Fast tooling

Rapid prototyping (RP) has become a popular and well-known technique for speeding time-to-market. The next step, rapid tooling, promises the same benefits but poses rather more problems. A development project is described. Rapid tooling is a technique that draws on both existing RP technologies and traditional engineering techniques, such as pattern making. Parts are manufactured via the intended production route and produced in the required production material. Laminated sheets are cut and assembled, then machined further to get a precise result. Problems of tooling pressure and accurate lamina assembly are considered     

Hybrid Electron Beam Powder Bed Fusion Additive Manufacturing of Ti–6Al–4V: Processing,Microstructure, and Mechanical Properties

Metallurgical and Materials Transactions A - Processing, microstructure, and mechanical properties of the hybrid electron beam powder bed fusion (E-PBF) additive manufacturing of...     

Rapid and cost-effective manufacturing of high-integrity aerospace components

This paper presents a comprehensive set of theoretical investigations and industrial applications of computer-based rapid manufacturing technology for high-integrity aerospace components. Two rapid manufacturing processes have been proposed by integrating rapid prototyping, high-speed machining (HSM), reverse engineering and geometric computation theory. They have been validated through trial manufacturing of a matrix of current aerospace components embracing critical design features to be found across the aerospace industry. Applied to future development programmes, this research will provide aerospace companies the benefits of significant decrease in product introduction lead-time, savings in non-recurring product introduction costs and considerable reduction in manufacturing costs for “one off” and low volume service parts. The findings can also be applied to rapid prototype development in other industries, such as automotive and military.     

Testing multiple variables on the growth of a mixed inoculum of Salmonella strains using gradient plates.

Six Salmonella strains were grown on two-dimensional sodium chloride-pH and temperature-pH gradient plates. Using image analysis the results were expressed in the form of three-dimensional wire frame graphs. On the temperature-pH gradient plates the optimum growth range was 20-30 degrees C and the minimum pH for visible growth was ca. pH 4, except for strain S. typhimurium CRA63 which grew over a narrower temperature and pH range. On the NaCl-pH gradient plates (whose NaCl gradient began at 2.75% (w/v) NaCl) the maximum concentration of salt at which growth was visible varied from 3.9% to 6.0%, and the minimum pH at which growth was observed varied from pH 4.7 to 5.4 according to the strain used. The incorporation of 0.02% (w/v) sodium nitrite reduced the maximum salt concentration and increased the minimum pH at which the strains could grow. The strains were combined and used in a mixed inoculum on NaCl-pH gradient plates containing 6 different concentrations of NaNO2 incubated at 6 different temperatures. Comparison of the data from the mixed inoculum with data from individual strains showed that, apart from one case, the mixed inoculum represented the extremes of the growth domains of the individual strains. The effect of NaNO2 on the ability of the strains to grow at different pH, NaCl concentrations and temperatures, was more clearly shown by subtracting the data of plates containing NaNO2 from the data of plates without NaNO2.     

Synergist effect of sucrose fatty acid esters on nisin inhibition of gram-positive bacteria

Nisin in combination with the sucrose fatty acid esters, sucrose palmitate (P-1570 and P-1670) or sucrose stearate (S-1570 and S-1670) was tested against a range of Gram-negative and Gram-positive bacteria. Initial liquid culture investigation showed that the sugar ester P-1670 resulted in a synergist enhancement of the bacteriostatic activity of nisin against Gram-positive bacteria and not Gram-negative bacteria. Some enhancement of the bactericidal activity of nisin against Listeria monocytogenes was also observed. This increased nisin inhibitory effect was confirmed on solid media using plates with gradients of pH and NaCl. Synergism was observed with all four sucrose fatty acid esters, which enhanced the antimicrobial activity of nisin against several strains of L. monocytogenes, Bacillus cereus (both cells and spores), Lactobacillus plantarum and Staphylococcus aureus. The combination of nisin and the sucrose fatty acid esters showed no inhibition of Gram-negative bacteria (Salmonella enteritidis, Salm. typhimurium and Pseudomonas aeruginosa).     

Procedures for assessing thaumasite sulfate attack and adjacent ground conditions at buried concrete structures

In 1998 Halcrow were appointed by the Highways Agency to investigate the thaumasite form of sulfate attack at the buried concrete foundations of structures on major highways in Gloucestershire, UK. Detailed investigations were completed at 28 structures and the results used to apply a risk assessment procedure to a further ninety structures. Standard procedures for sampling, testing and classifying soil, groundwater and concrete were devised to ensure that rigorous statistical analyses of the data could be applied. The procedures were also designed to meet the then current UK guidance notes, BRE. Digest 363 [Building Research Establishment, Sulphate and acid resistance of concrete in the ground, BRE Digest 363, CRC Press, Boca Raton, 1996] and the Thaumasite Expert Group Report [Thaumasite Expert Group, The thaumasite form of sulfate attack: Risks, diagnosis, remedial works and guidance on new construction, DETR, 1999] and are compatible with the subsequent BRE Special Digest 1 [Building Research Establishment. Concrete in aggressive ground, Part 1: assessing the aggressive chemical environment, BRE Special Digest 1, CRC, Boca Raton, 2001]. Recommendations are made for applying many of the procedures that have been developed to future site investigations to enable consistency, compatibility and easier data transfer for future research on the thaumasite form of sulfate attack.     

