Improving the manufacturing process quality using design of experiments: a case study

Design of experiments (DoE) is a strategy of planning, conducting, analysing and interpreting experiments so that valid conclusions can be drawn efficiently and economically. It has proved to be very effective for improving the process yield, process performance, and process variability. The paper highlights common problems and gaps in the state‐of‐the‐art in DoE. The paper also presents a case study for optimising the product life using DoE methodology. A significant improvement in the product life was observed. The results of the case study were fascinating and would encourage the engineering team within the company to apply this powerful technique in other core processes to achieve process improvement at low costs.

Infantile-onset paroxysmal dystonia: a diagnostic dilemma

A 4-year-old boy presented with a history of paroxysmal dystonic posturing since birth. Episodes were triggered by stress, fatigue, and cold. Sleep, for as short as 1 minute, resulted in complete resolution of dystonia. He was developmentally normal, with no focal neurologic deficits. Cerebrospinal fluid, homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA) were borderline low. On ictal spectroscopy, there was reduced blood flow to the right temporal region, caudate nuclei, and thalami. The typical infantile form of dystonia is benign, resolving by 2 years of age in an otherwise normal child. Our patient remains symptomatic at 4 years of age.

A new insight into the Taguchi method

To obtain high quality products at low cost and in a short time is an economical and technological challenge to today's engineering community. Design of Experiments based on the Taguchi approach is a powerful technique to attain this objective. In some processes, it is necessary to consider not only two factors but also the ratio of their levels 'as a factor.' This paper introduces a new look at the Taguchi method that makes it possible, by choosing the proper levels, to evaluate the ratio of two factors as a new factor in the same orthogonal array. An experiment to study four three-level factors was designed, and a case study is presented to illustrate the ratio of the two three-level factors as a new factor using the same L9 orthogonal array.

A practical methodology for analysing and improving the measurement system

Measurement systems are used widely in manufacturing organisations in order to make many important decisions. These decisions range from the acceptability of a given product against tolerance requirements to the level of statistical control of a process or its capability to consistently perform a given task. In most situations, however, little thought is given to the quality of the data generated by such measurement processes. By using potentially flawed data in making fundamental manufacturing decisions, organisations undermine the quality of the decision-making process itself. This paper reviews the approaches presently available from both a technical and a practical point of view, based on the priorities of process improvement practitioners. The conclusion of the paper is that the Evaluation of the Measurement Process proposed by Wheeler and Lyday offers the best balance of accuracy and utility.

Teaching fractional factorial experiments via course delegate designed experiments

Industrial experiments are fundamental in enhancing the understanding and knowledge of a process and product behavior. Designed industrial experiments assist people in understanding, investigating, and improving their processes. The purpose of a designed experiment is to understand which factors might influence the process output and then to determine those factor settings that optimize the process output. Teaching "design of experiments" using textbook examples does not fully shed light on how to identify and formulate the problem, identify factors, and determine the performance of the physical experiment. Presented here is an example of how to teach fractional factorial experiments in a course on designed experiments. Also presented is a practical, hands-on experiment that has been found to be extremely successful in instilling confidence and motivation in course delegates. The experiment provides a great stimulus to the delegates for the application of experimental design in their own work environment.

The value of partial sleep deprivation as a routine measure in pediatric electroencephalography

For more than 50 years it has been known that in patients with epilepsy, sleep markedly increases the diagnostic yield of the electroencephalogram (EEG). Sleep deprivation could have an additional activating role. Many laboratories do not use these methods routinely but reserve them for a second EEG if equivocal or negative findings are present in the initial EEG. We studied a regime of routine partial sleep deprivation without the use of hypnotic agents in 396 children younger than age 17 years who were referred for EEG with a diagnosis of epilepsy or suspected epilepsy. Sleep was achieved for the EEG in 77% (96% in the 1 month to 2 year age group, 78% in the 2 to 8 year age group, and in 64% of those more than 8 years old). In a comparison group of 72 children who had not been sleep-deprived, sleep was achieved in 44% (69% of those less than 2 years old, 27% of those between 2 and 8 years of age, and 33% of those older than 8 years). The differences were highly significant. The regime was well tolerated. Routine partial sleep deprivation is a practical and effective method of obtaining sleep and thus maximizing the information obtained from a single EEG.

