Preventing Investment Casting Defects
Investment casting dates back to the late 1800’s, but not all investment cast parts are created equal. Investment casting is a pillar in industrial part manufacturing, known for producing high-volumes of parts that require a near-net shape, an even surface finish, and dimensional accuracy. Investment casting defects are preventable with the right investment casting partner and foundry.
The Investment Casting Process & Benefits
The process includes pouring liquid metal into a ceramic, plaster, or plastic shell mold, which forms around a wax pattern. The component then goes into a furnace where the wax melts. Once the wax is removed, metal is then poured into the shell, creating the cast. Investment casting delivers precision parts through a six-step process. Using this casting provides many benefits.
Investment Casting Benefits
Why use investment casting? Here are some of the advantages:
- Size variety: Most investment castings are small, but there is the opportunity to produce very large ones if necessary.
- Versatility and intricacy of shape: The cast creates consistency with very close tolerances. Multiple components can combine into a single casting, and it’s a good alternative to welding or fabricating.
- Smooth surfaces: These castings don’t have a parting line since it’s only one mode. Because of this, the parts have a fine and consistent surface.
With this level of precision, the process has many applications. But those using it need to know about the possible defects and how to prevent them.
Common Investment Casting Defects
There are four main categories of investment casting defects:
Hot Tear or Shrinkage Cracks
This defect occurs when the shell mold restricts the molten metal from contracting during cooling or solidification. These imperfections materialize as jagged cracks. Experienced foundries eliminate these defects by reducing the “strain rate” by preheating molds, using venting holes, and choosing the right type of metal for the project.
Inclusions
This issue describes small, round, or irregular craters and results from foreign on-metallic particles in the casting. They may also look like depressions in a variety of shapes and sizes. A reputable metal casting foundry will ensure that all slag particles are removed from the molten metal prior to pouring it into the mold cavity.
Misrun
If the molten metal doesn’t completely fill the mold cavity, this defect can happen. It’s most attributable to the shell being too cold, the fill rate being too slow, or a faulty design mold. Work with a foundry that is known for delivering quality mold making services to avoid misruns.
Porosity
This defect includes the formation of bubbles within the investment casting during the cooling phase. Liquid materials contain dissolved gas, and, when expelled, these bubbles form. With the right equipment, investment casting foundries can prevent porosity defects.
Preventing Defects: Using Ultrasonic Flaw Detectors
The investment casting process is complex and rife with opportunities for irregularities. Reputable foundries will invest in the best equipment and technology to analyze production quality and accuracy.
Ultrasonic flaw detectors are modern-day reflectoscopes used to identify defects in prototypes. It can discover various defects, including cracks, inclusions, voids, shrinks, porosity, flaking, and other subsurface imperfection.
How a Flaw Detection Works
Pulse echo instruments can work in two ways: straight beam testing and angle beam testing. Straight beam testing detects flaws parallel to the plane of the part. Angle beam testing offers more detail. It can identify defects at angles and other areas not reachable by straight beam testing. It can also find issues in the parent metal from welds.
Flaw detection is important for every industry, but it’s critical for aerospace investment castings and automotive casting services.
Quality Equipment Is a Top Priority for KICastings
When choosing a foundry for investment casting, make sure they have a defect prevention process. In our investment casting services, we use a variety of equipment, including an ultrasonic flaw detector, to prevent defects. With our own dedicated mold shop, our customers receive quality, accurate, and consistent productions.
Get a quote for your investment casting project today:
