When Changing from Hand Lay-up to Closed Mold Process, should I Choose Vacuum Infusion or RTM?

 

Environmental protection requirements are becoming more and more stringent, and individuals’ awareness of self-protection is also getting stronger. In addition, young people nowadays are unwilling to work in “dirty and messy” hand-layup workshops, and customers’ requirements for products are getting higher and higher, which has led many companies to consider the issue of process upgrades.

In the case of no major changes to the resin system, if you want to reduce VOC, changing the hand-layup process to a closed mold process is a very effective method.

Common closed mold processes include: vacuum infusion, RTM, molding, autoclave, etc. Among them, vacuum infusion and RTM are two commonly chosen processes.

With choices, there will be doubts. Is it more appropriate to choose vacuum infusion or RTM? Today, Dymriton tells you how to choose.

 

2. Differences and similarities

 

To make a choice, we must first understand the characteristics of each of the two processes so that we can make a judgment. By comparing the similarities and differences between the two, we may be able to find the answer.

The similarities between the two are:

① Both the vacuum induction process and the RTM process belong to the closed mold process. There are few volatiles in the production process, which is environmentally friendly and can provide workers with a relatively comfortable construction environment.

② There are requirements for resin. The viscosity is low, generally 100-300Pa·s, and the wettability should be good. The gel time should be relatively long to facilitate the infiltration of the reinforcing material, but the curing speed should be fast to achieve high production efficiency. Because the product is formed in one step, the exothermic peak of the resin should be low to prevent the product from being deformed due to excessive temperature and causing adverse effects such as thermal shock to the mold.

③ Most of the reinforcing materials choose axial fabrics, Continuous Filament Mats, Closed Mold Mats, etc. with good flow-guiding effects to facilitate the flow and infiltration of resin.

④ The product has good stability. Since the ratio of resin to reinforcing material is certain, it will not change greatly due to different operators, and it is formed under a certain pressure, so the uniformity of the product is relatively good.

 

The differences between the two are:

① The vacuum infusion process belongs to a single-piece mold, so the product can only be made into a single-sided smooth product. The RTM process is a top-to-bottom mold, so it can make a two-sided smooth product.

② The mold costs of the two are different, and the RTM mold cost is higher than the vacuum infusion mold. In particular, wax sheets are needed to remake the RTM upper mold. The price of wax sheets is known to everyone who uses it.

③ The vacuum infusion process requires a variety of vacuum auxiliary materials, which are basically disposable materials, which will increase the cost of the product.

④ The resin content is different. The resin content of vacuum infusion products is generally 30-40%, while the resin content of RTM products is higher, generally 40-50%. Relatively speaking, the strength of the product made by the vacuum infusion process is better than that of RTM, but it is not absolute, and it can be adjusted through the layer design.

⑤ The equipment investment is different. The vacuum infusion process only requires a vacuum pump device, while RTM requires an injection device. Although lightweight RTM can be produced with only a vacuum pump, injection equipment is still required for mass production, and the cost investment is relatively high.

 

3. By comparing the similarities and differences, we can see that although both are closed mold processes, they have very distinct characteristics.

A great man once said: Everything starts from reality. If you want to choose, you still have to look at your family conditions. I suggest making a comprehensive consideration from the perspectives of technology, product and cost.

 

Technology

Whether it is the vacuum infusion process or the RTM process, the technical requirements for mold and product production are higher than those for hand lay-up. Therefore, specialized talents are needed in this regard, either externally hired or internally trained. There are also some differences in the technical requirements of the two.

 

The mold of the vacuum infusion process is simpler than that of RTM, and the manufacturing process is basically the same as that of the ordinary hand lay-up mold. The main thing is to increase the thickness and reinforce the process to ensure sufficient rigidity, and reserve sufficient flanges for sealing with adhesive tape. At the beginning, many companies will directly use the original hand lay-up mold for testing. As long as there is no problem with air tightness and rigidity, it can be used for testing.

 

The mold making of RTM is relatively complicated, and it is not just a piece of upper mold on the surface. For example, for the layout of the flow channel and the air outlet, the technicians need to have rich experience to succeed.

