Staying Connected - July 2014

Mold Tool Design for Insert Molding



Mold tooling being run on Arburg press

Cable assembly design is much like the build of a new home; it begins with a foundation design that is instrumental to the arrangement of other areas within, and around that house.  That foundation is the beginning of the house’s overall strength, shape and eventual encapsulation of its future contents- furniture, photographic memories and people.  Much like building a new house, the foundation, or mold tooling in this case, of a cable assembly will eventually encapsulate contents of value - contacts, PCBs, and other components.  The manufacture of high-quality, custom medical cable assemblies typically begin with the foundation of proper mold tool design and fabrication.

Design Requirements for Mold Tooling

Whether designing an outer mold tool for aesthetics or tactile considerations, an inner mold to enhance mechanical integrity or facilitate encapsulation or unique strain reliefs, mold tool design is an important part of most new cable development projects.  Engineering and design work is also required when the cable or connector project includes enclosures, handles, switches or custom nose pieces.

Design requirements can include:

  • Encapsulation: An inner-mold for the sealing of critical components (such as PCBs, resistors, capacitors)
  • Flexibility: For added flexibility, strain reliefs maintain the structural integrity, flexibility and overall robustness between the cable material and connector or grommet
  • Gripping: Non-slip finger grips built into the connector over-mold for ease of use
  • Security: Latching features which lock connectors in place and prohibits disconnection during use
  • Handling: Uniquely designed handles for maneuvering flexibility, often desirable for surgical applications.


3D model showing detail of
strain relief and runner system


Mold tooling may be designed for maximum versatility, meaning that the mold components may be designed to be interchangeable.  Many customers have different configurations of a certain product; having interchangeable tooling allows for the accommodation of different cable diameters, number of lead wires, snaps, etc.   Mold tooling is typically designed using a 3D modeling software such as SolidWorks or Pro/ENGINEER.

Mold Tool Components

The components that make up tooling for insert molding are common and typically include:

  • Mold Cavity: The part of the tool which will produce the body of the molded component
  • Loading Bars: Securely holds the connector housings, pins or other components in the proper position within the tool during the overmolding process
  • Gripper Bars: Holds the cable exiting the strain relief in the proper position during overmolding.  It is often desirable to be able to use cable with different overall diameter for the same connector.  If the gripper bar tooling is separate from the strain relief tooling this is easily accomplished.
  • Strain Relief: The portion of the tool which molds a solid or segmented  bend relief joining and potentially sealing between the connector to the cable jacket material

Mold Tool Design

While the intended use and functionality will drive overall mold tool design, the selection of cable material and connectors play a significant role.  For both off-the-shelf connectors and custom connectors, the cable assembly will commonly require three tools: inner, outer and strain relief.

Many connector companies offer pre-manufactured slip-on “boots” as an alternative to custom over-molding a strain relief.  Overall tooling cost may be reduced by using an off-the-shelf component, but the cost of a pre-manufactured boot is typically higher than a custom overmolded strain relief.  Over the life of the program a custom overmolded strain relief will typically result in savings due to lower part cost.

If an off-the-shelf connector which meets all product requirements is not available, a custom connector or hybrid connector – a modified off-the-shelf connector - can be designed.  Custom connectors typically require multiple tools to mold the connector housing, nosepiece/contact insulator, latch and other components.

In addition to considering product design, other important considerations when engineering mold tooling include what material will be molded, the shot size, wall thickness of the finished molded part and the material that the tool will be fabricated from.


Mold cavity showing runner and gate

Gate vestige on molded part – magnified 4X

Specifically for insert molding, the location and size of the gate(s) plays a significant role.  The gate is the orifice through which the melted plastic is injected into the mold.  Achieving uniform wall thickness, reducing shrinkage, eliminating mold voids and reducing gate vestige are all part of tool design.  Engineers designing mold tooling will also take into account the material flow and composition.  Typically, polyurethane requires a larger gate than thermoplastic resins such as Santoprene® or PVC.

Easily visible witness lines, also called parting lines, can occur where the two halves of the mold meet and are generally considered undesirable.  Engineering mold tooling to reduce flash (excess material that escapes the mold) is another design consideration.



Horn and nest comprise
ultrasonic weld tooling


Tooling for Ultrasonic Welding

Ultrasonic welding is an alternative to insert molding for connector bodies and housings.  Typically, two hard, plastic shells, also known as clamshells, are injection molded.  The shells are designed to properly fit and seal together through the ultrasonic welding process.  One of the shells is typically designed with a spiked energy director which makes contact with the mating shell.  The energy from the ultrasonic vibrations causes the material to melt at the point contact creating a strong and typically permanent joint.

