In this blogpost we will examine powder metallurgy vs. casting, more specifically investment casting. There are different ways to produce metal parts. In development of metal parts, it should be considered which production route is the best for the specific part in question. In this section we will focus on powder metal compared to investment casting.
First a short description of the 2 processes:
Powder metal process: Powder mix which is compressed at room temperature to a green body and then sintered below the melting temperature in a furnace.
Casting process: Metal melt is poured into a mold and then cooled down and solidified.
The main difference in the 2 processes is that powder metal parts are produced below the melting point of the material where the casted parts are produced at the melting point of the material. In both cases there are dimension changes due to the solidification of the casting and the diffusion between particles of the powder metal.
The differences between powder metal and investment casting
|Powder metal||Investment casting|
|Base material||Powder mix.||Metal melt.|
|Part shape||Net shape or near net shape. Sizing is needed for narrow tolerances.||Near net shape. Post machining is normally needed where narrow tolerances are required.|
|Part design||Uniaxial design.||Complex design.|
|Part size||Typical smaller parts from few grams up to round 300g.||Typical bigger parts from 30g up to several kilos.|
|Tolerances||From microns to tenths – typical ±0,1 mm.||From tenths to millimeter – typical ±0,5 mm.|
|Materials||Ferrites, steel, stainless steel, bronze, soft magnetic.||Steel, stainless steel.|
|Process route||Powder pressing, sintering and
|Wax parts, pattern tree assembly, shell parts, steel pouring, shell removing, cutting and cleaning.|
|Waste||Nearly no material waste.||Recycling of pouring cup, runner and gate material. Shell material is waste.|
|Cost||High tool costs – low part price.||Low mold cost – higher part price.|
|Volume||Typical medium to high volumes.||Typical small to medium volumes.|
The powder metal method, also known as the sintering process, needs a pressing tool to make the shape of the parts in production. The pressing tool is produced by machining, hardening, electro erosion, grinding and polishing and the material used is typically high-speed steels and tungsten carbides. The number of tool parts depends on the complexity of the parts to be produced. As a minimum a die and 2 pistons are needed but can be up to 6 pistons with internal cores making internal holes and splines. The process is a uniaxial pressing process where the powder is compressed to a fragile green body. The green bodies then go through a furnace, typical belt furnace, to obtain the properties of the material. After the sintering the parts will typical be de-burred to remove the burrs from the edges.
This casting method, also known as lost wax casting or precision casting, begins by producing a wax pattern with the exact same shape as the finished product. This takes place in a metal mold. The cast wax pattern is mounted on a so-called pattern tree and then dipped into a ceramic slurry which produces a hard shell around the pattern. The wax is then heated and removed from the ceramic mold which can now be used for casting of the steel units. The finished steel units are cut off from the pattern tree for further processing. Note that investment casting is for steel, not iron.
What is the best processing method for you?
At FJ Industries we have decades of experience manufacturing metal parts for various industries. Our specialists are happy to share their expertise, so contact us to find the right solution for your component.