Most organic pigment manufacturers uses their own test method and most of them are molding a chip in a homogeny thickness with a certain length and width (longer length) and then measures the shrinkage in length vs transverse direction to provide what could be called a warping index. The uniso-tropical shrinkage is a sign of warping and an iso-tropical index of 1 is of course the best (= same shrinkage in length as well as in transverse direction).
All pigments act as nucleators and will influence shrinkage and warping in semi crystalline resins. Some organic pigment chemistries are really powerful nucleators and will provide a high degree of warping (e.g. Phtalocyanine pigments). Besides general aspect as part- and mold design and a careful selection of pigments, nucleating agents may be added to overcome warping effects.
In injection molding, for any faults error on any 3M (Material, Machinery/Molding variables, Mold) maybe responsible. If you have earlier used similar combination of material & got satisfactory results (Reference sample may be available), then compare MFI values of base resins, if the values are same, then grade may differ & you have to get characterization results ( DSc/TGA) to ensure same combination being used.
For satisfaction, you may test MFI, density of raw material (Resins) used for product molding to compare with old raw material specs. Chemistry wise, materials molecular weight may differ (MFI will change) or MWD (molecular weight distribution) may not same as old stock. If you are getting compounded PC+ABS blend from compounder, then percentage of individual resin components (PC & ABS) may vary or they might have used different grades of PC & ABS in preparation of blend.
Rib is a frequently used feature in plastic injection molded parts design for the purpose to enhance the strength of the plastic parts, typical rib design see below figure.
The thickness and location is essential of the rib design. Usually, ribs should be designed with a thickness of 1/2 of the wall thickness to avoid a thick section at the base of the wall, which would cause sink marks on the part surface. Ribs are usually spaced at a distance at least twice the wall thickness to allow enough steel between the ribs for adequate cooling.
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
The simulations results have a qualitative accuracy for this reason many companies and the academia are working in this area. The reason is that all models use strong assumptions that can be weak depending on the material, geometry and process conditions. I can give an example for fiber filled injection molded composites. For short fiber composites in a center-gated disk test sample, we have found that the actual models fail to predict the orientation near the gates and up to r/H =39. The actual model implemented in most software is reasonably good above 39, but still prediction of fiber orientation near the walls is challenging. Additionally, the quality of the predictions reduces noticeably as you increase the fiber content and the thickness of the parts. These two conditions reduce the validity of the assumption used in the simulation packages. The area of interest of many software developers is the prediction of fiber orientation of long fibers. This is an area of opportunity because we are still unable to predict a reliable fiber orientation due to the semi-flexibility of the fibers.
The easiest way to check the tonnage at mold parting line would be to use the pressure sensitive film. There are many factors that can cause the machine tonnage to change. Toggle clamps can vary the tonnage due to thermal expansion of the mold. Hydraulic clamps produce the same amount of clamp tonnage once they achieve full pressure position.
Pressure sensitive paper or die blue allows you to determine if the tonnage across the mold clamping surface is consistent. Factors that negatively affect squareness:
- Mold construction
- Platen surfaces
- Clamp squareness
- Tie bar stretch
- Tool offset
Specific decisions for the best approach (material, process, design detailing) can only be made with a detailed knowledge of all the constraints (structural, dimensional and financial) and all the must-have, nice-to-have and absolute must-not-have features and attributes. Is there not a web address where we can get more detailed information? Another process (actually, a hybrid process) came to mind and this might suit the combination of requirements that I think you have. This is offered by a couple of machine manufacturers. You'd need to contact the machinery manufacturers direct for contact details of processors offering this service. A thin skin (can be vacuum-formed) is normally inserted in the relatively low-cost mold, to give high-quality surface. The robotic head dispenses PUR foam with reinforcing fibers - that are chopped in the head also - into the open mold. Once the mold is closed, the "B" surface is formed, complete with any ribbing and fixing points, etc. However, the total thickness will tend to be significantly well above the 5mm maximum that you have defined. Rigidity is very impressive. Impact strength will depend on surface material and density/reinforcement variables in the backing material.
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.
Getting to a true high class AGMA mesh in a molded gear and maintaining that over a production run is difficult. I have found that very few molders worldwide can achieve this. This can be said for any gear class but the higher the class the more rare. HP is the worlds number one high-class gear user, finding molders competent in making gears that meet these standards is an ongoing challenge.
