Advances in electrical discharge machining (EDM) have improved cost performance and complex shape capabilities, making this process a viable alternative to broaching bone screws and other medical fasteners.
Traditionally, broaching has been regarded as the most economical method of producing medical screws (such as cortical screws, cancellous bone, bone pull and puncture screws), which are used to fix implants in the body and accurately position them during surgical procedures The equipment used. However, today, compared with broaching, sinker electrical discharge machining (EDM) (also known as traditional EDM or stamping EDM) has proven to have performance advantages and become a cost-competitive alternative.
Generally, the screws left in the body after the operation, that is, the bone screws, are made of titanium or cobalt-chromium alloy, while the screws used only during the operation are made of stainless steel. Although machining on a computer numerical control (CNC) Swiss-type machine is the most common process for generating medical threads, there are other methods to create the driving characteristics of the screw. The internal shape of the screw head includes hexagonal and six-lobed (quincunx)) , Squares and many customer-specified shapes.
Manufacturers often use broaching techniques to create the internal shape of the screw head. Broaching uses tools to remove material in a linear or rotational manner. In linear broaching, the tool moves linearly against the surface of the workpiece to create a cut. In rotary broaching, the broach is rotated and pressed into the workpiece to cut the shape.
In order to create the internal shape of the screw head using an EDM machine, the electrode and workpiece are immersed in a dielectric liquid and voltage is applied. Although the electrode and the workpiece are not in contact, the current between the two causes the reversely charged material to be removed, resulting in various shapes in many types of conductive materials.
The internal shape of the medical screw head must be completely burr-free, accurate, consistent, and reasonable in structure, and can be economically produced in a short turnaround time. Screws also need to be produced in various sizes, shapes and materials. Although many manufacturers use broaching, the sinker EDM process meets all these requirements and exceeds the capabilities of broaching.
The MV series has been improved in terms of machine structure, automatic thread processing, internal machine communication, power supply technology and operating costs. It uses the M700 series controller with a 15" touch screen, including Mitsubishi's non-contact cylindrical drive system, to achieve the advancement of wire cutting technology. https://goo.gl/wiQQvh
The MV4800 can perform underwater cutting up to 20" with the support of an automatic tapping system. The annealing length exceeds 27", and the system can tap the maximum workpiece height (if necessary) at the start point and gap to recover from wire breakage. MV4800 has a non-contact cylindrical drive system and M700 series controls with a 15" touch screen. https://goo.gl/ccQZSl
The performance of FA40V Advance in hardened D2 steel is up to 36in2/hour. FA40V is a faster, large workpiece, high-precision wire cutting machine, also has M700 series controller and 15" touch screen. https://goo.gl/1fVkbT
Burr-free-any type of burr left after the manufacturing process may eventually fall off and cause discomfort (or worse) to the patient. Broaching is a high-impact metal removal method that may produce burrs when the tool is worn. Sinker EDM is a material erosion process, so no chips are generated. In addition, because there is no contact between the EDM tool (electrode) and the workpiece, there will be no tool wear that can cause burrs on the drive feature of the bone screw.
Precision-As long as the broaching tool is kept in good condition, broaching has proven to be a precise production method, but the precision of EDM machining is higher. The sinker EDM process can maintain a total dimensional tolerance of 0.0002" and a total depth tolerance of 0.0005". This ability has become increasingly important as customers tighten product tolerances to ensure that the drive tool inserts screws as easily and efficiently as possible during surgery.
Consistency-Broaching can produce good consistency between parts, but it is highly dependent on the condition of the material being cut and the broaching tool. Since there is no tool wear, Sinker EDM produces more consistent results. The electrode must be modified after each run to ensure the best performance. Mitsubishi EDM machines provide a consistent spark gap during production, while System 3R tools provide positioning repeatability because the tray aligns and secures the electrode holder and the screw holder.
Structural integrity-Broaching is a fast, high-impact manufacturing process that puts stress on the workpiece and may lead to material degradation. This degradation is usually not immediately visible, but it can lead to premature failure of the part. Since there is no tool contact or heat-affected zone on the part, the EDM does not introduce such stresses, thereby improving the structural integrity of the medical device.
