-
Compression Molding:
- Charge Mold
- Close Mold
- Fill the mold with plasticized paterial
- Cure by addition of heat
- Open the mold
- Eject using ejector pins
- Clean the mold of flash
-
Pressure range extremes:
15 --> 1,000,000 PSI
-
Material physical forms:
- Granular
- Nodular
- Pellets
- Flakes
- Liquid
-
Stages of material:
- A: liquid, solids, high flow
- B: Partially polymerized
- C: Cured, polymerized
-
Describe additives used in molding compounds:
- UV Stabilizers
- Fillers
- Plasticizes
-
First Molding Compounds:
- Urea:A cellulose filler is normally used in formulating the molding compound, Excellent colorability and compounds are produced using wet process.
- Applications:Decorative housings Closures for drug/cosmetic products
- Wiring devices
-
Second molding compound:
- Melamine-Phenolic:Combining of one-stage phenolic with melamine resin, not used in large volume applications and produced in black or dark colors.
- Applications:Appliance parts where color may be needed Electrical
- Electrical switch gear parts
-
Why use preforms
- Bulky material is reduced
- Easier to handle
- Reduces mold cost
- Cleaner
- Pre-weighed
- Heat Faster
-
Automatic Methods of mold loading
- Weigh feeding system
- Volumetric feeding system
- -Loading borards
- -Hand Cups
- -Tube
- Preforms of any of the material types used in compression molding
-
Bulk factor problem
Ratio of loose material volume divided by the molding part volume.
-
When to use low and high flow materials
- High: Delicate parts, molding inserts
- Low: Thicker, more durable parts
-
Name of procedure to futher complete cure
Post cure or Normalizing
-
Reasons for deflashing
- Aesthetics
- Safety
- Fit/Function
-
Methods for deflashing
- Tumbling
- Tumbling with media
- Wheelabrasion
-
Minimum/Maximum thickness of C.M. parts
-
Terms used for main mold sections
- Male: Core, Ram
- Female: Cavity
-
Mold component hardening
Final hardening should be done after finalizing part
-
Complexity of producing T.S. vs. T.P. molds
More steps involved in making the molds
-
Types of molds
- Flash:10%
- Semi-positive:Most common, little flash
- Positive: A lot of money, High accuracy
-
Basic mold heating methods
- Steam
- Oil
- Electric cartage heater
-
Use and placement of vents
- Eliminates the gasses
- On parting line
- Corner of the mold
- Last place to fill across the face of the mold
-
Safety Factor- Molding pressure
90%
-
-
How are presses rated
- Number of tons of Clamp pressure
- Size of platen
-
How does our "Hull" press actuate/develop pressure
Pneumatic Toggle
-
Define Double Shrinkage
- Use melamine
- Shrink Faster
-
Why use Shrink fixtures
Reduce shrinkage and warping
-
Use of drafts on molds and amount
Makes it easier to remove parts over 1/4"
-
Minimum number of K.O. pins
3
-
Placement of K.O. pins
On the back of the part
-
Max L/D for pins under 1/4" diameter
2.5:1
-
What factors affect mold filling
- Amount % of fillers
- Type of thermoset polymer
- Use of bulk material vs. preform
- Temperature of mold
- Pre-heating
- Part size/mold
- Mold pressure
-
Hot Strength
Material has cured enough that it can be removed from mold without damaging it
-
Holds parts to one side of the mold
Undercut or hooker
-
Use of bump cycle
Momentary opening after heating material to relieve gasses
-
Advantages of Compression Molding
- Minimum amount of material used
- No erosion of gates and runners
- Internal stresses and warpage is less
- Automatic material handling equipment available
- Shrinkage is less than transfer molding
-
Disadvantages of Compression Molding
- Cant use inserts
- Problem occur with cleaning of the mold insert sections
- Uneven parting line can happen
- Flash is thicker than transfer molding
-
Hardening of mold components
- Heat treatment to increase hardens
- Only the surfaces are heated
- Partially heat treated material
|
|