Knut Sørby

A Review on Minimum Quantity Lubrication for Machining Processes

In the pursuit toward achieving dry cutting, air machining, minimum quantity lubrication (MQL), and cryogenically cooled machining are the stepping stones. Nevertheless, machining is always accompanied by certain difficulties, and hence none of these methods has provided a complete solution. Hence, this article reviews various MQL methods used by various machining processes for different materials. It also highlights the future work directions for research in this area.

Determining optimal replacement time for metal cutting tools

Traditional tool life models do not take into account the variation inherent in metal cutting processes. As a consequence, the real tool life rarely matches the predicted values. To compensate for this uncertainty, tools are usually replaced prematurely, which leads to unnecessarily high tool costs. In some cases, however, wear-out occurs earlier than predicted, which imposes a risk of workpiece damage or rework and can lead to other extra charges. To balance these costs, this paper proposes an age replacement model. It is assumed that penalty costs are incurred each time a tool fails before the planned replacement. The probability of such an event is determined from the tool reliability function, which models the wear-out by a mixture of Weibull distributions, while failures due to external stresses are accounted for by a homogeneous Poisson process. The optimal replacement time is then determined from a total time on test (TTT) plot. The adequacy of the proposed approach for practical application is tested and confirmed in a case study on turning of Inconel 718 with cubic boron nitride (CBN) tools.

High-pressure cooling of face-grooving operations in Ti6Al4V

Abstract This paper presents results from an experimental study with high-pressure cooling on the rake face and on the flank face of the cutting tool. The technique was tested in face-grooving operations in Ti6Al4V, which are common and time-consuming turning operations in the aerospace industry. Grooving is a difficult operation because the cooling effect is low, owing to the geometry of the groove and also because of the chips that obstruct the coolant flow. The results show that 10–30 MPa high-pressure cooling on the rake face of the tool can increase tool life by 200–300 per cent as compared with conventional flood flushing. However, when high-pressure rake face cooling is applied, the workpiece surface may be adversely affected by the chip flow. Applying high-pressure coolant to the tool flank face increases tool life by 50–100 per cent relative to conventional flood flushing. No damage to the workpiece surface was observed. It can be concluded that a complete high-pressure cooling system should include options for both cooling methods.

Improving High Speed Flank Milling Operations in Multi-Axis Machines

Abstract This paper describes a method for selection of cutting tool and machining data for high speed flank milling. The method is based on models for tool life and cutting force. Restrictions that are related to maximum allowable force, maximum allowable chip thickness, and machine tool limitations are taken into consideration.

Formation of Built-Up Layer on the Tool in Turning Operation of Magnesium Alloys

The present work highlights some factors which affect formation of a protective built-up layer (BUL) on the rake face of the cutting tool when cutting magnesium alloys. This work suggests that BUL can positively affect tool life, surface roughness, cutting speed and tool forces. The BUL is formed in cutting magnesium alloys with the PCD tool inserts at cutting speed range from 500 to 2500 m/min and at the carbide tool inserts at lower cutting speed range around 550 m/min. It has been found that deposit layers primarily have similar chemical composition as MnAl inclusions which are incorporated in the structure of the examined AZ91 magnesium alloys.

Additive-manufactured sandwich lattice structures: A numerical and experimental investigation

The utilization of additive-manufactured lattice structures in engineered products is becoming more and more common as the competitiveness of AM as a production technology has increased during the past several years. Lattice structures may enable important weight reductions as well as open opportunities to build products with customized functional properties, thanks to the flexibility of AM for producing complex geometrical configurations. One of the most critical aspects related to taking AM into new application areas—such as safety critical products—is currently the limited understanding of the mechanical behavior of sandwich-based lattice structure mechanical under static and dynamic loading. In this study, we evaluate manufacturability of lattice structures and the impact of AM processing parameters on the structural behavior of this type of sandwich structures. For this purpose, we conducted static compression testing for a variety of geometry and manufacturing parameters. Further, the study discusse...

Metal Penetration in Additively Manufactured Venting Slots for Low-Pressure Die Casting

Venting of excess gas and air in casting moulds is of critical importance to avoid defects such as misruns and porosities. Additive manufacturing give mould designers a possibility to make venting slots in large areas and geometrically complex mould sections. The venting slots must be wide enough to allow air to escape, but narrow enough to restrict metal flowing into the venting slots. In this paper, an experiment was conducted to identify which process parameters cause metal penetration in venting slots in low-pressure die casting (LPDC). Parameters having the largest influence on the degree of penetration is found to be filling pressure and slot width. For a typical LPDC process a slot width of 0.14 mm is recommended.

Estimation of cutting tool failure costs

Probabilistic cutting tool replacement models assume that tool life is stochastic in nature. This implies that a tool can wear out before the planned replacement, as a result of which penalty costs are incurred. If these costs, as well as the tool failure function and the cost of scheduled replacement, are known, optimal tool replacement time can be found. While many researchers have focused on the latter two elements, there are very few articles explaining what penalty costs are and how they should be calculated. Therefore this article presents an approach for estimating the costs of tool failure for a one-stage machining operation.

Hazop Analysis Applied on Critical Milling Operations

Abstract Restarting of machine tools after undesired stops is a critical operation that often leads to damage of the workpiece or machine tool, and thereby causing significant costs. This paper describes how the Hazard and Operability (HAZOP) Analysis technique can be used to identify potential deviations of a restarting procedure in a milling operation. The work has shown that the HAZOP Analysis technique is a suitable tool for increasing the reliability of machining operations