Economical and short turnaround time-linear and rotary broaching are fast operations that can meet the needs of low-cost, short-turnover production. However, advances in sinker EDM technology and tools have reduced the processing costs of this alternative. For example, custom-designed multi-electrode parts holders are suitable for multi-piece applications and can complete up to 100 parts in a production cycle. Companies such as New Jersey Precision Technologies Inc. (NJPT) have a large number of machines that can produce multiple sets of operations to ensure a short production turnaround time. Similarly, due to the large inventory of electrode sizes and shapes, tool costs-which has always been a focus of EDM machining-have been greatly reduced. For example, since the NJPT tool library already contains more than 1,000 screw and shape configurations, most customers may not incur tool costs. If the electrode size required by the customer is larger than the one in the inventory, the Mitsubishi CNC EDM machine tool can be operated in any mode to achieve the specified size.
Diversity of part sizes, shapes, and materials—Metal cutting processes (including broaching) have historically faced numerous challenges when producing titanium and cobalt-chromium alloy parts for the medical industry. Any conductive material can be processed equally well with an EDM, and the difficulty of processing these materials is reduced. Broaching can only machine the internal shape produced on the broach (in the case of rotary broaching, it can be rotated) and is limited to producing a flat or uniform base in the drive feature.
Sinker EDM can provide drive features of any shape, such as three-dimensional sidewall shapes with tapered and non-vertical sidewalls. It can also make the basis of screw drive features any 3D contour or shape, and can even generate multi-step features as needed.
There is no doubt that EDM machines have a place in the manufacture of multifunctional screws used in the medical industry. Many medical device manufacturers are already calling for electrical discharge machining as the preferred method of manufacturing the internal features of medical screw heads.
Due to massive advancements in technology and tools, the limitations of EDM as a viable alternative to broaching have almost disappeared. The latest EDM machine uses the most advanced power supply, which greatly reduces the heat at the metal removal point. Therefore, designers can specify unique, thinner-walled features in the screw head to reduce costs without adversely affecting the performance of the product's entire life cycle (or worrying about the screw head cracking or breaking during broaching).
New Jersey Precision Technology Corporation www.njpt.com
About the author: Bob Tarantino, President of New Jersey Precision Technologies, can be contacted by: bob.tarantino@njpt.com or 800.409.3000.
NEW JERSEY PRECISION TECHNOLOGIES INC. (NJPT) is one of the largest all-Mitsubishi EDM processing service shops in the Northeast. It has more than 40 machines, including many MV2400-R, MV4800 and FA20V machines, which operate 24 hours a day and are staffed. 7 days a week.
In 1989, they started in a high-tech business incubator on the campus of New Jersey Institute of Technology, and began prototyping in the fields of electronics and medical equipment.
“When the company was founded, as a team, we considered buying EDM machines of different brands,” said Bob Tarantino, President of NJPT. "We chose Mitsubishi machines because of their functionality and reliability. Other brands are just not as easy to use as we need or have the reliability we need."
Since NJPT was reorganized in 1995 as an EDM company focusing on wire cutting and high-precision molds for medical devices, they have become more diverse. Although most of its work is focused on orthopedics and cardiovascular instruments, about 70% are in the field of medical devices. The company is also a contract manufacturer for the aerospace, tools and molds, plastic extrusion molds, and defense industries. A 10,000 square foot building was purchased in Hillside, New Jersey in 1999 and later expanded to 21,000 square feet.
The two advantages that keep NJPT in the lead are the expert software system they developed for programming EDM machines and the focus on employee training. The software extracts geometric shapes, material type annotations, heat treatment requirements, and labels from the drawings, and then interprets the data to create process decisions without operator intervention. This simplifies program development and delivers parts to the machine faster.
NJPT is also a high-intensity engineering training company. Engineers must pass 75 points of training to obtain EDM certification-I believe that the only way to develop business and continue to provide the best service is to provide continuous learning.
"Mitsubishi machines are very reliable, easy to program and use," Tarantino said. "From a practical point of view, we can transfer our operators from previous models to new generation models because the machines continue to use the same terminology. This helps us increase throughput and provide faster turnaround times, thereby Shorten the time to market for customers and reduce their related listing costs."
In the rapidly changing medical device industry, the geometry of parts becomes more and more complex, and in many cases it can only be produced using the EDM process. NJPT uses Mitsubishi machines to quickly adapt to these changes in medical equipment and special functions. The special function of 45-degree line cutting on medical equipment does not require special fixtures. And 45° corner cutting feature does not require special fixtures.
