Hard metals and soft metals: What issues need to be considered during CNC machining?
- Hard metals and soft metals: What issues need to be considered during CNC machining?
- What are hard metals?
- What are soft metals?
- What is the difference between soft metals and hard metals?
- Hardness in metal processing
- the hardness or softness of a metal affect the final product ?
- What issues should be considered during machining?
- Key considerations when CNC machining hard and soft metals
- Hard metal and soft metal materials in CNC machining
- Industries and applications of CNC machining of hard and soft metal parts
- Summarize
CNC machining technology is crucial in the current field of custom parts manufacturing. The choice of materials often determines the success or failure of a project, leading to successful products and parts. Hard metals and soft metals possess different properties, are suitable for different applications, and each has its own advantages and limitations. Understanding their characteristics, differences, and selection strategies makes it easier to achieve optimal results in custom parts CNC machining projects. In this article, I will guide you through an in-depth look at these two metals and the key considerations when machining them using CNC, helping you make informed and practical decisions for your projects.
What are hard metals?
Hard metals generally refer to metallic materials that exhibit high resistance to plastic deformation, wear, and surface damage under load. Their properties are typically measured by indicators such as hardness, yield strength, and elastic modulus. This high hardness stems from strong atomic bonding, a dense crystal structure, and microstructural features such as fine grains, solid solution strengthening, precipitation strengthening, or the presence of hard phases like carbides and intermetallic compounds.
While hard metals exhibit excellent durability, dimensional stability, and performance under stress or high temperatures, they generally have lower ductility and toughness compared to soft metals, making them more susceptible to brittle fracture if part design or machining settings are inappropriate. Therefore, if your part design uses hard metal materials, you need to carefully consider load conditions, operating environment, and manufacturing constraints during the design phase to balance hardness, fracture toughness, and overall reliability.
What are soft metals?
Generally speaking, soft metals refer to metallic materials with relatively low hardness and yield strength. They can undergo plastic deformation under relatively small stress while maintaining good ductility and toughness. This softness mainly stems from weaker metallic bonding, lower lattice resistance to dislocation movement, and crystal structures that are prone to slip, such as face-centered cubic structures.
Soft metals can typically be easily formed, machined, or shaped through processes such as rolling, extrusion, and drawing. Soft metals generally possess high thermal and electrical conductivity and good resistance to brittle fracture; however, their wear resistance and load-bearing capacity are usually limited under harsh mechanical or abrasion conditions. In practical applications, soft metals should be chosen when easy machining, energy absorption, corrosion resistance, or functional conductivity are required compared to parts with high hardness or extremely high mechanical strength.
What is the difference between soft metals and hard metals?
The difference between hard metals and soft metals lies not only in hardness; from a materials science perspective, they also differ in atomic structure, mechanical properties, and processing characteristics. Therefore, understanding these differences helps engineers design and select appropriate materials based on the specific application requirements of parts. Below is a comparison of the two different types of metals.
| Comparison Aspect | Soft Metals | Hard Metals |
| Hardness Level | Low to moderate hardness; easily scratched or indented | High hardness; strong resistance to indentation and wear |
| Yield Strength | Low yield strength; plastically deform under relatively small loads | High yield strength; resist plastic deformation under high stress |
| Ductility and Toughness | High ductility and good toughness; capable of significant plastic deformation without fracture | Lower ductility; may exhibit brittle behavior if toughness is insufficient |
| Atomic and Crystal Characteristics | Weaker lattice resistance to dislocation motion; crystal structures that readily allow slip (often FCC) | Strong atomic bonding and lattice resistance; often strengthened by carbides, intermetallics, or refined grain structures |
| Wear Resistance | Poor to moderate wear resistance | Excellent wear and abrasion resistance |
| Machinability and Formability | Easy to machine, form, roll, or extrude | Difficult to machine; higher tool wear and more demanding processing conditions |
| Typical Examples | Aluminum, copper, lead, tin, low-carbon steels | Tool steels, tungsten alloys, cobalt-based alloys, cemented carbides |
| Typical Applications | Electrical conductors, structural components, heat exchangers, formed parts | Cutting tools, molds, dies, wear-resistant and high-load components |
Hardness in metal processing
Hardness is an important consideration in metalworking. It tells engineers the forces and methods required for machining. Hardness is typically measured by the size of the indentation that appears on the material surface after a standard force is applied. Therefore, hardness must be considered before designing metal parts, and the type of metal to be machined must be taken into account during preparation to achieve a suitable design and ultimately effective application.
