Product Overview
Machined stainless steel castings integrate Silica Sol lost-wax investment casting with CNC post-processing. This hybrid approach delivers near-net-shape components with complex geometries, internal passages, and thin-wall cross sections, followed by tight-tolerance CNC machining on critical mounting surfaces, bores, threads, and sealing faces.

Manufacturing Pathway
• Silica Sol Investment Casting Near-net-shape production | Smooth cast surface finish (Ra 3.2 to 6.3 micrometers) | Complex internal and external geometries
• Precision CNC Machining & Finishing Tolerances held up to +/-0.010 mm | High-precision sealing surfaces (Ra 0.8 micrometers) | Threads, bores, and critical interfaces

Engineering Capabilities & Envelope

Unit Weight Range	0.01 kg to 50 kg
Wall Thickness Minimum	1.5 mm (structural dependent)
As-Cast Linear Tolerance	ISO 8062 CT4 to CT7
Machined Surface Tolerance	Up to +/-0.010 mm (0.0004 in)
As-Cast Surface Roughness	Ra 3.2 micrometers to Ra 6.3 micrometers
Machined Surface Finish	Up to Ra 0.8 micrometers (Ra 0.4 micrometers with fine grinding/lapping)

Manufacturing Process

Our facility uses the Silica Sol Lost-Wax Investment Casting Process exclusively for stainless steel production. Compared to water-glass casting, silica sol binder produces superior dimensional stability, higher refractoriness, and minimal surface defects such as pitting and inclusions.

Production Sequence
• Tooling & Wax Pattern Creation: Precision aluminum dies are CNC-machined to account for metal shrinkage rates (typically 1.8% to 2.2% depending on the alloy grade). High-purity pattern wax is injected under controlled temperature and pressure.
• Cluster Assembly: Wax patterns are attached to a central runner tree via gating systems engineered to prevent shrinkage porosity and cold shuts during pouring.
• Silica Sol Shell Building: Assemblies are dipped into silica sol slurry and stuccoing sand (zircon and fused silica). This process is repeated 5 to 7 times to build a rigid ceramic shell. Each layer undergoes controlled drying in temperature- and humidity-monitored chambers.
• Dewaxing & High-Temperature Firing: Dewaxing takes place in a steam autoclave at 8 to 10 bar pressure. Shells are then fired in a gas kiln at 1,000 deg C to 1,150 deg C to eliminate wax residue, sinter the ceramic binder, and preheat the mold for metal pouring.
• Induction Melting & Pouring: Stainless steel scrap and primary alloys are melted in medium-frequency induction furnaces. Melt chemistry is verified per heat using an optical emission spectrometer (OES) prior to tapping. Molten metal is gravity-poured into preheated ceramic molds.
• Knockout & Cut-Off: After solidifying, ceramic shells are removed via pneumatic vibrators or high-pressure water jets. Parts are severed from the sprue using abrasive cut-off wheels.
• Solution Heat Treatment: Castings undergo high-temperature solution annealing (typically 1,040 deg C to 1,120 deg C followed by rapid water quenching) to redissolve chromium carbides, restore corrosion resistance, and achieve uniform metallurgical phase structure.

Materials and Technical Specifications

We cast standard austenitic, duplex, martensitic, and precipitation-hardening stainless steels compliant with ASTM, EN, and DIN specifications.

Material Grade Comparison Table

Material Grade	Equivalent Standards	Tensile Strength (MPa)	Yield Strength (MPa min)	Elongation (% min)	Key Characteristics & Primary Applications
CF8 (SS304)	ASTM A351 / EN 1.4308	>= 485	>= 205	35	General corrosion resistance, excellent weldability. Used in valve bodies, food machinery, pump housings.
CF8M (SS316)	ASTM A351 / EN 1.4408	>= 485	>= 205	30	2% to 3% Molybdenum addition for enhanced pitting resistance in chloride environments. Used in marine hardware and chemical pumps.
CF3M (SS316L)	ASTM A351 / EN 1.4404	>= 485	>= 175	30	Ultra-low carbon content (C <= 0.03%) to prevent intergranular corrosion after welding. Used in pharmaceutical and sanitary components.
17-4PH (CB7Cu-1)	ASTM A747 / EN 1.4542	>= 930 (H1050)	>= 725	10	Precipitation hardening grade providing high mechanical strength, fatigue resistance, and moderate corrosion resistance. Used in high-load structural brackets and impulse shafts.
2205 (Duplex)	ASTM A890 4A / EN 1.4462	>= 620	>= 450	25	Dual-phase ferritic-austenitic structure offering high yield strength, stress corrosion cracking resistance, and erosion resistance in saltwater.
CA15 (SS410)	ASTM A217 / EN 1.4006	>= 620	>= 415	18	Martensitic, heat-treatable stainless steel providing high hardness and wear resistance. Used in turbine blades and valve trim.

Key Product Features

Integrated Cast-Machined Geometry

By combining investment casting with multi-axis CNC machining, complex structural elements like weight-reduction pockets, stiffening ribs, and fluid channels are cast directly into the part. Precision features such as O-ring grooves, bearing seats, and metric or NPT threads are added via subsequent machining operations.

Dimensional Consistency

• As-Cast Linear Tolerance: ISO 8062-3 CT4 to CT7 standards.
• Machined Feature Tolerance: Linear dimensions held to +/-0.010 mm; bore roundness within 0.008 mm.

Surface and Geometry Profile

• As-Cast Surface: ISO 8062-3 CT4 to CT7 | Ra 3.2 to 6.3 micrometers | Features like internal flow channels are cast directly to near-net shape.
• Machined Surface: Precision CNC Controlled | Ra 0.8 micrometers for sealing areas | Bearing seats and high-precision mating faces held to +/-0.010 mm.

Corrosion & Mechanical Performance

All austenitic grades undergo full solution annealing to ensure zero carbide precipitation along grain boundaries. Duplex and precipitation-hardening alloys are heat treated to tailored temper conditions (such as H900, H1050, H1150) to achieve target hardness, impact toughness, and stress-corrosion cracking resistance.

Typical Applications

Fluid Handling & Process Equipment
• Components: Impellers, pump casings, valve bodies, butterfly valve discs, sanitary pipe fittings.
• Operating Demand: Pressure-tight castings resistant to cavitation erosion and organic or inorganic acid attack.

Marine Hardware & Offshore Engineering
• Components: Deck cleats, hinges, underwater brackets, pipe couplings, propulsion fittings.
• Operating Demand: Resistance to pitting corrosion in saltwater environments; high yield strength to withstand dynamic wave loading.

Food & Pharmaceutical Processing
• Components: Mixing paddles, homogenizer blocks, filling nozzles, sanitary valve housing.
• Operating Demand: Cavity-free, non-porous surfaces cleaned to Ra <= 0.8 micrometers to satisfy hygienic clean-in-place (CIP) standards.

Automotive & Heavy Machinery
• Components: Turbocharger brackets, exhaust flanges, EGR valve housings, hydraulic manifold blocks.
• Operating Demand: Thermal fatigue resistance at elevated operating temperatures, high dimensional stability, pressure tightness.

Machining and Secondary Operations

Investment castings are post-processed in our internal machining shop to eliminate interface mismatch and meet tight mechanical assembly requirements.

In-House Machining Capabilities
• CNC Turning Centers: Turning diameters up to 400 mm; live tooling capabilities for cross-drilling and tapping.
• 4-Axis Vertical Machining Centers (VMC): Multi-axis contouring, complex valve seat pocketing, and index drilling.
• Thread Cutting & Tapping: Metric, NPT, BSPP, and BSPT precision internal and external threading.

Surface Finishing & Passivation
• Chemical Passivation: Nitric or citric acid chemical treatment per ASTM A967. Removes free iron contamination from machining tooling, restoring the corrosion-resistant chromium oxide passive film.
• Electropolishing: Electrochemical surface leveling that reduces micro-roughness down to Ra 0.2 to 0.4 micrometers, enhancing corrosion resistance and removing surface stress.
• Shot & Bead Blasting: Stainless steel shot or glass bead blasting to produce uniform matte surface finishes across unmachined cast areas.
• Pressure & Leak Testing: 100% pneumatic underwater testing (up to 6 bar) or hydrostatic testing (up to 300 bar) for pressure-retaining components.

Quality Control and Inspection

Quality verification covers raw material receipt, melt chemistry, cast integrity, heat treatment, and finished part dimensions.

Quality Inspection Gates
• Incoming Raw Material: Chemical verification via Optical Emission Spectroscopy (OES) prior to tapping.
• In-Process Quality Control: Non-Destructive Testing (PT / RT) and microstructure analysis post-heat treatment.
• Final Inspection: 3D inspection using CMM, thread gauging, and hydrostatic pressure testing.

Chemical & Metallurgical Testing
• Optical Emission Spectroscopy (OES): Chemical composition verification per heat prior to pouring, ensuring compliance with specified ASTM grade limits.
• Mechanical Testing: Tensile strength, yield strength, elongation, and Charpy V-notch impact testing at ambient or sub-zero temperatures.
• Hardness Testing: Brinell (HBW) and Rockwell (HRC/HRB) measurements recorded post-heat treatment.

