LIGHT-CURE ADHESIVES

I wrote the following document for PDHonline.org some months ago to demonstrate the possible uses of light cure adhesives.  This is a fascinating technology and one gaining importance as differing materials become commercialized.  Hope you enjoy it and please send me your comments as you see fit. 

At the present time, adhesive manufacturers offer products classified as Cyanoacrylates, Epoxies, Hot Melts, Silicones, Urethanes, Acrylics (one-part and two-part) and Light-cures.  These classifications provide products from manufacturers with specific characteristics that allow for bonding, gasketing, potting and encapsulating, retaining, thread-locking and thread-sealing.

Light-cure adhesive technology offers a new approach to bonding similar or dissimilar substrates by using either ultraviolet light (UV) or light within the visible spectrum.  Extremely rapid cure times, superior depth of cure, (up to four inches) and easy dispensability are only three of the benefits when using these adhesives combined with the appropriate processes.   The newer visible light-cure materials can offer adhesion comparable to most commercially available UV adhesives, with particularly high adhesion on polycarbonate and polyvinylchloride (PVC) materials.  All equate to lower cost of assembly, more freedom when designing components and products and the saving of valuable production time.  This method of adhesion is extremely valuable when bonding thin films, needing heightened safety relative to skin and eyes and when bonding heat sensitive materials.  This process can lessen, or eliminate, the need for costly and harmful chemicals from the workplace and can be solvent-free and non-hazardous.  The use of light-cure adhesives will result in a very clean and “friendly” worker environment with no significant material disposal costs.  There is no need to mix, prime or rush to apply the adhesive due to minimal time to dispense.  We will discuss other benefits and some disadvantages later on in our course.

ADVANTAGES AND DISADVANTAGES:

Let us list now the relative advantages and disadvantages of using UV and V light-curing adhesives.

ADVANTAGES:

1.)     Reduced labor costs

2.)    Simplified automation when automation is used

3.)    Easier alignment of parts before cure

4.)    Improved in-line inspection

5.)    Reduced work in-process

6.)    Shorter cycle times due to rapid curing of components

7.)    Shorter lead times to customer possibly leading to reduced inventories

8.)    Fewer assembly stations required due to rapid cure times

9.)    No racking during cure

10.) No mixing generally required

11.) No pot life issues meaning generally much less waste of materials

12.) Reduced dispensing costs

13.) No hazardous waste due to purging or poor mixing

14.) No static mixers

15.) Easier to operate and maintain dispensing systems

16.) Better work acceptance

17.) No explosion proof equipment required

18.) Reduced health issues

19.) Reduced regulatory costs; i.e. reduced restrictions on volatile organic compounds

20.) Reduced disposal costs

21.)  Very fast cure times

22.)  Ideal for heat sensitive films and thin components

23.) Lower energy consumption required during processing of adhesive systems

24.) Visible light-cure adhesives cure through colored or tinted substrates

25.) Allows for miniaturization of component parts needing bonding or potting

26.) Improved manufacturing yield, quality and reliability

27.) Low odor

28.) RoHS compliant

29.) UL recognized materials available

30.) Low entrainment of moisture due to rapid cure times

31.) Solvent free

32.) Reduced material and process costs

DISADVANTAGES:

As with any process or adhesive material, there are several disadvantages. These are as follows:

1.)    Expenditure for curing equipment is necessary

2.)    Shielding when UV light is used may be necessary

3.)    UV blocking eye protection may be necessary depending upon the processing equipment

4.)    A radiometer may be necessary to measure the intensity of the UV light

5.)    When using UV light, the light source MUST reach the bond line if complete cure is to be had.  This means that transmission of light through at least one substrate is crucial.  Some substrates have UV inhibitors to lessen or eliminate degradation of the component.  These inhibitors will inhibit the penetration and lessen adhesion necessitating another method of bonding.  (This is by far the biggest disadvantage for UV curing.)  A graphic depiction is given below that illustrates the principal.

6.)    The mechanical properties may not meet specified requirements for tensile strength, shear strength, peel strength, etc.

7.)    In some cases when potting depth is a factor, materials may not cure through.

8.)    Rapid cure may be too fast allowing no repositioning of mating components

9.)    Engineering specifications must be exact and specific denoting brand, part number and method of application relative to adhesive.

10.) Educating workers applying light-cure adhesives is a MUST.

TYPICAL APPLICATIONS:

When we discuss applications, we find they generally fall into one of several basic categories; i.e. 1.) Bonding, 2.) Sealing, 3.) Cured-In-Place Gaskets, 4.) Potting and 5.) Coating.  With this in mind, we can see the following product applications now using the light-cure technology:

1.)    Musical instruments

2.) Toys

3.) Sporting equipment

4.) Jewelry

5.) Optics (eye glasses)

6.) Needles

7.) Syringes

8.) Lighting

9.) Electronic Asms.

10.) Appliance assembly (refrigeration, laundry, etc.)

11.) Strain relief for wires and cord sets

12.) Conformal coating for PC boards

13.) Parts tacking

14.) Coil terminating

15.) Tamper-proofing

The development of light-curing adhesives has been enhanced by the latest generation of curing equipment.  This equipment includes both flood and point source configurations using bulb or lamp based systems.  In addition, equipment utilizing LED technology is now available for use with these adhesives.  The benefit here is that LEDs generate focused wavelengths that create appreciably tighter output range relative to regular visible lamp technologies.   Furthermore, because superfluous light and heat are not emitted, LED technology has proven to be both highly efficient and highly cost effective.  As might be expected, as a result of their small size, LED curing systems provide an LED light source that is perfect for curing tiny component parts.

As you can see, many industries use this technology and as materials improve, more and more will continue to do so.  FASCINATING TECHNOLOGY.

HACKERS AT YOUR GATE

I am reprinting an article written by Rob Spiegel, Senior Editor, Automation & Control – Design News Daily.  The article points out what is and will be significant issues with online work and work accomplished in this “digital age”.  This is a huge problem; growing on a yearly basis.  The technology to avoid hackers and digital intrusion is far behind efforts to access data bases using digital means.  It must be apparent that intellectual property as well as national security is at stake.   Please take a look and comment as you see fit.

Hackers are trying to get into your plant data and your intellectual property. Think you’re safe? Hackers may have already attacked your data. The average length of time from a cyber-attack to the moment that attack is detected is a whopping 416 days, according to the National Board of Information Security Examiners (NBISE).

Michael Assante, director of NBISE painted a dire picture of the growing threat of cyber-security at the Rockwell Automation Fair in Houston Tuesday. In a panel discussion on the connected enterprise and industrial control system security, Assante noted that “94 percent of organizations that were victims of cyber-attacks were not able to detect the attack.” He also pointed out that 100 percent of the organizations that were attacked had security. “Conventional security is simply not keeping up,” he said.

Assante classified cyber-attacks into three categories:

• General cyber-attacks are less structured. The hackers are out for notoriety and fame. They’re part of the hacker community.
• Targeted cyber-attacks are directed to specific goals. The attacks could be for monetary gain or to steal intellectual property.
• The third category is the most dangerous, strategic cyber-attacks. These are highly structured attacks with intent to commit major economic disruption or cyber-terrorism. Assante noted that strategic cyber-attacks are growing. “We have passed the inflection point,” he said.

As for warding off attacks, Assante believes the answer is an educated staff and networks that require authentication. “People pave the way to cyber-security,” he said. “We have to secure people, and we have to make people cyber-aware.”

Joining Assante on the panel was Frank Kulaszewicz, senior vice president of architecture and software at Rockwell Automation. Kulaszewicz acknowledged that security is a growing problem. “Major security events are increasing,” he said. “Security is one of the fastest changing landscapes in technology.” He explained that cyber-threats are growing partly because of the expanding connectivity in automation. “Whenever you add devices, you create more access points.”

Working on a solution
Kulaszewicz noted that Rockwell and Cisco Systems have developed a strategic relationship to increase connectivity and productivity, but also to work on security. “We’re using role-based security. We design for security and audit to identify gaps,” he said.

