GETTING STARTED WITH MANIFOLD DESIGN
Our standard surface finish is a maximum of 32 microinch RA (.8 micrometer RA). We will finish all surfaces to that roughness unless otherwise stated.
Flat areas: We can finish areas of large flat surfaces to an optical finish below 4 microinch RA (0.1 micrometer).
Valve mount surface finish is maximum 32 microinch RA (0.8 micrometer RA). If specified, it can machine to 16 microinch RA (0.4 micrometer RA).
Ports Upchurch ¼-28 flat bottom fittings are the most common for our manifolds. We manufacture the bottom of the ports to 32 to 20 microinch RA (0.8 micrometer RA) with a circular lay.
Pockets (bubble traps, reservoirs, accumulators) are maximum of 40 microinch RA.
Channels are a maximum of 32 microinch RA. Channels used for imaging may need to be square with a better finish. Please discuss with Controlled Fluidics your specific requirements.
Methods of polishing manifolds
Buffing uses cotton cloth to smooth the surface. Buffing is not flawless as it leaves thousands of multi-directional scratches on the surface. Buffing is only suitable for large flat pieces with limited holes and projections. It will round corners and edges.
Flame polishing uses a flame to melt the surface creating a very smooth, visually clear surface. As this method is done by hand, some waviness is expected. Flame polishing is limited to larger features at or near the surface. It will round corners, straight edges and hole edges. Acrylic only.
Vapor polishing uses a solvent to reflow the surface and make it smooth. Vapor polishing can be used on internal features like threads and bores. Economical solution for an entire manifold however not as clear as flame polishing for Acrylic. Method of choice for polycarbonate and UltemⓇ. Does not distort or change feature size.
Best practice – The best mix of functionality and price is to polish the large faces where components mount and leave the edges as machined. The clear faces provide good sealing for the valves and visualization of the channels. The edges are left translucent as they are typically a non-working surface.
Glass bead blast produces a uniform smooth frosted finish. Colored parts especially black can look whiteish.
Tumbling produces a matte finish. Length of time a part is tumbled and media choice will affect the finish. Useful for large, heavy-duty parts.
As machined is simply the part after a machining process with no additional polishing. The surface will be 32 microinch Ra (.8 micrometer Ra) or better. Clarity for a machine finish can vary from translucent to opaque depending on cutting efficiency of the tool. The overall presentation will vary slightly depending on milling or turning operations.
Cost of polishing
A common working location of a fluidic subassembly is within an instrument and outside the view of normal operation. Customers wanting to save money will consider removing the polishing step. Things to consider:
- Polishing allows for visual confirmation of fluid flow.
- Has a high degree of aesthetic value
- Polishing can be done in a cost-efficient manner
- For manifolds, request polish only on the large flat areas to save money.
- Leave manifold edges as machined.
- Specify as machined only for highly cost competitive manifolds
- Grade 2 (vapor) is the most cost effective polishing
- Flame polishing is not a precision process. Expect corners to be rolled.
- Apply grade 3 polishing sparingly.
- Angular or curved surfaces are harder to polish than flat
Manufacturing plastic parts from clear material is a common request for manifolds and machined components. Clear parts allow a user to monitor the internal activity of a process. Many amorphous materials in their raw state are clear. However, after machining they become translucent to opaque depending on tool wear and cutting efficiency. To return the machined part to clear, a secondary polishing operation is often required. Specifying the proper clarity to match the application can be a challenge. Controlled Fluidics has defined 4 levels of clarity to aid the design effort.
Grade 1 – As machined: This finish is the standard machined plastic finish. Surface roughness is better than 32 microinch (.8 microns). Surfaces range from translucent to opaque depending on the feature geometry and cutting conditions. This is appropriate for non-visual applications.
Grade 2 - See through finish: This finish allows for activities like visual fluid flow and bubble detection. It is the most common request and meets a broad range of design requirements. Processes such as vapor polishing are appropriate for this clarity. Polishing the entire part is typical. Parts can vary in haze and clarity. Tool marks are present and do not affect functionality. Some scratches. This is the most cost-efficient method with limited quantitative measurements for quality.
Grade 3 - Optical window finish: This finish is appropriate for imaging thru the manifold or plastic part for detection sensors. To the unaided eye, a Grade 3 finish looks similar to window glass. Tool marks are not readily apparent. Few scratches. To achieve this clarity, specifying a surface finish of less than 2 microinch Ra (.05 micron) is appropriate. This clarity is specified in a localized area beneath the optical sensor and not used for entire parts.
Grade 4 - Optical finish: This finish is a true optical finish specified in both surface finish and surface form. Surface finish for optics is measured with a white light interferometer and specified in angstroms. Surface form represents waviness of the surface and its adherence to the ideal profile. Form is also measured with an interferometer and specified in fringes. This level of clarity is appropriate for lenses and doesn’t find use in manifold applications.
One of the pitfalls of polished components is the ease in which any defect can be seen. Customers can raise concerns about debris in the material.
According to the ASTM standard D4802-16 (the standard regarding cast acrylic sheets) there is an allowable level of particulate debris in acrylic sheets. This standard states that any amount of particles under 0.8 mm (0.031 in) are acceptable provided they do not affect the serviceability of the sheet. Particles between 3.2 mm (0.125 in) and 0.8 mm are allowed given no more than one particle of this size is found in 0.4 m2 (4.3 ft2) of the sheet. As the sheets of plastic, we purchase conform to this standard, we also hold our products to this standard (including parts in other clear materials).
While debris can be aesthetically not pleasing, it usually does not have an impact on functionality including those directly above a channel. A common debris, carbon specs are fully encapsulated in the material (though they might not look that way). For those applications requiring debris free material, please define the requirements during the quoting process. It is possible to cull material based on contamination levels with an additional cost impact.