Investment Casting (精密鋳造)

Reference sectionInvestment Casting (精密鋳造 / seimitsu chūzō)

Quick look

• Process: Lost-wax casting—a wax pattern is coated in ceramic, the wax is melted out, and molten steel fills the void.
• Key benefit: Complex, near-net shapes achievable without expensive forging dies.
• Cost position: Lower tooling investment than forging; moderate per-unit cost.
• Where used: Taiwanese and Chinese production facilities, some handle and finger-rest components on otherwise forged scissors.

Why it matters

Investment casting (also called lost-wax or precision casting) lets manufacturers produce complex three-dimensional shapes that would be difficult or impossible to stamp from flat sheet. Ergonomic handle curves, integrated finger rests, and decorative details can all be cast in a single pour rather than machined from a forged blank.

The limitation is structural. Cast metal solidifies from a liquid state, and as it cools it can trap microscopic gas pockets (porosity) and form a coarser, less directional grain structure than forged or even rolled steel. For scissor blades, that means lower fatigue strength and a higher risk of micro-fractures at the cutting edge under repeated stress.

Process routeHow it works

1. Pattern creation: A master scissor shape is tooled, and wax replicas are injected from the master mold. Multiple wax patterns are assembled onto a wax “tree” for batch processing.
2. Shell building (鋳型 / igata): The wax tree is dipped repeatedly in ceramic slurry and coated with fine refractory sand, building up a hard shell 5-10 mm thick.
3. Dewaxing: The shell is heated in an autoclave or flash-fired to melt and drain the wax, leaving a hollow ceramic mold.
4. Pouring: Molten steel—typically heated to 1,550-1,650 °C—is poured into the ceramic shell under gravity or vacuum.
5. Cooling and knockout: After solidification, the ceramic shell is broken away (knocked out), revealing the rough castings.
6. Cut-off and finishing: Individual scissor blanks are cut from the tree, gate stubs are ground off, and the blanks proceed to heat treatment and grinding.

Trade-offs

• Pros: Complex shapes in a single step, low die/tooling cost compared to forging, good dimensional accuracy, suitable for small batch runs.
• Cons: Porosity risk (gas pockets weaken the metal), coarser grain than forged steel, lower fatigue life, and slower cooling can produce larger carbide clusters. Controlling porosity is the foundry’s job, which is why inspection practice matters to the result.

DetailWhere you will find cast scissors

Full investment-cast scissors are common in the economy-to-mid tier, particularly from Taiwanese and mainland Chinese factories. Higher-end manufacturers sometimes use casting selectively—for ornate handles, integrated finger rests, or ergonomic grip sections—while forging the blade portion separately and welding the two together.

DetailWhat to ask a manufacturer

If a scissor has unusually intricate handle sculpting at a moderate price, it may be cast. Ask whether the blade and handle are made from the same process. A forged blade welded to a cast handle is a reasonable engineering compromise; for a fully cast blade, the sources’ retail commentary holds that cast shears generally do not hold an edge as long as forged ones, while heat treatment and inspection still decide the finished result.

Source trailSources

1. sint.co.jp—Manufacturing Reference (Japanese)
2. Investment casting—Wikipedia

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