Er CNC stærkere end rollebesætningen?

1. Indledning

In recent years, the quest for lightweight, holdbar, and cost-effective components has intensified.

Aerospace engineers seek turbine blades that withstand 1,400°C combustion temperatures;

automotive designers push engine blocks to handle 200MPa peak cylinder pressures; orthopedic surgeons demand titanium implants that endure 10⁷ loading cycles without failure.

Amid these challenges, the debate rages: Are CNC-machined parts inherently stronger than cast parts?

At svare på dette, we must first clarify what “strength” entails—tensile and yield values, træthed liv,

påvirkning af sejhed, and wear resistance—then compare how CNC machining and various casting methods measure up across these criteria.

I sidste ende, the most robust solution often lies in a tailored combination of processes, Materialer, and post-treatments.

2. CNC Machining Metal

CNC (Computer numerisk kontrol) bearbejdning er en subtractive manufacturing process, meaning it removes material from a solid workpiece—usually a wrought metal billet—to produce a precisely defined final geometry.

The process is controlled by computer programs that dictate tool paths, speeds, and feeds, enabling the consistent production of high-accuracy parts.

Subtractive Process: From Billet to Finished Part

The typical workflow begins with selecting a wrought billet of metal such as 7075 aluminium, 316 Rustfrit stål, eller Ti-6Al-4V titanium.

The billet is then clamped into a CNC mill or lathe, hvor rotating cutting tools eller turning inserts systematically remove material along programmed axes.

The result is a finished part with exceptionally tight dimensional tolerances, high surface quality, og mechanically robust properties.

Typiske materialer: Smed legeringer

• Aluminiumslegeringer: F.eks., 6061‑T6, 7075‑T6 – known for light weight, bearbejdningsevne, and strength-to-weight ratio.
• Steel Alloys: F.eks., 1045, 4140, 316, 17-4PH – offering superior mechanical strength and wear resistance.
• Titaniumlegeringer: F.eks., Ti-6Al-4V – valued for corrosion resistance, biokompatibilitet, and high strength-to-weight performance.
• Andre metaller: Messing, kobber, Magnesium, Inkonel, and more can also be CNC-machined for specialized applications.

Nøglefunktioner

• Dimensionel nøjagtighed: ±0.005 mm or better with advanced multi-axis CNC machines.
• Overfladefinish: As-machined finishes typically achieve RA 0,4-1,6 um, with further polishing reaching Ra < 0.2 µm.
• Gentagelighed: Ideal for both low and medium batch production with minimal variation.
• Tool Flexibility: Supports milling, boring, drejer, kedelig, Tråd, and engraving in one setup on 5-axis machines.

Pros of CNC Machining

• Superior Mechanical Strength:
  Parts retain the fine-grain structure of wrought metals, typically showing 20–40% higher strength than cast counterparts.
• High Precision and Tolerance Control:
  CNC machining can meet tolerances as tight as ±0,001 mm, essential for aerospace, medicinsk, and optical components.
• Excellent Surface Integrity:
  Glat, uniform surfaces with low roughness improve fatigue resistance, tætningsydelse, og æstetik.
• Materiel alsidighed:
  Compatible with virtually all industrial metals, from soft aluminum to hard superalloys like Inconel and Hastelloy.
• Rapid Prototyping and Customization:
  Ideal for small to medium batches, iterative design testing, and unique part geometries without expensive tooling.
• Minimal Internal Defects:
  Machined parts are generally free from porosity, Krympehulrum, or inclusions—common issues in casting.

Cons of CNC Machining

• Materielt affald:
  Being subtractive, CNC machining often results in 50–80% material loss, especially for complex geometries.
• High Cost for Large Production Runs:
  Per-unit costs remain high without economies of scale, and extensive tool wear may further increase operational expenses.
• Longer Cycle Times for Complex Parts:
  Intricate geometries requiring multiple setups or tools may significantly increase machining time.
• Limited Internal Complexity:
  Internal passages and undercuts are difficult to achieve without special fixtures, and often require EDM or modular designs.
• Requires Skilled Programming and Setup:
  Precision programming and tooling strategies are essential to achieve optimal efficiency and part quality.

3. Metalstøbning

Metal casting remains one of the oldest and most versatile manufacturing methods, enabling the economical production of parts that range from a few grams to multiple tons.

