Mold Textures in CNC Machining for Improved Part Quality(sheet metal laser cutting Barret)
- source:DAHLER CNC Machining
One critical factor that affects the quality of CNC machined parts is the texture left on the workpiece surface from the cutting tools. Controlling and optimizing surface finish is important for both functionality and aesthetics. Parts with rough textures are more prone to wear, fatigue, and corrosion. Smoother finishes allow parts to assemble correctly, reduce friction, and improve appearance.
This article will examine the factors that contribute to surface texture in CNC machining and discuss techniques machinists use to manipulate mold textures for optimal results.
What Causes Surface Texture in CNC Machining?
In CNC machining, the cutting tool edge is dragged across the workpiece surface, removing tiny chips of material. This creates micro-grooves and defects in the surface. The size, spacing, and directionality of these imperfections determine the visible texture left on the part.
Several variables impact the final surface texture, including:
- Cutting tool geometry - The angle of the cutting edges and flutes has a significant effect. Sharper tools typically produce a smoother finish.
- Tool material - Carbide and diamond cutters stay sharper longer than high-speed steel. This reduces surface roughness.
- Feeds/speeds - Faster feeds and speeds increase cutting forces, causing more prominent grooves and ridges. Slower settings provide a finer finish.
- Toolpath strategy - Some toolpaths, like zig-zag patterns, leave obvious track marks. Curvature-matched paths are smoother.
- Depth of cut - Light final finishing passes remove less material for a polished surface texture.
- Workpiece material - Gummy materials like aluminum can stick to tools, while harder metals like steel cause more tool wear. Both increase surface roughness.
- Vibration/chatter - Any resonance or vibration between the tool and workpiece roughens the finish. Proper fixturing and parameters reduce chatter.
- Coolant - Effective coolant washes away chips and lubricates the cut, leading to a better surface finish.
Given these parameters, machinists must choose the right combinations to achieve the mold texture required for their parts. This is both an art and a science.
Improving Mold Textures Through Tool Selection
Selecting the best tool is one of the most important considerations for optimizing mold texture. Using a worn or inferior tool will clearly result in a poorer finish.
Carbide inserts with sharp edges and fine grain sizes leave a smooth, finely striated surface. However, carbide is prone to chipping, especially in interrupted cuts. It also has limits on the fineness of surface finish it can achieve.
For the most precise finishing of steel and hard alloys, polycrystalline diamond (PCD) cutters are superior. The PCD edges stay sharp for a very long time and can obtain mirror-like finishes measured in nanometers. PCD is expensive though, so it is reserved for finishing passes.
Recently, new classes of ceramic cutters have been developed to bridge the gap between carbide and PCD. Ceramics like silicon nitride provide exceptional wear resistance for smoother textures. They are more affordable than PCDs but can still produce nanometer finishes.
Proper Insert Orientation Matters
The orientation of the cutting tool insert also affects the pattern and look of surface textures. There are several possibilities depending on the operation being performed.
For facing, turning, and boring, a low angle orientation is preferred. The lead angle allows a more gradual engagement and release from the workpiece for reduced rubbing. Angled inserts produce straight, longitudinal micro-grooves that look more uniform.
For milling and drilling, the insert orientation impacts the direction of the finish pattern. Radial textures look circular, while axial textures have a back-and-forth appearance. Which option is best depends on the individual part geometry and aesthetic preferences.
Toolpath Strategies to Control Mold Textures
In addition to tool selection, creating an optimal toolpath allows control over the finished mold texture. Using toolpaths matched to the workpiece geometry minimizes start/stop marks and ensures even surface patterns.
Constant scallop toolpaths involve offsetting the toolpath inward or outward from the model contours by the tool radius. This maintains a fixed distance between passes while eliminating sharp corners. The result is uniform groove spacing and consistent surface finish. A smaller scallop height reduces roughness further.
Another option is an adaptive toolpath that morphs to maintain the optimal stepover spacing, angle, and overlap as the cutter moves across changing workpiece curvatures. This prevents over-cutting in tight areas or under-cutting in open areas for the most consistent finish.
Post-Processing for Improved Mold Textures
As a final step, various post-processing methods can improve mold texture and appearance. Vibratory mass finishing uses abrasive media to deburr and polish surfaces. Brushing or micro-machining with miniature cutters can texture surfaces with precision cross-hatch patterns.
Electropolishing applies an electrolytic bath to smooth and brighten metal alloys through controlled dissolution. Laser polishing works similarly but uses a pulsed laser beam to re-melt the top layer of the workpiece and reduce roughness.
Mold texturing techniques like acid etching or electro-discharge texturing intentionally imprint patterns onto die and mold surfaces to impart decorative textures. This produces visible textures on cast or molded end-use parts.
Applications for Mold Textures in CNC Machining
The ability to accurately control mold textures gives engineers flexibility to achieve both functional performance and aesthetic goals with CNC machined components.
Fine mold textures are crucial for moving parts like bearings, bushings, pistons, shafts, and cylinder bores where friction, wear, and lubrication are important. Smooth surfaces in these applications prevent galling, pitting, and excessive power losses.
For medical implants and surgical tools, biocompatible finishes with minimized porosity discourage bacteria growth and make cleaning easier. This reduces infection risks and contamination.
In consumer products and high-visibility components, appealing visual and tactile textures enhance user experience and perceived quality. Soft-touch grips, finely brushed metals, or textured plastic surfaces improve ergonomics and feel.
Architectural building products like decorative metal panels rely on texturing to create custom designs andVisual textures add richness and interest to any CNC machined parts, from industrial components to consumer goods. By optimizing tooling, parameters, and toolpaths, CNC programmers can achieve exceptional control over surface finish and mold textures. This allows them to strike the right balance between precision, performance, and aesthetic appeal. The expanding capabilities of CNC machining will continue providing more options to creatively employ textures in manufacturing. CNC Milling CNC Machining