Mechanical Design: What Material Knowledge Do You Need to Master?

This is one of the so-called design capabilities. In fact, a good product design is very important in the selection of materials, even to the point of life and death.

“If the materials are wrong, everything will be in vain”, which is not a simple industry advertisement, but a lot of people’s blood and tears.

In fact, mechanical design is a very broad overview, which is divided into many sub-industries and specialties, and the materials that each sub-industry pays attention to and uses are completely different.

This is also why many inter-bank mechanical design always has many failures and twists in the early stage, which is also a trial and error cost.

Then let’s share my industry and my superficial knowledge of the material.

Of course, this content must be limited and not necessarily correct, but the selection method I share is still universal and can be used for your reference.

Usually we choose a material for designing parts from the following aspects.

1. Whether the material rigidity is sufficient

According to your design requirements, the first thing to consider is the rigidity of the material, because the rigidity of the material determines the feasibility of your product design.

Remember, we are making a product, and the product needs to be used in actual work, and needs a certain degree of stability and roughness resistance, so we must consider the range of use and use environment of the product when selecting the material.

Use strength and other factors to comprehensively consider the selection of part materials.

For example, when we build a vertical machining center, we usually choose HT300 gray cast iron for large foundation parts.

Because this material has good rigidity, why don’t we choose plastic material to do it?

Because plastic material has no strength and rigidity at all, it will hang up when it is stressed, so this is a principle we choose.

Of course, there are many kinds of gray cast iron, such as HT200, HT250, etc, Why should we choose HT300?

Because the hardness of HT300 is a little higher, in fact, HT250 is also a common choice, but it is basically these two kinds.

There is a lot of experience accumulated by previous people. Many of our designs are actually based on the experience of many previous people.

If we do a series of strength or reliability tests for each product, it is really cool, and the market demand is not waiting.

Only by making full use of the experience and achievements of our predecessors can we truly win a future.

In fact, many “friends” have always liked to compete.

They always say that the design without verification and test is irresponsible, but the products designed by predecessors have been running in the market for decades, and the market holds more than tens of thousands of units.

There is no need to conduct so-called argumentation for this mature product, and the improvement of design should also be realistic.

The enterprise gives you money to help you make more money. It is not for you to complete your academic pursuit.

In the enterprise, what we talk about is how to quickly connect with the market and quickly realize our ability through the market demand. This is the most real current situation of the workplace.

So as an enterprise, we must be good at using the experience and achievements of our predecessors. That is a golden mountain, waiting for your exploration and adoption.

According to the characteristics of the industry and non-standard tooling design, I personally think that 45 # steel and aluminum alloy should be used more.

If it is the tooling design of machining, 45 # steel and alloy steel will be used more.

If it is the tooling design of the automation industry, the aluminum alloy may be used more.

It is mainly more rigid to judge. Of course, the specific situation should be from your own perspective.

2. How to deal with material rust prevention

Many mechanical designers tend to ignore this problem. How to prevent rust is actually a very important problem.

It is not only related to the stability of the product application, but also related to the appearance quality of the product.

Today, when industrial technology products are slowly beginning to integrate with art, ignoring the appearance of the product is simply an unforgivable mistake.

Many people are willing to pay for your product, not just a function. It is also to buy a mood and a practical object based on appreciation.

Therefore, as a product designer, we must pay great attention to the rust prevention of parts.

For example, how to prevent rust of the 45 # steel we often use, we usually choose “bluing” treatment, which is the most popular anti-rust treatment method for industrial products for this material.

This method is cheap, and can make the parts glow with a sense of thickness, give people confidence and reliability, or paint and spray plastic on the parts.

This is also the way that many products, especially the appearance treatment, are used, or according to the use requirements of the environment, the parts are not treated separately, but are protected by sealing oil or anti-rust fluid in the process of use.

This is also the way that is used more often in machining tooling, no matter what way we have to choose.

Of course, if the above methods are not suitable, then we must change the material. For example, we can choose stainless steel, which can basically eliminate the embarrassment of anti-rust treatment.

But many so-called stainless steel is not completely rust-free, just relatively difficult to rust, so in the process of use, we still need to fully consider the anti-rust problem of parts or products.

