Established in 1974 by David Arnold and currently under the direction of David’s son Ian, Arrow Precision continues to abide by the founder’s guiding principles of quality, innovation and service. The Hinckley, Leicestershire based business’ highly skilled workforce have access to a wide range of premium quality machine tools enabling the company’s high-quality connecting rods and crankshafts to deliver ultimate levels of performance.
Having gained a global reputation for the components it produces Arrow Precision now supplies three main automotive sectors. The company manufacture OE connecting rods and crankshafts for use in performance production road cars for prestigious customers throughout the world. In addition, a custom service is provided offering unique forgings, custom designs and the one-off manufacture of complete sets of rods for classic and vintage cars. Last but not least, the motorsport industry’s insistence on dealing with vendors with high-levels of technical expertise, flexible manufacturing process, and fast delivery times, means that Arrow Precision is now a major supplier to this most challenging of automotive sectors.
Increasing global demand for Arrow Precision’s crankshafts recently prompted a search for a premium-quality, highly-productive grinding machine that had the capabilities to grind crankshaft main bearing journals and pins to the company’s challenging dimensional and surface finish standards. Having assessed several machines from leading manufacturers against a demanding list of criteria, a practical demonstration of a Studer S41 CNC universal grinding machine convinced company MD Ian Arnold that the advanced Studer offering was the ideal answer to the company’s requirements.
The recently installed S41 is now fully operational on 2-shifts and delivering on all of the claims made by Studer. Also, in some areas the machine is exceeding Arrow Precision’s expectations. For example, as the flexible machine can perform both external and internal precision grinding tasks, in addition to the external grinding of crankshafts journal and pins, the S41 is used to grind internal features such as flywheel location bores. Crankshaft bores that previously took 30 minutes to grind on a manual machine now take less than 3 minutes to complete. As well as producing outstanding levels of surface finish on crank journals and pins, the Studer S41 is now achieving sub-micron levels of diameter grinding accuracy.
Company MD, Ian Arnold explained the reasons for the S41’s purchase. “As demand for our crankshafts has grown to such an extent that a strain had been placed on our existing grinding resources, we decided to source a new, high-precision CNC universal cylindrical grinding machine.
“As achieving the specified diameter and surface finish characteristics of crankshaft journals and pins constitutes the most critical crankshaft machining process, the highest standards of precision grinding is of paramount importance, therefore our new grinding machine needed to be of the highest possible technical standard.
“Also, as we manufacture crankshafts in series production and in short runs, in addition to producing one-offs, we required a machine with great flexibility and quick change over times. Furthermore, as we are often tasked with manufacturing crankshafts with really short lead times by our autosport customers, we needed a fast, extremely efficient machine.
“In addition to the S41 proving its outstanding flexibility, speed and technical capabilities, it helped our purchasing decision that we were aware of Studer’s excellent reputation for the quality of the company’s machines and for if its levels of customer service. The assistance provided by Mark Maurice of UK Studer agent Micronz, was invaluable in helping us to specify the machine, arranging a demonstration at Studer’s HQ in Switzerland, ensuring a trouble-free installation and organising our operators’ training.
“As our operators received excellent on-machine training, and as Studer’s controls and software is so intuitive, our staff soon mastered the S41. Although, it helps that on the rare occasion that we have a problem, Studer personnel are just a phone-call away and able to provide and instant solution.
“Not only has the exceptional speed and efficiency of our new Studer CNC universal cylindrical grinding machine removed the possibility of production bottlenecks from our grinding department, the extra capacity it has created and the additional capabilities it provides has opened-up addition commercial opportunities for us.
With distances between centres of 1000 / 1600 mm, centre heights of 225 / 275 mm and the capability of machining workpieces with a maximum weight of 250 kg, the Studer S41CNC universal cylindrical grinding machinewas designed to accommodate large workpieces. The majority of daily grinding tasks can be efficiently performed on the machine, whilst the S41 can also be configured for single-purpose use.
