Free AMIA Practice Questions

Question 1

A cover fills completely, but a thick mounting pad remains underpacked. The gate stays molten for 8 s after velocity-to-pressure transfer; the pad's only feed path is a thin web that is fully frozen by 3 s after transfer. Increasing holding time from 6 to 10 s leaves the pad's sink unchanged. What explains the lack of improvement?

Accepted Answer

The still-open gate cannot supply the pad through its already frozen connecting web.

Answer

The holding interval is too short to compensate for the pad's cooling shrinkage.

Answer

The gate controls packing access because it seals before the longest hold ends.

Answer

The unchanged sink demonstrates inadequate filling pressure before the holding stage.

Question 2

During filling of a housing, melt advances steadily along a 3.0 mm wall but nearly stops in an adjacent 0.8 mm rib. Filling pressure remains below the machine limit, and the rib has an open vent. Flow into the rib resumes only when the main wall is almost full. This sequence is characteristic of:

Accepted Answer

Hesitation as melt preferentially follows the thicker adjoining wall

Answer

Gas trapping caused by compression of air at the end of the rib

Answer

Jetting caused by an unsupported melt strand entering the thicker wall

Answer

A pressure-limited short shot caused by insufficient machine pressure

Question 3

A reinforced bracket requires one gate. The design specification prohibits a weld line across its loaded mounting lug and a gate vestige on its sealing face. The allowed nozzle pressure is 105 MPa. Four candidate studies fill completely and satisfy all other requirements. Which gate arrangement should advance?

Accepted Answer

An edge gate at 92 MPa, with the weld line crossing an unloaded flange.

Answer

A central gate at 74 MPa, with the weld line across the loaded lug.

Answer

A sealing-face gate at 68 MPa, with the weld line away from the lug.

Answer

An opposite-edge gate at 118 MPa, with the weld line away from the lug.

Question 4

A faster filling profile lowers the apparent viscosity at a gate from 180 to 120 Pa·s but raises the local shear rate from 1,000 to 3,000 s⁻¹. The values are evaluated at the same temperature. The resin supplier limits shear stress to 0.30 MPa; both profiles meet the other material and machine limits. How should the faster profile be assessed?

Accepted Answer

Reject it: the resulting shear stress is 0.36 MPa, above the limit.

Answer

Accept it: lower viscosity gives a shear stress of 0.12 MPa.

Answer

Accept it: shear stress is 0.24 MPa and remains within the limit.

Answer

Reject it: tripling the local shear rate increases shear stress to 0.54 MPa.

Question 5

A thin open tray has a Midplane mesh. Every free edge lies on the tray's actual perimeter or an actual cutout; assigned thicknesses and element connections are correct. A reviewer applies a closed-surface mesh check and flags these edges. What disposition is appropriate?

Accepted Answer

Retain the edges; they are valid physical boundaries in a Midplane model.

Answer

Suspend the analysis until every flagged free edge has been closed.

Answer

Replace it with tetrahedra; a Midplane mesh must enclose a volume.

Answer

Cap the cutouts with triangles to make the model watertight.

Question 6

Before a molding trial, the plant requires rated clamp capacity to be at least 1.20 times the predicted peak mold-opening force. At that instant, four cavities each have a projected area of 2,500 mm² and an area-average cavity pressure of 60 MPa. Cold runners contribute another 1,000 mm² at an average pressure of 80 MPa. The nonoverlapping areas are projected perpendicular to mold opening. Nozzle pressure is 95 MPa. All listed machines are otherwise suitable. What is the smallest clamp rating that meets the trial requirement?

Accepted Answer

900 kN

Answer

750 kN

Answer

1,100 kN

Answer

1,500 kN

Question 7

A cold feed-system analysis reports these pressures at the same filling instant: nozzle 104 MPa, sprue exit 100 MPa, runner exit 90 MPa, and cavity side of the edge gate 54 MPa. The part geometry must remain unchanged, but a larger gate vestige is acceptable. Which geometry trial most directly targets the largest feed-system pressure loss?

Accepted Answer

Increase the edge-gate section and check the later gate-seal time.

Answer

Increase the sprue diameter and check the longer sprue cooling time.

Answer

Increase the runner diameter and check the additional cold-runner mass.

Answer

Shorten the runner path and check the reduction in runner pressure loss.

Question 8

Two polycarbonate grades are being compared for a housing. Both have a Moldflow Viscosity Index of VI(280)150, but their available melt mass-flow rate values were measured at different temperatures and loads. What can the analyst conclude from the reported indices?

Accepted Answer

Both have a viscosity of 150 Pa·s at 280°C and a shear rate of 1,000 s⁻¹.

Answer

Both have a viscosity of 150 Pa·s across all injection shear rates.

Answer

The higher melt mass-flow rate identifies the easier-filling grade.

Answer

Their packing and shrinkage behavior can be treated as equivalent.

Question 9

At 90% cavity fill, a part-only Fill analysis predicts 62 MPa at an injection node placed directly at the cavity gate. A molding trial using the specified resin and matched filling conditions records 91 MPa at the nozzle and 63 MPa just inside the gate at that same fill fraction. The analysis contains no sprue, runner, or gate passage. What should be addressed before treating the discrepancy as a material-model error?

Accepted Answer

Include the omitted feed passages and compare pressures at matching locations.

Answer

Raise resin viscosity until the predicted inlet pressure reaches 91 MPa.

Answer

Reject the gate location because its predicted pressure is too low.

Answer

Refine the cavity mesh until its inlet pressure reaches the measured 91 MPa.

Question 10

A Molding Window study labels a chosen point 'feasible, not preferred.' Follow-up Fill+Pack analyses at that point and across the anticipated temperature and fill-time variations satisfy all specified pressure, shear, filling, and packing criteria. The preferred region lies outside the mold-temperature range available on the production tool. Select the defensible next step for this operating point.

Accepted Answer

Proceed to a controlled molding trial to verify the required part quality.

Answer

Discard it because only points classified as preferred can produce acceptable parts.

Answer

Raise mold temperature into the preferred region before considering a molding trial.

Answer

Approve it for production because passing the analyses establishes the required part quality.

Free AMIA Practice Questions

Domain 1: Analysis workflow

Question 1

Domain 2: Feed systems

Question 2

Domain 3: Gate location design guidelines

Question 3

Domain 5: General tool design

Question 4

Domain 6: Injection molding process

Question 5

Domain 7: Materials

Question 6

Question 7

Domain 8: Model preparation

Question 8

Domain 10: Molding Window

Question 9

Domain 11: Results interpretation

Question 10

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