Non-Destructive Testing (NDT)
• Penetrant Testing (PT): Surface defect inspection in accordance with ASTM E1417 / ISO 3452.
• Radiographic Testing (RT): X-ray inspection for internal shrinkage, gas porosity, and inclusions in critical structural zones per ASTM E1928 / ISO 5579.
• Magnetic Particle / Ferrite Measurement: Ferrite contents in duplex steels measured via Ferritscope to verify phase balance.

Dimensional & Geometric Inspection
• Coordinate Measuring Machine (CMM): Hexagon 3D CMM equipment with automated touch-probe systems for verifying GD&T specifications (positional tolerances, concentricity, runout, surface profile).
• Optical Profile Projectors & Air Gauges: Fast, repeatable verification of high-volume threaded ports and bore diameters.

OEM and Custom Manufacturing

We operate as an OEM/ODM manufacturing partner, providing rapid turnaround from initial technical drawing review to serial mass production.

OEM Development Cycle
• Drawing / 3D Model Review: Engineering inspection of CAD data.
• DFM Engineering Optimization: Porosity prevention and gating optimization.
• FAIR / PPAP Approval: Initial Sample Inspection Report and CMM layout.
• Mass Production & QC: Serial casting, CNC machining, and 100% quality verification.

Engineering Workflow
• DFM (Design for Manufacturability) Review: Our engineering team analyzes your 3D models (STEP, IGES, X_T) to optimize wall transitions, draft angles, gate locations, and machining allowances, reducing weight and casting defect risks.
• Rapid Prototyping: 3D-printed wax or PMMA patterns are used to deliver functional prototype metal samples within 2 to 3 weeks without hard aluminum tooling.
• Tooling & Sample Production: Aluminum dies are CNC-machined for production runs. Initial sample inspection reports (ISIR) and 3D CMM layout data are provided for first-article approval.
• PPAP Documentation: Production Part Approval Process (PPAP Level 3) packages available upon request, including control plans, FMEA, process flow diagrams, and material trace certificates.

What Buyers Should Provide for an RFQ

Including complete technical requirements in your initial inquiry accelerates quote turnaround and ensures accurate mold, material, and machining pricing.

RFQ Data Checklist
• 2D Drawings: PDF/DWG format including critical tolerances, thread specs, and surface finishes.
• 3D CAD Models: STEP, IGES, or X_T file formats.
• Material Specification: Specific grade standards (such as ASTM A351 CF8M / SS316).
• Order Volumes: Initial sample quantity, estimated batch size, and total annual volume.
• Critical Tolerances & GD&T: Key fitment dimensions and functional interfaces.
• Surface Treatments: Requirements for passivation, electropolishing, or shot blasting.
• Quality & NDT Requirements: Radiographic inspection percentages, pressure testing pressure (PSI/Bar), or CMM layout reports.
• Logistics & Delivery: Incoterms (FOB, CIF, DDP) and custom packaging specifications.

Frequently Asked Questions

Q: What is the standard linear tolerance capability for as-cast surfaces?

A: As-cast dimensions conform to ISO 8062-3 Grade CT4 to CT7. For a casting dimension between 10 mm and 50 mm, as-cast tolerance ranges between +/-0.2 mm and +/-0.5 mm. Tighter requirements are achieved through secondary CNC machining.

Q: How do you prevent subsurface porosity in critical sealing zones?

A: We use ProCAST thermal simulation software during gating design to predict shrinkage hotspots. Additionally, clean silica sol binder systems, vacuum-assisted pouring options, and 100% X-ray (RT) and Liquid Penetrant (PT) inspections ensure subsurface integrity prior to machining.

Q: Can you provide material test reports traceable to EN 10204 3.1?

A: Yes. Every production batch includes an EN 10204 3.1 Inspection Certificate detailing heat chemistry via Spectrometer (OES), mechanical tensile test results, hardness values, and heat treatment charts.

Q: What is the typical lead time for tooling, samples, and production runs?

A: Aluminum Tooling & First Article Samples: 3 to 4 weeks.
Mass Production: 4 to 6 weeks following sample approval.
Emergency Prototype Runs: 10 to 14 days using 3D-printed patterns.

Q: What are the primary cost drivers in stainless steel investment casting?

A: Key cost factors include alloy grade selection (316L and Duplex cost more than 304 due to Nickel and Molybdenum content), part weight, cluster gating yield, complexity of internal cores, total machining time, and NDT requirements (such as 100% X-ray vs. spot check).

Machined Stainless Steel Castings