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It is important to understand that all the air in the mold cavity must escape to atmosphere in order for the plastic to properly fill the mold cavity. Inadequate venting is an extremely common cause of molded part defects. At Routsis Training, customers sometimes ask us how many vents a particular mold should have. It’s a simple question to answer:

Q: “How many vents are required?”
A: “As many as possible.”

While this information is obviously critical to mold designers and mold makers, it is also important for production personnel to understand this concept when troubleshooting molded part defects. Let’s review what is happening with the mold, plastic material, and your process with respect to venting.

Air Volume = Plastic Volume

The moment you start pushing plastic into the mold, air must escape the mold cavity. This means the more avenues the air has to escape, the faster and easier the material can enter the mold. It is important to allow the volume of air in the cavity and runners to escape the mold to atmosphere so it can be effectively displaced by the incoming plastic.

Mold designers often indicate an end-of-fill location as the best place to vent, but this just one of many vents you must cut into your mold. In fact, you should vent the runners, sprue puller, cold slug, slides, bosses, lifters, ejector pins, ejector blades, stripper plates, start of fill, middle of fill, and the end of fill.

All these vents must have a clear path out of the mold to atmosphere. When the plastic resin enters the cavity, you want an even, uninterrupted flow. Venting everywhere ensures this.

Aqueous Volatiles

Plastics have all sorts of additives, moisture, stabilizers, plasticizers, lubricants, low molecular weight chains, colorants, etc. When the plastic pellets are subjected to the heat and sheer during the molding process, they give off gas — resulting in aqueous volatiles. You often see this as a waxy buildup along the vents and the ejector pins.

Over time, these volatiles collect on mold surfaces, causing inconsistent part finish and gloss, and decreased surface texture quality.

Internal Stresses

If most of the air does not escape, the part will have internal stresses and will deform after it is ejected from the mold. This often results in cracking, crazing, and part warpage. Looks for signs of bad venting such as consecutive circles or a cloudy area at the gate, shiny spots at the parting line, as well as inconsistent gloss.

Narrow Process Window

Your process window is greatly affected by the range of pressures in which you can fill and pack the mold cavity. If a great amount of pressure is needed to push the gas out of the mold, you have a very small process window between filling the mold cavity and flashing the tool. It is not uncommon to see molds where the venting is so inadequate that the mold cavity cannot fill without flashing — because the escaping gas forces the mold open.

We hope this information has helped educate you on the important of proper mold venting. Tooling personnel can learn more from our Mold Design & Moldmaking Series. The importance of venting is also discussed in Scientific Troubleshooting for Injection Molders.

Bottom Line ROI for Plastics Manufacturers

Today’s plastic parts are more complex and processing equipment is more advanced — while highly skilled and experienced employees are becoming harder and harder to find. This is costing plastics processors a lot of money at an increasingly faster rate. Because of this, most plastics manufacturers lose thousands of dollars a month in scrap, downtime, and equipment damage.

Here are five specific areas where in-house skills-development training will directly increase your company’s bottom line.

Reduced Mold Damage

This damage can occur before, during, or after it is run as well as during storage. This is typically reported as a mold repair cost, but much of this cost can be avoided when proper handling, storage, and maintenance skills are implemented.

Fewer Accidents

Your employees are coming to work each day to do the best job that they can. Most accidents occur when employees do not properly understand the equipment, machinery, environment, or process. Many times, they take short cuts because they do not fully understand the consequences of their actions. For example, there have been many burns that occur when an operator or technician pulls a stuck runner from the sprue and some hot pressurized plastic is released at the same time. To avoid this the employee needs to be properly trained to back the carriage up, thereby not allowing pressure to build before reaching into the mold area, because there is pressurized plastic behind sprue when this is not done.

Increased Customer Satisfaction

Everyone wants happy customers. The best approach to customer satisfaction is through Quality Assurance. In plastic processing Quality Assurance relies on a company being able to verify they are using the same process to manufacture the same product each and every time your customer’s job is run. This provides the highest confidence in shipping quality product to your customer each and every time.

Extended Tool & Machine Life

Things wear and break, but improper procedures, handling, and maintenance will always affect your bottom line. For example, when the mold is properly handled during setup, production, and storage, the likely hood of damage is significantly reduced. It’s when an improperly trained employee pries a part from the mold with a screwdriver that you encounter completely avoidable damage which is very costly.

Lower Employee Turnover

When you train one employee, they are likely to leave because they do not have the co-worker support, they need to improve. If you properly train your workforce, then they all have the knowledge and skills to support new processing methods and make improvements that affect the bottom line. Training your entire production workforce results in much more confident and capable employees who will prefer to work together with their fellow employees rather than take their chances somewhere else.

