Comparing Metal Fabrication Methods

Investment Casting vs. Powder Mettalurgy

The powdered metal process is simple, but requires many different steps. First, the premixed metal powder is compressed in a mold by a high powered press, providing its shape and increased density. This is the “green state” — the parts, called compacts at this stage, are shaped but not technically solid. Next, compacts are fed through a sintering oven, which heats them to a temperature just below the melting point of the metal. This allows the metal particles to fuse together without melting and thereby keeping their shape.

Additionally, parts made from powder metallurgy can be very dense, which can be good or bad depending on applications, but controlled porosity can also be achieved. Mold creation for powder metallurgy is expensive and, though complex parts can be manufactured, there are limits to geometry that investment casting does not encounter. In comparison, Investment casting allows for ferrous and non-ferrous metals (aluminum, brass, bronze, etc) to be cast.

Investment casting methods can cut down labor time and offer one continuous part that provides a consistently clean look to the end user. Additionally, the reduction of labor time reduces lead times and the overall cost.

Investment Casting vs. Metal Stamping

Metal stamping is a more primitive metal shaping method. Metal stamping is performed when a sheet or strip of metal is delivered into a hydraulic or mechanical press which uses a die and high pressure to shape the metal fabrication into the desired parts.

A negative aspect of metal stamping is that there is not much flexibility in the shape and thickness of the sheet metal, so the greater the complexity of the part, the more additional components that must be added to the metal stamping process, which raises the cost. Metal stamping also produces a lot of waste, as there is a significant amount of unused scrap metal that results from a stamping project, much more than with investment casting methods.

Investment castings reduce waste, labor time, and machine time that creates a costly metal fabrication process.  Investment casting can also incorporate varying metal thicknesses and blind holes.

Investment Casting vs. Metal Forging

Forging is the metal fabrication process in which either hot or cold material is pressed with a massive hammer to push the material into the desired shape. This process requires extremely expensive tooling that often needs to be replaced. While the strength of a part is slightly better with forgings, the heightened level of danger inherent to forging, along with specialty equipment, drives the cost of forgings higher. Many forgings need to be heavily treated after completion for hardness, as well as to be machined due to lack of tolerance holding.

Investment casting methods require less expensive equipment, and is inherently less dangerous, allowing costs to remain lower. Investment castings also can hold much tighter tolerances, reducing the amount of machining typical to forgings.

Investment Casting vs. Permanent Mold

Permanent molds consist of mold cavities machined into metal die blocks and designed for repetitive use. The process lends itself very well to the use of expendable cores and makes possible the production of parts that are not suitable for the pressure diecasting process. However, since this process has a higher cost of tooling it requires a higher volume of castings to make economic sense. Permanent molds are also generally limited to the production of somewhat small castings of simple exterior designs.

Investment casting methods are suitable for large or small quantities of parts and are suitable for most ferrous/non-ferrous metals.

Investment Casting vs. Plaster Molding

Plaster molding is a casting process with similarities to sand casting. Instead of using sand in the process, a mixture of water, gypsum and strengthening compounds are used. Plaster molding delivers a smooth, as-cast finish, but it requires a minimum of a 1-degree draft. It is also a more expensive process when compared to permanent mold and sand casting. In addition, this method may require the frequent replacement of plaster molding materials.

Investment casting offers a flexibility in design and is a useful process for casting alloys that are difficult to machine. Investment casting methods also allow for complex shapes, intricate core sections, finer details and thinner walls.

Investment Casting vs. Sand Casting

Sand castings are made by creating a negative in a bed of sand to create the cavity for casting. A sand shell creates a rough exterior to castings. Typical surface finish of sand castings are 250 Ra as cast, and need extensive work afterwards to create a surface finish that is acceptable in most applications. Sand castings can also not hold as tight of tolerances as Investment Castings, and will likely need more machining than an Investment Casting.

Investment casting uses a ceramic mold that can produce a much smoother finish, typically averaging 125 Ra surface finish as cast. Investment castings also greatly reduce the amount of machining that will be required after casting by holding a .005”/inch tolerance for the majority of the applications.

Investment Casting vs. Metal Fabrication

Metal fabrications are metal structures produced by cutting, bending, and welding multiple pieces of material together. This method produces increased steps, and results in a higher scrap rate. The increase in wasted materials, along with increased labor time, causes metal fabrications to be expensive and time consuming.

A fine-tuned Investment casting method can cut down labor time, while providing a continuous part that delivers a clean and consistent look to the end user. The reduction of labor time also reduces lead times and all applicable costs. Casting consistency can also lead to lower scrap rates, which can lower your overall metal fabrication costs even further. 

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