Plastic Injection Molding Quality Standards

cheaper tip of plastic mold and injeciton molding soltutionIf you are engaged in plastic injection molding business or job, you must have some basic quality idea on how to control the quality of injection molded products. Otherwise you might get trouble for your final products later. Therefore we would like to share some useful skills as below.

Visual Inspection
When you get the molded parts from injection machine, you should check the appearance immediately by eyes. (some of defects should be identified by measurement tools). Here below are some common injection molding defects that will happen with your products.

  • Flash
  • Deformation
  • Sink marks
  • Flowing marks
  • Short shots
  • Welding line
  • Burn marks
  • Warping

Even thought the above mentioned are some common defects, however if you get a good mold manufacturing, you can prevent them also. So this is really depends the mold tooling, material, and injection molding parameters.

Dimensional control

Most of time, we will encourage our clients to release us 2D drawing with tolerance, material, and other specification defined, so that the manufacturing system will be able to follow and meet those specifications. Otherwise you will never know how your plastic parts and final products will be.

Of course, those dimensions should be measured with accurate measurement tools, like CMM, projector, calipers, pin gauge, etc. and collect the inspected data on a sheet for final assessment.

Assembly and function test

If the visual and dimensional inspection are OK, it’s time to check the assembly and function. Since this process is to check the overall results. It can avoid some critical faulty to happen.

All in one word, the quality control of injection molding process is very important to a product. We should take it serious.

 

Everything About Plastic Injection Molding Sourcing

The injection mold cost calculationWhy have to make plastic injection mold in China?

Everyone knows it’s costly to manufacture a plastic injection mold tool, especially in European and American countries, to save the mold manufacturing cost, in early 1990, many foreign companies moved their mold making factories to Asia, like mainland China, Hong Kong, Taiwan, Korea, etc. and you might think that why they have to make plastic injection mould in China?

Yes, Perhaps they have lots of choice to make your mold in other regions even in other Asian countries except for China, like in India, Vietnam, and Indonesia. And those countries also become more and more popular in the role of global manufacturing industry, however they are still not so matural in mold making industry compared to China, even though they do have lower cost labor and expenses, and they still have a long way to catch up Chinese mold makers. like lazy workers, poorer infrastructure, and worse mold technology, On the opposite, China has a very matured environment for plastic mold tooling making as well as injection molding, it’s estimated that China has nearly 40 years of mold and plastics industries, and accumulated lots of experienced toolmakers and technical workers. They can offer European and American quality standard mold, but with at least 40% of cost cheaper than those Western countries, like USA, Germany, France, Poland, England, etc. This is the main reason why people love to make their plastic mold tooling in China. Meanwhile China has the most matural manufacturing supply chain for full product development, and you can find anything you need conveniently and efficiently.

The reality of Chinese plastic injection mold makers

Since 1978, China had opened the door to foreign investors and started to take the role of worldwide factory. From that time, a lots of international companies moved their mold manufacturing facility to China for cost-saving purpose. This is also the biggest opportunity for Chinese people to learn mold making technology. At that time, many Chinese workers were working for some foreign mold manufacturers who had mold factories in China, this is how the original genus of Chinese mold  making technology is from.

From 1990, more and more Chinese local mold makers quit their job and started to set up their own mold factories for mold making and injection molding services. Because mold making is really a good business for them at that time.

Compared to European and American countries, China has much bigger advantage in lobar cost and other facility expense. Meanwhile Chinese plastic mold makers are very brilliant and diligent to purse their career. They can work 12~14 hours a day without monthly holiday, which is an unbeatable advantage for any other countries’ workers.

Nowadays there are totally about 10,000 plastic mold manufacturers in China, they are mainly sprayed in Southern China (Shenzhen, DongGuang, Guangzhou cities)and Eastern China(Shanghai, Zhejiang,Jiangsu provinces). And you might be wondering where to choose a proper mold supplier. Honestly to say, If you are looking for high quality mold makers, you should always go to Shenzhen or DongGuang mold makers, as they really provide very super quality mold and trustable services. However if your project doesn’t need a precision mold making, you can choose a mold manufacturer in Eastern China.

