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in the following, you will find information about plastic injection molding processes, techniques, and specialized moulding technology, defects.
What Is Plastic Mold/Molding Technology?
Plastic mold technology is also known as plastic molding (or moulding) technology which is a process that has been around since 1872, it is the process of creating and manufacturing plastic components by injecting molten materials into a plastic mold. The process of plastic molding technology is actually quoted as a complex one. First, the part designer needs to design the desired model or hire your supplier to design the model according to your requirement, then mold designer must come up with a completely final mold design. Once this has been created, then start to manufacture the mold, like drilling, CNC machining, EDM, polishing and the last step to make the mold is mould fitting, when everything is finished in mold making, that the actual injection moulding process can start, at the beginning of the molding process we called mold trial, from mold trial to massive production, still needs to take some time and doing several times mold trial, because the first mold trial will more or less have some issue that needs to be finished, after two or three-times mold trial until custom approval the samples, so we could start massive production, this is a simple working procedure to explain from part design, mold design, mold manufacturing to get the perfect ending plastic products.
Although plastic molding technology is not something that most will be knowledgeable about. We all use products that will have been manufactured by using this method. Things like bottle caps, automobile plastic parts, home appliances, furniture components & accessories, bicycle accessories, cosmetics molding & packaging containers, cooking equipment, toys, medical plastic parts, and construction part, etc. We can say everything needs molds & plastic molded parts.
The future of plastic molding
Over the decades, the process of plastic injection molding technology has changed and advanced significantly. Thanks to huge leaps in technology, it is now possible to use 3D printing to use photopolymers for plastic moulding parts. The advantage of using 3D printing for the plastic parts is that will lower the price for lower volume because make custom plastic mold is very expensive. If you need only a few plastic parts for your market testing or function test then use 3D printing instead of using plastic moulding technology will be the better option, this will save the mold making cost for you, but finally, when you need high-quality plastic moldings and the high volume of plastic products to speed up your market you still need to make plastic molds.
How To Make High-Quality Injection Plastic Mold
The quality of plastic injection mold is as same as important to the molding process. The plastic molding company you choose to help you with your product will eventually fight common molding issues. If you have high-quality plastic mold plus good plastic injection molding process that will bring out the kind of results you expect from the end product. The injection plastic molding process is used to produce all kinds of items such as garden tools, electronics, and kitchenware, etc. Components can be made from glass, polymers, metals, plastics, and more, but working on high-quality molds is the only way to ensure the high quality molded parts.
Defects can be attributed to the type of raw material used in the injection plastic moulding process, as well as the quality of the plastic mould, injection molding process skill, injection molding machine, etc. Fortunately, processing and preventing injection molding defects, and using these approaches, manufacturers can create the high-quality injection plastic molds, because if you make a high-quality mold, all other issue is easy to be solved.
Here are some actions you can do to solve the common molding defects and ultimately get high-quality molded parts, there are some key defects that most happened during the mold manufacturing and molding process,
1. Flow Marks – this molding defects normally will happen close to the gate area, and the joint area (joint line), common in narrow sections of components and may be considered minor or serious defects depending on the part wall thickness and expected use. In order to solve appearance defects, during the molding process we need to increase the injection speed, injection pressure, molten material temperature, and the mold temperature, increase the gate size or change the location of the gate is helpful as well (last option). below left picture of flow marks defects, we increased the gate size to improve flow marks because of the wall thickness to too thicker (7mm)
2. Dull Areas – The most common is a dull concentric ring that can appear around a halo-like a sprue. This usually occurs when the material flow is poor and the viscosity is high. Contrary to what many think, this is not a packaging defect, but a defect that occurs at the beginning of the billing cycle. To minimize the possibility, the injection rate profile should be adjusted to ensure a uniform flow front speed throughout the filling phase. It is also helpful to increase the back-pressure and barrel temperature of the screw to reduce dull surfaces resulting from lower melting temperatures, increase the mould temperature can reduce this issue as well. but there must have a cooling system as the feeding area, especially if it is hot runner systems, otherwise is not easy to solve this issue. For dull surfaces generated by design-related issues, this can be improved by reducing the radius between the part and the gate,
3. Burns Mark defects – The burns Mark defects often seen on plastic injection molding parts and looks like a light yellow or black discoloration. This may be a minor defect due to excessive melting temperature, overheating in the presence of trapped air, and excessive injection speed.
