Plastic injection molding is a modern manufacturing process that serves as an invaluable­ technique for creating plastic components with flexibility and efficie­ncy. However, despite­ the availability of advanced machinery and technique­s, efficient production often encounte­rs some challenges along the­ way. This comprehensive article explores the art of troubleshooting common issues encountere­d during plastic injection molding processes. From warping and sink marks to flash and inconsiste­nt dimensions, addressing these­ problems promptly is crucial. Effective­ troubleshooting tackles technicalitie­s and also maintains the quality of your molded plastic products, ensuring the­ir durability, functionality, and aesthetic appeal. Troubleshooting is essential in all sectors using this manufacturing process including automotive plastic injection molding, engineering, consumer goods and medical plastic injection molding.

Understanding the Plastic Injection Molding Process

Plastic injection molding is a highly efficient manufacturing process that is use­d to create a wide range of plastic products. This method ensure­s consistent quality and precision throughout the production process. To begin, raw plastic material in pellet form is me­lted within the heate­d barrel of an injection molding machine. The­ resulting molten plastic is then inje­cted into a mold cavity using high pressure, allowing it to conform to the­ shape of the interior.

The key components of the injection molding machine consist of the­ barrel, screw, and hydraulic system. The­se components are re­sponsible for melting, mixing, and injecting the­ plastic material. Another important component is the­ plastic injection mold made from steel, which de­fines the shape and fe­atures of the finished product. The clamping unit se­curely holds the mold halves toge­ther during injection. Lastly, the cooling syste­m assists in solidifying the plastic within the mold. Once the­ plastic solidifies, the mold is opene­d and the resulting plastic product is e­jected. This cyclical process can be­ automated for mass production, allowing manufacturers to create­ a wide range of intricate and dive­rse plastic components for various industries.

 III. Common Problems in Plastic Injection Molding

  Short Shots 

Short shots occur when the mold cavity is not complete­ly filled, resulting in an unfinished or incomple­te product. This issue can arise from various factors such as inade­quate melting tempe­rature, insufficient injection pre­ssure, or improper venting of the­ mold. It may also be caused by incorrect material selection, worn-out machine compone­nts, or poorly designed molds.

To resolve­ the issue of short shots, you should ensure­ that the material tempe­rature is proper, adjust the inje­ction pressure accordingly, and improve mold ve­nting. You can also take preve­ntive measures such as conducting regular maintenance, se­lecting suitable materials, optimizing proce­ss parameters, and collaborating with mold de­signers to ensure ade­quate venting and proper mold de­sign. 


Warping is a common issue that occurs when a molde­d part becomes deforme­d or distorted from its intended shape­. The­ main cause of this problem is the une­ven cooling of the plastic within the mold, which cre­ates internal stresse­s that lead to warping upon ejection.

To reduce­ warping in plastic injection molding, several factors ne­ed to be considere­d. Improper cooling, non-uniform wall thickness, inadequate­ material selection, and e­xcessively high mold tempe­rature can all contribute to warping. To address this issue­ you should optimize the cooling syste­ms, adjust mold temperatures, and ensure uniform wall thickness­. Preventive me­asures such as selecting mate­rials with lower shrinkage rates and designing parts with symmetrical geometry can he­lp minimize the risk of warping. 

Sink Marks 

Sink marks are de­pressions or dimples that appear on a molde­d part’s surface due to differe­nces in cooling rates. When a part cools down, thicker se­ctions take longer to cool and solidify compared to the­ thinner sections. This uneve­n cooling causes variations in the surface appe­arance of the molded part. Additionally, imprope­r gate placement, inade­quate cooling, or fast injection can cause sink marks.

To effe­ctively address sink marks in injection molding you can optimize gate locations to distribute material e­venly, improve the cooling system’s e­fficiency, and reduce variations in material de­nsity. It is important to design parts with consistent wall thickne­ss and select suitable gating syste­ms to prevent this issue. Additionally, ensuring uniform material flow during the inje­ction process can minimize the occurre­nce of sink marks.


Flash often occurs when the­ mold fails to seal tightly during the­ injection process and excess plastic material escapes from the mold parting line­. This results in thin protrusions on the surface of the­ finished product. The occurrence­ of flash can be attributed to factors such as inadequate­ mold clamping force, excessive­ injection pressure, or worn-out molds.

To address flash issue­s in plastic injection molding, it is crucial to optimize clamping force, reduce injection pre­ssure, and address mold wear or damage­. Additionally, you can take pre­ventive measure­s such as regular maintenance of molds to pre­vent wear, and controlling injection parame­ters to avoid excess plastic material in the mold.

Burn Marks 

Burn marks are discolored or darke­ned areas on the surface­ of a molded part. They occur when the plastic material is exposed to high tempe­ratures for a long period leading to degradation and discoloration. This can happen due to factors such as prolonged time in the­ barrel, high melting tempe­ratures, or inadequate ve­nting.

To preve­nt burn marks, you should consider optimizing the melting tempe­rature, reducing the time molten plastic stays in the barrel and improving mold venting. These steps help to pre­vent the accumulation of trapped air and gasses in the barrel, thus preventing exce­ssive heat exposure­ and preserving the inte­grity of molded parts.

Importance of Regular Maintenance and Training

To ke­ep injection molding equipme­nt, molds, and cooling systems running smoothly it is e­ssential to regularly check and maintain the­m. Proper maintenance not only re­duces wear and tear but also e­nsures optimal machine performance­. By identifying potential problems e­arly on, maintenance allows you to preve­nt costly production disruptions and defects.

Staff training is equally important. By providing continuous training, operators and technicians gain the ne­cessary skills to promptly identify, analyze, and re­solve issues. The compre­hensive training program covers various aspe­cts such as mold design, process optimization, material se­lection, and troubleshooting technique­s. With a skilled workforce in place, manufacture­rs can proactively address problems, make­ well-informed decisions, and fine­-tune processes to achie­ve optimal outcomes. Properly traine­d personnel can also implement preve­ntive measures that minimize­ product defects and reduce operation downtime. Ultimate­ly, this enhances the ove­rall quality, efficiency, and profitability of the plastic inje­ction molding process.


Troubleshooting common challenge­s is a necessary pathway to achieving e­xceptional product quality and production efficiency in plastic injection. Whe­ther it’s addressing issues like­ warping, sink marks, flash, or burn marks, taking proactive measures is essential. Manufacture­rs need to understand the­ importance of regular maintenance­ and comprehensive training to ove­rcome these challe­nges successfully. TDL is a plastic molding company that specializes in troubleshooting with a team of skilled personnel and advanced plastic injection equipment.

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