The use of screws on its new vacuum cleaners

Challenging undercut profile simplifies die-cast headlamp cover for vacuum cleaner.

Kirby Co. recently redesigned the aluminum die-cast headlamp cover for its line of vacuum cleaners. The previous design relied on two screws to hold the cover in place. The new design incorporated a hook that would allow the cover to snap in place. The change would speed final product assembly, eliminate two screws, and make cleaning and repair of the vacuum cleaner easier.

However, the hook feature would require the precision casting of an undercut profile, and building a die to produce aluminum die-cast parts with an undercut profile typically presents many problems. Costly and time-consuming machining and other secondary operations on the undercut cast parts is usually necessary.

Using angled, moving lifters to create the undercut is straight-forward and routine with plastic injection molds, but there are problems when using moving parts in a casting die. Casting dies are subject to much greater heat, stress, dirt and abrasion, than plastic injection molds. Therefore, the mechanisms used in casting dies must he designed to minimize die maintenance and downtime.

Pro Mold and Die of Schaumburg, Ill., with 25 years of experience in building molds with undercuts requiring slides and lifters, created an innovative solution for Kirby. Drawing upon established and proven design concepts used in the plastics industry, Pro Mold and Die designed an undercut profile for use in the hostile die-casting environment. Features were incorporated that would assure consistent movement from shot to shot and minimize die maintenance.

When the prototype die was delivered to the die caster for tryout, there were concerns about how the die would function with an angled lifting section, as well as concerns about the durability of the insert and lifter. The design concept was tested using one cavity of a four-cavity production die.

Anticipating problems, three days were scheduled for testing. The die was set-up in the morning of the first day and before noon over 100 parts were successfully produced. Then on the second day, 500 parts were cast without a problem. The angled lifting mechanics worked to perfection. After studying the results, Pro Mold and Die began building a four-cavity die for ongoing production.


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