By pouring molten metal into molds—either single‑use or reusable—casting delivers near‑net shapes, complex internal features, and large cross‑sections that would be difficult or prohibitively expensive to machine from solid billets.

Overview of Common Casting Methods

1. Sandstøbning

• Behandle: Pack sand around a pattern, remove the pattern, and pour metal into the resulting cavity.
• Typical Volumes: 10–10,000 units per pattern.
• Tolerancer: ± 0.5–1.5 mm.
• Overfladeruhed: RA 6–12 um.

2. Investeringsstøbning (Lost -Wax)

• Behandle: Create a wax pattern, coat it in ceramic slurry, melt out the wax, then pour metal into the ceramic mold.
• Typical Volumes: 100–20,000 units per mold.
• Tolerancer: ± 0.1–0.3 mm.
• Overfladeruhed: RA 0,8-3,2 um.

3. Die casting

• Behandle: Inject molten non‑ferrous metal (aluminium, zink) into high‑precision steel dies under high pressure.
• Typical Volumes: 10,000–1,000,000+ units per die.
• Tolerancer: ± 0.05–0.2 mm.
• Overfladeruhed: RA 0,8-3,2 um.

4. Lost‑Foam Casting

• Behandle: Replace sand patterns with expanded polystyrene foam; the foam vaporizes upon metal contact.
• Typical Volumes: 100–5,000 units per pattern.
• Tolerancer: ± 0.3–0.8 mm.
• Overfladeruhed: Ra 3.2–6.3 µm.

5. Permanent formstøbning

• Behandle: Reusable metal molds (often steel) are filled by gravity or low pressure, then cooled and opened.
• Typical Volumes: 1,000–50,000 units per mold.
• Tolerancer: ± 0.1–0.5 mm.
• Overfladeruhed: Ra 3.2–6.3 µm.

Typical Casting Materials

1. Støbte strygejern (Grå, Dukes, White)

• Applikationer: motorblokke, Pumpehuse, Maskinbaser.
• Karakteristika: high damping, compressive strength up to 800 MPA, moderate tensile strength (200–400 MPa).

2. Rollebesætning Stål

• Applikationer: Trykfartøjer, Tunge maskinkomponenter.
• Karakteristika: tensile strength 400–700 MPa, toughness up to 100 MPa·√m after heat treatment.

3. Aluminium Cast Alloys (A356, A319, osv.)

• Applikationer: automotive wheels, aerospace structural parts.
• Karakteristika: tensile strength 250–350 MPa, density ~2.7 g/cm³, God korrosionsmodstand.

4. Kobber, Magnesium, Zinklegeringer

• Applikationer: elektriske stik, aerospace fittings, dekorativt isenkram.
• Karakteristika: excellent conductivity (kobber), lav densitet (Magnesium), tight tolerance capability (zink).

Key Features of Casting

• Near‑Net Shape Capability: Minimizes machining and material waste.
• Kompleks geometri: Easily produces internal cavities, ribben, underskærder, and bosses.
• Skalerbarhed: Fra a few hundred til millions of parts, depending on method.
• Large Part Production: Capable of casting components weighing several tons.
• Alloy Flexibility: Allows specialized compositions not readily available in wrought form.

Pros of Metal Casting

• Cost‑Effective Tooling for High Volumes: Die casting amortizes tooling over hundreds of thousands of parts, reducing per‑piece cost by up to 70% compared to CNC.
• Design Freedom: Intricate internal passages and thin walls (så lavt som 2 mm in investment casting) are possible.
• Materialebesparelser: Near‑net shapes reduce scrap, especially in large or complex parts.
• Size Versatility: Produces very large parts (F.eks., marine engine blocks) that are impractical to machine.
• Rapid Batch Production: Die-cast parts can cycle every 15–45 sekunder, meeting high-volume demands.