Finding a knowledgeable gear engineer to define your mesh is the best place to start. Gear engineering is not trivial and not something you can just do with a "text book" understanding. This is an engineering specialty, especially concerning molded gears as their manufacturing issues and behavior in use is very different than machined gears. I know many premier gear providers who use such outside consultants to do their meshes though this is done behind the scenes. I recommendation is, still, to use a qualified gear engineer to provide you with the mesh you need.
The thickness of skin layer is inversely proportional to mold temperature, melt temperature as well as injection speed. In principle, it is possible to obtain minimum thickness of skin layer with elevated mold temperature and melt temperature, at high injection speed. Typically, the skin layer is amorphous because of fast cooling of melt. In addition to that, the shear stress is low. Therefore, both the thermal induced and stress induced crystallization processes are inhibited.
If one likes to crystallize semicrystalline polymer with bare minimum or no skin thickness, shear induced orientation of injection molding could be adopted. The Brunel University and University of Minho use this technique to optimize the crystallization.
A appearance issue on a rear lamp part for automotive due to first use of a PMMA material. This is a blue opaque colored plastic including metallic particles in order to get a shiny aspect. There is important visual defect such as flow mark due to poor aggregation of particles with material.
This sounds more like the melt front losing injection pressure allowing the metallic particles to separate out or a knit line, which will be very difficult to solve. The melt fronts collide and then the particles fail to align in the same direction, creating a different look. Melt and mold temperatures will help, and valve gate changes as well, if used in the injection mold.
When using compression molding the cavity is slightly open when injecting and thus has more room for material. This way all the needed material can be injected rapidly into the cavity and instead of applying pressure in the material the mold clamps and thereby closes the cavity to the intended size (or volume). This reduces the internal stress in the part as you can image the molecules finding their own space so to say. Compression molding is very useful in thin wall parts to better be able to fill the part during injection and optical parts where stress will disturb the optical quality of the part, that's the pros.
However many beverage caps use continuous rotary compression molding which is altogether a different process. We used this process at a company I worked at for 35mm film cans and covers and it can be hypnotic to watch it run at full speed. If you look at a beverage cap and there is no indication of a gate mark on the part, it was most likely compression molded.
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.
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.
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.
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.
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.
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.
The best way for you to learn mold design would be to work for a company that designs and makes a lot of molds. Do some research and try to get a job with a mold company that has a very good reputation. Try to find someone to learn from that has a lot of experience, good working skills and knowledge of mold design, and then learn everything from him or her that you can.
While having an education is good it will not give you everything you need to be a successful mold designer. You can learn to use CAD software and get a general idea of how molds are made in school but there is nothing like real life hands on experiences in the factory to learn from.
We spoke with a local injection molder who is very experienced and produces high end plastic parts for the medical industry. When they examined the parts, they noted the flow path, how it creates and positions the weld line, and was almost sure that the flow was trapping air in the part, at the weld line. There was a very slight discoloration along the weld line, but no voids or bubbles in the part. The air is compressed at the weld line and weakens the line. Several mold design features can be incorporated to resolve or prevent this (some of which we have incorporated into the mold modifications):
- move the gate to change the flow direction and path (done in the modification of our injection mold)
- add an ejector pin at the site of the trapped air, to vent the air (added pin at the remaining weld line after gate was moved, ensuring venting).
- vent the whole perimeter of the part mold.
- locate the gate at the thickest section of the part.
To get a quality injection molded part, besides a quality mold, you need to know how to setup the process working condition correctly, optimum working condition setting provides the minimum cycle time, lower scraps rate, stable performance and quality parts, a complete injection molding process includes: filling stage, compression stage(packing), holding pressure stage, cooling stage, ejection. There are three major elements to consider to setup a correct working condition: temperature, pressure time.
Let's face it, those of us in the plastics molding industry typically have to deal with sink marks with most parts. We all understand that the Geometry, Variations in Wall stock and Interior features sometimes go beyond design guidelines and result in sink marks. For reducing sink marks there are some process adjustments that may resolve the problem. If you have Quality Tooling and an accurate water temperature controller, you might be able to "Freeze Off" the Cavity side of the part while keeping a good hold pressure on the resin. This technique would usually add time to the total cycle but perhaps worth it. I have also used the RHRC (Rapid Heat Rapid Cool) process which is not used at many molders since it requires a Steam System that is piped to the Molding Presses
There are some reasons to cause the lack of material in final injection molded parts. First of all it starts with the mold design. Second we have the plastics. Third we have the injection molding machine. Forth we have the people involved orchestrating the whole concert. Fifth we have the machine and sixth we have the environment. Last but not least we have the process itself.
