This week we took an in-depth look at Harvey Tool compression cutters. This one was an easy choice; first off we have had a few requests lately for tools specifically designed for composites and secondly Harvey Tool provides some excellent technical articles on their website. If you do any machining at all you are already familiar with Harvey tool but on the outside chance that you are unfamiliar contact Engman-Taylor - we would be delighted to ship or deliver a catalog you.
Composite Materials
First of all let's explain "composite" materials. Composites are materials, and the machining of, are growing in popularity mostly because of the aerospace industry and in performance automobile manufacturing. These materials though are also appearing in bicycles, bathtubs, guitars and other commonly produced products.
Composites are a group of materials made up of at least two unique constituents, that when combined produce mechanical and physical properties favorable for a wide array of applications. These materials usually contain a binding ingredient, known as a matrix, filled with particles or fibers called reinforcements. Composites have become increasingly popular in the Aerospace, Automotive, and Sporting Goods industries because they combine the strength of metal, light weight of plastic, and rigidity of ceramics. Many times a composite is used in cases where an extremely high strength to weight ratio is needed. A composite is also often layered with varying fiber and tape orientations, which help to increase strength in the material.
Composite materials are generally machined using standard metal cutting end mills. These unidirectional helix mills bring a few issues to the machining process such as lifting, fiber pullout, and de-lamination in layered composites.
Machining composites can be difficult because of two primary factors.
First of all composites are very abrasive, and can prematurely wear most
cutting tools including carbide tools. Secondly, composites tend to
de-laminate during milling and drilling operations. Sharp edges and
space -age coating can increase tool-life but tool geometries can help
here too.
Harvey Tool Compression Cutters
To combat these machining challenges, the compression cutter has both an up and down-cut helix. The top half of the flute, closest to the shank, has right hand cutting teeth with a left hand spiral, forcing chips down. The bottom portion of the flute, closest to the end, has right hand cutting teeth and a right hand spiral, forcing the chips up. When cutting, the opposing flute directions generate counteracting up and down-cut forces. The opposing cutting forces stabilize the material removal, which causes a superb finish on both the bottom and top of the workpeice, limits fiber pullout, and stops de-lamination.
Choosing the Right Diamond
Another factor to consider when machining composites is the abrasiveness of the material. Glass and carbon fiber filled materials have the tendency to wear down the edges of carbide cutting tools. To account for the rough nature of composites, the compression cutter is offered coated with Amorphous Diamond, a PVD coating with DLC properties, and CVD Diamond, a diamond coating that is chemically grown onto the carbide. Each coating is better suited for different materials. The Amorphous Diamond is a thin layer of diamond that does not experience edge rounding from the thickness of the coating, making it suitable for materials that contain less than 30% of abrasive fill. Since these materials are more matrix than fill, they will create a chip when machined. When cutting materials with a higher concentration of fill, the CVD diamond coating is found to be very beneficial. The CVD coating is five times thicker, and has superior abrasion resistance to the Amorphous Diamond. At the micro-level, the cutting action is similar to that of a grinding operation, which makes the coating best suited for heavily filled composites that will produce a powder-like chip when machined.
Example of Milling Carbon Fiber:
https://youtu.be/6-RjLwMOQBk
Sources:
http://www.harveytool.com/cms/TechnicalResources_266.aspx
https://en.wikipedia.org/wiki/Composite_material
Let us know some of the challenges you face in machining composites or show your composite material finished products.
