A Summerville, South Carolina, job shop invests in HORN USA, WTO, and Doosan for large tool life improvements.
Faced with an aggressive 400,000 parts-per-year order, a Summerville, South Carolina- based job shop needed to develop a process that would give the required cycle time and tool life to maintain the desired profitability. The task was to machine a high-volume component made from 8620 steel that was designed with a complex internal spline.
The job shop owner initially purchased two Doosan lathes from Machinery Solutions Inc., a machine tool distributor in Lexington, South Carolina, (no longer representing the Doosan line) and a standard SBU105 broaching system from HORN USA Inc. Early in the project, it was observed that the broaching unit originally installed with the machines was not nearly rigid enough, so other options were discussed.
“We started with a standard broaching insert, and we began to have issues with tool life because of a substantial amount of chatter,” explains Michael Morgan, application/sales engineer at HORN USA, Franklin, Tennessee. “Our tool would chatter when used in the reciprocating broaching unit, but would not chatter when using just the machine axis.”
This is when Morgan and the Doosan application engineer realized they needed to find another source for the broaching unit. Morgan turned to WTO USA Director of Operations Allen Rupert for a solution.
Morgan, having worked with Rupert for several years on numerous projects, facilitated the transaction of his customer receiving a WTO Driven Broaching Unit from WTO in Charlotte, North Carolina.
“We could tell right away that the unit was substantially more rigid because the chatter issues we experienced in the beginning had gone away,” Morgan says. “It was decided this was the route that everyone wanted to go, so the customer ordered three additional units from WTO right away.”
Morgan then began to look at other ways to further improve his tool life.
“I discussed the application in great detail with my technical engineers at Horn USA who helped design and develop a special broaching toolholder and insert specific to the customer part drawing, which made our setup as rigid as possible.”
The customers’ tool life improved by another 30% just by increasing the neck diameter and reducing the overall length of the toolholder.
In addition to improving tooling performance, Morgan says WTO’s broaching unit also improved the overall broaching process on the Doosan lathes.
“They actually have a third machine they don’t need to run because the original two machines are keeping up with the volume,” Morgan says. “WTO, HORN, and Doosan all came together to make this project a success. It was vital that the tool life was optimized because a substantial increase in performance is more money in our customer’s pocket.”
Workpiece material: Up to 1,000N/mm2
Max. feed per stroke: 0.15mm
Direction of cut: X+ or X-
Follow the link to learn more about the range of machine tools available from Doosan Machine Tools America: https://goo.gl/h9v9DV.
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Investing in precision workholding equipment and high performance tooling enables first-pass machining and finishing in a single setup.
New designs, technologies, and materials in the manufacture of medical devices, appliances, and tools has increased the need for precision workholding devices that can meet stringent product quality standards and increased production capabilities.
“The medical industry presents unique challenges for manufacturing,” says James F. Woods, president of Hainbuch America, North American distributor for Germany’s Hainbuch GmbH. “The combination of requirements – high degrees of precision and surface finish with a wide proliferation of part geometry in sophisticated materials – demand workholding that is not only precise and rigid but allows for efficient and accurate changeover. Because even the newest machines often come equipped with conventional chucks, it is necessary for manufacturers to source higher quality workholding equipment capable of meeting their present and future operational needs.”
Highly specialized medical applications have redefined accuracy and precision. In conventional machining, these have traditionally referred to the ability to hold tight tolerances. Modern requirements are often involved with other factors as well. Components demanding a high finish are typically moved from turning or machining centers to specialized grinding or polishing machines. Today, this is less than practical for many reasons, including the fact that moving workpieces between machines risks inaccurate positioning. Multiple machine operations are also more expensive because of equipment costs, tooling, and the time involved in making the transfers. With precision workholding equipment and high-performance tooling, it is possible to complete first-pass machining and finishing operations in the same setup – an increasingly important flexible workholding consideration, especially for orthopedic devices.
Pete Peterson, national sales manager for Germantown, Wisconsin-based Hainbuch America, explains, “Whatever the application, we emphasize how important it is to partner with a supplier offering quick-change capability for multiple-size clamping heads (collets), combined with the ability to handle both ID and OD machining. We recently assisted a plant producing joint cups that involved multiple machine operations. By reducing their changeover time for various sizes, they maintained high levels of precision while increasing production by more than 40%. This not only resulted in a more streamlined operation, but enabled them to seek additional business.”
