Extrusion Dies, because Abrasive Flow Machining matters
18 May 2011
By Bruno Boutantin
Kennametal Extrude Hone
While Abrasive Flow Machining, AFM, is a well established technique for polishing new extrusion dies, recent developments in polishing media and machines is making this a competitive and effective process for production die applications.
Dies used in production will periodically require reconditioning in order to maintain their effectiveness and performance. AFM is a suitable technique to clean and recondition these dies by removing surface imperfections and polishing the surfaces to meet a defined set of specifications including dimensional tolerance and surface roughness.
Historically both new and used dies have been polished using a manual polishing operation. AFM ensures quicker, more consistent results and does not require a highly skilled die polishing expert to achieve these results. The consistency of the polishing process through AFM far exceeds anything that can be achieved in a manual polishing operation. Unlike hand polishing, the AFM process provides balanced resistance. This enables the die to reach an average production rate of 40 to 50 tons, which equates to double the tons produced by the traditional hand polished die. This balanced resistance also helps increase the strength of the die, which reduces the risk of failure during the extrusion process. Die failure leads to expensive and time consuming production outages. AFM processing also allows for more material to be produced between the cleaning and reconditioning cycles.
AFM can be used for dies of all shapes, sizes and complexities and, in fact, the more complicated and intricate passage geometries that provide a high challenge for other methods are easily processed using the AFM process.
At Kennametal Extrude Hone, the focus is on meeting the needs of the extrusion sector and satisfying the technical requirements of industry sectors spanning aerospace, boat industry, automotive and architecture. These sectors are really creative and accordingly profile design is becoming more and more demanding. Automated die polishing is also a good application for crimping dies, dies for coins where the die need to be perfectly polished to avoid metal bonding.
Kennametal Extrude Hone current machines are based on an abrasive flow machining process where the media loaded with abrasive is flowing through the die like the aluminum or plastic. Usually limited or no fixtures are required to hold clamped between the top and bottom cylinders of the machine.
The media used is crucial and properties such as viscosity, grit size as well as abrasive type – Silicon Carbide, boron or diamond- have an impact on the final polishing result. In addition process parameters such as pressure, media flow speed, temperature and volume of media used are also important.
Kennametal Extrude Hone, for example has a range of machine offering solutions from small dies used in the wire or pills industry up to 400kg / 320mm diameter large dies from the aluminum industry. The company’s latest high performance die polishing media have been specifically engineered to meet the demands of die polishing applications. The unique characteristics of this media deliver immediate quality improvements, cost savings and productivity benefits. Dies for cold forging are also one of the main application for which diamond media is usually used, for example.
1. Improve productivity during die manufacturing.
2. Improve quality by providing more consistent material removal over the entire die surface and consistency from die to die.
3. Extend life span of the die by minimizing the material removed from the die during the cleaning operation.
4. Improve quality of the end product. Polished dies produced by AFM allow for the highest quality surface finish on the extruded material.
Extrude Hone invented and patented the Abrasive Flow Machining Process in 1966 and is now offering patented Autoflow software which controls media flow rate and provides back pressure for the best processing results.
AFM Processing of New Dies
When recast removal is required, the AFM process uniformly removes material and provides a high quality surface finish in less time than traditional methods. It also ensures a uniform edge break to the entrance of the die with minimal entrance effect. This leads to a high quality surface finish that die manufacturers and extruders have come to expect.
AFM Processing of Used Dies
When cleaning and reconditioning is required, the AFM process is a timely and cost effective way to restore the high quality surface finish by removing extrudate build up and surface imperfections, ensuring the die will again produce a high quality extruded product.
In recent years, the company’s focus has been on bringing new types of medial to the market to contribute to an improvement of the overall process. Such developments take place at the company’s dedicated laboratory in Irwin PA (USA).
Abrasive flow media is the crucial “cutting tool” in the AFM process. The composition, quality and consistency of the AFM media provide the unique behavior and dynamic performance that truly controls how this process achieves its results. Extrude Hone’s chemists, engineers and formulation technicians have worked to understand and model the chemistry of the AFM media to develop and consistently produce optimal media formulations. Specially designed media manufacturing equipment, coupled with unique testing and analysis instrumentation and close attention to ISO certified manufacturing procedures provide repeatable, quality materials to assure a dependable AFM process. The AFM Center of Excellence, in Irwin, PA, can perform feasibility testing with customer specific parts to provide the optimal media needed for each process.
Tight tolerances in the order of microns are a feature of die polishing application with surface roughness requirements of Ra 0.02 or Ra 0.05 microns are common in the die polishing industry. Material can be steel like a 35NCD16 hardened up to 63HRC or for carbide dies as an example a tungsten carbide grade 13D. In conclusion, AFM is now a broad ranging process that can be applied effectively in critical production environment.
About the company
Kennametal Inc. (NYSE: KMT) delivers productivity to customers seeking peak performance in demanding environments by providing innovative custom and standard wear-resistant solutions. This proven productivity is enabled through our advanced materials sciences and application knowledge. Our commitment to a sustainable environment provides additional value to our customers. Companies operating in everything from airframes to coal mining, from engines to oil wells and from turbochargers to construction recognize Kennametal for extraordinary contributions to their value chains. In fiscal year 2010, customers bought approximately $1.9 billion of Kennametal products and services – delivered by our approximately 11,000 talented employees doing business in more than 60 countries – with more than 50 percent of these revenues coming from outside North America. For more information visit www.kennametal.com.