Three tool breakages and extended machine downtimes led to costly production interruptions at Atlas Copco's hydraulic hammer manufacturing facility. After analyzing the problem, a service technician identified the workpiece supports with grip inserts as the cause, influencing clamping forces and resulting in incorrect clamping. The solution: a machine vice with a pressure gauge to securely clamp the forged parts, costing only a few hundred euros more.

The issues arose in spring 2011 following a change in processing machines. Michael Beer, an equipment engineer at Atlas Copco Construction Tools in Essen, explained, “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.”

This problem affected forged steel parts weighing up to 1.2 tons, which are used to make the main components for Atlas Copco's hydraulic hammers. The largest parts measure up to 900 mm in length and 490 mm in width.

The hydraulic hammer range includes tools varying from 1,000 to 1,900 mm in length and comprises 13 variants of the MB and HB series. Around 250 employees manufacture hydraulic attachments for use in various industries, including mining, quarries, demolition, and construction.

Precise Clamping for Consistent Quality

Due to the uneven surfaces of the forged parts upon delivery, they are milled off by 12 to 15 mm in several machining operations. During this process, mechanical-hydraulic HILMA Varioline VL 160 machine vices with a clamping force of five tons hold the components. Initially, Beer suspected the clamping system was causing 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.”

Supported by Andreas Menn from the ROEMHELD service and assembly team, Beer discovered that the grip inserts used by Atlas Copco caused the workpieces to settle during clamping, reducing the clamping force and leading to tool failures.

Reliable Processes with Pressure Gauges

Menn proposed equipping the HILMA machine vices with pressure gauges, allowing accurate clamping force application and monitoring throughout the machining process. This ensures optimal clamping forces, preventing tool breakages and enhancing process reliability. For roughing, the workpiece can be clamped with maximum force; for finishing, the clamping force can be precisely adjusted. The pressure gauge also prevents deformation of soft materials by excessive clamping pressure.

Beer was immediately convinced by the benefits of the pressure gauges. Christoph Neuhaus from the ROEMHELD sales team and Menn provided two vice slides with pressure gauges for testing and suggested using specially coated clamping jaws to increase retention force. This approach enabled higher machining forces and safer, more precise workpiece holding.

Over Two Decades in Use

Hilma clamping devices have been used at Atlas Copco for over two decades. Beer, who started at the company as a mechanical fitter in 1976, recalls, “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 success of the machine vices with pressure gauges was immediate, with no tool breakages since their implementation. Michael Beer notes, “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 only took an impressive 15 minutes. “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.”

The investment of 800 euros has already proven its worth by preventing a single tool breakage, highlighting its cost-effectiveness. According to Beer, the service was “as always very fast”. With this, Atlas Copco is highly satisfied with the service provided to them by Andreas Menn. “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.”

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.”

Clamping technology specialists from Hilchenbach in the Siegerland region of Germany, Stark Spannsysteme GmbH from Austria, and Roemheld GmbH in Laubach, belong to the ROEMHELD Group. This group is one of the world’s leading experts in industrial manufacturing, assembly, clamping and drive technology. The three companies are represented by joint sales and service companies in over 50 countries throughout the globe and employ over 450 people. In 2011, they achieved cumulative sales of around 86 million euros, or 93 million USD.