The owner of a medium-sized shop that produces bone pins and surgical tooling explains, “When we went over to precision workholding equipment on all our machines, we incurred an expense both in terms of initial outlay as well as training. We knew that it might not be necessary for every job but, by being equipped, we’re prepared for whatever our customers engineer next. It’s also enabled us to bid more work. If you’re going to stay competitive in this business, it’s something that you have to do – the sooner the better.”
The highly competitive nature of medical manufacturing also has redefined the concepts of economics and competitive advantage. This has created a management model that places as great a value on preparedness as it does on meeting present-day challenges, making the flexibility of their workholding system paramount.
Matt Saccomanno’s Microconic collet-type workholder for small part machining was inspired by his experience in a Swiss screw-machine job shop.
In 1996, Matt Saccomanno, co-founder of Masa Tool, was frustrated with the limitations of conventional collets and workholding systems when performing secondary machining operations as engineering manager at Allied Swiss Screw Products. This was in the early days of CNC Swiss-type machines, when machining capabilities were limited, requiring lots of secondary operations. His solution – a high-precision, collet-type workholding device for small parts machining.
As machining capabilities advanced and precision requirements became more challenging, Saccomanno realized that the legacy collet systems used in micro-machining were a serious limiting factor that prevented full use of modern machine capabilities. That prompted Saccomanno to design the next generation, the Microconic system.
“The Microconic system consists of a cartridge and collet, with the cartridge fitting in the machine just like a standard legacy collet,” Saccomanno says. “The cartridge, a self-contained precision mechanism using the machine’s standard collet closing function, brings Microconic features to any machine.”
Cartridges fit an expanding range of machines, and are currently available for those using TF20, TF25, or 5C collets. Microconic UM10 collets fit into the cartridge to hold the workpiece and because of the design and closing action, it is inherently more accurate and consistent than traditional collets.
“The origin of the word Microconic alludes to the precise way in which the collet closing taper is formed to cancel the effects of heat-treat warp and grind tolerances, providing concentricity every time,” Saccomanno explains. “There are two basic types of Microconic collets – standard and over-grip, and both types fit in any of our cartridges. Our over-grip collets deliver rigidity, concentricity, and the ability to open 4mm (0.156") larger than the gripping diameter.”
Explaining that the patented design of the system enables the improved over-gripping performance, Saccomanno notes – from his own experience – that this is impossible to do in a legacy collet system alone.
Included with the over-grip collet is an ejection guide sleeve blank for ejecting the part from the collet – an often challenging task because the larger head of the part inside the collet can get stuck if not securely guided out when opening.
The Microconic system benefits orthopedic bone screws, miniature precious metal components for pacemakers, and other implantables; machined surgical components made of hypodermic needle tubing; and surgical instrument components. Here’s one example – dental implants.
Materials: Titanium alloy bar stock
Machine: Star SR20 Swiss-type CNC automatic lathe
Previous method: The dental implant was machined almost entirely on the main spindle of the machine due to the need to have a powerful grip on the bar for a high-force, blind-hole, hexagon broach. Very little work was done on the pick-off spindle, so that sat idle for most of the cycle.
Cycle time reduction: 164 sec. to 98 sec. per part; 40% improvement achieved by moving all ID machining operations to the pick-off spindle, where they were performed in shaded time while the main spindle completed the OD. This was previously impossible to do with legacy collets, because the broaching force would push the part back in the collet. The 0.001" concentricity requirement of ID to OD could not be reliably achieved with legacy extended-nose collets, and they damaged the critical surface finish on the OD of the implant.
Cost savings: Production rate went from 18pph to 32pph, a 44% cost savings. In addition, a hand deburring operation was eliminated due to the cut-off being on the opposite end.
ROI: Cost of the Microconic system was recouped in 64 production hours; a $14,015 saved in direct production costs of a 10,000-piece order.
Saccomanno says the system alleviates challenges machinists face when setting up for small part machining by addressing the limitations of legacy collet systems.
“Collet-type workholding has a history of being the best method to hold small workpieces in production situations, because of rapid closing action, high clamping force, rigidity, and accuracy. To grip various workpieces of different diameters, a specifically sized collet is pre-made to match the gripping diameter,” Saccomanno says. “The exterior size and shape of the collet does not change, only the internal diameter of the gripping surface. So, a collet system for any given machine must be made large enough to fit the maximum workpiece diameter capacity of the machine. The result is the collet mechanism is designed to handle the largest workpieces, which means it is excessively forceful and bulky when used for the smaller workpieces. Smaller parts get sacrificed, because they typically require a higher degree of accuracy and the workholding is more critical.”
Prescott explains that there are three ways the Microconic cartridge optimizes machines for small parts.