Similarly, hardness is crucial when designing parts that need to slide against each other during mechanical movement. In this case, choosing the appropriate material hardness is very important because if one metal is softer than the other, the softer metal is likely to wear out faster than the harder metal. Therefore, hardness should be considered regardless of the type of part you are designing or the application you are applying.
the hardness or softness of a metal affect the final product ?
Machining, or metalworking, is a manufacturing method that cuts or reshapes metal into usable parts and applications. It is affected by the hardness of the metal. Machining hard metals into usable shapes takes a long time, while machining soft metals takes much less time.
Serious problems arise when machines are used to process or cut metals that they themselves cannot bear or support. For example, suppose a machine has been designed, but the type of material used and its mechanical strength are insufficient to support the lifespan of the equipment; this product is a failure. What if the user who purchases this equipment uses it intensively? Disaster could strike quickly, as the machine may malfunction, leading to financial losses and work stoppages.
What issues should be considered during machining?
Different considerations are required when CNC machining soft and hard metals of varying hardness. We will compare and explain these considerations based on material properties, tool selection, process parameters, quality control, and overall manufacturing efficiency.
| Consideration | CNC Machining Soft Metals | CNC Machining Hard Metals |
| Cutting Forces | Low cutting forces, which allow higher feed rates and spindle speeds but can lead to instability if not properly controlled | High cutting forces requiring rigid machine setups and conservative feeds to avoid tool breakage |
| Tool Material Selection | Standard carbide tools are usually sufficient; sharp cutting edges are critical | Advanced tool materials such as coated carbide, cermet, CBN, or ceramic tools are often required |
| Tool Wear Mechanism | Adhesive wear and built-up edge formation are common due to material ductility | Abrasive and diffusion wear dominate because of high hardness and elevated cutting temperatures |
| Surface Finish Control | Risk of material smearing and burr formation, especially on edges | Risk of chatter marks and micro-cracking if cutting parameters are not optimized |
| Chip Formation | Continuous, ductile chips that may wrap around the tool or workpiece | Short, segmented, or powder-like chips that are easier to evacuate but more abrasive |
| Heat Generation and Dissipation | Heat is lower but tends to transfer into the tool due to good thermal conductivity | Significant heat generation at the cutting zone; localized high temperatures are common |
| Cutting Speed and Feed Strategy | High speeds and feeds are feasible, but excessive speed may worsen built-up edge | Lower cutting speeds and carefully controlled feeds are required to maintain tool life |
| Coolant and Lubrication | Emphasis on lubrication to reduce friction and prevent built-up edge | Emphasis on cooling to control temperature and protect cutting tools |
| Machine Rigidity Requirements | Less demanding on machine stiffness | High rigidity and vibration damping are critical to maintain accuracy |
| Dimensional Accuracy | Potential dimensional errors from material springback after machining | Dimensional accuracy is stable, but tool deflection and wear must be closely monitored |
| Cost and Productivity Impact | Lower tooling costs and shorter cycle times | Higher tooling costs, longer cycle times, and increased process planning requirements |
Key considerations when CNC machining hard and soft metals
It’s good to have different material choices for the same part design. If you’re about to need to manufacture a project using CNC machining, it’s best to have a clear material target and choose a material that will be used in it. This can be a critical factor that is essential in the production process. Below is a summary of issues to consider when starting to manufacture parts made of materials with different hardness.
Functional performance requirements
The primary consideration is the functional performance of the final parts or applications manufactured using different metal materials under actual usage conditions. Hard metals are suitable for components that withstand high loads, wear, or high temperatures, where long-term durability and dimensional stability are extremely important. Soft metals are better suited for applications that prioritize ductility, corrosion resistance, conductivity, or lightweight design.
Processability and cost-effectiveness
You also need to consider machinability. Soft metals are easier to machine, allowing for higher cutting speeds, reduced tool wear, and shorter machining cycles, thus lowering overall production costs. Hard metals increase machining complexity and tooling requirements, so their higher cost must be justified by significant performance advantages.
