Try to schedule machines so that they will be running the same resin types: i.e.- leave a press to run clear and white resins or one that runs all of the nylon jobs. That will reduce the amount of purging required to get rid of the ABS when switching to PC and so on. Run a press empty before starting a changeover. Make sure everyone is prepared for the change over before it happens. If you must do a color change between molds, run a bit of natural through the last mold, providing it has a hot runner. Cold runners will be more about cleaning the hopper, barrel and screw out. Make sure the material handlers know how to properly clean a resin line or hose/hoppers. Use Nerf balls with WD-40 on them is one of the best ideas I've used over the years.
It's a common way to assemble plastic components or achieve functionality by creating hole features, Location and measurement of holes need to be carefully designed to minimize the complexity of mold manufacturing and negative influence to the part strength, in this article we are going to discuss what elements we should consider when doing rib design.
If you want to eliminate or reduce the parting line on you plastic products, there are too many ways to solve it.
- The mold design must be very robust and the sliding cores that form the parting line are located in such a way that the slides come together in exactly the same position every time.
- There is enough pre stress on the heel blocks so that no movement occurs during injection.
- Most important the faces that butt together must be a very good finish using a surface grinder and a fine polishing wheel. Be allowed to spark out thus taking a longer time than normal.
- The mold design must allow the parting line to part assembled accurately and be clamped together during machining edm and of course must be polished together.
All plastic have a rate in which they transfer there heat, so in this case depending on the type of plastic will depend on the amount of time needed to allow the plastic to transfer the heat into the cooling channels of your injection mould. This is better known as the heat transfer coefficient and it's different for all materials, plus all heat dissipates at 90 degree angles. Cooling design is very unique, there's no 2 parts alike so your cooling designs are going to be different for every injection mould you build, but the guide lines you use should be the same, so many water lines for amount of surface area of the part, the lines need to be within a certain distance to each other, the lines must be within a certain distance to the part surface and so on.
For manufacturing also other "sticking" phenomena will be important: most common problem can be vacuum in the cavity, while the core is well vented by all ejector pins and inserts. When using an ejector pin to determine adhesion, be aware of the dynamics of the ejection process, the possible pulling of vacuum on the pin and deformation of material surface at release (notch-effect). These effects can give quite a complex release force graph.
COF also can vary widely with mold temperature and the pre-heating of the sheet prior to injection molding. Also, no mold surface should be smooth, and the RMS or roughness chosen can make huge differences. Finally, I've seen the same mold used on different resins - e.g., ABS vs. PP-based TPO resins. Each had to be taylored with the proper release. This is done anyway for extrusion purposes, but subtle shifts in mold release additives for the sheet extrusion step can affect thermoform mold release as well. A simple ladder experiment would help, or you can design an injection mold with many different RMS finishes too and do a full designed experiment. This would include sheet temperature going into the thermoformer as well as heat dwell time. Dwell and temp affect the rate the mold release can bloom to the sheet surface, which affects release.
COF also can vary widely with mold temperature and the pre-heating of the sheet prior to injection molding. Also, no mold surface should be smooth, and the RMS or roughness chosen can make huge differences. Finally, I've seen the same mold used on different resins - e.g., ABS vs. PP-based TPO resins. Each had to be taylored with the proper release. This is done anyway for extrusion purposes, but subtle shifts in mold release additives for the sheet extrusion step can affect thermoform mold release as well. A simple ladder experiment would help, or you can design an injection mold with many different RMS finishes too and do a full designed experiment. This would include sheet temperature going into the thermoformer as well as heat dwell time. Dwell and temp affect the rate the mold release can bloom to the sheet surface, which affects release.
There is nothing wrong with using the same material for the lifter and the lifter pocket. The issues to check for are
- Is there a difference between the angle of the back wall of the lifter and the lifter rod (usually if the back wall is greater by at least 3 deg you should be good there).
- Are all the other lifter walls drafted sufficiently?
- Are the lifter carriages sliding freely? No binding etc.
- Is the ejector plate flexing?
- Use the ejector plate guided sufficiently to ensure it is not cocking?
It is very common to use PP to test the function of a mould re slide movements venting flash etc. before using the more expensive and more demanding resins. PP is also used at the end of the run to purge along with a suitable purging compound and ensure there are no deposits of the high temperature resin left in the system as can play havoc with a hot runner mold being hung later. There are also wax injection systems available for testing moulds on the bench. I haven't used one for a long time now. Or the old trick of burning a candle under the sprue. The resulting soot deposits inside the mold can tell you a lot. i.e. mismatch and flash.
