Tornos Machines Aid Production of Medical Parts
'Products for the medical industry are becoming more complicated, and as the products become more complicated we've started to incorporate Tornos machinery,' said LeNoir Zaiser, chief executive officer and co-founder of Structure Medical. Zaiser's son, also called LeNoir Zaiser, co-founder and senior vice-president of the company, added that the machine enabled the company to do a wider variety of work. For instance, the percutaneous poly-axial housing part - produced by Structure Medical's lead Tornos programmer Victor Georgier - is a complex, 140mm-long component.
The challenge was producing a very long hole with deep, long threads at the bottom of the hole. Georgier said: 'The challenge was not to make that part, but to make a few hundred. 'We produced the part from a specially ground titanium and considered that it had to be a stable process as this customer is very demanding, scrutinising parts to the smallest detail,' he added. Structure Medical implements a production protocol that requires non-disclosure agreements from anyone who spends time on the shop floor. The protocol is based on utilising multi-axis milling techniques over simpler cutting processes and grouping multiple parts into single-program operations and buying the best equipment, cutting tools, oil and raw material available.
Structure Medical often utilises surface milling processes with a ball mill tool on the Tornos over traditional form tool turning processes. This allows the company to achieve perfect blends on the corners of parts. Georgier continued: 'We use a ball mill and take one cut across and follow the surface based on the CAD [computer-aided design] model. 'We make a step-over and that will be determined by the diameter of the tooling and part parameters, so we move three to four thousandths of an inch and then we take another cut and repeat that motion.
'The tool is driven on the surface of the part, like sculpturing,' he said. Up until now, turning centres were not meant to do this type of work. However, Structure Medical found that its Tornos Deco Sigma 20s and Sigma 32 could do it very accurately without sacrificing cycle time. Georgier said: 'Wherever there are irregular surfaces, I cannot use a form tool as it won't blend well when I go around the corner, because our parts have a different curvature on both sides. 'So that's where the accuracy of Tornos comes into place. 'Because the machine has minimal thermal expansion, all the blends will be perfect,' he added.
Zaiser said: 'Turning is just a small part of what these machines do. 'One of the key things about Tornos [machines] is they seem to run the hardest the longest. 'And the interface of the bar feeder to the machine is superior to anything we've found so far - its very reliable. 'They also have an extremely good temperature compensation system,' he added. According to Georgier, the company can now machine very complex parts and carry out unusual applications. All the surface milling that Structure Medical performs on its Tornos machines results in very long programs.
On other turning centres, long programs present a problem when the machine runs out of memory. However, the Tornos Deco Sigmas incorporate 31i control systems that can easily handle complex programs. It is critical that Structure Medical's machine tools can handle the long programs inherent with complex surface milling processes. It is also important to the company that its Tornos machines share the same control, so parts can easily be swapped from one machine to another. Owing to the small lot sizes in the medical industry, Structure Medical finds it has to carry out a lot of setups. 'We have four different Sigma models - four Sigma 20s and one Sigma 32 - but since the machines are nearly identical, we have the flexibility to move parts to whichever machine is available at the time,' said Georgier.
In the last year, he has reduced 40-50 per cent of the time cycle out of several jobs by moving from other turning machines to the Tornos. Zaiser said: 'Georgier's goal is not squeezing the last second out of a cycle time; it's squeezing the most runtime without intervention. 'If you can get a one-minute time cycle where you change tools every hour and a half versus a two-minute time cycle where you change the tool once a day, we'll go with the two-minute time cycles. 'We are mainly concerned with how many parts we have in the bucket at the end of the week,' he added.
Georgier continued: 'Cycle time alone for us is not an indication of whether we're doing a good job or not. 'The process needs to be stable. 'Sometimes we find that if we break that part into different operations it's more efficient for us,' he said. Next year, Structure Medical will take delivery of four new Swiss turning machines - Tornos's latest Evodeco machines.
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