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Abstract The working conditions of the plastic mold are complex. They touch directly with the plastic, withstand the pressure, temperature, friction and corrosion and so on. The main failure modes of the plastic mold surface wear, deformation and fracture. The main failure reasons depend on working conditions,mold materials and heat treatment,etc.So material selection and heat treatment of the plastic mold are more important. Material selection of plastic mold is decided by their using performances.According to the mold types, material types and performance requirements,we select different heat treatment.24172
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© 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of [name organizer] Key words: plastic mold, failure, material selection, heat treatment
1 Introduction
In China, the plastic product takes a more and more important role in the national economy. Plastic
production by volume in the world has exceeded steel production. The proportion of plastic mold
production in the total mold production is increasing year by year. It consumes a large quantity of
steel,has different specifications and more complex structure,has low surface roughness requirement,but
It is difficult to manufacture it. Therefore, It has become an important research topic that comprehensive
analyses plastic mold working conditions and failure on the basis of how to reasonable choose plastic
mold materials in order to increase it's working life, assurance it's quality, reduction it's cost. But the
plastics industry in China started late, the research in this area is still not deep enough.
We should understand the basic requirements of plastic mold parts molding when analyse plastic
mold working conditions and failure modes. First of all, the appearance requirements of plastic parts are
very strict, especially in clear plastic parts, which requires the mold formed surface has low roughness,
generally in the range of Ra0.2～0.025mm or less, a small amount of wear or corrosion can lead to the
failure of important working parts such as cavity or core of mold. Secondly, the dimension accuracy
requirements and reciprocal accuracy requirements of the molding part are high, in order to ensure
juncture closed and avoid overflow or juncture trace on plastics surface. In addition, when the shape of
plastic mold parts is complex, the mold cavity structure is correspondly complex, which results stress
concentration in parts of the cavity, and affects the carrying capacity of the mold. Because these three
reasons are related to mold precision machining , which makes it difficult to manufacture plastic mold,
manufacturing costs increase. Therefore, it is of great significance to prevent the early failure in the
plastic mold.
2 The working conditions of plastic mold
The working parts of plastic mold mainly consist of the cavity, core, inserts, molding and forming ring.
They form the plastic mold cavity and a variety of surfaces of plastic parts. They touch directly with the
plastic, withstand the pressure, temperature, friction and corrosion and so on.
Plastic injection mold cavity pressure is generally at 40～140MPa, closed die pressure is at 80～
300MPa or more.Heating temperature is at 140～300℃, the specific parameters are related to the variety
of plastics. Cavity surface withstand friction and corrosion, and its intensity depends on the type of plastic
and the nature of the filler. For manual mold, such as portable compressed molding or pressure injection
molding, in installing mold and releasing mold,mold often knocked by hand percussion instruments and
collision.
3 The main failure modes of plastic mold
The basic forms of failure of the plastic mold are surface wear, deformation and fracture, because the