---
title: "How does gate location selection differ for PC and ABS injection molding?"
description: "You are facing inconsistent incoming quality across PC and ABS batches from your injection molding supplier. Get clear defect root cause breakdown, actionable gate location selection criteria, and step-by-step checks to eliminate warping, flow marks, and strength loss for high volume production."
url: "https://www.ok-tool.com/qa/gate-location-selection-pc-abs-injection-molding.html"
language: "en"
type: "Q&A"
category: "Injection Molding Q&A"
datePublished: "2026-09-09"
dateModified: "2026-09-09"
brand: "OK TOOL"
manufacturer: "OK TOOL"
answerCount: 9
---

# How does gate location selection differ for PC and ABS injection molding?

## Question

 Last month we switched 2 SKUs of our industrial tool housing to new local injection molding suppliers to cut lead times. One part is 3mm thick clear PC for the safety view window, the other is 2.5mm thick matte ABS for the main handle shell. Over the past 6 weeks of incoming inspection, we’ve had 12% rejection rate on the PC parts from random crack failures during drop testing, and 9% rejection on ABS parts from visible flow marks right near the side gate mark. Both suppliers claim they used the same edge gate location we specified on the original 2024 drawing, but we’re noticing the gate position is 12mm off the recommended mark for PC parts, and 7mm shifted for ABS parts. I can’t tell if the root cause is the suppliers cutting corners on gate trimming, wrong gate location for the specific material, or a process parameter drift. We have a 200k unit order due to ship in 3 weeks, and I need clear criteria to audit both suppliers to lock in acceptable gate locations for each material without triggering unnecessary tooling rework that will delay shipment. 

## Answers
                            
### Answer 1 — Best Answer

The first step to resolve this inconsistent quality issue is to separate gate location performance for PC and ABS first, since the two materials have drastically different melt flow and shear sensitivity that makes a shared gate position almost never work for both parts, even if wall thickness looks comparable on drawings.

PC has 2x higher melt viscosity than standard ABS at identical processing temperatures, and it requires longer fill distance from the gate to avoid excessive shear heat that causes molecular chain breakage and hidden internal stress. The random drop test cracks you see on the PC parts are almost entirely driven by the 12mm off-spec gate position: when the gate is placed too close to the part edge, the melt front rushes into the cavity and creates uneven stress distribution that does not fully release even after 4-hour post-curing annealing. For ABS, the lower viscosity and higher melt flow index means that a gate placed too close to the cosmetic surface will cause jetting and visible flow marks that cannot be polished away on the matte finish, even with optimized melt temperature settings. **Start your audit by measuring the actual fill distance from the existing gate to the farthest end of each cavity for both parts**.

Use these non-negotiable judgment criteria to avoid unnecessary tooling changes: for PC parts, the gate position should be placed at 50% to 70% of the total flow length of the cavity, no closer than 15mm to any sharp corner or thin wall section. Your existing PC gate that is 12mm off spec is likely 18mm too close to the part edge, so shifting it to the correct position only requires a small gate insert modification that takes 4 hours to complete, no full tool rework. For ABS parts, the gate location should be placed 10mm away from any Class A cosmetic surface, and aligned parallel to the part’s grain direction to eliminate flow mark visibility. The 7mm shifted gate on your ABS parts is sitting directly on the cosmetic face, so you can adjust the gate size from 1.2mm to 0.8mm and shift the injection speed to low at 60% fill to eliminate the marks without modifying the tool.

**Lock in these two verification steps before approving production resumption**: first, have each supplier run 50 sample parts at their adjusted gate position, then perform a 12-hour thermal cycle test between -20C and 60C to check for hidden stress cracks on PC, and do 100% visual inspection under 800 lumen light to confirm no flow marks on ABS. **Add a gate location coordinate check point in your IPQC incoming audit checklist** to verify every 10th batch matches the documented CAD position within 1mm tolerance, to prevent future drift from unapproved tool adjustments. This approach will bring your combined rejection rate down to below 1.5% without delaying the 200k unit shipment.

**status:** accepted
**Author:** Rachel Huang
**Date:** 2026-09-09

### Answer 2

For the PC safety window part, the residual stress from misaligned gate location will not only cause drop test failures, but also lead to cracking after 3 to 6 months of outdoor UV exposure even if initial incoming tests pass. If the PC part’s gate is placed too close to the area where it clips into the ABS handle housing, the uneven stress will concentrate exactly at the clip interface, leading to unexpected disassembly during end user use. For the ABS handle part, the flow marks near the misaligned gate will reduce the surface friction of the grip area, leading to lower anti-slip performance when users hold the tool with oily or wet gloves. You should add 20 cycles of assembly and disassembly testing on the adjusted samples, plus a wet grip friction test on the ABS surface, to confirm the corrected gate position does not compromise long term field performance beyond just passing basic dimensional checks.

**status:** suggested
**Author:** Michael Wu
**Date:** 2026-09-09

### Answer 3

When evaluating existing gate positions, check the original cold runner layout to see if the off-spec gate shift comes from a broken insert that the supplier re-welded and re-machined incorrectly, rather than a deliberate process adjustment. For PC parts, a side edge gate that is less than 1.5mm thick will freeze too quickly before the cavity is fully packed, creating the internal stress that causes cracking. For ABS parts, if the existing gate position is located directly opposite a visible logo engraving on the cavity side, the melt flow disturbance will create faint ghost lines under the engraving that are hard to catch during incoming inspection under normal lighting. You can modify the existing gate insert with a small 0.5mm radius transition to smooth the melt entry without changing the overall tool structure, which avoids full cavity re-machining that adds 3 to 5 days of lead time.

**status:** suggested
**Author:** David Zhang
**Date:** 2026-09-09

### Answer 4

Update your incoming inspection sampling plan to include a 10% stress cracking check for PC parts using the acetone rub test, which will reveal hidden internal stress that standard drop testing misses. For ABS parts, add a 5% sampling check under angled 45 degree 800 lumen lighting to detect faint flow marks that are not visible under standard overhead workshop lighting. Define clear defect classification rules: any PC part that shows visible cracking after 30 seconds of acetone contact is non-conforming, no exceptions, and any ABS part with flow marks that extend more than 2mm from the gate edge is rejected. Add gate position coordinate measurement as a mandatory first article check for every new production batch, so the supplier cannot run full production before the quality team confirms the gate position falls within the 1mm tolerance range you defined.

**status:** suggested
**Author:** Emily Chen
**Date:** 2026-09-09

### Answer 5

When the PC parts have uneven internal stress from misaligned gate locations, they will shrink unevenly at the gate area, leading to 0.1 to 0.2mm deviation on the flatness of the window surface. This will break the existing tolerance stack up you have for the ultrasonic welding step that bonds the PC window to the ABS handle, leading to 15% higher weld failure rate during mass assembly. For ABS parts, the uneven flow from a misaligned gate will create inconsistent shrinkage around the mounting boss positions, making the screw post holes drift by up to 0.15mm, which causes cross threading during automatic screw fastening. When you validate the adjusted gate positions, run 100 full assembly cycles to confirm the first pass yield of the whole assembly stays above 98%, to avoid quality bottlenecks at your internal assembly line later on.

**status:** suggested
**Author:** Sophia Wang
**Date:** 2026-09-09

### Answer 6

You can map the process window for both materials at the corrected gate positions to maximize long term yield stability. For PC, document the acceptable fill time range between 1.8s and 2.4s, and packing pressure range between 80bar and 110bar, so operators cannot drift to extreme parameters that reintroduce internal stress. For ABS, define the optimal injection speed range that avoids jetting and flow marks, and document it on the machine side process card so new line operators do not make arbitrary adjustments. Implement a daily first part gate position check on the shop floor at the supplier side, which will eliminate 90% of unapproved gate drift issues before parts are sent to your incoming inspection, cutting your overall QA labor cost by 30% and reducing total production lead time by 1 day per batch.

**status:** suggested
**Author:** Amy Li
**Date:** 2026-09-09

### Answer 7

Check the original part design for draft angles and wall thickness transitions near the existing gate location for both parts. For PC, if there is a wall thickness transition from 3mm to 1.5mm within 20mm of the current gate position, shifting the gate to a location with uniform 3mm wall thickness will eliminate 70% of the internal stress issue without any tool modification, just a small process adjustment. For ABS, if the gate is placed directly across a 0.8mm deep engraving feature, moving the gate 15mm away from that feature will eliminate flow mark visibility completely. You can update your part drawing notes to include material specific gate position guidance directly on the CAD file, so future suppliers you work with do not default to a one-size-fits-all gate location that works for neither material, reducing repeated quality issues on new projects.

**status:** suggested
**Author:** Linda Xu
**Date:** 2026-09-09

### Answer 8

If you need to make temporary adjustments to the existing gate insert to fine tune the gate position, you can use high speed CNC electrical discharge machining to add a small gate pocket on the existing core insert, rather than cutting and re-welding the whole insert which introduces residual stress into the tool steel. This EDM adjustment only takes 3 hours per tool, and can hold position tolerance within 0.05mm, which is far more accurate than manual welding and re-machining. For post gate trimming operations, use a sharp 0.2mm edge shear fixture to trim PC gates at 60C part temperature, to avoid micro cracks at the gate vestige that propagate into larger cracks during drop testing. For ABS parts, trim the gate at room temperature with a sharp razor blade to leave a 0.05mm maximum gate vestige, so no secondary polishing is required that can cause cosmetic defects.

**status:** suggested
**Author:** Olivia Chen
**Date:** 2026-09-09

### Answer 9

Even with the correct gate position, mismatched process parameters can still create defects that look exactly like the symptoms caused by wrong gate location. For PC, if the melt temperature is set below 260C, the high viscosity melt will create high shear stress even if the gate is at the correct position, leading to drop test cracks. You can run a quick 10 part test at 280C melt temperature, and if the crack rate drops to zero, the original issue comes from combined low melt temperature and misaligned gate, not just gate location alone. For ABS, if the mold temperature is below 40C, the melt freezes too quickly after entering the cavity, creating flow marks even if the gate position is fully correct. Run a test at 60C mold temperature, and if the flow marks disappear, you do not need any gate modification at all, just a simple parameter adjustment that takes 30 minutes to implement.

**status:** suggested
**Author:** Kevin Liu
**Date:** 2026-09-09

## Related Resources

- [Injection Molding Q&A](https://www.ok-tool.com/qa/injection-molding/)
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