4 erros comuns de peças e suas causas no fresamento CNC

4 common part errors and their causes in CNC milling

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CNC milling is one of the most commonly used part machining methods when you need to produce a high-precision part. Modern CNC milling tools offer great opportunities to quickly create complex free-form surfaces. They have also evolved into highly accurate machines, so when used correctly you can achieve mirror-smooth surfaces. However, machining is a profession that you learn throughout your life, and there are many problems that can ruin your part or even your cutting tool if you don't know how to avoid them. We list the most common defects in a CNC milled part and provide suitable solutions to resolve them.

1. Dents left by tool after CNC milling

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When machining brass, copper, bronze, or aluminum alloys, you may sometimes notice that the part has dents where it was clamped during the CNC milling process.

Caused

This happens due to excessive clamping forces on your tool. If your tool is manual, that is, you will have to take a wrench and tighten the screws on the lamps and supports, the solution is simple. You can simply stop tightening devices early or buy a special wrench that shows what the clamping force is at a given time, so you can better control the clamping force. However, many CNC machines are equipped with pneumatic or hydraulic cylinders for constant clamping forces. These are also generally greater than manual clamping forces.

solutions

The economical solution to avoid dents in parts fastened with pneumatic and hydraulic tools is simple. You should make a steel intermediate plate and place it between the workpiece and tool accessories. The plate serves to evenly distribute the pressure on the part and increase the contact area. This prevents deformation. Even if the clamping force is still too large, dents will form on the plate rather than the workpiece.

Another solution is to purchase special mandrels and accessories that are softer and do not damage the part even when deformed. If you want to learn more about other solutions for fixing various dents, you can also visit our key technologies page: CNC Aluminum Machining.

2. Different surface finishes on a single surface

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One of the most common problems with CNC milling concerns surface quality. There are several causes for poor or variable surface quality of a workpiece.

causes

The first reason is conversation. This term refers to excessive vibration in the machine tool or cutter. As a result, you will end up with an uneven, ruined surface rather than a smooth one. There are a few reasons to chatter, the first of which is it's a blunt tool. A dull cutter deforms the part much more before the chip separates from the main part. This results in additional cutting forces and causes the cutting edge to penetrate deeper into the workpiece as deformation increases and the chip breaks off abruptly, leaving a small hole. Too many of them on the surface will make the surface finish much worse.

Another reason is the CNC milling strategy. There are two types of milling strategies: synchronous and counter-rotary. In the first strategy, the direction of rotation of the cutter coincides with the direction of advancement of the work table. During down milling, the tool enters the part with an impact and leaves it slowly with minimal material expenditure (on the surface created after machining). The result is an excellent surface finish. Counter milling occurs when the directions of rotation and feed are opposite. In this way, the tool penetrates the part from the finished surface. Due to slight vibrations and process fluctuations, the tool can easily damage the finished surface. However, this is enough to alter the final surface finish. New machinists often inadvertently use both strategies, programming the tool to move back and forth. This results in the surface having both types of surface finish. Softer on one track and harsher on the next.

The final reason for poor surface finish is poor choice or lack of coolant. Many people underestimate the role of coolants and lubricants and ignore them or use the simplest and cheapest ones. In fact, the use of a suitable refrigerant lubricant can further increase the quality of the finish. Of course, the opposite is also possible. Lack of cooling and lubrication leads to overheating and reduced tool life

Solution

To keep the surface finish as smooth as possible, you must take care of the cutting tool, use the right strategy, and pay attention to the coolant. In general, it is much better if the tool always enters the part from one side and exits from the other.

3. Burns on the surface of the workpiece

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A common defect with this type of error is burns along the surface of the machined part. Burns mean that the workpiece has overheated.

Caused

Incorrect cutting parameters can lead to errors in the part. A poorly chosen combination of feed and speed can cause significant damage to the workpiece, the cutting tool and even the machine tool itself.

Solution

One way to solve the problem is to reduce the cutting speed in relation to the feed. This slows down the processing process and the temperature drops. Another option is to improve the process cooling rate. In some extreme cases, such as titanium, which is a poor conductor of temperature, both methods are necessary.

4. Burrs

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Burrs are pieces of material left over after the cutting process. The most common burrs form during drilling or milling on the lower edges of the part. They are more common in materials with good plasticity and low hardness.

Caused

The final layer of material often deforms and moves away from the cutting tool, making it impossible to remove while the part remains in the same position. The deformed material remains on the part as a thin film at the edges. It is sharp and needs to be removed.

Solution

Deburring is a process of removing burrs and actually represents an entire chapter of mechanical engineering and machining. There are several ways to remove burrs. The simplest method is to remove burrs manually, but there are also advanced deburring techniques such as thermal and vibratory deburring.

University Degree

As you can see, CNC milling is a complex task. People have mastered this for decades and sometimes still make mistakes. You can easily ruin your piece if you have invested a lot of time in milling and money in purchasing the material. A much better option would be to order professional CNC milling surfaces. A group of qualified machinists working on the same machine every day is guaranteed to machine your part without defects or errors.

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If you want to know more about our CNC milling tips, here are some related articles for you:

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