HSC milling: Highly Productive, High-Volume Production for Surgical Instruments

Surgical instruments require highly precise machining and are manufactured with great care, usually in small quantities. The structures and equipment of manufacturers specializing in these products therefore prioritize a high level of flexibility in retooling. A separate process chain should be set up accordingly for single-use products in large quantities, and a key element is a two-spindle machine from SW North America with impressive repeatable accuracy. 

“The requirements are stringent and the competition is hard in the manufacturing of precision mechanical surgical instruments,” confirms Frank Pauschert, Regional Sales Manager of SW in Waldmössingen, Germany. 

Among his customers is a company in the medical sector that has grown from its modest beginnings in the 1980s to where it is today as a mid-sized enterprise with about 130 employees. Upwards of 1,000 different utensils are manufactured there fulfilling a wide range of surgical applications, all of which come ready for use. The individual parts are made of premium biocompatible materials such as stainless steel and are manufactured in machining centers. 

Despite the existence of modern NC-controlled machine tools, manual operations continue to take up a great deal of the manufacturing processes for these instruments. This is due to the approximately 40 different components that must be refined, surface-treated and meticulously assembled by hand. Additionally, numerous variants are often needed, which necessitates small batch sizes. Therefore, flexible tooling is a prime requirement for the relevant manufacturing systems. Due to the extraordinary diversity of variants, there is also no way to work from common stock, which would thereby lower costs by enabling the manufacturing of larger batches.

Strategy for the future: A challenging one-time product

Since this manufacturer has not previously produced any of its own products, it is constantly compared with numerous competitor products already on the market. This limits profitability and future growth possibilities. 

To safeguard the future for the long-term, a decision was made about two years ago to enter an extremely challenging large-scale production project—manufacturing a type of one-time use forceps for neurosurgery that is used so often that hundreds of thousands of units are needed annually. These forceps are made of aluminum so that they can grasp tissue components while simultaneously preventing minor bleeding with electrical pulses. Minute tubes are integrated into each arm of the forceps to direct irrigation fluid into the operating area. 

Despite its straightforward appearance, the instrument requires time-consuming manufacturing involving many mechanical and manual work cycles—all the while adhering to strict quality standards. Many of these work cycles must be carried out under a microscope. Setting up the process chain requires extensive development efforts as well as substantial investments in machines and special equipment. Additional employees are currently being hired and qualified for this purpose.

High efficiency machining center

Both the starting point and the key element of the process chain is an automated dual-spindle BA 321 machining center from SW. The system has a working area of 300 x 500 x 375 mm per spindle. Both spindles are equipped with an HSK A63 interface and can reach speeds of up to 17,500 rpm with a chip-to-chip time of 2.5 s. The tool change system has a capacity of 2 x 20 to a maximum of 2 x 60 tools.

The BA 321 is used to mill aluminum forceps halves. The custom-made automation unit supplies material and removes milled parts. Although it is only intended for a limited range of parts, it outperforms the other milling centers in the plant, in terms of productivity within that range. 

With its horizontal, dual-spindle design, the new machining center delivers two completely milled forceps halves in just three minutes. Thanks to the automation system, it can do this around the clock, largely without supervision. The machine also features impressive repeat accuracy and thus produces a high quality of manufactured parts.

Development partnership in automation

The primary reason SW was chosen was their impressive productivity of their double-spindle concept. Another reason the company presented a promising option was due to its trusted reputation and its proximity to the plant. Travel times would be short, and responses would be prompt through the joint development phase and beyond.

Initial contacts a few summers ago led to a partnership-based collaboration during which the possibilities for automation of machining processes were clarified. This was followed by joint design and development of a special machine based on the BA 321 model. Here’s five clear steps to show how we made it all work:

  • Special press-drawn sections in three different dimensions are used for raw material. 
  • The forceps halves are machined out of the sections and are not separated by sawing until the last work cycle. This neatly sidesteps clamping problems that accompany the extremely slender and delicate forceps halves from the outset. 
  • The final cut from the saw is made so that a minimal amount of burr remains to prevent the pieces from falling. This prevents the delicate tips of the forceps from being damaged. 
  • Eventually, the forceps are removed by special adapters loaded into the spindles from the tool magazine. They hold the forceps parts and break off remaining burrs. 
  • Then they are deposited individually on a transport drawer and moved via conveyor belt to the removal station, where they are manually inserted in basket racks for the next work cycles.

“The joint development of automation was very efficient thanks to the professionalism of both teams,” recalls Pauschert.

Delivery and commissioning

Joint development, project planning, setup and trials prior to acceptance lasted until June. The necessary tools were implemented during this phase and an initial NC program was created based on customer requirements. 

After acceptance was completed, the system was placed in operation at the operating site in June/July. Since then there have been tests and programming for a total of 18 product variants. The actual ramp-up began in November. 

Since then, production has been running in 24/6 operation, with the system sometimes running for up to one (1) week at a time with no human interaction other than supplying material and removing finished milled parts.

Satisfied with quality, support and service

Thanks to our “life startUp” production monitoring in the first week after commissioning, the employees were quickly familiarized with operating the machine effectively and were able to work independently with it. 

With “life data”, an online service of SW, the machine is continually connected online to SW, where essential machine parameters are monitored nonstop. If problems arise, action is taken immediately. Good use has already been made of this service, as the machine operator was supported by remote diagnostics. 

“life Help” also proved quite helpful: When problems did occasionally occur, it provided quick and competent consulting, and if a service employee was needed at all, they are often on site for less than an hour. Without this service, things would have been much more complicated or would have taken much longer. 

Since launch, an additional BA 321 has already been ordered, and production capacity and efficiency has never been better. 

For background, the BA 321 is the two-spindle variant in a series that consists of a one, two or four-spindle CNC machining center depending on the task for which it is used. It is suitable for machining workpieces made of aluminum, cast iron, titanium or steel. The working area with dimensions of 300 x 500 x 375 mm is in the heart of the monoblock, and the spindles are movable in three axes. The spindles with HSK-A63 interface reach speeds up to 17,500 rpm with an output of 32 kW (4200 rpm, 40 % duty cycle) and a torque of 72 Nm. The distance between spindles is 300 mm. The system weighs about 8500 kg, while the standard installation dimensions are 3.60 x 3.13 x 6.00 m (W x H x D). The 3 series is available as a single-station machine or with a double swivel carrier. The feed of the three-axis unit is provided by sturdy ball screw drives, with rapid traverse axis reaching speeds of 65/75/75 m/min (X, Y, Z-direction) and axis acceleration rates of 10, 10 and 15 m/s2 respectively with a maximum feed force of 8000 N. The pick-up tool changing system has a capacity from 2×20 to max. 2×60 tools in the two-spindle variant. Tools up to Ø 70 mm (160 mm with free adjacent slot) with a maximum length of 275 mm and a maximum weight of 7.5 kg can be picked up. The chip-to-chip time is about 2.5 s. The Sinumerik 840 D sl, Bosch Rexroth IndraMotion MTX or Fanuc 30i are available as control unit. Learn more on the BA 3 series machines here.

For questions or support, contact SW North America