Ultra-precision diamond turning enables the manufacturing of parts with mirror-like surfaces and highest form accuracies out of non-ferrous, a few crystalline and plastic materials. Furthermore, an ultrasonic assistance has the ability to push these boundaries and enables the machining of materials like steel, which is not possible in a conventional way due to the excessive tool wear caused by the affinity of carbon to iron.<p> </p> Usually monocrystalline diamonds tools are applied due to their unsurpassed cutting edge properties. New cutting tool material developments have shown that it is possible to produce tools made of nano-polycrystalline diamonds with cutting edges equivalent to monocrystalline diamonds. In nano-polycrystalline diamonds ultra-fine grains of a few tens of nanometers are firmly and directly bonded together creating an unisotropic structure. The properties of this material are described to be isotropic, harder and tougher than those of the monocrystalline diamonds, which are unisotropic. This publication will present machining results from the newest investigations of the process potential of this new polycrystalline cutting material.<p> </p> In order to provide a baseline with which to characterize the cutting material cutting experiments on different conventional machinable materials like Cooper or Aluminum are performed. The results provide information on the roughness and the topography of the surface focusing on the comparison to the results while machining with monocrystalline diamond. Furthermore, the cutting material is tested in machining steel with ultrasonic assistance with a focus on tool life time and surface roughness. An outlook on the machinability of other materials will be given.
Ultra precision diamond turning of hardened steel to produce optical quality surfaces can be realized by applying an ultrasonic assisted process. With this technology optical moulds used typically for injection moulding can be machined directly from steel without the requirement to overcoat the mould with a diamond machinable material such as Nickel Phosphor. This has both the advantage of increasing the mould tool lifetime and also reducing manufacture costs by dispensing with the relatively expensive plating process. This publication will present results we have obtained for generating free form moulds in hardened steel by means of ultrasonic assisted diamond turning with a vibration frequency of 80 kHz. To provide a baseline with which to characterize the system performance we perform plane cutting experiments on different steel alloys with different compositions. The baseline machining results provides us information on the surface roughness and on tool wear caused during machining and we relate these to material composition. Moving on to freeform surfaces, we will present a theoretical background to define the machine program parameters for generating free forms by applying slow slide servo machining techniques. A solution for optimal part generation is introduced which forms the basis for the freeform machining experiments. The entire process chain, from the raw material through to ultra precision machining is presented, with emphasis on maintaining surface alignment when moving a component from CNC pre-machining to final machining using ultrasonic assisted diamond turning. The free form moulds are qualified on the basis of the surface roughness measurements and a form error map comparing the machined surface with the originally defined surface. These experiments demonstrate the feasibility of efficient free form machining applying ultrasonic assisted diamond turning of hardened steel.
Diamond turning of steel parts is conventionally not possible due to the high tool wear. However this process would
enable several different application with high economical innovative potential. One technology that enables the direct
manufacturing of steel components with monocrystalline diamond is the ultrasonic assisted diamond turning process.
This technology has been investigated over years within the Fraunhofer IPT and has proven its potential. Surface
roughness in the range of Ra = 5 nm are reached and the diamond wear is reduced by a factor 100 or higher. Up to now
this process has been investigated in lab conditions manufacturing only plane surfaces. In order to prove its industrial
suitability, two relevant aspherical shapes, convex and concave respectively, have been defined and manufactured. The
reached form accuracies and surface roughness values will be described in this paper.
In this paper the most recent investigations in ultrasonic assisted diamond machining of hardened steel at the Fraunhofer
IPT is presented. The goal of this technology is to unify the outrageous specifications of diamond machining process
with steel material. The focus lies on the kinematic influence of the discrete frequencies 40 kHz and 60 kHz. Special
interest is given to the reachable surface roughness depending on process parameters. The machined steel (1.2083,
X40Cr14, STAVAX ESU) is a common mold die material for optical replication processes.Results of the accomplished
investigations show the potential of the ultrasonic assisted process and recent developments. By increasing the frequency
from 40 kHz to 60 kHz the overall process stability is increased. This makes the process less vulnerable towards feed rate
variation or towards the variation of machined material hardness. Furthermore no tool wear is detected at high material
removal rates or high cutting distances during component machining.