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MACH Exhibition 2016 Preview Information
Hall 5, Stand 5601

Problem-solving approach to vibratory finishing

While the humble rumbler is often consigned to a dark corner in a factory and is one of the least likely machines to be replaced until it collapses, there is much more to vibratory finishing than meets the eye, as PDJ Vibro will explain to visitors attending MACH this year.

The company will use its presence to explain the many different aspects a manufacturer should take into account if it is considering automating the finishing function. A customer might be investing for health and safety reasons or to improve consistency of finish. Alternatively, if it already uses a vibratory bowl or trough, the firm may have started manufacturing different types of component and needs alternative vibro finishing equipment to process them.

A family owned and run company, PDJ Vibro has accumulated an extensive database of vibratory and centrifugal finishing solutions that it is able to share with existing and prospective customers. Its directors have 100 years of experience between them in the industry and offer a consultancy service that is unrivalled in the business. It covers everything from deburring, edge breaking, radiusing, superfinishing, degreasing, rinsing and drying to pretreatment for anodising, chemical blacking or painting.

Finishing of sheet metal components

Deburring and edge breaking of solid metal components that have been turned or prismatically machined is by far the most common type of application for vibro finishing machines in use around the country. Few problems arise, provided that the correct machine capacity is selected to suit the sizes of component to be processed and appropriate abrasive media and perhaps additives are used.

Finishing of sheet metal components is more complicated, however, and here PDJ Vibro can call on practical advice from numerous customers that can help other manufacturers thinking of going down the vibratory finishing route.

Take, for example, Braintree subcontractor J Reeves Engineering, which specialises in machining and fabricating components and assemblies from sheet metal and tube. The company is a long-time user of PDJ Vibro abrasive finishing and maize drying bowls for processing sawn and machined sheet metal and tubular parts.

A bowl does not handle some sheet metal parts well, however. If they are too long, they cannot follow the toroidal path of the abrasive medium or at least the efficiency of the finishing action is inhibited. Parts that are too small, on the other hand, tend to stick in the sides of the mechanism that automatically separates components after processing.

The solution suggested by PDJ Vibro was a rectangular trough in which the vibrations cause the ceramic abrasive media to tumble linearly across the width of the machine. It means that batches of sheet metal components measuring up to the internal length of the trough can successfully be finished automatically, benefiting from consistency of finish and elimination of labour cost.

In sheet metal processing companies that use laser profilers rather than waterjet or punch presses to cut out the parts, a heat-affected zone (HAZ) can occur around component edges. When automatically finishing these parts in a vibratory bowl or trough, the rumbling action has the added effect of stress-relieving the case hardening around the component edges.

One sheet metal subcontractor that exploits this technique is Rotherham-based ESP Laser Cutting, which part-exchanged its decade-old PDJ Vibro vibratory bowl in January 2016 for a new model. The company says that the HAZ on sheet metal edges caused by a high temperature laser beam is problematic for several reasons.

First, it can complicate fabrication by distorting the weld. Second, it prematurely wears milling cutters and drills if the parts are being machined around the outside. Additionally, paint and other coatings such as zinc tend to flake away, necessitating costly rework. All of these problems are resolved if parts are processed in a vibratory bowl.

Vibratory finishing of 3D printed parts

Suppose that a firm specialising in metalcutting decides to add the flexibility of an additive manufacturing (AM) machine to produce complex metal or plastic components. PDJ Vibro can explain the multiple considerations when finishing such components and where the dangers lie by calling on the experience of customers like 3D printing bureaux Ogle Models and 3T RPD.

Among the important things to remember is that the ceramic abrasive should be of a size and shape that will fall away from the smallest, most confined spaces within 3D printed components, otherwise the stones can become lodged. For finishing external surfaces only, larger media should be selected to ensure that none becomes embedded inside the component.

Due to the abrasive nature of vibro finishing, sharp edges are rounded slightly and this must be taken into account. Parts with thin edge detail should not be finished in this way, as they are delaminated and a burr is created. Similarly, large sections of mesh are unlikely to survive vibratory finishing.

Flat surfaces and areas of gradual curvature are smoothed well in PDJ Vibro bowls, hiding the stepped appearance that results from the layer-by-layer build process and creating a satin-like finish. Plastic parts become more flexible after vibratory finishing, as they absorb water from the bowl, replacing some of the material’s natural moisture that is lost during laser sintering at around 180°C.

Lead-time in preparing the surfaces of 3D printed items for subsequent painting is reduced by one-third using vibro processing compared with hand finishing with abrasive cloth, allowing jobs to be turned around faster. More importantly, experienced operatives are free to carry out other skilled work, improving customer service by taking both cost and time out of the process.

Technical centre consultancy

Technical center

PDJ Vibro’s problem solving goes further than advice on the optimal choice of vibratory finishing and polishing equipment. At its technical centre and demonstration facility in Bletchley, visitors can see 120 new and used machines for ex-stock delivery, with part-exchange offered in most cases. Over 6,000 varieties of consumable including ceramic and porcelain media, superfinishing compounds, liquid detergents and chemicals are available, 70 tonnes of which are held in stock.

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 the resulting effectiveness. This offer will naturally be open to visitors to the company’s stand at MACH. 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.

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.

Low-cost vibratory bowls

To complement its high-end vibratory finishing and polishing bowls, a range of three competitively priced models with process chamber capacities of 300, 150 and 75 litres were unveiled by PDJ Vibro at MACH 2014. They will feature prominently at this year’s show, as these economy models have taken a large slice of the market for low volume, intermittent finishing applications and as an alternative to buying a pre-owned vibratory bowl. They therefore now form an important part of the company’s product portfolio.

The economy models are built to a high specification with a durable, stress relieved bowl and cast polyurethane lining, driven by a heavy-duty, three-phase electric motor. Although normally supplied without additional equipment, a comprehensive range of options is available including PLC control of additive dosing, water metering and recirculation, as well as effluent control, automatic parts separation from the media and acoustic suppression.

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