The various factors from the plunger tip, plunger gap, shot sleeve, temperature and other factors are important to get right to avoid scrap.
In this article, Paul Robbins, with Castool Tooling System, identifies multiple methods to improving die casting processes of injecting molten alloy to the die cavity.
(Illustration provided by the Hill and Griffith Company)
Factors to consider
The best opportunities for improvement is found in the delivery of the alloy to the die. Both the shot sleeve and the plunger offer opportunities for improvement. Read the entire article here, on the Castool.com site.
The Moment of Casting
• The plunger tip and shot sleeve are the most critical in the die casting process. A vacuum seal is vital and should remain intact at all times throughout the die casting process.
Maintaining the Gap
• Avoid flash or blowby by keeping the max gap between the plunger tip and shot sleeve under 0.004".
• Metal expansion occurs when heated. Even with this knowledge the gap should remain below 0.004". Controlling the Plunger Tip
• Plunger tips are exposed to more heat than the sleeve
• Plunger tips of beryllium copper are better than steel due to half of their coefficient of thermal expansion
• Manage plunger tip expansion with proper coolant
• Construction of new plunger tips allow for improved coolant through the shot rods where a turbulent flow is generated to maximize heat transfer: Steel wear rings allows for expansion and contraction, The beryllium copper plunger doesn't wear, The rings are flexible and allow for continuous contact with the wall to the shot sleeve
A High-Strength Plunger Tip
• The Allper high-strength plunger tip was designed for production of large, complex castings
• Engineers designed this plunger to remain stable and maintain required gap with the shot sleeve, but remain strong enough to handle the extreme pressures and impact of short shots
• Cycle times and cost of consumables is reduced with these plungers Cooling the Shot Sleeve
• Typically, the variance in temperature between the bottom and top of the shot sleeve can be 200-300°F. This cause wear to the tip and sleeve. Cool the bottom of the shot sleeve so it doesn't exceed 100°F
Cooling plunger tips
• The pour end of the shot sleeve is the hottest
• Focus plunger tip coolant on the pour end
• Consider a reusable pour-end cooling jacket Porosity and Vacuum
• Porosity is caused by: turbulence of the alloy as it is forced at high pressure into the die cavity, complex shapes of casting molds, air or gas trapped in the metal
Causes of Porosity
• Very thin castings
• Air or gas inclusions
Impacts of Porosity
• Affected mechanical properties
• Acts as a stress concentrator allowing cracks
• Customers discover the issue after processing. This builds dissatisfaction.
• Solve porosity through efficient vacuum systems
• Draw a vacuum in the shot sleeve and mold cavity before injection
• This allows alloy to flow freely into blind recesses and metal to merge without forming shuts
• Additional benefit is reducing force required on the plunger
Read the entire article here, on the Castool.com site.
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