Assante sees a path to security in knowledge and skills, both to identify vulnerabilities and also to detect breaches. “The biggest challenge to security is skills,” Assante told Design News. “The answer is education, the right set of knowledge. We leverage that knowledge to improve security.” He noted that security comes in two forms, the ability to ward off attacks, and the ability to determine if an attack has been launched. “Not only must the connected device be secure, but the network must be able to detect if the device has been compromised,” he told us.

Who are the bad guys?
Attacks can come from anywhere in the world. (At a hackers conference you can buy a Russian toolkit to crack plant systems for $2,500.) However, the biggest threat may be plant employees. “It can be malicious insiders,” Kulaszewicz told us. “They do it for spite, or to get intellectual property before they leave.” He also noted that breaches can happen by mistake. “It can be an accident, say a maintenance guy tweaks a variable that opens up a network.”

Rockwell identified Cisco as the right partner to create viable cyber-security. “We developed a relationship with Cisco to improve security,” said Kulaszewicz. “Cisco has been successful in security with other verticals such as the financial industry. They have domain expertise. Their technology is great, so why should we develop our own?”

 

RAPID PROTOTYPING(RP&M)

Rapid prototyping is definitely a technology that has, and is, changing the way companies and commercial entities do business.   We can certainly say this “emerging technology” has gained tremendous momentum over the past decade.  The applications and uses represent a “best practice” for manufacturers and producers in general.

Being able to obtain prototype parts quickly allows a company to test for component form, fit and function and can help launch a product much faster than its competition.   This can allow for adjustments in design, materials, size, shape, assembly, color and manufacturability of individual components and subassemblies.   Rapid prototyping is one methodology that allows this to happen.   It also is an extremely valuable tool for sales and marketing evaluation at the earliest stages of any program.   Generally, an engineering scope study is initially performed in which all elements of the development program are evaluated.  Having the ability to obtain parts “up front” provides a valuable advantage and definitely complements the decision making process.   Several rapid prototyping processes are available for today’s product design teams while other prototyping processes utilize traditional manufacturing methods, such as 1.)  CNC Machining, 2.)  Laser Cutting, 3.)  Water Jet Cutting, 4.) EDN Machining, etc.   Rapid prototyping technologies emerged in the ‘80s and have improved considerably over a relatively short period of time.   When I started my career as a young engineer, the only process available for obtaining and producing prototype components was as follows:

• Produce an orthogonal drawing of the component. This drawing was a two-dimensional rendition, including auxiliary views, and generally did NOT use geometrical dimensioning and tolerancing methodologies, which opened the way for various interpretations relative to the part itself.  Solid modeling did not exist at that time.
• Take that drawing or drawings to the model shop so initial prototypes could be made.     Generally, one prototype would be made for immediate examination.   Any remaining parts would be scheduled depending upon approval of the design engineer or engineering manager. We were after “basic intent”—that came first.  When the first prototype was approved, the model shop made the others required.
• Wait one, two, three, four, etc weeks for your parts so the initial evaluation process could occur.  From these initial prototypes we would examine form, fit and function.
•  Apply the component to the assembly or subassembly for initial trials.
• Alter the drawing(s) to reflect needed changes.
• Resubmit the revised drawing(s) to the model shop for the first iteration of the design.  (NOTE:  This creates a REV 1 drawing which continues the “paper trail” and hopefully insures proper documentation.)
• Again, apply the component for evaluation.
• Repeat the process until engineering, engineering management, quality control and manufacturing management, etc signs off on the components.

The entire process could take weeks or sometimes months to complete.   Things have changed considerably.  The advent of three dimensional modeling; i.e. solid modeling, has given the engineer a tremendous tool for evaluating designs and providing iterations before the very first “hard” prototype has been produced.  As we shall see later on, solid modeling of the component, using CAE and CAD techniques, is the first prerequisite for rapid prototyping.   There are several options available when deciding upon the best approach and means by which RP&M technology is used.   As prototyping processes continue to evolve, product designers will need to determine what technology is best for a specific application.