Starting with the injection mold. The mold has to have a design that allows you to produce good plastic parts. Clear for all of us every injection mold has a process window. That means that whatever your molding machine is doing at a certain viscosity the mold needs a certain pressure within a certain time limit in the cavity. This is unique for each and every injection mold like a finger print.
The injection molding machine outputs cannot be set, but the inputs can be each time you set the injection mold. Some of these set points, like mold temperature and barrel temperatures can be set. Of course this depends on which factors are the most critical to the injection molding process
. If you had ability to perform a simple screening DOE before you put a specific injection mold into production, Minitab can pare to out the most significant inputs. If nothing else, these would be the ones to monitor. However, you'd likely want to capture fill time, cushion, screw recovery (loading time) and cycle time (especially if the machine is not run automatically.
Bottom line, if you have unlimited funds to purchase advanced monitoring systems and have employees that know how to operate them properly and analyze the data they produce, then by all means use them. But if you are dependent on your machine operators to produce good product, you must give them simple tools that they can understand and use while they are right at the injection molding machine. And they can monitor virtually every shot in real time, so if something does drift, or a machine or mold issue does arise, they can notify appropriate engineering personnel immediately.
Mold assembly is one of the most critical steps of mold making
procedure, all the parts machined or purchased need to be put together and required to be work functionality. Mold assembly job requires comprehensive understanding of mold structure as well as injection molding
. Quality of mold assembly determines the mold precision, injection productivity. The work instructions below can be treated as a guide for mold makers.
All parts are machined correct and clean, the work tools required are available and the workplace is well organized, before assembling the mold, all the components must be check and verified.
There are more for different types of mold structure, such as 3 plate mold, they have unique design of latch lock, limited pull plate, runner plate etc. and for hot runner molds, they have special design for hot runner manifold plate, and installation of hot nozzle wiring, plugging etc.
Soft start is designed to make sure any moisture that may get into the heaters will be baked out at low slow temperature rise before higher temperatures are applied. This will prevent your heaters burning out prematurely. Many times when I have to trouble shoot a hot runner in the field, a customer has issues starting up a system that has been running a filled resin. The suggestion of cleaning out the filed resin at shut down would not void a warranty. In fact, if the hot runner supplier heard that they would support it.
Using the mold to make plastic parts or Nylon part, depending on the application, one long core pin from one end of part. Cores mounted on top of mold.
The plastics are molded in the vertical position in the mold. The ID of these parts or Zero draft, to allow for the mixing elements to be inserted without regard to position - they fit either way and must be a snug fit to the ID of the nozzle. Water bubblers run the entire length of each core with a threaded tip on the end- water tight with a little super glue.
Proper location of the gate point will be directly affect the quality of the injection molded parts gate location selection should follow the following principles:
- Gate location should be chosen in parting surface, so that it would be easier for machining and maintenance.
- The runner should be designed even, mold flow distance and sectional size in balance can achieved stable molding quality.
- Gating location should be on the thick-wall area so it ensure the cavity can be filled completed.
- The mold flow should not be right on the inserts or lifter, high pushing pressure of melt flow would probably deform the inserts.
- Try to avoid weld marks or weld lines created in the critical surface, changing location of gating and try to make the weld line on uncritical surface.
- Consider the venting when design the gating, make sure the end of the mold flow have good venting.
- Gates should be easily removed and gate mark should not affect the appearance of the molded parts.
By applying all the above it is arrived per cavity about 3.4 KN force will be required to pull out the core, then for 4 cavities and multiplying by 1.5 as w.o spring load concept consideration, total force needed to pull out the 4 core pins for this 4 cavity mold will be around 21 KN or 2140 Kgf.
Draft will be, for the ID:15mm, the core pin dia will be at the end it is Dia 15mm and in the bottom 14.1, even the core pins are provided as two halfs (155mm Length each) to match the overall length 310 from top and bottom. Both side the core pulling will be done.
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.