Surveillance of acute flaccid paralysis in Australia, 1995-97. Australian Paediatric Surveillance Unit

OBJECTIVE

Acute flaccid paralysis (AFP) surveillance in Australia as part of the World Health Organization (WHO) certification process for polio eradication in the Western Pacific region.

METHODS

Active monthly AFP surveillance through the Australian Paediatric Surveillance Unit, from March 1995 to December 1997.

RESULTS

Based on 80 cases, the reported overall rate of AFP was 0.73 per 10(5) children < 15 years (below the expected 1 per 10(5)). The major causes of AFP were Guillain-Barré syndrome (51%) and transverse myelitis (19%). According to the WHO virological classification, there was no case of poliomyelitis, 37.5% were 'non-polio' and 62.5% cases were 'polio compatible' due to inadequate stool testing and follow-up. However, case review by an expert panel enabled 95% to be classified as 'non-polio'.

CONCLUSION

Australia must improve AFP surveillance to confirm absence of wild poliovirus. Paediatricians can help Australia meet its certification requirements and contribute to the global eradication effort by reporting and investigating all cases of AFP.

Gauge Capability Analysis: classical versus ANOVA

In order to use Statistical Process Control (SPC) efficiently and effectively in today's modern industrial environment, it is essential to analyze and determine the extent of gauge variability. The variation that occurs on a control chart is essentially a combination of product and gauge variation. Studies of measurement or gauge variation are absolutely a waste of resources unless they can lead to a substantial reduction in process variability or to an improvement in process and product quality. The goal of gauge capability analysis is an understanding and quantification of the various sources of variability present in the measurement process. The purpose of this paper is to illustrate the fundamental difference between Classical Gauge Capability Analysis (CGCA) and the use of a more powerful approach based on the Analysis of Variance (ANOVA). The author recommends that the latter approach is more useful and powerful in the presence of an interaction between the parts and the operators involved in the measurement process. An example is illustrated in the paper to demonstrate the two approaches.

Improving the process quality using statistical design of experiments: a case study

A technique known as Statistical design of experiments is a powerful technique for process characterization, optimization, and modeling. It has been widely accepted in manufacturing industry for improving product performance and reliability, process capability, and yield. This article illustrates the application of statistical design of experiments based on the Taguchi approach in a certain company that manufactures electromagnetic clutch coils. The objective of the study was to improve the quality of the existing process and thereby achieve heightened customer satisfaction for the product. An eight-trial experiment was conducted with the aim of reducing the number of rejects from the process. The expected savings per month was estimated to be over $11,500. The results of the study have provided a greater stimulus for the wider application of statistical design of experiments in other core processes within the company.

Benign intracranial hypertension in childhood: a review of 23 patients

Twenty-three patients with benign intracranial hypertension (BIH) were seen at the Royal Alexandra Hospital for Children, Sydney over an 18 year period to 1988. Age at presentation ranged from 6 months to 13 years and 5 months. The female to male ratio was 2.3:1. The aetiological factors (sometimes multiple) included: chronic middle ear infection, 30%; dural sinus thrombosis, 22%; head injury, 13%; Vitamin A overdosage, 4%; tetracycline exposure, 4%; and no apparent cause, 43%. Headache was the most common presenting symptom occurring in 91% of patients, followed by vomiting in 65% and blurred or double vision in 57%. Papilloedema occurred in 96% of patients, abducens palsy was noted in 48% and visual impairment in 45%. All patients improved clinically after treatment, one with lumbar puncture only. Of 17 patients treated with steroids, 10 patients recovered and seven patients went on to lumboperitoneal shunt. Two patients recovered with steroid and diuretic treatment. Of two patients initially treated with diuretics only, one recovered and one subsequently required a shunt. Only one patient was initially treated with a lumboperitoneal shunt. Three of the shunted patients had shunt block requiring revision. None had permanent visual loss or other significant sequelae. The visual prognosis of BIH in childhood is good. In view of the relatively high complication rate of steroids and shunting, a controlled comparison of steroid vs acetazolamide/diuretic therapy should be undertaken.