Cons of Metal Casting

• Inferior Mechanical Properties: As‑cast microstructures—dendritic grains and porosity—yield tensile strengths 20–40% lower and fatigue lives 50–80% shorter than wrought/CNC counterparts.
• Surface and Dimensional Limitations: Coarser finishes (Ra 3–12 µm) and looser tolerances (± 0.1–1.5 mm) often necessitate secondary machining.
• Potential for Casting Defects: Shrinkage voids, gas porosity, and inclusions can act as crack initiation sites.
• High Initial Tooling Cost for Precision Molds: Investment casting and die casting molds can exceed US $50,000–$200,000, requiring high volumes to justify expense.
• Longer Lead Times for Tooling Fabrication: Designing, Fremstilling, and validating complex molds can take 6–16 weeks before first parts are produced.

4. Material Microstructure and Its Influence on Strength

The microstructure of a metal—its grain size, form, and defect population—fundamentally governs its mechanical performance.

Wrought vs. As‑Cast Grain Structures

Wrought alloys undergo hot or cold deformation followed by controlled cooling, producing bøde, equiaxed grains often on the order of 5–20 µm i diameter.

Derimod, as‑cast alloys solidify in a thermal gradient, dannelse dendritic arms og segregation channels with average grain sizes of 50–200 um.

• Impact on Strength: According to the Hall–Petch relationship, halving grain size can boost yield strength by 10–15 %.
  For eksempel, wrought 7075‑T6 aluminum (grain size ~10 µm) typically achieves a yield strength of 503 MPA, whereas cast A356‑T6 aluminum (grain size ~100 µm) peaks around 240 MPA.

Porøsitet, Indeslutninger, and Defects

Casting processes can introduce 0.5–2% volumetric porosity, along with oxide or slag inclusions.

These microscale voids act as stress concentrators, drastically reducing fatigue life and fracture toughness.

• Fatigue Example: A cast aluminum alloy with 1% porosity may see a 70–80 % shorter fatigue life under cyclic loading compared to its wrought counterpart.
• Brudsejhed: Smed 316 stainless steel often exhibits K_IC values above 100 MPa·√m, while sand‑cast 316 SS may only reach 40–60 MPa·√m.

Heat Treatment and Work‑Hardening

CNC‑machined components can leverage advanced heat treatments—slukning, temperering, eller nedbørshærdning—to tailor microstructures and maximize strength and toughness.

For eksempel, solution‑treated and aged Ti‑6Al‑4V can reach tensile strengths above 900 MPA.

By comparison, cast parts typically receive homogenization to reduce chemical segregation, and sometimes solution treatment,

but they cannot attain the same uniform precipitation microstructure as wrought alloys.

Som et resultat, cast superalloys may achieve tensile strengths of 600–700 MPa post‑treatment, solid but still below wrought equivalents.

Work‑Hardening and Surface Treatments

Desuden, CNC machining itself can introduce beneficial compressive residual stresses on critical surfaces,

particularly when combined with shot‑peening, which improves fatigue resistance by up to 30%.

Casting lacks this mechanical work‑hardening effect unless subsequent treatments (F.eks., cold rolling or peening) are applied.

5. Sammenligning af mekaniske egenskaber

To determine whether CNC-machined components are stronger than cast ones, a direct comparison of their Mekaniske egenskaber—including tensile strength, Træthedsmodstand, and impact toughness—is essential.

While material choice and design both play a role, the manufacturing process itself significantly affects the final performance of the part.

Træk- og udbyttestyrke

Tensile strength measures the maximum stress a material can withstand while being stretched or pulled before breaking, mens udbyttestyrke indicates the point at which permanent deformation begins.

CNC-machined parts are typically made from wrought alloys, which exhibit refined microstructures due to mechanical working and thermomechanical processing.

• Wrought Aluminum 7075-T6 (CNC Machined):

• • Udbyttestyrke: 503 MPA
  • Ultimate trækstyrke (Uts): 572 MPA

• Cast Aluminum A356-T6 (Heat Treated):

• • Udbyttestyrke: 240 MPA
  • Uts: 275 MPA

Tilsvarende, wrought titanium (Ti-6al-4v) processed via CNC machining may reach a UTS of 900–950 MPa,

whereas its cast version typically tops out around 700–750 MPa due to the presence of porosity and a less refined microstructure.

Konklusion: CNC-machined components from wrought materials typically offer 30–50% higher yield and tensile strength than their cast counterparts.

Fatigue Life and Endurance Limit

Fatigue performance is critical in aerospace, medicinsk, and automotive parts subjected to cyclic loading.

