Injection Molding 101
Quick link of the Troubleshooting Guide:
Years ago I struggled with a product molded in nylon, and though we received it in 25 kilo bags, closer inspection revealed that almost 25% of the bags had been punctured and re-taped upstream by either the shippers or our own material handlers. As you know, it doesn't take much exposure to moisture for this material to get too "wet" to process. I dried everything, even right from the bag. Punctured bags received from our supplier were rejected and returned. Also, it was a requirement to load the whole bag into a dryer. No open bags were ever saved. And at the end of a run any remaining material was discarded if it remained in the dryer more than 4 hours after stopping the press. "Overcooking" this resin will degrade it rapidly.
Mould shrinkage can be manipulated by nearly all process variations- melt temps, cooling temps, in. pressures and hold pressures, injection speeds and so on, as well as gate location and part geometry. All materials have a specific shrinkage rate range that provides a guideline to use that is based upon "best moulding practice'. The further you deviate from specified parameters, the further you will deviate in a normal shrinkage of the part. If you skirt the boundaries or exceed the boundaries of the material specification, the less likely you are to achieve a statistically reliable part. No one has more understanding of this than the material supplier technical group. So if looking for a more comprehensive understanding base upon a specific resin and a specific part, a comprehensive and complete mould flow analysis based upon the part and mould with runner and cooling will give you the best indication...... Which MF program is best--- is up for debate and needs to be analyzed and quantified against actual real life results...... So far, I've never seen such an independent analysis.
We had a clear nylon vessel that exhibited a "splay like" condition that emanated from the gate region. In our case, the mold had valve gates and what was happening is that some of the melt was being left on the face a sides of the valve pin. The next shot these now solidified pieces of nylon would break loose as the incoming melt stream re-melted the prior shot but because of the viscosity differences would result in a splay like appearance to the naked eye. Only under 30X microscopic exam could you actually see the residual debris and the flaring trails behind them like comets.
Mold parts that are excessively heated, like spure bushings and areas near the gates, must be cooled intensively. Rapid and even cooling is enhanced by the use of highly conductive metals, such as berylliumcopper. These metals are used to full advantage in places where it is impossible to place sufficient cooling channels. Copper transfer twice as much heat as carbon steel and four times as much heat as stainless steel. This does not mean copper mold will run 4 times faster than a stainless steel mold but they will run some thin walled parts significantly faster.
This technology can be very effective in eliminating or substantially reducing the stress in flatter molding. In internal gas injection, where the gas is injected into one or more gas channels. For a flattish, panel-type part such as this, this is not always the gas injection process to be recommended. The added gas channels can leave a slight witness mark on a cosmetic 'A' surface and depending on the part geometry, the gas packing pressure will probably not be equal across the whole surface area of the part, especially with thinner wall sections and wider surface areas.
Design For Manufacturing (DFM) report, it's a bridge between product developer and mold manufacturer. It has been implemented in many manufacturing industries and proved to a sufficient way to improve efficiency. A comprehensive DFM report for mold making project would be the first step to success. As a mold maker
, the more potential problems you foresee, the less risks you had in the manufacturing process. Here are a summary for it.
Many kinds of raw material are frequently used, such as PC, PC+ABS, ABS, PS, HIPS, Nylon, Material with glass or fiber filled suitability and price different of them are different. More importantly, the shrinkage rate is different, which is key factor to measurement and tolerance precision.
You will have to examine your application and choose accordingly, but I will try to explain briefly some of the advantages to a hot runner solution. As I currently work for a hot runner company I see many parts that benefit from this application. Here are a few basic reasons to look into hot runners:
- Less waste -which in turn reduces contamination
- Controlled melt temperature - reduces warping of part as well as plastic degrading
- Great gate vestige - Reduces the need for second operations
- Lower injection pressures - allows for more cavities per mold
- Shorter cycle times - improves production efficiency
There are many reasons for Quick Mold Change. We have customers who have multiple tools and also run them all in multiple colors. Prior to installing quick mold change equipment they would run a mold, change the color multiple times, then change the mold and run the next mold through various colors... This required huge inventories and all the problems that come with large batch sizes.
With our quick mold change systems installed on all of their presses they now run every mold prior to making a color change. Change time is less than 10 minutes. Lot sizes are much smaller. Many problems solved. The flexibility and efficiency now allow them to change scheduling on a dime when needed. And the cost per quick mold change system installed on a press is a fraction.
There are thousands reason to use hot runner system in injection molding but seems lacking of info not prefer the hot runner. As I know the hot runner can be considered as the extension of the barrel. In some cases it combines with the injection gate that it can inject to the part directly.