On the other hand, we have to reminder that there are 8,000 mold trading companies in China, most of time you might deal with those trading companies instead of real mold factory, as those trading companies pretend very well that just looks mold factories. Normally it is very hard to distinguish who are the traders. and you should always audit your potential partners carefully before doing business with them. Otherwise you might take your project on high risk.

How to find reliable plastic injection molding manufacturers in China?

As we just mentioned above, there are ton of plastic injection mold companies in China, some of are large scale of mold factories, and some of are only grouped with few people, even some of are mold trading companies without any facility. Most of time, foreign companies often deal with those trading companies and being charged high cost and offered poor quality products. Since those trading companies pretend to be a mold factories, and it’s quite hard for a foreign company to know their real identities.

But how can a foreign company find a reliable China mold manufacturer? Here below are some useful tips:

  • Collect Supplier Information—You can go both internet or business fair to collect some rough information from the potential plastic mold making companies, like factory name, contact number, email address, company location, etc.
  • Finding The Detail Factory Address—You should require a detail factory address, since there are so many mold trading companies in China
  • Reference Customer – Ask for few reference customers, this is a useful way to know their experience and capability in mold making industry.
  • Reference Sample—Check if they have a similar product before, in this way, you can know the mold maker’s experience and capability, it’s also to put your project at relatively lower risk.
  • Mold Making Equipment– Check if they have CNC, EMD, Wire-cutting, injection machine, and CMM inspection machines, since those machines are essential for high quality mold making.
  • Number of Employee—The number of employee determines their factory size and cost.
  • Annual Sales Performance—Knowing about their annual performance is important for their overall capability
  • Certificates – Ask if the factory is approved with any quality system, which is a practical warranty of your products.

How to manage your China injection molding companies efficiently?

After you choosing a right Chinese injection molding company, you should work out a controllable and efficient solution for future’s work. It will be quite helpful to hit your timing, quality, and cost targets. And we also would like to share some practical experience on how to work with your China injection molding manufacturers as below:

  • Quality Control –You should contract the quality agreement with your mold supplier and get the products approved on site before shipping.
  • Timing –Get a timeline from your injection molding manufacturers, and follow up it tightly
  • Efficient Communication Window –You should get efficient communication window from your mold suppliers so as to move forward your project smoothly and efficiently.
  • Requiring for a Weekly Project Status Update –You must require to obtain weekly project update from your Chinese mold factory, So that you will have a clear tracking on how and where your project is going on.
  • Milestone Meeting–While complex mold project, you should have a milestone meeting to review with your plastic mold makers, otherwise there will be lots of trouble for your project management.
  • Mark a Score for your supplier quarterly –If you are simultaneously working with different plastic injection molding companies, you should prepare a supplier evaluation list, and make a quarterly score from them based on overall satisfaction, quality, timing, interactive altitude, and capabilities.
  • Annual Audit –If the China plastic injection molding manufacturer is a vital role of your business, you should always annually audit them in person, or you can send the third party of supplier management agency to perform the annual audit. In this way, you will know the reality of your molding partner instantly which enables the stability of your plastic mold making and injection molded products.

 

7 Important Factors to Plastic Injection Molding Process

The plastic injection molding process parameter is very important to produce injection molded parts. It directly influence the quality and efficiency of a molding production. Sometimes it will affect the mold making process, therefore we would like to share some useful experience on how set up a correct injection molding process parameter

Image result for plastic injection molding processCLAMP PRESSURE

Before injection molding process, we must install the plastic mold onto an injection machine.  The clamp pressure usually exists at the other end of injection machine, which gives clamp pressure is to keep the injection mold closed against injection pressure. normally, different type of resins requires totally different clamp pressure, the material with good flow-ability requires less clamp pressure. but the stiffer flow material will requires more clamp pressure. Therefore we need to see specific plastic part and material to determine how much clamp force we should use.

