Talking about production technology of injection molding parts for automobile products

Time:2022-09-24 10:16:00 / Popularity: / Source:

China has many complete and huge automobile production bases, and corresponding customer supply chain for auto parts is also growing. More and more factories are interested in processing and manufacturing of various auto parts, and with production technology mature, production process is no longer mysterious. Under influence of fierce competition in the market, more energy of auto parts production factories has been transferred from client to control of production process, to meet customer needs with quality, and to "produce quality".
Let's talk about advantages of complex plastic parts for automobiles:
1. Plastics can be processed at one time, processing time is short, and accuracy is guaranteed; it can be recycled for secondary molding if experiment allows and customer's permission, and recycling of waste products is also very high.
2. Plastic product itself is light and has good elastic deformation, which can absorb a lot of collision energy, and its buffering effect on strong impact is obviously better than that of other materials, which will play a better role in protecting vehicle and occupants.
Front and rear bumpers of many cars are made of plastic to reduce impact of objects outside car on the body. Plastic also has effect of absorbing and damping vibration and noise, which can improve ride comfort. Many mold factories have already received bumper orders from Ford, GAC, and even Land Rover, and they are very mature in manufacturing technology.
3. Plastic has strong corrosion resistance, and local damage will not corrode. It is almost difficult to find non-plastic parts for automotive air conditioning and refrigeration systems.
4. Modified materials are made by adding different fillers, plasticizers, hardeners and elastomers to adapt to uses and requirements of different parts of car. 18 Division of BYD Group has been able to transform corresponding raw materials many years ago to fully adapt to its own product needs. What is more convenient is that color of plastic can be adjusted by color masterbatch and toner, which saves trouble of painting, and electroplating performance of plastic is better than that of other materials.
How to use management means to achieve technical requirements of customer needs. For basic level of production, technology, which is very experienced, cannot be achieved by means of management. Now I will use complete process of a product to give my personal opinion:

1. Project management of auto parts

1. Introduction of new products

Technology and management methods at this stage should be based on explicit and implicit needs of customers. These needs can be seen in customer's information. Source of internal transmission is project manager, project manager transmits information in a timely, effective and accurate manner, can well realize information in development process, which is correct start of production.
Project introduction is not just a matter for project manager and project engineer. His realization must be completed only when an effective logistics can be formed, approved and paid back. So it takes a small core team and a lot of production resources to get there.
We briefly describe basic project team members and responsibilities:
Project Manager (PM)
Receive, save, issue and manage customer demand information; organize relevant personnel to review customer needs; communicate with customers in a timely manner for unclear or unclear customer information
Project Engineer (PE)
Ensure that customer requirements are effectively transformed into project development requirements, and communicated to relevant units in a timely manner to ensure implementation in the subsequent project development process
Quality Engineer
Review quality aspects of customer's needs; convert customer's quality standards into internal quality requirements; realize customer's quality standards in project development process, supervise and control.
Team of new project is very small and simple. The biggest responsibility is to analyze customer information and realize explicit requirements in data. Everyone expects good results from the start, and any new product is carefully planned to produce good results. Therefore, we say that projects are also technology, and how to use technology is cleverness of management methods.

2. Technology in project process

Many people think that this stage does not involve any technology, because everyone ignores key to transforming information into reality in this stage - realization of documents. Many people think that documents are just typing a few words in front of computer. Ignoring that basis of documents comes from production reality, such as FMEA, APQP, etc., we now look at a few technical relationships:
injection molding parts for automobile products 
Main means of converting information into production capacity is to use execution of various documents to control process, so there are the so-called "five tools". Goal is to facilitate contact with everyone involved and ensure that required steps are completed on time. It is not possible for one person or one department to complete all work and must be a cross-departmental collaboration.
Make detailed planning in advance, identify risks such as human, machine, material, method, environment, and measurement, and take countermeasures. Even if short-term economic goals are sacrificed, try to ensure that product is done right at the first time, and to do any of these. No matter how good a project manager is, it can't be solved, only each department can complete it with the help of professional technicians.
In the first stage of the project, from establishment of team to establishment of project, only a simple project manager can complete all work. Main task at this time is to receive and digest information. After establishing a suitable team, project manager needs to deliver digested information to relevant responsible engineers for classification and implementation.

