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VIBRATORY FINISHING SPANS A MULTITUDE OF APPLICATIONS

Family-run PDJ Vibro, a leading provider of vibratory bowls, troughs, associated consumables, technical consultancy and subcontract finishing, will focus at MACH on the depth of experience and expertise it offers to customers. Now in its second generation and run by managing and technical directors David and Paul Hurley respectively, the company was established in 1983 by their father John, the current chairman.

Hurley Brothers

With an eye to succession, passing this knowledge down to David's son Tom and Paul's two sons, James and Adam, and acclimatising them to the world of manufacturing will form an important part of the event. All three third-generation family members will be in attendance during this year's show, Tom having made his MACH debut in 2014. At MACH 2018 they will be on stands H20-48 and 50

Another theme of the stands will be to communicate the advantages of eliminating hand finishing, namely reduced labour costs and scrap, less reworking and increased consistency of finish compared with processing parts by hand. Interested parties are invited to visit www.vibratoryfinishing.co.uk/cost-calculator.html to find out how much this repetitive and unpopular job is actually costing them.

Two further topics will be highlighted. One is PDJ Vibro's ability to deliver competitively priced, high quality equipment quickly ex-stock from the company’s Bletchley showroom and technical centre, together with the requisite consumables. The company also provides a machine replacement service if the customer's original choice of bowl or trough was not optimal or their requirements change.

The other area of focus will be the vast range of components that can be efficiently and safely processed using the vibratory process. Anything from rusty old chains to parts machined to extremely tight tolerances are suitable candidates for vibro finishing. As the latter may not be generally appreciated, a number of case studies will be cited where PDJ Vibro equipment is being used to automate the finishing of very high precision components, without surface damage or dimensional change.

Finishing of high precision parts

In one illustration, they will point to an application at the Poole factory of Westwind Air Bearings, where automatic deburring in a pair of PDJ Vibro bowls has successfully taken over from hand finishing of precision-machined housings. This is despite the components being CNC turned from mild steel bar to within 5 microns dimensional accuracy and Ra 0.4 micron surface roughness.

High levels of application engineering and technical support were needed to ensure that batches of up to 400 housings could be vibro-finished without compromising the fine tolerances. As a consequence, Westwind has been able to save a lot of time and money and reduce work-in-progress. In addition, uniformity of finish is better using the automated procedure.

John Bradley, senior manufacturing engineer at Westwind commented, “Overall there has been a 7.5-fold saving in labour cost and a 60 per cent reduction in lead-time by changing from hand to vibro finishing. The apparent incongruity of machining parts to within microns and then mass finishing them without damage in a vibratory bowl made us nervous, but PDJ Vibro made it work well.”

In another application, at AS9100 and NADCAP accredited subcontractor Bowmill Engineering, also coincidentally located in Poole, high precision aerospace parts machined from aluminium billet are automatically rumbled in a vibratory trough supplied by PDJ Vibro.

In the company's finishing and assembly department, machined parts are deburred carefully by hand using a variety of finishing practices. These have been augmented by vibro finishing to smooth sharp edges and improve the surface of some components, such as for Airbus landing gear. Any slight imperfection in manual deburring or marks left by polishing out cutter stepovers are now removed efficiently in the trough during a 10-minute cycle.

Component dimensions at the factory have been steadily increasing, the largest requiring rumbling now being 385 x 315 x 70 mm. To be effectively finished, a component of this size would require a very large circular bowl, so Bowmill Engineering opted for a rectangular trough. To help keep track of the high value components during finishing and to facilitate processing different sizes of part simultaneously, the machine was supplied with two partitions to provide three separate finishing compartments.

Sometimes, vibro finishing is not required to maintain dimensional accuracy but to improve surface finish, such as at marine subcontractor Mathison Engineering, Gosport. Superyacht fitting components machined from 316 stainless steel are cleaned and deburred in a PDJ Vibro bowl equipped with continuously recirculating water, automatic dosing of detergent, an acoustic cover for noise suppression and a screen to enable convenient automatic parts separation from the finishing media.

Steve Mathison said, "Compared with our existing, smaller vibratory bowl, the improvement in the standard of finish has been dramatic. Not only are components cleaner due to the continuous flow of water, but the abrasive action is more efficient as well. It results in effective edge deburring and an improved finish on the surfaces. Machining marks are no longer visible, yet components do not lose their shape as they would if aggressive linishing were to be used. Typically, our components are ready for shipping to the customer a week earlier than before."

He added that exchanging the porcelain stones in the bowl for a ceramic medium allows polished surfaces to be achieved. Mathison Engineering gains significant financial advantage this way, as any components that need an even higher cosmetic finish, requiring them to be sent out to a polishing specialist, are now quicker and less expensive for the third party to process.

A fourth example of PDJ Vibro ensuring the dimensional stability of its customers' high accuracy parts is its recommendation to use porcelain and paste for superfinishing applications, rather than the more aggressive acid-isotropic process. The company can cite two gear manufacturers successfully using porcelain and paste for superfinishing race car and superbike gears - subcontractor All Gear Services in Finchampstead and superbike racing gearbox producer, Nova Racing, Partridge Green.

In both cases, the process efficiently produces polished surfaces without removing any discernible amount of metal, protecting drawing tolerances down to ± 5 microns. Evidence of the microscopically small amount of metal removed by the porcelain medium is provided by very fine machining marks, such as a single-point turned finish on a shaft, that are still visible on the surface of the metal after superfinishing.

The benefit to race teams is reduced friction in the transmission, leading to increased speed on the track, longer service life and less maintenance. An advantage of having polished moving gearbox parts is that the time needed for running-in a gearbox is shorter.

Technical centre consultancy

At PDJ Vibro's technical centre and demonstration facility in Bletchley, visitors can see 120 new and used machines for immediate delivery, with part-exchange offered in most cases.

The company’s main, high-end vibratory bowl range has process chamber sizes from 7.5 to 6,000 litres, while three competitively priced, entry-level models have capacities of 300, 150 and 75 litres. Rectangular troughs in 13 sizes with capacities from 22 to 2,200 litres are the preferred choice for finishing larger prismatic items and those made from sheet metal.

Over 6,000 varieties of consumable including ceramic and porcelain media, superfinishing compounds, liquid detergents and chemicals are also available, 100 tonnes of which are held in stock.

PDJ Vibro’s problem solving goes further than just advice on the best choice of vibratory equipment for everything from deburring, edge breaking, radiusing, superfinishing, degreasing, rinsing and drying to pretreatment for anodising, chemical blacking or painting. Nine out of 10 people bring in sample components to be finished on a free trial basis so they can see the process in action and its effectiveness. Many parameters are taken into account, including the number of parts to be finished per batch, frequency of production, drainage and noise issues, the size of components and how vulnerable they are to impingement damage.

Another strand of PDJ Vibro’s service designed to make life easier for customers is the 24/7 subcontract vibratory finishing and polishing service in a unit adjacent to the company’s showroom. It is ideal if there is a temporary bottleneck in finishing capacity at a manufacturer, or if the firm decides that it does want to undertake on-site finishing. Component batch turnaround at the Bletchley centre is typically within 24 hours. A collection and delivery service is provided, but customers can arrange their own transportation if preferred or even wait for the parts to be ready.

Upgrades to existing vibratory equipment in the field can also get customers out of trouble if applications change. Perhaps automatic component separation is needed to boost productivity, or an acoustic cover needs to be retrofitted to meet health and safety requirements, or an increase in throughput means that a machine becomes too small and needs to be swapped for a larger model. All of these scenarios are factored into the service offered by PDJ Vibro.

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