Porøsitet, indeslutninger, and surface roughness in cast parts severely reduce fatigue resistance.

• Wrought Steel (CNC): Endurance limit ~ 50% of UTS
• Cast Steel: Endurance limit ~ 30–35% of UTS

For eksempel, i AISI 1045:

• CNC-maskinet (wrought): Endurance limit ~ 310 MPA
• Cast equivalent: Endurance limit ~ 190 MPA

CNC machining also provides smoother surfaces (Ra 0.2–0.8 μm), which delays crack initiation. I modsætning hertil, as-cast surfaces (RA 3-6 μm) can act as initiation sites, accelerating failure.

Impact Toughness and Fracture Resistance

Impact toughness quantifies a material’s ability to absorb energy during sudden impacts, and is especially important for parts in crash-prone or high-strain environments.

Cast metals often contain microvoids or shrinkage cavities, reducing their energy absorption capacity.

• Wrought Steel (Charpy V-notch at room temp):>80 J
• Cast Steel (same conditions):<45 J

Even after heat treatment, castings rarely reach the fracture toughness values of wrought products due to persistent internal flaws and anisotropic structures.

Hårdhed og slidstyrke

While casting allows for surface hardening treatments like saghærdning eller induction hardening,

CNC-machined parts often benefit from work hardening, precipitation treatments, eller nitriding, yielding consistent surface hardness across the part.

• CNC-machined 17-4PH stainless steel: op til HRC 44
• Cast 17-4PH (aged): typisk HRC 30–36

When surface integrity is critical—for example, in bearing housings, Forme, or rotating shafts—CNC machining provides a superior, more predictable wear profile.

6. Residual Stress and Anisotropy

When comparing CNC-machined and cast components, evaluating Reststress og anisotropy is vital to understanding how each manufacturing process influences structural integrity, Dimensionel stabilitet, og langsigtet ydeevne.

These two factors, though often less discussed than tensile strength or fatigue life,

can significantly affect a component’s behavior under real-world operating conditions, particularly in high-precision applications like aerospace, medicinsk udstyr, and automotive powertrains.

Residual Stress: Origins and Effects

Residual stress refers to the internal stresses retained in a component after manufacturing, even when no external forces are applied.

These stresses may lead to warping, revner, or premature failure if not properly managed.

▸ CNC-Machined Components

CNC -bearbejdning, being a subtractive process, can induce mechanical and thermal stresses primarily near the surface. These residual stresses arise from:

• Cutting forces and tool pressure, especially during high-speed or deep-pass operations
• Localized thermal gradients, caused by frictional heat between the cutting tool and material
• Interrupted cuts, which can create uneven stress zones around holes or sharp transitions

While machining-induced residual stresses are generally shallow and localized, they can influence Dimensionel nøjagtighed, especially in thin-walled or high-precision parts.

Imidlertid, CNC machining from wrought materials, which already undergo extensive processing to refine grain structures and relieve internal stresses,

tends to result in more stable and predictable residual stress profiles.

Datapunkt: In aerospace-grade aluminum (7075-T6), residual stresses introduced during CNC machining are typically within ±100 MPa near the surface.

▸ Cast Components

I casting, residual stresses originate from non-uniform solidification og cooling contraction, especially in complex geometries or thick-walled sections.

These thermally induced stresses often extend deeper into the part and are harder to control without additional post-processing.

• Differential cooling rates create tensile stresses in the core og compressive stresses at the surface
• Shrinkage cavities and porosity can act as stress risers
• Residual stress levels depend on mold design, alloy type, and cooling conditions

Datapunkt: In cast steels, residual stresses can exceed ±200 MPa, especially in large castings that have not undergone stress-relief heat treatment.

Sammendragssammenligning:

Aspekt	CNC-Machined	Rollebesætning
Origin of Stress	Cutting forces, localized heating	Thermal contraction during cooling
Depth	Lavvandet (surface-level)	Deep (volumetric)
Predictability	Høj (especially in wrought alloys)	Lav (requires stress-relief processes)
Typical Stress Range	±50–100 MPa	±150–200 MPa or more

Anisotropi: Directional Properties of Materials

Anisotropi refers to the variation of material properties in different directions, which can significantly affect mechanical performance in load-bearing applications.

