1. Zavedení
Investiční obsazení, often known as lost‑wax casting nebo Přesné obsazení, delivers complex metal parts with exceptional precision.
By employing a disposable wax pattern and a refractory ceramic shell, this process reproduces intricate geometries and tight tolerances in materials ranging from stainless steel to superalloys.
Historicky, artisans in Mesopotamia and China used early forms of lost‑wax techniques over 5,000 years ago;
Modern industrial applications emerged in the early 20th century when Robert B. W. Taylor patented a wax‑pattern method in 1907.
Today, investment casting underpins critical industries—namely aerospace, zdravotnické prostředky, and energy—because it combines design freedom with repeatable accuracy.
2. Co je to investiční obsazení?
Investment casting combines precision wax patterning with ceramic shell molds.
First, technicians inject molten wax into a metal die, producing a pattern that replicates the final part. Další, they attach multiple wax patterns to a central sprue, forming a “tree.”
Then, they dip this assembly into alternating layers of ceramic slurry and fine sand. After ceramic layers harden, operators melt out the wax (“dewax”), leaving a rigid shell.
Finally, they pour molten metal into the cavity, let it solidify, and break away the shell to reveal a near‑net‑shape component.
Two binder systems dominate the industry:
- Water Glass (Sodium Silicate) Proces: Engineers favor this economical route for large batches.
The water glass binder costs approximately USD 2.50 per kilogram, making it ideal for high‑volume automotive parts. - Silica Sol Process: Manufacturers select silica sol when they need finer ceramic grains, superior surface finish, and thinner shells.
Však, silica sol costs about USD 6.50 per kilogram, roughly 2.6× the expense of water glass.
3. Proces obsazení investic
The investment casting process transforms a simple wax model into a high‑precision metal component through a series of tightly controlled steps.
Although total cycle times vary—from as little as 24 hours with rapid water‑glass shells to around seven days for standard silica‑sol systems—the method consistently yields near‑net‑shape parts with excellent surface finish.
Wax Pattern Fabrication
Initially, technicians inject de‑aired wax (typically a blend of paraffin and micro‑crystalline additives) into precision steel dies.
They maintain wax temperatures between 60 °C and 80 °C and apply pressures of 2–4 MPa. Each injection cycle completes in roughly 10–30 seconds.
After ejection, operators visually inspect patterns for defects, rejecting any that deviate more than ±0.1 mm in critical dimensions.
Pattern Assembly and Ceramic Shell Building
Další, workers “tree up” individual wax patterns onto a central sprue, creating an assembly of up to 50 parts.
They then build the ceramic mold by alternately dipping the tree into a refractory slurry and stuccoing fine silica sand.
Foundries typically apply 6–8 slurry‑and‑stucco cycles to achieve a shell thickness of 6–10 mm.
With water‑glass binders, this shell build takes about 24–72 hours; high‑temperature silica sol systems can require up to 7 days to fully cure.
Dewaxing and Burnout
Subsequently, foundries remove molten wax in an autoclave or steam autoclave at around 150 ° C., often as an overnight soak to ensure complete wax evacuation.
They then ramp the temperature at 1–2 °C/min up to 600–900 °C and hold for 4–6 hours to decompose any residual organics, preventing shell cracking and ensuring a clean cavity.
Metal Pouring and Shell Removal
After burnout, technicians preheat ceramic shells to 760–870 °C.
They pour molten alloy—such as stainless steel at 1,500–1,550 °C—using gravity, centrifugal, or vacuum‑assist methods to minimize turbulence.
Once the metal solidifies, workers break away the ceramic shell via vibration or high‑pressure water jet, typically yielding 95–98% usable castings.
Heat Treatment and Final Machining
Finally, castings undergo heat treatment—such as solution annealing at 1,050 °C or age hardening at 700 °C—to refine the microstructure and relieve stresses.
Machinists then perform CNC milling, EDM, or grinding, achieving tolerances as tight as ±0.05 mm and surface finishes down to Ra 0.8 µm.
By actively controlling each variable—from wax temperature and slurry viscosity to burnout profiles and pouring rates,
Investment casting consistently delivers complex, high‑performance parts with minimal scrap and reduced post‑machining requirements.