3. How about material stability

In the process of product design, we should select the material of a part, and also consider the stability of the material.

For example, the HT300 gray cast iron we illustrated earlier is why the large parts of the machine tool are made of this material.

It is because this material has very good material stability during the use of the product, whether it is thermal stability or its material organization stability.

For products with the characteristics of high-precision machine tools, such materials are a very good choice.

If you choose to use steel as the substrate, it may be that the parts you process are qualified, but after assembly, various geometric deformations will occur, and they will be deformed again in the hands of customers.

In short, they can change at any time with the changes of temperature, humidity, vibration and other environments during continuous deformation.

 This is a nightmare for a product with high precision requirements.

Therefore, considering the temperature of the material is a very critical factor and also a factor determining the success or failure of a product.

Our company recently purchased a product whose workbench is gray cast iron, which may be HT200.

Because the design strength of the parts is not enough, it is too thin, and there may be no secondary aging treatment after the casting of the parts, so the accuracy of the workbench has been changing since the purchase of the machine tool.

After we regrind and debug ourselves, it is still changing.

There is no way to debug, Not to mention how to use it normally in the future.

Such a product is actually a waste product. Although from the appearance, all functions are complete, all kinds of actions can be done, and the operating system is normal, the most important accuracy is not.

What we need is processing accuracy, which is meaningless to us.

So as a design engineer, we must consider the stability of materials.

The stability of materials is like the loyalty between lovers. Without this loyalty, any vows, rhetoric, men and women are false, meaningless and unreliable.

4. How about material processing performance

The processing performance of materials is actually the internal skill of mechanical process engineers.

Of course, a mechanical design engineer should have a basic concept.

This is also why a mechanical process engineer must sign a joint review name after the drawing design is completed, because he needs to evaluate the processing performance of the material of this part.

What is the processing performance of the material? To put it bluntly, it is whether the parts are easy to process.

For example, 45 # steel is easy to process, but stainless steel is not easy to process.

This kind of material not only sticks to the knife, but also has poor cutting performance and high hardness.

So in many cases, although we choose stainless steel for rust prevention, there are some processing problems.

For example, machining small holes on stainless steel, especially threaded holes, such as M3 threads, is very troublesome. It is easy to break the drill bit and tap, and many workers are unwilling to do it.

If it is forced to do it, the price is also very high, not only the material cost is high, but also the processing cost is higher. Compared with 45 # steel, I don’t know how high it is.

The processing performance of HT300 is very good, which is one of the reasons why large parts of machine tools choose this material.

This material is easy to process, and the processing stress is not large, which is relatively easy to remove.

A good processing process will add an aging treatment process before the semi-finishing of parts, which can greatly remove the processing stress generated by the previous processing processes of parts. And finally ensure the stability of the precision of the finishing process.

The processing performance of materials is not only related to the processing of parts, but also involves the selection of cutting tools, the loss of the processing machine, the low processing efficiency, etc.

This is a very comprehensive factor, which is worth studying and studying by every design engineer. This is also the standard configuration ability of a design engineer.

5. How about the material cost

The production cost of parts is actually a comprehensive reflection based on the above factors.

If the material you choose is poor in rigidity and does not meet the standard, it means to overturn and start again, which means the cost.

If the material you choose is not good in rust prevention, it means instability and poor in appearance.

It can not be sold, and it is also a cost backlog. If the material you choose is poor in stability and the product is not easy to use, it can not be sold. 

It is still the cost backlog. If the processing performance of the material you choose is not good, the processing cost will rise. This is still related to the cost.

The quality of a product design needs to be evaluated not only from the function, but also from the cost.

If you spend one million yuan to make a perfect screw, do you think it is meaningful? Is there market value? No, although you have done it beautifully, it is meaningless.

6. Summary

A good mechanical design engineer must consider the design of products and parts based on the above factors.

If he does not have such knowledge, then he is basically not a design engineer. At most, he is just a draftsman.

They have no thought and soul, that is, a tool, a breathing tool, low energy and many complaints.

Of course, what I want to share here is the method of selecting a part material, which aspects to start with and where to start. Only by mastering these methods can you find materials suitable for your specific needs through these methods, otherwise you really have no way to start.

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