Bristol-based Nerc Precision Engineering (NPE) Ltd has been on a rapid growth trajectory since its inception in May 2018, marking the fourth anniversary of its founding with the recent installation of a DMG Mori CMX600V machining centre. Investing in prestige technology is a philosophy of this small business, as highlighted by its newly formed partnership with cutting fluid specialist ITW Rocol.

Commenting upon the growth of the business, managing director Konrad Nerc says: “When my wife and I started the business, we aimed to invest in the best technology to ensure that we could deliver the highest quality components and service with lead times and pricing that would be the industry benchmark. As a small and agile manufacturer with innovative technology investments that include five-axis machining, our philosophy and customer service is enabling us to evolve rapidly.”

In the past two years, the subcontract manufacturer has invested in a DMG Mori DMU50 five-axis and a CMX600V three-axis machining centre that are supported by zero-point clamping from Lang, cutting tools from Ceratizit, Hoffmann and Tungaloy and, of course, cutting fluid from ITW Rocol. Producing everything from one-offs and prototypes to batch production, the ISO9001-accredited subcontract manufacturer typically serves customers in the defence, offshore, automotive and general subcontract sectors, with the aerospace industry rapidly emerging as its most prominent market.

Like any fledgling business, finding the best quality products and services is a learning curve, and this has certainly been the case for the company located near Bristol airport when considering its cutting fluids.

“Our initial cutting fluid supplier was a well-known name in the industry, but the quality of the fluid was quite poor,” says Nerc. “The fluid consumption was high, the coolant left a lot of residue on our components, we suffered from tramp oil and foaming, and the staff suffered with skin irritation. We soon moved to a very high-end brand of cutting oil. This premium brand eliminated tramp oil, foaming and skin irritation for staff, while the consumption was also reduced and it improved tool life and surface finishes. However, we found the poor service unacceptable, especially considering the increased cost for a barrel of oil. We eventually moved to a third vendor with a brand equally well recognised as a premium product. Although the quality of fluid, performance and cost were relatively similar to the second supplier – once again, it was the service and support that was lacking.”

This trial and error process led Nerc to cast a hopeful query on LinkedIn for advice and support. It was here that ITW Rocol answered the call for help.

“ITW Rocol came to investigate our cutting fluid requirements,” says Nerc. “Following an initial consultation, we trialled three different Rocol fluids. Testing more than one product was due to the diversity of the materials we were cutting, the varying operations and machining parameters, and some of the products being new to market for Rocol. Rocol emptied and cleaned the sump of a machine, and we tried our first fluid, and the results were impressive. The quality of the fluid was excellent, and the support has been second to none.”

Since the trial commenced last year, Nerc has won a series of new customers and sizeable orders in the aerospace industry, with work in this sector now accounting for 95% of turnover. This has seen the materials machined narrow from stainless steel, steel, copper, brass and a multitude of ferrous and non-ferrous metals, to primarily aluminium and aerospace-grade alloys. With this evolution, ITW Rocol identified its TRI-Logic cutting fluid as the most suitable solution. TRI-Logic is a range of maximum-life, extreme-pressure cutting fluids which demonstrate inherent stability and cutting performance that improves surface finish and tool life while reducing foaming and odours. Furthermore, as a fluid formulated from a proprietary blend of specially selected additives that maximise sump life, TRI-Logic also offers high corrosion protection.

To undertake the trial, ITW Rocol supplied a 55-litre barrel of its TRI-Logic to Nerc. This barrel was utilised in the initial trial that required the emptying and cleaning of one machine sump to demonstrate the difference between Rocol and its fellow ‘premium-brand’ rivals. With the results rapidly becoming evident, the remainder of the barrel was used to continually ‘top-up’ the fluid of the remaining three machines to limit disruption to production while maximising results for Nerc.