It’s important that you leverage the skills of your entire production workforce and take advantage of the equipment that your company has already invested in. A skilled, competent workforce is the key to success.

Routsis Training offers a wide range of products and services that can help increase the profitability of your plastics processing operation. Please visit our website to learn more.

Poorly skilled employees are the root cause of most quality-related losses. Our customers typically realize reductions of over 61% in scrap and rework while eliminating most customer returns. All of this was a result of improving the skills and confidence of their workforce.

Here are 5 quality-specific areas of improvement where proper training of production staff has a direct effect on your company’s profitability.

Lower Scrap Rates

Every operation needs to document scrap percentage and rework time. This includes the actual cause and which necessary corrective actions were taken. More capable processors will help troubleshoot more efficiently and effectively — with a reduced overall scrap rate over time.

Fewer Defects

With the right skills and scientific documentation, your technicians will be able to better duplicate and maintain the standard documented process. This will give faster and more consistent startups — with more reliable runs from first piece to last piece.

More Consistent Part Quality

As your processes become better defined and your technicians understand how to use this information, they will be better at maintaining the standardized and approved process, shift-to-shift and run-to-run.

Highly Repeatable Processes

Skilled process technicians become will develop processes that are more capable of handling normal variation. There have been many advances in our industry’s best practices and your technicians need to be skilled in scientific process development, documentation, and troubleshooting.

Process Optimization

A processor needs to understand the material, part, mold, and machine along with the scientific molding process to develop a capable, reliable, and repeatable process. Once developed they leverage what they learned in the development process to optimize critical process parameters to improve the process without sacrificing quality.

Processing is a science, not an art. Quality assurance in plastic processing relies on a company being able to verify that they’re using the same process to manufacture the same product — each and every time the job is run.

Routsis Training offers a wide range of products and services that can help your company improve part quality and increase the profitability of your plastics processing operation. Please visit our website to learn more.

A recent industry survey revealed most plastics manufacturers lose over $250,000 dollars in scrap and downtime every year. The companies that participated in this survey attributed most of these losses to daily mistakes made by an under-skilled workforce. This is true even in facilities that utilize the latest processing technologies.

While modern machines are much more capable and accurate, your production personnel need proper training in order to take advantage of these technologies. Here, we’ll share 6 specific areas where proper training can directly improve your company’s bottom line.

Decreased Machine Downtime

Every operation needs to keep accurate records of uptime & downtime. You also need methods of differentiating between different types of downtime, such as changeovers, troubleshooting, maintenance, or when there’s just nothing on the schedule.

Some downtime is helpful, such as process development, maintenance, or mold trials. Other downtime, such as troubleshooting and repairs, directly affect your profitability. You can quickly improve this with proper training.

Improved Troubleshooting Time

Your operation should document exactly why a process requires troubleshooting and how long it’s down. You can typically find this information in a process log, which is kept at each molding machine. It’s important to measure this time, but it’s even more important to measure the number of times a process needs troubleshooting. This information will help you determine if techs are using an effective scientific approach to troubleshooting or just pushing buttons.

Faster Machine Startup

Establish startup times to determine specifically what outside influences contribute. For example, tracking and properly documenting delays such as materials not properly prepared or dried, tools unavailable, hot runner controller maintenance, and auxiliary equipment not ready will let you know where to improve.

Shorter Cycle Times

Through proper training, a technician or process engineer can systematically develop a robust process that will lead to shorter cycle times without sacrificing part quality. Keep in mind just a 2% improvement in cycle time gains you an additional week of production capability each year.

Quicker Changeovers

This point was often brought up when we ran our survey of 42 plant managers. They noted a huge improvement in changeover time — especially when tracking the entire changeover from last shot to first piece approval. This metric covers not only the capability of the techs but also the ability of everyone in the production environment to work together, from planning to quality.

Since changeover time is typically the biggest contributor to downtime, it stands to reason a more capable workforce can coordinate better to get one job out and the next one up and approved.

More Energy-Efficient Processes

YYou can easily measure the cost of energy with your company’s monthly electric bill. This may be adjusted based on the percentage of machine utilization, but also note that proper training will ensure you have much greater percentage of productive uptime vs. non-productive downtime.

As an example, let’s say your part removal time is 1 second longer than it needs to be. That means your molding machine will operate 27 hours longer than necessary to produce 100,000 parts. That’s a lot of energy-consuming machine time.

Routsis Training offers a wide range of products and services that can help your company defray production-related expenses and increase the profitability of your plastics processing operation. Please visit our website to learn more.