Why is Surface Roughness So Important in Manufacturing?

Excerpted from SME Technical Paper MR79-569 by J. Bernard Hignett edited and updated by Cole Mathisen, Sales Manager at MFI For additional technical assistance or to make arrangements for sample processing your parts contact: Dave Davidson | Deburring/Surface Finishing Technologist at | Metal fatigue is the most common cause of fracture in metal components. It [&#;]

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UNTOUCHED by human hands&#; almost. Here is a batch of our little Creative Design  and Additive Manufacturing Lab bottle openers after effortless polishing. The top picture is straight off the machine, and the bottom picture is after centrifugal isotropic finishing. Other than breaking them off the build platform, and transferring them from one barrel of media to another, there was almost no other handling involved.

Ray Chalmers Contributing Editor at Modern Machine Shop magazine interviews Dave Davidson, Deburring/Finishing Technologist about processes for the surface finishing of gears.  &#;Vibratory finishing, centrifugal barrel finishing and turbo-abrasive machining are the three top techniques for finishing gears, improving performance and extending service life.&#; For additional information or assistance with arranging free sample part finishing [&#;]

The Process: Achieving a polish on a 3D Printed part depends greatly on the material and the initial roughness and scale left over from the printing process. On relatively clean (no heavy heat scale or atmospheric discoloration) titanium or stainless steel 3D printed parts with an initial surface roughness of 300-400 micro-inch Ra here is a typical example process that is used with Centrifugal Iso-Finishing Machines.:
Step One: Heavy grinding with aggressive plastic or ceramic media for 60 &#; 90 minutes
Step Two: Pre-Polish with lighter plastic for 30 Minutes
Step Three: High Polish with dry corn cob polishing media or porcelain for 30 Minutes
Total process time Two Hours (Not including loading)

SME (formerly: Society of Manufacturing Engineers) is a nation-wide networking and technical organization for manufacturing professionals. It sponsors plant tours, seminars, networking events, technical papers and articles, manufacturing and lean certification exams and has technical interest groups, local chapters and industry forums. See also: sme.org

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Complete it and fax it, or mail it. If you have trouble downloading the form me at my address and I will send you an attachment by .
One of the signature activities at SME, especially at the local chapter level are the technical plant tours and other area manufacturing-related events and networking opportunities that the chapter organizes. Shown below are photos taken at SME Technical Plant Tours that were organized by the Spokane, WA chapter. Check out the SME.org website and check to see if there is a local chapter near you or please contact SME Membership at 800.733., 313.425. or for further information

The mechanism that allows for improved &#;functionality&#; for all surfaces is basic to surface performance &#;to accept the loads imposed and resist wear. Traditional processes that generate form and control fit do not necessarily dictate how that part or assembly will function over time. In recent years, it has been realized that there is another contributor to long term part performance&#;surface finish. If a manufacturer does not account for surface finish characteristics like lube retention, micro burr removal, identification of torn and folded material, directionality, and load-bearing capability, the performance of components in the system cannot be predicted. High-energy finishing processes can also contribute to more predictable and extended service life by developing useful and uniform compressive stress equilibrium in parts as a hedge against premature fatigue failure.

For additional information contact the Contributing Editor: David A, Davidson Deburring/Finishing Technologist | +1.509-563. Cell and | dryfinish.wixsite.com/iso-finish Many medical companies are using Centrifugal Iso-Finishing machines for finishing medical parts such as hips, knees, bone screws as well as dental partial, implants and orthodontic components. That tradition continues today as the medical industry [&#;]

Guest column by Mike Klein at Isofinishing Inc. For additional information or to make arrangements for free sample processing of your parts contact: Dave Davidson | Deburring/Finishing Technologist |  https://dryfinish.wixsite.com/iso-finish Surface roughness is a component of surface texture and plays an important role in determining how an object will interact with its environment. Roughness [&#;]

What kind of parts are being deburred, finished and polished with Centrifugal Iso-Finishing?

High-speed and Hands-free Deburring and Super Iso-Finishing Precision Components from many Industries. The industries served include:
&#; Medical Implants and Orthopedic Devices
&#; Dental and Orthodontic Parts
&#; Aerospace Engine Components
&#; Aerospace Airframe and Structural Components
&#; Automotive Engine and Powertrain Components (Isotropic Finishing)
&#; High-Performance Motorsports and Powertrain (Isofinishing)
&#; Motorcycle engine and powertrain
&#; Machine Tooling,
&#; Metal 3D Printed Parts
&#; Plastic 3D Printed Parts
&#; Injection Moldings and Machined Plastics
&#; Springs
&#; Acrylic and Acetate Polishing
&#; Precious Jewelry and Fashion Accessory Polishing
&#; Screw Machine Part Deburring and Super-Finishing
&#; Eyewear Components
&#; Firearms and ammunition
&#; Metal Injection Molded Parts (MIM)
&#; Investment Castings
&#; Powdered Metal Parts Smoothing and Polishing
&#; Deflashing and smoothing of plastics and rubber
&#; Surface Burnishing for Compressive Stress
Ask about the (free) sample part processing program
See also our sample part processing form here: https://lnkd.in/guGnPZG

Surface Roughness Measurement and Applications

A question sometimes asked is "At what point does surface roughness become waviness?" This is almost impossible to answer.

The change from the concept of roughness to that of waviness often depends on the size of the workpiece.