▸ CNC-Machined (Smed) Materialer

Wrought alloys—used as the base stock for CNC machining—undergo rullende, ekstrudering, or forging, resulterer i en refined and directionally consistent grain structure.

While some mild anisotropies may exist, the material properties are generally more uniform and predictable across different directions.

• High degree of isotropy in machined parts, especially after multi-axis milling
• More consistent mechanical behavior under complex loading conditions
• Controlled grain flow can enhance properties in the desired direction

Eksempel: In forged titanium alloy (Ti-6al-4v), the tensile strength varies by less than 10% between longitudinal and transverse directions after CNC machining.

▸ Cast Materials

I modsætning hertil, cast metals solidify from a molten state, often resulting in directional grain growth og dendritic structures aligned with heat flow.

This causes inherent anisotropy and potential weakness in off-axis loading conditions.

• Greater variability in tensile, træthed, and impact properties across different directions
• Grain boundary segregation and inclusion alignment further reduce uniformity
• Mechanical properties are less predictable, especially in large or complex castings

Eksempel: In cast Inconel 718 Turbineblad, tensile strength can differ by 20–30% between radial and axial orientations due to directional solidification.

7. Surface Integrity and Post‑Processing

Surface integrity and post-processing are essential considerations in determining the long-term performance, Træthedsmodstand, and visual quality of manufactured components.

Whether a part is created through CNC -bearbejdning eller casting, the final surface condition can influence not only aesthetics but also mechanical behavior under service conditions.

This section explores how surface integrity differs between CNC-machined and cast parts, the role of post-processing treatments, and their cumulative impact on functionality.

Surface Finish Comparison

CNC -bearbejdning:

• CNC machining typically produces parts with fremragende overfladefinish, especially when fine tool paths and high spindle speeds are used.
• Common surface roughness (Ra) values for CNC:

• • Standard finish: Ra ≈ 1.6–3.2 µm
  • Precision finish: Ra ≈ 0.4–0.8 µm
  • Ultra-fine finish (F.eks., lapping, polering): Ra ≈ 0.1–0.2 µm

• Smooth surfaces reduce stress concentrators, enhance fatigue life, and improve sealing properties, critical in hydraulic and aerospace applications.

Casting:

• As-cast surfaces are generally rougher and less consistent due to mold texture, metal flow, and solidification characteristics.

• • Sandstøbning: Ra ≈ 6.3–25 µm
  • Investeringsstøbning: Ra ≈ 3.2–6.3 µm
  • Die casting: Ra ≈ 1.6–3.2 µm

• Rough surfaces can harbor residual sand, skala, or oxides, which may degrade fatigue and corrosion resistance unless further finished.

Subsurface Integrity and Defects

CNC -bearbejdning:

• Machining from wrought billets often results in tæt, homogeneous surfaces with low porosity.
• Imidlertid, aggressive cutting parameters can introduce:

• • Micro-cracks or heat-affected zones (Haz)
  • Residual tensile stresses, which may reduce fatigue life

• Controlled machining and coolant optimization help maintain metallurgical stability.

Casting:

• Cast parts are more susceptible to subsurface defects, såsom:

• • Porøsitet, gas bubbles, and shrinkage cavities
  • Indeslutninger (oxider, slag) og segregation zones

• These imperfections can act as initiation sites for cracks under cyclic loads or impact stresses.

Post-Processing Techniques

CNC Machined Parts:

• Depending on functional requirements, CNC parts may undergo additional treatments, såsom:

• • Anodisering – improves corrosion resistance (common in aluminum)
  • Polishing/lapping – enhances dimensional precision and surface finish
  • Skudblæsning – introduces beneficial compressive stresses to improve fatigue life
  • Coating/plating (F.eks., nikkel, Chrome, or PVD) – enhances wear resistance

Cast Parts:

• Post-processing is often more extensive due to casting’s inherent surface roughness and internal defects.

