Refined, Redesigned Equipment for Balloon & Stent Manufacturing

Blockwise Engineering, founded just 10 years ago, bases its company on the concept of providing innovative, simple, and refined equipment for medical device manufacturers. “There was no cost-effective, refined equipment for balloon and stent manufacturing,” says Blockwise Engineering’s Mechanical Engineer Justin Knight. “Our competitors were essentially selling over-complicated prototypes.”

This premise is what helped the vision of the company. Blockwise Engineering designs, develops, and builds specialized manufacturing equipment, with a focus on the balloon and stent manufacturing industries. As they strive to see the relationships between product, process, and equipment, they have built a portfolio of new and innovative tools, such as the stent band swager.

“Band swaging is a forging process in which the diameter of a thin-walled metal band is reduced to secure it to the outside diameter of a tube,” Knight explains. “A typical application would be to secure platinum-iridium marker bands to a plastic tube to make a balloon catheter.”

 A) A metal band swaged onto a tube. B) Model SFA (standard) is typically used for soft precious-metal radiopaque marker bands,
while model SFB (high force) is typically used for strong stainless steel bands. C) Blockwise Engineering Band Swagers
deliver consistent band diameter, with the die design resulting in the lowest variablity in swaged diameter.

When Blockwise engineers began development of their machine, they considered other models on the market in order to address the requirements they felt these other systems were lacking. Their list was to develop a band swager with the following features:

• Small machine footprint;
• Cleanroom ready;
• Quiet;
• Clean;
• Repeatable process – most importantly in terms of band diameter;
• Easy to use;
• Reliable;
• Cost-effective; and
• Low mandrel pull force.

A Team Approach
Blockwise Engineering has 12 employees, with this lean team including an in-house engineering team, machinists/toolmakers, and specialists in machine assembly, software, production planning, and purchasing. In addition to their staff, they have strategic relationships with several specialized machining and fabrication suppliers, and component suppliers, while featuring a complete in-house machine shop with CNC capabilities.

One such supplier is Intelligent Motion Systems Inc. (IMS), a Schneider Electric company. IMS supplies the NEMA 17 linear actuator stepper motor with motion control used in the Blockwise Model SFA Band Swager. “We chose the NEMA 17 linear actuator because it would not require an expensive and bulky ballscrew slide to implement,” Knight explains. “Additionally, we chose the motion control version because we used the IMS motor to not only provide motion, but to control the machine instead of a PLC or other computer.”

The MDrive 17 Motor+Driver Plus linear actuators combine all-in-one integrated step motor and driver technology with linear motion to deliver long life, high accuracy, and repeatability – all in a compact package. The MDrive 17 linear actuators feature high torque NEMA 17 1.8° brushless linear actuator stop motors integrated with electronics.

At less than 1.7" square in size, the actuators offer a broad input voltage range – from +12VDC up to +48 VDC – and an extended operating range of -40°C to +85°C, which delivers long life and trouble-free service in demanding environments. The systems have a load limit of up to 50 lb, while the precision rolled lead screws are corrosion resistant stainless steel, also available with an optional coating.

The MDrive is available in two MDrive linear actuator styles or two MDrive 17 Plus versions. The first option is the MDrive linear actuator with a non-captive shaft where a threaded shaft extends through the MDrive product and moves axially as the motor rotates. The other option is the external shaft with a rotating screw, integral to the MDrive rotor, which moves the nut axially along the threaded shaft. In the MDrive 17 plus version, which has the integrated motor and driver there is the micro-stepping motor+driver for step and direction input or the motion control, motor+driver+controller. The latter – the option Blockwise Engineers chose – is fully programmable, has an RS-485 or CANopen interface, and is a stand-alone solution for use without a PLC.

Obvious that the IMS NEMA 17 linear actuator delivered the requirements engineers from Blockwise Engineering sought, it additionally delivered more benefits – such as IMS’ second-generation current control, which applies techniques to control current flow through the motors, significantly dampening resonance over the entire speed range, also means delivering a reduction in noise.

Some other key features of the motion control version include:

• Low cost;
• Compact;
• 20 programmable micro-step resolutions to 51,200 steps/rev – including degrees, metric, and arc minutes;
• Stainless steel lead screws;
• Electronically configurable;
• Programmable motor run and hold currents;
• Included interface software;
• Parameters switchable on-the-fly;
• Selectable 10-bit analog input;
• High speed position capture input or trip output; and
• 0MHz to 5MHz step clock rate selectable in 0.59Hz increments.

Success
“Blockwise currently offers two swager models – the Model SFA is for swaging bands made of platinum-iridium, platinum, gold, and other similar yield strength materials,” Knight says. “Model SFB swages thin-walled stainless steel bands in addition to platinum-iridium or similar.”

The purpose of band swaging machines is to swage, or permanently deform by repeatedly squeezing, metal bands onto plastic tubes.  The swaging machine uses a rotating die with a round opening to reduce the diameter of the metal band while keeping it round with a fine surface finish. Blockwise Engineering’s machines do not position or pre-crimp the bands.

In designing the models, attention to detail was a must. According to Knight, “One highly-engineered component on both machines is the swaging die. We needed to ensure that the dies applied sufficient force to swage while keeping the die flexure stresses low enough such that the die would never fatigue. We started by determining the force required to swage typical marker bands. We then hand calculated the stresses of the die. Next, we performed finite element analysis (FEA) on the die. The results of the FEA were very similar to our hand calculations, which validated our stress calculations. Using FEA we were able to optimize further the die geometry to lower stresses. We then created a prototype and ran an endurance test. Finally, from that endurance test, further refinements were made before delivering our first machine to our customer.”

Blockwise Engineering uses the IMS NEMA 17 linear actuator stepper motor with motion control in their high-speed rotary swaging machines.Both machines are extremely productive because they have a fixed swaging frequency that exceeds competitive machines by a factor of three. The proprietary, flexure-based die, designed to close fully with every blow, eliminates the swaging frequency as a process setting – meaning setup is simplified and swaged band diameters are consistent. Additionally, the machine is very simple to set up and use while the flexure-based die is much cleaner than competing mechanisms with sliding die segments.

A key factor in the consistency of machine operation comes from the specification of the right mix of components. Blockwise Engineering originally found IMS by chance, while looking to specify parts. Since that random encounter, they have remained an IMS customer for years – having used IMS products on multiple projects prior to implementing the MDrive Motor+Driver 17 Plus linear actuators on their band swager models – and plan to continue this successful relationship.

Today, Blockwise continues pursuing its mission, which is to design and build machines for medical and nonmedical manufacturers and equipment sellers, working daily to make most of the world’s catheter balloons and many other products by applying creative mechanical design to unique manufacturing challenges.

Intelligent Motion Systems Inc.
(IMS) A Schneider Electric
Motion USA Company
Marlborough, CT
imshome.com

Blockwise Engineering
Phoenix, AZ
blockwise.com