[{"data":1,"prerenderedAt":326},["ShallowReactive",2],{"\u002Fblog\u002Fshort-shots-injection-molding-causes-fixes":3,"related-\u002Fblog\u002Fshort-shots-injection-molding-causes-fixes":316},{"id":4,"title":5,"articleType":6,"author":7,"body":8,"category":299,"date":300,"description":301,"extension":302,"image":303,"lastModified":300,"meta":304,"navigation":305,"path":306,"seo":307,"stem":308,"tags":309,"__hash__":315},"blog\u002Fblog\u002Fshort-shots-injection-molding-causes-fixes.md","Short Shots in Injection Molding: Causes and Fixes","howto","IMSPARES Technical Team",{"type":9,"value":10,"toc":276},"minimark",[11,15,19,22,27,30,37,49,59,63,66,71,74,77,81,84,100,103,107,110,114,122,126,129,133,137,140,143,154,157,160,171,174,178,181,184,188,191,194,198,202,205,212,216,219,245,248,252,273],[12,13,5],"h1",{"id":14},"short-shots-in-injection-molding-causes-and-fixes",[16,17,18],"p",{},"Short shots — parts that don't fill completely — are one of the most common defects in injection molding. The textbook lists about fifteen causes. In practice, it's usually one of about five things.",[16,20,21],{},"Here's how we approach short shot troubleshooting, based on what we actually see in the field rather than what a theory book says.",[23,24,26],"h2",{"id":25},"first-rule-out-the-obvious","First: Rule Out the Obvious",[16,28,29],{},"Before you start adjusting process parameters, check these:",[16,31,32,36],{},[33,34,35],"strong",{},"Is there enough material?"," Sounds silly, but we've seen machines running with nearly empty hoppers, material bridges in the hopper, or feed throat blockages. Check that material is actually reaching the screw.",[16,38,39,48],{},[33,40,41,42,47],{},"Is the ",[43,44,46],"a",{"href":45},"\u002Fparts\u002FMC-BC-01","check ring (non-return valve)"," worn?"," If the check ring doesn't seal properly, the screw pushes plastic backward during injection instead of into the mold. You'll see an unstable cushion position — it varies shot to shot. A worn check ring is one of the most common causes of short shots on older machines and it gets worse gradually, so people don't notice until parts are clearly incomplete.",[16,50,51,58],{},[33,52,41,53,57],{},[43,54,56],{"href":55},"\u002Fparts\u002FMC-BC-07","nozzle"," blocked?"," Partially blocked nozzles restrict flow. Cold slugs, degraded material, or foreign objects can obstruct the nozzle bore.",[23,60,62],{"id":61},"process-related-causes","Process-Related Causes",[16,64,65],{},"If the mechanical basics check out, start looking at process parameters:",[67,68,70],"h3",{"id":69},"insufficient-injection-pressure","Insufficient Injection Pressure",[16,72,73],{},"The most obvious cause. If you're already at maximum injection pressure and still getting short shots, the problem isn't really about pressure — it's about why you need that much pressure. Maybe the gate is too small, the wall section is too thin, or the material viscosity is too high.",[16,75,76],{},"But yes, sometimes the answer is just to turn up the pressure. Machines that have been running the same mold for years might need more pressure as the screw and barrel wear, because the effective injection rate drops.",[67,78,80],{"id":79},"insufficient-shot-size","Insufficient Shot Size",[16,82,83],{},"The calculated shot size needs to account for:",[85,86,87,91,94,97],"ul",{},[88,89,90],"li",{},"Part volume (all cavities)",[88,92,93],{},"Runner and sprue volume",[88,95,96],{},"Cushion (typically 5-10mm, depending on machine size)",[88,98,99],{},"Decompression amount",[16,101,102],{},"If the total exceeds the machine's maximum shot capacity, you'll never fill the part. This also happens when someone puts a mold on a machine that's technically too small for it.",[67,104,106],{"id":105},"injection-speed-too-slow","Injection Speed Too Slow",[16,108,109],{},"In thin-walled parts, the plastic starts freezing as soon as it contacts the mold. If injection speed is too slow, the flow front freezes before reaching the end of fill. Increase injection speed — sometimes dramatically — for thin-wall molding.",[67,111,113],{"id":112},"melt-temperature-too-low","Melt Temperature Too Low",[16,115,116,117,121],{},"Cold melt = high viscosity = hard to push through thin sections. Check barrel temperature settings and actual melt temperature (air shot into a pyrometer). Also check that the ",[43,118,120],{"href":119},"\u002Fparts\u002FEC-HT-01","heater bands"," are all functioning — a dead zone on the barrel means cold material enters the mix.",[67,123,125],{"id":124},"mold-temperature-too-low","Mold Temperature Too Low",[16,127,128],{},"Similar effect to low melt temperature. The plastic freezes faster against cold mold surfaces. For engineering resins (nylon, PC, POM), mold temperature has a huge influence on fillability.",[23,130,132],{"id":131},"mold-related-causes","Mold-Related Causes",[67,134,136],{"id":135},"poor-venting","Poor Venting",[16,138,139],{},"This is the cause that gets underestimated the most. As plastic fills the mold cavity, it pushes air out through vents at the parting line, ejector pin clearances, and intentional vent channels.",[16,141,142],{},"If vents are:",[85,144,145,148,151],{},[88,146,147],{},"Too shallow (plugged with deposits over time)",[88,149,150],{},"Missing entirely (bad mold design)",[88,152,153],{},"Blocked (flash from previous over-packing)",[16,155,156],{},"...the trapped air compresses and acts as a cushion that prevents