Tooling for ultrasonic welding includes the anvil or nest where the parts are held and the horn which augments and transfers the vibratory energy to the parts being joined.  Anvils and horns are typically fabricated from aluminum alloys, titanium alloys or stainless steel.  The design and fabrication of ultrasonic welding tools is often contracted to the manufacturer of the ultrasonic welding machine intended to be used.

Not Cut from the Same Mold

Mold tooling can be fabricated from a number of materials.  Aluminum, stainless steel and hardened steel are the most common for production of medical cable assemblies.  Choosing the most appropriate material to fabricate mold tooling from depends on production volume and life expectancy of program.  Two of the most popular mold material styles include:

Aluminum:

  • Commonly used for lower-volume production
  • Often used for prototyping or to prove out tool and part design
  • Lower service-life due to softer material- produces less parts than hardened steel
  • Lower tool fabrication led time
  • Lower cost than steel

Hardened Steel:

  • Best for high-volume production
  • Appropriate for proven designs, or designs which are frozen
  • Excellent service life - typically up to one million parts
  • Typically more costly to fabricate, but longer-lasting

The selection of the tool material is also driven by the resin which will be used.  Thermoplastic resins (such as PVC, TPE/TPR, TPU) are room temperature materials that are heated up and injected into a cold mold.  These resins can be molded using aluminum, stainless steel or hardened steel molds, and are typically chosen based on the product design, mechanical specifications and cost considerations.  Most thermoplastic resins can be molded using aluminum or steel tools.

For Liquid Injection Molding (LIM) silicone applications, cool liquid silicone resin is injected into a hot mold where vulcanization takes place.  Because of this, hardened steel is used for tools that run silicone resins.  Liquid silicone flows easily and tends to be more prone to flash than thermoplastic resins.  Therefore, silicone molds must be designed and fabricated with high precision so that there are literally no gaps for any material to escape from the mold as flash.


Example of a two-cavity tool for
medium production volume parts



Single or Multi-Cavity Molds

Production volume over the lifetime of the product is a key factor when considering how many cavities should be designed into the tool.  While typically more costly, multi-cavity molds allow two or more parts to be molded at once, increasing output and reducing the cost of each molded part.  Designing and fabricating tools with a single cavity is less costly than for multi-cavity tools, but lower up-front costs may be offset by higher production unit costs.

Collaboration and Timeline

Customer communication and design input is essential to tool design and on-time completion.  Early and regular collaboration between the customer’s engineering team and the cable manufacturer’s engineering team is important throughout the project, but is even more significant until the product design is frozen.  Tooling fabrication is typically the longest lead item of a project, ranging from 8 - 14 weeks.  While tooling is being fabricated, documentation is completed and components are ordered.  Scheduling weekly design reviews, will help ensure that both the customer and cable manufacturing partner stay on-target and on-time while meeting established product requirements.

Tool Ownership

It is common for OEM customers to pay for and therefore own production tooling.  When this is the case, the tooling is only used to produce parts for the tool owner.  In some instances, the OEM may elect to share the cost and ownership of the tool in which case, use is not exclusive.  Cable manufactures, such as Affinity, may own tooling for common connectors and components which may be used on a non-exclusive basis for little or no tooling cost.

Summary

The design of mold tooling is an essential part of most custom cable assembly projects, and should be the fundamental focus of the project from concept until design freeze.  Understanding what the connector and cable assembly is expected to look like, how it will be used, and the desired life of the product is critical to tool design.

The Affinity engineering team has decades of experience designing mold tooling to meet the mechanical and aesthetic features for medical cable assemblies.  Let us partner with you on your next new cable or connector project.

For additional information, contact your local Molex Sales Engineer or Account Manager or call Affinity at +1 949.477.9495 or email us at custcare2@molex.com.

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Meet Jose Mendez - Project Engineer



Jose Mendez

Jose joined Affinity Medical in June after a nine year career as a mechanical engineer at a metal fabrication company.  "I wanted to use my engineering skills in a company that helped people," said Jose.  "One of the things that attracted me to Affinity was having the opportunity to design medical products.  I was excited to join a company whose products really helped people.  I was happy when I was offered the Project Engineer position.

"We had been searching for an engineer for several months, and Jose's experience managing new product development projects was one of the things that we were looking for," said Affinity Engineering Manager, Matt Pathmajeyan. "Jose had a solid background in mechanical engineering and that coupled with his project management skills made him a good fit for the Affinity Engineering team."