• • Surface grinding or machining for dimensional accuracy
  • Hot Isostatic Pressing (HOFTE) – used to eliminate porosity and increase density, especially for high-performance alloys (F.eks., titanium and Inconel castings)
  • Varmebehandling – improves microstructure uniformity and mechanical properties (F.eks., T6 for aluminum castings)

Comparative Table – Surface and Post-Processing Metrics

Aspekt	CNC -bearbejdning	Metalstøbning
Overfladeruhed (Ra)	0.2–3.2 µm	1.6–25 µm
Subsurface Defects	Rare, unless over-machined	Common: porøsitet, indeslutninger
Træthedsydelse	Høj (with proper finishing)	Moderat til lavt (unless treated)
Typical Post-Processing	Anodisering, polering, belægning, skudblæsning	Bearbejdning, HOFTE, Varmebehandling, slibning
Surface Integrity	Fremragende	Variabel, often needs improvement

8. CNC vs. Rollebesætning: A Comprehensive Comparison Table

Kategori	CNC -bearbejdning	Casting
Fremstillingsmetode	Subtractive: material is removed from solid billets	Additive: molten metal is poured into a mold and solidified
Materiel type	Wrought metals (F.eks., 7075 aluminium, 4140 stål, Ti-6al-4v)	Cast alloys (F.eks., A356 aluminum, støbejern, low alloy cast steels)
Mikrostruktur	Fine-grain, homogeneous, work-hardened	Dendritic, coarse grain, porøsitet, potential shrinkage defects
Trækstyrke	Højere (F.eks., 7075-T6: ~503 MPa, Ti-6al-4v: ~895 MPa)	Sænke (F.eks., A356-T6: ~275 MPa, grey cast iron: ~200–400 MPa)
Træthedsmodstand	Superior due to cleaner microstructure, absence of voids	Lower fatigue life due to porosity and surface roughness
Påvirkning & Sejhed	Høj, especially in ductile alloys like forged steel or titanium	Brittle in many cast irons; variable in cast aluminum or steel
Dimensionel nøjagtighed	Very high precision (±0.01 mm), suitable for tight-tolerance components	Moderate accuracy (±0,1–0,3 mm), depends on process (sand < die < Investeringsstøbning)
Overfladefinish	Smooth finish (Ra 0.2–0.8 μm), post-processing optional	Rougher as-cast finish (RA 3-6 μm), often requires secondary machining
Residual Stress	Possible cutting-induced stress, generally mitigated by finishing operations	Solidification and cooling induce residual stresses, possibly leading to warping or cracks
Anisotropi	Typically isotropic due to uniform rolled/fabricated billets	Often anisotropic due to directional solidification and grain growth
Designfleksibilitet	Excellent for complex geometries with undercuts, riller, and fine details	Best for producing complex hollow or net-shape parts without material waste
Volume Suitability	Ideal for prototyping and low-volume production	Economical for high-volume, low-unit-cost manufacturing
Værktøjsomkostninger	Low initial setup; quick iteration	High upfront tooling/mold cost (especially die or investment casting)
Ledetid	Fast setup, rapid turnaround	Longer lead times for mold design, approval, and casting execution
Efterbehandlingsbehov	Minimal; optional polishing, belægning, or hardening	Often required: bearbejdning, peening, Varmebehandling
Omkostningseffektivitet	Cost-effective in small batches or for precision parts	Economical in large-scale production due to amortized tooling
Applikations pasform	Rumfart, medicinsk, forsvar, custom prototypes	Automotive, byggeudstyr, pumper, ventiler, motorblokke
Strength Verdict	Stronger, more consistent – ideal for structural integrity and fatigue-critical components	Weaker in comparison – suitable where strength demands are moderate or cost is a major driver

9. Konklusion: Er CNC stærkere end rollebesætningen?

Ja, CNC-machined components are generally stronger than cast parts—particularly in terms of tensile strength, træthed liv, and dimensional precision.

This strength advantage arises primarily from the refined microstructure of wrought metals og precision of machining.

Imidlertid, the right choice depends on the specific anvendelse, bind, design complexity, og budget.

For safety-critical, load-bearing, or fatigue-sensitive components, CNC is the preferred solution.

But for large-scale, geometrically complex parts with less demanding mechanical loads, casting offers unmatched efficiency.

The most innovative manufacturers are now combining both: near-net casting followed by CNC finishing—a hybrid strategy that merges economy with performance in the era of smart, high-performance manufacturing.

DENNE is the perfect choice for your manufacturing needs if you need high-quality CNC machining or casting products.

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