"Mitsubishi EDM machines are easy to operate and reliable, and the service department is by far the best in the industry," Tarantino said. "Since their service department provides regular preventive maintenance or any rare event of emergency repairs, we have achieved an impressive uptime."
NJPT also uses MC Remote 360, which transmits real-time machine data to mobile devices and desktops. Operations can increase productivity and efficiency while preventing interruptions and upgrade service issues.
MC Machinery Systems Inc. www.mcmachinery.com
The M3-LS-3.4-15 linear intelligent platform directly drives the precision piezoelectric micro-platform with an embedded controller designed for integration into compact OEM instruments.
Absolute coding eliminates errors and interruptions in the process and experiment, without the need to return to the stage when power is applied.
The intelligent stage has the characteristics of low noise and no high voltage, and can be used for instruments and wearable devices close to the patient. The embedded controller simplifies the integration of the intelligent platform and OEM instruments, and provides simple and advanced motion commands directly from the system controller to the platform.
The WBR series thin film wire bond resistors provide a rugged structure up to 250mW DC, and provide stable and reliable performance in a thin package. In addition to films, substrates, termination materials, temperature coefficient of resistance (TCR) values, and resistance tolerances, the series also provides customizable resistance values ranging from 1O to 4MO, with chip markings to be matched. WBR series resistors are specially designed for applications that require stable hot pressing, epoxy or ultrasonic bonding connections. They are suitable for: hybrid circuits, medical implantable devices, multi-chip modules (MCM), test and measurement instruments, and microelectronics As well as military and defense applications.
The plastics processing company whr Hossinger Kunststofftechnik uses the Zeiss O-Inspect multi-sensor measuring machine to accurately measure its neonatal continuous positive airway pressure (CPAP) generator.
Every ten babies are born prematurely, many of whom weigh less than 4 pounds. The survival and health of these newborns depend to a large extent on perfect respiratory support and increased oxygen levels when necessary. This is where the continuous positive airway pressure (CPAP) generator produced by whr Hossinger Kunststofftechnik GmbH in northern Bavaria, Germany comes into play.
“Our generator can save lives in the 24th week of pregnancy or at a birth weight of 14 ounces,” explains Managing Director Armin Hossinger. "This is something we are very proud of."
The CPAP generator delivers oxygen-rich air through the tube and exerts a slight positive pressure to help babies breathe spontaneously—stimulating lung development. Positive pressure is generated in the plastic shell of the CPAP generator, and oxygen is transferred to the patient's nasopharyngeal area through the silicone pins or mask without leakage. In order to reduce the burden on babies as much as possible, whr Hossinger Kunststofftechnik uses a connector system instead of adhesives to connect the various plastic components of the product to maintain the airtightness of the CPAP generator.
Christian Bindl, head of quality management at whr Hossinger, listed the challenges he faced when measuring CPAP generator components: "The wall thickness is only 0.3 mm, the tolerance is only a few hundredths of a millimeter, free-form components with complex shapes, and different products. colour."
Capturing the complex geometries of free-form surface components can be very time consuming because this step must be performed from different angles. The thin wall thickness also makes contact measurement difficult, and certain product colors require illumination, which must be adjusted appropriately for optical measurement.
In the past, these requirements made it difficult, time-consuming, and sometimes costly to use the company's existing optical measuring machines for quality inspection. Measurements sometimes have to be outsourced, which increases costs and reduces throughput. In addition, there is no space on the company's optical measuring machine to inspect other products.
Watch the video of Hossinger Kunststofftechnik GmbH using Zeiss equipment to improve internal measurement accuracy and reduce measurement time: https://goo.gl/9oMONI.
In 2014, Hossinger and Bindl began to look for new measurement strategies and expand their existing optical measurement machines. They want to measure more products internally faster and more accurately. Their search revealed the Zeiss O-Inspect multi-sensor measuring machine, which combines three measuring principles in one machine-contact sensor, camera sensor and color white light sensor. This machine promises higher accuracy and higher efficiency, but its measuring range (400mm x 400mm x 200mm) is too small for the large workpieces they manufacture, so Hossinger and Bindl got in touch with Zeiss to obtain What they need is a machine with a larger measuring range-500 mm x 400 mm x 300 mm.
