Key Injection Molding Fundamentals:

The key to any successful molding operation is recording all data that is available when the process is producing minimal scrap and is at optimum efficiency. By replicating these variables at machine start-up, you assure that you are repeating your previous run. Here are some other factors that can help to determine the success of your operation:

Melt temperature is a key variable that is often overlooked! It is imperative that once processes are validated, melt temp should be recorded and when problems occur, melt temp should be one of the primary checks made prior to process adjustments. It is one of the focuses that can identify problems with your machine, or changes within the molding environment.

Measure and record the GPM of your tool's circuitry.. by measuring this variable on every circuit, you are able to test your mold in the future when molding conditions show signs of overheating. It can help you to determine if the tool requires descaling. Each circuit should have a unique identification number. This is done by repeating your watering procedure. Keep the same supply and return pattern by either hard plumming your loops, or by establishing a watering diagram that maps out the watering layout. It is also recommended that your circuits should be uniquely identified IN or OUT and use color identification (green,yellow,white,etc.). This not only improves your watering time, but will reduce the potential of miswatering.

A validated process should not require change. Process parameters should be able to be repeated each time a mold is set and started. Before changing your process, it is important to look at your monitoring variables first! What changed? For instance...if fill time is slower, look at your temperature actuals. Check your thermolator...is the actual temperature the same as your setpoint? Yes, there will be times you need to change your process to correct a molding condition. First, check for mechanical changes..after confirming that your machine, mold and auxilliary equipment are in a correct state, make changes to your process that replicate your process monitoring variables (fill, peak, etc.).

Prior to process changes, monitor your molding variables for significant fluctuations. A cushion that varies spurratically can be a sign of a worn check ring, or barrel wear. Barrel temperature fluctuations can point towards bad heater bands, or thermocouple positioning/ failure. Also consider recent mechanical changes made while servicing a press, and whether they might impact the validity of your process.

Always consider whether your operator could be affecting your process. Inconsistent cycles can reap havoc on your consistencies. Improper part handling can cause defects that might be mistaken for a processing problem.

Part weight is a key recordable variable. Once a process has been validated, part weight (full shot, including runner) should be recorded. The data should not only include part weight after cycle, but also part weight with pack and hold removed. This can help you identify where in the process you are experiencing a change. Part weight should be verified at the beginning of each start up.

A clean and well serviced mold is imperative to any successful molding operation. Tools should be cleaned no less than once per shift, and materials that are prone to gassing may require twice per shift. Slides and guide pins should be lubed, but it is important to remember that overgreasing can be detrimental to your process efficiency. Always clean your mold prior to any process change...defects could be directly related to dirty vents.

Material moisture is a key function that is often overlooked when process defects occur.Moisture analysis should be part of your start up procedure, and is completed prior to start up. Upkeep of your dryers is essential to your success. Dryer filters should be cleaned every shift, and you should routinely feel the supply and return hoses on your dryer. When a dryer is functioning properly, the supply hose will be hot and the return will be warm.

It is imperative that you analyze the effectiveness of your fill time. Some materials require a fast fill..but if you max out your velocities you lose control of consistency. Monitor your fill and verify that your setpoint is being reached consistently. Whenever possible, your fill speed should be determined by performing a fill time study. There is a form on the homepage of the site for this that includes instructions on performing the test.

Hold time is a crucial element of your cycle...establishing this time too low results in part weight variations and process inconsistency. Too much time adds time to your cycle that isn't needed. Performing a gate seal study not only verifies that you are achieving gate seal consistency, but is a crucial step towards process optimization.There is a form on the homepage of the site for this that includes instructions on performing the test.

It is important to understand that adding regrind to your process changes material response. The best approach to introducing virgin/regrind into your molding equation is to treat it as a different material. Determine the optimal virgin to regrind ratio that reutilizes your regrind effectively without increasing your scrap rate. Once you've established an effective blend and process, record the process separately from a virgin run. Also record the process monitoring data separately, then consistently repeat the blend ratio. You can further your ability to mold consistently by re-extruding your regrind with virgin base. This will reduce the potential of drop-down inefficencies (pellet size/ weight vs. regrind size/weight) and promote consistency.

Scientific molding is best described as the science of replication. Optimized and validated processes are repeatable...successfully producing low scrap start-ups and product runs, optimized cycle efficiencies and productive and profitable returns.

There are many larger reference books that can provide more detailed information of how to acheive standardization of your molding operation. Here are some of the molding resources that we highly recommend:

Scientific & Injection Molding

Lean Manufacturing