment must meet medical-grade cleanliness standards (such as 10,000-level clean workshops), and the processed parts need to be cleaned with medical alcohol to avoid impurities and ensure compliance with FDA certification requirements.

3. How to solve the problem of delamination always occurs during the processing of carbon fiber composites?

Carbon fiber composite layering is mainly due to excessive cutting force or insufficient tool sharpness. Solution: (1) Choose a special carbon fiber processing tool (such as a double-edged tool with a helix angle of 15°-20°) to reduce the pull on the fiber during cutting; (2) Reduce the cutting depth (each cutting depth ≤ 0.5mm), and adopt the method of “multiple shallow cuts” to avoid excessive cutting force in a single time; (3) Continuously blow away chips with compressed air during processing to prevent delamination caused by chip backlog, and avoid using coolant (some coolants can corrode the resin matrix).

4. How can I control the cost of CNC materials when mass production?

Mass production can start from three aspects to control material costs: (1) optimize the design and reduce the amount of material used under the premise of meeting performance (e.g., the wall thickness of the part is reduced from 5mm to 3mm, which needs to be verified by mechanical simulation); (2) Supplier cooperation, sign long-term agreements with 2-3 core suppliers, and enjoy 5%-10% price discount for bulk purchases, while ensuring stable delivery cycles; (3) Waste utilization, the metal waste generated by processing is sorted and recycled, some can be remelted for non-critical parts, and plastic waste is crushed to make simple tooling fixtures to reduce the amount of raw material purchase.

5. How can I tell if a CNC material is of qualified quality?

It can be judged through the two steps of “visual inspection + performance inspection”: (1) visual inspection to see whether there are scratches, cracks, impurities on the surface of the material, and whether the size meets the requirements of the order (measured with calipers and micrometers); (2) Performance testing, sampling for key index testing, metal material hardness measurement (such as Rockwell hardness tester), tensile strength (universal testing machine), plastic material density measurement (density meter), heat resistance (thermal deformation temperature tester), composite material interlayer shear strength, and requiring suppliers to provide material certificates (such as ISO standard test reports) to ensure that all indicators meet the standards.