For example, the irregular spacing which would be regarded as roughness on a machine spindle would be regarded as waviness on a watch staff. The number of waves in the functional length also has some influence on how we classify the irregularities. One wave on a watch staff might be considered as curvature, but a larger number of waves on a longer shaft may be accepted as waviness.

It is better to separate roughness, waviness and form according to their cause, as this also relates to the performance factors. So, we can define surface roughness, waviness and form as follows.

What is Surface Roughness or Roughness?

Surface roughness or roughness is defined as the irregularities which are inherent in the production process (e.g. cutting tool or abrasive grit). Surface roughness is quantified by the deviations in the direction of the normal vector of a real surface from its ideal form. If these deviations are large, the surface is rough; if they are small, the surface is smooth.

What is Waviness?

Waviness is part of the texture on which surface roughness is superimposed. It may result from vibrations, chatter or work deflections and strains in the material. It is also impossible to specify precisely where waviness stops, and the shape becomes part of the general form of the part.

What is Form?

Form is the general shape of the surface, ignoring variations due to roughness and waviness.

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Roughness, Waviness and Form

These distinctions are therefore qualitative not quantitative yet are of considerable importance as defining them this way is well established and functionally sound. Surface roughness is produced only by the method of manufacture resulting from the process rather than the machine. Marks can be left by the tool or grit itself: these will be of a periodic nature for some processes and more random in others.

There is also a finer structure formed by tearing of the part during machining, the build-up of debris at the edge and small blemishes in the tool tip. Waviness, however, is attributed to the individual machine, imbalance in the grinding wheel, lead screw inaccuracy and lack of rigidity.

Form errors are often caused by the part not being held firmly enough or a slideway not being straight, or heat generated during the process that can cause a surface to bend.

It should be emphasized that these three characteristics are never found in isolation. Most surfaces are the result of a combination of the effects of surface roughness, waviness and form.

How to Measure Surface Roughness?

Since the individual surface roughness irregularities are too small to see with the naked eye, a Surface Roughness Measurement Tester is required. A small stylus is drawn across the surface at a constant speed for a set distance. An electrical signal is obtained and amplified to produce a much-enlarged vertical magnification.

This signal result is displayed in a graphical output, together with numerical values that characterize the surface texture or surface roughness. Watch the video below of the Form Talysurf® PGI NOVUS Surface Profilometer.

The ISO standard for surface roughness measurements is a 60° or 90° conical stylus with a spherical tip of 2μm radius. However, this is quite a delicate stylus, and needs a surface roughness measuring instrument with excellent mechanical properties to achieve this.

The Surtronic® Duo II Surface Roughness Measurement Tester is designed to measure surface roughness, and can be utilised in conjunction with the HSE Slips assessment tool software to check flooring surface roughness.

In addition, the Surtronic® S-100 Series Surface Roughness Measurement Tester offers a versatile solution for all your surface finish measurement requirements.

What are the Surface Roughness Measurement Parameters?

In order to predict the behaviour of a component during use or to control the manufacturing process, it is necessary to quantify these surface characteristics by using surface texture parameters.

Surface texture parameters can be separated into three basic types; Amplitude Parameters (vertical characteristics), Spacing Parameters (horizontal characteristics) and Hybrid Parameters (combination of spacing and amplitude parameters).

Examples of typical surface roughness measurement parameters can be seen below:

• Ra - The universally recognised, and most used, international parameter of roughness. It is the arithmetic mean of the absolute departures of the roughness profile from the mean line.
• Rv - The maximum depth of the profile below the mean line within the sampling length.
• Rp - The maximum height of the profile above the mean line within the sampling length
• Rt - The maximum peak to valley height of the profile in the evaluation length
• Rz - The maximum peak to valley height of the profile within a sampling length

Click Here to find out more about Surface Roughness Measurement Parameters

What are the Applications of Surface Roughness?

In many applications surface roughness is closely allied to function, for instance where two surfaces are in close moving contact with each other their roughness will affect their sealing or wear properties. This might suggest that it is a case of "the smoother the better", but this is not always true as other factors may be involved.

Where lubrication is involved it has been found that roughness valleys are required to hold oil. Also, the financial aspect must be considered: it costs a lot of money to produce very smooth surfaces and the expense of this exercise can add to the bill considerably without gaining a great deal of performance.

However, when two surfaces in relative motion (e.g. a shaft and its bearing) are lubricated, some wear will occur. If the surfaces are rough, they will soon become smoother as the peaks wear away. Since this removes metal there will be a quicker change in the fit of the two parts than if the finish was at the optimum from the start. On the other hand, some parts such as clamping devices or a pin with an &#;interference fit&#; depend on friction for their functionality.

Another application where surface roughness can have an influence on performance is the use of lip seals to prevent the escape of hydraulic fluids. If the finish is too smooth it is difficult to maintain a fluid film between the shaft and the seal. If the finish is too rough it can cause abrasion and consequent breakdown, leading to failure. Inspection of the texture left on a component after machining will often reveal tool defects, incorrect tool settings or wrong tool speeds and feeds. 

The appearance of a surface can be of some importance. For instance, sheet steel used for motor car bodies must have a finish which will allow paint to bond to the surface without any "orange peel" effect and with an even appearance. Anybody who has tried to paint onto a glass surface will appreciate the difficulty in getting a firm bonded finish. Metallic parts are not the only components to require control; both paper and plastic parts need the same degree of repeatability.

If you are looking for more details, kindly visit Roughness Gauge Manufacturer.