Investment Casting Process | Yujiaxin Tech

Investment Casting Process: Nine Steps from Wax Pattern to Finished Part

How does an internal valve body with 2 mm walls form in a single shot with no parting line? That is what the investment casting process delivers. It builds an exact wax replica, coats it with ceramic layer by layer, melts the wax out, fires the shell hard, then fills the cavity with steel above 1500 °C.

Yujiaxin Tech runs this sequence on a silica sol line as nine controlled steps. Below we cover what each step does, its key control parameters, and the defects that appear when it drifts, with a process-to-defect map at the end.

Key takeaways

• As-cast tolerance lands around CT4 to CT6 and surface roughness reaches Ra1.6 to Ra6.3; tighter accuracy needs secondary machining.
• Typical ranges: wax injection 70 to 75 °C, shell firing 800 to 1100 °C, stainless pour near 1600 °C.
• The investment casting process runs nine steps:

1. Wax
2. Assembly
3. Shell
4. Dewax
5. Firing
6. Pouring
7. Knockout
8. Post-processing
9. Inspection

• Gas porosity, shrinkage and inclusions cannot be fully eliminated; process control only lowers their rate.

Investment Casting Process Overview: Why Lost Wax Suits Complex Parts

The investment casting process is also called lost wax casting, and its core idea is a meltable pattern. The wax disappears at the end, so the ceramic shell becomes the mould and needs no draft angle or parting line. Parts with internal cavities, deep holes or thin walls often come out close to drawing in one shot.

By our process standard, as-cast tolerance lands around CT4 to CT6 and roughness reaches Ra1.6 to Ra6.3, with tighter accuracy handled by secondary machining. To place it among the wider shop floor, see the six precision parts processes at Yujiaxin Tech. Third-party data from 360iResearch on the investment casting market covers the market size.

Step 1 · Wax Pattern: Injection, Dies and Wax

Step one of the investment casting process is the wax pattern. Molten wax is injected into a metal die to copy the part shape, then each pattern is trimmed. Medium-temperature wax runs at about 70 to 75 °C, injection pressure rises with wall thickness, and the blend is usually paraffin with stearic acid. Watch for distortion, flash and surface porosity, often from wax that is too hot or short hold pressure.

Step 2 · Assembly and Gating System Design

Several patterns are welded onto one sprue to form a wax tree, together with gates, risers and the sprue itself. Tree density, gate cross-section and riser position set the fill path and feeding ability. Short shots, incomplete fill and poor feeding trace back to undersized gates or an over-packed tree.

Step 3 · Shell Building: Slurry, Stucco and Layered Drying

The tree is dipped repeatedly in silica sol slurry and stuccoed to build a ceramic shell. Stucco grit coarsens with each layer. The shell runs 4 to 10 layers, 5 to 7 mm thick, and the drying room holds 20 to 25 °C at 50 to 70 % RH. Shell cracking, delamination and rough surfaces follow weak drying or unstable slurry viscosity.

Step 4 · Dewaxing: Autoclave and Flash Fire

The investment casting process removes the pattern here, so the shell goes into an autoclave and the wax melts out for recovery. Residual wax burns off in a flash fire furnace. The autoclave runs near 120 °C at 6 to 8 bar. Incomplete dewaxing, shell swelling and run-out during pour link to pressure rising too fast or a shell that is too weak.

Step 5 · Shell Firing: Strength, Permeability and Preheating

The hollow shell enters the firing furnace to burn off residual wax and raise strength and permeability. Firing runs 800 to 1100 °C with several hours of soak, and the shell is preheated close to pouring temperature before the pour. Watch shell strength and permeability here; inclusions start at this stage too. The same temperature and atmosphere logic appears in the powder metallurgy sintering process: temperature and atmosphere control.

Step 6 · Melting and Pouring: Vacuum or Gravity

An induction furnace melts the charge, a spectrometer checks chemistry, and the metal is poured into the hot shell. Yujiaxin Tech sets pour windows by grade, with stainless near 1600 °C while 304, 316L and 42CrMo each hold their own melt and pour range, and shrinkage compensated by grade. Porosity, shrinkage, cold shuts and inclusions are the four to guard against. Alloy chemistry and solidification behaviour are documented by ASM International.

Step 7 · Knockout, Sand Removal and Cut-off

The shell is broken by vibration or hammering, cleaned by water blast, and the gates are cut and ground flush. Cut position follows the gate root allowance, and grinding must not touch functional faces. Cutting damage and leftover shell cause the most rework here.

Step 8 · Post-processing: Heat Treatment, Machining and Finish

Parts are solution treated, aged or quenched and tempered by grade, then ground, shot blasted or passivated, with critical mating faces finished by CNC. Grade 304 is solution treated at 1050 to 1100 °C with a water quench; 316L sits at 1080 to 1120 °C; 42CrMo follows a quench-and-temper route. Heat treatment usually shows up as distortion or uneven hardness. Read more on powder metallurgy post-processing: heat treatment and finishing, and see finished forms in precision metal component product lines.

Step 9 · Inspection: Dimensions, Chemistry, Internal Defects

A CMM checks key dimensions, a spectrometer verifies chemistry, and X-ray or dye penetrant finds internal and surface defects. Dimensions are judged against drawing tolerance and ISO 8062 grades, with hardness and penetrant results recorded together. Cross-checking across methods reduces escape risk. Quality and inspection control at Yujiaxin Tech covers all of these checks.

Process-to-defect Map: Where Porosity, Shrinkage and Inclusions Originate

Placing investment casting process defects against their step speeds up troubleshooting. The table below maps nine steps to their defects and countermeasures.

Investment Casting Process FAQ

Why use medium-temperature wax? Its melting point is moderate and flow is good, so it fills thin walls and dewaxes cleanly.

Why dewax with steam instead of hot water? Steam heats the whole shell evenly, which limits cracking from wax expansion and recovers the wax.

What firing temperature is right? By our process standard, 800 to 1100 °C, set by alloy and shell system.

How is pouring temperature set? By grade, near 1600 °C for stainless, balancing fill ability and grain control.

How is shrinkage compensated? Measured shrinkage for the grade is added to wax and die dimensions.

Conclusion: How the Investment Casting Process Sets Part Consistency

Consistency in the investment casting process comes from stable parameters at all nine steps. Wax temperature, slurry viscosity, dewax pressure, firing temperature and pour temperature each shift the defect rate when they drift. Yujiaxin Tech manages these parameters under ISO 9001 and IATF 16949 aligned systems, with GJB 9001C for defence work.

Defects cannot be fully eliminated, and as-cast tolerance is bounded by ISO 8062 grades, so tighter accuracy still needs secondary machining. Need an executable parameter plan for your part? send your drawing and process requirements to our engineering team.