From a results perspective, fluid life has improved drastically and oil consumption has reduced by over 50%. Logic would tell any engineer that a 50% consumption reduction would naturally reduce the fluid costs by 50%, yielding a huge saving. However, the ITW Rocol TRI-Logic EP has a retail cost 50% less than its rival premium brands. With a 50% reduction in the purchase price and a 50% fluid consumption reduction, the savings are even higher.

“The 50% cost reduction is something that every small business wants to take advantage of, but when the consumption also reduces by 50%, the cost of coolant stops being a concern,” says Nerc. “Our initial 55-litre barrel lasted from July to February and we’ve recently taken delivery of a 200-litre drum of TRI-Logic. Our initial projections were that Rocol’s TRI-Logic would provide a cutting fluid consumption reduction of 25%. However, with the new aerospace work, we’re running four machining centres up to 16 hours a day and we are busier than ever before. Running at optimal production rates, we’re recognising that our cutting fluid consumption is at least 50% less.”

The performance of the two previous premium brands far exceeded that of the first brand used by Nerc in terms of extended tool life, sump life, improved surface finishes, and reductions in foaming, tramp oil, oil residue on parts, and skin irritation. The ITW Rocol TRI-Logic has matched and even exceeded the performance of its rival brands in all areas.

The 200-litre barrel of ITW Rocol’s TRI-Logic cutting fluid has been supplied with an automatic fluid mixer that accurately mixes and dispenses the correct dilution of cutting fluid and water. With a built-in double-check valve and vacuum breaker that is WRAS approved, the system meets the most stringent of safety requirements for category 3 fluids and ISO EN 1717 regulations.

“For our business, specifying cutting fluid has been the hardest thing to get right and find an improvement,” states Nerc. “Unlike capital and ancillary equipment, the challenges with cutting fluid can be the most difficult aspect of the business to optimise. The challenge of trialling new coolants has several implications. For example, emptying and cleaning machines to trial fluids can be time-consuming with machine downtime – and then there is the concern that the new fluid may not improve your productivity, fluid life and tool life; or it may not be compatible with the materials machined. There’s also concern over tramp oil, foaming, residue on components, skin irritation, disposal and much more. Thankfully, Rocol resolved all of this, and the results have been fantastic.”

With service and support from all three of its previous cutting fluid vendors being an issue for the company, Nerc concludes: “The service and support from Rocol is second to none. They reviewed our business, listened to our concerns and then provided a solution that has exceeded everything else that went before. Most importantly, a Rocol engineer is always on call to check our machines and support us accordingly.”

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Glasgow-based Castle Precision Engineering has been an advocate for the use of VERICUT CNC simulation software from CGTech on its shop floor for many years, protecting high-value customer components, as well as its own advanced machine tools. More recently, the company has embraced the efficiency and productivity gains offered by the Force software module.

While Castle supports a number of advanced sectors, such as medical devices and power generation, the majority – around 90% – of its circa £20m annual turnover comes from the aerospace and defence industries. To cater to the diverse needs of its customer base there are three focused sub-divisions that encompass what the business has to offer: Rotatives, Prismatics and Toolroom.

Roy Yuile, manufacturing engineering manager at Castle, explains: “Rotatives and Prismatics are the two core areas of our production business, and both require extremely high levels of precision and machining expertise. Over the years, we’ve carved out a niche for ourselves in manufacturing critical rotating parts for the aero engine market. The failure of these parts can bring an aeroplane out of the sky, so our OEM customers are not only trusting us with their reputations, but also with the safety of the pilots and passengers whose flights they power. We also manufacture a wide range of complex prismatic products to very exacting tolerances for applications such as defence optronics and hydraulic actuation systems for control surfaces and landing gear.”

The company typically machines prismatic parts from relatively straightforward materials, primarily aluminium alloys along with some steel and titanium. However, rotating aero engine components usually involve more exotic and difficult-to-machine materials, including titanium and nickel-based super alloys, where forgings valued up to $100,000 for a single workpiece are not uncommon.