"Contact, optical, white light sensors: The interaction of these three measurement methods is unparalleled because they make us very efficient," Bindl said, demonstrating the function of using one of the half shells of the CPAP generator. These half sleeves will later form a hollow space that generates CPAP pressure, which will be measured at the beginning and end of production and used for random sampling. The goal is to achieve zero defects during the final functional test of all CPAP generators in the clean room.
Random sampling of half-shells on the multi-sensor measuring machine in the measurement laboratory involves three stages. In the first step, ZEISS O-Inspect performs a contact scan on the workpiece, which takes about one minute. During this period, the contact sensor will capture the location of the positioning holes of the pins, which will connect the two halves after assembly. The location and diameter of the sealant housing, to which the pipe adapter for oxygen delivery is connected, is also defined using contact measurement. This requires a tolerance between 0.01mm and 0.02mm to prevent component leakage or cracking.
In the second step, the machine automatically switches from contact measurement to optical measurement. In about 1.5 minutes, the camera sensor measures the receiving profile of the pipe joint. The translucent half shell-yellow in this version-is illuminated by blue, accentuating the structure. The measuring machine provides blue or red illumination, depending on the color of the workpiece, to create different contrast levels. The sensor can image wall structures raised by 0.02 mm or 0.03 mm. These are later used to modify the CPAP generator to fit the shape of a particular patient's nose. The use of a camera for optical measurement is best suited for this task because it can image geometric elements quickly and flexibly.
Then the process enters the third step. The color white light sensor captures the topography of the workpiece within 15 seconds. The point cloud is composed of 3,000 features and is used to identify the sealing contour of the half-shell of the matched part.
"Multi-sensor measuring machines provide metrologists with a lot of freedom to decide which sensor to use and what to use. If the program is already set up, you can even switch from one method to another without much effort," Bindl said.
Bindl and his colleagues use Calypso software to program the measurement program, regardless of which of the three sensors they use.
Calypso uses different sensors and different machines, so the two colleagues only need to use one software, although they also added a Zeiss Contura coordinate measuring machine (CMM). The contact measurement program of one machine can be used on another machine. The data captured by the service provider on the computed tomography scanner can be exchanged with data from other measuring machines.
"This allows us to be very flexible when choosing a measurement method," Bindl said.
Due to its flexibility, accuracy and speed, the acquisition of the multi-sensor measuring machine paid off for whr Hossinger. Today, the company outsources fewer and fewer measurements, and with the help of Zeiss O-Inspect, Bindl and his colleagues can perform measurement tasks with a high degree of accuracy and repeatability.
According to Bindl, adding Zeiss O-Inspect provides a breathing space for metrologists.
whr Hossinger Kunststofftechnik www.whr-hossinger.de
Zeiss Industrial Metrology Co., Ltd. www.zeiss.com/metrology
whr Hossinger Kunststofftechnik GmbH is located in Roding, Germany. With 60 employees, it develops, designs and manufactures technical plastic systems for the medical technology and automotive industries. The family business was founded in 1925 and now covers the entire process chain of plastic injection molding-including design and engineering, tool manufacturing, plastic part manufacturing, as well as assembly and customer-specific packaging, delivery and logistics strategies.
SR-32JII B Swiss automatic lathe adopts modular design and adopts inclined guide rails to improve rigidity, accuracy and stable production. The eight-station post-processing unit with Y-axis provides flexibility in overlapping processing requirements. The rigid machine structure allows precise continuous processing within the processing time. SR-32JII is designed for work with or without guide sleeve.
It also provides an improved SV-20R Swiss-type automatic lathe, a built-in multi-tool B-axis, and an eight-station tool post for post-processing overlap. Turning with two tools reduces production time and improves accuracy. SV-20R has a variety of tools, rigid structure and flexibility to produce complex components in one operation.
WESTEC 2017 Booth #1735 Star CNC Machine Tool Corp. www.starcnc.com
VNMG inserts and tool holders adopt the chipbreaker geometry and thickness of conventional size inserts, which can achieve cutting performance up to 3 mm (0.12 inches) of cut.
