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COMPRESSION MOLDING  (MATCHED-DIE MOLDING) COMPRESSION MOLDING  (MATCHED-DIE MOLDING)

COMPRESSION MOLDING (MATCHED-DIE MOLDING) - PowerPoint Presentation

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Uploaded On 2022-06-18

COMPRESSION MOLDING (MATCHED-DIE MOLDING) - PPT Presentation

COMPRESSION MOLDING PROCESS materials fiberresin preweighed to a specific size charge placed in a closed mold and heat and pressure applied in a press RESINS AND REINFORCEMENTS USED IN COMPRESSION MOLDING PROCESS ID: 920041

mold molding cure resin molding mold resin cure time paste charge part compound process press compression plastic temp smc

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Slide1

COMPRESSION MOLDING (MATCHED-DIE MOLDING)

Slide2

COMPRESSION MOLDING PROCESS

materials (fiber/resin) preweighed to a specific size charge, placed in a (closed) mold, and heat and pressure applied in a press

Slide3

RESINS AND REINFORCEMENTS USED IN COMPRESSION MOLDING PROCESS

resins

polyester (most common)

low shrink systems

up to 10% thermoplastic polymers by weight

mold shrinkage as low as 0.1%

easily pigmented

low profile systems

10% - 15% thermoplastic polymers by weight

mold shrinkage as low as

@

0% - 0.05%

not readily pigmented

most common fiber is glass

Slide4

SHEET MOLDING COMPOUND (SMC)

automated, continuous flow process

resin paste (resin, filler, initiator, mold release and thickening agents) properly proportioned and mixed

uniformly metered onto lower plastic (polyethylene, nylon) film

reinforcement is placed onto lower plastic film

top plastic film is coated in a similar manner with resin paste

top plastic film feeds into moving belt to form continuous sandwich of fiber/resin

compacted under controlled pressure

taken up on rolls (2 ft - 5 ft width)

Slide5

DIFFERENT FORMS OF SMC

random chopped (0.5 in - 2 in) fibers (SMC-R)

continuous unidirectional fibers (SMC-C)

combination of above (SMC-C/R)

thickness varies between 0.25 in - 0.5 in

thick molding compound (TMC) available in thicknesses up to 2 in

Slide6

MATURATION OF THE MOLDING COMPOUND

thickens between processing and molding in order to provide tack free molding compound that releases cleanly from plastic film

viscosity of resin paste depends on resin formulation

viscosities between 10 - 100 million cps usually chosen for molding

storage time varies from 1 day to 7 days depending on resin formulation (most common formulation 3 days)

Slide7

BULK MOLDING COMPOUNDS (BMC)

mixing process usually consists of two separate mixing stations

one station prepares the resin paste

resin system, initiator, mold release, fillers

high speed, high shear mixer

resin paste transferred to second station

(glass) fibers (0.5 in) added

sigma blade, spiral blade or combination of blades and single or twin screws

final mixing

@

3 mins

packaged in vapor barrier for maturation of resin paste or transported directly to molding pressalternately, may be extruded in log form for easier weighing at the press

Slide8

COMPRESSION MOLDING PROCESS

measured charge of compound placed between halves of split mold

heated mold is closed

pressure is applied so that compound flows to fill mold cavity

compound is allowed to cure before removal from the mold

process variables to consider in compression molding

molding temp

charge pattern and placement

molding pressures

press closing speed

cure time

Slide9

MOLDING TEMPERATURE

temperature control is extremely important - variations of a few degrees can result in premature gelling in areas of mold if it is too hot and longer cure times than expected if some areas of mold are too cold

objective is to achieve fastest possible cure settings that are easy to maintain and result in near uniform heating throughout the charge and no degradation

accurate temp control

improve productivity

reduce internal stresses in molded part

ensure reproducible part properties

Slide10

CHARGE PATTERN AND PLACEMENT

should be as simple as possible

consistent placement of charge in mold

assures reproducible flow time to all parts of the mold

important for proper temp distribution

charge placement affects fiber orientation due to flow in mold - can result in variation in part properties

obstructions cause interruption and subsequent rejoining of flowing material resulting in knit lines (local regions of weakness)

various automated loading and unloading devices have been developed for molding presses

Slide11

MOLDING PRESSURES

factors to consider in establishing molding pressures

viscosity of resin paste

part design

quality of part surfaces

pressures up to 2,000 psi can be required for relatively large molds with deep draws

for parts with flat surfaces satisfactory flow and fillout will be obtained at slightly lower pressures

Slide12

PRESS CLOSING SPEED

depends primarily on mold temperature and resin paste gel time

higher molding temp and faster curing formulations require faster press closure for rapid pressure build in mold

if closing too slow, material will pre-gel in mold

if closing too fast, fiber wash will result

typical closing times 1 - 10 secs

Slide13

CURE TIME

factors controlling cure time

resin initiator

mold temp

part thickness

cure times typically range from 1 - 5 min

cure time is presently limiting factor with respect to increasing production rates

actually molding of part often occupies only about 10% of total press cycle time, remaining 90% is cure time