With a population of around 60 CNC machine tools representing the very latest multi-axis manufacturing technology from DMG Mori, Makino, Doosan and Grob, the shop floor at Castle Precision is a lesson in housekeeping and efficient organisation for all to see. Protecting this advanced manufacturing capability is VERICUT CNC simulation software.

Roy Yuile says: “CAD is at the front end of our engineering workflow. We’ll either import a 3D model supplied by the customer or draw one up from a 2D definition, and break this down into the various stages of manufacture from material supply to finished part. These stage models and their accompanying fixtures or work-holding devices are transferred to CAM, where we’ll build tools, generate tool paths, post NC code and then port the whole job straight into VERICUT using their CAM interface.”

He continues: “VERICUT has been an established part of our workflow for well over a decade. Nothing goes out to a machine without first going through VERICUT. It’s an essential safely net, not just for the product but for our machines and our personnel. We’ll have some programs in our factory that have been around for 10 or 20 years, alongside jobs that are fresh out of CAM. VERICUT simulates any new or modified code before it goes out to a machine. We have a digital twin for almost every machine tool, and because VERICUT reads the same G-code as the machine controller, it’s completely CAM-agnostic and can simulate code from any source.”

Very often, VERICUT drives process improvements because the software offers the opportunity to prove edits in a virtual environment.

“We don’t edit at the machine console because of the risk involved,” says Yuile. “If you mess up you have no safety net. Instead, our engineers will bring the code back into VERICUT, make their edits and then hit simulate to check that the program is safe to release. Smashing pixels is a whole lot cheaper and safer than writing off a machine tool, so verifying code using a digital twin before we actually put anyone or anything at risk is an integral part of our workflow. This risk-based approach is absolutely crucial, not just in aerospace and defence, but for any high-value product and business.”

With VERICUT an established part of Castle’s business for the past 12 years, the software has proven its ability to protect the company, along with being a key improvement tool for its manufacturing processes.

Yuile states: “VERICUT Force is a step further along this curve. Moving beyond goalkeeper functionality, Force allows us to start optimising our processes, as well as proving that they are safe.”

Every manufacturing business faces the same three challenges from its customers: quality, delivery and cost.

“Generally, quality and delivery are a given, and cost is where we win or lose,” Yuile says. “The pressure within the aerospace industry on cost is enormous and, for us to be competitive against global competition, we have to be smarter, faster and more efficient. Physics-based optimisation software has been on our radar for a while, and we started looking at it seriously a couple of years ago.

“There are a few key players in that market and we evaluated them all,” he adds. “There’s a lot of clever maths behind it, but the basic idea of physics-based optimisation is to analyse a toolpath line by line, calculate the forces acting on the cutting tool at any given point in time and then adjust the feed rate in order to balance or control that force and chip load. This means there’s a lot of number crunching involved, but before you even get there you need to build an accurate digital model of the machining process. Since we already simulate every job in VERICUT, the major advantage of VERICUT Force is that building this model takes almost no additional effort – all Force needs is a bit more information on tool geometry and material characteristics, everything else is already there. The cycle time savings you can expect to get from this kind of optimisation are typically 10-20% and VERICUT offered an almost ‘plug and play’ solution for both milling and turning that was really attractive.”

Force has been in use at Castle for about a year, and Yuile is keen to highlight one of the often-overlooked benefits: consumables spend.

“Carbide cutting tools are a major expenditure for us,” he states. “When we’re costing a job, the two key variables are how long it’s going to take and how much we’re going to consume in carbide. Any reduction in cycle time that Force can deliver is good, but so is any improvement in tool life. Although cycle time is a monetary saving in the sense that you free up machine capacity that which you can sell to somebody else, consumables are a direct cash spend. If it takes £100 of carbide to make a particular part and we can reduce that to £80, we are literally not spending £20. That £20 stays in our bank account. Cycle time savings are soft money, they’re potential revenue, while consumables spend is hard money, it’s cash.”

Concludes Yuile: “We trust VERICUT, and that trust comes from experience. When manufacturing high-value components for critical applications, we need to have confidence that we’re using the very best tools for the job, and VERICUT delivers.”