 

From the perspective of mold making, the technical difficulty of the vacuum infusion mold is lower than that of the RTM mold.

 

The process of making products is different. In addition to pre-laying the reinforcing materials, the vacuum infusion process also requires the laying of release cloth/isolation film, guide net, vacuum bag film, resin tube, winding tube, sealing tape and other auxiliary materials. In order to ensure air tightness and resin penetration of the reinforcing materials, the laying of auxiliary materials also requires technicians to have sufficient experience to do a good job.

 

RTM is relatively simple. After pre-laying the reinforcing materials, the mold can be locked and the glue can be injected for production. However, the injection equipment must be operated well and the injection situation must be paid attention to at any time.

 

From the perspective of product production, the technical difficulty of the vacuum infusion process is relatively high.

However, in general, the technical requirements of the RTM process are higher. After all, the mold is the mother of the product. If you can make a good RTM mold, then there is basically no problem in understanding how to lay the vacuum auxiliary materials.

 

Start from where you can do it, don’t be too proud.

 

Products

Products contain a lot of information, such as shape and size, strength requirements, surface requirements, price, quantity, etc., so the product ultimately determines your process.

If your product requires double-sided gloss, you can only consider RTM. If it is a structural part with high strength requirements, then consider vacuum introduction. The quantity and unit price of the product involve costs.

The clearer you understand the product and process characteristics, the easier it is to know which one is more suitable. Think about the product thoroughly before doing it.

Cost

 

The cost mentioned here does not refer to the material cost of the product alone, but to a comprehensive cost.

 

In the above comparison, we can see that the mold and equipment costs of RTM are relatively high, while the production cost of vacuum induction is relatively high.

 

The cost of the product is directly linked to the mold cost and equipment cost. The greater the investment, the higher the unit price of the product. But we cannot ignore one problem, that is, the number of products. If the number of products is larger, the mold cost and equipment cost will be smaller.

 

Obviously, the RTM process is suitable for single-piece batch products (annual production of more than 5,000 pieces is recommended). The larger your batch, the more likely you are to share the mold and equipment costs, otherwise it will directly increase the product cost.

 

4 Summary

 

Finally, let’s summarize.

I have seen many cases of changing hand lay-up process to vacuum infusion process or RTM process. However, many companies still have certain limitations in their thinking when upgrading their processes. The first question that the boss or manager asks you is mostly: Can this change reduce costs?

 

The purpose of a company’s survival is to make money. If it doesn’t make money, it is not called a company, it is a charity. So I understand their questions very well.

 

But any new change that only focuses on cost at the beginning will often not succeed.

 

If you only calculate the current investment cost, whether it is vacuum infusion or RTM process, it may not be able to compete with hand lay-up. The cost of fiber resin is high, the auxiliary materials are also high, and equipment needs to be added. No matter how you look at it, it doesn’t seem to be able to reduce costs.

And efficiency may not help. After many companies changed their processes, they found that the efficiency was not as good as the previous hand lay-up process. So how should this account be calculated?

Originally, I wanted to make a table to show you a comprehensive cost calculation method, but I think that accounting is the boss’s strong point, and I am sure I can’t calculate it better than them. Let’s talk about other directions.

In the foreseeable future, environmental protection requirements will only become higher and higher, so the previous way of playing will definitely not work. The rising labor costs and picky customer requirements are all squeezing the living space of hand lay-up technology.

 

If you don’t change, the times will abandon you without even saying goodbye.

From another perspective, opportunities are often reserved for those who are prepared. The upgrade of technology not only represents the technical strength of the company, but also broadens your scope of orders.

In the end, it comes down to cost, you get what you pay for. Many times, companies also need to screen customers. Customers who don’t have requirements are often not good customers, because such products can’t be sold at a high price. Therefore, you don’t have to worry about the cost increase caused by technology upgrades, because rising tides lift all boats.

When you have a thorough understanding of the technology, you can even make further improvements from the design end. For example, the original hand-laid product had to be 10mm thick to meet the strength requirements, but after changing to the vacuum introduction process, 8mm thickness can meet the requirements. Isn’t the raw material saved money? It’s really delicious…

Life needs to constantly challenge peaks, and so do companies.

Are you ready for the challenge?