Surface Finish of Lost Foam Cast Parts
The surface finish of lost foamed parts are excellent, as a permeable refractory coating is applied around the smooth foam pattern, resulting in a surface finish in the 60 -250 RMS range. In cases where a cosmetic surface finish is required, surfaces can be targeted to maintain an exceptionally smooth finish.
Because of the absence of a core in the product part, it is virtually free of burr and only the gate and gate risers need to be removed. This is done by using a press machine or grinding techniques.
Casting Surface Finish Standard
Lost foam casting is able to achieve an excellent as-cast surface finish, well within the 60 to 250 RMS range. Below, a comparison of the different casting processes and their as-cast surface finishes
Metal Casting Process
60 - 250
20 - 120
60 - 200
120 - 300
Types of Surface Finishing Processes
ChinaSavvy offers a variety of heat treatments for lost foamed parts, including:
- Quenching and Tempering
- Diffusion Annealing
- Stress Relieving
- Austenizing Annealing with Quenching
Used in order to gain an uniformity in grain size throughout the alloy used. This process produces pearlite, bainite and sometimes martensite, delivering a stronger and harder steel, but with less ductility.
Quenching and Tempering
Quenching is the process of rapidly cooling a metal (done in order to produce a martensite transformation, resulting in a harder metal in ferrous alloys and a softer metal in non-ferrous alloys). Quenched parts now need to be tempered - a process by which the metal is heated to lower than its critical temperature, resulting in a better 'toughness'.
The metal is steadily heated to a very specific temperature after which it is cooled at such a rate (generally at a slow rate) as to produce a refined microstructure. Annealing is used in order to achieve the following:
- Soften a metal for use in cold working processes.
- To improve the metal's machinability.
- To enhance specific properties, such as the materials electrical conductivity.
This is a heat treatment process by which metal is treated in order to promote homogeneity through the diffusion of components. Also known as homogenizing annealing, it is observed in heavy plain carbon steel castings, ignots and high alloy steel castings
In this process, the metal is heated to above its upper critical dimension, held at this specific temperature for a period of time, and then slowly cooled. This enables segregated zones to be eliminated and chemically homogeneous steel is obtained, as a result of diffusion.
The removal or reduction of the internal stresses created within the metal. This is done by heating the metal below its lower critical temperature, and then allowing it to cool uniformly
Austenizing Annealing with Quenching
Austenizingis the process of heating the metal above its critical temperature, keeping it there for a period of time - long enough for transformation to occur. If this metal is then quenched at a fast enough rate, it will transform the austenite formed into martensite, effectively hardening the metal.
Martensite is formed through the soaking of a metal at high temperatures above the recystallization phase, followed by a rapid cooling process.
Martensite: Very hard and brittle, it is a steel which consists of a distorted, body-centered tetragonal crystal structure.
Austenite: Is also known as gamma phase iron, and is metallic, non-magnetic allotrope of iron or a solid solution of iron with a n alloying element present, and exists above the metal's critical temperature.
Bainite: A combination of cementite and ferrite in ferrous metals. It is harder than peralite and contains needle-like grain structures. Bainite requires an initial rapid cooling followed by a gradual cooling process.
Pearlite: Also a combination of cementite and ferrite, pealite grain structures very much resembles human fingerprints. A good example of where uniform pearlite is seen (at room temperature), is in steel with exactly 0.77% carbon
Our machine shop is equipped to deliver machining services up top standard with ISO 9001specifications, our capabilities include milling, turning, drilling, CNC lathes, CNC grinding and more. By being able to deliver machining services as well as welding services, we are capable of delivering parts that are ready for installation.
To learn more about our CNC Marching Services, please visit our CNC Precision Machining page.
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Further Suggested Reading:
- How Lost Foam Casting Works
- Metals that can be Lost Foamed
- Lost Foam Casting Tolerances
- Problems of Surface Carbon in Lost Foam Cast Parts