Number
types of letters, sign or pattern are used on plastic injected parts, generally
for purposes of identification such as trade mark or decoration. Fig 1.a shows
raised letters. Raised letters are often less costly than depressed letters,
because the raised letters are molded from letters recessed in the mold cavity,
while depressed letters require the mold steel to be cut all around them Fig 1.b.
Fig 1.c is better design. The letters are
embedded within the injection mold in the form of blocks (Fig 1.d) , easy to process
mould and plastic pieces of the mark or symbol not easy to be wear.
Fig 1 Letters design
Hobbing
of the mold, wherever possible, will often aid in reducing the total cost of
making raised letters on the injection mold. The letters in this case would be cut into
the hob, and the hob itself would be forced into a softer steel, after
hardening, would become the mold. Raised decorations generally allow some savings
in molding. Many types of letters and numerals, as well as some types of
decorative design, can be raised in the cavity by hobbing.
A
raised letter is visible if it is only 0.003 in. high. Letters normally 1/64 in.
high are easily read, because they catch sharp highlights. Letters that are
over 0.030 in. high should be tapered and have fillets at the base. Raised
letters can be decorated or painted by roll coating.
The
cost of applying molded-in letters to a plastic injected parts will vary. Tab 1
gives comparative costs for raised, depressed or photo etched letters that are
made by either a machined or hobbed cavity.
Tab 1 Comparative tool cost
of producing letters
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