Investment Casting Process Complete Video https://www.youtube.com/watch?v=NugdCiQ0uU8
4. What Materials Can Be Investment Cast?
Investment casting accommodates the widest range of alloys among all casting processes,
allowing engineers to tailor parts for demanding applications by balancing strength, temperature resistance, corrosion performance and, when needed, biocompatibility.
Ferrous Alloys
- Stainless Steels (300, 400 & PH series): Common grades include CF‑8 (AISI 304), 316L and 17‑4 PH.
They offer tensile strengths from 600 na 1,300 MPa and yield strengths between 500 a 1,100 MPA, making them ideal for corrosion‑resistant components in harsh environments. - Uhlík & Low‑Alloy Steels: Grades such as 4140 a 4340 provide toughness and fatigue resistance at lower cost, with tensile strengths typically ranging from 700 na 1,200 MPA.
Nickel‑Base Superalloys
When high‑temperature strength and creep resistance matter, foundries turn to Inconel 718 a 625.
Například, precipitation‑hardened Inconel 718 delivers yield strengths up to around 1,035 MPa and ultimate tensile strengths near 1,240 MPa at room temperature, while retaining significant strength above 650 ° C..
Cobalt‑Chrome Alloys
CoCrMo blends combine exceptional wear resistance with biocompatibility, making them staples in medical implants and gas‑turbine components.
These alloys typically exhibit ultimate tensile strengths of 1,000–1,350 MPa and yield strengths of 700–1,000 MPa.
Titan Alloys
Ti‑6Al‑4V (Grade 5) stands out for aerospace and biomedical parts.
It offers ultimate tensile strength between 862 a 1,200 MPA, yield strength from 786 na 910 MPA, and a density of around 4.43 g/cm³, delivering an outstanding strength‑to‑weight ratio.
Hliník Alloys
Alloys such as A356 (Al‑Si‑Mg) remain popular for lightweight components in aerospace, automobilový průmysl, and electronics.
They typically provide tensile strengths of roughly 250–350 MPa along with inherent corrosion resistance.
Copper‑Based Alloys
Bronze and mosaz variants serve wear‑resistant and decorative applications, with tensile strengths generally spanning 350–600 MPa, depending on the specific composition.
Navíc, foundries are expanding into glass‑ and ceramic‑core systems to produce advanced composites and next‑generation materials.
By adjusting shell chemistry, burnout profiles, and pouring temperatures, they accommodate each material’s unique requirements.
Selection Criteria
When choosing an alloy for investment casting, engineers focus on:
- Mechanical Performance: Required tensile and yield strength, hardness and fatigue life
- Thermal Stability: Operating temperature range, creep resistance and thermal conductivity
- Odolnost proti korozi: Chemical environment, pitting and stress‑corrosion susceptibility
- Biocompatibility: Cytotoxicity, ion release and passivation behavior for implants
5. Design for Casting (DfC)
Effective Design for Casting (DfC) translates directly into higher yields, lower costs, and faster turnaround.
By applying the following guidelines, engineers typically cut scrap rates by 20–30% and reduce post‑machining time by up to 40%.
Maintain Uniform Wall Thickness
- Recommendation: 2–10 mm for most alloys (variation ±0.5 mm)
- Rationale: Uniform sections cool more evenly, preventing hot spots and reducing the risk of porosity. Consequently, you’ll see fewer internal defects and tighter dimensional control.
Incorporate Adequate Draft Angles
- Recommendation: 0.5°–2° per side on vertical faces
- Rationale: Even a small taper eases ceramic‑shell removal and minimizes shell damage. V důsledku toho, your yield increases and rework decreases.
Use Generous Fillets and Radii
- Recommendation: Fillet radii ≥ wall thickness or ≥ 1 mm, whichever is larger
- Rationale: Rounded transitions improve metal flow, lower stress concentrations and help ceramic layers adhere uniformly. In turn, you achieve more consistent microstructure and higher fatigue strength.
Avoid Undercuts and Internal Cavities
- Strategy: Wherever possible, redesign undercuts as through‑holes or split features; minimize core use.
- Benefit: Simplifying geometry cuts tooling complexity, shortens lead times and trims per‑part cost by up to 15%.
