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Numerical control cnc surface milling processing skills

The milling of curved surfaces belongs to the category of contour/contour CNC milling. It involves machining irregularly shaped contours or continuous curves with different angles (sloping, concave or convex). This is the critical process for completing most custom parts with unique shapes and requires CNC machinists to have advanced expertise in basic machining procedures and principles.

This article will introduce the surface CNC milling technology in detail. What aspects should be paid attention to when milling surfaces? What should a complete surfacing process look like?

The processing flow of curved surface parts

The processing of curved surface parts also follows the processing rules of CNC machining centers. Before reaching the final machined part, they are first subdivided into different categories: roughing/semi-roughing, semi-finishing, finishing and super-finishing. Since the geometric diagram and mechanical diagram cannot clearly express the free curve and surface, it becomes the primary problem to be solved in the rough machining stage of the machining center.

Open rough machining

In order to improve the milling efficiency of the initial machining of the rough part of the curved surface part, the end mill can be used to mill layer by layer according to the contour surface according to the given allowance of the processed surface. . After rough milling, the shape of the curved surface will be distributed in layers, and the height of the steps depends on the precision of rough milling. During rough machining, due to the large machining allowance and cutting amount, a large amount of cutting heat will be generated during the cutting process, which will easily cause the tool to wear quickly. At this time, the temperature in the cutting area should be reduced, and cutting fluid should be applied at this stage. Lubrication and cooling action.

Semi-rough machining

Semi-rough machining is essential. This is an important stage from rough machining to finishing. Its purpose is to mill out the excess left over from the roughing step. Semi-finish milling should be carried out with a ball-end milling cutter, and its line distance and step distance should be greater than that of fine milling. It should be noted that a machining allowance of about 0.5mm should be left for the semi-finishing milling process for the subsequent finishing milling process. After this process, the shape of the machined surface is close to the theoretical surface.

Finishing is the process of final processing the theoretical surface. Ball nose milling cutters are the tool of choice for finishing, usually with wire EDM. When programming, attention should be paid to the choice of turning point and the determination of feed speed. For parts with better openness, the turning point should be selected outside the curve table, that is, the surface should be properly extended outward during programming.

If the part requires a mirror finish or an ultra-smooth profile, the operation will be super-finishing. For this, high-speed machining techniques and high-precision tools are used.

Tool faces for CNC milling machine surfaces

We use a variety of ball nose milling cutters to machine smooth curved surfaces on manufactured parts. These include ball nose indexable end mills, round inserts and ball nose solid carbide. In contouring we prefer to use a round contour tool as it does not leave any noticeable marks on the toolpath.

Insert end mills with round inserts

These types of end mills have larger diameters. Radius end mills are ideal for roughing due to their impressive productivity and high stability.

Integral ball end mill

These types of end mills usually leave a very fine surface finish on the machined part. Due to their structure, they may have lower stability. Therefore, it can be used for finishing rather than roughing.

Indexable head ball end milling cutter

These types of end mills are similar to solid carbide end mills but have removable heads. This is a special tool with a detachable end that can be easily replaced as needed.

What are the general techniques of curved surface CNC milling technology?

1. Prepare in advance

Before choosing to manufacture custom parts through contour milling, it is important to first understand the various factors that can affect the overall milling process. In addition, in order to choose the ideal processing method, some specific items must also be determined. Here's a closer look at the main preparations we've undertaken.

Pay attention to the cavity depth of the part design.

This plays a key role in helping us choose the right cutting tool. We also determined how long the meter length would take. Determines how much material must be subtracted from the original block. This helps us plan the operations required to manufacture the part. Afterwards, we evaluate whether additional procedures are required after semi-finishing and semi-roughing.

Consider how to clamp the workpiece in place. This will help prepare the necessary fixtures we may need.

2. Get the correct feed and speed

Feed and Speed determine how fast we subtract material from the part. That's why it has a major impact on achieving an excellent surface finish. To achieve this goal, we need to follow some calculation methods. The feed rate may also depend on the tool being used, the depth of cut, the material being cut, the precision required, and the profile of the machined part.

3. Tool utilization

In today's market, there are many tools available. We prioritize roughing tool rigidity to meet feed requirements and aggressive depths of cut for roughing. At the same time, the end mill must be very sharp during finishing so as not to leave any noticeable toolpath marks. Another difference is tool diameter. Typically, the diameter of the roughing tool is larger than the diameter of the finishing tool.

4. Minimize vibration during CNC milling

Vibration is one of the leading causes of poor surface finish, chatter and tool damage. During milling operations, vibrations can come from a variety of sources, including clamping stability, tool stiffness, material hardness, and machine tool spindle errors. Here are some tips for reducing this processing block:

Use tools with high beating precision

During the rough machining process, avoid the overhanging time of the end mill, and use an extension rod or an extension tool holder.

Make sure to maintain proper grip and balance to secure your work fixture during cutting operations.

When working with hard metals, avoid sharp cuts.