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03
Manufacturing Process
JOINING (PLASTIC)
The forming of plastic parts is usually followed by joining multiple parts together to
create assemblies with certain functionality, or to contain functional components. The
way parts are joined can vary widely based on functionality, forming processes, use
conditions, reparability, durability, and cost. Assembly is usually one of the most
costly aspects of producing a product. Therefore, carefully choosing the methods of
joining parts during the design process is critically important. The joining of parts is
determined well in advance of creating tooling, so that the appropriate features to aid
in specific joining methods can be designed into the parts. This section describes
common methods for joining plastic parts.
Adhesive bonding
is the process of joining two or more parts by using an adhesive.
Often when adhesive bonding is used, the parts include mechanical features that pre-
vent misalignment. Prior to bonding, parts are usually cleaned to ensure that mold
releases are removed to ensure a secure bond. Adhesive bonding is compatible with
most plastic-forming processes.
y
ADHESIVE BONDING
Adhesive
Mechanical Interlock
Fasteners
, such as screws, are often used to attach components to housings and for
joining multiple housings. This method of joining allows parts to be disassembled for
repair or recycling. Injection-molded parts may have molded-in features (bosses) that
accept the screws. Self-tapping screws are often chosen when assembling plastic
parts because they tap into the plastic, creating a matching thread pattern. Thermo-
formed parts may require inserts to accept the screws.
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52 PROCESS, MATERIALS, AND MEASUREMENTS
Snaps
are molded-in features that allow
parts to join by interlocking. Snaps are
designed into a molded part and take
advantage of the flexibility of plastic. This
method allows for the quick assembly of
parts at a ver y low cost. This type of fas-
tener is used for joining injection-molded
parts.
Ultrasonic welding
is the process of joining parts using ultrasonic vibration to create
friction between two parts, causing them to heat up, melt, and fuse together. The
edge of one of the mating molded plastic parts contains a thin ridge of plastic
(energy director), which focuses and controls the area of the weld. This method of
joining yields a strong bond, enhancing the rigidity of a housing assembly. Once parts
are welded, they cannot be disassembled. This is the process used for permanently
joining injection-molded parts.
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FASTENER
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Job on:93996 CTP Title : RP_Process Material Measurements Client : Pro_Vision
Scn :
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175 Size : 146.05(w) 209.55(h)mm _M2_Mac D
Dept : DTP D/O : 16.12.05 (Job on:000000 D/O : 00.00.01 Co: CM0)
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