Mold temperature

The mold temperature is very critical to an injection molding parts. As it will affect part shape defect, (deformation), dimensional precision, surface appearance, and mechanical properties. For example, if you make an ABS or polycarbonate plastic part, we should set the mold temperature as a relative lower level, since the higher mold temperature would result in bad impact resistance, strength resistance, as well as fatigue performance parts.

Melt Temperature

Melt temperature is one of the most important factors in the injection molding process. It directly or indirectly affect the resin flow-ability. If the melt temperature is too low, the resin might not be able to be melted that the resin keeps the original hardness of raw material. If the melt temperature is too high, the resin will be burned and looks worse appearance.

To set up a proper mild temperature, you should balance the material flow-ability, part shape, and usage. In case you are not sure what temperature you should give, you can gain it from your raw material supplier.

Injection volume

Injection volume means how many meld raw material to be injected to the injection mold, so as to obtain the desired part shape and dimension. If a oversize material injected, it will result in flash in part, conversely, if a less amount of material injected, the part might be incomplete. While injection molding process, we can adjust different volume of injection material,

Injection Pressure

The injection pressure is another important molding parameter . Normally, the highest pressure and fastest fill rate are the best condition. However, high pressure will increase molded-in stress. If the injection pressure is too low, an incomplete part could happen. If the pressure is too high, the part will come with flash.

Nozzle Temperatures

Nozzle temperatures impacts the flowability, the cooling speed, and the performance of plastic parts, If it is too high, the melting plastic material will drool in the nozzle, if the temperature is too low. Materials may also block the nozzle. And you have to take times to fix out the block material problem. If a high production volume, we can design the mold with hot runners that extend the nozzle system inside the plastic mold. In this way, there is less waste material and quicker for injection process.

Material Flow Rate

It is very critical for a injection molding process, since the material flow rate will direct affect the injection time, filling time, and filling condition of a plastic molded parts. For example, ABS has much worse flow rate than PP material, if for a large size of part, we should choose a better flow rate material when product design. Otherwise there will result an incomplete shot problem

Injection Mold Making Process

anatomy-of-a-mold manufacturingMold Design

Mold design is the first step to make an injection mold, no one can make a mold without a mold design. Since the mold design process is a little bit complicated, so it’s hard to explain how a mold is exactly designed.

However there are some basic rules and terms that you must know it.

  1. You should never design a mold without any basic information the part, like the part material, color, total usage of the mold, part function, etc.
  2. Make the mold design to adapt for customer requirements in cost, quality, and timeline.
  3. You should confirm with your customer if any information you are not sure, otherwise it’s risk to make mistakes.
  4. Before mold making, you should send the mold design drawing to your customer for confirmation.
  5. Document all the design drawing, BOM, and sketches, since those information might be traceable for future’s modification.

Here below are some critical concerns that a mold design should consider:

  1. What is the mold life?
  2. Number of cavity for the mold?
  3. How to design the parting line?
  4. What way does the sliders deploy?
  5. How about the gate system?
  6. What is the estimated injection cycle?
  7. How to make the mold running at automatic system?
  8. What will be potential defect if we design the mold in this way?

Preparation of mold steel, mold base, and other accessories

After the finalization of mold design, we should get all of material prepared to mold making, because a mold factory can never produce raw steel, mold base, and other mold accessories. Here below are the main list of all outsourcing components:

  1. Mold Base
  2. Mold steel of core
  3. Ejection Pin
  4. Copper for EMD machining
  5. Sleeve Pin
  6. Ejection Spring
  7. Screws
  8. Cylinder for sliders(if have)

Rough Machining

When we get all of the mold material on site, we are about for rough machining for mold cavity and mold core. At this stage, most of work will be done by milling machine and CNC machining. Because it’s a rough process, we will leave about 0.3~0.5mm extra material on the part so as to make the precision process at next step.

