The titanium stampings’s small size – smaller than a scalpel blade – demonstrates the precision capabilities needed to make the product a success. Our engineering, design and production expert’s combined innovative thinking with advanced technologies to manufacture a Part of Something Greater.
A provider of innovative medical devices for vascular access management was looking to penetrate the rapidly growing vascular sealing market with a new product that would quickly close vessels with the pull of a trigger. The device inserts a 3mm titanium staple, which first expands to maximize the area requiring sealing, then closes.
Manufacturing the staple posed a major challenge because of the forming characteristics of titanium, the small size and complex shape of the part, and the tolerances on key dimensions. The company considered machining the part, but that would be very costly for the volumes that the customer anticipated. OKAY showed them the advantages of a stamped solution.
OKAY’s Production Proven Prototyping™ process utilizes the same tooling concepts, sequence of operations, and grain direction that will be used in the production tool. Replicating the stamping manufacturing process during the prototype stage minimizes costly changes later in the project that would not have been identified using machining or other prototyping methods. Component strength, cracking, surface finish, burrs/edge condition, and feature tolerance capability are all assessed and verified. The dissimilarities between metal injection molding, machining, and stamping are all affected by these factors.
Titanium is very cold workable but is extremely abrasive, soft and gummy, and has a higher resistance to forming than other annealed low-carbon metals. It requires more attention to spring-back in forming when compared to other materials – it exhibits about 25% more “spring back” due to its lower elastic modulus, and it tends to gall more easily than steels, so tooling designs need to be modified appropriately.
Another challenge of stamping Titanium is its susceptibility to gluing itself to the tooling surfaces. “Sometimes this has an effect like sandpaper where it just abrades and causes minute gritty particles to collect in the tools,” says OKAY engineering. Other times pickup on the tools will actually grip the material being bent, stretching the features of the staple out of tolerance. These conditions are caused by heat and friction.
To mitigate all these problems, OKAY developed tools with very generous wipe radii on the form dies and punches and surface finishes were held to 5 micro or less. In addition, die lubrication created a barrier between the titanium part and the die material.
Another challenge with stamping the staple is its size. For example, the short legs are gutted all around with a slot in the middle leaving the width of the blank just slightly larger than material thickness. Typically, stamping operations require blanking areas that are greater than material thickness. This requires special holding and guiding techniques in the tool. The staple tips are very critical to hold, guide, and support. The tips of the staple are held to +/- 0.0002″ (.005 mm) maximum spherical radius, an almost perfect point. “Many people believe that stampings must maintain material thickness throughout the component. However, coining, swaging, and extruding operations can be used to form complex features in a stamped product,” says OKAY engineering.
The shape of the staple creates a unique forming challenge while trying to maintain dimensional stability. The distinctive shape has all eight legs interconnected at the top, and the bend radius of each leg has no relief around it where it connects to the main body. This results in a portion of each bend radius to fall partially inside the top flat area, which causes interference with the bend radius of neighboring legs. This causes a lack of isolation and control of the previously formed long legs when forming the four short legs. OKAY Engineers overcame this with a sequence of rotary forming tools, which set each bend independently.
The staple has over bent-legs that posed a challenge for designing the progressive die. OKAY designed a transfer station system to form and eject the part from the tooling. It transfers the part to and from 6 tooling stations and part ejection.
Nearly all medical applications for stamped titanium components require them to be free of any scratches, nicks and burrs. OKAY’s refined progressive-die tooling designs can minimize or eliminate these conditions. One example is the use of coining. Coining uses a punch and die to compress the burr into the edge of the material, eliminating the need for secondary deburring operations. Vibratory or barrel tumbling or an electropolish process can also eliminate burrs and enhance surface quality.
Since the staple is an implantable device, the parts require cleaning. OKAY developed a proprietary method of removing the staples directly from the progressive die tooling, sending them through a “flush” system, and then automatically loading into the packaging. The packaging is then incorporated directly into the customer’s assembly process.
“OKAY provided us with the proper expertise and guidance to meet the challenge of stamping our unique staple from the early prototype stage to final production tooling. Their staff is extremely knowledgeable, professional and committed to the customer / vendor team concept for problem solving,” says the customer’s Director of Operations.
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