Corrective actions for this type of burn mark defect: Reducing temperature, reducing cycle time, and reducing injection speed. Plastic Mould Manufacturers must also ensure that they have the proper gate size and gas vents gloves to resolve the trapped air problem that leads to this defect, because the air trap issue is a most common reason to cause this burn mark issue, and could never be completely solved by adjusting the molding process, to completely solve this burns Mark defects adding venting is the best solution, like increase the venting grove, add venting inserts to the deep ribs, etc.
4. Gloss difference defects – Gloss differences on textured surfaces tend to be more pronounced, and even if the surface texture is uniform, the gloss of the part may appear irregular. This is a problem that occurs when there is insufficient replication of the mould surface in some part areas, and sometimes there are lots of ribs at the core side that can increase the gloss changes issue on the textured surface. It can be corrected by increasing the melting temperature or mold temperature or holding pressure. The longer the holding time, the more likely the mold surface will be replicated accurately, if there ribs design caused this issue, to improve this issue we can add some radius to all of the ribs, this will reduce the internal stress so that the textured surface can be improved as well.
5. Warping defects (deformation) -plastic molding parts have warping defect is normal, especially the long size molding part, distortion defect is hard to solve, improving the mold design is the mean solution, it is very limited to solve this issue by adjusting the parameter of the moulding machine, the reason and solution to improve warping, distortion is listed as below for reference.
- When the deformation is caused by the residual stress of the molding process, it can reduce the injection pressure, increase the mould temperature to improve this.
- If the deformation caused by part sticking, can improve the ejection system or add more draft angle to solve this issue.
- If the warping defects caused by poor cooling channel or poor cooling time, we can add more cooling channels and increase the cooling time to improve this, for example, add more cooling water closing to the deformation area to improve warping defects, or use different mold temperature to cavity and core, this method could normally solve the small warping defects.
- If the distortion issue caused part shrinkage, to solve this warping defect must be adjusting the mold design, sometimes we need to measure the distortion size from the molding part and do the pre-deformation design to the part, the resin has large shrinkage rate, usually crystalline resin (such as POM, PA66, PP, PE, PET, etc) has more warping rate than Amorphous resin (such as PMMA, polyvinyl chloride (PVC), polystyrene (PS), ABS, AS, etc.), sometimes the gloss fiber material has more deformation issue as well, this is the hardest solution because you may need to adjust the part design two or three times to completely solve this issue, but the only way to solve the distortion issue.
6. Short shot defect – Short shot means not completely full filling to the mold, this molding defect normally happens at the end of the filling area, or end of the rib, or some thin wall area, there are some reasons to cause this defect below.
- The mold temperature is too low. When material fills in the mold cavity since the mold cold too fast to cause the liquid material is not able to full fill to the end of part or some deeper ribs. Increase the mould temperature could solve this molding issue,
- Material temperature is too low. This issue could also cause the short shots issue, this reason is similar to the issue of low mold temperature, to improve this issue we can increase the melt temperature of the material to solve this molding defect.
- Injection speed is too slow. The injection speed is directly related to the filling speed, if injection speed is too low, the liquid material filling speed will be very slow, slow flow material will be easy to cold, this will cause the short shot since material getting cold in advance, to solve this issue we could increase the injection speed, injection pressure and holding pressure.
- Venting issue. This is the most common molding defect we meet during mold trial, all other defects we could solve by adjusting the molding parameter. If short shot issues caused by venting issue, to completely solve the short shot, the best solution is finding the way to release the air out of the cavity, if the air stuck in the cavity or in the dead-ending area (end of ribs for example) so the short shot issue will happen at that area, to solve this issue we need to increase the venting grooves on the parting line and add venting insert to the dead-ending spot to guide the air out.
7. Sink mark – It sinks spot on the molded part, it caused by unbalancing plastic material shrinking in the mold cavity, looks like lack of material on that sink area which is not matching to the part geometry, this issue happens to the thick wall area or lack of cooling system in the mold, the mean reason to have this sink mark issue is the uneven wall thickness on the part design. If some ribs or some area have a thicker wall than the other place (rib thickness should around 1/2 – 7/10 max of the mean wall), then this thicker area will be easy to have sink mark issue. Below are some suggestions to improve this defect.
