Curved Surface Milling Essentials: Process Sequencing, Toolpath Direction Changes, and Feed-in

Curved surface parts are often machined by milling, and different processes have different focuses. The original text from Duigouwang covers rough milling through finish milling, reminding machinists to pay attention to the direction switching of the line-cutting toolpath, the ball-nose end mill tip, the feed-in method, and the material and clamping condition.

Illustrative figure: VPsharpen equipment reference image.

Let rough milling, semi-finish milling, and finish milling each play their role

Rough milling can remove material in layers along constant-height surfaces based on the curved surface allowance, leaving a stepped surface. Semi-finish milling is used to reduce these steps, bringing the machined surface close to the theoretical curved surface and leaving allowance for finish milling. The original text introduces the process concept of using a ball-nose end mill to complete semi-finish milling.

Finish milling usually uses a ball-nose end mill and line-cutting method. For parts with good openness, the direction-change position of the line-cutting toolpath can be arranged outside the curved surface; when limited by obstructing surfaces, attention must be paid to the toolpath direction-change position and the feed rate during direction changes to reduce tool marks left by pauses and vibration. A separate root-clearing program can be set for intersecting areas.

Focus on cutting at the tool tip and the plunge method

The cutting speed at the tip of a ball-nose end mill is relatively low. When the tool is perpendicular to a relatively gentle curved surface, if cutting relies mainly on the tool tip, the surface quality may be affected. On this basis, the original text proposes that cutting should be avoided at the tool tip as far as possible.

The original text also notes that a vertical plunge may generate a large axial force; this is especially important for flat-bottom end mills whose end cutting edges do not reach the center when no pre-drilled process hole is available. The infeed approach described in the text is to enter at an angle to a certain depth and then use the side cutting edges for lateral cutting; on groove surfaces, the plunge can also be arranged through a pre-drilled process hole.

Include inspection and subsequent finishing in the preparation

Machining a complex cavity takes a relatively long time, so the machine tool, fixture and cutting tools should be checked before startup. If problems such as poor heat treatment, cracks or an uneven microstructure are found in the material, machining should be stopped. The filing allowance should be arranged according to the milling difficulty and surface roughness, so that large-area filing does not affect the surface accuracy.

Source and compilation notes

Source: VTOALL machining encyclopedia; original publication date: 2024-08-12. This article is a summarized compilation of technical material.