Optimize Gating and Riser Locations
- Best Practice: Place gates in the heaviest section and risers above the highest‑risk hot spots.
- Outcome: Controlled metal flow and solidification reduce shrinkage porosity, yielding a typical scrap reduction of 5–10%.
Plan for Finish‑Machining Allowances
- Allowance: Add 0.5–1.5 mm of stock on critical surfaces
- Reasoning: Ensuring sufficient material for CNC or grinding guarantees you meet tolerance targets (often ±0.05 mm) without chasing undersized castings.
Leverage Symmetry and Modular Design
- Technique: Mirror‑image features or split complex parts into simpler sub‑assemblies
- Advantage: Fewer unique patterns and shells lower tooling costs by 10–20%, while standardizing processes across multiple parts.
6. Advantages of the Investment Casting Process
Investment casting delivers a powerful combination of precision, flexibility and efficiency. Key benefits include:
- Exceptional Dimensional Accuracy
Achieve tight tolerances (often within ±0.1 mm) on highly intricate geometries, so parts meet specifications directly out of the mold. - Superior Surface Finish
Produce smooth as‑cast surfaces (Ra 1.2–3.2 µm), which in turn reduces the need for extensive polishing or machining. - Wide Material Versatility
Cast everything from stainless steels and nickel‑base superalloys to titanium and aluminum, allowing you to pick the ideal alloy for each application. - Complex Geometry Capability
Mold undercuts, thin walls and internal passages in a single pour, thereby eliminating assembly steps and fastener requirements. - Monolithic, Seamless Parts
Create single‑piece components without parting lines or weld seams, which improves structural integrity and simplifies finishing operations. - Scalability for Any Volume
Adapt easily to both small prototype runs and high‑volume production, balancing tool costs against unit economics. - Near‑Net‑Shape Efficiency
Minimize scrap and material usage by producing parts very close to final dimensions, cutting down on waste and machining time. - Design Freedom
Incorporate sharp corners, right‑angle features and intricate details without extra shrinkage allowances, streamlining the path from CAD to cast part. - Environmental and Cost Advantages
Reduce energy consumption and raw‑material waste compared with subtractive methods, helping to lower both production costs and environmental impact.
7. Limitations of Investment Casting
While investment casting offers significant advantages, it also comes with certain limitations that engineers and manufacturers must consider when selecting the appropriate production method:
- Higher Initial Tooling Costs
Creating precision wax injection dies and ceramic shell systems requires significant upfront investment, making it less economical for low-volume or prototype production unless design complexity justifies it. - Longer Lead Times
The multi-step process—from wax pattern creation to shell building, burnout, obsazení, and finishing—can take several days to weeks.
This extended cycle time limits suitability for projects requiring rapid turnaround. - Size Constraints
Investment casting is best suited for small to medium-sized components. While parts up to 100 kg can be produced, dimensional accuracy and shell integrity become harder to maintain as size increases. - Limited Wall Thickness
Very thin walls (typically under 1.5 mm) are challenging to cast consistently, especially for large parts, due to rapid cooling and shell breakage risks. - Material Restrictions with Reactive Alloys
Certain reactive metals like pure titanium, require specialized environments (NAPŘ., vakuové lití) to avoid contamination, which adds complexity and cost. - Not Ideal for High-Volume, Low-Complexity Parts
For simple geometries produced at very high volumes, processes like die casting or sand casting often deliver better cost-per-part performance. - Shell Fragility During Handling
The ceramic shell is fragile before firing. Any mishandling during drying or dewaxing stages can cause cracks, leading to casting defects or scrap.
8. Aplikace investičního obsazení
Investment casting is widely adopted across high-performance industries due to its ability to produce complex, high-precision components in a variety of materials.
Its versatility makes it especially valuable in sectors where dimensional accuracy, material performance, and surface finish are critical.
Aerospace
- Turbine Blades: Complex aerodynamic profiles and internal cooling channels are investment cast to withstand high temperatures and stress.
- Fuel Nozzles & Combustion Components: Precision casting ensures tight tolerances and heat resistance.
- Structural Housings: Lightweight, strong, and corrosion-resistant alloys (NAPŘ., titanium and Inconel) are commonly used.
