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.
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.
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.
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.