INDUSTRIES USING RP&M PROCESSES:

As you might expect, there are many disciplines and industries willing to take advantage of new, cost-saving, fast methods of producing component parts.  RP&M has become the “best practice” and the acceptable approach to “one-off” parts.  Progressive companies must look past the prototyping stereotypes and develop manufacturing strategies utilizing additive manufacturing equipment, processes and materials for high volume production. The pie-chart below will indicate several of those industries now taking advantage of the technology and the approximate percentage of use.

 

One of the statistics surprising to me is the percentage of use by the medical profession.   I’m not too surprised by the seventeen percent from automotive because the development of stereolithography was actually co-sponsored by Chrysler Automotive.    Consumer electronics is another field at eighteen percent (18.4%) that has adopted the process and another industry benefiting from fast prototyping methodologies. When getting there first is the name of the game, being able to obtain components parts in two to three days is a remarkable advantage.    Many times these products have a “lifetime” of about eighteen month, at best, so time is of the essence.

The bar chart below will give a comparison between sales for RP&M services provided by vendors and companies providing RP&M machines to companies and independent providers.  As you can see, the trends are definitely upward.  Rapid prototyping has found a very real place with progressive companies and progressive institutions in this country and the world over.

 

RAPID PROTOTYPING & MANUFACTURING (RP&M) TECHNOLOGIES:

There are several viable options available today that take advantage of rapid prototyping technologies.   All of the methods shown below are considered to be rapid prototyping and manufacturing technologies.

• (SLA) Stereolithography
• (SLS) Selective Laser Sintering
• (FDM) Fused Deposition Modeling
• (3DP) Three Dimensional Printing
• (Pjet) Poly-Jet
• Laminated Object Manufacturing

Stereolithography was the first approach to rapid prototyping and all of the other methods represent “offshoots” or variations of this one basic technology.   The processes given above are termed “additative manufacturing” processes because material is “added to” the part, ultimately producing the final form detailed by the 3-D model and companion specifications.  This course will address the existing technology for all of these processes and give comparisons between them so intelligent decisions may be made as to which process is the most viable for any one given part to be prototyped.

As a result of the prototyping options given above, there are many materials available to facilitate assembly and trial after completion of the model.   We are going to discuss processes vs. materials vs. post-forming and secondary operations later in this course.   The variety of materials available today is remarkable and to a great extent, the material selection is dependent upon the process selected.   We will certainly discuss this facet of the technology.

BASIC PROCESSES:

As you might expect, there is a definite methodology for creating actual parts, and the processes do not vary greatly from method to method.    We are going to detail the sequential steps in the process.  This detail will form the “backbone” for later discussions involving the mechanical and electronic operation of the equipment itself.  These steps apply to all of the RP&M processes.

• Create a 3-D model of the component using a computer aided design (CAD) program.  There are various CAD modeling programs available today, but the “additative manufacturing” process MUST begin by developing a three-dimensional representation of the part to be produced.  It is important to note that an experienced CAD engineer/designer is an indispensable component for success.  As you can see, RP&M processes were required to wait on three-dimensional modeling before the technology came to fruition.
• Generally, the CAD file must go through a CAD to RP&M translator.  This step assures the CAD data is input to the modeling machine in the “tessellated” STL format.  This format has become the standard for RP&M processes.  With this operation, the boundary surfaces of the object are represented as numerous tiny triangles.  (VERY INDENSABLE TO THE PROCESS!)
• The next step involves generating supports in a separate CAD file.  CAD designers/engineers may accomplish this task directly, or with special software.  One such software is “Bridgeworks”.  Supports are needed and used for the following three reasons:

1. To ensure that the re-coater blade will not strike the platform upon which the part is being built.
2. To ensure that any small distortions of the platform will not lead to problems during part building.
3. To provide a simple means of removing the part from the platform upon completion.
   1. Leveling—Typical resins undergo about five percent (5%) to seven percent (7%) total volumetric shrinkage.  Of this amount, roughly fifty percent (50%) to seventy percent (70%) occurs in the vat as a result of laser-induced polymerization.  With this being the case, a level compensation module is built into the RP&M software program.  Upon completion of laser drawing, on each layer, a sensor checks the resin level.  In the event the sensor detects a resin level that is not within the tolerance band, a plunger is activated by means of a computer-controlled precision stepper motor and the resin level is corrected to within the needed tolerance.
   2. Deep Dip—Under computer control, the “Z”-stage motor moves the platform down a prescribed amount to insure those parts with large flat areas can be properly recoated.  When the platform is lowered, a substantial depression is generated on the resin surface.  The time required to close the surface depression has been determined from both viscous fluid dynamic analysis and experimental test results.
   3. Elevate—Under the influence of gravity, the resin fills the depression created during the previous step.  The “Z” stage, again under computer control, now elevates the uppermost part layer above the free resin surface.  This is done so that during the next step, only the excess resin beyond the desired layer thickness need be moved.  If this were not the case, additional resin would be disturbed.
   4. Sweep—The re-coater blade traverses the vat from front to back and sweeps the excess resin from the part.  As soon as the re-coater blade has completed its motion, the system is ready for the next step.
   5. Platform Drops–The platform then drops down a fraction of a MM.    The process is then repeated.  This is done layer by layer until the entire model is produced.  As you can see, the thinner the layer, the finer and more detailed the resulting part.
   6. Draining–Part completion and draining.
   7. Removal–The part is then removed from the supporting platform and readied for any post-processing operations. .

• Next step— the appropriate software will “chop” the CAD model into thin layers—typically 5 to 10 layers per millimeter (MM).  Software has improved greatly over the past years, and these improvements allow for much better surface finishes and much better detail in part description.  The part and supports must be sliced or mathematically sectioned by the computer into a series of parallel and horizontal planes like the floors of a very tall building.  Also during this process, the layer thickness, as discussed above, the intended building style, the cure depth, the desired hatch spacing, the line width compensation values and the shrinkage compensation factor(s) are selected and assigned.
• Merging is the next step where the supports, the part and any additional supports and parts have their computer representations combined.  This is crucial and allows for the production of multiple parts connected by a “web” which can be broken after the parts are molded.
• Next, certain operational parameters are selected, such as the number or re-coater blade sweeps per layer, the sweep period, and the desired “Z”-wait.  All of these parameters must be selected by the programmer. “Z”-wait is the time, in seconds, the system is instructed to pause after recoating.  The purpose of this intentional pause is to allow any resin surface non-uniformities to undergo fluid dynamic relaxation.  The output of this step is the selection of the relevant parameters.
• Now, we “build the model”.  The 3-D printer “paints” one layer exposing the material in the tank and hardening it.    The resin polymerization process begins at this time, and the physical three-dimensional object is created.  The process consists of the following steps:

• Next, heat treating and firing may occur for further hardening.  This phase is termed the post-cure operation.
• After heat treating and firing, the part may be machined, sanded, painted, etc until the final product meets initial specifications.  As mentioned earlier, there have been considerable developments in the materials used for the process, and it is entirely possible that the part may be applied to an assembly or subassembly so that the designed function may be observed.  No longer is the component necessarily for “show and tell” only.

The entire procedure may take as long as 72 hours, depending upon size and complexity of the part, but the results are remarkably usable and applications are abundant.

APPICATIONS:

The applications for RP&M technology are as numerous as your imagination.  With the present state of the art, extremely accurate, detailed and refined prototypes may be produced.  Components and structures that were impossible or extremely difficult to model are made possible today with existing methods and equipment.  We will now take a look at figures representing very “real” components fabricated with rapid modeling techniques.   Some of the applications are as follows:

• Dental Prototypes
• Orthopedic Prototypes
• Sculpture prototypes
• Prototypes for manufactured components
• Items used to decorate sets for plays, operas, etc
• Forensic investigations
• Surgical procedure planning
• Molds for investment castings
• Architectural models
• Scaled models
• Complex trays for fiber optics
• Light pipes for electronic devices

In addition to speed, very fine and intricate surface finishes may be had depending upon the material and process used to create the part.    We have taken a look at those industries using RP&M, Figure 1, so let us now consider the various uses for the technology itself.  Looking at Figure 3 below, we find the following major uses for the technology:

• Visual aids for engineering           16.5 %
• Functional models                           16.1%
• Fit and assembly                              15.6%
• Patterns for prototype tooling   13.4%
• Patterns for cast metal                  9.2%

Over seventy percent (70%) of the total uses are given by the five categories above.  This in no way negates or lessens the importance of the other uses, but obviously, visual aids, functional models and models to prove form, fit and function top the list.

