xiehe model

CNC milling can cause defects in precision parts, which reduce the quality of the final product. Listed below are some examples of common defects in the milling of CNC parts and appropriate solutions to fix them.

Glitch

During CNC milling, the milling machine leaves residual material on the workpiece. This remaining material is called burr. They are usually formed along the bottom edge of the workpiece during milling or drilling. In addition, it is more common in softer materials, characterized by low hardness and high plasticity.

Reason

The last layer of workpiece material moves away from the milling bit as it deforms. Therefore, it is impossible to remove these excess materials without changing their position. Burrs remain on the workpiece and appear as films at the edges, they are sharp and reduce the aesthetic value of the manufactured part.

Solution

There are several ways to remove burrs. An easy way to deburr is to do it manually. We use tools such as grinding heads, files or sandpaper to polish and deburr workpieces. This simple option doesn't require much technical expertise, but gets the job done. Alternatively, advanced deburring techniques do perform better than manual processes. They include thermal and vibration deburring.

Variable surface finish of workpiece surfaces

Poor surface finish is an important defect caused.

Reason

There are many reasons for the change or poor surface finish of the workpiece. The first is due to tool chatter. The term refers to excessive vibration of the tool or machine tool. It results in an uneven surface on the workpiece instead of a smooth surface. The main cause of tool chatter is the use of dull tools. Even before the chip separates from the main part, it causes the workpiece to deform. Consequently, the formation of holes results in a much lower surface finish.

Secondly, the coolant used in the milling process is not properly selected. Some milling machines do not acknowledge the importance of choosing the right coolant. They end up buying a simple and cheap optional coolant that won't protect your tools. A good lubricant increases the quality of the achievable surface finish. In addition, the tool is less likely to overheat, thereby increasing tool life.

Solution

We need to keep the sharpness of the tool and use the correct coolant to achieve a smooth surface.

Dent after CNC milling

Metals such as copper, aluminum alloys, brass, and bronze sometimes dent when the tool is clamped. This is due to their lower hardness levels compared to other tougher metals.

Reason

The main reason is usually too much clamping force from the tool. Especially for manual clamps where the clamping force cannot be measured correctly, other milling machines use pneumatic or hydraulic cylinders to generate this clamping force.

Solution

A good solution to prevent dents from forming is to use steel plates. We can place them between the fixture and the workpiece. The purpose of these plates is to distribute the pressure evenly across the workpiece, preventing deformation of the part. In addition, even with high clamping force, dents are formed on the steel sheet. Alternatively, we can use softer special blocks and clamps. The chance of part deformation when using them is much lower.

Burnt marks on the surface of the workpiece

A common defect caused by CNC milling errors is surface burn on the workpiece. Burns occur when the workpiece overheats. Examples of such defects on the workpiece include corners or edges of the material. It appears as cut marks, rough edges or raised marks on the surface. Also, the tool is wearing out faster than normal.

Reason

Defects occur when incorrect cutting parameters are entered. Especially on a milling machine, an inappropriate combination of feed and speed ratio is chosen. It usually causes workpiece damage and tool damage. Another reason is choosing the wrong tool for the job. The size, quality and dimensions of the tool should be suitable for the workpiece.

Solution

We can easily fix this defect by reducing the cutting speed to feed ratio. It slows down the entire machining process, thereby reducing the amount of heat generated on the surface of the workpiece. Alternatively, we can increase the cooling rate of the workpiece during the milling process. Both of these help reduce the chance of burn marks on the workpiece, and materials with poor thermal conductivity, such as titanium, can benefit from a combination of the two techniques.

What is the final conclusion?

CNC milling is a complex process that requires the right partner to achieve great results. At Concord, we have professional engineers ready to work on your important projects, just send your CAD files to get started. For any questions about CNC milling services, please contact us today.