Bulbar and pseudobulbar palsy complicating therapy with high-dose cytosine arabinoside in children with leukemia

Three of 38 children given high-dose cytosine arabinoside therapy developed a previously undescribed complication. Neurological problems are a frequent occurrence in patients given this therapy, particularly cerebellar ataxia, but the development of bulbar and pseudobulbar palsy has not been reported. In two of these cases, it was sufficiently marked for the course of treatment to be curtailed and occurred at a relatively low cumulative dose of the drug. Neurotoxicity can occur at any time using high-dose cytosine therapy.

Dural tears associated with lumbar burst fractures

A retrospective review of 817 spinal fracture patients revealed a 7.7% (20 of 258) incidence of dural tears in surgically treated patients. Dural tears were most common in the lumbar burst fractures (10 of 85). Twenty-five percent of patients with lumbar spine burst fractures and a neurologic deficit had a dural tear requiring repair. Eighty-six percent of patients with lumbar burst injuries and dural tears had a neurologic deficit. An initial posterior approach with inspection of the dura and stabilization of the fracture is recommended when treating lumbar burst fractures with a neural deficit.

Non-contiguous spinal fractures

A retrospective review of 817 spinal fracture patients revealed a 6.4% (52/817) incidence of non-contiguous spine fractures. Seventy-three per cent of the non-contiguous injuries were comprised of combinations of injuries in the cervical and thoracic regions or in the thoracic and lumbar regions. Forty-five per cent of fractures were a combination of compression fractures, 40% a combination of a compression fracture and a major spine fracture (i.e., one more likely to cause a neurologic deficit), and 15% a combination of major fractures.

Chronic experimental allergic neuritis. An electrophysiological and histological study in the rabbit

Ten adult outbred New Zealand white rabbits were inoculated with a single multiportal dose of purified bovine peripheral nerve myelin and Freund's adjuvant containing 500 mg of nerve antigen. Seven animals developed chronic relapsing or progressive disease which was followed by clinical examination for 14 months. Electrophysiological studies showed marked slowing of motor conduction velocity, dispersion of the evoked muscle action potential (MAP) and reduction in amplitude of the MAP derived from distal stimulation. Histological examination of the peripheral nervous system showed at 12 months a marked hypertrophic neuropathy in the nerve roots with well developed onion bulbs, active demyelination and a moderate nerve fibre loss. It is suggested that these animals provide a reliable and predictable model for human chronic inflammatory demyelinating polyneuropathy (CIDP) which should prove valuable for therapeutic trials and studies of pathogenetic mechanisms.

Vascular access for extracorporeal therapy in the rabbit

A technique allowing short-term blood access for extracorporeal therapy in rabbits is described. The technique utilizes silicone rubber cannulae and teflon vessel tips to construct an externalized carotid-jugular arteriovenous shunt. The insertion procedure takes 1 h and extracorporeal blood flows in excess of 10 ml/min are obtainable for up to 7 days. Blood flow may still be obtained following shunt clotting by insertion of smaller diameter catheters through the arterial cannula. This technique has been successfully used for extracorporeal therapy in rabbit disease models.

A method of repair of recurrent recto-vesico-prostatic fistula following prostatectomy

A recto-vesico-prostatic fistula is a rare complication of prostatectomy. Because of its rarity the literature on the subject is scanty and an individual surgeon's experience in the field is limited. Recurrence of such fistulas are common after repair, posing a difficult problem for the surgeon. A method of repair is presented, which is a combination of procedures based on sound surgical principles. This repair also holds a promise of cure for recurrent fistulas.

Complete duplication of female urethra with vaginal atresia and supernumerary kidney

Supernumerary kidney is the rarest of renal anomalies and complete duplication of the female urethra with a single bladder is even more unusual. A case of a supernumerary kidney associated with complete urethral duplication in a female patient with vaginal atresia is reported.