Precision control – The cartridge provides complete internal control of collet closure, regardless of how forceful the machine’s mechanism is. Micrometer-graduated adjustment of the precise amount of collet closure, set with the MicroGrad wrench, allows even the most fragile parts to be held securely and without damage. The closure setting can be recorded on the set-up plan and accurately repeated without relying on the feel or experience of the machinist.
Improved part access – With small parts reaching the part with small cutting tools can be difficult due to interference with relatively large spindle noses. Legacy systems often use an extended nose collet to give adequate clearances, causing problems with lack of concentricity while the flexing of the long collet jaws leads to poor rigidity and holding power. Machinists then apply more force to grip the part securely, which can cause part damage. Also, with increasing force comes increasing flex, so the collet jaws start to flare outward, causing less gripping strength at the end where the cutting force is happening. High-force machining operations, such as blind hole broaching, can’t be performed because the part slips and pushes back in the collet. With Microconic, the solid extended nose of the cartridge applies the closing force directly over the workpiece. Maximum rigidity is achieved, so the part can be held securely without too much force, allowing operations that legacy collets can’t perform.
Rapid setup – The collet can be changed and adjusted entirely from the front of the spindle nose. Also, the concentricity and rigidity means no troubleshooting or swapping of collets to find one that runs true. It is guaranteed that the system will not add more than 0.0002" (5µm) total indicated runout.
When making the change to the system, machinists will remove the legacy collet (and spring, if any), and install the Microconic cartridge the same way a legacy collet would be installed. The Microconic collets then thread in from the front of the cartridge, which makes collet changing easier.
When the cartridge is first installed, the machinist should use a dial test indicator to measure the runout of the cartridge nose, which is ground to gage-like tolerances.
“If there is any runout, it is a result of the machine spindle condition and should be diagnosed as required. Usually this just involves a very thorough cleaning of the seating surfaces, but may also be due to production wear or damage,” Prescott notes. “The key here is that concentricity issues can be properly diagnosed and corrected right away, without having to run parts or try multiple collets. Once corrected, concentricity will be good every time, saving hours of troubleshooting during future setups.”
About the author: Elizabeth Modic is the editor of Today’s Medical Developments and can be reached at emodic@gie.net or 216.393.0264.
Microconic’s cartridge is made of exotic high-chromium tool steel, triple tempered and cryogenically treated to provide stable construction. All functional seating surfaces are ground with extreme precision on a one-piece, ultra-rigid body structure.
“The cartridge can be used as a calibration gage to verify the machine spindle accuracy,” Co-owner Chip Prescott notes.
Microconic collets are finished to exacting standards with a five-step grinding process that removes the effect of heat-treat warpage. Also, the proprietary Microconic form of the closure surfaces is inherently more accurate than traditional collets, providing for a greater full-accuracy working range.
Cartridges are available to fit in push-type dead-length collet closers and also draw-type closers: F20M10 (for TF20 collet replacement), F25M10 (for TF25 collet replacement), and 5CM10 (for 5C collet replacement). All of these cartridges use the same Microconic UM10 collets, with more cartridge sizes in development to be released soon.
For many medical device manufacturers, proprietary coatings and surface treatments can play a significant role in product development.
Silicon dioxide, or silica, is one of the most fundamental elements on earth. Most commonly found in nature as quartz, it is the major constituent of sand and a primary component in silicone and glass. Now, this basic chemical compound is being applied using plasma-enhanced chemical vapor deposition (PECVD) techniques as an anti-microbial barrier, a primer to promote adhesion between stainless steel and proprietary coatings, or to create hydrophobic or hydrophilic surfaces.
For many medical device manufacturers, proprietary coatings and surface treatments can play a significant role in product development and upgrading legacy medical devices under 510(k) guidelines. As a result, the medical device industry is aggressively investigating and applying plasma-applied coatings to products such as stainless steel guide wires, catheters, stents, and vascular surgical tools.
“We are always looking for unique and novel ways to make our products more robust and become the market leader, but to do that we need to bring more technology to our devices. Often, that is going to involve some form of coating to functionalize the surface,” explains Aaron Baldwin R&D project group leaders at MicroVention, a company that offers neuro-interventional products including access products, intraluminal stents, occlusion balloons, and polymer coils.
“PECVD can take a product to the next level by addressing surface reaction issues such as biocompatibility or lubricity. It is a unique and eloquent way to deposit and enhance coatings because it allows you to tailor the surface while retaining the bulk material’s properties you need.”