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For almost 50 years Southend-based Rega Research has, to the point of “obsession”, used engineering as the basis for the design and manufacture of its home audio systems. Employing engineering to produce the best music for its customers, while maintaining a high level of reliability and affordability and, wherever possible, a strong UK-supplier base, has led to innovative designs that are both aesthetically pleasing and produce the highest sound quality. This combination has created a loyal customer base, with the past two years seeing significant sales growth, which resulted in its latest investment in an XYZ 750 LR vertical machining centre.

Rega Research is owned by company founder Roy Gandy, who struggled to find an audio system that met his expectations. He was advised, possibly by a frustrated audio dealer, to “build his own” if he could not find what he wanted. The rest, as they say, is history.

Using engineering skills gained in the automotive sector Gandy reviewed what was available, and even the best turntables at the time were said to “offend his sensibilities”, so the quest to re-engineer and create new concepts in audio began. The company now designs and assembles a full range of home audio equipment, including turntables, amplifiers, phono stages, CD players, tonearms, cartridges and speakers. Production stands at over 5000 turntables every month made up of 3000 units a month of its entry-level P1 turntable, over 1000 a month of its mid-range P3 turntable and even 70 units a month of its range-topping P10 turntable, which retails at around £5000. Add these to its other products and production tops 10,000 units every month. The company assembles all products in-house, with components sourced mainly in the UK.

There is a subtle difference between music lovers and hi-fi enthusiasts and Rega’s products appeal to the former: “Our customers love music – many would go to concerts daily if possible – so we strive to deliver a level of quality that can replicate that experience for them,” says Ky Gandy, supplier co-ordinator at Rega Research.

The blend of high quality, design and value for money has seen Rega grow from 130 employees at the start of 2020, with a turnover of £13m, to a £20m turnover and 180 employees at the end of 2021.

“The lockdown arrived and, while the first few weeks impacted on operations, it also had a positive effect,” says Ky Gandy. “Sales boomed due in part to people being stuck at home, many with more disposable income.”

This significant growth added pressure to Rega’s tool room, which was populated with manual machines to produce assembly jigs and test rigs, as well as some prototype machining. A move to CNC had been on the cards for many years, but had been put off for several reasons, particularly lack of space. A re-organisation combined with increased workload finally allowed the purchase of an XYZ 750 LR vertical machining centre to go ahead. The machine will be used on a variety of materials from aluminium and high-pressure laminate through to MDF, so Rega opted for the 12,000 rpm model and, for added versatility, the 4th axis and 24-position arm-type tool-changer options. Notably, the XYZ 750 LR features linear rail technology.

“We had been looking at introducing CNC to our tool room for several years,” says Ky Gandy. “We did our research, as we do with all our suppliers, and while the machine was important, ongoing support and service was a priority. This resulted in a shortlist of one: XYZ Machine Tools. During our search we kept coming back to XYZ and, in the end, it became a straightforward choice due to the confidence we had in their ability to support us with technical and aftersales help.

“We also received glowing reviews from our existing component suppliers,” he adds. “Another factor that made the decision easier was that during the quotation process they didn’t try to upsell. We indicated an interest in their HD machines, but they did the right thing and sold us the machine we needed, not what we thought we wanted.”

The aftersales service was immediately put to the test for the delivery of the machine, which due to limited access had to be stripped back to its carcass and re-assembled in-situ, a process that took just four days from unloading to powering up and running.

Throughout the pandemic, focus was on delivering audio systems to meet demand, so product releases were put on hold. Now, with a degree of normality returning, new products are on the horizon with new turntables and amplifiers ready for launch this year.

As a result, Rega Research will see an increased workload for the XYZ 750 LR in terms of machining development parts, as well as the testing fixtures required. Having the machine will enable Rega to respond quickly to change, and meet increased demand for fixtures from its assembly department.