High speed tooling

Creating tooling for a new product can be a long and expensive process. The authors explore the use of rapid prototyping technology for producing metal tools     

On Optimization of Surface Roughness of Selective Laser Melted Stainless Steel Parts: A Statistical Study

In this work, the effects of re-melting parameters for postprocessing the surface texture of Additively Manufactured parts using a statistical approach are investigated. This paper focuses on improving the final surface texture of stainless steel (316L) parts, built using a Renishaw SLM 125 machine. This machine employs a fiber laser to fuse fine powder on a layer-by-layer basis to generate three-dimensional parts. The samples were produced using varying angles of inclination in order to generate range of surface roughness between 8 and 20 µm. Laser re-melting (LR) as post-processing was performed in order to investigate surface roughness through optimization of parameters. The re-melting process was carried out using a custom-made hybrid laser re-cladding machine, which uses a 200 W fiber laser. Optimized processing parameters were based on statistical analysis within a Design of Experiment framework, from which a model was then constructed. The results indicate that the best obtainable final surface roughness is about 1.4 µm ± 10%. This figure was obtained when laser power of about 180 W was used, to give energy density between 2200 and 2700 J/cm² for the re-melting process. Overall, the obtained results indicate LR as a post-build process has the capacity to improve surface finishing of SLM components up to 80%, compared with the initial manufactured surface.     

Evidence from the highways agency thaumasite investigation in Gloucestershire to support or contradict postulated mechanisms of thaumasite formation (TF) and thaumasite sulfate attack (TSA)

In March 1998 the thaumasite form of sulfate attack (TSA) was identified in the reinforced concrete foundations of Tredington Ashchurch Road Bridge on the M5 Motorway in Gloucestershire, UK and the UK Government’s Highways Agency appointed Halcrow to investigate the problem. A total of 28 structures were selected for investigation to encompass sites where bridge works were planned and structures were assessed to be at greatest risk as well as to provide a representative sample of sites and structure types.

Desk study work and peer reviews were continued throughout the project to establish protocols for the site work and facilitate the interpretation of the data. The latter included a dual approach of a systematic examination of the data collected to identify trends coupled with a review of postulated mechanisms for the formation of thaumasite from the desk study work against the data from the investigation. This paper summarises the findings of this review, which examines in detail four proposed stages in the development of TSA.     

A summary of the Highways Agency Thaumasite Investigation in Gloucestershire: the scope of work and main findings

A summary of the scope of work, the interpretation approach and some of the main findings of the Thaumasite Investigation carried out on behalf of the Highways Agency on the trunk roads in Gloucestershire is given. The reinforced concrete structures investigated were approximately 30 years old and had been cast in situ using predominantly Grade C35-C40 concrete made using Portland cement with limestone coarse aggregates.

All of the backfill surrounding the buried concrete at each structure predominantly comprises reworked Lower Lias Clay, occasionally mixed with some alluvium. There was found to be an decrease in pyrite content and an increase in acid-soluble sulfate as the Lower Lias Clay weathered. The amount of pyrite lost in the Made Ground was generally found to be in the range 50–75%. There was no evidence of acidic ground conditions at the time of the investigations. No significant relationships were found between chemical, mineralogical or physical soil parameters and distance from concrete or degree of thaumasite attack.

Groundwater characterisation by means of Piper plots indicated that the groundwater in the Made Ground classifies as a sulfate-type and in the Lower Lias Clay as a sulfate/chloride-type. Sulfate levels in the groundwater extracted from the backfill showed a good correlation with the amount of TSA at a structure.

The extent of thaumasite attack was found to be strongly related to groundwater level. Where there was no attack, the concrete was usually above the maximum water level (i.e. permanently dry, except for percolating water) and where there was full attack, the concrete was usually below the minimum water level (i.e. permanently wet). It was found that the process of thaumasite formation leading to TSA creates four zones within structural quality concrete with a sharp reaction front. In the most severe cases of attack, the surface had a white pulpy appearance and often there was expansion. The typical pattern of attack to the buried vertical members was: no attack within 1 m of ground level; local patches of softening or blistering at mid-height; increasingly severe and more widespread attack towards the base. The maximum depth of softening was found to be approximately 45 mm and the maximum amount of expansion of the face of the concrete was 33 mm.

Bituminous coatings appeared to have provided partial protection to some structures.