complete filling. The last area to fill comes up short.",[16,158,159],{},"Signs of venting problems:",[85,161,162,165,168],{},[88,163,164],{},"Short shots consistently in the same area (last area to fill)",[88,166,167],{},"Burns or discoloration near the short shot area (diesel effect — compressed air heats up)",[88,169,170],{},"Increasing injection pressure doesn't help (you're fighting compressed air)",[16,172,173],{},"Fix: clean existing vents, deepen if necessary (0.01-0.03mm for most materials), add vents in the short-shot area.",[67,175,177],{"id":176},"gate-too-small-or-frozen","Gate Too Small or Frozen",[16,179,180],{},"If the gate freezes before the cavity packs out, you get a short shot or a dimensionally small part. Gate freeze time depends on gate size, material, and mold temperature.",[16,182,183],{},"Signs: short shot appears fine initially but worsens at lower mold temperatures or with longer cycle times.",[67,185,187],{"id":186},"unbalanced-runner-system-multi-cavity","Unbalanced Runner System (Multi-Cavity)",[16,189,190],{},"In a multi-cavity mold with naturally balanced runners (geometrically symmetrical), the flow should be equal. With artificially balanced runners (different runner lengths or diameters), one cavity may fill faster than others.",[16,192,193],{},"You'll see some cavities complete while others are short. The solution is runner balancing — adjusting runner sizes to equalize fill.",[23,195,197],{"id":196},"machine-related-causes","Machine-Related Causes",[67,199,201],{"id":200},"worn-screw-and-barrel","Worn Screw and Barrel",[16,203,204],{},"Wear between the screw flight and barrel bore lets plastic backflow during injection. The effective injection rate and pressure drop. This is a gradual process — short shots get worse over months or years.",[16,206,207,208,211],{},"Check the ",[43,209,210],{"href":45},"screw and barrel"," clearance. New clearance is typically 0.1-0.15mm on the diameter. Over 0.3mm means significant wear and diminished injection performance.",[67,213,215],{"id":214},"hydraulic-system-issues","Hydraulic System Issues",[16,217,218],{},"On hydraulic machines, anything that reduces hydraulic pressure or flow to the injection cylinder causes weak injection:",[85,220,221,228,231,234,242],{},[88,222,223,224],{},"Worn ",[43,225,227],{"href":226},"\u002Fparts\u002FHY-PW-06","hydraulic pump",[88,229,230],{},"Leaking injection cylinder seals",[88,232,233],{},"Incorrect proportional valve settings",[88,235,236,237,241],{},"Clogged ",[43,238,240],{"href":239},"\u002Fparts\u002FO-TC-02","hydraulic filters"," causing pressure drop",[88,243,244],{},"Low oil level",[16,246,247],{},"If injection speed and pressure are both lower than expected, start with the hydraulic system.",[23,249,251],{"id":250},"a-practical-troubleshooting-sequence","A Practical Troubleshooting Sequence",[253,254,255,258,261,264,267,270],"ol",{},[88,256,257],{},"Check material supply and hopper",[88,259,260],{},"Do an air shot — check if the machine delivers full shot weight in air",[88,262,263],{},"If air shot is short, check barrel\u002Fscrew wear and check ring",[88,265,266],{},"If air shot is normal, check mold (venting, gate condition, temperature)",[88,268,269],{},"Gradually increase injection pressure and speed",[88,271,272],{},"If maximum settings don't fill, the mold needs attention (vents, gates) or the machine is too small",[16,274,275],{},"Most short shot problems get resolved within steps 1-4. Keep it simple and systematic.",{"title":277,"searchDepth":278,"depth":278,"links":279},"",2,[280,281,289,294,298],{"id":25,"depth":278,"text":26},{"id":61,"depth":278,"text":62,"children":282},[283,285,286,287,288],{"id":69,"depth":284,"text":70},3,{"id":79,"depth":284,"text":80},{"id":105,"depth":284,"text":106},{"id":112,"depth":284,"text":113},{"id":124,"depth":284,"text":125},{"id":131,"depth":278,"text":132,"children":290},[291,292,293],{"id":135,"depth":284,"text":136},{"id":176,"depth":284,"text":177},{"id":186,"depth":284,"text":187},{"id":196,"depth":278,"text":197,"children":295},[296,297],{"id":200,"depth":284,"text":201},{"id":214,"depth":284,"text":215},{"id":250,"depth":278,"text":251},"Troubleshooting","2026-09-30","Short shots mean incomplete parts. Here are the real causes — not just the textbook answers — and what actually fixes them on the shop floor.","md",null,{},true,"\u002Fblog\u002Fshort-shots-injection-molding-causes-fixes",{"title":5,"description":301},"blog\u002Fshort-shots-injection-molding-causes-fixes",[310,311,312,313,314],"short shots","incomplete fill","injection pressure","mold venting","troubleshooting","2_rAVbYHvnd-uEDVLThY2hdSxdKS6eYGJV6Kh12XR90",[317,321],{"title":318,"path":319,"description":320,"date":300,"category":299},"Troubleshooting Hydraulic Pressure Loss in Injection Molding Machines","\u002Fblog\u002Ftroubleshooting-hydraulic-pressure-loss","Diagnose and fix hydraulic pressure loss problems in injection molding machines. Common causes, step-by-step troubleshooting, and replacement parts guide.",{"title":322,"path":323,"description":324,"date":325,"category":299},"5 Hydraulic Oil Problems That Kill Your Injection Molding Machine","\u002Fblog\u002Fhydraulic-oil-problems-injection-molding","Dirty oil, wrong viscosity, overheating, aeration, and water contamination — these five hydraulic oil issues cause most machine breakdowns. How to spot them before they cause real damage.","2026-03-22",1790784691908]