I was on site for process consulting and trouble shooting of a customers mold. They had some issues with gate blush and unbalanced parts in a family mold or 1+1 mold with unlike parts. for more detail in how I come about troubleshooting a problematic mold please read the process page on this site.

By following the scientific molding principles I was able to properly locate the injection stage for the gate area of the part and therefore control the speed of flow for the ABS material and eliminate the gate blush.

Another issue they were having was improper packing of one of the parts. One part was flashing and the other had sink marks (pits or areas that look like shallow pot holes.) This particular mold had good sprue, and runner size, although the gate size was not optimal. It is more difficult to determine proper gate size with dissimilar parts as they have different weights and wall thickness. I suggested we focus on the under filled part only instead of adjusting both sides. The larger part had gates that were under specification for depth and width. The gate depth determines the seal off time and the width determines the amount of volume that can be flowed. I had the customer increase the width by 50% as the optimal depth is usually 80% of wall thickness and width is 150% of gate depth.

Upon putting the mold back in the machine the parts were now balanced and issues resolved. The packing time had been reduced by 50%  or 20 seconds reducing the cycle time by 5 seconds and significantly reducing the machine power usage. It was now sitting under no load in a cooling stage instead of applying pressure during a longer than normal packing stage. I also had the customer remove some of the loops in the cooling lines as the parts were dissipating a lot of heat into the mold which was not being removed.

Related pages

• Process (1)

Injection Molding Consulting Process

For process consulting of an injection mold I apply the following scientific molding principles. I have included numbered highlights and bullet points for additional detail. All principles, processes, and methodologies are scalable as GeForce Technologies grows. This is an overview and does not include everything.

These methodologies are not my own but a result of training and study. The principles were created by engineers, scientists, and the community in an effort to eliminate problematic parts and molds due to process guesswork. Internal plastic part stress can’t be seen by the naked eye and can cause catastrophic failure of parts in the field. I am passionate about doing things right and to the best of my abilities with the many resources that are available. GeForce Technologies is grounded in these principles and they will continue to evolve as the industry does.

These principles will only work optimally on a mold and machine that is setup properly for the material that is being ran. A common mistake is to design every mold the same when it comes to size specifications. This includes mold specifications as follows: sprue orifice, sprue size, runner size, subrunner size, gate size and type, vent width and depth, draft, textures, and proper quantity and location of ejector pins. Machine specifications such as screw type, nozzle type and size. Plastic part design that follows material specifications for wall thickness, draft, texture, rib thickness, gate location and wall thickness at gate.

There are specific specifications for all of these sizes and types based on each material type. It is ideal to follow these guidelines to ensure optimal cycle time, and part quality.Which in turn will increase profits significantly. Especially when you consider reducing the amount of times a mold is taken in and out of the machine and sent to the machine shop for costly adjustments and delivering parts to market late, or delivering parts that will fail.

1. Confirmation that machine settings comply with martial manufacturers specifications.
   • I request the material data sheets and check them to the material that is being ran. I confirm that all temperatures, pressures, and timings are within material specifications.
   • A common issue or problem is that the mold temperature is much colder than specification in an effort to shave a few tenths of a second. This usually is followed by material temps that are to high. So now you have an overheated degraded material being shocked by a cold mold. Presto you get internal stress and weak parts that sometimes shatter.
2. Utilize scientific molding principles to visibly set injection stages to critical part elements for cosmetic control.
   • I shut off the packing pressures or holding pressures, and set the injection into stages. The first stage of the filling should be for the gate area for controlling gate blush or blemishes. A lot of problems are caused by adjusting the speed for the first injection stage and it doesn’t have any effect on gate issues. This is due to the first stage not actually controlling the gate area but instead the runner or beyond the gate. Applying scientific molding principles to stop injection at each stage to physically see where it fills the part allows for proper control of cosmetics in different areas of the part.
3. Set the transfer stage is to 97% of part fill to ensure proper separation and control between injection and packing.
   • An analogy I like to use is if the transfer is not set right instead of your car gradually coming to a stop at a stop sign under control, you get your car whizzing past the stop sign and hitting a wall. It should be a smooth transition which gives control and safety.
   • The transfer stage is where the process changes from filling the part to packing the part. The filling stage is for getting the part filled as quickly as possible without blemishes to about 97% part weight and then switching to packing where the part is given its shape and size. This transfer stage is one of the most important and commonly looked over parts of the process and the root of many problems.
4. Setup the process to optimize use of machines closed loop capabilities.
   • Most machines have the ability to adjust machine pressure when material viscosity, room temperature, or other factors change that effect the material flow. This is only true if the process is setup correctly, which includes proper transfer stage position, and that all injection speeds are not limited by pressure. This means that the maximum allowed injection pressure needs to be set above what the machine is currently using to inject the plastic at the set speeds.
5. Optimize the packing or holding stage to maximize the part cosmetics, minimize internal stress, decrease material waste, and reduce machine power consumption.
   • Internal stress that can’t be seen can cause premature failure of the part in the field. This type of internal stress was the primary reason for premature cracking of plastic parts when injection molding was first introduced. This gave plastic a bad name which still effects the plastic industry. The internal stress is caused by a process that does not follow the material specifications and has been improperly setup.
   • Find the gate seal off time based on weighing the part at every increase of holding time until part weight increase is insignificant based on percentage. The result of this step will reduce material waste by not packing beyond gate seal off which then unnecessarily packs the runner. This also reduces power consumption because the machine is holding at a set pressure instead of sitting under no load and cooling.

Related pages

• Solving Mold Gate Blush and Cavity Balancing Issues (0)