2. Technical management of production workshop

1. Raw materials

Application of plastics in automobiles has expanded from interior decoration to exterior structures. In addition to large increase in amount of polyolefin materials in automotive field in recent years, use of polyurethane and reinforced composite materials in automotive products has also increased. Injection molding products account for an increasing proportion of auto parts.
Use of dehumidification and drying systems must be considered before raw materials are formed. Raw materials with strong hygroscopicity must be fully dried before molding, and dehumidification dryer is the first choice for drying raw materials. Compared with hot air dryer equipped with injection molding machine, drying effect is better. Setting of drying temperature must be based on physical property table. Here we focus on a situation that is often mentioned in system audits.
When baking hopper of injection molding machine can bake 50KG raw materials, and baking time is 4H, there are often two problems:
If 50KG of raw materials can be produced within 3H, it means that newly added raw materials cannot meet requirements of baking materials at all, does that mean that raw materials have not been baked thoroughly, and whether product can be regarded as bad;
If it takes 30H to produce 50KG of raw materials, it means that raw materials that cannot be produced within a few hours need to be baked at a temperature that exceeds specified time several times, whether this will cause defects to raw materials.
Common way to deal with this kind of problem is to tell customer that we can ask raw material supplier for a material certificate to prove that raw material will not have any abnormality within this time frame. This method will be accepted by both parties in the case of no hope of review, but crux of problem has not been finally resolved, so we must require limit test of raw materials. Use experimental data to prove feasibility and reliability of production process. Only by introducing data into each technical link, quantification of work content data is reasonable.

2. Injection molding equipment

Because auto parts are very different from plastic products such as conventional mobile phone cases and household appliances, a considerable part of products have large dimensions, cavity surface is very complex, structural position is subjected to different forces during plastic process, and stress distribution is naturally very high. It is difficult to balance, and key consideration in design is processing capacity it needs.
Generally speaking, processing capacity of an injection molding machine is reflected in two aspects: clamping force and injection capacity (represented by maximum theoretical injection volume). When injection molding machine is molding products, clamping force must be greater than mold opening force generated by pressure of mold cavity, otherwise parting surface of mold will produce flash.
Formula for determining clamping force of injection molding machine: P clamping ≥ P cavity × F/100
P clamping is clamping force (or clamping force) KN of injection molding machine;
P-cavity is average pressure of cavity;
MPa, which is related to product structure shape, accuracy requirements and number of cavities per model, etc., value range is generally between 25-40MPa;
F is horizontal overlapping projected area CM3 of mold cavity, runner and feed port.
To ensure reliable clamping, process clamping force during injection molding must be less than rated clamping force of injection molding machine. Generally, value is about 70%. Of course, for same reason, injection pressure of a set of molds during injection molding process should not be higher than 70% of rated equipment.
Molding compound surface accuracy of large and complex plastic parts of automobiles is fully guaranteed. But no matter how we talk about these theoretical knowledge, everyone must still have great doubts about accuracy of product in manufacturing process.
injection molding parts for automobile products 
This table comes from MP company in United States. It is a professional information for training technicians within company and for global partners and suppliers. Any company can make a similar table to check equipment oil under rated pressure. Pressure change is measured, and change curve is measured, it is clear at a glance whether equipment can work under normal conditions.