There are no plans for the XYZ 750 LR at Rega to be used for production work, but it is filling a need for reworking existing stock components that may need rectifying or adjusting. A recent example was a batch of plinths that were out of concentricity tolerance on two bores.

“The obvious solution was to return the entire batch to our supplier, but that isn’t the Rega way of doing things,” says Ky Gandy. “We respect our suppliers and accept that occasionally errors arise, so we took the decision to rectify the parts ourselves. We used the XYZ 750 LR to manufacture a fixture, which it was then able to use for reworking the parts to within microns, something that saved time and money thanks to the efficiency of the machine.”

For the past 50 years Rega Research has stuck to its belief that applying the best engineering processes not only creates value for money, but the highest sound quality.

“There’s an assumption that to be high-end, and made in the UK, it has to be expensive, but through application of engineering disciplines we’re able to deliver what our customers want: a product that generates high-quality music in a cost-effective and an aesthetically pleasing way,” concludes Ky Gandy. “This isn’t always easy, as developing parts to meet our founder’s guiding principles can sometimes take two years, and they may not be the easiest components to manufacture. One example is our one-piece tonearms, which require detailed tooling for die casting. However, the result gives high stiffness and reduces their weight down to 34 g, enhancing their performance. Working with our suppliers there is always an engineering solution to be found.”

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Manufacturing gear wheels in 34 seconds

Minimising production times to ensure competitiveness is one of the most important challenges in the automotive industry, a factor recognised by Henry Ford over a century ago. After decades of optimisation, it is difficult to reduce machining times further while maintaining the same level of quality. Nevertheless, Volkswagen (VW), near the German town of Kassel, has managed to achieve this in its gearbox production facility using Kapp Niles gear grinding machines available in the UK from the Engineering Technology Group (ETG).

The Volkswagen plant in Baunatal is one of the group’s larger German locations with a workforce of about 17,000. Production here focuses mainly on car gearboxes in 10 different series. Half of the manufacturing lines feature gear production centres from Kapp Niles.

Kapp Niles machines also find use in the production of the DL382 dual-clutch gearbox for Audi. A total of 16 gearings are required to shift the seven gears within this type of gearbox – 10 ground and six honed. The production unit runs 24 hours a day, 5 to 6 days per week, depending on demand. VW strives to achieve an EPEI (every part every interval) value of 1 day in the production unit, which means that all components can be produced on each day for the aforementioned gearbox. This type of streamlined production requires seamless processes and a high degree of flexibility.

Technical clerk Christian Hahn is in charge of the production process of the DL382 dual-clutch gearbox: “We have five gearing centres from Kapp Niles in the wheel production unit and two more in the shaft production unit. To achieve an EPEI value of 1 day, we change over the machine in the wheel production unit twice every 24 hours. This way, we can produce 10 different wheels per day.”

The challenge with flexible production is the short cycle times. With an output of 880 gearboxes per day, one machine in wheel production must produce 1760 parts per day. Including all set-up times and failures, this yields a line cycle time of 34 seconds. An average line cycle time is 39 to 40 seconds.

Bernd Kümpel, application technician at Kapp Niles, analyses these figures: “Saving 5 to 6 seconds per cycle does not sound like a lot at first, but together it can be a 15% reduction. If I consider that at least 40% of segments cannot be influenced, I have to reduce the actual process time by 30 to 40%. Seen in this way, 34 seconds is a real challenge.”

A total of seven Kapp Niles machines are deployed which, with their low space requirement, are suited to the highly automated production lines at Volkswagen. The machines include three KX 100 Dynamic, two KX 260 Twin in wheel production and two KX 160 Twin in shaft production.

Hahn and Kümpel agreed from the very beginning that the desired cycle time could only be achieved with a combination of several measures. To minimise the daily set-up effort, Hahn makes sure that the wheels which are to be produced on one machine have bore holes of the same size. Thus, he has to change over the machine, but not the clamping tools. The remaining set-up time is minimised by the intelligent set-up concept of the KX 100 Dynamic. For one machine, he needs just 20 to 25 minutes.

