Flash

Flash refers to the unexpected occurrence of the liquid alloy/metal in an unpermitted die area. Places under the slides, parting lines, ejector pin sides, etc. shouldn’t expect molten flow. However, this die-casting operational defect invades those places with liquid alloy/metal.

Flash is an excessive layer of metal coming out of the mold to settle on the final casting. The scalding metal liquid inherits the properties of fluidity, pushing some of the molten alloy/metal out of interior segments to cause flash.

The formation of flashes during a high-pressure die-casting process can be very bothersome for manufacturers. This article briefly sheds some light on its causes, effects, and prevention.

Causes of Flash

Temperature control, mechanical adjustments, metal pressures, and machine-die conditions are the leading sources of die-cast flash. These factors eventually call in the troublesome defect.

1. Poor Die Sealing –Compromised die fitting at operational temps due to uneven heating at different casting phases causes random expansion. And the increased internal pressure pushes some liquid outside, triggering a flash.
2. Improper Temperatures –Operating temps going beyond the normal/recommended range is a prime factor of flash. Excessive temperature without revising the cast design factors often leads to this defect to a significant extent.
3. Metal Pressure –Going beyond the recommended maximum static pressure intensifies shrink porosity. It eventually contributes to developing high inner pressure to send out the liquid flow to trigger flash on casting surfaces.
4. Incorrect Machine Setup –Any imbalanced adjustment in the setup initiates mechanical distortion. The subsequent failure of processing accuracy leads to flash over a wrong arrangement of tie bars, platens shoes, and toggle links.

Effects of Flash

The flash formation is somewhat continuous as it accumulates at the breaching die spots. And this pileup triggers some eventual problems for die-casts, like –

• Safety Concerns –Extreme and large-scale manufacturing processes may see flash shooting. The hot semi-solid/semi-liquid throws can burn skins and light machinery.
• Dimensional Problems –The flash forming under the slides accumulates to prevent full seating. This affects the settling dimensions to distort the desired size.
• Compound Damage –Even the final product made of metal/alloy can be damaged. Parts like horn pins can experience ruptures, slide carriers, keyways, and even the core.
• High Contamination –The flash-accumulated trash under the dies gets contaminated with other impurities. And the material becomes completely obsolete for any remake or remelt.
• Poor Productivity –The accumulation over several hours can significantly drop the quality and usability. Even the restart starts to take more time and effort over extensive flash.

Prevention of Die Cast Flashs

Cautious implementation is essential to avoid the formation and accumulation of flash in castings. The following ones can effectively help confront the challenges concerning flash defects –

1. Proper Temp Range –The recommended operating temp range is (1200°F – 1250°F) ± 10°F or (650°C – 675°C) ± 6°C for aluminum and magnesium. It’s 800°F ± 5°F or 426°C ± 3°C for zinc. Exceeding these ranges is applicable upon adjusting the dependent parameters. However, the true challenge lies in maintaining a stable temperature condition.
2. Precise Machine Locking –Perfect machine setup remains crucial in controlling nearly all processing-related defects. Balancing the tie bar strain based on the applied load can help set an accurate adjustment. All major bends, roughness, wear, loose connectivity, excessive tear, etc., must be avoided for optimized casting mold.
3. Low Metal Pressure –Keeping the static metal pressure to a minimum reduces flash tendency. The limit counts 3000psi – 5500psi for aluminum, 3000psi – 4000psi for magnesium, and 2000psi – 4000psi for zinc. However, pressure adjustment often varies from machine to machine, requiring a proper and calculated review to set the allowable one.
4. Exact Cooling Disposition –An accurate thermal analysis with the appropriate cooling system placement prevents the die expansion. It’s an associated consideration with even temperature across the casting. Nonetheless, the analysis should provide detailed insight into the exact mold size for a fit. Good maintenance will also lessen the flash.
5. Exhaust of Slag Bag –An advanced design concept adopts the integration of slag bag exhaust. It helps increase the sealing surface for low-temp and low-pressure casting. Therefore, a relatively small amount of flying flash occurs in the process. Also, deductive energy consumption is another advantage to reduce costs without compromising the quality.

Sunrise Metal found only 20% of the accumulated flash is usually recoverable from the extensive die-casting experience. The overflow adds weight to the system, altering the desired physical properties. Controlling every step in the casting process as per the targeted outcome can minimize the issue.