# Injection Molding Defects Troubleshooting Guide > Source: https://netray.co/tools/injection-molding-defects-troubleshooting-guide > Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems. > Section: Free Tools ## Short answer A searchable table of common injection molding defects with the usual causes and the first thing to check, grouped by process area. ## Category quality ## Industry Plastics ## Audience - Molding technician - Process engineer - Quality engineer ## Tool **Kind:** worksheet **Mode:** reference **Columns:** #### Defect **Key:** defect **Type:** text #### Main area **Key:** area **Type:** select **Options:** - Fill - Pack and cool - Material - Mold - Machine #### What you see **Key:** look **Type:** text #### Common causes **Key:** causes **Type:** text #### First checks **Key:** first **Type:** text **Rows:** **Defect:** Short shot **Area:** Fill **Look:** Cavity not completely filled, missing corners or ribs **Causes:** Low shot size, low injection pressure or speed, cold melt or mold, blocked vent or gate, worn check ring **First:** Shot size and cushion, melt and mold temperature, vents, check ring **Defect:** Flash **Area:** Mold **Look:** Thin excess plastic at the parting line or around pins **Causes:** Clamp force too low, worn parting line, excess pack pressure, high melt temperature, vents too deep **First:** Clamp tonnage, parting line condition, pack and hold pressure **Defect:** Sink marks **Area:** Pack and cool **Look:** Depressions over thick sections, ribs or bosses **Causes:** Low pack pressure or time, gate freezes early, thick walls, hot mold, rib too thick **First:** Hold pressure and time, gate size, rib to wall ratio **Defect:** Voids **Area:** Pack and cool **Look:** Internal bubbles in thick sections **Causes:** Insufficient packing, early gate freeze, volatile moisture in material, melt too hot **First:** Pack time, gate seal time, resin drying **Defect:** Weld lines **Area:** Fill **Look:** Visible line or weak seam where flow fronts meet **Causes:** Cold flow fronts, low injection speed, poor venting at the meeting point, gate location **First:** Melt temperature, injection speed, vents at the line **Defect:** Burn marks **Area:** Fill **Look:** Dark or brown marks at the end of fill **Causes:** Trapped air compressed by fast injection, blocked vents, overheated melt, long residence time **First:** Vent cleanliness, injection speed, melt temperature **Defect:** Splay or silver streaks **Area:** Material **Look:** Silver streaks along the flow direction **Causes:** Moisture in hygroscopic resin, volatiles, high melt temperature, excess decompression **First:** Dryer temperature and dew point, drying time, decompression **Defect:** Warpage **Area:** Pack and cool **Look:** Part bends or twists after ejection **Causes:** Uneven cooling, differential shrinkage, high ejection temperature, high packing stress, orientation **First:** Cooling balance, mold temperature split, cooling time **Defect:** Jetting **Area:** Fill **Look:** Snake-like flow pattern from the gate **Causes:** Melt jets into open cavity, fast initial injection speed, gate facing open space **First:** Initial injection speed, gate type and location **Defect:** Flow lines **Area:** Fill **Look:** Wavy lines or rings near the gate **Causes:** Cold melt or mold, slow fill, thin sections after thick ones **First:** Melt and mold temperature, fill speed profile **Defect:** Delamination **Area:** Material **Look:** Surface layers peel off like skin **Causes:** Contamination with another resin, moisture, excessive shear, wrong regrind **First:** Material contamination, drying, regrind source **Defect:** Black specks **Area:** Material **Look:** Dark particles in the part **Causes:** Degraded resin in the barrel or hot runner, contamination, long residence time **First:** Purge, residence time, hot runner temperatures, material handling **Defect:** Ejector marks **Area:** Mold **Look:** Pin impressions or whitening on the part **Causes:** Part too hot or too soft, uneven ejection, high ejector speed, insufficient draft **First:** Cooling time, ejector speed and position, draft **Defect:** Drag marks **Area:** Mold **Look:** Scratches along the ejection direction **Causes:** Insufficient draft, rough or undercut cavity, heavy packing **First:** Draft angle, surface polish, pack pressure **Defect:** Brittleness **Area:** Material **Look:** Parts crack under light load **Causes:** Degraded polymer, excess regrind, moisture hydrolysis, residual stress, wrong grade **First:** Drying, regrind ratio, melt temperature, residence time **Defect:** Gate blush **Area:** Fill **Look:** Dull ring or halo around the gate **Causes:** High shear at the gate, fast injection, small gate **First:** Injection speed at gate, gate size, melt temperature **Defect:** Nozzle drool **Area:** Machine **Look:** Resin leaks from the nozzle between shots **Causes:** Nozzle too hot, excess decompression, wrong back pressure, open nozzle type **First:** Nozzle temperature, decompression, nozzle style **Defect:** Inconsistent shot weight **Area:** Machine **Look:** Part weight varies shot to shot **Causes:** Worn check ring or screw, inconsistent cushion, feed throat problems, variable melt **First:** Cushion variation, check ring, feed throat temperature **Notes:** General guidance only. Always change one parameter at a time, wait for the process to stabilise, and record the change. Confirm material limits with the resin supplier. ## Content **Intro:** When a part comes out wrong, a structured list of likely causes saves time at the press. This reference table groups common injection molding defects by process area and lists the causes and first checks that usually resolve them. **Sections:** #### How to use it **Body:** Search or filter by the defect name or by what you see on the part. The main area tells you where to start: fill problems relate to melt, speed and venting, pack and cool problems to hold pressure and cooling, material problems to drying, contamination and degradation, mold problems to venting, wear and ejection, and machine problems to screw, check ring and nozzle. Export the table to Excel to add your own plant specific notes. #### A disciplined approach **Body:** Defects often have several causes, so a table narrows the field but does not decide it. Start with material, since moisture and contamination mimic process faults. Then confirm the process is stable using cushion and shot weight. Change one variable at a time and wait for several cycles before judging. Document the setting that fixed the defect on the process sheet, because the next shift will meet the same problem. **Bullets:** - Check the material and drying records first - Check cushion and shot weight repeatability - Adjust one parameter, wait, then re-evaluate - Log the cause and fix for the next time #### Defects that mislead **Body:** Splay is often blamed on the mold but is frequently moisture. Flash looks like a clamp problem but may be excess pack or a worn parting line. Sink and voids are the same mechanism in different places: shrinkage with no melt available to feed it. Warpage can be a cooling issue, a packing issue or a design issue, and should be studied across several parts. #### Common mistakes **Body:** Changing several settings at once, adjusting the process to hide a worn mold, ignoring regrind ratio, and fixing the symptom without recording it. Another frequent error is raising melt temperature to cure everything, which can trade one defect for degradation and longer cooling. **Cta:** Netray can connect defect codes captured at inspection to molds, machines and resin lots in your ERP, so repeat problems show up in a report instead of a memory. **Faq:** #### What causes most short shots? **Answer:** Usually insufficient melt reaching the cavity: low shot size, low injection pressure or speed, cold melt or mold, or blocked vents and gates. Check shot size and cushion first, then temperatures and vents. #### How do I tell flash from a clamp problem? **Answer:** Look at where it appears and whether it grows with pack pressure. Flash at a worn parting line or along pins points to the mold. Flash that disappears when pack or injection pressure drops points to process. #### Why do I get splay with dried material? **Answer:** Moisture can be re-absorbed between the dryer and the barrel, or the dryer may not reach its dew point. Also check excess decompression, high melt temperature and residence time, which create volatiles. #### Is this table complete? **Answer:** No. It covers frequent defects with typical causes. Your resin, mold and machine will have specific behaviors, so add your own notes after export. ## Search terms injection molding defects, injection molding troubleshooting guide, short shot causes, flash in injection molding causes, sink marks causes and fixes, splay silver streaks causes, plastic molding defects chart, warpage injection molding causes --- Talk to an engineer: https://netray.co/contact?intent=erp_ai | Machine catalog: https://netray.co/agent/catalog.json