D. Olvera

HOLE MAKING USING BALL HELICAL MILLING ON TITANIUM ALLOYS

In this article, results of helical ball milling for hole making on Ti-6Al-4V alloy are presented and compared with drilling. Two different machining strategies were tested with a ball end mill. In the first strategy only a helical milling path was used to achieve the nominal diameter. The second strategy has two stages; first, helical milling considering a diameter 50 µm below the nominal, and second, the tool flank of the ball end mill were used to remove the stock left with a single contouring operation. Experimental tests were performed taking into account the process time, final quality of holes, hole diameter, roughness and burr formation at tool entrance and exit. With helical milling two advantages were concluded: the process is versatile because one tool is suitable for a range of diameters and negligible burrs are produced. However hardness in the zones close to hole internal surfaces machined with the ball end mill tool decreases with respect to twist drilling. The information obtained from this research work defines suitable cutting parameters for the helical milling process in the titanium alloy Ti-6Al-4V with ball end mills.

DRILLING OF INTERMETALLIC ALLOYS GAMMA TIAL

Due to their high strength/weight ratio and resistance to corrosion and wear, superalloys such as gamma TiAl or Inconel 718 appear as the best choice for the high mechanical/thermal demands in the vicinity of the combustion chamber of aircraft engines. There are assembled parts such as cases, disks or blisks; in the manufacturing of these components the last drilling operation could jeopardize the full work integrity adding new costs to the just very expensive parts. Therefore drilling is a high‐added value step in the complete sequence. The present work is framed within the study of hole making in advanced materials used for lightweight applications in aerospace sector. Within this context, the paper presents the results from milling tests on three types of gamma TiAl alloys (extruded MoCuSi, ingot MoCuSi and TNB) to define an optimal set of cutting parameters, which will contribute to open the increase in use of these special alloys. Drilling tools made of integral hard metal were used, applying differe...

Stability Lobes in Turning of Low Rigidity Components

An accurate prediction of the dynamic stability of a cutting system involves the implementation of tool geometry and cutting conditions on any model used for such purpose. This study presents a dynamic cutting force model based on the collocation method by Chebyshev polynomials taking advantage from its ability to consider tool geometry and cutting parameters. In the paper, a simple 1DOF model is used to forecast chatter vibrations due to the workpiece and tool, which are distinguished in separate sections. The proposed model is verified positively against experimental dynamic tests.

Flank Milling of Complex Surfaces

In this chapter the main methods, machining strategies and possible problems when flank milling complex surfaces, are deeply explained. Flank milling is an operation defined by using large axial depth of cut with end milling tools, high cutting speed and relatively small radial depths of cut. This process is especially recommended for ruled surfaces machining, whose tangential contact of the involving cylinder with the cutting tool body is the key factor to define the tool paths. Due to the complexity of these kinds of surfaces, 5-axis milling is required taking special care of the geometrical interferences between the tool and the complex geometry of the pieces in order to avoid collisions. Finally, a new model for the prediction of roughness and dimensional accuracy on thin-walled component is presented, along with examples of parts with surfaces which need the flank milling operations due to their complexity.

New Strategies For Hole Making In Ti‐6Al‐4V

The working conditions for the aircraft engines components demand a good response of their mechanical properties at high temperatures and aggressive environments. Those challenging conditions force the use of new materials like titanium (and nickel) based alloys, qualified as difficult‐to‐cut materials due to their low machinability. Among them, the Ti‐6Al‐4V is very widespread because of its high strength/weight ratio. On the other hand, a very demand task for aeronautical components is the hole making operation, being in most cases, the last performed operation. For this reason, drilling operation is strongly related to the quality and productivity since any machining error could damage the component in the final steps. Thus, drilling operation determines the minimum machining time which is reflected upon the cost per unit. This study focuses the attention on a relative new technique that could replace the conventional drilling resulting in a more added‐value operation: ball helical milling (BHM). This ...

Identification of Stability Cutting Parameters Using Laser Doppler Vibrometry

High-speed milling operations of thin walls are often limited by the so-called regenerative effect that causes poor surface finishing. To optimize the cutting process in terms of quality surface and productivity, the frequency response function (FRF) of the wall needs to be measured in order to identify the modal parameters of the system which are used to obtain the stability lobes that help identify the optimal system’s parameter values to warrant stable cutting conditions. The aim of this work is to experimentally show the variation on the frequency response function (FRF) values obtained by using a laser Doppler vibrometer (LDV) device and accelerometer sensors during a milling operation processes of an aluminum thin-walled workpiece of 1 mm thick and 30 mm height. It is shown that the FRF values variations has strong influence on the stable cutting bounds. To further assess our findings, we used the collected experimental data obtained by using the LDV during milling machine cutting operation processes of several thin-walled workpieces to identify the cutting parameters values that allow us to obtain good quality and acceptable surface finish.

Sand moulds milling for one-of-a-kind pieces

Time to market is a critical measurement for todays foundry market. Combining 3D digitizing and sand blocks milling is possible to reduce this time. Avoiding the use of a wood pattern, this technique is useful for art pieces or unique parts, when only one component is necessary. The key of the proposed methodology is to achieve enough tool life with conventional tool qualities, avoiding the risk of sand destruction or damage. A special study of tool wear is presented in this work, studying different tool materials and different sand types. Two examples of unique parts are also presented in this work following the proposed methodology in order to reduce time and cost for the rapid reproduction of very short batches.

Collocation method for chatter avoidance of general turning operations

An accurate prediction of the dynamic stability of a cutting system involves the implementation of tool geometry and cutting conditions on any model used for such purpose. This study presents a dynamic cutting force model based on the collocation method by Chebyshev polynomials taking advantage from its ability to consider tool geometry and cutting parameters. In the paper, a simple 1DOF model is used to forecast chatter vibrations due to the workpiece and tool, which are distinguished in separate sections. The proposed model is verified positively against experimental dynamic tests.

Rapid Reproduction of Unique Parts by Sand Block Milling

Time to market is a critical measurement for todays foundry market. Combining 3D digitizing and sand blocks milling is possible to reduce this time. Avoiding the use of a wood pattern, this technique is useful for art pieces or unique parts, when only one component is necessary. The key of the proposed methodology is to achieve enough tool life with conventional tool qualities, avoiding the risk of sand destruction or damage. A special study of tool wear is presented in this work, studying different tool materials and different sand types. Two examples of unique parts are also presented in this work following the proposed methodology in order to reduce time and cost for the rapid reproduction of very short batches.

Drilling Titanium Aluminides with Twist Drills

Due to their high strength/weight ratio and resistance to corrosion and wear, superalloys such as gamma TiAl or Inconel 718 appear as the best choice at the sight of the demands in the vicinity of the combustion chamber. Such kind of parts suffer one last drilling operation at the end of the manufacturing process. The present work is framed within the study of twist drilling in advanced materials used for lightweight applications in aerospace sector. Within this context, the paper presents the results obtained from different tests in gamma TiAl alloys. Tool life tests were performed on three types of γ-TiAl (extruded MoCuSi, ingot MoCuSi and TNB) to define an optimal set of cutting parameters.