Bengaluru, India

Mold Flow Analysis for Syringe Pump


Moldflow Analysis to determine reasons for Plastic Parts cracking in Syringe pump Mechanism.

Problem Observed

Three plastic parts are found to have developed cracks and have failed in assembly.


To Carry out Moldflow Analysis and find out the reason of parts are crack.


Input Details: Material: PC+ABS, Grade : Cycoloy C1100HF (assumed)

Process Input Details:

Mesh Type : Fusion

Processing Conditions:

Mold temperature : 70°C.

Melt temperature : 260°C.

Absolute Maximum Melt Temperature: 300℃

Ejection temperature: 90℃

Maximum shear stress: 0.4 MPa

Flow Rate : Automatic.

Injection time : 2.2 Sec.

V/P switch over : 98%

Packing Time is : 20 sec

Cooling Time : 21 sec

Cycle Time : 43 sec

Injection tonnage: 120


Mesh Type: Fusion

Part Volume: 43 cm³

Feed System Volume: 4.5 cm³

Projected Area: 115 cm³

Total volume: 43. 1184 cm³

Volume filled initially: 0.00 cm³

Total volume: 43. 1184 cm³

Part volume to be filled: 38.5595 cm³

Sprue/runner/gate volume to be filled: 4.5598 cm³

Total projected area: 115.7953 cm²


Analysis results show the following issues.

1.Suggestion: Parts are likely to crack in the areas where high residual stresses are observed during mold filling or packing. Here the shear stresses > 0.4MPa (recommended material limit).

2.Feed system/ Gate imbalance is almost 40%. This is creating overpacking of some of the parts resulting in residual stresses in them. Weld lines are occurring in these stressed zones. This may be a major reason for cracks.

Solution: Feed system should be corrected to at least 90% balanced (<10% imbalance allowed). Individual Moulds would have been better for application-critical parts.

3.CLAMP BRACKET is taking a very long time after the first cavity is filled. This is leading to overpacking and hence stresses on the other parts, particularly SLIDER BRACKET and SMALL MOUNTING BRACKET.

Solution: So Gate size should be increased for CLAMP BRACKET.

4.Edge Gate is not good for CLAMP BRACKET, BIG MOUNTING BRACKET and GEAR HOLDER as it is making the plastic flow slower than the other cavities.

Solution: Fan Gate is recommended to achieve more uniform fill and less stresses in these parts. Flow leaders/ overflow wells should be provided to divert weld lines from critical areas.

5.Cooling line seems insufficient.

Solution: Need to add additional cooling lines parallel to the existing ones, running over the cavities.

6.Suggestion: Air vents to be provided around ejector pins to improve flow and fill, thus reducing any possible stresses.

7.Weld lines are forming around the hole areas where two flow fronts are meeting and the weld line gets prorogated because of high residual shear stresses at walls around the holes. This may lead to part failure during part application.

Solution: In order to control weld lines that may lead to cracks, Mould temperature should be strictly maintained as per raw material datasheet.

8.Mould Temperature is kept lesser (55°C) than the recommended range (60-80°C).

Solution: It should be maintained at the average value (70°C).

9.Melt Temperature is kept at the lower end (240°C) of the recommended range(240-280°C).

Solution: It should be maintained at the average value (260°C).

10.Tried Analysis with Nylon but did not get any better result.

Solution: A Less viscous material like ABS is better

Fill Time Animation: