Tenable Turns to MultiSwiss For Productivity Beyond Sliding Heads

Almost 78 years after Tenable Screw was founded by a Swiss watchmaker as a manufacturer of screws, the company has become one of the UK’s largest subcontract manufacturers of turned parts. Remaining deeply loyal to its roots, Tenable has unparalleled expertise in turned component production, something that is evident by the company’s relentless growth.

With three manufacturing sites in Marlborough, Coventry and its headquarters in Wimbledon, South London; Tenable has more than 250 machine tools that include 71 coil-fed Escomatics, 26 Multi-spindle machines, 56 sliding head turning centres and four fixed head turning centres. The machines produce millions of components every month. Committed to a culture of quality assured engineering excellence, Tenable Screw invests 10% of annual turnover in modern technology to support its live customer base of over 250 companies. Part of this investment strategy has seen the arrival of a Tornos MultiSwiss 6X14.

The modern face of Tenable Screw sees the company manufacture everything from connector pins and sockets through to bolts, screws and much more for the electronics, instrumentation & control, automotive, aerospace, medical, defense, transport and telecommunications sectors in quantities that range from prototypes and small batch production up to 100,000+ runs. With London property at a premium and a 45,000sq/ft Wimbledon headquarters packed with machine tools, the philosophy behind the MultiSwiss 6X14 purchase was to add flexibility and capacity to a business with limited floor-space.

Commenting upon the arrival of the Tornos MultiSwiss 6X14, Tenable Screw Commercial Director Mr Nigel Schlaefli says: “We initially acquired the MultiSwiss to alleviate capacity issues on our single spindle sliding head machines whilst having the production capacity of multiple single spindle machines in a floor area significantly smaller than 5-6 single spindle machines. Whilst we initially used the MultiSwiss as a flexible centre that was supporting our single spindle machines; like any subcontract manufacturer that has a fluid workflow, customer base and component types, the MultiSwiss is now dedicated to producing just one component family. Despite being restricted to a single family of parts, the productivity, precision, cost reduction and floor area benefits are evident.”

Producing Automotive Components 6 Times Faster
Just a few months after installing the MultiSwiss 6X14, Tenable Screw won a long term automotive contract. The family of stainless steel pins require numerous external turning processes as well as knurling, drilling and parting-off. The UK contract requires 1,500,000 parts every year, a quantity equal to 30,000 parts every week. Tenable Screw trialled the automotive part on one of its sliding head turning centres and the cycle time was 1.5 parts per minute. In stark contrast, the MultiSwiss 6X14 was capable of producing 9 parts per minute – an output equal to 6 sliding head turning centres.

“We calculated that we would have needed to run 6 single spindle turning centres for 24 hours a day to meet the contract capacity level. We generally run our machines for 8-8.5 hours through the day and re-set the machines at the end of a shift to run for an additional 8-9 hours unmanned. To meet the demands of this specific contract, we would have had to commit staff to running 6 sliding head machines around the clock. In comparison to the 24/7 running of 6 machines, the MultiSwiss 6X14 hits the same output by just running for 17-18 hours a day. This means we can run the machine during a day shift, change tools and re-stock the barfeed at the end of the shift and then run for an extra 8-9 hours unmanned,” says Mr Schlaefli.

The Quality Benefits
As with all manufacturers with relentless quality standards, Tenable Screw has a dedicated quality control department and its production adheres to ISO:9001 2016. With regard to production, Tenable applies SPC and CPK procedures to its production. The CNC Manager responsible for more than 60 CNC machine tools at Tenable Screw, Mr Paul Kelley comments: “If we were producing this automotive part on 5-6 machines there would inevitably be a variation in CPK values between the machines. Whilst the part has an average tolerance band of +/-20microns, the MultiSwiss easily maintains a band of less than +/-10microns and this improves our CPK and SPC values considerably.”

“What we have also found is that each spindle on the MultiSwiss works independently, unlike conventional multi-spindle or CAM-auto machines. This allows us to change the spindle speeds for each spindle and operation. This considerably improves surface finishes and contributes to improving tool life compared to other production machines.”

Hydrostatic Spindle Technology
Contributing to both quality and tool life is the hydrostatic spindle technology integrated into the Tornos MultiSwiss 6X14. As Mr Kelley continues: “Over an extended period of time, roller bearing technology on machine tools will generate wear and this results in diminishing component quality. However, the hydrostatic spindle technology on the Tornos eliminates wear; this means precision and consistency will not diminish. The hydrostatic spindle also eliminates vibration in the spindle head and this enhances component quality and surface finishes.”

Referring to the tool life on the MultiSwiss, Mr Kelley continues: “The MultiSwiss will run for two days without any need for tool changes. Even then, we are only changing inserts as a precautionary measure. The only tool we change on a daily basis is the knurling tool. To put this in context, we are producing 18,000 stainless steel parts before we change inserts. The MultiSwiss is achieving at least double the tool-life of the single spindle machines.”

Tornos Reduces Costs for Tenable
The MultiSwiss at Tenable Screw has demonstrated how it can reduce floor space requirements and reduce power consumption, tooling and general running costs compared to 5-6 single spindle machine tools with a comparable production output. The consumable costs are further reduced by the hydrostatic fluid technology, as Mr Kelley continues: “The MultiSwiss uses the same oil throughout the machine. The hydrostatic spindle oil is also used to lubricate and cool the machine. The swarf conveyor in the machine base has 4mm holes that filter the smallest chips and oil. The oil and chips are then filtered through 20micron filtration paper that collects all remaining swarf and particles. The oil is continually re-cycled through two further filters before returning to the spindle and machine envelope. We change the oil every 6 months on the MultiSwiss. However, this continually filtered oil is of such a high quality that after 6 months of use, we then use it in our single spindle sliding heads as ‘new oil’.”

Ease of Use
The MultiSwiss 6X14 at Tenable Screw has a FANUC CNC control interface that is particularly easy to use. Concluding upon the CNC control and the ease-of-use characteristics of the MultiSwiss, Mr Kelley says: “The MultiSwiss has 14 linear axes and 7 C-axes with up to 18 tool stations. Despite the number of axes and tool positions, the machine is significantly easier to program than single spindle sliding head machines. We apply G-Code programming and determine the number of operations for each spindle. Combining these features with a well-lit and easy-to-access work envelope, the MultiSwiss is easier and faster to set-up than single spindle machines.”

“This ease-of-programming is certainly beneficial; but one equally important factor is the operator. There is a distinct lack of skilled CNC machine operators and programmers in the UK. Combining the ease-of-use characteristics with the facility to be as productive as 6 alternate machines, the MultiSwiss reduces the reliance and requirement for highly-skilled staff; something that certainly suits our company in the face of skill shortages.”