“The semi-automatic set-up makes the KX 100 Dynamic extremely user-friendly,” says Kümpel, describing the process. “All you need is an Allen key for the entire set-up operation. With it, you operate the hydro-expansion clamping chuck of the dresser roll. Everything else is connected without any screws via HSK interfaces.”

An additional visual aid is available in the form of a menu guide and an easy-to-understand cycle on the machine controller. By completing the step-by-step process and the acknowledgement screen, the operator ensures that no work steps are executed incorrectly or forgotten. It thus becomes possible to prevent high-cost failures. The tools are dressed using full profile rolls, allowing all threads of the cylindrical worm to be approached and moulded simultaneously. Thus, with a five-pass full profile roll, the dressing time can be reduced by more than half without compromising on quality.

The integrated measurement system is another important time-saver. Hahn explains the advantage: “After each changeover, quality measurement has to be made outside the machine. We continue to require this, but I can already check the basic, quality-related parameters with the integrated measurement sensor in the machine itself. It saves a lot of time since we can start production before the results of the external measurement are available.”

The integrated measurement system of the Kapp Niles machines thus accelerates the restart process considerably. Furthermore, the external measurement merely checks more teeth and generates the measurement report to monitor the gear.

The search for optimisation potential also includes the actual grinding process. Cubitron II machine tools by 3M show a highly promising approach with geometrically-specific, triangular-shaped cutter heads, compared with conventionally dressable grinding wheels.

“With these, you can step it up a notch, to say it plainly,” states Hahn. “That is, remove more material in one thread, and remove it faster.”

For this purpose, Kapp Niles provided relevant preparatory work with a large number of grinding tests in-house to use the benefits of this machine tool on the DL382 components.

Says Kümpel: “With CII you can remove a considerable amount of material without any thermal damage to the component. This way, we reduce time consumption by a solid 30% compared with other grinders, depending on the component.”

Production is characterised by a belt chaining (or linkage) that goes through the entire production hall. Among the employees, it has gained the nickname ‘the highway’. The available space is limited, hence the compact KX 100 Dynamic machines are the preferred choice. This machine type has two separate rotatable mounted columns, each with vertically movable pick-up axes featuring one workpiece spindle. While a workpiece is being machined, the other pick-up axis places the machined workpiece and loads a non-machined part on to the workpiece spindle. The workpiece is aligned outside the work area. This allows the workpiece spindle, already accelerated to machining speed, to be swivelled in the work area, keeping non-production times to a minimum.

A transfer unit does the loading and unloading from the conveyor belt. Kümpel says: “We usually move with the belt directly below the machine. However, this was not possible here. With the transfer unit, we compensate for height and distance from the belt to the machine. An integrated automation solution would have been significantly more expensive, at about 25% of the price of the machine. A simple transfer unit costs less than 10% of the machine price.”

The time for conversions and commissioning is, in most cases, very limited. But the highly ambitious goals have been achieved.
“Throughout the process, I‘ve been very satisfied with the on-site support and the local service,” says Hahn. “We were convinced by the machine concept and managed to overcome any obstacles together. The cycle time was a critical aspect. But, we did it.”

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To ensure the optimal function of artificial hips in a patient’s body, certain surface areas on the hip stem must have different finishes. For example, the neck area of the stems requires a very smooth, polished surface. Recently, a manufacturer of precision components replaced a combined manual grinding/electropolishing operation with a fully automated two-stage mass finishing process. The Rösler R 4/700 SF drag finisher allows the simultaneous, precise finishing of 12 hip stems in one operation. This performance resulted not only in significant cost savings and lower cycle times, but in drastically improved quality and absolutely consistent finishing outcomes.

For 20 years, MBN Präzisionstechnik GmbH, located in the Austrian town of Pottendorf, has been specialising in the manufacture of machined precision components and assemblies. The company’s main focus is on the production of orthopaedic implants and surgical instruments made from titanium and stainless steel. MBN Präzisionstechnik, certified to DIN 13485, is not only equipped with ultra-modern machinery, including laser marking systems, but also has clean rooms for the coating and germ-free packaging of its products.

