Do you know
if it will flow. We recommend flow testing before having your molds
built.
Custom Injection Molding
disadvantages and problems
The molding process has several
disadvantages to other molding processes. The following is a short list of
some of the disadvantages to Injection Molding.
-
This is not a preferred
method of manufacturing for short production runs. This is mainly due to
the cost of tooling and the cost of operation. However B.J. Molding can handle
smaller runs than most shops.
-
Design and development of
parts that will work well with Injection Molding often takes a very long
time. Many parts are just not suited to the process.
This list will highlight problem
areas of Injection Molding and a typical cause and method of resolving that
problem.
| Problem |
Cause |
Resolution |
| Black specks spots of streaks |
-
Plastic burning onto the cylinder walls and then flaking off
into the melt.
-
Air trapped in mold causing the burning.
-
Partial burning of granules against the wall.
|
|
| Bubbles are showing in the finished part |
- This is typically due to the fact that there is moisture
on the plastic granules.
|
- Dry the material before using.
|
| Flashing |
- Material is too hot
- The injection pressure is too high
- The clamping pressure is too low.
|
- Reduce the temperature
- lower the injection pressure.
- Reface the parting line
- Increase the clamping pressure
|
| Pore Finish |
- Mold too cold
- Injection pressure too low
- Water on mold face
- Excessive mole lubricant.
- Pore part finish
|
- Raise the mold temperature
- Increate the injection pressure
- Clean mold and check for cooling leaks.
- Refinish or polish the mold
|
| Short Shots |
- Mold is too cold causing a premature freezing and higher
resistance to flow
- Pressure too low
- Gates too small
- mold is not balanced for proper melt flow
|
- Increase the mold temperature
- Increase the injection pressure
- Increase the gate area
- Increase or add venting
- modify the runner system
|
| Sink Marks |
- There is not enough plastic in the mold for proper
packing
- Plastic is too hot
- Injection pressure is too low
|
- increase the injection speed and increase the gate size
- Reduce the cylinder temperature
- Increase injection pressure
|
| Warping |
- Part is ejected too hot
- Plastic is too cool
- unbalanced gates
|
- Reduce the plastic temperature
- Increase the cylinder temperature
- Modify the gates
|
| Surface Marks |
- Cold material
- Slow injection
- Unbalanced flow in the gates and runners
|
- Increase the plastic temperature
- Increase the mold temperature
- Increase the injection speed
- Rebalance the gates and runners
|