If for some high volume production mold, we will have to harden the mold steel after rough machining. This is only to obtain high better duration when injection molding process. But after hardening of mold steel, it’s hard for machining.

However if a mold life doesn’t require high volume, we don’t need to harden the mold steel. Certainly the manufacturing cost and lead-time will be much different. Therefore you should always tell your mold manufacturers on your mold life.

Precision Machining

Normally we have to make precision manufacturing for a mold, so that we can obtain better surface and precision dimension of the part. The EMD, CNC, wire cutting machines are most commonly used for precision mold manufacturing. As the manufacturing time is very slow, so these process makes high quality mold, surely the cost is much higher.

In China, we operate those machines by workers. However in some advanced countries(Like Germany, Japan, USA), they can make the mold by automatic system, instead of labor cost facility. This is why people think Western countries can produce better injection molds than China.

Mold Assembly and Fitting

After every mold components are manufactured based on our design, it’s the time to get them assembled and fitted together. The mold assemble and fitting time takes about hours to complete, however a skillful mold maker can even make it quicker, because they have rich experience on how to fit the mold, however the beginner might take much longer to get it ready. Otherwise the mold tool will need to be fixed again after the first of mold trial.

Mold Trial

When mold fitting is done, we need to get the mold for a trail(we call T0), so that we will know if any problem with our mold making. At this stage, we should keep some sample for inspection or measurement.  For the first trial sample, there will exist some injection defects, like flash, flowing marks, deformation. But these defects can be fixed by mold improvement.

Actually mold trial is an important process to verify a new mold. During the mold trial, our mold trial technician, QC, and project engineers should follow up it until the mold is running normally.

Product Optimization Before Mold Making

When a plastic design, most of the product designers consider less about the manufacturing process, like mold making and injection molding. So it will be easy to get trouble when injection molding if you don’t look the process carefully.

While clients transfer their design drawing to a injection mold factory, their drawing should be optimized before mold making. Here below are some common optimization work we are working for our customers.

 

Wall thickness

The thickness of wall is to make the plastic part flowing smoothly without any shrinkage issue. When we take over a project from our clients, we always check out the material filling by moldflow software. And it’s easy to find out some features that existing uneven wall, which are not good for resin filling, as well result in shrinkage problem. So we will either advise our clients to modify the 3D drawing or we update from clients.

 

Draft angle

Draft angle is a very common design for plastic parts. However lots of product designer forgot to add some draft on the part. It will directly affect the part to be ejected from the mold.

Normally for a part size within 100mm, we advise a 0.5~1.0 degree draft, for a part size 100mm~300mm, we should make it 1.0~3.0 degree of draft. However if a part size is bigger than 300mm, we have to suggest it at least 5 degree as possible. The bigger draft angle, the easier for injection molding.

 

A draft angle should be added on the 3D model at the very beginning of a product design. If you ignored this concern, you have to re-create your 3D drawing, even adjust other relative parts. All in one, you will waste your time to remake drawings.

 

Fitting feature defined by tolerance

We saw a lots customers make a 3D drawing with zero to zero tolerance, which is a terrible tolerance policy for product design, especially for product with precision fitting features. For example, if you design a shaft with diameter of 5.0mm while the assembly hole diameter is also 5.0mm, it’s a big problem to get the shaft and hole assembled together, since there are some dimensional deviation from any manufacturing process. In this case, we suggest customers either set the shaft 5.0mm and the hole 4.9mm, or create a 2D drawing to define the tolerance as properly as you needed.

You should know, when mold making process, the mold maker only follow the 3D drawing for CAM manufacturing system. (if they received a 2D drawing, they might be change the nominal dimension for 3D drawing. We should always pay attention to this issue.

 

Aestetics line

Aestetics line is actually a tolerance design for manufacturing, since the line will absorb any dimensional deviation or part deformation. When a product design, we strongly recommend to add this aestetics line to your 3D drawing. Otherwise the assembly will be a big problem.