The development of NEXT STEP beyond Lean Production - The link between technology and economics with focus on sustainable developments

The paper provides a brief presentation of different production philosophies and their characteristics. How the one builds upon the other, and how those characteristics considered to be positive and of strong current interest are taken advantage of by developments underway in any given period are examined. Developmental trends that are evolving (NEXT STEP) or that can serve to complement the Lean production philosophy which is dominant today, are taken up. A detailed cost model that can be used to assess different technological production development scenarios is also introduced

NEXT STEP in Cost-based Sustainable Production Development - Cases from different Production Operations

This article discusses the NEXT STEP (beyond Lean production philosophy) and its relation to Sustainable Production Development. One of the most important factors affecting long-term sustainability is the degree to which resource-efficient production can be achieved. From this standpoint, Lean Production is similar to Sustainable Production. The research reported on here suggests there to be no contradictions between having an efficient production process and this process being sustainable from a long-term perspective. Various production-cost models that can be used for evaluating different development scenarios with the aim of achieving resource efficient production in a wide variety of situations are discussed. The production cost models taken up deal with the following: 1) general losses in connection with downtimes, rejection rates and set-up times, in particular, 2) the degree of utilization of a production system 3) optimization of batch size with regard to setup times and inventory costs, 4) optimization of the manpower within a given production sector and 5) achievement of an optimum level of automation. The production cost models presented are applied to production elements of different types: machining operations, automated production lines for manufacturing sheet-metal products, and semi-manual assembly. This is done to exemplify the development steps necessary for achieving long-term sustainability in connection with different production scenarios

An integrated cost model for metal cutting operations based on engagement time and a cost breakdown approach

In all manufacturing processes, it is important to determine the costs and their distribution between different sequential processing steps. A cost equation based directly on the losses during manufacturing, such as rejection rate, stops and waste of workpiece materials, also provides a valuable aid in giving priority to various development activities and investments. The present work concerns how a cost model presented earlier for calculating part costs can be developed to describe part costs as a function of the cutting data and tool life time T selected. This enables a tool life model to be a directly integrated into the cost model by use of tool engagement time. The model presented also takes into account the part costs for scrap incurred in connection with forced tool changes. Examples are also given of how the model developed can be used in the economic evaluation of various cutting tools and workpiece materials

Effect of Cutting Conditions on Machinability of Superalloy Inconel 718 During High Speed Turning with Coated and Uncoated PCBN Tools

Inconel 718, an efficient superalloy for energy and aerospace applications, is currently machined with cemented carbide tools at low speed (vc≈60 m/min) due to its unfavorable mechanical and thermal properties. The article presents results of superalloy machinability study with uncoated and coated PCBN tools aiming on increased speed and efficiency. Aspects of tool life, tool wear and surface integrity were studied. It was found that protective function of the coating, increasing tool life up to 20%, is limited to low cutting speed range. EDX and AFM analyses suggested dominance of chemical and abrasive wear mechanisms. Residual stress analysis has shown advantageous compressive surface stresses

True equivalent chip thickness for tools with a nose radius

A majority of the established systems for choice and optimization of cutting data are based on Woxén’s equivalent chip thickness, heW. In metal cutting theory and models, the equivalent chip thickness is of vital importance when the depth-of-cut ap is in the same order or smaller than the nose radius r. Woxén made considerable simplifications in his chip area model, that form the basis for calculations of the equivalent chip thickness. Basic mathematical solutions, e.g. describing the chip area on circular inserts, are lacking. This article describes the geometrical implications when machining with round inserts. The error in Woxén’s equivalent chip thickness is largest when the depth-of-cut is less than ¼ of the nose radius. The calculations of the equivalent chip thickness based on the Woxén model are up to 50 % wrong, for some combinations of cutting data in the finishing range. The presented results explain the difficulties in getting a good validity in the models used to calculate tool life in finishing machining. The error leads to an underrating of the tool load in many machining situations

Manufacturing costs and Degree of Occupancy Based on the Principle of Characteristic Parts

In making capacity estimates and cost calculations in the manufacturing industry, many products and production systems are often involved, making the data in their totality difficult to grasp. Introducing the concept of the characteristic part, which is a fabricated part seen as representative of all parts produced in terms of demand, setup time, cycle time, average batch size and total number of batches involved, makes the calculations required much more manageable and much less time-consuming. The article takes up how the characteristic part is defined and how it can be used in calculating production capacity, system utilization and manufacturing costs

Tolerance Cost in Relation to Surface Finish during Longitudinal Turning Operations

Tolerances are an important part of production where the desire to produce quality products have to be weighed against the increased production costs. The desired tolerance will influence the choice of both production method as well as the machine used. Given that machining is an adequate production method, variation of the required surface roughness will imply a variation of the part cost which needs to be taken into account during production planning. This paper presents a method for evaluating the tolerance cost in regards to surface roughness during longitudinal turning operations, thus enabling a better comparison between different production situations

Wear mechanisms of silicon carbide-whisker-reinforced alumina (Al2O3-SiCw) cutting tools when high-speed machining aged Alloy 718

The paper is aimed at the identification and characterization of wear mechanisms of SiC whisker-reinforced alumina when turning aged Alloy 718 under different cutting conditions and when machining dry and with coolant. Secondary and backscatter electron microscopy accompanied by focus ion beam milling and EDX techniques were used for analysis of worn-out tools. Notch wear on the major cutting edge was found to consist of two notches: depth-of-cut notch and secondary notch located outside the chip area. The last was found to be governed by adhesion and attrition associated with adverse chip flow conditions. Formation of a minor notch was related to attrition by the defects found on the machined surface. Diffusion of Ni, Fe, and Cr into SiC whiskers was found to degrade them and facilitate adhesion. Chemical wear mechanisms were found to be responsible for degradation and decomposition of whiskers and formation of tribolayer on tool surfaces, which in turn was related to the reduced adhesion of Alloy 718 on the tool. Cracking on the tool rake and localized plastic deformation were found to further accelerate tool deterioration

Coldings tool life model applied on tool wear when machining the Maxthal material

Coldings tool life equation for metal cutting tools has been modified to suit the difficult to machine material Maxthal. The dominant tool wear mechanisms during machining of Maxthal are abrasive and adhesive wear and a strongly temperature dependent chemical deterioration. The combination of these three mechanisms leads to a considerable variation in tool life, even when the cutting speed has been varied in a relatively close range. Metal cutting experiments has been carried out as straight turning, were the wear level of the tool has been monitored by cutting force measurement. Sample tests have been performed with 3 different insert types. The results show that the best cutting conditions are obtained with a cermet insert. The difference in tool life and total cutting capacity between the studied insert types is ca 10%. The experimental data has been adapted to Coldings tool life model. Within the cutting data interval 25<vc<50 m/min, Coldings model can suggest a cutting speed for a total tool life of 7 minutes with an average accuracy better than 10%. For carbide inserts, maximum chip vol-ume flow is obtain for a fixed value of the equivalent chip thickness he, for a given tool life