DIGITAL PHOTOS DEPICTING USES FOR RP&M TECHNOLOGY:

Everyone says a “picture is worth a thousand words” so let’s take a very quick pictorial look at some of the many applications noted by the text and the figures above.  The following JPEGs should give you an idea as to what uses of RP&M technologies exist.  These digital photographs are from actual models created for very specific purposes.  Let’s take a look at parts actually produced by “additative” manufacturing.

 

 

These are just a few of the possibilities.  Great detail–with remarkable surface finish.  Just as the technology is improving, the materials are improving also with greater choices for the design engineer.  I definitely hope you will use this post to investigate further this remarkable technology

FAILURE MODE EFFECT ANALYSIS

The following discussion on failure mode effect analysis was published through PDHonline.org and written by this author.  In the “world of reliability engineering” this process is extremely valuable in determining those components and sub-assemblies that may fail and may fail early in their life.  This one is a little “off the wall” but hope you enjoy it anyway.

Failure Mode and Effect Analysis is the cornerstone of the reliability engineering process. It is a methodology for analyzing potential reliability problems early in the development cycle.   It is a technique to identify potential failure modes, determine their effect on the operation of the product and identify actions to mitigate the failures.   With this being the case, an engineer can “design out” components or modify those components to make them more robust relative to the operational conditions that will be encountered during use.  Please note that FMEAs are always conducted after critical subassemblies are identified.  There are several types of FMEAs, as follows:

• System—focuses on global system functions
• Design-focuses on components and subsystems
• Process focuses on manufacturing and assembly processes
• Service focuses on service functions
• Software-focuses on software functions

We look at, and rate, three areas: severity, probability of occurrence and the ability to detect the specific failure.  There is a very simple template that will capture the possible failure modes and designate actions to be taken at a later date.  An example of that template is as follows:

 

The “header” for the template would show the Product Name, the Date, the System or Subsystem Name, the Name of the Design Leader and the Revision Number.

The process of conducting a FMEA for any product is as follows:

1. Assemble a team of individuals who have product knowledge.  These people should come from the following disciplines: a.) design engineering, b.) manufacturing, c.) service, d.) quality, e.) repair.
2. Make sure the  Failure Block Diagrams (FBDs)  and “P”-Diagrams are available to adequately represent the system, subsystem or component.
3. Construct the FMEA template or work sheet.
4. Convene the team to identify the possible failure modes and assign importance to the severity, probability of occurrence and the probability of detecting the failure. Generally, the rating system goes from one (1) to ten (10) with ten being the most severe and creating the greatest operational issues.  A recommendation from Mr. Stephen Curtis posted on the Six Sigma.com web site recommends the following classifications for the three- line items:
5. Multiply the assigned numbers for severity, occurrence and detection together for a final score and record that score for later use.  A score of 1,000 would indicate a failure that should definitely be addressed and one that would be coded as a “red” item.  Red items must be fixed before pre-pilot builds occur and certainly before pilot runs occur.  Some companies designate any score above 600 as a “red” item.
6. For each failure mode, identify what you feel to be the “root cause” of the failure.  This will take experience and you may wish to consult the services of field technicians for their comments relative to product use and problem areas.
7. Describe the effects of those failure modes; i.e. injury to user, interoperability of product, improper appearance of product, degraded performance, noise, etc.
8. Determine what must be the initial recommended action.  This is done for each failure mode.
9. Assign responsibility for addressing the “fix”.
10. Assign a “get well” date
11. .Before adjourning, establish a time to reconvene for a status on the failures and the “fixes”.Before adjourning, establish a time to reconvene for a status on the failures and the “fixes”.

This is a marvelous tool for reliability practitioners and engineers of all “stripes”.  One used by  manufacturers and designers in every branch of engineering and technology.  Hope you enjoy this one.