Studer’s S41 boasts a wide range of advanced technical features, such as the revolutionary StuderGuide® guideway system, high-precision axis drives with linear motors and extremely fast direct drive of the B-axis, ensuring great flexibility, high precision and short auxiliary times. Given the diverse nature of the S41’s users, potential customers are able to choose from a large number of wheelhead variants. With up to four grinding wheels, the S41 fulfils virtually every requirement for complete machining.
The S41 is based on a robust Granitan® S103 mineral casting machine bed. The advantageous material structure, developed and produced in the company’s own plant using the most modern industrial techniques, has proven its value over many years. The excellent dampening characteristics of the S41’s machine base ensures outstanding surface quality of all ground workpieces. The use of Granitan® S103 extends the service life of the grinding wheels, leading to reduced downtimes. In addition, temporary temperature fluctuations are compensated by the favourable thermal behaviour of this remarkable material.
The StuderGuide® guide system for longitudinal and cross slides is moulded directly into the machine base and finished with a wear-resistant Granitan® S200 surfacing material. These guideways offer the highest possible accuracy through the entire speed range and provide high load capacity and excellent dampening levels. Thanks to their robust and maintenance-free design, the guideways deliver long lasting characteristics. The large distance between the guideways and the extremely rigidly constructed slides form the basis of the machine’s precision and productivity. Studer offers an automatically swivelling A-axis on the S41 for efficient, high-precision thread grinding. The standard swivel angle is ±15 deg, although, even greater pitch angles can be achieved with the aid of StuderThread, thanks to profile error compensation.
The Studer S41’s versatile universal workhead enables both live spindle grinding and grinding between centres. The machine can also be fitted with a specially designed chuck workhead for chuck applications. The workhead is mounted on low-maintenance roller-bearings that have an excellent roundness accuracy of below 0.0004 mm (optionally 0.0002 mm). Fine adjustment allows for cylindricity corrections in the1 µm range during live spindle operations. As with the machine’s tailstock, its workhead is also equipped with an air cushion lift-off to simplify movement during setup and resetting.
The machine’s direct-drive workhead is primarily used for live spindle grinding of heavy workpieces and for high-precision C-axis applications. When form grinding, the range of parts is expanded by the design configuration of the S41’s direct drive. This ingenious design also allows the installation of a high-precision measuring system directly on the spindle.
To an ever-increasing extent, the claim of ‘complete machining’ includes the ability to efficiently perform accurate form and thread grinding operations. These processes are made possible by the position of the S41’s speed-controlled C-axis. The standard C-axis with measuring system on the drive motor is suitable for thread grinding. A direct measuring system is mounted on the workhead spindle (C-axis) to ensure the highest form accuracy. Acceleration and grinding forces are absorbed without difficulty through the high dynamic rigidity of the axis drives.
The machine’s generously dimensioned Tailstock barrel, designed for the deployment of Morse 4 taper centres, glides in the tailstock housing. Its centre pressure can be adjusted with the delicate precision required for grinding high-precision workpieces. If required, the tailstock can be equipped with a hydraulically actuated barrel retraction for workpiece changeover. Fine adjustment enables cylindricity corrections in the range below 1 µm when grinding between centres. An air cushion lift-off facilitates simple movement during setup and resetting. A cooling lubricant is passed through the tailstock and totally covers the barrel and diamond holder, to guarantee optimum thermal stability.
As an easy-cutting grinding wheel is essential for performing cost-effective and high-quality grinding, Studer offers a large selection of dressing units. These units allow the efficient completion of the dressing process mindful of the workpiece, tool or materials. The grinding wheel profile and dressing parameters are easily defined via macros. Another Studer speciality is the grinding wheel reference points (T-numbers). These reference points enable programming with normal dimensions, which considerably simplifies the programming of grinding programs. A software package is available to fine tune the dressing process and includes additional dressing functions.
The S41 is equipped with a 31i-A series Fanuc control with an integrated PC. The 15" touch screen facilitates intuitive operation and programming of the machine.
The StuderWIN user interface and StuderGRIND software module create a stable programming environment and contribute to the S41’s efficient use. If required in-process gauging and sensor technology for process monitoring as well as contact detection and automatic balancing systems, can be integrating into the control.