Dimensional accuracy and surface integrity
When you need high-precision custom parts, dimensional control and surface quality are also critical factors. Hard metals have good stability but require strict process control to prevent chatter and surface damage. Soft metals are easier to machine but are more prone to burrs, built-up edges, and elastic recovery, all of which affect tolerances and surface finish.
Material supply and production scalability
Parts and product design engineers must also assess material availability, delivery times, and the feasibility of subsequent processing. Soft metals are generally easier to source and process, while hard metals can limit subsequent processing operations and extend production cycles. Effective material selection requires a balance between performance, machinability, cost, and scalability.
Hard metal and soft metal materials in CNC machining
| Category | Material Type | Common Materials | Key Characteristics | Typical CNC Machining Applications |
| Soft Metals | Aluminum Alloys | 6061, 6063, 7075 | Lightweight, high machinability, good corrosion resistance | Structural housings, brackets, aerospace frames |
| Soft Metals | Copper and Copper Alloys | Copper, Brass, Bronze | Excellent electrical and thermal conductivity, good ductility | Electrical components, bushings, fittings |
| Soft Metals | Low-Carbon Steels | AISI 1018, 1020 | Good formability, moderate strength, low cost | Shafts, plates, general-purpose mechanical parts |
| Soft Metals | Magnesium Alloys | AZ31, AZ91 | Very low density, good machinability | Lightweight enclosures, aerospace and automotive parts |
| Hard Metals | Tool Steels | D2, H13, A2 | High hardness, wear resistance, heat resistance | Molds, dies, cutting and forming tools |
| Hard Metals | Stainless Steels (Hardened) | 420, 440C, 17-4 PH (H900) | Corrosion resistance with high strength | Valves, shafts, precision mechanical components |
| Hard Metals | Titanium Alloys | Ti-6Al-4V | High strength-to-weight ratio, heat resistance | Aerospace, medical, high-performance parts |
| Hard Metals | Nickel-Based Alloys | Inconel 718, Hastelloy | Excellent high-temperature and creep resistance | Turbine parts, aerospace, energy equipment |
| Hard Metals | Tungsten and Carbide Materials | Tungsten alloys, Cemented carbide | Extremely high hardness and wear resistance | Cutting tools, wear-resistant components |
Industries and applications of CNC machining of hard and soft metal parts
| Material Category | Application Area | Typical CNC-Machined Parts | Key Reason for Material Selection |
| Soft Metals | Structural Components | Brackets, frames, mounting plates, enclosures | Easy machinability, low weight, adequate strength |
| Soft Metals | Electrical and Thermal Systems | Busbars, heat sinks, connectors | High electrical and thermal conductivity |
| Soft Metals | Fluid and Pneumatic Systems | Fittings, manifolds, valve bodies | Good corrosion resistance and formability |
| Soft Metals | Automotive and Consumer Products | Housings, covers, decorative components | Cost efficiency and surface finish quality |
| Soft Metals | Prototyping and Low-Stress Parts | Test components, fixtures, adapters | Fast machining and low tooling cost |
| Hard Metals | Tooling and Molds | Injection molds, stamping dies, cutting tools | High hardness and wear resistance |
| Hard Metals | High-Load Mechanical Parts | Gears, shafts, cams, bearing components | High strength and fatigue resistance |
| Hard Metals | High-Temperature Applications | Turbine parts, exhaust components | Thermal stability and creep resistance |
| Hard Metals | Precision and Wear-Critical Parts | Valve seats, nozzles, guide rails | Dimensional stability and abrasion resistance |
| Hard Metals | Aerospace and Medical Components | Structural fittings, implants, surgical tools | High strength-to-weight ratio and durability |
Summarize
Carbide and soft carbide each have their own characteristics in CNC machining. Carbide, due to its high strength, wear resistance, and high temperature resistance, is suitable for high precision and extreme environments; while soft carbide, due to its good machinability and low cost, is more suitable for mass production and lightweight design. In actual selection, we need to choose based on a comprehensive set of factors such as specific application scenarios, machining efficiency, and economy to help our projects be completed successfully.