As a Project Engineer, Jose is responsible for not only designing the product - cable assembly and/or connector, but also designing tooling, selecting materials, writing work instructions and managing the project from conception and into production.  Affinity Project Engineers typically handle four to six projects at a time depending on how complex the projects are.  Each project will typically have a weekly teleconference with the customer's engineering team where design and development issues and the project timeline are discussed.  "By regularly communicating with our OEM customer, we are able to keep projects on time and not have unpleasant surprises," commented Jose.


Jose working on design in SolidWorks


Asked what his impressions of Affinity have been Jose replied, "Everyone is really friendly which makes the work environment great.  My biggest challenge has been getting used to working under Affinity's FDA and ISO 13485 procedures.  Working for a medical device company is different from what I've been used to, but appreciate the structure and am learning quickly."

"I consider myself a gearhead," said Jose.   "Another challenge has been learning about the electrical components we use and the methods we use for shielding.  My background has been mechanical, but I am enjoying learning the electrical side.  One of the differences between working at Affinity and my previous job is that I can walk into production any time that I want because it is on-site.  In my previous job, the plant was a three hour drive away."

Jose grew up in Southern California and earned a Bachelor of Science degree from Loyola Marymount University. While working, he earned his M.B.A. from University of California Irvine.  "Getting my M.B.A. was challenging, but I wanted to be of value to my employer and prepare myself to advance in my career, "said Jose.

Besides working, Jose enjoys a very active life.  "I do about one triathlon a year," said Jose. "To train for that and to stay in shape, I run six to seven miles a week and bike about 20 miles a week.

Jose and his wife live in nearby Mission Viejo.  They have two children, an eight year old son and a five year old daughter.  "We are a very busy family," said Jose.  “Both our kids are active in sports and school; so we spend a lot of family time with that. We also like going to the beach and traveling.  My wife has family in Australia and we have taken several trips back to see them.  The flights are really long, but the kids have handled them really well."

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Affinity Adds Capabilities



One of two CNC machines
now in Affinity’s tool shop


One of the reasons Affinity Medical expanded its plant earlier this year was to provide room for a tool fabrication shop and dedicated injection molding area.
In mid-July, Affinity acquired the assets of a long time tooling fabricator and injection molding partner, Engineering Today.  Equipment was moved from Torrance to Affinity’s Costa Mesa plant on July 10th and installation and qualification activities began the next day.

Equipment moved and installed at the Affinity plant includes:

  • 5 Injection Molding Machines
  • 2 CNC Machines (HAAS and Mitsubishi programmable machining centers)
  • 2 Sinker EDM Machines (Electrical Discharge Machining for precision cutting)
  • 2 Surface Grinders
  • 3 Multi-axis (1-2-3) Milling Machines


Four of the five injection molding
machines moved to Affinity




“The addition of the Engineering Today staff and mold-tool fabrication equipment gives Affinity greater long term stability and allows us to offer our OEM partners additional flexibility and capabilities,” said Affinity General Manager, Bob Frank.

“In addition to tool fabrication, Affinity will now be doing its own injection molding,” said Bob.  “We are really happy that the Engineering Today employees have joined the Affinity team.  This will help make the integration a seamless transition.”

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Announcements, Information and Trivia



Summer south polar ice cap of Mars which consists of a layer of frozen CO2 over a layer of water ice - Image by NASA/JPL/MSSS - Licensed under public domain via Wikimedia Commons


The dry, barren surface of Mars - Image by NASA/JPL - Licensed under public domain via Wikimedia Commons


Water ice clouds above Mars – Image by NASA/JPL/MSSS - Licensed under public domain via Wikimedia Commons

Mars Trivia

Smaller than Earth – Mars is approximately half the diameter of Earth.  The entire surface area of Mars, which is dry, is about the same as the total dry land area of Earth.

A Dry Place – Due to the low atmospheric pressure, liquid water does not appear to exist on Mars.  Water, in the form of polar ice, exists, but if it melted, it would evaporate.

Martian Climate – Within our Solar System, Mars is the one planet with seasons resembling those on Earth.  Because of the greater tilt of Mars axis and the more eccentric orbit, the seasons are not as equal as on Earth.  In the northern hemisphere of Mars, spring lasts 7 months.

Long Years – A Martian year is 687 Earth days.  However a day on mars is only 39 minutes longer than an Earth day.  Would we be half our age on Mars?

Moving Backwards – Looking at the sky, planets and stars appear to move from east to west when viewed at the same time at night.  For about 70 days, Mars appears to move backwards – that is from west to east – which is called “retrograde motion.”