- Change the gate location close to the thick wall place
- Add more holding pressure, holding time, and injecting more material in the mold cavity. When using this method you need to double-check the part dimension is still in the tolerance requirement
- Increase the cooling time and the cooling channels to improve this issue, plastic has shrinkage rate is normal. If the cooling time is too short, the part still warm after mold opened, then the part shrinks quickly without anything cooling system, this will be easy to have sink mark, increase the cooling time until the plastic moulding part completely cool in the mould cavity, this defect will be solved.
- If the part design has a serious thick wall on some of ribs or bosses, to solve this issue we need to improve the part geometry, add some insert to the thick area to reduce the wall thickness, this issue could be solved, for this unbalance wall issue, we could use software to analysis then and prevent in advance, before mold manufacturing we will make fully DFM report and send to our customers for approval, below is sink mark analysis report samples.
The manufacturing world has been increasingly confusing over the years. If you are in this industry, you probably already have this sense of confusion. What’s happening is that the global market is really starting to come true. A few years ago, there were a few outsourcing companies in some countries like China, but now it is impossible to track production. Looking at industries such as injection molds, you can see that this trend has really begun. However, it may be overwhelming at first, but there is no doubt that productivity will increase significantly. Today, injection molding China has become even more efficient due to a faster turnaround.
How to get plastic mold and plastic injection molding products Cost?
In order to get a price for your plastic molding project, then you need to get both costs for your plastic mould and moulding parts.
1. How to get a price for export plastic mould
To get a price for plastic injection mould there are a few things that you are going to provide to your supplier, in order to make sure that you have given the supplier all of the information that they need to check the price accurately, below are some key points for mold price estimating, this is the most important information for export molds.
- First of all, you are need to make sure that you have a 3D part design in your hands, if you do not have the drawing then you need to have the pictures of a sample with approx. part size and show your supplier that part structure.
- Second. You need to know how many shots of the mold your requirement, for example. 0.5 million shots of a lifetime or 1 million shots of a lifetime requirement, because those two requirements will cause different price.
- Third. You need to inform them how many cavities you expect for the injection mold. Because this will affect the mold price as well.
- Forth. It is a cold runner or hot runner do you require for your mold, if hot runner what brand of hot runners. YUDO, INCOE, etc, all of that information will have different prices, so you need to specify your requirement.
- Fifth. The number of cavities, you need to specify how many cavities do you need for your mold. Because of one cavity and multiple cavities mold are totally different prices, the single cavity is low than multiple cavities mod.
The above items are very import information to quote a mold price for export mold (you will bring the mold back to your country for production) because all of the information will change the mold price.
2. How to get a price for Injection Molding products
If you only need plastic molding parts, then you only need to tell us (or other plastic molding company) what plastics will be and how many parts do you need per time, what is a surface requirement and colors of the parts, then they will take the rest for you.
To get the cost for your plastic injection molding products it is much easy than getting a price for export plastic mold, simple steps as below to get plastic injection molding service price easy.
- What plastics will be?
- What color do you require for your molding parts?
- What is the part surface requirement? Texture (graining or matt) or high polishing?
- 3D part design (STP or IGS format file will be great for all of the companies), if you do not have a 3D part design, then send your sample pictures with part size and part weight, or idea picture and explaining to us, we still can get the price for you.
- How many parts do you need per time?
- If have any special function requirement?
With the above information, you will get a mold cost and unit molding cost, that information is important factors to estimate the plastic injection molding cost. Otherwise, any price will not have any references.
Are you ready to start working on your new project and search for your plastic molding supplier? If yes then let’s go, today for your plastic molding project to find A reliable Chinese mold company is more important. Because this will bring your market up very quickly, and you will win more profits on your project with spending less cost, please think about today 80% of big companies are sourcing goods from China. Like the iPhone and some other famous companies buy things from China. So what are you worry about? If you are ready then speed up to open your market immediately and join your profits.
If you are looking for some good Chinese plastic molding manufacturing partner you can contact us. We. SINCERE TECH which is a professional precision plastic mold and plastic molding company, sell moulds and molding parts to the world. We guarantee you will be 100% happy with our service and quality, we have the very professional technical team to handle your project very carefully and make the perfect molds and parts for you, some of our customers moved the molds to our factory for troubleshooting since their current mold supplier is not as professional as us, we can send you some of our current customers for you to verify our service, quality, and price. send us an email to [email protected] to get a price, we will never share your design with others. we are willing to sign an NDA to protect your project.