Automobilový průmysl
- Turbocharger Wheels: Investment casting produces the intricate vanes and durable materials needed for high-RPM operation.
- Exhaust Manifolds: Able to handle extreme thermal cycling and corrosive gases.
- Gear Components: Precision casting reduces the need for secondary machining.
Lékařský
- Ortopedické implantáty: Biocompatible alloys like titanium and cobalt-chrome are cast into hip joints, knee components, and dental frameworks.
- Surgical Instruments: Complex shapes with smooth finishes support hygiene, funkce, and ergonomic design.
Energie, Oil & Gas
- Valve Bodies & Pump Impellers: Koroze- and wear-resistant castings handle high-pressure, high-temperature environments.
- Drilling Equipment Components: High-strength alloys ensure durability under extreme mechanical loads.
Emerging Sectors
- Robotika: Lightweight, precise components are cast to reduce assembly complexity and improve motion efficiency.
- Obnovitelná energie: Wind turbine components, hydraulic control parts, and solar mounts benefit from corrosion resistance and structural precision.
- Spotřební elektronika: Housing components and small mechanical parts in premium devices utilize aluminum and stainless steel castings for design and function integration.
9. When to Choose Investment Casting
You should select investment casting when:
- You Need Complex Shapes: Internal passages, Tenké stěny, or intricate features.
- You Require Tight Tolerances: Part accuracy within ±0.1 mm.
- Volumes Fit the Scale: Obvykle 50 na 100,000 units per year justify the tooling investment.
- Material Demands Run High: Alloys demand precise control and fine grain structure.
10. Innovation & Future Trends
Industry 4.0 and digitalization are reshaping investment casting:
- Hybrid Workflows: Producers now 3D‑print wax or polymer patterns, eliminating steel dies for low‑volume runs.
- IoT‑Enabled Monitoring: Smart sensors track shell temperature and humidity, feeding AI models that optimize process parameters in real time.
- Next‑Gen Materials: Researchers explore refractory metals and metal‑matrix composites, pushing temperature limits beyond 1,000 ° C..
- Automated Shell Handling: Robotics reduce manual labor and improve safety, while digital twins simulate entire casting cycles to predict defects before they occur.
11. Závěr
Investment casting stands at the intersection of art and high technology.
Its ability to produce complex, high‑performance parts with tight tolerances makes it indispensable in aerospace, medical, automobilový průmysl, and energy industries.
As digital tools, additive manufacturing, and advanced materials converge, investment casting will continue to evolve—fueling innovation and driving precision manufacturing well into the future.
At TENTO, we are happy to discuss your project early in the design process to ensure that whatever alloy is selected or post-casting treatment applied, the result will meet your mechanical and performance specifications.
To discuss your requirements, email sales@casting-čna.com.
Frequently Asked Questions (Časté časté)
1. What is investment casting used for?
Investment casting is used to produce complex metal components with excellent dimensional accuracy and surface finish.
It’s commonly applied in aerospace, automobilový průmysl, medical, energy, and industrial machinery industries.
2. How accurate is investment casting?
Investment casting can achieve dimensional tolerances as tight as ±0.1 mm for small features. With proper design and process control, minimal post-processing is needed.
3. What materials can be used in investment casting?
A wide range of ferrous and non-ferrous alloys can be cast, včetně nerezové oceli, Uhlíková ocel, hliník, titan, cobalt-chrome, and nickel-based superalloys.
4. Is investment casting cost-effective?
While tooling costs are higher than some other casting methods, investment casting becomes cost-effective for complex parts, high-performance alloys, and when minimal machining is desired.
5. What’s the difference between silica sol and water glass in investment casting?
Silica sol casting offers higher precision and better surface finish, making it suitable for critical aerospace or medical parts.
Water glass casting is more economical and typically used for industrial applications with looser tolerances.
6. Can investment casting replace machining or welding?
Ano. Investment casting often eliminates the need for machining or welding by producing near-net-shape components as single, monolithic parts—improving strength and reducing assembly time.
7. What are the size limits for investment casting?
Most investment castings range from a few grams up to 100 kg, though smaller parts benefit most from the precision and detail the process offers.
