A. Attanasio

Influence of Material Microstructures in Micromilling of Ti6Al4V Alloy

In the most recent decades the introduction of unconventional machining processes allowed the development of micromachining techniques. In this work, the influence of material microstructures on the micromilling process was investigated. Ti6Al4V alloy was selected as workpiece material since it is a very common material for micro applications and because its duplex microstructure can be easily changed by proper thermal treatments. Four different microstructures (namely bimodal, fully equiaxed, fully lamellar and mill annealed) were obtained through recrystallization annealing treatments carried out at different times and temperatures. The mechanical properties of the samples were assessed by microhardness measurements. Nano-indentations were also performed on single grains to understand how the different hardness of phases and structures present in the Ti6Al4V alloy can affect the micromilling process. Microchannels using two flute flat end mills with a diameter equal to 200 µm were realized on the treated samples. Two different feed-per-tooth values were used during the tests. Cutting force, channel shape and burr dimension were investigated. Morphological and energy dispersive spectroscopy (EDS) analyses were performed on tools by means of a scanning electron microscope (SEM): in this way the phenomena mainly influencing the tool status were also identified. Lower cutting forces and reduced tool wear were observed when working fully lamellar microstructures compared to the other ones.

Micromilling of Lamellar Ti6Al4V: Cutting Force Analysis

The aim of this article is to study the influence of a Ti6Al4V microstructure on cutting forces during the micromilling process. Samples were annealed above the β-transus at three different temperatures—1020, 1050, 1080°C—and then cooled in a furnace, air, and water, in order to produce different Widmastätten microstructures. Micromilling tests were carried out on heat-treated samples, and the cutting forces were measured by means of a load cell. The results were correlated to the sample microstructures, which were thoroughly investigated by means of an optical microscope, X-ray diffraction, and microhardness measurements. The highest cutting forces were observed for soft and ductile furnace-cooled samples, suggesting that the most important factor affecting workability is the material ductility, while hardness is a less relevant parameter.

Use of TPIF or SPIF for Prototype Productions: an Actual Case

The present research deals with sheet incremental forming (SIF), a recently developed technique characterized by high flexibility, reduced production times and costs. This is ideal when low volume batches or customized parts or prototypes have to be manufactured. Two different SIF techniques can be identified: Single Point Incremental Forming (SPIF) and Two Points Incremental Forming (TPIF). The main difference between them consists of the presence or not of a die under the sheet. The aim of the present research is to experimentally compare these two different approaches when producing the same part, that is a door handle cavity. In addition, a FE analysis of the process has been developed.

Experimental Device to Study Surface Contacts in Forming Processes

Friction plays a fundamental role in forming processes since it influences many aspects of the process such as: material flow, forces, die wear and part quality. There are many different models for representing friction and many different tests to evaluate it. Friction is very different when considered in cold, warm and hot forming operations. To have an equipment giving the possibility of performing simple tests is fundamental to evaluate friction as a function of contact pressure, sliding velocity, piece roughness, tool and piece materials, tool coating, temperature. The present paper illustrates the equipment realized at the Brescia University Lab based on a large scale pin‐on‐disk and some preliminary tests to evaluate friction forces under different process conditions. The equipment covers a wide range of process parameters and can be fully controlled in normal force and sliding speed.