Inserts and tool holders provide ECO tool turning solutions. For example, VNMG 2.33 (VNMG1204) inserts are used for inner diameter turning as small as 1.25" (32mm), while the minimum inner diameter of traditional VNMG 33 (VNMG1604) inserts is 1.45" (37 mm).
The blade can be used for: CVD grade T9100 for steel; CVD grade T6100 and PVD grade AH600 for stainless steel; and two cermet grades, NS9530 and GT9530. Chipbreakers include options for semi-finishing or finishing steel and stainless steel. Tool holders for OD and ID turning are also available, as well as tool holders with TungCap connectors.
WESTEC 2017 Booth #1022 Tungaloy America Inc. www.tungaloyamerica.com
The Maxumizer blower system constructed using the Maxum bearing bridge drive system uses less energy, runs at lower horsepower, and is slower. The drive system replaces the belt drive system. Two independent bearing boxes are used on both sides of the drive pulley to correctly distribute the bearing load, reduce heat, increase service life, and increase the life of the L10 bearing by 10 to 15 times over the old cantilever driver.
Maxum air equipment includes standard output flow and pressure data. The blower housing can reduce the operating sound level at 3 feet to below 75dB. It is made of corrosion-resistant polymer and has a small footprint. It is equipped with standard meters, an oversized filter with a pre-filter, and an integrated skid-mounted bracket. The system's convergent laminar flow technology allows air to reach the parts in a stronger, faster, and more concentrated form, thereby increasing efficiency and saving energy. Maxum LLC www.maxumair.com
A cartilage-like material created by researchers at Duke University could one day allow surgeons to 3D print custom-shaped knee replacement parts.
Human knees have a pair of built-in shock absorbers-meniscus-cartilage blocks, which can cushion every step we take. Daily wear or a wrong step can permanently damage these critical supports, leading to pain and increased risk of arthritis.
The adult meniscus has a limited ability to heal on its own, and attempts to repair torn or damaged tissue usually result in partial or complete removal. Available implants either do not match the strength and elasticity of the original cartilage or are not biocompatible-they do not support cell growth to promote healing around the site.
Hydrogel has always been concerned as a substitute for lost cartilage. The biocompatibility of the molecular structure is similar to that of cartilage, and researchers have been working hard to create a synthetic hydrogel formulation.
"The gels currently available are indeed not as strong as human tissues, and generally speaking, when they come out of the printer nozzle, they will not remain intact-they will flow around because they are mainly water," said Benjamin Wiley Associate Professor of Chemistry at Duke University in Durham, Carolina, and co-author of a paper on printable hydrogels published in ACS Biomaterials Science and Engineering.
Feichen Yang, the co-author of the paper and a graduate student in Wiley Lab, tried to mix two different types of hydrogels—one harder and stronger, the other softer and more elastic—to make dual-network water. gel.
"These two networks are intertwined," Yang said. "This makes the entire material very strong."
By changing the relative content of the two hydrogels, Yang can adjust the strength and elasticity of the mixture to create a formula that best matches human cartilage.
He also mixed nano-particle clay to make the simulated cartilage 3D printable. The addition of clay makes the hydrogel flow like water under shear stress, such as when squeezed through a small needle, but once the stress disappears, the hydrogel will immediately harden into its printed shape.
"We now allow anyone to easily print things with mechanical properties that are very close to cartilage, and the process is relatively simple and low-cost," Wiley said.
This hydrogel-based material is the first to match human cartilage in strength and elasticity, while maintaining 3D printability and stability in the body. To demonstrate, the researchers used a $300 3D printer to create a custom meniscus for a plastic model of the knee.
"The meniscus is not a homogeneous material," Yang said. "The middle is harder and the outside is softer. Multi-material 3D printers allow you to print different materials on different layers, but with traditional molds, you can only use one material."
Researchers say that meniscus implants can also benefit from 3D printing's ability to create custom and complex shapes.
In a simple demonstration, Yang performed a computed tomography (CT) scan of a plastic model of the knee and used the information from the scan to 3D print a new meniscus using his dual-network hydrogel. The process from scanning to completing the meniscus took only about one day.
"This is indeed a young field, just getting started," Wiley said. "I hope that proving that this can be done easily will help make many others interested in making more realistic printable hydrogels that have mechanical properties closer to human tissues."
Duke University www.duke.edu