3. Injection molding process

Since advent of scientific injection molding, it has become famous in injection molding industry for a while. For technicians on production site, it is a question whether scientific injection molding can bring about much revolutionary technological changes, but it has to be said that his influence on improvement of refined production on production site is not a little bit, anyone who uses scientific injection molding will deeply understand this.
Compared with complicated technical lectures, "scientific injection molding method" can be simply divided into six parts:
Glue Freeze Test
Flow balance test
Viscosity test
Water flow test
Best Cooldown Test
Mold dry run test
In above six sections, I think this latest technology can be briefly summarized. Of course, many foreign companies have begun to adjust the products by using cavity analysis technology by embedding induction equipment in cavity.
Today we only make a simple technical presentation for thick-walled products in automotive parts, and in thick-walled products we use production of light guides for analysis.
injection molding parts for automobile products 
Cost of light guide products has always been high, and injection molding of thick-walled optical products made of transparent plastic requires more than technical challenges. In general, wall thickness of similar products in automotive industry ranges from 10 to 30 mm, which not only requires high precision in size, but also has a long production cycle. Cooling time after ejection still takes 5-20 minutes or even longer, which is inefficient. At the same time, trouble is that product as a whole often has a large wall thickness difference. Thicker injection area, solidification rate will be significantly slower than thinner area, premature solidification will affect pressure transfer of melt, thereby affecting accuracy of injection molding production.
In addition to cycle time and molding accuracy, all of which can be seen intuitively through injection molding machine's curved interface, bond strength of finished component is also critical, and bond strength of different transparent plastics in multi-stage injection molding varies greatly. Even if same plastic is used, under condition of higher temperature, pressure will be generated, so that produced cooled preform will show a larger amount of shrinkage. Therefore, selection of water channels, processing parameters and temperature control at wall thickness distribution are extremely important.
In most cases, once an ordinary mold is formed, it is difficult for a company to open a new mold at a higher cost. How can ordinary multi-stage injection molding meet molding of this product?
1) Many tuning processes are based on personal experience or inherent parameters, but when abnormal problems occur, they are often at a loss. Therefore, temperature setting in initial preparation data must include raw material property table provided by supplier. Correct material temperature and mold temperature should be formulated on the basis of this data. In principle, we must carry out initial adjustment in two ways, that is, to adjust upper and lower limits of raw material temperature. In the case of ensuring product quality, the lower temperature, the better.
2) Speed is generated by pressure. We can often see a situation where injection pressure is as high as 90%, and speed is only 10%. Have we observed oil pressure gauge to see what actual pressure is. Similarly, speed is 90%, but pressure is only 30%. In this case, are you sure that speed can reach 90%? Therefore, this is reason why the technicians are required to observe lack of glue before start of multi-stage injection molding, only parameters formulated in this no abnormal situation can be more reasonable and can better realize interchangeable production.
3) Holding pressure is only based on absence of defects in naked eye of product, which is of course wrong. Main influencing factors of plastic sealing time of product are holding pressure and holding time. Generally speaking, when holding pressure is enough to save data when product is formed, holding time is continuously increased by 1 second from this stage until unit weight of product is completely stable. At this time, unit weight of product is the most stable and size is also the most stable.
4) Melting glue and back pressure, these two factors are often overlooked by technicians. These two factors directly affect state of molten glue entering mold cavity. If back pressure is too small, actual measurement will be much higher than demand measurement. At the same time, due to poor state of melted glue, product will have silver wires, bubbles, shrinkage and other defects.
A colleague once experienced shrinkage and lack of glue when adjusting machine. Temperature has exceeded limit, pressure and speed are also very large, but problem has not been finally solved. Later, after analysis, molten glue stayed in barrel for too little time, and it was not completely melted. As long as a simple adjustment was made to let molten glue stay in barrel for a little longer, all anomalies were resolved.
Thick-walled products are not as difficult as we thought. Key lies in familiarity with equipment and operation of technical details.
So let's go back and review "scientific injection molding method" mentioned at the beginning of this section. Of course, I am not saying that this method must be used in order to make a good product, but I am just instilling a theory to everyone, using data and spot checks to constrain purely technical process of machine tuning, and harvest is very different. It may take a long time to complete a parameter process from T0, but when parameters are completely stabilized, no adjustment is made. Only factors including mold and injection molding machine are corrected, and production can naturally proceed smoothly.

4. Quality control

Not a professional quality management personnel, it is difficult to deeply understand quality work. Quality of cooperation is by no means blind obedience, nor is it ignorant waiting for judgment. The most direct way to cooperate with production is "first three bad managements".
Using regular or irregular inspections as supervision method for daily production report, sorting out non-performing ratio in production process of each product on duty, using technical team inside workshop to count and review the first three non-performing products, and analyze non-performing products. Phenomenon is constantly improving, and this improvement never stops.
In many factories, no matter what kind of high-level attention is given to quality, there are various contradictions with production. Reason is that any cooperation matters beyond scope of department's work. If senior leaders always stay out of way and treat results regardless of process, it is certain that quality will come to a complete standstill.
In fact, many things in production process can be prevented in advance:
When a certain abnormality occurs continuously in initial stage of product, if improvement method does not form a resume, resume report will be the first basis for improvement when same abnormality occurs in production process. This resume will be an important reference for production review.
Establish a mold resume file, evaluate all possible abnormalities and make basic vulnerable parts. There are similar requirements in system, and many abnormalities in production can be solved in corresponding preventive measures.
Focus of production engineer's responsibilities is on prevention and improvement, rather than simple on-site technical assistance. When an abnormality occurs, engineers try to make two countermeasures, emergency measures and long-term improvement measures, and follow up results.
Any problems that appear to be technical on the surface can be resolved through management means in final review results. Similarly, many issues that everyone thinks belong to management category can be dealt with through some implicit technical means.
In fact, each company has a group of strong people who are familiar with production management methods and process technology. Their experience is enough to support sky. I hope that companies can make reasonable use of their skills to make our factory stronger and bigger. Then it is a processing plant, but a technology-based company that can independently complete design, development and independent engineering.

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