Surface finishing is a critical stage of the manufacturing process. This can be especially true of micromanufacturing, which inherently requires the highest standards of precision. The right surface finish ensures that a part or product will be durable and perform well. The wrong finish can increase friction, allow corrosion, or impede sanitization.
The roughness lay, and waviness of the surface all play into the final surface quality, although not all are relevant to micro-sized components. Trio Labs uses a proprietary process known as Resin Infused Powder Lithography (RIPL) to produce micro-scale parts with precise Ra32 micro surface finishing. Let’s take a closer look at the factors that impact the finish and determine quality results on the smallest parts.
What Is Surface Finish?
The term “surface finish” refers to the visual and tactile properties of the outermost layer of a metal part or product. Surface finish plays multiple roles in the manufacturing process, including:
- Aesthetics
- Durability
- Performance
- Reduction of friction
Characteristics of surface finish can vary from large to micro scale:
- Lay: The largest surface features, such as tool marks, which are easily visible to the naked eye.
- Waviness: Smaller features, which might not be immediately apparent upon visual inspection.
- Roughness: The smallest surface features, which contribute to the overall texture of a part or product.
Roughness is the most important component of micro metal finishing. Different types of parts have distinct parameters for surface roughness. For example, the right surface roughness can reduce friction and prevent bacterial growth in medical devices with micro-manufactured parts. Micro finishing techniques must be able to ensure that surface roughness fits within the applicable limits.
How Is Surface Roughness Measured?
Several methods exist for measuring surface roughness. Most methods measure the peaks and valleys in a surface over a defined area and produce a value. The average of the peak heights is known as the “mean line.”
Measurement methods include the following:
- Ra, or “roughness average”: The average value of the peak heights above the mean line.
- Rz: The average difference between the five consecutive highest peaks and lowest valleys.
- RMS: The root mean square average of the difference between profile height and the mean line.
Trio Labs uses the Ra method to measure roughness. Our RIPL process can produce metal parts with Ra32 native surface roughness. This is the same level of roughness as parts produced by CNC machining.
The higher the Ra value, the rougher the surface will be. A perfectly smooth surface would have a Ra value of zero. A coarse surface, such as sandpaper, would have a high Ra value.
Microinches vs. Micrometers (Microns): Typically, a Ra measurement value represents the average number of microinches (µ-in) between the peaks and the mean line. Ra32, for example, refers to a distance of 32 µ-in. Some measurements might use micrometers, also known as microns (µm), instead of microinches. A micron is much larger than a microinch, so a surface with a Ra measurement of 32 µm would be equal to almost 1,260 µ-in.
How Does Surface Finish Affect the Cost of a Part?
Changes to the surface finish produced by a micro-manufacturing process can add to the cost of that part. Some micro-manufacturing processes require additional work to get a part to the Ra32 surface finish. This might involve extra machining, polishing, or other processes. Technology that produces the right native surface finish, without the need for further work, maximizes efficiency and cost effectiveness.
Can You Achieve Quality Surface Finish With Only 3D Printing?
Yes, unlike traditional 3D printing, RIPL technology can provide a quality surface finish without expensive and time-consuming extra steps. Many forms of 3D printing require processes like tumbling, polishing, or blasting to reach the desired finish. Trio Labs’ RIPL process, however, produces a Ra32 native surface finish, with no need for additional work. This saves time over not only other 3D printing methods but also over CNC machining and injection molding processes.
Learn More About Trio Labs’ Micro Metal Finishing Techniques
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