Como a mecânica de precisão CNC cumpre suas tarefas

How CNC precision mechanics fulfill their tasks

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Most modern CNC industries rely on parts machined to tight tolerances, smooth finishes, and high reliability. All of this makes modern products robust, efficient and competitive. All of this drives industrial progress. However, these pieces will not be produced alone. We owe CNC precision engineering all the high-quality parts that allow us to drive cars, fly to different continents, and sit here reading this text. Producing accurate parts is an arduous task that involves several steps in the prototype manufacturing industry.

Development of precision parts projects

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There is a constant dispute between designers and mechanical engineers about the precision of the parts developed. Designers approach the problems they encounter from a theoretical perspective and ideally want every part of the machine to be perfectly accurate and as close to ideal geometry as possible. However, if we did things the way the designers would like, it would all cost an insurmountable amount of money and provide little additional efficiency. In fact, the same could be said about geometric complexity.

This is why production engineers and designers struggle. There is even a joke that says that the production engineer's ideal part is a block of wood, while the designer wants to build an airplane. The result is a product that features high-precision surfaces rather than high-precision parts. This fight eliminates economically inefficient resources and reduces product costs while maintaining high performance.

Determination of the main technological tasks

Now that we have established that high-precision parts are actually parts with high-precision surfaces or groups of surfaces, it is clear that the manufacturing process can be divided into two phases. In the first phase, the required part is manufactured with normal quality, leaving some excess material on the surfaces that require greater precision.

The second phase deals with achieving the required precision and performance requirements (such as material hardness, tensile strength, additional surface finish parameters). Each part represents a separate individual task with its own combination of characteristics, and it is important to consider how these tasks can be accomplished before designing the manufacturing process. If the part has many precise surfaces with different TI values, the second phase of the manufacturing process can be divided into TI groups.

CNC engineering strategy

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CNC precision machining is mainly done by grinding as it produces the best results. The material must have a minimum hardness to be ground efficiently, so parts are usually heat treated to some extent. However, most of these parts require complex multi-stage hardening, so you really need to worry about how to restore the base surfaces after treatment.

For example, the final task can be accomplished by machining both surfaces in a single configuration or clamping the part to one surface while machining the other.

How to meet performance requirements

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Many high-quality parts have special requirements. Gears, for example, must have very hard surfaces, maintaining the soft mass of the material. This is achieved by hardening the surface. Other parts require the use of carbon or nitrogen in conjunction with heat treatment to achieve the required hardness. There are parts that need to be coated and the coating layer is so thin that it contains individual ions or atoms. And all methods are quite complex and require specific parameters for each material and hardness or coating property.

How do you resolve this? Imagine you have a special axle that needs to be nitrocarbonized. You have never done this before and investing in this method is time-consuming and useless because it may turn out that you never use it after the batch is ready. Well, I found two solutions. They outsource. There may be a machine or prototype shop nearby that can perform these operations for you.

The cost per part may be higher, but in reality you save on investment and labor costs. The other option is to talk to the designer and convince him to switch to a more expensive material that doesn't require such complex treatment. The overall machinability of the material may be lower, but you may still save money by forgoing the introduction of a previously unknown technology.

High-precision measurement and quality control

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One of the most important tasks in CNC precision engineering is figuring out whether the part you are creating actually has the required quality. This is not a trivial task, as high-precision CNC machined parts often have a tighter tolerance than most measuring devices. What recommendations are there here?

  1. Avoid using templates as much as possible. Each element of the measurement system introduces additional errors, so it is best to avoid them completely. Modern high-precision measurements are carried out by placing the workpiece (if possible) on a very flat stone slab.
  2. Optical measurements are a good option. Most measuring tools rely on physical contact to measure tolerance or surface finish. However, the parts in contact wear out and lose precision. This is not the case with optical measuring tools and no unwanted substances can interfere when the tool and the workpiece come into contact.
  3. If there is no way to determine the accuracy of the part, test it. This is the only way to truly determine whether the performance requirements of the part are sufficient. You can also measure part requirements indirectly. For example, high-speed shafts, such as those used in grinding tools and drug mixing equipment, require a runout of IT4 or less, which is virtually impossible to measure. They are therefore simply installed into wing bearings and tested. If the operating temperature of the shaft is within the limits, it means that the deviation is small enough.

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