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

This falls under the category of design capabilities. In fact, good product design is crucial in the selection of materials and can even be a matter of life and death.

“Wrong materials can render everything useless,” which is not just a catchy advertisement, but the result of many people’s hard work and sacrifices.

Mechanical design is a vast field that is divided into numerous sub-industries and specialties, each of which requires different materials.

This is also the reason why inter-bank mechanical design often faces numerous failures and obstacles during the early stages, incurring trial and error costs.

Now, let me share my industry knowledge and experience with materials.

Please note that this information may be limited and not necessarily accurate, but the selection method I will outline is still universally applicable and can serve as a reference for you.

When selecting materials for designing parts, we typically consider the following aspects:

1. Whether the material rigidity is sufficient

When selecting materials for your design, the first thing to consider is the material’s rigidity, as it determines the feasibility of your product design. The product must be sturdy and have a certain degree of stability and resistance to rough handling, so the range of use and environment in which the product will be used must be taken into account.

Consider the strength and other factors to make a comprehensive choice for the material of the parts. For example, in the design of a vertical machining center, we usually choose HT300 gray cast iron for large foundation parts because of its good rigidity.

Why not choose plastic material instead? This is because plastic lacks strength and rigidity and will break under stress. This is a fundamental principle in material selection.

There are several types of gray cast iron, such as HT200 and HT250, but why choose HT300? HT300 is a little harder, and HT250 is also a common choice, but these two types are commonly used.

The experience of previous designers is invaluable and many of our designs are based on their experience. While conducting a series of strength or reliability tests for each product may be ideal, the market does not wait. By making full use of the experience and achievements of our predecessors, we can truly succeed in the future.

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Some people like to compete and argue that design without verification and testing is irresponsible. However, products designed by previous designers have been in the market for decades, and the market holds more than tens of thousands of units. There is no need to argue over a mature product, and improvement of design should be practical.

In an enterprise, the focus should be on how to quickly connect with the market and quickly realize our abilities through market demand. This is the reality of the workplace. As an enterprise, we must be skilled in using the experience and achievements of our predecessors, as they represent a goldmine waiting to be explored and adopted.

Based on the characteristics of the industry and non-standard tooling design, I personally think that 45 # steel and aluminum alloy should be used more frequently. In the design of machining tooling, 45 # steel and alloy steel will be used more often, while in the automation industry, aluminum alloy may be used more frequently, mainly due to its rigidity. The specific situation should be evaluated from your own perspective.

2. How to deal with material rust prevention

Many mechanical designers often overlook the issue of preventing rust, which is actually a very crucial problem. Not only does it impact the stability of the product’s performance, but it also affects the product’s appearance quality.

In today’s world, where industrial technology products are gradually merging with art, neglecting the appearance of the product is a serious mistake. People are willing to pay for the product not only for its functionality, but also for its aesthetic appeal and the mood it evokes.

As product designers, it is imperative that we pay close attention to rust prevention of parts. For instance, to prevent rust on the commonly used 45# steel, the most popular method is “bluing” treatment. This method is cost-effective and gives the parts a sense of thickness and reliability. Alternatives include painting or spraying plastic on the parts or protecting them with sealing oil or anti-rust fluid during use.

In the case of machining tooling, using anti-rust fluid is the most common method. However, if these methods are not feasible, changing the material might be necessary. For example, using stainless steel can largely eliminate the need for anti-rust treatment, but it’s important to note that not all stainless steel is completely rust-proof and anti-rust precautions should still be taken during use.

3. How about material stability

In product design, the selection of materials and their stability are critical considerations. As an example, the use of HT300 gray cast iron in large machine tool parts is due to its excellent stability, both thermally and in terms of material composition. For high precision machine tools, this material is a great choice.

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On the other hand, using steel as a substrate may result in qualified parts during processing, but after assembly, geometric deformations may occur due to temperature, humidity, vibration and other environmental changes during continuous use. This can pose a problem for products with high precision requirements.

Thus, temperature stability of the material is a crucial factor in determining the success or failure of a product. Our company recently purchased a product with a gray cast iron workbench, possibly HT200, but its thin design and lack of secondary aging treatment after casting have resulted in changing accuracy since purchase.

Despite our efforts to regrind and debug, the accuracy continues to change. This product, despite having all the necessary functions and operating normally, is ultimately a waste product for us as we require processing accuracy.

As a design engineer, it is important to consider the stability of materials, as it is like the loyalty between lovers. Without stability, any other aspect of the product becomes unreliable and meaningless.

4. How about material processing performance

The processing performance of materials is a key skill for mechanical process engineers.

However, it is important for mechanical design engineers to have a basic understanding of this concept as well. This is why a mechanical process engineer must sign a joint review document after the drawing design is completed, as he needs to evaluate the processing performance of the material for that specific part.

The processing performance of a material refers to its ease of processing. For example, 45 # steel is relatively easy to process, while stainless steel is more challenging. This is due to the material’s tendency to stick to the tool and its poor cutting performance and high hardness.

As a result, using stainless steel for rust prevention can sometimes lead to processing difficulties. For example, machining small, threaded holes in stainless steel, such as M3 threads, can be particularly challenging, as it can easily break the drill bit and tap and discourage workers from performing the task. If it must be done, it comes at a high cost, not only in terms of material expenses but also processing costs, which can be significantly higher compared to 45 # steel.

On the other hand, the processing performance of HT300 is excellent, which is why it is commonly used for large machine tool parts. This material is easy to process and generates little processing stress, making it relatively easy to remove.

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An effective processing process includes an aging treatment step before semi-finishing the parts, which helps to remove any processing stress generated in previous processing steps and ensures the stability of precision in the final finishing process.

The processing performance of materials is a complex factor that encompasses various elements such as the selection of cutting tools, machine wear, and low processing efficiency. This is an important aspect of design engineering and requires a comprehensive understanding and continuous study by every design engineer, which is considered as a standard capability for a design engineer.

5. How about the material cost

The cost of producing parts is a comprehensive reflection of several factors, including the choice of material. If the material selected is lacking in rigidity and does not meet industry standards, it may result in having to start over, incurring additional costs. Similarly, if the material is not effective in preventing rust, it can lead to instability and a poor appearance, making it difficult to sell and resulting in a cost backlog.

Additionally, if the material selected has poor stability and the resulting product is difficult to use, it will also be difficult to sell, further adding to the cost backlog. Finally, if the material selected has poor processing performance, it will lead to an increase in processing costs, also affecting the overall cost.

It’s important to evaluate the quality of a product design from not only a functional perspective, but also from a cost perspective. Spending a large sum of money, such as one million yuan, to create a perfect screw may result in a beautiful product, but it may not have any market value or practical meaning.

6. Summary

A competent mechanical design engineer must take into account various factors when designing products and parts.

If they lack this knowledge, they cannot be considered a design engineer, but at best, a draftsman.

Draftsmen lack creativity and passion, serving merely as a tool, lacking energy and often receiving complaints.

What I aim to impart is the method for selecting the appropriate material for a part. It is important to understand the starting points and considerations for this process. Only by mastering these methods can one effectively find materials that meet their specific requirements, without which one would not know where to begin.

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