Even though N2 is green, for PP N2 assisted foaming is not the most cost efficient process. Nitrogen has too low solubility in PP. So much higher pressure is required to get consistent foam. Maintaining high melt pressure in PP is not easy. Higher pressure means also higher cost. At lab scale - all of these looks dandy. Proof is in producing at commercial scale.
Part you are considering is too large to use a typical structural foam injection molding process. Structural foam injection molding process can never achieve low densities of EPP. For large part (even much smaller than what is discussed here), Treacle process is not suitable.
Part you are considering is too large to use a typical structural foam injection molding process. Structural foam injection molding process can never achieve low densities of EPP. For large part (even much smaller than what is discussed here), Treacle process is not suitable.
There is a list of things to look at when you do troubleshooting on silver streaks. For example: 1) Material is not dry enough, masterbatch also need to be dry. 2) Gate size is too small to cause high shearing rate, then material break down. 3) Melt temperature not to be too high. 4) Back pressure too low make air come in. 5) Runner has shape edge. 6) Injection speed too fast. 7) Last factor maybe material is not good. Look on the web for many excellent troubleshooting guides.
First of all, this defect is commonly known as splay - it is often due to wet material or contamination. Before you go and start doing lots of troubleshooting in the processing set-up, I suggest that you look at whether the material is properly dried before processing, whether you may have contamination from other materials, or see if you purged adequately before the current job. When you look at the material to see if it is wet, also check that any color used is also dry if you are blending it in. Thorough cleaning of any dryers and feeders is also an absolute before material is placed into them for conditioning.
First of all, this defect is commonly known as splay - it is often due to wet material or contamination. Before you go and start doing lots of troubleshooting in the processing set-up, I suggest that you look at whether the material is properly dried before processing, whether you may have contamination from other materials, or see if you purged adequately before the current job. When you look at the material to see if it is wet, also check that any color used is also dry if you are blending it in. Thorough cleaning of any dryers and feeders is also an absolute before material is placed into them for conditioning.
We have to some correction of water flow and temperature of water with mold temperature control unit, but it is extra cost and setting it to optimum level with minimum extra energy cost is critical and time consuming.
At corners, forces are in 3d for shrinkage, some corners require the design to be compromised or if not to compromise an another pre made filler plastic insert to added while molding and/or extra cooling at corners externally and/or by giving feeding material (hot), ie an extra gate point with, and its direction of feeding material, towards the shrink pulling.
At corners, forces are in 3d for shrinkage, some corners require the design to be compromised or if not to compromise an another pre made filler plastic insert to added while molding and/or extra cooling at corners externally and/or by giving feeding material (hot), ie an extra gate point with, and its direction of feeding material, towards the shrink pulling.
Ribs that are deep should be quite narrow with as much draft as you can get. Use you tolerances and DRAW POLISH the mold. The more and deeper the ribs, you have to have that much more ejection area just to get the plastic part out without marks or distortion of the part, just based on friction of the shrinking part and the steel; and the likely result of not filling the rib at all (even more shrinkage). As a rule of thumb, the rib should be no thicker than the wall that it is attached to (sink marks), in fact only 50% of the wall and 2-3X wall for the depth would be a lot better.
There is virtually no way to completely eliminate the appearance of glass fibers at the surface of an injection molded part, particularly with this high a loading percentage.
As you probably know, the glass fibers are like logs floating in a stream of water, as long as the channel is wide enough and the flow through the channel is not turbulent, the logs will orient themselves axially, parallel to the stream flow. When the channel changes in depth or width to create turbulence the logs will begin to randomly orient themselves and get bunched into clumps of logs. If two streams of logs come together the collision of the two log flows will randomly orient where they come together jamming and restricting flow.
As you probably know, the glass fibers are like logs floating in a stream of water, as long as the channel is wide enough and the flow through the channel is not turbulent, the logs will orient themselves axially, parallel to the stream flow. When the channel changes in depth or width to create turbulence the logs will begin to randomly orient themselves and get bunched into clumps of logs. If two streams of logs come together the collision of the two log flows will randomly orient where they come together jamming and restricting flow.
