Against tool breakage and machine downtime

Clamping systems with pressure gauge against tool breakage and machine downtime

Three tool breakages and longer machine downtimes within a short time caused production interruptions and costs in the manufacturing of hydraulic hammers at Atlas Copco.

Problem analysis of the service technician: The workpiece supports with grip inserts used by the customer influenced the clamping forces and led to incorrect clamping. The solution, a machine vice with pressure gauge to safely clamp the forged parts for machining, costs only a few hundred euros more.
The problems arose in spring 2011 after a change of the processing machines.

Michael Beer, equipment engineer of fixture construction at Atlas Copco

Construction Tools in Essen: “On the old machine, the components were machined from two sides, on the new machine only from one. Since the pressure came from one side only, the workpiece shifted.” The problem occurred during the machining of forged steel parts weighing up to 1.2 tons, from which the main components for Atlas Copco's hydraulic hammers are made. The largest parts are up to 900 mm long with side lengths of 490 mm.

The hydraulic hammer range, which has tools varying in length from 1,000 to 1,900 mm, consists of a total of 13 variants of the MB and HB series. Around 250 employees manufacture hydraulic attachments at the site for use in mining, quarries, demolition, restoration and other tasks in the construction industry.

Precise clamping instead of over-turning

As the forged parts have an uneven surface on delivery, this is milled off by 12 to 15 mm in several machining operations. During machining, mechanical-hydraulic HILMA Varioline VL 160 machine vices with a clamping force of five tons hold the components.

Michael Beer assumed first that the defects at the clamping system were the reason for the tool breakages. “Another recurring problem was” said Beer, “that some operators were erroneously of the opinion that the more the crank handle of the machine vice is tightened, the higher is the clamping force.” An error that led, amongst other things, to the fact that several crank handles were defective and had to be replaced.”

Michael Beer was supported by Andreas Menn of the ROEMHELD service and assembly team from Hilchenbach in his search for the cause. The fitter quickly discovered that the workpiece supports with grip inserts used by Atlas Copco were responsible for the tool breakage: Because the workpieces settled during clamping so that they were no longer held with the full clamping force. This incorrect clamping, which can occur with all machine vices with power transmission, led to expensive failures.

Reliable processes at all times

Menn proposed to equip the HILMA machine vices with pressure gauges; an option offered thanks to the mechanical-hydraulic power transmission of the clamping device. The accurate clamping force display via the pressure gauge enables the exact application of the desired clamping force, which can also be read at any time during the entire machining process. This means that too low or too high clamping forces can be easily avoided and process reliability is increased. For roughing, the workpiece is clamped with maximum force; for finishing, it can be set sensitively and precisely. With recurring orders, the desired clamping force can be precisely reproduced at any time, so that uniform conditions prevail for production of consistently high quality. If the workpiece is a housing-like part or if soft material is clamped, the pressure gauge can also be used to prevent deformation due to excessive clamping pressure.

Michael Beer was immediately convinced by the advantages described to him by the fitter. Christoph Neuhaus from the ROEMHELD sales team in Hilchenbach and Andreas Menn initially provided him with two vice slides with pressure gauges free of charge for testing purposes and assembled them.

Also, they suggested using specially coated clamping jaws whose roughened surface significantly increases the retention force, so that the workpiece could be held safely and precisely even with reduced clamping force. With this approach, higher machining forces can also be used in production.

More than two decades in use

Clamping devices from Hilchenbach have been in use at Atlas Copco for more than two decades, recalls Beer, who started an apprenticeship as a mechanical fitter at the company in 1976: “I know that HILMA products are a bit more expensive to buy, but they are better and the service is good, fast and cheap.” The clamping technology specialists from Hilchenbach in the Siegerland region, together with Stark Spannsysteme GmbH, Götzis/Austria and Römheld GmbH, Laubach, belong to the ROEHMHELD Group, one of the world's leading experts for industrial manufacturing, assembly, clamping and drive technology. The three companies are represented by joint sales and service companies in over 50 countries on all continents and employ 450 people. In 2011, they achieved cumulative sales of around 86 million euros.

The pressure gauge convinced immediately

The success of the machine vices with pressure gauges was not long in coming, as there has been no tool breakage since the workpieces were clamped with them. Michael Beer is thrilled: “If I had known beforehand that the VL 160 with pressure gauge only costs about 200 euros more and is so useful, I would have ordered all machine vices with it right away.” The retrofitting of the remaining four vices took place within a quarter of an hour during operation.

A time that the fixture builders were happy to spare. Beer: “In principle, we are not clamping differently today than we used to. I turn until I see that I have reached the desired pressure. But now the pressure gauge gives me the certainty - and not just the deceptive feeling - that I'm clamping in the right way.”

Maintenance prevents failures

The additional costs of 800 euros have already been more than paid off by a single avoided tool breakage. The service was according to Beer “as always very fast”. The advantage is that everyone involved agrees that Andreas Menn is regularly requested for maintenance by Atlas Copco. “This not only allows me to see at an early stage if and when which parts need to be replaced so that we can prevent failures,” explains Menn, “I am also quick to deal with problems and can sometimes provide first aid on the phone.” 

Affordable, fast and without obligations

So that the customer does not have to commit himself through expensive and long-term maintenance contracts, HILMA converted its offer a few years ago to a simple and inexpensive system: For a fixed price of currently 99 euros, a fitter visits the company and inspects all existing HILMA machine vices. If no further work is necessary, the amount is also the final price. If a repair is necessary, the same amount - plus possible material costs - will be charged again per vice. If desired, an employee of the customer can look over the shoulder of the fitter during maintenance and thus learn to carry out smaller tasks himself.

Sales representative Christoph Neuhaus learns from many customers that they appreciate this form of maintenance: “It is designed so that we achieve the shortest possible machine downtime. The fact that a HILMA machine vice has to be returned for maintenance and is then not available for a more extended period is one of our major exceptions.”

The mechanical-hydraulic machine vice HILMA-NC-M introduced in 2010 is one of the few models on the market that can be equipped with a pressure gauge for accurate display of the clamping force.
Precisely adjustable clamping force by means of pressure gauge.
During machining, mechanical-hydraulic machine vices with pressure gauge of the type HILMA Varioline VL 160 with a clamping force of up to five tons hold the components in place.
(from left to right) Andreas Menn, ROEMHELD service technician, Michael Beer, equipment engineer for jig and fixture construction at Atlas Copco Construction Tools, and Christoph Neuhaus, ROEMHELD sales representative from the Hilchenbach site.
The surface for the forged steel parts for the housings of the hydraulic hammers is milled by 12 to 15 mm in several machining operations until the desired quality is achieved.
Finished milled steel forgings.
Hydraulic hammers from Atlas Copco.

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