The PECVD process deposits thin films from a gas state (vapor) to a solid state on a substrate. PECVD deposition of silicon dioxide often requires organic silicons are as the feedstock. Within this family, the best known are hexamethyldisiloxane (HMDSO) and tetramethyldisiloxane (TMDSO).
HMDSO is an affordable, flexible reagent that is commercially available in a high purity, liquid form. The volatile, colorless liquid can be plasma-polymerized to create a variety of surface coatings that are safe for medical use. Depending on the composition of oxygen to HMDSO, the property of the surface can be hydrophobic or hydrophilic.
This flexibility makes HMDSO and other siloxanes the ideal choice for PECVD. By adjusting the parameters and other gasses added, chemists can tightly control the material to address a wide range of applications.
For the medical device industry, organic silicon use falls into the primary categories of protective barriers (antimicrobial, antifungal, anti-corrosion), as a primer between stainless steel and exotic metals and proprietary surface coatings, or to modify the surface to become hydrophobic or hydrophilic.
Adhering coatings to surfaces can be difficult with metallic substrates such as stainless steel or exotic alloys. Hexamethyldisiloxane (HMDSO) can be used as an intermediate layer to improve the adhesion between a coating and substrate.
For example, stainless steel guide wires are often coated to make them more lubricious to ease insertion. By applying a thin layer of silicon dioxide, the lubricious coating grafts nicely to a stainless surface.
Organic silicons also can be applied as a linking chemistry between other difficult-to-adhere-to surfaces such as ceramics and Polytetrafluoroethylene (PTFE Teflon). Drug delivery devices that use ceramic nozzles with micron-sized openings are coated with PTFE to prevent clogging. Depositing a 100nm to 150nm layer of HMDSO promotes the bond between the two substances.
To protect electronics, HMDSO coatings are applied in a relatively thick coating of a micron or more. HDMSO is water and gas repellent – properties required to prevent corrosion. A thin layer (~100nm) of PTFE can also be applied if the HMDSO will be exposed to harsh chemical acids or bases.
For vascular surgical tools and instruments that become fouled with tissue debris or blood, coatings can keep a surgeon’s tool cleaner, longer.
Applying a hydrophobic (water-repellent) coating on surgical devices creates a surface that blood and tissue sheets off easily, giving the surgeon better visibility.
At the other end of the spectrum are hydrophilic (affinity to water) devices. Depending on what is required, organic silicons can be used to create such surfaces with either polar or dispersive surface energy.
There are many strategies to achieve an anti- microbial surface including cell harpoons, amphipathic surfaces, antiseptics bound to the surface, and non-stick coatings.
In a unique application, chemical vapor deposition is being used to embed nanosilver particles in a thin layer of organic silicon to prevent microbial adhesion and protect against corrosion. Silver ions can be embedded in a thin layer of silicon dioxide to kill any bacteria present.
Despite the flexibility of PECVD- applied organic silicons, developing the precise chemistries, added gases, and plasma equipment design requires a close, collaborative relationship between medical device designers and equipment manufacturers.
Because MicroVention already had an established relationship with PVA TePla – several of its plasma chambers were already being used to aide in coating adhesion – Baldwin began consulting with them on a project to determine the benefits of coatings for stents.
Plasma equipment manufacturers fall into two categories, Baldwin says, those that produce commodity, off-the-shelf products and those that design and engineer systems to fit the needs of a specific application and/or to resolve unique surface energy challenges. So, when companies present PVA TePla with a challenging surface chemistry problem they are encouraged to visit the lab in Corona, California, giving them an opportunity to brainstorm with their technical team and run experiments together.
Many of the best experimental matrices and ideas are produced during these technical customer/supplier meetings. In addition to designing and manufacturing plasma systems, the company also serves as a contract manufacturer and has in-house equipment needed to run parts and conduct experiments with full customer involvement.
“When we start on something new, instead of poking around in the dark, it is better to get expertise involved and [PVA TePla] is very willing to do experimentations – often free of charge – to get the project moving and improve the characteristics of the system and chemistries involved,” Baldwin says. “We were able to go there and work on their plasma machines to determine our parameters and evaluate the equipment.”
Every PVA TePla system is designed to meet the application requirements, which can include unique fixtures, unique electrodes, and chamber modification to accommodate throughput and coating uniformity.
The ability to thoroughly clean the chamber after each application of organic silicons is a major consideration as it coats the entire interior of the chamber (including the electrodes) in addition to the products receiving the coating. As a result, PVA TePla modifies the chamber to make it easier for the user to clean it after every coating application.