A particular challenge is the finishing of targeted surface areas on different hip stems. The company’s production is to a large extent automated and allows tracing the entire manufacturing chain, from raw material to finished product. Until recently, polishing of the neck area of the hip stems took place by a manual pre- and fine-grinding step, followed by an electropolishing process. This surface refinement operation was time-consuming, required a lot of manpower and was very costly. In addition, it was less than perfect with regard to consistency of the finishing results and general sustainability. Therefore, Thomas Müllner, general manager at MBN Präzisionstechnik GmbH, had been looking for an automated alternative for quite some time.

“Since only a precisely defined surface area must be polished, and a variety of different hip stem shafts must be processed, automating the surface finishing operation turned out to be quite challenging,” he says. “The first processing trials were undertaken by a supplier competing with Rösler. However, the results did not meet our quality standards.”

Based on the recommendation of one of MBN’s customers, the Rösler sales branch in Austria conducted further processing trials. This company is not only located nearby but also maintains a combined test and service centre. The Rösler experts decided to run the processing trials in a drag finisher. This proprietary mass finishing system allows the precise and targeted surface finishing of high-value workpieces with complex shapes. With the process parameters established, the operation runs without any variations, ensuring absolutely repeatable finishing results.

Says Müllner: “Rösler’s comprehensive know-how and experience from the job shop operation quickly helped to develop a two-stage process with drag finishing technology. The process, consisting of a wet grinding/pre-polishing step, followed by a dry polishing stage, produces a consistently high quality in surprisingly short cycle times.”

A major feature of the Rösler drag finishing technology is the vibratory motor mounted below the processing bowl.

“The vibration of the processing bowl ensures the optimal mixing of the processing media,” says Müllner. “This results in the absolutely homogeneous finishing of all relevant surface areas on the hip stems.”

In the end, MBN Präzisionstechnik chose a compact drag finisher, the R 4/700 SF model. This plug-and-play machine consists of a processing bowl with a diameter of 700 mm and a carousel with four rotating working spindles, each spindle allowing the mounting of three workpieces. The carousel and rotating spindles are equipped with separate drive systems so that the carousel and spindle speeds can be set independently of each other. Notably, the drag finishing machine comes with a second processing bowl. Using a lift truck it is possible to easily and quickly exchange the two bowls.

Prior to the grinding operation, the surface areas on the hip stems requiring no finish are masked, prior to the manual mounting of implants to special workpiece fixtures.

“For this purpose, we developed a clamping device that can be used for all stem types and sizes,” explains Müllner.

MBN’s team then attach workpiece fixtures (with secured hip stems) to the working spindles. Once the respective program has started, the carousel is lowered so that the rotating spindles are immersed in the processing media. For the wet grinding process, a mix of plastic media with different geometric shapes and a special compound are utilised. Carousel and spindles rotate at the pre-defined speed in opposite rotational directions. After about half of the cycle time – amounting to less than one hour – the rotational direction is reversed. This ensures that the neck areas of the hip stems receive an all-around perfect homogeneous finish.
For cleaning of the process water from the wet grinding process, MBN Präzisionstechnik purchased a Rösler semi-automatic Z 800 centrifugal process water recycling system. Recycling of the process water protects the environment and helps to reduce the finishing costs significantly.

For the polishing operation, a plant-based dry polishing media is utilised. At this process step, which requires a cycle time of well under 20 minutes, the processing bowl containing the finishing media is simply exchanged with the bowl filled with polishing media.

Müllner concludes: “With the automatic drag finishing process we could significantly improve the quality and consistency of the finishing results. At the same time, compared with our previous finishing operation, we could reduce the costs for grinding and polishing the hip stem neck by two thirds. Therefore, this investment will be amortised within a three-year period.”

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